|Ahead of print publication
Evaluation of field-in-field, three-field, and four-field techniques for treatment planning of radiotherapy of pancreatic cancer
Mohamad Pursamimi1, Mahdi Ghorbani2, Wrya Parwaie3, Ahmad Shakeri4, Ali Soleimani Meigooni5
1 Department of Medical Physics, School of Medicine, Semnan University of Medical Sciences, Semnan, Iran
2 Biomedical Engineering and Medical Physics Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
3 Department of Medical Physics, Faculty of Paramedical Sciences, Ilam University of Medical Sciences, Ilam, Iran
4 Vali-e Asr Radiotherapy Oncology Center, Vali-e Asr Hospital, Qom, Iran
5 Comprehensive Cancer Centers of Nevada, Las Vegas, USA
|Date of Submission||16-Feb-2020|
|Date of Decision||23-Jun-2020|
|Date of Acceptance||26-Jul-2020|
|Date of Web Publication||12-Dec-2020|
Biomedical Engineering and Medical Physics Department, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Velenjak, Tehran
Source of Support: None, Conflict of Interest: None
Background: Pancreatic adenocarcinoma is a lethal condition with poor outcomes by various treatment modalities and an increasing incidence. Aim: The aim of this study is to evaluate the advantages of field-in-field (FIF) versus three-field and four-field radiation treatment planning techniques in three-dimensional treatment of patients with pancreatic cancer. Materials and Methods: The evaluations of these planning techniques were performed in terms of physical and biological criteria. Radiotherapy treatment data of 20 patients with pancreatic cancer were selected and evaluated for FIF, three-field, and four-field treatment techniques. The patients were treated by 6 MV photon beam of a medical linac, and these three treatment planning techniques were evaluated for all the 20 patients. The plans were compared based on dose distribution in the target volume, monitor unit (MU), and dose to organs at risk (OARs). Results: The results have shown that, with assuming the same prescribed dose to planned target volume, FIF plans have some advantages over three-field and four-field treatment plans, based on MU values, V20 Gy in the right lung, V20 Gy in the left lung, Dmean in the left kidney, Dmean in the liver, and Dmean in the spinal cord. Based on the obtained results, the use of FIF technique reduces MUs compared to the three-field and four-field techniques. Conclusion: Having a less MU for performing treatment reduces scattered radiation and therefore reduces the risk of secondary cancer in normal tissues. In addition, the use of FIF technique has advantage of less radiation dose to some OARs.
Keywords: Field-in-field, four-field, pancreatic cancer, radiotherapy, three-field, treatment planning
|How to cite this URL:|
Pursamimi M, Ghorbani M, Parwaie W, Shakeri A, Meigooni AS. Evaluation of field-in-field, three-field, and four-field techniques for treatment planning of radiotherapy of pancreatic cancer. J Can Res Ther [Epub ahead of print] [cited 2021 Apr 16]. Available from: https://www.cancerjournal.net/preprintarticle.asp?id=303251
| > Introduction|| |
Ductal pancreatic cancer currently represents the seventh most common cause of cancer mortality worldwide, accounting for about 4% of cancer-related deaths in males and females. It is more common in the elderly population and rarely diagnosed in people younger than 40 years of age. Unfortunately, <20% of patients in radiotherapy have localized, respectable, and therefore potentially curable tumors. The overall 5-year survival rate among patients with pancreatic cancer is <5%. Currently, there are four common methods to treat cancer: surgery, radiation therapy, chemotherapy, and radioimmunotherapy., In radiation therapy, ionizing radiation is used to control or destroy malignant cells. Most patients referring to radiation therapy are treated by a linear accelerator., The major aim in radiation therapy is to deliver a uniform and lethal dose to tumor, while the dose to organs at risk (OARs) should be below their tolerance. Therefore, it is important to use methods that can provide greater adaptation between the treated volume and the planned target volume (PTV).
