Evaluation of Testis as Organ at Risk in Carcinoma Rectum with Various Radiotherapy Delivery Techniques

Background: Due to the close approximation of testis to radiotherapy treatment field in male carcinoma rectum patients, it receives either scattered or direct radiation. The present study aimed to investigate the impact of considering testis as organ at risk with different radiotherapy techniques.Method: This mono-centric, multi-arm, prospective, observational study was conducted with 160 male rectal cancer patients between 2019 and 2024, aged >18 years treated with neo-adjuvant radiotherapy followed by total mesorectal resection. We designed two-dimensional, three-dimensional, intensity modulated and volumetric modulated arc radiotherapy, with 40 patients in each technique. Tumor stage, length and thickness, testicular dose and volume, planned target volume and its distance from anal verge in each technique was considered, along with the assessment of testis as organ at risk. SPSS-22.0, R environment-3.2.2 and Microsoft excel were used for data analysis. The two-tailed t-test and analysis of variance (ANOVA) were performed to assess the level of significance with P < 0.05.Results: The mean dose to right and left testis (in centi-gray) with two-dimensional radiotherapy was 925.79 and 776.70, while the dose contribution to testis when considered as organ at risk resulted in 336.23 and 206.65 with three-dimensional radiotherapy, 165.15 and 140.25 in intensity modulated radiotherapy and 209.2 and 229.2 in volumetric modulated arc therapy. Planned target volume, testis as organ at risk and treatment technique showed statistical significance with testicular dose received.Conclusion: Considering testis as organ at risk contributed to significant dose reduction in conformal technique, with better sparing observed in intensity modulated radiotherapy whereas testicular shielding is needed in two-dimensional radiotherapy.