Prospective Evaluation of Probabilistic Dose-Escalated IMRT in Prostate Cancer

Coverage-Probability based dose-escalated IMRT of Prostate Cancer

Abstract

Background:

Cure- and toxicity rates after intensity-modulated radiotherapy (IMRT) of prostate cancer are dose- and volume dependent. We prospectively studied the potential for Organ at Risk (OAR) sparing and compensation of tumor movement with the Coverage probability (CovP) concept.

Methods

Twenty-eight prostate cancer patients (median age 70) with localized disease (cT1c-2c, N0, M0) and intermediate risk features (PSA<20, Gleason score ≤7b) were treated in a prospective study with the CovP concept. Planning-CTs were performed on three subsequent days to capture form changes and movement of prostate and OARs. The clinical target volume (CTV, prostate) and the OARs (bladder and rectum) were contoured in each CT. The union of CTV1-3 was encompassed by an isotropic margin of 7mm to define the ITV (internal target volume). Dose prescription/escalation depended on coverage of all CTVs within the ITV. IMRT was given in 39 fractions to 78Gy using the Monte-Carlo algorithm.

Results

Long-term toxicity was evaluated in 26/28 patients after a median follow-up of 7.1 years. At last follow-up, late bladder toxicity (RTOG G1) was observed in 14.3% of patients and late rectal toxicities (RTOG) of G1 (7.1%) and of G2 (3.6%) were observed. No higher graded toxicity occurred. After 7.1 years, biochemical control (biochemically no evidence of disease, bNED) was 95.5%, prostate cancer-specific survival and the distant metastasis-free survival after 7.1 years were 100% each.

Conclusions

CovP-based IMRT was feasible in a clinical study. Dose escalation with the CovP concept was associated by a low rate of toxicity and a high efficacy regarding local and distant control.