4–7 September 2014

Aim: To assess whether intensity modulated radiotherapy (IMRT) offers any advantages compared to three-dimensional conformal radiotherapy (3DCRT) when treating the ilio-inguinal lymph-node basin after therapeutic lymphadenectomy for melanoma. Method: 15 consecutive patients receiving adjuvant radiotherapy (48 Gy in 20 fractions) were selected for the study. Simulation, volume generation and goals for target volume coverage and organ at risk (OAR) avoidance followed departmental protocols. For each patient optimised 3DCRT and IMRT plans were generated with prescriptions in accordance with International Commission on Radiation Unit 50 and 62 (3DCRT) and 83 (IMRT) guidelines. Dose volume histograms were produced for each plan in order to allow direct comparisons of 3DCRT and IMRT plans for each patient. The Wilcoxon signed-rank test was used to compare dose received to both target and OARs from each plan for individual patients. Results: Conformality index was improved by the use of IMRT; median 0.649 (range 0.476–0.808) vs 0.442 (0.288–0.605); W = 2, p ≤ 0.05 for IMRT and 3DCRT respectively. No difference was seen in the homogeneity index; median 10.92 (7.65–28.67) vs 11.17 (8.96–26.69); W = 31, p > 0.05. Median dose to the bowel closest to the target volume was significantly less for IMRT. D1 cc, 10 cc and 40 cc were 48.5 Gy vs 49.7 Gy; 47.8 Gy vs 49.0 Gy and 45.8 Gy vs 48.2 Gy for IMRT and 3DCRT respectively. W values 14, 2 and 10; p ≤ 0.05 for all. Also reduced with IMRT was dose to the ipsilateral femoral neck; median V43.2 Gy, 3.9% (0.1–22.0%) vs 43.2% (12.4–68.5%), W = 0, p ≤ 0.05; and median V36 Gy, 29.5% (14.8–42.3%) vs 61.1% (40.4– 100%), W = 0, p ≤ 0.05 for IMRT and 3DCRT respectively. Conclusion: A homogenous coverage of the target volume can be achieved with both IMRT and 3DCRT (homogeneity index <15). However, the use of IMRT appears to allow superior conformality of dose to the target volume while relatively sparing (and potentially reducing the risk of toxicity to) adjacent OARs such as the bowel and femoral neck. Volumetric modulation arc therapy compared with intensity-modulated radiation therapy for malignant pleural mesothelioma C Albiez, D Papworth, A Kaminski and J Frantzis Genesis Cancer Care, Queensland, Australia