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Year : 2016  |  Volume : 12  |  Issue : 6  |  Page : 71-77

Medical Physics

Date of Web Publication30-Nov-2016

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How to cite this article:
. Medical Physics. J Can Res Ther 2016;12, Suppl S2:71-7

How to cite this URL:
. Medical Physics. J Can Res Ther [serial online] 2016 [cited 2021 Mar 1];12:71-7. Available from: https://www.cancerjournal.net/text.asp?2016/12/6/71/194971

Abstract: 102

Dosimetric study on indigenous slab-pinewood-slab phantom for developing the heterogeneous chest phantom mimicking thoracic region of human

Om Prakash Gurjar 1,2 , Priyusha Bagdare 1 , Surendra Prasad Mishra 2,3 , Radha Kishan Paliwal 2

1 Roentgen-SAIMS Radiation Oncology Centre, Sri Aurobindo Institute of Medical Sciences, Indore, Madhya Pradesh, 2 Department of Physics, Mewar University, Chittorgarh, Rajasthan, 3 Department of Radiotherapy, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India, E-mail: [email protected]

Introduction: Advanced radiotherapy techniques are being used with more accurate dose calculating algorithms, therefore advanced heterogeneous phantoms mimicking human body must be developed and used for patient specific quality assurance (QA). Materials and Methods: 6 megavoltage photon beam with field size 10 × 10 cm 2 was put on computed tomography (CT) images of patient thoracic region, slab-pinewood-slab (SPS) phantom and SP34 slab phantom (polystyrene). Anisotropic-analytical-algorithm was utilized to calculate doses. Density of each medium was calculated using Hounsfield-units. Depths of isodose-lines in all three set of CT images were measured. Variations between planned doses on treatment-planning-system (TPS) and measured on linear accelerator (LA) were calculated for three points viz. near slab-pinewood interfaces (6 and 18 cm depths) and 10 cm depth in SPS phantom and at same depths in SP34 phantom. Results: Densities of chest-wall, lung, soft-tissue behind lung, pinewood and SP34 slabs were found as 0.898, 0.291, 1.002, 0.329 and 0.999 g/cc respectively. 100% and 90% isodose-depths in all three set of CT images were found similar. 80%, 70%, 60% and 50% isodose-depths in SPS phantom images were found to be equivalent to that in chest images. Variations in calculated and measured doses at 6, 10 and 18 cm depths were found to be -0.36%, 1.65% and 2.23 respectively in case of SPS phantom, while 0.24%, 0.90% and 0.93% respectively in case of SP34 slab phantom. Conclusions: Dosimetric results indicate that patient specific QA should be done using chest phantom mimicking human thoracic region, which can be manufactured using polystyrene and pinewood.

Abstract: 117

Do anchor type intraprostatic fiducial markers allow us to acquire planning CECT immediately after it's implant: A preliminary study

Gedela Lakshmi Deepthi, Renu Madan, Anindya Mukherjee, Santosh Kumar 1 , Ravi Teja, Arun S. Oinam, Narendra Kumar

Departments of Radiotherapy and 1 Urology, Post Graduate Institute of Medical Education and Research, Chandigarh, India, E-mail: [email protected]

Introduction: Intraprostatic fiducial markers are frequently used for position verification during radiation treatment. Any marker migration after planning CECT will defeat the purpose of fiducial implantation, which occurs with seed markers where we acquire planning CECT 2 weeks after implantation. Anchor types markers claim for allowing to acquire planning CECT immediately after placement. This preliminary study was conducted, with anchor markers, to see for any significant migration, one week after implantation. Materials and Methods: This analysis was performed on 10 patients of carcinoma of prostate in whom three anchor type gold fiducial markers were inserted transrectally, under ultrasound guidance - two at the base, 1 cm apart, and one at the apex of the gland. A CT scan was taken on the day of fiducial implantation and another after one week, for radiotherapy planning purpose. Intermarker distance (IMD) was derived in both the CT scans and their median variations were compared to see for any significant marker migration. Results: It was observed that the absolute median deviation between the apex and right lateral (RL) fiducial was 0.01 (SD-0.13), apex and left lateral (LL) was 0.03 (SD-0.14), and LL & RL was 0.1 (SD-0.08). These median shifts were non-significant compared to our set up margins. It was also seen that the shifts between RL & LL IMD's were more as compared to apex & LL or apex and RL IMD's. Conclusion: This study shows no significant migration with anchor type fiducial markers. Hence Planning CECT can be acquired immediately after implant of anchor type intraprostatic fiducial markers to start radiation without any further delay.

Abstract: 150

Impact of modulation index on VMAT plan delivery efficiency

Midhun Kumar, Durai Manigandan, Mohan Das, Narendra Bhalla, Abhishek Puri

Department of Radiation Oncology, Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, India, E-mail: [email protected]

Introduction: The QA of VMAT dosimetry is a laborious task and it needs to analyse the results to find the possible reasons of failures. The goal of this work is to evaluate the effect of Modulation Index (MI = Monitoring Units/cGy) on deliverability of VMAT plans using PTW 729 ion-chamber Array and OCTAVIOUS TM Phantom. Materials and Methods: For this study, 80 VMAT-Dual Arc plans (6MV X-rays) and verification plans were generated with Monaco™ 5.1 Treatment Planning system (TPS) for Elekta Synergy TM linear accelerator (MI ranging from 2.31 to 7.35). The dose-plane measured on the effective plane of array and calculated plane were compared with 2D Gamma index (<1) analysis method with 2 mm distance-to-agreement (DTA) and 3% percentage dose difference with reference to maximum dose measured on dose-plane. Analysis was done using verisoft TM software. Results: From the results observed, among the 80 plans, 21 plans were with MI from 2.31 to 4, which having an average MI of 3.23 showed average pass-rate of 96.26 ± 2.96%. The 31 plans from 4.1 to 5 having an average MI of 4.26 showed pass-rate of 96.23 ± 4.83%. Other 28 plans MI ranging from 5.01 to 7.35 having an average MI of 6.15 showed pass-rate of 92.55 ± 9.95%.

