# Real-Time Adaptive Motion Management in Prostate Stereotactic Body Radiation Therapy: Clinical and Dosimetric Analysis of 25 Patients

## TL;DR

This study shows that real-time motion tracking during prostate cancer radiation therapy improves treatment accuracy and leads to good outcomes with minimal side effects.

## Contribution

The study introduces real-time adaptive motion management in prostate SBRT using the Radixact Synchrony system and evaluates its clinical and dosimetric effectiveness.

## Key findings

- Real-time motion management successfully corrected prostate displacement in nearly all patients.
- Median post-treatment PSA was 0.30 ng/mL, indicating strong tumor control.
- Most patients experienced only mild genitourinary toxicity, with no severe cases reported.

## Abstract

Purpose: Stereotactic body radiation therapy (SBRT) is a well-established treatment for localized prostate cancer, offering excellent tumor control with reduced treatment fractions. However, prostate motion due to physiological processes poses a challenge to precise dose delivery. This study evaluates the dosimetric outcomes, prostate-specific antigen (PSA) response, and toxicity profile of prostate SBRT using real-time adaptive motion management with the Radixact Synchrony system (Accuray Inc., Madison, WI).

Methods: A retrospective analysis was conducted on 25 prostate cancer patients treated with SBRT (40 Gy in 5 fractions) using the Radixact Synchrony system between January 2021 and December 2023. All patients underwent CT simulation with fiducial markers, and 24/25 patients had MRI fusion for target and organ-at-risk (OAR) delineation. Treatment plans were generated using either the “Classic” or “VOLO Ultra” algorithms. Intrafraction prostate motion was analyzed, and toxicity was assessed using the Common Terminology Criteria for Adverse Events (CTCAE) v4.03 scale at regular follow-up intervals.

Results: The median clinical target volume (CTV) for the prostate was 46.8 cm³ (range, 22.6-107.3 cm³), and the median pre-treatment PSA was 6.52 ng/mL. All plans achieved favorable target coverage while adhering to OAR dose constraints. The median post-treatment PSA value was 0.30 ng/mL with a median follow-up time of 28 months, with all patients achieving PSA levels below 2.0 ng/mL at 15 months. Motion >2 mm was observed in at least one treatment fraction for all but one patient. Real-time adaptive motion management successfully corrected for prostate displacement, with an average imaging interval of 8.4 seconds. A total of 14 patients reported new grade 1 genitourinary (GU) symptoms, and three patients experienced grade 2 GU toxicity post-treatment.

Conclusion: Prostate SBRT with real-time adaptive motion management using the Radixact Synchrony system achieves excellent target coverage while mitigating the effects of intrafraction motion. The observed PSA response supports its efficacy, and OAR dose metrics remain within acceptable limits. While real-time motion adaptation was beneficial for nearly all patients, further studies with larger cohorts and patient-reported outcomes are warranted to assess long-term toxicity and quality of life.