Radiation therapy, in addition to destroying cancer cells, has some adverse effects on healthy tissues. Each organ of the body has a certain degree of tolerance to radiation, and receiving radiation doses more than the tolerated dose has side effects on the function of the organ. Given the potential adverse effects of radiation therapy, treatment planning should be performed with the aim of delivery of the least dose to normal tissues and organs sensitive to radiation and at the same time a sufficient dose to the tumor., For this purpose, wedges, compensators, beam-shaping devices, blocks, and computer-driven multileaf collimators (MLCs) can be used., However, there are several drawbacks in using wedge filters. For example, wedges increase the unwanted dose delivered to the healthy tissues, which is due to increase in the radiation scattering.,, Field-in-field (FIF) technique is accounted as a type of forward intensity-modulated radiation therapy (IMRT) treatment which is performed manually. One type of FIF includes adjusting a number of fields which are formed by MLCs to generate subfields. One advantage of FIF is higher conformity of the radiation field with the tumor, compared to other conventional fields. Different planning techniques can be used for treatment of pancreatic cancer. These techniques include three-field, four-field, FIF, IMRT, and volumetric modulated arc therapy. Each technique can have some advantages and disadvantages compared to the other techniques in pancreatic cancer radiotherapy, and this was the subject of different studies in this field.
Onal et al. has reported that the FIF method is useful in reducing the size of the focal spot and improving the homogeneity index (HI) in radiotherapy of breast cancer compared to the sophisticated radiotherapy methods., In the study by Onal et al., it was performed a dosimetric comparison of FIF technique and tangential beams for breast irradiation. They have shown that the dose distribution within the target volume was more homogeneous, and the doses in healthy tissues were less by the FIF plan compared to the tangential wedge plans. In a study, Al-Rahbi et al. compared planning and delivery efficiency of three-dimensional (3D) conformal radiotherapy and FIF techniques in radiotherapy of breast cancer. Their study has shown that FIF technique significantly reduces the size of the hot spots and improves the coverage of the target volume. Previous studies,, which have been performed on the FIF technique have mainly been based on analysis of dose–volume histogram (DVH), two dimensional and 3D spatial dose distributions. To the best of our knowledge, the efficacy of the FIF treatment plans has not yet been analyzed for pancreatic cancer patients. The aim of this study is to evaluate the potential benefits of FIF treatment in conformal 3D radiation therapy for treatment of patients with pancreatic cancer in terms of physical and biological criteria.
| > Materials and Methods|| |
Twenty patients with different stages of pancreatic cancer were planned by three techniques including FIF, three-field, and four-field (box) in the form of 3D conformal radiation therapy (3D-CRT). The treatment planning of the patients was based on their computed tomography (CT) images, and they were treated by a 6 MV Shinva linac (Shinva Medical, Shandong, China) based on their clinical radiotherapy treatment. Conformity index (CI), HI, Dmean, Dmax, tumor control probability (TCP), V20 Gy of lungs, normal tissue complication probability (NTCP), and monitor units per fraction (MU/fraction) were analyzed to evaluate the three treatment plans. The dose to healthy OARs, such as spinal cord, liver, right kidney, left kidney, right lung, and left lung, was also evaluated.
Characteristics of patients
The radiotherapy treatment data of 20 patients with pancreatic cancer with Stage II of tumor according to an oncologist were selected in Vali-e-Asr Oncology and Radiotherapy Center (Qom, Iran). The characteristics of the patients such as number of male and female patients, age, prescribed dose (Gy), PTV volume (cc), and volumes of OARs (cc) are presented in [Table 1].
|Table 1: Characteristics of the patients with pancreatic cancer in the present study|
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CT scanning was performed on all patients to obtain their anatomical information. Due to the similarity of treatment and imaging conditions, the patients were placed on a flatbed in supine position. The scanning thickness of 3 mm was selected, and the imaging was performed with a Neusoft CT scanner (NeuViz 16, Neusoft Medical Systems, PR, China). All patients received a prescribed dose of 45.00 Gy in 25 fractions and treated with 3D-CRT treatment.
The gross tumor volume (GTV) was determined according to the guidelines published by the Radiation Therapy Oncology Group by a professional radiologist. Clinical target volume (CTV) is defined as GTV plus a 15-mm margin, which includes areas where tumor cells may be present. In defining planning target volume (PTV), a 10-mm isotropic margin is also considered for tumor [according to [Figure 1]. PTV is defined to account for the uncertainties of the patient adjustment, changes in CTV position, and patient movement. After this stage, the healthy OARs, such as the spinal cord, liver, right kidney, left kidney, right lung, and left lung, were determined in the patients by the oncologist., The kidneys, lungs, liver, and spinal cord were contoured on the axial CT images. Dose calculations were performed in a PCRT 3D treatment planning system (RF Tecnicas Radiofizicas, Zaragoza, Spain) using convolution/superposition algorithm.
|Figure 1: Isodose curves and color wash dose distributions in cross-sectional, sagittal, and coronal views of a pancreatic cancer patient obtained when the field-in-field (a1–a3), three-field (b1–b3), and four-field (box) (c1–c3) techniques were applied for treatment planning|
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Three treatment plans (FIF, three-field, and four-field [box]) were designed for each patient. All beams were delivered at a dose rate of 200 MU/min.