When the modulation index increases, pass-rate of pre-treatment QA results reduces. It is clear in the results that the complexity in the beam modulation reduces the deliverability of the treatment plan. Conclusions: Treatment deliverability of the plan plans should be considered while accepting a highly modulated VMAT treatment plan and it is advised to keep modulation index within 5.

Abstract: 167

Radiation induced myelopathy: A retrospective analysis with respect to the factors affecting

Trupti O. Kothari

Department of Radiotherapy, Acharya Tulsi Regional Cancer Treatment and Research Institute, Bikaner, Rajasthan, India, E-mail: [email protected]

Radiation-induced myelopathy is a chronic handicap, though usually reversible in mild forms but is frightening because it could be severe, progressive and irreversible. It usually starts appearing several months to years after radiotherapy. Materials and Methods: We collected data for 150 patients treated (66 Gy/33 Fr; 2 Gy/Fr; 5 Fr/week) between June 2013 to December 2013, with respect to radiation dose delivered to the spinal cord in head and neck cases. Different types of data were collected including max dose received by spinal cord, spinal cord length being irradiated, the volume of spinal cord receiving more than or equal to 45 Gy. The patients were followed and histry for post RT neuritic symptoms was taken. Results: In our study, 2% of patients who received ≥50 Gy dose showed some early and mild symptomes of myelopathy such as Lhermitte sign, tingling or burning sensation in limbs, the appearance of symptomes was strongly associated with the maximum dose received >50 Gy (P < 0.01), volume of spinal cord receiving ≥45 Gy (P < 0.01) also the length of the spinal behind the field opened by secondary collimators (<20 cm vs >20 cm; P < 0.01), females were affected slightly more than males but the difference wasnt statisticlly significant (P > 0.05). Conclusion: Myelopathy is a rare but serious complication of radiation therapy (RT). Radiation myelopathy is white matter damage to the spinal cord developed after a certain period of application of ionizing radiation. The latency of symptoms being 6-24 months. Not just the maximum dose but other factors also influence the chances of appearance of myelopathy symptoms.

Abstract: 170

Cisplatin based chemotherapy induced vasculopathy: A case report

Manraj Kang, Pavan Kumar, Piyush Kumar, Sudeep Bisht

Department of Radiotherapy, Shri Ram Murti Smarak Institute of Medical Sciences, Bareilly, Uttar Pradesh, India, E-mail: [email protected]

Introduction: Cerebrovascular accident is a burdensome side effect of platinum-based chemotherapy that prevents administration of the full efficacious dosage and often leads to treatment withdrawal. Vascular occlusion is not an uncommon event in malignancy. However, the frequency of ischemic stroke after platinum based chemotherapy has been mentioned only occasionally in clinical studies. Case History: A 28 year old male presented as a case of carcinoma nasopharynx with chief complaint of pain in the throat, swelling over neck, cough with expectoration and loss of appetite since 2-3 month. CT scan was done in April 2015 which showed nasopharyngeal mass with right side bulky, matted cervical level II, III lymph nodes. Biopsy was undifferentiated squamous cell carcinoma nasopharynx. He was planned neoadjuvant chemotherapy (Paclitaxel, Cisplatin, 5FU) followed by chemoradiation. On 2 nd day of the 1 st cycle of neoadjuvant chemotherapy patient stopped talking and responding to verbal commands, right sided hemiplegia in spite of stable vitals. MRI brain showed multiple non hemorrhagic lacunas/infarcts in bilateral deep white matter region, left periventricular area and left basal ganglia ? vaculitis? drug induced. Colour Doppler carotid showed non visualization of right internal jugular vein, possibility of thrombosis is more than significant compression due to lymphdenopathy. Neurologist opinion was taken and started on symptomatic management for stroke which showed improvement in hemiplegia. Conclusion: Our knowledge about the pathophysiology of platinum induced vasculitis and cerebral stroke have suggested neuroprotective strategies is diverse but not thorough. Therefore, a thorough investigation of available evidence is important to design a trial.

Abstract: 190

Standardisation of volumetric modulated arc therapy based frameless stereotactic technique using large treatment plan ensemble aided knowledge based planning in an X-ray voxel Monte Carlo planning system

Biplab Sarkar, P. Sateesh, Harpreet Kaur, Jassal Kanan, Giri Upendra, P. Sashikumar, K. Saneg, S. P. Jeen, T. Ganesh, Munshi Anushhel, B. K. Mohanti

Department of Radiation Oncology, Fortis Memorial Research Institute, Gurgaon, Haryana, India, E-mail: [email protected]

