Impact of planning target volume margins and rectal distention on biochemical failure in image-guided radiotherapy of prostate cancer

Background and purpose: A previous study in our department demonstrated the negative impact on freedom from biochemical failure (FFBF) of using too narrow planning target volume (PTV) margins during prostate image-guided radiotherapy (IGRT). Here, we investigated the impact of appropriate PTV margins and rectal distention on FFBF. Methods and materials: A total of 50 T1-T3N0M0 prostate cancer patients were treated with daily IGRT by implanted markers. In the first 25 patients, PTV margins were 3 mm laterolateral, 5 mm anterioposterior and 4 mm craniocaudal. The subsequent 25 patients were treated with isotropic margins of 6 mm. The rectal cross-sectional area (CSA) was determined on the planning CT. Median follow-up was 61 months. Results: The overall 5-year FFBF was 83%. A 6 mm PTV margin was related to increased 5-year FFBF on univariate analysis (96% vs 74% with the tighter PTV margins, p = 0.04). The 5-year FFBF of patients with a rectal distention on the planning CT was worse compared to those with limited rectal filling (75% for CSA >= 9 cm(2) vs 89% for CSA < 9 cm(2), p = 0.02), which remained significant on multivariate analysis (p = 0.04). Conclusion: This retrospective study illustrated the positive impact of PTV margin adaptation and addressed the importance of avoiding rectal distention at time of the planning CT. (C) 2014 Elsevier Ireland Ltd. All rights reserved.