Sci-Sat AM(1): Planning - 06: SBRT Lung: From Homogeneous to Heterogeneous Dose Calculation

Abstract

A viable treatment option for inoperable early stage non-small cell lung cancer is stereotactic body radiation therapy (SBRT) using 4DCT to incorporate tumour motion in the planning stage, hypofractionation, and cone beam CT for image guidance on the treatment unit. At our cancer centre, lung SBRT treatments were originally planned with no heterogeneity correction and prescribed to a point and with a penumbra. Even though no correction was applied to these plans, the monitor units delivered were injected into a separate plan where heterogeneity corrections were applied thus giving a true sense of the delivered dose. The goal was to plan future patients using heterogeneity correction only and the question became whether the original dose prescription of 48 Gy to the dose point should be changed. Ten plans had heterogeneity correction applied using monitor units calculated from the homogeneous distributions (Group A), and ten patients had heterogeneity correction only (Group B); 3D conformai plans in both groups. A comparison was made in terms of target volume dose coverage to determine whether the target coverage moving forward is comparable to what was delivered previously. ITV received a minimum dose of 50.5±1.4 Gy and 48.7±0.9 Gy, Group A and B respectively. The PTV received a minimum of 95% of prescribed dose in Group A 45.8±1.6 Gy, by comparison Group B was lower 44.4±0.7 Gy (p < 0.02). Overall target volume coverage is decreased as we move from homogeneous to heterogeneous dose calculation and the prescription should be modified as we move forward.