Aim: Primary aim of this study is standardisation of the treatment plan that is minimization of the influence of individual treatment planner skill and knowledge, based on a large library of treatment plans. Corollary is to reduce the planning time as minimum as reasonably achievable. Materials and Methods: An ensemble of 120 VMAT based brain stereotactic plans (SRS/SRT) were categorised on basis of (1) PTV dose coverage challenged by presence of organ at risk (OAR) or not (2) Prescription dose (3) Number of PTVs (4) laterality (left /right) (5) tumour volume (6) shortest distance between OAR and PTV (7) centre to centre distance between OARs and PTV (8) lateral dimension of external contour (brain). Further, on arrival of a new patient most appropriate library plan was chosen on the basis of above categorisation using Microsoft Access; programing. The programming was associated with a micro enabled exel worksheet. Most appropriate library plan was copied with all parameters unchanged to the PTV centre (default isocentre) in new patient. Optimization and dose calculation was carried out in MONACO (v 5.00.04) with no or very minimal changes in the optimization constrain and arc length. Another independent treatment plan using the same beam configuration arc was generated by an experience medical physicist for comparison. Results: Independent plan (IP) was better than the knowledge based plans (KBP) in PTV coverage and dose conformity. However PTV coverage and OAR doses were not statistically different between two sets. PTV coverage V100% for In However for the PTVs where dose distribution is not challenged by OAR; PTV dose conformity is higher and statistically significant (P < 0.04) in case of IP. IP requires on average 3.5 optimization/dose calculation which is about 3.5-5 hrs, where KBP does not require more than 1.5 runs (1.5-2) hrs. Conclusion: KBS plans save a considerable planning time and almost independent of the treatment planner skill and knowledge. IP produce a better dosimetric result credited to an experience treatment planar with a high planning time. KBP works well with Monte Carlo planning system like MONACO.

Abstract: 193

Verification of stability and accuracy of an IGRT system to obtain the local image coordinates from a known spatial deviation

Harpreet Kaur, A. Satheesh Kumar, Biplab Sarkar, Kanan Jassal, Upendra Giri, T. Ganesh

Department of Radiotherapy, Fortis Memorial Research Institute, Gurgaon, Haryana, India, E-mail: [email protected]

Introduction: The purpose of this study was to verify the IGRT system's ability and stability by using a QUASAR TM Penta-Guide phantom for accurate patient positioning. Materials and Methods: For conducting this study, a QUASAR TM Penta-Guide phantom was used which has an off-center cross hair marking at a known spatial coordinates (x, y, z) from the calibrated isocenter. Penta-guide phantom was placed by aligning these coordinates with radiation isocenter i.e. cross wire and then CBCT images of the phantom were obtained using a standard acquisition procedure for seven months. Coordinates of off-center cross wire were obtained from the isocenter using CBCT system software and it was compared with the phantom specification of those coordinates. Results: The average value was 1.064 +/- 0.03, -1.23 +/- 0.06, and -1.15 +/- 0.28 in X, Y, Z directions respectively. The data in all the 3 directions were statistically significant with p-value of 0.0001, 0.0001, and 0.04 respectively. Standard error of differences were 0.003, 0.002, and 0.02 in X, Y, Z directions respectively. Standard deviation was more in Z direction as compared to other directions. Conclusions: The deviation obtained in the coordinates were highly reproducible in all the directions. The radiation isocenter should be correctly calibrated to rule out the system's discrepancies. In this study, the daily phantom setup uncertainties are not included but IGRT system's reproducilbilty and accuracy are within the acceptable range.

Abstract: 228

Socio-demographic and malignancy profile of patients treated on linear accelerator at a university hospital in Eastern Uttar Pradesh during 2015-2016

Swapnil Porwal, Uday Pratap Shahi

Department of Radiotherapy, Sir Sunderlal Hospital, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India, E-mail: [email protected]

Introduction: To study and analyse the records of the patients treated on 6MV Linear Accelerator at our hospital during 2015-2016. Materials and Methods: Files and records of the 85 patients treated on Linear Accelerator since its installation and functioning at our hospital in April, 2015 upto April, 2016 were studied and retrospectively analysed for socio-demography of patients and their malignancy profiles i.e. male-female proportion, age group analysis, site of the malignancy, early/late stage of the malignancy, and whether treatment decision on LINAC is patient preference or disease requirement. Results: Out of 85 patients treated on LINAC, forty-two were male (49.4%), rest i.e. forty-three (50.6%) were females. Age group <=19 yrs (4) 4.7%, 20-60 yrs (59) 69.4%, >60 yrs (22) 25.8%. Site wise: Head & Neck (31) 36.5%, GI (6) 7.1%, Breast (9) 10.6%, Gyn (21) 24.7%, Brain (12) 14.1%, others (6) 7% which included prostate (1), NHL tonsillar fossa (1), tracheal tumour (1), D3-D4 SOL (1), prophylactic cranial irradiation in ALL (2). Early stage (50) 58.8%, Late stage (35) 41.2%. Patient preference (28) 32.9%, Disease requirement (57) 67%. Conclusions: According to the data analysed, most of the patients treated on LINAC during a year period from installation were of Head & Neck, had an early disease, were of 20-60 years age group, were males and females in almost equal proportion and required treatment on LINAC as an indication of the disease.

