|Year : 2017 | Volume
| Issue : 6 | Page : 1050-1052
Intrarectal fixative for positioning of the prostate for intensity modulated radiotherapy
Janos Stumpf1, Subathira Balasundaram1, P. G. G. Kurup2, Rathnadevi Ramadas1, Murali Venkatraman2, Karthikeyan Perumal1
1 Department of Radiation Oncology, Apollo Speciality Hospital, Chennai, Tamil Nadu, India
2 Department of Medical Physics, Apollo Speciality Hospital, Chennai, Tamil Nadu, India
|Date of Web Publication||13-Dec-2017|
Department of Radiation Oncology, Apollo Specialty Hospital, 320, Anna Salai, Padma Complex, Teynampet, Chennai - 600 035, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Dose escalation improves local control in carcinoma prostate, but rectal toxicity remains a concern. Various techniques have been there to reduce the dose to the rectum. Mobility of the prostate results in a necessary expansion of the target volume. We describe a new intrarectal fixative, developed in-house with transrectal ultrasonography through the fixative itself for localization of the organ by reporting a case with early carcinoma prostate. Concerns of rectal toxicity limit dose escalation in the treatment of prostate cancer. Intra- and interfraction prostate motion is a concern in dose conformity techniques. The intrarectal fixative system developed in-house physically separates the prostate and rectum during radiation treatment. Thus, both intra- and inter-fractional movement of the organ are addressed, therefore planning target volume expansion can be kept minimal.
Keywords: Dose-escalation, external beam radiotherapy, prostate cancer, prostate-rectum spacer, rectal toxicity, side effects
|How to cite this article:|
Stumpf J, Balasundaram S, Kurup P, Ramadas R, Venkatraman M, Perumal K. Intrarectal fixative for positioning of the prostate for intensity modulated radiotherapy. J Can Res Ther 2017;13:1050-2
|How to cite this URL:|
Stumpf J, Balasundaram S, Kurup P, Ramadas R, Venkatraman M, Perumal K. Intrarectal fixative for positioning of the prostate for intensity modulated radiotherapy. J Can Res Ther [serial online] 2017 [cited 2019 Nov 17];13:1050-2. Available from: http://www.cancerjournal.net/text.asp?2017/13/6/1050/179163
| > Introduction|| |
Increased use of prostate-specific antigen (PSA) screening has increased the number of diagnoses of prostate cancer (PC). Radiation therapy (RT) is a standard therapeutic option for PC. Dose escalation was correlated with better biochemical control but also with higher rectal toxicity.
Depending on filling up of rectum and bladder, prostate shows inter-fractional and intra-fractional movement. The smaller the margin to protect rectum the higher the risk that posterior aspect of prostate escapes prescribed dose.,,
Physically separating the anterior wall of the rectum from prostate (e.g., by injecting a spacer) can reduce the rectal dose. But with obvious risks.
Based on a patient study, we describe the use of a special fixative device with ultrasound (US)-based position monitoring developed in-house 9 years ago and used for some patients.
| > Case Report|| |
A 67-year-old gentleman was diagnosed with low-grade adenocarcinoma prostate in January 2005. Local examination revealed nodule in the right lobe. PSA was 14.5 ng/ml. Magnetic resonance imaging pelvis revealed grossly enlarged prostate with nodular configuration and heterogeneous signal intensities. Bone scan was normal. PSA in March 2005 was 17.50 ng/ml. Patient opted for intensity modulated radiotherapy (IMRT) after discussing various options of surgery and radiation.
Utmost care was taken to minimize exposure to the rectum and preserving erectile function (as per patient's wish). The applied principle was precise high dose RT can eradicate cancer without “killing” the function fully.
Fixing the prostate in reproducible position allows minimal gross tumor volume-clinical target volume (CTV)-planning target volume (PTV) expansion. Different methods have been developed to spare rectum like an endorectal balloon for fixed rectal distention. Inflating the balloon pushes the prostate toward the pubic bone. Random day-to-day variation of the prostate position ,, is reduced at least in anteroposterior (AP) direction and reduction of rectal toxicity by pushing the dorsal rectal wall away from the PTV.
