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A Method to Select Optimal Candidates for Adaptive Radiation Therapy (ART) in Anal Cancer

O Dona1*, D Horowitz1,2, M Savacool1, K Rayn1, F Li1, M Price3, C Wuu1, L Kachnic1,2, (1) Columbia University, New York, NY, (2) Herbert Irving Comprehensive Cancer Center, New York, NY, (3) Vanderbilt University Medical Center, Nashville, TN,

Presentations

TU-IePD-TRACK 3-1 (Tuesday, 7/27/2021) 3:00 PM - 3:30 PM [Eastern Time (GMT-4)]

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, 0.650.85). Every fraction was classified as pass/fail based on the true daily bowel V4500cGy meeting constraint. Daily bowel V4500cGy significantly (p<0.05) correlates with daily bladder volume. A scatter plot of the daily/planned bladder volume ratio vs. the V4500cGyRatio of the initial plan for every fraction shows which combinations of these lead to passing or failing the plan-specific constraint. For inter-fraction bladder volume variability at our clinic, V4500cGyRatio <0.65 needs little adaptation (2/30 fractions), 0.650.85 requires daily adaptation (29/30).

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.

ePosters

    Keywords

    Treatment Techniques, Targeted Radiotherapy, Radiation Therapy

    Taxonomy

    TH- External Beam- Photons: adaptive therapy

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