Planning outcomes and acute toxicity of intensity-modulated radiotherapy (IMRT) for treatment of bladder and pelvic lymph nodes.

Abstract

297 Background: We implemented an IMRT protocol for simultaneous treatment of bladder and pelvic lymph nodes (LN) and report the planning outcomes and acute toxicity of patients treated using this technique. Methods: 13 patients were treated with a 5-field step and shoot IMRT technique. Inclusion criteria were: radiological evidence of pelvic LN metastases; stage T3/T4; high risk pathology or post-cystectomy with persistent/recurrent disease. Anisotropic margins were applied to the whole bladder CTV (0.5 cm laterally/inferiorly, 1 cm posteriorly, 1.5 cm superiorly/anteriorly) to create PTV1. 0.5 cm margins were applied to the pelvic LN CTV to create PTV2. PTVs 1/2 were prescribed 52 Gy in 32 fractions. 1 cm margins were applied to the involved bladder to create PTV3 (prescribed 64Gy). 0.5 cm margins were applied to the involved LN volumes to create PTV4 (prescribed 60 Gy). Post cystectomy patients were planned using PTVs 2/4 only. Dose volume histograms for organs at risk (rectum, femoral heads and other bowel) were calculated and compared with local dose constraints. Acute toxicity was assessed according to common toxicity criteria v3.0 and recorded weekly during treatment. Treatment verification was performed by cone beam CT. Results: All treatment plans achieved target coverage of > 95% volume to > 95% prescription dose for each PTV. All patients achieved rectal and femoral head dose constraints. 2 patients did not meet V45 other bowel constraints but proceeded with treatment as all other dose limits were achieved. At the time of abstract submission 13 patients had completed treatment. 2 were treated for relapse post-cystectomy and did not have GU toxicities recorded. Maximum experienced acute toxicities were recorded. 9/11 patients experienced acute GU toxicity (G1=3, G2=1, G3=5). 6/13 patients experienced acute GI toxicity (G1=3, G2=3). 9/13 patients developed other acute toxicities (G1=7, G2=2). No patients developed ≥G3 non-GU toxicity. Conclusions: Bladder and pelvic LN IMRT allows patients with high risk locoregional bladder cancer to meet preset dose constraints, appears feasible and has a comparable rate of acute toxicity to conventional bladder-only radiotherapy treatment. No significant financial relationships to disclose.