Impact of Planning Target Volume Reduction on Toxicity and Outcome in Prostate Carcinoma Treated with Image Guided-Intensity Modulated Radiotherapy

Abstract

Introduction: Image Guided Intensity-Modulated Radiotherapy (IG-IMRT) with marker based prostate localisation could potentially reduce the Planning Target Volume (PTV), thus reducing radiation toxicity. Aim: We retrospectively evaluated the influence of PTV reduction on radiation induced toxicity and biochemical control. Materials and Methods: This study was a single institution retrospective evaluation. Patients with histopathologically proven adenocarcinoma of prostate, age 18-80 years, Karnofsky performance status ≥70, T1c-T3bN0M0 and treated with definitive Radiotherapy (RT) were considered in the study. Patients were treated with two different approaches. The HRPTV in the PTV_7 arm was obtained by giving a 7 mm uniform PTV expansion of High-risk Clinical Target Volume (HR-CTV), except posterior margin (6 mm). While the HRPTV in the PTV_5 arm was formed by a 5 mm isotropic expansion. IG-IMRT was delivered in 2 phases with a total dose of 78 Gray in 39 fractions. Acute toxicities were graded weekly as per common terminology criteria for adverse events and late toxicities by the radiation therapy oncology group late morbidity criteria. Biochemical failure was defined by phoenix guideline. Results: Fifty patients (25 each arm) were evaluated with a median age of 68 years. At a median follow-up of 37 months (range 11-76), Grade 1, 2 and 3 overall late (3-year) Genitourinary (GU) toxicities were 68%, 24% and 8%, Gastrointestinal (GI) toxicities were 72%, 18% and 10%, respectively. The PTV_7 group had significantly higher Grade ≥3 chronic GI toxicities (10% vs. 0%, p=0.05), compared to PTV_5 group. However, there was non-significant difference in Grade ≥3 chronic GU toxicities (6% vs. 2%, p=0.6). Acute proctitis was significantly higher (48% vs. 16%, p=0.03) in the PTV_7 arm. The 3-year biochemical progression free survival rates were similar in both arms {89.5% (PTV_5) vs. 85.9% (PTV_7), p=0.47}. Conclusion: PTV reduction can be safely used with dose escalated radiotherapy while using marker based IG-IMRT. This may result in the reduction of chronic GI toxicity without compromising biochemical control.

Keywords

• acute proctitis
• fiducial marker
• radiotherapy