ESTRO 2025 - Abstract Book

S1876

Clinical - Urology

ESTRO 2025

40

Digital Poster Reassessing the need for a bladder filling protocol in the current era of SBRT prostate Vrushab Rao, Soumya Singh, Bhooshan Zade Department of CyberKnife Radiosurgery and Radiation Oncology, Ruby Hall Clinic, Pune, India

Purpose/Objective: Stereotactic body radiation therapy (SBRT) has gained preference as a treatment option for low and low intermediate risk prostate cancer due to its precision targeting and high dose administration. Conventional radiotherapy highlights the importance of reproducible bladder filling to minimize irradiation and associated toxicities. Nevertheless, there exists a divergence of opinions regarding the necessity of specific bladder protocols for SBRT in prostate cancer treatments, particularly given the prevalence of urinary symptoms at presentation. In this study, we assess whether a bladder protocol is absolutely necessary or whether it may be safely omitted in SBRT prostate. Material/Methods: Low and low-intermediate risk prostatic adenocarcinoma who received SBRT in 5 fractions treated on alternate days were retrospectively selected for this study. Plans were evaluated to assess the estimated mean bladder dose prior to treatment. Cone beam computed tomography (CBCT) scans were then fused with bony landmarks and the target volume. The bladder was contoured on these images and registered on the simulation scan. Mean bladder dose for each individual fraction was noted and the total dose delivered to the bladder was recorded. Patients were followed up routinely to note any bladder toxicity. Results: 35 patients were evaluated with a median follow up of 22.4 months (range 8-64 months). The median prescription dose was 36.25Gy. The doses and volume recorded are stated in the following table.

Parameter

Median Range

Bladder volume at simulation

126.47 cc 44.8-683.69 cc

Predicted mean bladder dose

8.27 Gy 0.34-24 Gy

0.004-37.429%

Volume % receiving the equivalent of ~24 Gy (V ~24 ) 12.22%

Volume receiving the equivalent of ~77 Gy (V ~77 ) 1.44cc

0-9.42cc

Bladder volume during each fraction

161.6 cc 38.7-583 cc

Final mean dose received by the bladder

7.55 Gy 0.33-19.83 Gy

1/35 patients developed grade 3 cystitis 1 week post radiation that resolved in 1 month with medical management. No other patients had >1 bladder toxicities. No correlation was noted between bladder toxicities and the mean dose, individual fraction mean doses, the predicted mean dose, V ~24 or V ~77 . Conclusion: The variation in bladder volume does not adversely affect it in SBRT of prostate cancer. Bladder protocol may safely be omitted in patients at the discretion of the treating oncologist provided normal tissue constraints and target dose distribution are achieved with an adequate plan.

Keywords: prostate cancer, bladder filling, SBRT