(P079) Linac-Based SBRT Delivered in Five Fractions for Definitive Prostate Cancer Treatment Using VMAT and Flattening Filter-Free Beams: The Phase II Lankenau Experience

Saritha Ravella, MD, Albert S. DeNittis, MD, MS, Harry Hu, MS, Lori DeNittis, RTT, David Wang, PhD; Lankenau Medical Center

Background: To evaluate the feasibility and toxicity of hypofractionated stereotactic body radiation therapy (SBRT) with volumetric modulated arc therapy (VMAT) and flattening filter-free (FFF) beams.

Methods: A prospective National Cancer Institute (NCI)-designated phase II study was approved by our institutional review board (IRB) (started in October 2011). Inclusion criteria were histologically proven prostate adenocarcinoma, Gleason Score 6–7, clinical stage T1b–T2b, prostate-specific antigen (PSA) ≤ 20 ng/mL, prostate volume ≤ 100 cc, Eastern Cooperative Oncology Group (ECOG) performance status 0–1, no prior prostatectomy, cryotherapy, or radiotherapy to the prostate. SBRT was delivered at a prescribed planning target volume (PTV) dose of 36.25 Gy in five fractions using the TrueBeam STx. Patients self-reported on validated quality of life (QOL) measures, such as American Urological Association (AUA) Index, Sexual Health Inventory for Men (SHIM), Utilization of Sexual Medications/Devices (USMD), Expanded Prostate Cancer Index Composite Short Form (EPIC-26) with five components (urinary irritative, urinary incontinence, bowel, sexual, and hormonal), and Short Form-12 (SF-12) with two components (physical and mental). Patients were analyzed at predefined time intervals.

Results: A total of 25 patients have been recruited to date. Mean age of the patients was 68 years (range: 52–80 yr). Mean Gleason score was 6.32 (range: 6–7). Mean PSA was 6.45 ng/mL (range: 0.63–18.7 ng/mL). All patients tolerated the treatment well with no acute adverse effects, as noted on their QOL questionnaires. Evaluating patients in a time period ranging from 6 to 24 months, the EPIC-26 showed a significant difference using the Kruskal-Wallis Test between average total score at pre-entry when compared with 1-month, 6-month, and 12-month evaluations. however, mean pre-entry score was not significantly different from mean score at 24 months, demonstrating a transient decline in the bowel-related QOL. Also patients’ perception of bowel urgency showed no impact on QOL on the EPIC-26.

Conclusion: Early findings indicate that SBRT with VMAT and FFF beams for low–intermediate-risk prostate cancer delivered in five fractions is feasible and tolerated well. Long-term follow-up is needed for assessment of late toxicity and outcomes.