For treatment planning of FIF technique, a number of boxing fields were used in the treatment planning software without wedge. Then, another incline condition of the boxing fields was applied by shielding the areas above the dose of 105%. The weights of these fields were adjusted to provide an optimal dose of adequate homogeneity in the PTV.
Treatment planning of three-field included anterior, posterior, and left lateral fields. In this treatment planning, wedges were used for all fields. Beam weights, wedge angles, and wedge directions were adjusted so that at least 95% of the 45.00 Gy prescription dose was received by the tumor volume.
Treatment planning of four-field (box) included anterior, posterior, and two lateral fields. In this treatment design, a wedge can be used for three-field and four-field (box) techniques, if needed, but the FIF technique lacked the wedge. Beam weights, wedge angles, and wedge directions were adjusted so that at least 95% of the 45.00 Gy prescription dose was received by the tumor volume.
The parameters compared for three treatment techniques included CI, HI, Dmean, Dmax, TCP, V20 Gy of lungs, NTCP, and MU/fraction. The patients were considered to be treated with a prescribed dose of 45.00 Gy to the PTV in fractions of 1.80 Gy, with five fractions given per week. The number of MUs needed for each plan was calculated, and then, MUs for these three treatment plans were compared together.
Calculation of dosimetric parameters
DVHs of the FIF, three-field, and four-field (box) plans were obtained for the PTV, kidneys, lungs, liver, and spinal cord for all patients. In order to quantitatively compare the three plans, various parameters were obtained. For the PTV, the maximum dose (Dmax) and mean dose (Dmean) as well as the TCP were used. For the OARs, maximum and mean doses, NTCP for the liver, lungs, and spinal cord, and also V20 Gy for the lungs were used. The standard deviation in each value was reported as the uncertainty.
After creating the DVHs and using the required parameters, the CI of radiation was calculated. It is defined as the ratio between the volume covered by the reference isodose, which according to the International Commission on Radiation Units and Measurements (ICRU) is 95% isodose, and the target volume was designated as the PTV. Based on this definition, the CI can be calculated by Formula (1):
where VTV is the treatment volume of the prescription isodose line, VPTV is the volume of the PTV, and TVPV is the volume of VPTV within the VTV. The high conformal coverage of PTV is indicated by a closer value of CI value to the value of 1.00., HI in PTV is defined by Equation (2):
where D2% and D98% are the minimum doses delivered to 2% and 98% of the PTV. A small HI value indicates high homogeneity.,
The calculation of NTCP was performed by Lyman-Kutcher and Burman models. By this model, which is also known as a normal or empirical model, the probability of normal tissue complications in organs which have nonuniform radiation is calculated using dose–response curves and possibly the complications of organs that have uniform radiation. For this purpose, the effective volume method was used, which is the nonuniform dose–response curve, with the volume equal to the effective volume. The dose is equal to the maximum organ dose, and the curve was plotted in the form of a uniform dose–response curve.
The late response of normal tissues to radiation is determined by NTCP model. Niemierko’s model proposes a logistic function for the NTCP based on equivalent uniform dose (EUD):
where TD50 is the tolerance dose leading to a 50% complication rate during a certain period of time, and EUD is the dose which is distributed homogeneously within the volume of a structure that results in equivalent biological effect to a specified nonhomogeneous dose distribution. γ50 is a unitless model parameter that is specific to the normal structure or tumor of interest and describes the slope of the dose–response curve. TCP of tumor, based on Niemierko’s model, is given by:
where TCD50 is the absorbed dose producing a 50% control rate of the tumor exposed to uniform radiation and g50 is a unitless model parameter for describing the slope of the tumor dose–response curve.,,,
Statistical analyses were performed with the Statistical Package for the Social Sciences (SPSS) software (version 16, SPSS Inc., Chicago, USA). For these results, Kolmogorov–Smirnov test was used to determine whether the distribution of the data was normal or nonnormal. The data with normal distribution were treated with paired t-test. P < 0.05 was considered as a significant difference between the two groups which were compared. Chi-square test was used for comparison of those data which had abnormal distribution.
