1085 - A Phase I/Ib, Single Arm Study of Two Fraction SBRT with SIB for the Treatment of Localized Prostate Cancer: Early Toxicity Outcomes
Presenter(s)
J. W. Lischalk1,2, V. Santos2, B. Vizcaino3, C. Mendez4, A. Sanchez4, A. Corcoran5, S. Taneja6, D. R. Wise7, J. Divers8, A. Katz5, H. Lepor6, T. J. Carpenter4, W. Huang6, A. Tong9, M. Zelefksy10, and J. Haas4; 1Department of Radiation Medicine, Georgetown University Hospital, Washington, DC, 2Department of Radiation Oncology, Perlmutter Cancer Center at New York University Langone Hospital - Long Island, New York, NY, 3Department of Radiation Oncology, Perlmutter Cancer Center at New York University Grossman School of Medicine,, New York, NY, 4Department of Radiation Oncology, Perlmutter Cancer Center at New York University Langone Hospital - Long Island, Mineola, NY, 5Department of Urology, Perlmutter Cancer Center at New York University Langone Hospital - Long Island, Mineola, NY, 6Department of Urology, Perlmutter Cancer Center at New York University Grossman School of Medicine, New York, NY, 7Department of Medicine, Perlmutter Cancer Center at NYU Langone Medical Center, New York, NY, 8Department of Foundations of Medicine, NYU Long Island School of Medicine, Mineola, NY, 9Department of Radiology, NYU Langone Health and New York University, Grossman School of Medicine, New York, NY, 10Department of Radiation Oncology, Perlmutter Cancer Center at New York University Langone Hospital, New York, NY
Purpose/Objective(s):
Stereotactic body radiation therapy (SBRT) has been established as an effective modality for localized prostate cancer with recent level 1 evidence supporting its comparative efficacy and toxicity. Simultaneous integrated boosts (SIB) to the dominant intraprostatic lesion have demonstrated improved oncologic outcomes based on the FLAME trial. The purpose of this phase I/Ib study is to evaluate the feasibility and safety of a novel 2-fraction SBRT regimen with an MRI-guided SIB to the dominant intraprostatic lesions (PI-RADS 4+) stratified by genomic risk classification.Materials/Methods:
This single arm, prospective study explored patients with biopsy-proven localized prostate cancer classified as low to intermediate risk per NCCN criteria. All patients underwent MRI based SBRT treatment planning with fiducial marker and rectal spacer placement. Two fractions of SBRT were delivered to a total dose of 25 Gy in 2 weekly treatment fractions to the whole prostate with a 28 Gy SIB to the dominant lesion in patients with unfavorable intermediate risk disease or favorable intermediate risk with an elevated decipher score. Primary physician reporting grade 2+ toxicity per CTCAE version 5.0 was the primary endpoint. Follow-up was performed 30 days posttreatment and subsequently every 3 to 4 months for 2 years.Results:
A total of 18 patients with a median age of 73 years completed treatment, with a median follow-up of 6.43 months. Prostate cancer distribution was as follows: low (n=2, 11%), favorable intermediate (n=10, 56%), and unfavorable intermediate (n=6, 33%). The decipher score distribution was as follows: low (n=8, 44%), intermediate (n=3, 17%), and high (n=7, 39%). Of the entire cohort, median prostate volume was 39.5 cc, 61% (n=11) underwent an intraprostatic microboost with 5 patients due to an elevated decipher score, and 17% (n=3) received ADT as a component of treatment. With early follow-up, we observed only one instance of acute grade 2 GU and GI toxicity (5.5%) that occurred 9 days after treatment completion and resolved at the 1 month follow up. No instance of severe GU or GI toxicity was reported.Conclusion:
This phase 1/1B study demonstrates that 2-fraction SBRT with or without an MRI directed SIB is a feasible and a well-tolerated approach for localized prostate cancer. Toxicities with early follow-up are minimal and lower than historical controls utilizing a 2-fraction regimen. Further follow-up is required to determine the long-term efficacy and late toxicity trends. This novel fractionation regimen may offer a highly efficient and a biologically effective treatment option for selected patients, minimizing treatment burden and optimizing disease control using modern genomic stratification and advanced treatment delivery.