Stereotactic Body Radiotherapy Boost for Intermediate Risk Prostate Cancer: A Phase 1 Dose Escalation Study
Mené sur 30 patients atteints d'un cancer de la prostate à risque intermédiaire de récidive (durée médiane de suivi : 72 mois), cet essai de phase I évalue la toxicité d'une radiothérapie corporelle stéréotaxique de type "boost"
Purpose : HDR brachytherapy boost plus external beam radiotherapy is an established option for intermediate risk prostate cancer (PCa). SBRT boost can potentially mimic HDR boost, and could be a viable alternative. Here we report the long-term outcomes of a phase I dose-escalation trial of single-fraction SBRT boost. Methods : Patients had intermediate risk PCa and were accrued to three different SBRT single fraction dose-level cohorts (10 Gy, 12.5 Gy and 15 Gy). All received supplemental radiotherapy afterwards (37.5 Gy in 15 fractions). Three gold fiducials were implanted for image guidance. Patients were simulated and treated with a foley catheter and intra-rectal balloon. A T2 MRI scan was used for contouring, and a cine MRI was used to calculate patient-specific ITV margins. Toxicity and QOL were collected using CTCAE v3.0 and EPIC. Results : 30 patients were accrued, 10 in each cohort. Median follow-up was 72 months. 60% had unfavorable intermediate risk PCa. Two patients in the 15 Gy cohort developed late grade ≥ 3 GI/GU toxicity with one patient suffering from a grade 4 rectal fistula after a rectal ulcer was biopsied repeatedly. Two patients had biochemical failure. Median PSA nadir was 0.4 ng/ml with 10 Gy, 0.09 ng/ml with 12.5 Gy and 0.07 ng/ml with 15 Gy. Median PSA at 4 years as well as proportion achieving a nadir < 0.2 ng/ml improved significantly with higher doses. There was no significant change in QOL from baseline in any of the domains, and the minimal clinically important change (MCIC) was not statistically different between the three cohorts. Conclusions : Other than a grade 4 toxicity which may in part be due to repeated biopsies of a rectal ulcer, single-fraction SBRT boost was feasible and well tolerated. Larger studies are warranted to better document the outcomes of such an approach.