Abstract: 230

Assessment of volumetric modulated arc therapy plan in sellar and suprasellar tumours: A JIPMER experience

Ajay S. Krishnan , S. Shyama Prem

Department of Radiotherapy, JIPMER, Puducherry, India, E-mail: [email protected]

Introduction and Objectives:
VMAT (Volumetric Modulated Arc Therapy) is a novel mode of conformal treatment delivery and has gained acceptance in treatment of many sites replacing the older techniques with accruing evidence. Sellar and suprasellar tumours are located in a precarious location surrounded by many organs at risk for radiation related complications. There is a paucity of studies in literature on VMAT in sellar and suprasellar tumors. Hence, we evaluate the utility of VMAT in treating tumours at these sites. Materials and Methods: CT data sets of patients with Sellar and suprasellar tumours treated with VMAT were collected from our institute's database from January 2012-2014. VMAT plans were made with dual arcs with sector avoidance as necessary to deliver a PTV dose of 45 Gy -54 Gy based on institute protocol. The plans made were optimised by Progressive Resolution Optimiser 3 algorithm. These plans are evaluated for Conformity, Homogeneity, Target volume coverage, and Organs-at-risk doses. Results: Standard Error of Differences where 0.003, 0.002 & 0.02 in X Y & Z Directions respectively. Standard deviation was more in two directions as compare to other direction [Tables 1 and 2]. Conclusions: VMAT provides superior target coverage, conformity and homogeneity and is better compared to 3-DCRT plans in literature. The doses to the organs-at-risk like optic chisama and optic nerves could be kept well below the tolerance. Hence, VMAT is unequivocally a better modality for sellar and suprasellar tumours compared to conventional 3-DCRT.

Abstract: 25

Volume doses from conventional 2D brachytherapy planning-why and when do we need image based dose optimization

Susan Mathews, Seetha Mohandas, Sharika Menon, P. Raghu Kumar, Preethi George, P. G. Jayaprakash

Department of Radiotherapy, Regional Cancer Centre, Thiruvananthapuram, Kerala, India, E-mail: [email protected]

In India Gynecologic brachytherapy continues to be planned using 2D X-rays in majority of patients. We have had good results, although we do not have sufficient 3-dimensional dosimetric data for the tumor or normal tissues. This study aims to evaluate the doses delivered to the brachytherapy target volume and organs at risk from standard 2D plans and compare with corresponding doses from MRI image based optimized plans. Materials and Methods: Twenty patients with cervix cancer treated with chemo-radiation and brachytherapy were included in this study. All patients had MR image based brachytherapy treatment plans generated for the first fraction of brachytherapy. The volume doses resulting from standard loading and Point A prescriptions were evaluated on the MR data set and compared with that of MR image based optimized plans. Results: Significant differences for HRCTV D90 doses between planning methods were observed in patients with gross residual disease (P < 0.0005) and when residual disease was asymmetric about the tandem and also when applicator placement was suboptimal. For patients with no gross residual disease at the time of brachytherapy the mean HRCTV D90 doses were similar for both planning modalities (P = 0.85). For HRCTV volumes <20cc, standard plans tend to deliver doses in excess of 7 Gy to D2cc bladder. Conclusions: Conventional x-ray based plans with moderate dose (7 Gy) Point A prescription delivers HRCTV D90 doses comparable with MRI based plans in patients with no residual, and centrally placed residual disease, provided proper applicator placement and ideal geometry can be ensured.

Abstract: 250

A comparative analysis of two different dose fractionation regimens of high dose rate intracavitar

B. Sreenivasa Rao

noneDepartment of Radiotherapy, Sree Venkateswara Institute of Medical Sciences, Tirupati, India, E-mail: [email protected]

High dose rate intracavitary brachytherapy is integral component in treatment of carcinoma uterine cervix. There is no consensus about optimal fractionation in HDR brachytherapy. Aim: To assess the feasibility, tolerability of high dose rate intracavitary brachytherapy schedule of 8 Gy per fraction per week for 3 fractions over 6 Gy per fraction per week for 4 fractions with or without chemotherapy in the treatment of carcinoma of uterine cervix. Methods: From 2013 to 2014 total 60 patients with carcinoma of the uterine cervix (Stages IIB and IIIB) were treated with EBRT and HDR ICBT. During course of EBRT if patients were fit for brachytherapy randomized to arm A 8 Gy per fraction per week for 3 fractions and arm B was received 6 Gy per fraction per week for 4 fractions. Results: The median follow up was 30 months, local control was 90% in Arm A and 83.3% in Arm B (P = 0.21) and the disease-free survival was 90% in Arm A and 83.3% in Arm B (P = 0.39). There is no significance of difference for late rectal and bladder toxicities between two arms (P = 0.43). Conclusion: Taking into account of increased hospital burden of locally advanced cancer cervix patients in Indian context, high dose rate intracavitary brachytherapy schedule of 8 Gy per fraction per week × 3 fractions is the preferable option over 6 Gy per fraction per week × 4 fractions with regard to comparable loco-regional control, acute and late toxicity, disease free survival and better patients compliance to lesser fractionation schedule.

Abstract: 252

New software for telethrapy calculations, patient management and record and verification

Thayal Singh Elias

Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, India, E-mail: [email protected]

