Dosimetric evaluation for head and neck cancer patients treated with helical TomoTherapy

Abstract

Objective To compare the differences between planning dose and actual dose of targets and organs at risk (OAR) for head and neck cancer patients with helical tomotherapy (HT).Methods 12 head and neck patients with HT were enrolled in this study.Prior to each treatment fraction,an MVCT scan was performed.The MVCT images of the first fraction of each week since the second week treatment were chosen,and dose distributions were recalculated on the MVCT images in Planned Adaptive application of HT,which were the actual dose of each fraction.Each single dose distribution and the corresponding CT image were sent to commercial software (MIM5.5),and deformable image registration was performed to the CT images,and the sum of actual dose was acquired.Dose distribution of targets and OAR of initial treatment plan (Plan-1) and the actual dose distribution (Plan-2) were compared.Results There were no significant differences between Plan-1 and plan-2 for D2,D50 of GTV (P =0.07,0.07) and D2 of PTV (P =0.08).D95,D98 and D100 of GTV in Plan-2 were lower than in Plan-l,with 2.1％,2.7％ and 5.6％ (P =0.02,0.02,0.02),respectively.D50,D95,D98 and D100 of PTV in Plan-2 were lower than in Plan-1,with 0.8％,1.9％,3.9％ and 13.5％ (P =0.01,0.00,0.00,0.01),respectively.Dose of spinal cordwas higher in Plan-2 than in Plan-1,increasing by an Dmax of 1.2％ (P =0.04).Conclusions In radiotherapy for head and neck cancer actual dose of targets was lower than initial plan dose.Max dose of the spinal cord,however,was higher than in initial plan.For patients who have a significant anatomic change,in order to achieve the best therapeutic effect,modification of targets and treatment plan at the appropriate time is essential. Key words: Head and neck neoplasms/helical tomotherapy; Image-guided; Deformable image registration; Dosimetry