  A survey was designed to inquire about the practice of proton SBRT treatment
for prostate cancer. The survey was distributed to all 30 proton therapy
centers in the United States that participate in the National Clinical Trial
Network in Feb. 2023. The survey focused on usage, patient selection criteria,
prescriptions, target contours, dose constraints, treatment plan optimization
and evaluation methods, patient-specific QA, and IGRT methods. Results: We
received responses from 25 centers (83% participation). Only 8 respondent
proton centers (32%) reported performing SBRT of the prostate. The remaining 17
centers cited three primary reasons for not offering this treatment: no
clinical need, lack of volumetric imaging, and/or lack of clinical evidence.
Only 1 center cited the reduction in overall reimbursement as a concern for not
offering prostate SBRT. Several common practices among the 8 centers offering
SBRT for the prostate were noted, such as using Hydrogel spacers, fiducial
markers, and MRI for target delineation. Most proton centers (87.5%) utilized
pencil beam scanning (PBS) delivery and completed Imaging and Radiation
Oncology Core (IROC) phantom credentialing. Treatment planning typically used
parallel opposed lateral beams, and consistent parameters for setup and range
uncertainties were used for plan optimization and robustness evaluation.
Measurements-based patient-specific QA, beam delivery every other day, fiducial
contours for IGRT, and total doses of 35-40 GyRBE were consistent across all
centers. However, there was no consensus on the risk levels for patient
selection. Conclusion: Prostate SBRT is used in about 1/3 of proton centers in
the US. There was a significant consistency in practices among proton centers
treating with proton SBRT. It is possible that the adoption of proton SBRT may
become more common if proton SBRT is more commonly offered in clinical trials.