Objective: To develop new software for manual calculations, patient management and record & verifying in radiotherapy. Materials and Methods: Accurate manual calculation, patient management in treatment planning & execution process and record & verification of all the patients with their treatment details who undergo radiotherapy is both mandatory and useful for conducting a successful radiotherapy practice. A systematic approach to the treatment planning procedure will be useful to the Oncologists as well as the Physicists in evaluating the treatment results. This may lead to devising future radiotherapy plans based on the previous treatment results. The patients will also be benefitted in programming their each visit & timing to the hospital and getting a detailed radiation treatment report. Major facilities available in the software are: Teletherapy Calculations: (1) Calculations for SSD, SAD, SSD On Field, SAD On Field, altered SSD techniques, multiple fields, etc, for both Telecobalt and Linac with multiple X-ray energies and Electron beams. (2) Correction factors for various beam modifying devices like wedges, shielding tray, neck/head rest, etc. (3) Weightage factors for different photon beams. (4) Gap Correction. (5) Acquisition of immobilization devise details for every treatment. Patient & Treatment Management: (1) Weekly, monthly and annual machine QA data acquisition and report. (2) Patient appointment scheduling for Treatment planning in different Simulators. (3) Patient appointment scheduling for computer treatment planning and each treatment machine. (4) Patient scheduling for treatment execution in various machines and treatment shifts. (5) Daily treatment execution recording and verification. Record & verify: (1) Recording patient's clinical data relevant to radiotherapy. (2) Their personal data can be directly entered or acquired from the existing hospital data, through hospital network. (3) Recording patient follow-up details, after Radiotherapy. (4) Retrieval of RT and follow-up data for research works. (5) Creation of treatment certificate for Radiotherapy on completion of treatment. Advantages: Through the record and verification system it is possible to verify the treatment parameters, calculations and prescription modifications, etc. It is also possible to get grouped patient data with the date of registration, age, sex, diagnosis, staging of disease, site of treatment, type of treatment, treatment techniques, name of treated Doctors, Physicists involved, treated machine, follow-up details, town/district, state, country of residence, etc for research activities. Results: This software and a Quality Assessment table to verify these calculations are developed and put in regular use in RCC (few screen shots are attached here with). Discussion: This software is very useful for Radiation Physicists and Radiation Oncologists to verify the treatment parameters, calculations and prescription modifications, treatment results through follow-up details, etc. The quantified evaluation of different kinds of treatments and their results will help the radiation oncologists to keep their future treatment decisions more scientific and evidence based.

Abstract: 254

Dose to the normal structures during treatment with interstitial brachytherapy

J. Mathangi , Vinay Muttagi, Surendra Reddy, Karthikeyan Srinivasan 1 , Marudupandian 1

Departments of Radiation Oncology and 1 Medical Physics, BGS Global Hospitals, Bengaluru, Karnataka, India, E-mail: [email protected]

Aim: To study the differences in the dose received by the normal structures during the time interval of continuous treatment with interstitial brachytherapy over two days. Materials and Methods: Carcinoma cervix is the most common women cancer and majority present in locally advanced stages of IIIB and above. These patients are planned for interstitial brachytherapy and undergo one insertion of interstitial needles under anesthesia and treatment with three to four sessions of HDR brachytherapy over 2 days. The CT based volumetric dosimetric planning is done on the first day following the insertion and the treatment is given based on this planning. We in our institute did a CT scan on the second day at the end of treatment for 100 continuous patients and analysed the change in the dose to the normal structures over the time period of 2 days and if that correlated with the clinical long term toxicity. Results: The volume of rectum was 52.4cc (SD ± 17.1) and 58.5cc (SD ± 6.04), the volume of bladder was 173cc (SD ± 35.9) and 197cc (SD ± 87.9), the volume of small bowel was 112.8cc (SD ± 54.5) and 86.4cc (SD ± 69.5) in the pretreatment and the post treatment CT scans respectively. The doses received by rectum, bladder and small bowel were 3.96 Gy (SD ± 0.27), 3.9 Gy (SD ± 0.23), 2.03 (SD ± 1.25) in the pretreatment CT scan and 4.2 Gy (SD ± 0.44), 4.62 (SD ± 0.67) and 1.85 Gy (SD ± 1.1) in the posttreatment CT scan. Conclusion: The volumetric CT based planning done for our brachytherapy patients in the pre and post treatment CT scans showed that the doses received were well within prescribed limits and not significantly changed.

Abstract: 26

A dosimetrical approch to identify the ideal location of isocenter in intensity modulated radiotherapy treatment plans

Abhijit Mandal, Anupam Kumar Asthana, Satyajit Pradhan, Uday Pratap Shahi, Sunil Chowdhury

Department of Radiotherapy and Radiation Medicine, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India, E-mail: [email protected]

Objectives: To search an ideal location of isocenter in IMRT treatment plan. Materials and Methods: Twenty Eight (28) clinical target volumes and Four (4) English capital letters (C, L, T and H) target volumes were considered in this study. Two IMRT treatment plans were generated for each target volume in ECLIPSE TM Treatment Planning System (Version 11.0.47, supplied by Varian Medical System, Inc., Palo Alto, CA, USA), first one with isocenter automatically placed (ISO AUTO ) by treatment planning System and second with geometric center based isocenter (ISO GEOM ). The geometric center of a cuboid volume, which was formed encompassing around the target volume in sagital, transverse and frontal planes, is considered as the geometric center of the target volume as well as the isocenter (ISO GEOM ) of the IMRT plans. While performing the IMRT treatment plans using Beam Angle Optimization (BAO) and Leaf Sequence Optimization, the normal tissue objectives and target volume objectives were kept similar in both the plans. The dosimetrical parameters between two groups of plans were compared. Results: The distance between ISO GEOM and ISO AUTO ranges from 0.16 cm to 3.04 cm a mean and median 0.85 cm and 0.69 cm respectively. The ISO GEOM based IMRT plans exhibits advantages in total MU reduction (100% cases), total number of field reduction (97% cases) and reduction of patient mean Dose (78% cases) over ISO AUTO base IMRT plans. The Conformity Index (CI), Homogeneity Index (HI) and target mean dose were comparable between both group of plans. Conclusion: To get optimal dosimetrical advantages the geometric center based isocenter may be considered as isocenter of an IMRT treatment plan, instead of automatically placed isocenter base IMRT treatment plan.