Isodose curves and color wash dose distribution in cross-sectional, sagittal, and coronal views of a sample pancreatic cancer patient for FIF (a1, a2, and a3), three-field (b1, b2, and b3), and four-field (box) (c1, c2, and c3) techniques are shown in [Figure 1], respectively. DVH comparison for a sample patient obtained for FIF, three-field, and four-field (box) techniques for treatment of pancreatic cancer is presented in [Figure 2]. In this figure, DVH plots for the PTV and OARs (lungs, kidneys, liver, and spinal cord) are shown. The values of parameters obtained from DVH analysis of all patients are listed in [Table 2] and [Table 3].
|Figure 2: Dose–volume histogram for a sample patient with pancreatic cancer for the field-in-field (a), three-field (b), and four-field (c) techniques|
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|Table 2: Dosimetric results for the planned target volume, tumor control probability, and monitor unit for the field-in-field, three-field, and four-field (box) plans|
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|Table 3: Dmean, Dmax, V20 Gy (%), and normal tissue complication probability (%) in the organs at risk obtained from field-in-field, three-field, and four-field (box) techniques|
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Dosimetric results (Dmean [Gy], Dmax [Gy], CI, and HI) for PTV, TCP (%), and MU obtained from FIF, three-field, and four-field (box) plans are listed in [Table 2]. All data were evaluated at a significant level of P < 0.05. Based on the data presented in [Table 2], the values of Dmax, Dmean, and TCP for PTV volume were not significantly different between the three techniques (FIF, three-field, and four-field [box]) (P > 0.05). There was also no significant difference in CI and HI values between the three plan groups. As it is shown in [Table 2], the MU/fraction requirement for treatment when using FIF technique is significantly reduced (P < 0.05). On the other hand, there is no significant difference between the MU/fraction for the three-field and four-field (box) techniques (P > 0.05). All of the parameters for FIF technique are very close to those for the four-field technique, except the MU.
Dmean, Dmax, V20 Gy (%), and NTCP (%) in the OARs obtained from FIF, three-field, and four-field (box) plans are presented in [Table 3]. The right lung, left lung, right kidney, left kidney, liver, and spinal cord were considered as OARs.
| > Discussion|| |
In this study, FIF, three-field, and four-field (box) plans were evaluated for treatment of pancreatic cancer. Based on the data on dose distribution in the target volume and TCP [Table 2], it was observed that there was no superiority in the application of the FIF technique than the other two techniques in terms of Dmean, Dmax, CI, HI, and TCP (%). However, the number of MUs is less with FIF technique compared to three-field and four-field (box) plans. This is accounted as an advantage of FIF over three-field and four-field (box) plans. On the other hand, there was not a significant difference between three-field and four-field (box) plans in terms of MU.
As it is shown in [Table 3], there is no significant difference in Dmax, Dmean, and NTCP values for the right lung between FIF and three-field, FIF and four-field (box), and four-field (box) and three-field (P > 0.05). Therefore, there is no advantage for the FIF technique over three-field and four-field techniques in terms of Dmax, Dmean, and NTCP values for the right lung. On the other hand, for V20 Gy, there is a significant difference between FIF and three-field, FIF and four-field (box), and between four-field (box) and three-field techniques (P < 0.05). Less value V20 Gy for the lung is accounted as an advantage because the lung is an OAR. With this regard, V20 Gy is less with three-field technique for the right lung. A comparison of the three techniques for the right lung and left lung shows that the differences in Dmax and Dmean values for the three treatment planning techniques were not significant (P > 0.05). Differences in the values of NTCP for the left lung between FIF and four-field (box) and between four-field (box) and three-field treatment planning techniques are not significant (P > 0.05). This cannot be accounted for as an advantage of one technique over the others. On the other hand, a significant difference was determined for NTCP values for the left lung between two treatment plans of three-field and FIF (P < 0.05). For V20 Gy (%) in the left lung, there is a significant difference between FIF and three-field, between four-field (box) and three-field, as well as between FIF and four-field (box) plans (P < 0.05). V20 Gy is less with the four-field technique, compared to the other two techniques, for the left lung. [Table 3] indicates that there is no significant difference at the P < 0.05 level between treatment plans of FIF and four-field (box), three-field and FIF, and also between four-field (box) and three-field in terms of dosimetric and radiobiological parameters for the right kidney. According to [Table 3] for the left kidney, there is no significant difference in the values of the Dmax and NTCP in terms of dosimetric and radiobiological parameters between the three techniques at the P < 0.05 level and also there is no significant difference in the Dmean between FIF and four-field (box) and three-field and four-field (box) at P < 0.05. Therefore, there is no advantage for one technique over the others in terms of dosimetric and radiobiological parameters for the right and left kidneys. Dmean is an exception with this regard, because there is a significant difference between three-field and FIF plans in terms of Dmean in the left kidney (P < 0.05). The results presented in [Table 3] indicate that there are advantages in some cases for FIF technique over three-field and four-field techniques, due to less radiation dose in the OARs.
