Actual absorbed dose in radiotherapy of patients with rectal cancer based on cone-beam CT

In the radiotherapy of rectal cancer, the actual dose received by the patient's body always differs from the planned design due to setup errors. Twenty rectal cancer cases undergoing RapidArc treatment were selected. The treatment plan of the pCT images was transplanted to the scatter-corrected cone-beam computed tomography (CBCT) images. Then, the dose was calculated to generate the revised CBCT plan after the raw CBCT plan was corrected using the weekly setup error data. Finally, a paired t-test was used to compare the results of the dose calculation between the CBCT and pCT plans. This showed that the dosimetric parameter average values of D₂, D₉₈, D₅₀, CI, and HI in the target of the CBCT plan were lower than those in the pCT plan. The differences of 2.8%, 2.5%, 2.9%, 2.0%, and 4.4%, respectively, were statistically significant (p < 0.001). The dosimetric parameter average values of D_mean, D₅, V₂₀, V₃₀, and V₄₀ in the small intestine of the CBCT plan were higher than those in the pCT plan. The differences of 3.0%, 3.1%, 2.5%, 3.1%, and 3.6%, respectively, were statistically significant (p < 0.001). The dosimetric parameter average values of D_mean, D₅, V₂₀, V₃₀, and V₄₀ in the bladder of the CBCT plan were higher than those in the pCT plan. The differences of 3.0%, 1.8%, 0.9%, 3.2%, and 3.4%, respectively, were statistically significant (p < 0.001). The difference between the left and right femoral heads was small (maximum difference: 0.3%, minimum difference: 0.1%); however, statistical significance was found (p < 0.001). The comparative analysis indicates that the CBCT plan, based on scatter-corrected CBCT images combined with setup error data, provides a reference for the actual absorbed dose of each tissue in rectal cancer radiotherapy. These findings are useful for the quantitative evaluation of the therapeutic effect of radiotherapy for rectal cancer. (authors)