Abstract: 267

PTW 2D-array seven29 and octavius II phantom for patient specific VMAT and IMRT QA verification

C. Prabagaran, S. S. Mokha, Piyush Jain, N. Bharath Kumar, Gaurav Kumar, Chhamta Dutt, D. Manigandan 1

Department of Radiotherapy, City Hospital and Research Centre, Jabalpur, Madhya Pradesh, 1 Department of Radiotherapy, Fortis Hospital, Mohali, Punjab, India, E-mail: [email protected]

Introduction: The evaluation between measured and calculated dose is essential in the patient specific quality assurance procedures for intensity modulated radiation therapy. The high complexity of volumetric arc radiotherapy, requirements of such techniques require new methods and potentially new tools for the quality assurance of such techniques. Studies evaluating the dosimetric performance of a 2D ionization chamber array quality assurance device have been performed in our institution. Our results showed that differences between the detector systems are small. The respective gamma index histograms showed that when 3% dose difference and 3 mm distance to agreement are used, more than 90% of the evaluated points were within the tolerance criteria. Materials and Methods: Total 50 cancer cases are studied and each sites 10 patients were evaluated. The PTW seven 29 2D-Array consists of 729 vented plane-parallel ionization chambers with a 0.6 g/cm 2 graphite wall arranged in a 27 × 27 matrix covering an area of 27 cm × 27 cm. Each single chamber is air-filled with a cross section of 5 mm × 5 mm and height of 5 mm. The chambers are separated from each other by 5 mm. The distance between the centers of adjacent chambers is 10 mm. The 2D array surrounding material is made up of polymethyl methacrylate (PMMA). The array interface and a data acquisition board for the personal computer. A dedicated phantom for the QA of rotational treatments focusing primarily on the use of the Seven 29 2D ion chamber array, called Octavius was used during measurements. Octavius is made of polystyrene, central cavity allows the user to insert the 2D ion chamber array into the phantom. The position of the cavity is such that when the 2D array is inserted, the plane through the middle of the ion chambers goes through the center of the phantom. The measurement ranges for PTW Seven 29 as specified by manufacturer are 200 mGy - 1000 Gy and 500 mGy min -1 to 8 Gy min -1 . The 2D array is calibrated for absolute dosimetry in a Co 60 photon beam at the PTW secondary standard dosimetry laboratory. In this work the detector array was used in absolute dose measuring mode and dose values were corrected for daily variation of linac output. Results and Discussion: Our results showed that the PTW Seven 29 measurements of IMRT, VMAT patient specific QAs (Table 1). The respective gamma index histograms showed that when 3% dose difference and 3 mm distance to agreement are used. Accurate dose validation is a key component in the successful delivery of patient treatments. The PTW Seven 29 with Octavius is accurate with the clinical criterion of 3% and 3 mm and is also accurate with more stringent criteria, 2% and 2 mm, for clinically used field widths and pitches. Based on these measurements however, the Seven 29/Octavius gives better results when using the clinical passing criteria of 3%, 3 mm as well as the more stringent 2% and 2 mm when comparing QA plans. Current 2D ionization array systems such as the PTW Seven 29 eliminate the need of film and ion chamber-based dose validation and further shorten the time associated with dose validation due to their ability of instantaneously reading, processing and analyzing the data.

Abstract: 36

A study on the effectiveness of electron filters designed for telecobalt treatment: Monte Carlo study

Narayan Prasad Patel , Rahul Shukla 1 , Hanuman Prasad Yadav 1 , Vivek Kaushal

Department of Radiotherapy, PGIMS, Pt. B D Sharma University of Health Sciences, Rohtak, Haryana, 1 Department of Radiotherapy, GGS Medical College, Faridkot, Punjab, India, E-mail: [email protected]

Objectives: The aim was to use a Monte Carlo simulation code on the study of the effectiveness of various thin metallic electron filters designed for the telecobalt radiotherapy treatment. Materials and Methods: The BEAMnrc Monte Carlo simulation code was used to simulate the electron filters of thickness of 0.5 gm/cm 2 just below the trimmer bar of Theratron Equinox-80 telecobalt unit for 35 × 35 cm 2 treatment field size. The electron filters were made of an aluminum, copper, nickel, tin, PMMA, and lead with single or composite materials. The phase space of radiation beams at treatment distance were analyzed by generating profiles along the X-axis of radiation field for photon and electron. The surface dose in water phantom for various filters and unfiltered bead were calculated using dosxyznrc code and compared. Results: The electron energy fluence for unfiltered beam was found to be 0.32% of the photon energy. The decrease in photon intensity due to presence of filter was about 3.7% for various filters. The filters with low atomic number show poor electron contamination removal efficiency. The tin, copper and nickel were found to be effective filters, removing nearly 38% of contaminant electron energy. The lead filter is equally effective as tin, however the Compton recoil electron emitted due to high Z material adds significant energy, diminishing its effectiveness. The tin filter dominants over to copper and nickel filter on the subject of surface dose reduction and dmax. Conclusion: It is concluded from this study that the tin filter gives maximum surface dose reduction of about 47% along with the significant increase in d max from 2 mm to 6 mm and the percentage depth dose beyond d max .