It was observed that normal structures such as left lung in the FIF plan have lower NTCP than that in the three-field plan [Table 3]. It means that the FIF technique reduces radiation-induced complication in this OAR in the patients with pancreatic cancer. However, this sparing trend was not observed for all of the OARs studied (i.e., right lung, right lung, right kidney, left kidney, spinal cord, and liver). The absolute differences between the two techniques with respect to these OARs are small, and they may be very difficult to be detected in terms of clinically relevant end points.
As is clear from [Table 3], the values of Dmean and NTCP of the liver do not differ significantly between three techniques of treatment planning (P > 0.05). There is also no significant difference between FIF and four-field (box) and three-field and four-field (box) in Dmax in terms of dosimetric and radiobiological parameters. There is no significant difference between the two treatment planning techniques of FIF and three-field for Dmax in the liver (P > 0.05). Therefore, there is no advantage for the FIF over three-field and four-field in terms of Dmean, Dmax, and NTCP in the liver. There is no significant difference in the values of the Dmean and NTCP parameters for the spinal cord between the three techniques (P > 0.05). A comparison between FIF and four-field (box) and three-field and four-field (box) techniques in the spinal cord for Dmax shows that there is no significant difference between FIF and four-field (box) and between three-field and four-field (box) (P > 0.05). However, there is a significant difference between the two treatment planning techniques of FIF and three-field for Dmax in the spinal cord (P < 0.05). With respect to the Dmax in the spinal cord, Dmax is less with the four-field technique compared to the other two techniques. Dmax in the spinal cord is also less with the FIF technique compared to the three-field technique. This is accounted for as an advantage of FIF over the three-field technique.
An important aim of conformal radiotherapy is to increase control of tumor without increase of treatment toxicity to OARs. The standard treatment beam is still being searched because, in particular clinical situations, different plans should be compared so that an optimum treatment plan can be found. In addition, such solution may be convenient in clinical practice, especially for radiation departments with great burden for work.,, There is no study on application of the FIF technique in pancreatic cancer, and most of the previous studies are on breast and esophageal cancer. It has been reported that the FIF technique can improve the homogeneity of dose distribution using individual multileafs to deliver a small amount of MUs to compensate for missing tissue in treatment planning region., The FIF technique has been also shown to have advantages for OARs, in terms of radiological aspects, in radiotherapy of breast and esophageal cancers., Moreover, it has been reported that FIF technique improves the homogeneity of dose distribution using individual MLC-shaped segments to deliver a small amount of MUs to OARs.,
The data analysis in the present study [Table 3] also shows that there is a significant difference between FIF and three-field in the left kidney in terms of Dmean. However, there is a significant difference in the NTCP between FIF and three-field for the left lung. The observations also show a significant difference in V20 Gy (right lung), V20 Gy (left lung), and MU between the three techniques. The present study demonstrates that, in some cases, FIF technique could reduce the radiation dose to patients and some hot spots which are existed in the three-field and four-field techniques.,
In previous studies, absorbed dose distribution in FIF technique was compared for esophagus, breast, brain, and head-and-neck cancers.,,, It has been reported that when dosimetric properties of the PTV are comparable in some different treatment techniques, the risk of normal tissue complications should be regarded as an important consideration., In the present study, in addition to dosimetric parameters, TCP and NTCP were used to compare the three different techniques in terms of tumor and OARs.,, It was observed that the FIF technique is superior to the three-field technique in terms of decreasing the maximum dose in the liver and the spinal cord, but there is no superior in FIF technique to the four-field. Furthermore, a comparison of the DVH data for each OAR, which was obtained with the three techniques, showed a significant benefit of FIF plan compared to the three-field and four-field (box) plans regarding the dose received by a specific volume of the right lung and the left lung (V20 Gy). This quantity is generally used to assess the risk of pneumonitis., In this study, it was found that V20 Gy of the left lung by the FIF technique was reduced compared to the three-field and four-field (box) techniques. Therefore, the significantly lower NTC P value for the left lung obtained with FIF versus three-field appears to be reasonable. These findings show that radiation-induced complications of these OARs can be reduced by the FIF technique during treatment planning.
