ABSTRACT
Objective To evaluate the effect of different methods of deformable image registration on the dose evaluation in adaptive radiotherapy for lung cancer. Methods By using Raystation Ver4. 5 treatment planning system platform, two algorithms ( Hybrid-and Biomechanics-based deformable image registration) and two orders (CT images before and during radiotherapy as reference images) were adopted. Four deformable image registration methods were utilized to calculate the accumulative dose. Eleven patients of lung cancer received adaptive radiotherapy for 35. 0-61. 6 Gy were recruited. The mean doses of lung,heart and GTV and the D98 and D2 of GTV were statistically compared using four methods. Results With the four deformable image registration methods, the standard deviation of the mean lung dose of 11 lung cancer patients was ranged from 0. 07 to 0. 70 Gy,0. 01 to 0. 79 Gy for the mean heart dose,0. 01 to 2. 23 Gy for the mean GTV dose,0. 02 to 6. 51 Gy for the D98 of GTV and 0. 01 to 0. 97 Gy for the D2 of GTV,respectively. Conclusion The selection of deformable image registration method causes uncertainty to the calculation of accumulative dose during adaptive radiotherapy for lung cancer.
ABSTRACT
Objective To investigate the gross tumor volume (GTV) changes in nonoperatively treated lung cancer patients during radiotherapy by off-line analysis using kilovoltage cone-beam computed tomography (KVCBCT).Methods Eighteen nonoperatively treated lung cancer patients were divided into group A (n =13) to receive conventional radiotherapy (1.8-2.2 Gy/fraction) and group B (n =5) to receive accelerated radiotherapy (5-8 Gy/fraction).Group A was further divided into subgroup A1 (n =10) and subgroup A2 (n =3) according to GTV changes.Each patient in group A underwent KVCBCT scan before treatment once a week,and each patient in group B underwent KVCBCT scan before each treatment.KVCBCT and CT images were registered in the treatment planning system to analyze GTV changes.Results Of all patients in group A,77％ showed ＞ 20％ GTV reduction.Subgroup A1 had the maximum GTV reduction in the 4th week of treatment (the 20th treatment) ;Subgroup A1 had a mean reduction of (0.94 ± 9.94)％,with a maximum value of-56.76％.Subgroup A2 showed no correlation between GTV changes and treatment time.Group B had a mean GTV reduction of (-7.41 ± 1.76)％,with a maximum value of -15.91％.Of all patients in group B,71％ showed ≤ 10％ GTV reduction.Small GTV changes were observed in group B.Conclusions There are no regular GTV changes in nonoperatively treated lung cancer patients during radiotherapy.Adaptive radiotherapy is recommended in the cases where GTV is reduced over 20％ in the 20th treatment.