Image guidance for post-prostatectomy radiotherapy: Are we missing the mark?

56 Background: Image-guided radiation therapy (IGRT) has been widely adopted for both definitive and post-operative prostate radiotherapy. In the postoperative setting, numerous studies of prostate bed motion have recommended tight planning margins (<10mm) if IGRT is used daily. The purpose of this analysis is to determine the effect of IGRT on the efficacy and toxicity of post-operative prostate radiotherapy. METHODS: Between 1998 and 2010, 286 patients received radiation therapy after prostatectomy at Duke. Recurrent disease following radiation therapy was defined as PSA >0.2 ng/ml and rising or initiation of salvage ADT. CTCAE v 4.0 and the RTOG/LENT late morbidity scores were used to grade acute and late toxicities. Risk for biochemical failure and late Grade 2+ GI toxicity were compared between IGRT (N = 113) and non-IGRT (N = 173) patients using multivariable adjusted Cox regression controlling for age, treatment technique (3D vs IMRT), radiation dose, androgen suppression, pathologic Gleason Score, margin status, pathologic stage, and pre-radiotherapy PSA level. RESULTS: The median margin size for patients with IGRT was 7mm (IQR 6-10mm) and 15mm (IQR 7-15mm) for those without IGRT (p < 0.001). Median follow up was 21 months (IQR 15-33 mo) for patients with IGRT and 49 months (IQR 30-73 mo) for those without IGRT (p < 0.001). On multivariate analysis, patients treated with IGRT had a greater risk of progression versus non-daily imaging (HR = 2.51, p < 0.001), as did patients who received salvage versus adjuvant radiotherapy (HR = 2.41, p = 0.005). Higher pathologic Gleason Score (HR = 1.96, p = 0.026) and pathologic stage (HR = 1.93, p = 0.003) conferred increased risk of progression, while positive margin status was protective (HR = 0.53, p = 0.002). Age, radiation dose, androgen suppression, and treatment technique did not affect biochemical outcome (p > 0.1). There were no differences in acute or late GI toxicity according to treatment technique or use of IGRT (both p > 0.1). CONCLUSIONS: The use of IGRT was associated with increased biochemical recurrence for patients receiving post-operative prostate radiotherapy. For these patients, we recommend using treatment margins of at least 10mm to address subclinical disease and organ motion.

Duke Scholars

Author Judd Wendell Moul Urology

Author W. Robert Lee Radiation Oncology