Abstract: 37

A prospective study of field in field versus wedge based plans for pelvic irradiation and its concurrence with ICRU 50: A dosimetric comparison

Milind Shetti, Bala Subramaniam

Department of Radiation Oncology, Karnataka Cancer Therapy and Research Institute, Hubli, Karnataka, India, E-mail: [email protected]

Introduction: In our department pelvic malignancies comprises 40% of our total cases. Most common cancers being cervix, endometrium and ano-rectum, with 50-60% being treated with radiation. In pelvic radiotherapy, we routinely use standard four field technique with 15 MV photons. Here the dose variation within the PTV ranges from 94% to 115% which is beyond ICRU 50 specifications. These high dose regions are mainly seen over urinary bladder, small bowel and rectum, which can be modified with the use of wedges. Other technique of improving the homogeneity within target volume is use of field- in- field technique (FIF). This technique is also called as forward planning IMRT where we use 5 to 6 fields instead of four fields. The aim of the present study is to compare the homogeneity within the PTV and total monitor units between wedge based plan and the FIF technique in whole pelvis radiotherapy. Materials and Methods: A total of forty patients having pelvic malignancies were selected for this study from January to July 2016 prospectively. These patients underwent contrast enhanced computed tomography (CT) scans with 5 mm sections. Bladder protocol of 500 ml for 30 minutes was followed. A three dimensional conformal radiotherapy technique was used for treatment. For each patient, two plans were generated simultaneously, one with a wedge based plan and the other with field in field (FIF) technique. As per ICRU 50, two plans were generated and later compared for mean, maximum and median doses for both Clinical Target Volume (CTV) and Planning Target Volume (PTV) and the total monitor units. The best possible plan was selected for undergoing the treatment. Results: For our study we selected forty cases of pelvic malignancies for FIF and wedge based planning. The following results were obtained in pelvis at 95% isodose using 15 MV photons. The CTV maximum values were 105.63% for FIF and 109.29% for wedges. Similarly the PTV maximum values were 107.34% and 110.5% for FIF and wedges respectively. The total monitor units were 242.96 for FIF and 276.21 for wedges. Conclusion: Field in field technique reduces dose inhomogeneity better than wedge based plan. Field in field technique reduces the total monitor units received by the patient compared to wedge based planning. The reduction in the total monitor units leads to reduction in the overall treatment time.

Key words:
Clinical target volume, field in field, International Commission of Radiation Unit

Abstract: 43

Impact of bladder and rectum volume changes on prostate positioning and dosimetric parameters and role of CBCT in minimizing the positional errors

Harsh Goyal , Om Prakash Gurjar, Krishna Lal Gupta, Virendra Bhandari, Priyusha Bagdare

Department of Radiotherapy, Sri Aurobindo Medical College and P. G. Institute, Indore, Madhya Pradesh, India, E-mail: [email protected]

Introduction: The outcome of prostate radiotherapy is affected by various factors e.g. geometric uncertainties during radiotherapy, including inter/intra fractional patient motions, organs size/motion, and daily setup errors. This may increase normal tissue complications when a high dose to prostate is administered. More accurate treatment delivery is possible with daily imaging and localization of prostate. Materials and Methods: Position verification in 20 patients with prostate cancer was performed by using kilo-voltage (kV) orthogonal-portal-imaging (OPI) followed by cone-beam-computed-tomography (CBCT) before treatment delivery in 25 sessions per patient. In each session, OPI was performed by using on-board-imaging (OBI) system and pelvic bone was matched. After applying the noted shift by using OPI, CBCT was performed and prostate matching was done. The isocenter shifts along all three translational directions were combined into a three-dimensional isodisplacement vector (IDV). The volume of rectum and bladder was measured by delineating these on CBCT images taken in all 25 sessions, and dosimetric impact due to change in volume was analyzed. Results: The mean IDV (cm) calculated during 500 imaging sessions was 0.843 (Standard deviation (SD): 0.584) for OPI and 0.493 (SD: 0.326) for CBCT. Even after perfect bone-to-bone matching by OPI, a significant shift in prostate was observed on CBCT. No significant variation observed in dosimetric data due the bladder/rectum volume change except in case of four patients. Conclusions: Imaging with CBCT provides a more accurate prostate localization than the OPI. The volume of bladder/rectum should be maintained which may make significant variation in the dosimetric data.

Abstract: 74

Comparison between static and dynamic intensity modulated radiosurgery planning: Single institution retrospective analysis

G. Ashwini, Deleep Kumar Gudipudi, B. Sukrutha, A. Abdullah, Heena Kauser, V. Chandipriya, L. Tasneem Swarna Kumari, Sudhakar Kumar, M. Suneetha, E. Vasundhara, A. Krishnam Raju

Department of Radiation Oncology, Basavatarakam Indo American Cancer Hospital and Research Institute, Hyderabad, Telangana, India, E-mail: [email protected]

