Impact of delivery time factor on treatment time and plan quality in tomotherapy

Abstract

Abstract Background The delivery time factor (DTF) is a new parameter introduced by the RayStation treatment planning system for tomotherapy treatment planning. This study investigated the effects of this factor on various tomotherapy plans. Methods Overall, 25 patients with cancer (head and neck, 6; lung, 9; prostate, 10) were enrolled in this study. For these patients, helical tomotherapy plans with a field width of 2.5 cm, pitch of 0.287, and DTF of 2.0 were created. All the initial plans were recalculated by changing the DTF parameter from 1.0 to 3.0 in increments of 0.1 (21 plans per patient). For each plan, we calculated the following evaluation indices: the treatment time, modulation factor, conformity index (CI), homogeneity index (HI), and doses to critical organs at risk (OARs). For every index, the values normalized by the corresponding values with a DTF of 1.0 were plotted, and fitted curves with polynomial functions were created as a function of the DTF. These curves were used to evaluate the impact of the DTF on both delivery efficiency and plan quality. Results Treatment time and modulation factor increased monotonically with increasing DTF. Increasing the DTF by 0.1 resulted in an increase in the treatment time and modulation factor by almost 10%. This relationship was similar for all treatment sites. An increase in DTF was found to improve CI, HI, and OAR doses compared to plans with a DTF of 1.0, except for the CI in the lung cancer case. However, the improvement in most indices ceased at a certain DTF; nevertheless, treatment time continued to increase in accordance with an increase in DTF. Conclusions DTF is a critical parameter for improving the quality of tomotherapy plans; however, increase of this factor above a certain level leads to an unnecessary increase in treatment time and deterioration of plan quality. Trial registration: None.