Phase II trial of 9 Gy SBRT PROSTATE BOOST after nomofractionated 60 Gy in high risk prostate cancer.

Introduction:
Extracranial stereotactic body radiation therapy (SBRT) allows delivering high doses per fraction with high accuracy to the prostatic gland in a low number of fractions. 
Dose escalation in normofractionaded radiation prostate cancer trials showed an increased toxicity. Low alpha-beta ratio of prostate cancer make suitable to escalate dose by extreme hypofractionation considering Linear Quadratic Model. Stereotactic Body Radiation Therapy (SBRT) in prostate cancer is a novel precise strategy which allows delivering high doses per fraction with high accuracy to the prostatic gland in a low number of fractions.   Two prospective phase I-II studies were approved by our institutional review and ethics board. Inclusion criteria were:

Trial1) T1-2N0M0, Gleason Score 6–7, PSA ≤ 20 ng/mL, and  IPSS 0–7. Dose 85 GyEqD2.
Trial 2) T3aN0M0 Gleason score 8 or less (N+risk<25%) and IPSS 0-12. Dose 87GyEqD2

Objectives: To evaluate the feasibility and toxicity of a single dose hypofractionated prostate stereotactic boost.

Material & Methods: Patient’s tumour stages were T3aN0M0, Gleason score 8 or less, N+risk<25%, and IPSS 0-12. Hormonal-therapy was prescribed for 3 years. IGRT with Cone Beam CT was mandatory. Dose SBRT was delivered at a prescribed planning target volume (PTV) 9 Gy after 60 Gy 2 Gy per fraction in 30 days, using VMAT with 6 MV FFF photons. RTOG-EORTC and CTCAE v4.0 morbidity scores were used to assess toxicities. Health-related quality of life questionnaire was administered centrally by telephone interview before treatment and during follow-up (at 3, 6 and 12 months). Study was planned following a Simon’s 2-stage design.

Results: First's 22 patients included were analysed. Mean age was 69.6 years old. Median follow-up was 9 months (2-34) with more than 60% having at least 6 months of follow-up. All patients completed the treatment as programmed. No toxicity greater than grade 2 was observed. EPIC urinary values were 81.26 and 80.49 at 6 and 12 months respectively. EPIC hormonal was 63,83 and 64.09 at 6 and 12 months respectively . EPIC bowel values for these points in time were 93,30 and 92,50. Non PSA relapse was seeing during this short follow-up.

Conclusion: SBRT regime of 9 Gy to the prostate after normofractionated 60 Gy for high risk prostate cancer is feasible and well tolerated in selected patients. Decline in QoL (EPIC hormonal QLQ) measures are related to prolonged hormonal treatment in high-risk patients.