Objective: Retrospective comparison between IMRS plans done by static IMRT (BRAINLAB) and dynamic IMRS (RAPID ARC) in terms of dosimetry, treatment time and MU delivered. Materials and Methods: Treatment plans of 22 patients (12 by static IMRS and 10 by dynamic IMRS) were retrospectively analysed and compared for V 8Gy, V 10Gy and V 12Gy to normal brain tissue, treatment time and monitor units (MU) delivered. All patients were treated in Varian Novalis Tx and planning was done in Brainlab TPS version 4.1 for static IMRS and Eclipse version 10.0 for dynamic IMRS. Statistical analysis was done by ANOVA t test using Windostat version 9.2 and a p value <0.05 was considered significant. Results: Both groups were comparable in terms of age (P = 0.05), sex (P = 0.20), number of lesions (P = 1.0), PTV volume (P = 0.14), PTV dose delivered (P = 1.0) and number of fractions delivered (P = 0.96). Mean V 8Gy in brain was 54.79cc vs 72.25cc (P = 0.421), V 10Gy was 37.45cc vs 51.66cc (P = 0.46), V 12Gy was 26.54cc vs 36.35cc (P = 0.51) in static and dynamic IMRS, respectively. Mean treatment time was 31.25 minutes vs 15.3 minutes (P = 0.04) and MU delivered was 6287 vs 4142 (P = 0.038) in static and dynamic IMRS respectively. Conclusions: Dynamic IMRS plans are comparable to static IMRS plans in terms of V 8Gy , V 10Gy and V 12Gy in brain with mean PTV volume at 26.8cc vs 18.8cc, respectively. Dynamic IMRS plan requires less MUs (P = 0.038) and lesser treatment time (P = 0.04) which is statistically significant. Academic institutions with high patient load should consider treating with Dynamic IMRS.

Abstract: 79

Daily IGRT: Is the burden justified in high volume centres

Diplu Choudhury, Vikas Jagtap, A. K. Kalita, M. Bhattacharyya, T. R. Borborah, Rubu Sunku

Department of Radiation Oncology, Dr. B Borooah Cancer Institute, Guwahati, Assam, India, E-mail: [email protected]

Prospective evaluation of different IGRT protocols in patients treated with IGRT/IMRT technique. Materials and Methods: Patients with various cancers treated with IGRT/IMRT (kV-CBCT Elekta synergy) at our institute were randomised into three IGRT protocols. In Protocol A (single fraction Protocol) patients were set as per the IGRT set up errors done at first fraction. In Protocol B (first 3 fraction) set up was done with average of first three fractions set up errors. In Protocol C (first 5 fraction) average value of first five fractions was used. Thereafter weekly IGRT-CBCT was done to assess the set up errors. If the set up errors in x, y or z axis is more than 5 mm the errors were applied in subsequent set up and again weekly CBCT was done. To avoid missing of target area due to study all patients were subjected to daily IGRT and if deviation is more than 5 mm, the correction was done for that particular day in each protocol. Results: In 21 patients (7 in each protocol) out of 502 IGRT fractions 103 (20.51%) fractions were deviated more than 5 mm. In Protocol A 18.56% (31/167), Protocol B 25.46% (41/161) and in Protocol C 17.81% (31/174) IGRT fractions were outside the acceptable error (>5 mm). On subset analysis, in Head and neck cancers 4.34% (3/69), 11.53% (6/52) and 10.48% (13/124) fractions were out of limit in each protocol respectively. The values for abdomino - pelvic cancers were 28.57% (28/98), 32.11% (35/109) and 36% (18/50) respectively. Conclusion: Daily IGRT protocol remains the most precise method to deliver RT without errors.

Abstract: 80

Uterine motion associated with strict bladder filling protocol during image-guided radiotherapy of carcinoma cervix: Do we need to redefine internal target volume margins for the uterus?

Anindya Mukherjee, Bhavana Rai, Maninder Singh, Sushmita Ghoshal, Ngangom Robert

Department of Radiotherapy, Post Graduate Institution of Medical Education and Research, Chandigarh, India, E-mail: [email protected]

Introduction: The Internal Target Volume (ITV) margins of the uterus and cervix take into account the inter-fraction motion (IFM) of uterus occurring mostly due to variations in bladder volumes over the course of radiotherapy. Traditionally, the ITV margins are 15 mm in Antero-Posterior (AP) and Supero-Inferior (SI) axes and 7 mm in lateral axes. The aim of this study was to assess whether the ITV margins need to be redefined when a strict bladder filling protocol is followed. Materials and Methods: Fifteen patients of carcinoma cervix, who were treated with Image-guided Radiotherapy (IGRT) (to a dose of 46 Gy in 23 fractions over 4.5 weeks) from February, 2016 to July, 2016 were recruited. During the course of IGRT, cone beam computed tomographic scans (CBCT) were taken, thrice in the first week of treatment and then weekly for the remaining 3.5 weeks, following our institutional protocol. Patients were asked to empty their bladder 1 hour prior to radiotherapy followed by 500 ml water intake in the first 30 minutes. Empty rectum was also ensured prior to radiotherapy. The Varian Eclipse Offline review v 11.0 was used to match the uterine contours of CBCTs with that in planning CT scan in all three axes- AP, SI and lateral. The median values of these corrections obtained with matching gave an estimate of the IFM and hence ITV margins. Results: The median values with standard deviations (SD) of IFM are as follows: Supero-Inferior (SI) - 1.9 mm (SD-3.39), Antero-Posterior (AP) - 2.6 mm (SD-4.64) and Lateral - 0.5 mm (SD-2.10). So, the maximum IFM (AP) is 2.6 ± (4.64 × 2) = -6.68 to + 11.88 mm = 18.56 mm and minimum IFM (lateral) is 0.5 ± (2.1 × 2) = -3.7 mm to + 4.7 mm = 8.4 mm. Hence ITV expansions should be 9.28 mm (AP) and 4.2 mm (lateral). Conclusion: ITV margins of 10 mm in all AP and SI directions and 5 mm in lateral directions are feasible with strict bladder filling protocol.


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