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

Background and purposeTo compare 6 MV and 18 MV photon intensity modulated radiotherapy (IMRT) for non-small cell lung cancer.Materials and methodsDoses 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).ResultsCS plans showed higher D95% (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), PTVoptim (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 (D33%; 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.ConclusionsSelection 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.