Our fixative [Figure 1] was however most promising in reproducibility of setup even with a lack of cone beam computed tomography (CT) at that time.
Treatment planning CT was done with fixative in situ. Target volume and the organs at risk were outlined and planning was done. Treatment position was verified before each session by transrectal ultrasonography (TRUS). By this technique, a dose of 78 Gy in 39 fractions in conventional fractionation over 8 weeks was delivered to the prostate by 7 field IMRT technique [Figure 2] and [Figure 3] in 2005.
|Figure 3: Sagittal section – intensity modulated radiotherapy with intrarectal fixative|
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Description of the device
The spacer applicator cylinder hosts a plastic obturator with a diameter matching the size of the US transducer. This dummy is removed when the device is already in situ; the US probe is inserted into the applicator. The applicator window in the upper end facilitates US screening verification of prostate's position. The concept is called FAT; Fix the prostate (F), Assess its position (A) by the US, and then Treat (T). The rectal dose can be reduced significantly by the minimal expansion of CTV to PTV, posterior wall of the rectum can be spared by IMRT.
The patient is put on the treatment couch. Applicator height is adjusted according to the position of the anus and inserted into the anus and connected to the fixing plate; latero-lateral position (LL) is corrected as per the US. The height from the base plate to the upper level of the applicator is fixed and measured. Thus, AP movement is arrested. From patient's pubis, measurement to the applicator horizontal length has to be taken and marked for reproducibility in a cranio-caudal direction (CC).
Once the US probe is inserted into the applicator, the prostate LL position is known. The probe is fixed to a stepper for CC measurements. The CC position of the organ will be measured by the outside stepper. These with the physical measurements are checked daily. During treatment planning CT, the same procedure is done and measurements are taken.
During radiation exposure, our special rectal spacer with obturator is inserted into the rectum and attached to base plate, ensuring a fixed geometry all through irradiation. Our device can host the transducer and a window at the ventral side makes scanning possible and the prostate position was verified by TRUS.
The patient was immobilized in the supine position using Vac-Lok. The probe automatically minimizes the prostate motion and keeps the posterior rectum away from the target.
This intermediate risk patient with stage T2aN0M0 target volume was 67.70cc. V95 and D95 of the target were 94.65% and 92%, respectively. The D100, D50, and D20 of the rectum were 14%, 53%, and 65%, respectively.
Two-third of the rectal wall received <50% of the dose to the target.
Patient tolerated the treatment well. In August 2005, his PSA was 0.12 ng/ml. PSA was monitored every 2 months for the 1st year and 3 months for the 2nd year and 4 months for the 3rd year [Figure 4].
The latest PSA in February 2015 was 0.04 ng/ml. During external beam radiation therapy patient had increased frequency of urine which subsided after treatment. His erectile function improved and is still maintained, 9 years after radiotherapy.
| > Discussion|| |
RT is a standard therapeutic option for PC. Innovative technologies and more robust radiobiological data favor hypofractionation and reduced treatment duration of radical RT without detrimental impact, both in terms of efficacy and safety.
RT was associated with a higher risk of late gastrointestinal toxicity. But, modern RT allows to overcome the major limits of the “older” RT: the impossibility of delivering higher total doses and/or high dose/fraction. In particular, a special attention should be given to the problem of organ motion.
There is considerable interest in physically separating the prostate and rectum during RT using injected spacers such as hyaluronic acid, human collagen, and polyethylene glycol gel injection., While promising, issues related to radiation sensitivity  and infections need to be addressed.
Our intrarectal fixative system developed in-house, which is a simple, noninvasive, and logical solution, which can be used on any linear accelerator; relocatability and geometrical precision, is mostly mechanical; assessment needs TRUS only. It assures a fixed and reproducible position and with no major rectal reaction though the dose delivered was high.
| > Conclusion|| |
A simple, acceptable, and inexpensive technique which fixes the prostate position during IMRT instead of monitoring has been described and demonstrated in an actual case. The treatment was successful without side effect. The device minimizes the toxicity to the rectum. Simple TRUS verifies the position and image-guided radiation therapy/cone beam CT are not mandatory.
We thank our technologists Mr. Kannan Srinivasan and Mr. Chinnappa Segadevan for their logistic support.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]