Main Session
Sep
27
PQA 01 - Gastrointestinal Cancer and Central Nervous System
2195 - A Novel Testicular Immobilization and Radiation Attenuation Device for Mitigating Testicular Dose During Radiotherapy for Colorectal and Anal Cancer Patients
Presenter(s)
Toni Roth, PhD - Memorial Sloan Kettering Cancer Center, New York, NY
T. M. Roth1, F. J. Arturi2, M. Gil2, E. K. Liu2, A. Kelly1, K. Episcopia1, J. Hertrich1, A. Damanto1, P. Booth1, V. M. Williams2, J. Cuaron2, M. Zinovoy2, M. Reyngold2, C. H. Crane2, P. B. Romesser2, and D. A. Roth O’Brien2; 1Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, 2Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY
Purpose/Objective(s):
A rising incidence of rectal and anal cancers in young patients raises concern regarding sexual, reproductive, and endocrine effects of radiation therapy (RT). We evaluated the dosimetric impact of a novel testicular immobilization and radiation attenuation device designed to displace and shield the testes, hypothesizing significant dose reduction during pelvic RT.Materials/Methods:
An institutionally developed, patent-pending testicular immobilization and radiation attenuation device was used for patients with rectal or anal cancer treated with curative-intent RT from April 2024 to November 2025. Baseline clinical and disease characteristics, as well as RT details were collected. Patients underwent CT simulation using a body mold and the testicular immobilization device (stand assembly) with CT-compatible simulation (dummy) shells. Unlike commercial stands, our device is couch-indexed for reproducible setup and engineered to incorporate a 3-degrees-of-freedom (3DOF) positioning arm, thus maximizing testicular displacement from the RT field, as this is a primary determinant of testicular dose. 3D conformal radiation therapy (3DCRT) or volumetric modulated arc therapy (VMAT) was used, at the discretion of the treating physician. In vivo dosimetry was performed for the first three fractions via a dosimeter placed on each testis. The first fraction used the dummy shells; subsequent fractions used shielded shells.Results:
Among 24 treated patients, 22 had evaluable dosimetry. Median age was 45 years (interquartile range [IQR] 41-51) and most patients (83%) had rectal cancer. Median prescribed pelvic and primary tumor doses were 4698 cGy (IQR 4509-4698) and 5400 cGy (IQR 5400-5400), respectively; a simultaneous integrated boost was delivered in most cases (79%). Nine patients (38%) were treated with 3DCRT and the remainder with VMAT. Mean testicular dose was 11 cGy with dummy shells vs. 3 cGy with shielded shells (p<0.001). Median pairwise-differences and reduction between dummy and shielded shell measurements were 5.8 cGy (IQR 1.5-9.0) and 2.7-fold (IQR 1.5-5.5), corresponding to a dose of 221 cGy vs. 76 cGy over the prescribed RT course. No significant differences in per fraction dose reductions were seen between subgroups: anal vs. rectal cancer (median 9.9 vs. 4.4 cGy, p=0.08), 3DCRT vs. VMAT (5.0 vs. 7.6 cGy, p=0.24), tumors <4 cm vs. =4 cm from the anal verge (6.5 vs. 3.8 cGy, p=0.24), and inclusion vs. exclusion of inguinal fields (9.9 vs. 4.4 cGy, p=0.14).Conclusion:
Our unique testicular immobilization and radiation attenuation device maximally and reproducibly displaces and shields the testicles, reducing mean testicular dose to <1 Gy over a typical course of pelvic RT for rectal or anal cancer. As more young patients are diagnosed with rectal and anal cancers, strategies that limit gonadal radiation exposure may help preserve fertility and endocrine function.