ESTRO 2024 - Abstract Book

S2584

Clinical - Urology

ESTRO 2024

School of Medicine, Department of Urology, New York, USA. 5 Perlmutter Cancer Center at New York University Grossman School of Medicine, Department of Radiation Oncology, New York, USA

Purpose/Objective:

The use of stereotactic body radiation therapy (SBRT) multi-parametric MRI intraprostatic microboosts (MIB) has garnered significant attention following the impressive results of the FLAME trial. Multiple ongoing studies are exploring the utility of a microboost in the SBRT setting predominantly to a unifocal lesion. However, limited data exists for the use of focal boost to multiple prostatic nodules in the SBRT setting. Herein, we will explore the early patient reported toxicity and quality of life outcomes of multi-nodule SBRT MIBs in the treatment of localized prostate cancer.

Material/Methods:

An institutional registry of patients undergoing five-fraction robotic prostate SBRT was interrogated to identify those who underwent an SBRT microboost from Feb. 2021 – May 2023. All patients were treated to a total dose of 3500 - 3625 cGy to the prostate and proximal seminal vesicles with or without a MRI directed boost. Patients were categorized into those without an MIB, with a unifocal MIB, and a multifocal MIB. In a sub-cohort of patients with an MIB, a microboost was performed with SBRT to a total prescription dose of 4000 to 4300 cGy. Patient reported EPIC quality of life summary and subscale scores were evaluated for the genitourinary and gastrointestinal domains. Quality of life endpoints were evaluated at 0, 3, 6, 9, and 12+ months. The minimally important difference (MID) was utilized to assess a clinically significant change in these measures from baseline, and was set as half a standard deviation (SD) as defined in prior publications. The GU and GI EPIC summary and subscale scores were assessed using generalized linear mixed models, including the main effects of time (0, 3, 6, 9, and 12 months), boost group, and the difference in groups across time. A result was considered significant at p < 0.05. A total of 119 patients underwent prostate SBRT with the distribution of risk grouping as follows: low 11.8% (n = 14), intermediate 81.5% (n = 97), and high 6.7% (n = 8). Focal boost distribution was as follows: none 72.2% (n = 86), unifocal 16.0% (n = 19), and multifocal 11.8% (n = 14). A prescribed MIB dose was most commonly 4200 cGy (n = 20, 61%) and with a mean MIB dose of 4275 cGy (IQR: 4215 - 4329 cGy) to a nodule volume of 2.69 cc (IQR: 0.93 – 2.72 cc). There was not a significant difference between MIB volume between the uni- and multifocal groups (1.11 vs. 2.15 cc, p = 0.196). With a median follow up of 13.2 months, there was no significant difference in overall or grade 2+ GU toxicity between the three cohorts (p = 0.254 and p = 0.559, respectively). Similarly, there was no difference in overall or grade 2+ GI toxicity between the three cohorts (p = 0.074 and p = 0.451, respectively). EPIC bowel summary scores did not reach the level of MID in any of the three cohorts, nor was the difference across time significant (p = 0.991). However, EPIC urinary summary scores did witness a transient MID at 6 months for both unifocal and multifocal MIB with recovery by month 9. In contrast, the no MIB cohort did not dip into the MID range for the urinary summary score or any urinary subscale. Results: