Comparison of 6 MV and 18 MV photons for IMRT treatment of lung cancer

Background and purpose: To compare 6 MV and 18 MV photon intensity modulated radiotherapy (IMRT) for non-small cell lung cancer. Materials and methods: Doses for a cohort of 10 patients, typical for our department, were computed with a commercially available convolution/superposition (CS) algorithm. Final dose computation was also performed with a dedicated IMRT Monte Carlo dose engine (MCDE). Results: CS plans showed higher D-95% (Gy) for the GTV (68.13 vs 67.36, p = 0.004) and CTV (67.23 vs 66.87, p = 0.028) with 18 than with 6 MV photons. MCDE computations demonstrated higher doses with 6 MV than 18 MV in D95% for the PTV (64.62 vs 63.64, p = 0.009), PTVoptjm (65.48 vs 64.83, p = 0.014) and CTV (66.22 vs 65.64, p = 0.027). Dose inhomogeneity was lower with 18 than with 6 MV photons for GTV (0.08 vs 0.09, p = 0.007) and CTV (0.10 vs; 0.11, p = 0.045) in CS but not MCDE plans. 6 MV photons significantly (D-33%; p = 0.045) spared the esophagus in MCDE plans. Observed dose differences between lower and higher energy IMRT plans were dependent on the individual patient. Conclusions: Selection of photon energy depends on priority ranking of endpoints and individual patients. In the absence of highly accurate dose computation algorithms such as CS and MCDE, 6 MV photons may be the prudent choice. (c) 2006 Elsevier Ireland Ltd. All rights reserved.