3343 - A Dosimetric Study on SBRT Dose De-Escalation in Prostate Cancer Patients

12:45pm - 02:00pm PT

Hall F

Screen: 24

POSTER

Presenter(s)

Taran Singh, BS - New York Institute of Technology College of Osteopathic Medicine, Old Westbury, NY

T. Singh¹, J. Antone¹, B. Gui², L. Potters², and B. Parashar³; ¹Department of Radiation Medicine, Northwell, New Hyde Park, NY, ²Northwell, New Hyde Park, NY, ³Department of Radiation Medicine, Northwell Health, New Hyde Park, NY

Purpose/Objective(s):

Stereotactic body radiation therapy (SBRT) is an efficacious treatment modality for prostate cancer but can introduce toxicity to peripheral structures including rectum, urethra, and bladder. This preliminary study investigates if proposed dose de-escalation on prostate volume uninvolved by tumor can reduce the dose to rectum, urethra, and bladder compared to current SBRT guidelines.

Materials/Methods:

Between 2022 and 2025, 50 patients with prostate cancer on SBRT treatment were selected from a single multi-site institution for this in-silico planning study, with a half of cases assigned to standard plan of 40 Gy in 5 fractions to entire prostate and the other half of cases assigned to de-escalation plan of 40 Gy to the biopsy confirmed gross lesions on MRI and 36 Gy to the rest of prostate volume simultaneously. Dosimetric parameters including rectum maximum dose, bladder maximum dose, urethral maximum dose, bladder mean dose and urethra mean dose were collected and compared with t-test. The correlation between these parameters and prostate volumes were evaluated with Pearson correlation analysis. All dosimetric parameters were divided into high and low categories by their medians. Multivariate logistic analysis was used to identify predictors for higher dosimetric parameters.

Results:

The mean patient ages were the same between standard group and de-escalation group (71 ± 7 years vs. 71 ± 8 years, p = 0.80). There was no significant difference in prostate volume between standard group and de-escalation group (52 ± 22 cc vs. 55 ± 22 cc, p = 0.66). Compared to the standard group, the group with de-escalation plan showed significant dose reduction in maximum doses for bladder, urethra and rectum (37.9 Gy vs. 41.9 Gy, 37.8 Gy vs. 41.6 Gy, and 33.2 Gy vs. 39.1 Gy respectively, all p values < 0.0001). For mean doses, bladder and urethra mean doses were significantly lower with de-escalation RT plan vs. standard plan (6.8 Gy vs. 9.1 Gy, p = 0.04, and 32.8 vs. 37.6 Gy, p < 0.0001). However, rectum showed similar reduction in both groups (13 Gy vs. 12 Gy, p = 0.28). Pearson correlation analysis showed rectum mean dose to be only positively correlated to prostate volume (r = 0.46, p = 0.0009). All dosimetric parameters except rectum mean dose were found to be exclusively associated with their treatment group (all p values < 0.001), but not with age or prostate volume.

Conclusion:

Our preliminary study shows a dosimetric advantage with de-escalation to rectum, urethra, and bladder sites in prostate cancer patients treated with SBRT regimen. Further studies with clinical follow up will be needed to validate the effect of this dose de-escalation plan on clinical outcomes including organ-at-risk related adverse effects and tumor control outcomes.