Multi-institutional retrospective analysis of the inhomogeneity correction for radiation therapy of lung cancer

The purpose of this work is to retrospectively analyze the effect of the inhomogeneity correction using clinically treated plan of stage III non-small-cell lung cancer within multiple institutions in Japan. Twenty-five patients among five facilities of radiation therapy were registered for this study. The isocenter dose or D₉₅ of PTV or other important values were compared with and without an inhomogeneity correction using model-based algorithm. The differences in isocenter dose were 4% average and 10% maximum for the first Anterior-Posterior opposed field plan to 40 Gy and 6% average and 11% maximum for the off-cord boost oblique field plan of 20 Gy. The differences in D₉₅ dose were 1% average and 9% maximum for the first plan and 1% average and 6% maximum for the boost plan. D₉₅ prescription seemed to be a superior method; however, its reliability depends on each clinical case. Additionally, maximum dose, minimum dose and mean dose for both the primary tumor and the metastatic lymph node were analyzed, and the minimum dose had the most impressive results. In some cases, the target volume had unintended underdose of more than 10%. Finally, an analysis of the organ at risk was added, and this showed no meaningful differences for the V₂₀ of the lung and the maximum dose of the spinal cord. These results provide a standard for the effects of the inhomogeneity correction.