The present results are consistent with the study of Allaveisi et al., who reported that the maximum dose values in the PTV, heart, liver, lung, and spinal cord were significantly reduced in FIF treatment plans for early-stage esophagus cancer. In terms of eliminating the scattered dose and reducing dose to OARs in treatment planning, FIF is more effective than conventional wedge-based fields, so the use of FIF should decrease the probability of secondary malignancies in the pancreas. Moreover, this study has shown that the MUs required to deliver the treatment plan were lower for the FIF technique than in the three-field and four-field (box) techniques. Studies have shown that increasing MUs can prolong treatment, so one of the advantages of the FIF technique is to reduce the time of radiation therapy. This result in MUs is in agreement with the previous study by Allahveisi et al. In their study, they have shown that there was a significant difference between FIF and four-field (box) techniques in 3D-CRT in terms of MU, which can be explained by the fact that MUs are higher with wedge-based plans due to radiation attenuation. Ghadimi et al. in their study have shown that FIF technique has advantages in terms of dose distribution in PTV and dose to OARs, compared with the 3D-CRT for esophageal cancer. It has been shown that there is no significant difference for MUs between the FIF techniques, compared to the 3D-CRT technique in esophageal cancer. The adjustment of a higher number of beams requires more time for treatment planning. Their results are in contrast with this study on pancreatic cancer due to differences in the types of cancers. In addition, it is well established that the dosage of each OAR should be less than their tolerance.,, Many studies have shown that the FIF technique improves the homogeneity of the dose distribution and also delivers a small amount of MUs to compensate for missing tissue than the other techniques.,,,
A few studies have been performed on the effects of FIF technique on organs other than the pancreas. This study demonstrated that, in general, the FIF technique had a better dosimetric outcome concerning the maximum dose in the liver and spinal cord than the three-field plan. FIF technique is a straightforward, feasible, and time-saving method that can be only used in centers which have computer-controlled MLCs for treatment delivery. In a study by Allaveisi, radiobiological parameters for wedge-based three-field and FIF techniques in treatment planning of pancreatic cancer were compared. The patients included 25 patients with pancreatic cancer. Mean dose and EUD to PTV and critical structures (including liver, kidneys, and spinal cord) were calculated and compared for these two techniques. V30 Gy and V28 Gy parameters for the liver and kidneys have shown that the irradiated volumes were larger in the wedged three-field technique compared to the FIF technique. In addition, the EUD and mean dose values in the PTV for the FIF were lower than the wedged three-field plan. In summary, the FIF method has shown a reduced dose received by the critical OARs, and this would lead to decreasing radiobiological complications. The study showed that FIF can be used as a substitute for the wedged three-field technique for treatment of pancreatic cancer. Based on the results by the study by Allaveisi, the results of both studies (Allaveisi and this study) are indicating the superiority of FIF technique over three-field technique in terms of dosimetric and radiobiologic parameters in target volume and in some cases in OARs.
| > Conclusion|| |
The results have shown that FIF plan for radiotherapy of pancreatic cancer has some advantages over three-field and four-field (box) treatment plans, based on less MU. There are also some advantages for the FIF technique over the three-field and four-field techniques in terms of dose to OAR in some cases, while in other cases, three-field technique has advantages. In summary, it was observed that the FIF technique overlaps well with the three-field and four-field (box) techniques in the target volume. In addition, by the FIF technique, MU value is significantly reduced compared to the other two techniques, which in turn reduces the amount of scattered radiation and also the load applied to the linear accelerator. This study showed that FIF technique has superior dosimetric characteristics in some cases over the three-field and four-field (box) techniques for pancreatic cancer. Using the FIF technique requires precision, knowledge, and practice of medical physicists because the FIF technique is a time-consuming technique due to the large number of beams which are used.
Financial support and sponsorship
Shahid Beheshti University of Medical Sciences has financially supported the work.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]