Tomotherapy With Synchrony Fiducial Tracking for Stereotactic Body Radiotherapy in Prostate Cancer: A Single-Center Experience on Toxicity

The use of stereotactic body radiation therapy (SBRT) in the treatment of prostate cancer (PC) has increased significantly in recent years. This study aims to evaluate the safety of patients with localized PC undergoing SBRT using Radixact Tomotherapy with Synchrony fiducial tracking, a real-time motion tracking and correction system. This retrospective work analyzes 43 PC patients treated with SBRT from June 2022 to February 2025. Among these, nine (21%) were classified as low risk, 15 (35%) as favorable intermediate risk, 13 (30%) as unfavorable intermediate risk, and six (14%) as high risk. Androgen deprivation therapy (ADT) was prescribed based on the risk group. Three gold fiducial markers were placed in the prostate under ultrasound guidance before a computed tomography (CT) scan to visualize the position and movement of the prostate before and during treatment, allowing for real-time corrections. The total dose administered was 36.25 Gy in five fractions, delivered every other day. The required target coverage was at least 95% of the planning target volume (PTV) with at least 95% of the prescribed dose. The Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 was used to evaluate acute and late toxicity, including gastrointestinal (GI) and genitourinary (GU) effects. The median age of the patients was 75 (range: 56-85) years. The median follow-up was 14 (range: 0-32) months. The treatment was well tolerated by the majority of patients, with all completing the planned treatment without interruptions. No acute or late GU and GI toxicities ≥ G3 were observed. For acute GU toxicity, 18 (42%) patients reported symptoms, but only two (5%) experienced G2 toxicity. For acute GI toxicity, 12 (28%) patients presented symptoms, with only one (2%) showing G2 toxicity. Currently, data on late toxicity are available for 40 patients. Nine (23%) patients experienced late GU toxicity, with only one (3%) having G2 toxicity. Eleven (28%) patients reported late GI toxicity, of which six (15%) were G2. All of these patients required only symptomatic topical therapy with clinical benefit, except for one who underwent endoscopic therapy with argon plasma coagulation. This work demonstrates that prostate SBRT using Radixact Tomotherapy with Synchrony is safe; however, it is necessary to expand the sample size and extend follow-up to evaluate late toxicity and clinical outcomes.