Dosimetric study of high-dose region overlap and cumulative dose in brachytherapy for cervical cancer

Objective: To explore the overlap of high-dose areas of organs at risk (OAR) in three close range radiotherapy techniques for cervical cancer using deformable registration (DIR) technology. Compare the difference in cumulative dose of OAR generated by DIR and direct superposition methods, and analyze the correlation between this difference and overlap. Method: A retrospective selection of 45 cases of cervical cancer who received close range radiotherapy was conducted, and they were divided into intracavitary treatment group (ICBT), intracavitary combined implantation treatment group (IC/IS-BT), and 3D printed guide plate group (3D), with 15 cases in each group. Use Boolean operation tools in the planning system to generate high-dose regions corresponding to the bladder and rectum D2 cM3 and D1 cM3. Perform DIR on the planned CT scans between stages, and use the similarity coefficient (DSC) to analyze the overlap of high-dose areas in the bladder and rectum between stages. After registering all segmented CT deformations together, use Jaccard to analyze the overall overlap of high-dose areas in the bladder and rectum. The values of DSC and Jaccard range from 0 to 1, with smaller values indicating smaller overlapping areas. Using DIR to perform deformation accumulation on all segmented planned doses and comparing them with the cumulative dose of direct superposition method, analyze the dose differences in the high-dose areas of the bladder and rectum and their correlation with DSC and Jaccard. The DSC values of the bladder D 2 c m 3 and D 1 c m 3 regions in the ICBT, IC/IS-BT, and 3D groups were (0.470 ± 0.112, 0.452 ± 0.099, 0.412 ± 0.131), (0.358 ± 0.110, 0.310 ± 0.110, 0.295 ± 0.139), and the DSC values of the rectum D 2 c m 3 and D 1 c m 3 regions were (0.521 ± 0.159, 0.502 ± 0.118, 0.463 ± 0.141), (0.411 ± 0.161, 0.365 ± 0.137, 0.347 ± 0.138), respectively; The Jaccard values of the D 2 c m 3 and D 1 c m 3 areas of the bladder are (0.110 ± 0.056, 0.076 ± 0.059, 0.083 ± 0.067), (0.049 ± 0.039, 0.032 ± 0.031, 0.042 ± 0.028), and the Jaccard values of the D 2 c m 3 and D 1 c m 3 areas of the rectum are (0.167 ± 0.130, 0.114 ± 0.089, 0.110 ± 0.094), (0.107 ± 0.095, 0.057 ± 0.065, 0.056 ± 0.067), respectively; The DSC and Jaccard values of the three techniques are relatively small, and the differences are not statistically significant. After DIR, there was no significant difference in the cumulative dose of D 2 c m 3 and D 1 c m 3 in the bladder and rectum compared to the direct superposition method, and there was no correlation with overlap. Conclusion: There is no significant difference in overlap between the three treatment techniques, and the size of overlap is not correlated with dose differences. The deformation superposition method can be used as an auxiliary method for evaluating the total dose between sub doses of close range radiotherapy for cervical cancer.