The impact of simultaneous dose escalation VMAT to the focal lesion micro boost of localized prostate cancer.

Abstract

e16592 Background: Dose Escalation to the prostate is showing promising results of increasing local control. The study aims to assess biochemical failure free survival (BFF) after dose escalation to the prostate 78Gy with simultaneous integrated boost (SIB) 87Gy to the focal lesion. Genito-urinary (GU) & gastro-intestinal (GI) toxicity was assessed by comparing investigational toxicity score & patient outcome reports. Methods: Thirty intermediate & high risk localized prostate cancer patients were treated with dose escalated VMAT protocol of 78 Gy/35 fractions to prostate & 87Gy boost to focal lesion detected by baseline multi-parametric MRI & TRUS as well. Neo-adjuvant, Concurrent & adjuvant hormonal therapy was applied. Risk structures dose statistics were matched to modified Quantec with EQD2 equation. For each patient, daily online fiducial markers image guided verification was done. Toxicity profile was assessed by RTOG for subjective assessment and FACIT quality of life protocol for objective assessment during the radiotherapy course & follow up period. Results: About 80% of patients received the pre-determined protocol, however three patients received 76Gy to prostate & 84Gy to the focal lesion to comply with the risk structure constrains. At median follow up period of 18 months-BFF was 93.3 %. By the end of radiotherapy, 80% developed G3 GU toxicity while 30% developed G2 GI toxicity. Correlation between bladder V40 (≥or≤ 40%) & GU toxicity (≤ G3 vs G3) was of border line statistical significance (P = 0.05). After radiotherapy, GU toxicity dropped to 17.2% G2 & 13% G3 at the 3rd month while 0 % G3 afterwards. Three patients developed G4 rectal toxicity (bleeding per rectum); one at 9th month of ending treatment & two at 12th month; two of them needed cautery for angio-dysplasia as post radiation sequelae confirmed by colonoscopy. However, the correlation between V40 of the rectum ≥ 40% was significant with rectal toxicity (G0 vs G4) (P = 0.02). Comparing FACIT assessment during radiotherapy or in follow up showed no significant difference affecting the quality of life. Conclusions: Dose Escalation with SIB should be done using advanced technique like VMAT with image guidance. Re-validation of risk structure & rectal dose constrains should be considered especially for dose escalation ≥ 72Gy. Clinical trial information: NCT03384199.