Purpose: Adaptive Radiation Therapy (ART) is a treatment technique that may allow for reducing radiation dose to normal structures, such as bowel. However, accessibility to this treatment modality is limited because it is resource intensive. Here, we propose a method to select anal cancer patients that will benefit most from ART in terms of bowel sparing, allowing more efficient allocation of resources.
Methods: Retrospective treatment data from 4 patients (5400cGy/30 fractions) were evaluated. Daily adapted CTs were created in Velocity v4.1 based on daily CBCTs. The structure sets from the planning CTs were deformed onto each adapted CT and ultimately corrected and revised by two qualified radiation oncologists. The original treatment plan was recalculated on each fraction’s adapted CT to establish the true dose received during treatment. Dose statistics (Mean, Max, Min) and DVHs were extracted and analyzed.
Results: The ratio (V4500cGyRatio) of the initial plan bowel V4500cGy to the plan-specific constraint was used to stratify patients into three groups (V4500cGyRatio <0.65, 0.65
Conclusion: Patient plan V4500cGyRatio can help determine which anal cancer patients will benefit most from ART in terms of bowel sparing. Decreasing inter-fraction variability of bladder volume may reduce the number of patients requiring ART.