Evaluations of set-up errors and target margins for super and middle part of esophageal carcinoma in image guided radiotherapy / 中华放射医学与防护杂志

ABSTRACT

Objective To investigate the set-up errors of super and middle part of esophageal cancer patients using cone-beam CT (CBCT) during intensity modulated radiotherapy (IMRT),hence determine various margins from CTV to PTV.The corresponding influence on the normal tissues (lung and spinal cord) was also discussed.Methods From December 2012 to December 2013,12 patients with upper and middle segment of esophageal cancer were chosen.Using their 60 sets of weekly acquired CBCT images prior to the treatment,the lateral,longitudinal,and vertical set-up errors of each patient were obtained.Based on these measured errors and the target motions,we adopted new margins to create new PTV.Then IMRT plans were created for the original PTV (5 mm margin in all directions on CTV) and new PTV respectively.On condition of the same target coverage (V95 ≥ 95％),the doses to lungs (V5,V20,V30,D) and spinal cord (D1 cm3) were compared statistically between the original and new plans.Results According to the 60 CBCT scans,the average left-right (RL),superior-inferior (SI),anterior-posterior (AP) set-up errors were (2.02 ± 1.74),(2.03 ± 1.93),and (2.02 ± 1.89) mm respectively.The margins were 5.6 mm (RL),8.5 mm (SI),and 4.7 mm (AP) for the upper esophagus and 6.2 mm (RL),11 mm (SI),and 5.0 mm (AP) for the middle esophagus.Comparison of both lungs and spinal cord suggested significant differences between the two plans (t =-8.23,-5.55,-4.66,-6.87,-4.67,P ＜0.05).Conclusions The margins from CTV to PTV should be created via CBCT-measured set-up errors and previous reports,which can be helpful for clinical treatment.