3301 - Frameless Robotic Radiosurgery System Stereotactic Body Radiation Therapy (SBRT) Dose Escalation Prostate Cancer Trial (CK-DESPOT) for Unfavorable Intermediate and High-Risk Prostate Cancer

12:45pm - 02:00pm PT

Hall F

Screen: 19

POSTER

Presenter(s)

Mark Nguyen, MD, BA - University of Washington School of Medicine, Seattle, WA

M. Nguyen¹, and R. M. Lanciano²; ¹Crozer-Chester Medical Center, Upland, PA, ²Crozer Keystone Healthcare System, Department of Radiation Oncology, Havertown, PA

Purpose/Objective(s): Since publication of the FLAME (focal lesion ablative micro boost in prostate cancer) trial, the NCCN guidelines incorporated focal boost for intensity modulated radiation therapy. However, limited data exist on micro-boost with SBRT. This phase II clinical trial sought to assess outcomes following simultaneous integrated focal boost during a course SBRT with a frameless robotic radiosurgery system. The primary objective is to assess biochemical disease-free survival and the secondary objective is to assess severe gastrointestinal and genitourinary toxicity beyond six months of follow-up.

Materials/Methods: Eligible patients had NCCN-defined unfavorable intermediate- or high-risk prostate cancer diagnosed within 360 days of enrollment. MRI and bone scan +/- PSMA PET/CT were required for staging. Patients received androgen deprivation therapy (ADT), and SBRT was initiated within 2 months of ADT. Space OAR gel and fiducials were required. Other inclusion criteria included prostate volume <100 cc, no prior pelvic radiation or TURP, AUA score <20, and no nodal or distant metastases. SBRT delivered 40 Gy to the prostate, with a PIRADS 4/5 nodule boost to 45-50 Gy. Proximal seminal vesicles received 36.25 Gy. Dose volume constraints were enforced for nearby at-risk organs. Toxicity was evaluated with standardized questionnaires. Biochemical control was determined by the Phoenix definition. Follow-up interval was 1, 3, 6, 12, 18, 24 months and yearly thereafter until year 5.

Results: Thirty-three patients (median age of 66, 85% Caucasian) completed SBRT. Sixty-seven percent were stage T1c, 84.8% had a Gleason score of 7 and 57.6% were primary grade 4. Median baseline PSA was 6.5, with a median of 42% positive cores. 85% of our patients had unfavorable intermediate risk prostate cancer. The median duration of ADT was 6 months. Seventy nine percent received PI-RADS 4/5 simultaneous integrated focal boost. Median follow-up was 36 months. Toxicity was low with AUA scores peaking at 1 month (median=11, vs. baseline median AUA of 4.5) improving by three months (median=5) and stabilizing at 3-4 from 24 to 60 months. No grade 3-5 RTOG acute or late urinary or bowel toxicity was observed. Among patients with at least 24 months of follow-up (n=23), median PSA was 0 (range 0-0.6). At 36 months (n=18), 48 months (n=13), and 60 months (n=10), median PSA remained 0, with maximum PSA of 0.2, 0.09, and 0.05, respectively.

Conclusion: This study describes a novel, safe, and low-toxicity radiation protocol for men with intermediate and high-risk prostate cancer, demonstrating that simultaneous integrated focal boost with SBRT is feasible and safe with low toxicity. Biochemical failure has not been seen in this study with 36-month median follow-up. Clinical Trial number: NCT03822494.