Published by Radformation Survey Team on 2/15/2021
Prostate Treatment Fractionation
Like breast and cervical cancer, prostate cancer benefits from a wide variety of available techniques ranging from brachytherapy to external beam radiation therapy (EBRT). Within each treatment type exists myriad other choices regarding dose, fractionation, and motion management. According to a 2017 survey regarding external beam fractionation, traditional fractionation (38-43 fractions) remains the most common, being the favorite for 66.7% of clinics (treating 76-100% of cases in this way).
Percentage of Patients Treated per Fractionation Method
Recent trials have demonstrated the effectiveness of hypofractionation (20-27 fractions) and SBRT (3-7 fractions) in treating cancers with low alpha-beta ratios. Despite these developments, the 2017 survey showed only 22.8% used hypofractionation, and 7.2% used ultra-hypofractionation in greater than 25% of treatments. One user noted this is likely a result of stringent patient selection limiting many candidates from eligibility as it is primarily useful for low and intermediate-risk prostate cancers.
It’s a possibility that more departments may shift toward fewer fractions as data continues to support it. For example, a 2019 publication showed that 28 fractions of 250cGy provided favorable 10-year outcomes for all prostate cancer risk groups. This is a drop of two weeks worth of treatments, which is much less burdensome for patients and allows for more efficient clinical operations.
Use of Gel Spacers for Prostate Therapy
Simultaneous Integrated Boost and Sequential Planning
For prostate cancers with nodal involvement, treating the surrounding pelvic lymph nodes is critical to a successful treatment. Typically, this is performed using sequential planning, with just 29.1% of 2016 survey respondents using a simultaneous integrated boost (SIB) to treat the region. This data is similar to the 2017 IMRT survey that showed 21.7% of respondents preferring the SIB approach.
Rectal balloons have been used clinically to create distance between the prostate and the rectum in an attempt to reduce rectal toxicity. These balloons are manually inserted for each treatment, with some using air and others using water to inflate the balloon. While some research indicates a favorable dose drop off, most clinicians (76.1%) chose not to use them, citing issues with reproducibility and patient comfort. Those who decided to use rectal balloons filled with water more often — 63.6% of the time— and others (36.4%) filled with air.
Breakdown of Rectal Balloon Usage
The prostate is prone to both intra-fraction and inter-fraction motion. Filling of the rectum or bladder and shrinkage of the prostate can cause significant displacements in anatomy during treatment compared to the simulation positioning used for treatment planning. One of the more popular methods for localizing the prostate is fiducial markers. In a 2016 survey, 67.5% of respondents used fiducial markers for localization. The most common material was gold at 81.1%, followed by polymer at 5.7%, carbon and stainless steel at 3.8% each, other at 3.0%, and titanium at 1.9%. Isolated seeds were used 68.8% of the time, coils 18.8% of the time, gold “anchors” 8.3% of the time, and linked seeds were the least popular option with just 4.2% of survey takers favoring that option.
“Even if the markers align well, you still need to assess bladder/rectum filling, bowel displacement, and/or target deformation to determine if any OARs are falling into a high dose area.”
A Special Thanks
Thanks to Scott Dube for providing access to over 275 medical physics community surveys for public use. For further reference, a JACMP article by Kisling, et al. provides a complementary analysis of survey results.