I Gallagher*, C Coughlin, J Riess, I Chetty, B Movsas, A Kretzler, Henry Ford Health System, Detroit, MI

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  I Gallagher

PO-GePV-M-116 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: A case study is presented to demonstrate the utility of adaptive radiation therapy in the management of radiation therapy treatments in which the patient anatomy is non-standard.

Methods: A 69-year-old male with a history of cystoprostatectomy (prostate and bladder removed) for bladder cancer and with incidental finding of prostate cancer was treated for recurrent prostate cancer to the prostatectomy bed. Without a bladder present to serve as a buffer, there was overlap between radiation sensitive organs and the tumor bed. The patient was treated with adaptive radiation therapy to maximize target coverage while accounting for daily variation in overlap between the prostate bed and radiation sensitive organs. Plan considerations included the daily contouring of relevant structures in addition to target constraints used to drive hot spots out of the periphery and into the central region of the target.

Results: Adapted plans were needed for 32 out of 39 treatment sessions. On average, treating the non-adapted plan would have resulted in a target D95% of 76.9% of the prescription. Treating the adapted plan, on average, would have yielded a target D95% of 77.9%. Average V50Gy and V54Gy of the bowel bag was 2.30cc and 1.02cc (non-adapted plan) and 0.61cc and 0.169cc (adapted plan). Average V60Gy and V64Gy of the sigmoid was 3.64cc and 2.5cc (non-adapted) and 0.05cc and 0.00cc (adapted plan).

Conclusion: The non-standard anatomy in this case presents justification for adaptive treatment. By being able to account to daily variation in the overlap between healthy tissue and target volume using adaptive radiotherapy, the target coverage was maximized and sparing of normal tissues was even more dramatic.

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