Objective: Although multiple studies continue to emerge demonstrating excellent biochemical control with extreme hypofractionation for prostate cancer there is still a matter of debate about the efficacy and toxicity. We examined clinical outcomes of extreme Stereotactic Hypofractionated Radiotherapy (SBRT) using Cyberknife.
Methods and Materials: From July 2007 through December 2015 a retrospective analysis was carried out on 228 consecutive patients (pts) with a median age of 74 years (range 52 – 86) years, mean prostate volume of 75.6 cc (range 37.03 - 163.16), and clinically localized prostate cancer. Pre-treatment PSAs ranged from 1.75 to 51.13 ng.ml (median 7.19 ng.ml). Cyberknife was used to deliver fiducials based image guided SBRT. According to the D'Amico risk classification the majority of pts 119 (52%) were low risk , 64 pts (28%) were intermediate risk and 45 pts (20%) were high risk. Among the entire study cohort 20 of 45 high risks pts received androgen deprivation therapy (ADT), ADT was not administered to any low – intermediate risk pts. A prescribed dose of 38 Gy in four fraction was delivered to the PTV, which was defined as the prostate (plus seminal vesicles in high risk patients). Real-time intrafractional motion tracking was used.
Results: Acute urinary symptoms (frequency, dysuria, urgency, hesitancy and nicturia) were common with 44 % of pts experiencing grade 1-2 RTOG acute urinary toxicity. No patients experienced RTOG grade 3 acute urinary toxicity while 7 pts (3%) experienced RTOG grade 3 late urinary toxicity (in 3 of them as consequences of repeated urological instrumentation, including cistoscopy and urethral dilatation). No RTOG grade 3 acute and late rectal toxicity was observed. The actuarial median follow up is 58 months (range 12 – 114 months). The six years actuarial PSA relapse free survival rate according to D'Amico risk classification is 94.3% (CI: 92.5%-96.1%) with 99.1% for low risk, 94.6% for intermediate risk and 83.7 % for high risk respectively. Overall 11 (5%) of 218 pts failed biochemical failure, occurring in 1 low risk patient, 4 intermediate risk pts and 6 high risk pts. 23 pts (10%) died during follow up for unrelated causes, only one patient (0.4%) died for prostate cancer (bone metastases).
Conclusions: The finding of our study was very encouranging. Cyberknife SBRT produces excellent biochemical control rates with mild toxicity and minimal impact on quality of life, comparable to other available radiation modalities.
