Stereotactic body radiation therapy for renal cell carcinoma: a small number of initial clinical experiences.

Stereotactic body radiation therapy (SBRT) has emerged as a promising and minimally invasive treatment option for patients with renal cell carcinoma (RCC). This study presents our initial clinical experiences with treatments following our center's protocol, which was formulated based on both national and international evidence. Six patients who had undergone renal SBRT at our center from January 2021 to December 2023 were included. Treatment planning used computed tomography (CT) and magnetic resonance imaging, with respiratory management conducted through breath-hold or free-breathing techniques. The prescribed dose was primarily 48 Gy in three fractions, with increased fractionations when dose constraints were challenging to achieve. Dose constraints were met for all patients, and treatment planning adhered to protocol guidelines. After the confirmation of cone-beam CT (CBCT) images by physicians, radiation was delivered. Five out of six patients completed the planned treatment, whereas one discontinued the treatment midway (the causal relationship to radiation therapy was unclear). Dose-volume histogram analysis revealed that doses to organs at risk depended on the position and size of the planning target volume but remained within acceptable limits for all cases. The intrafractional patient motion was 2.7 mm, as calculated from the pre- and post-CBCT images, confirming the appropriateness of a 3-mm setup margin. Although this study provides initial insights, further clinical trials are warranted to establish standardized protocols and optimize treatment strategies for RCC. In the future, it is also necessary to generate evidence that is tailored to the current situation in Japan.