Objective: The aim of this study was to determine which physical delivery parameter changes are most suitable for multiple-level dose-painting treatment plans with helical tomotherapy (HT).
Methods: A total of 96 treatment plans were generated for 12 patients who had undergone fluorine-18 fludeoxyglucose positron emission tomography/CT ((18)F-FDG-PET/CT) scan to plan head and neck cancer treatment. Based on these PET-CT images, the dose was escalated to 96 Gy in 32 fractions as a function of PET intensity values. The intensity-based prescription was converted into seven discrete dose levels. For the same patient, different HT plans were optimized by varying parameters such as field width (FW), pitch (PF) and modulation factor (MF). Dose conformity was evaluated using quality-volume histograms, quality factors (QFs), weighted index of achievement (IOAw), coldness (IOCw) and hotness (IOHw). Moreover, doses to organs at risk (OARs), target volumes and execution time were analyzed.
Results: Median QFs were the best for FW = 1.05 cm (QF = 2.10) and the worst for FW = 2.5 cm (QF = 3.04). The same trend was observed for IOAw, IOCw and IOHw. Combination of FW = 1.05 cm and MF = 5 leads to the longest beam-on time (above 25 min), whereas FW = 2.5 cm and MF = 3 lead to the shortest time (below 8 min). Data analyzed based on dose-volume histogram showed that changes in FW had the strongest impact on plan quality, whereas the effect of MF and PF changes was moderate.
Conclusion: HT is suitable for multiple-level dose-painting treatment plans.
Advances in knowledge: Changes in FW and MF had the greatest impact on dose distribution quality and beam-on time. Changes in PF only influenced doses to the OARs.