Comparing Organ-At-Risk (Oar) Doses For High-Dose-Rate Vaginal Brachytherapy (Hdr-Vb) Patients Between 3 Different Planning And Delivery Workflows

Purpose/Objective(s)To compare the OAR doses to the rectum and the bladder in postoperative endometrial cancer patients receiving HDR-VB, between 3 different methods of planning and delivery: computed tomography (CT)-based planning before each fraction with an individualized treatment plan created for every fraction (M1); applying the individualized treatment plan for the first fraction to subsequent CT simulation images for the following fractions (M2); and using a template plan based on applicator choice and prescription specifics without patient-specific imaging or planning (M3).Materials/MethodsFor 22 patients who previously received postoperative HDR-VB using a vaginal cylinder and planned using M1 (creating a patient-specific plan for each fraction) for endometrial cancer, alternative plans were retrospectively created using plans M2 and M3 under institutional review board approval. The prescription ranged from 500 to 700 cGy per fraction for 3 to 4 fractions, using 25- to 35-mm diameter cylinders treating upper 35 to 55 mm. For M2, a patient-specific plan was created for each patient based on Fraction 1 CT and applied to the CT simulation acquired prior to subsequent fractions. For M3, a template plan matching the cylinder/prescription was selected from an institution-established library applied to the CT simulation acquired before each fraction. The rectum and bladder were contoured on the CTs of each fraction for dose comparison between the 3 methods. D50, D2cc, D1cc, D0.1cc, and V100 of the bladder and the rectum were compared using the 2-sided Wilcoxon signed rank test. Using M1 as the gold standard, M2 and M3 were each compared against M1.ResultsA total of 49 fractions (with distinct plans for M1 vs M2) were available for M1 versus M2 comparison, and 74 fractions for M1 versus M3 comparison. For M1 versus M2, there was no statistically significant difference (P75 cGy for only 2 fractions, in which M3 was higher than M1 in D.1cc to the bladder.ConclusionM1 and M2 showed no statistically significant differences in rectal or bladder doses, while M1 led to higher rectal dose yet lower bladder dose than M3, though this difference was minor. Plan standardization in HDR-VB may result in considerable time and cost savings with minimal OAR dose differences. Purpose/Objective(s)To compare the OAR doses to the rectum and the bladder in postoperative endometrial cancer patients receiving HDR-VB, between 3 different methods of planning and delivery: computed tomography (CT)-based planning before each fraction with an individualized treatment plan created for every fraction (M1); applying the individualized treatment plan for the first fraction to subsequent CT simulation images for the following fractions (M2); and using a template plan based on applicator choice and prescription specifics without patient-specific imaging or planning (M3). To compare the OAR doses to the rectum and the bladder in postoperative endometrial cancer patients receiving HDR-VB, between 3 different methods of planning and delivery: computed tomography (CT)-based planning before each fraction with an individualized treatment plan created for every fraction (M1); applying the individualized treatment plan for the first fraction to subsequent CT simulation images for the following fractions (M2); and using a template plan based on applicator choice and prescription specifics without patient-specific imaging or planning (M3). Materials/MethodsFor 22 patients who previously received postoperative HDR-VB using a vaginal cylinder and planned using M1 (creating a patient-specific plan for each fraction) for endometrial cancer, alternative plans were retrospectively created using plans M2 and M3 under institutional review board approval. The prescription ranged from 500 to 700 cGy per fraction for 3 to 4 fractions, using 25- to 35-mm diameter cylinders treating upper 35 to 55 mm. For M2, a patient-specific plan was created for each patient based on Fraction 1 CT and applied to the CT simulation acquired prior to subsequent fractions. For M3, a template plan matching the cylinder/prescription was selected from an institution-established library applied to the CT simulation acquired before each fraction. The rectum and bladder were contoured on the CTs of each fraction for dose comparison between the 3 methods. D50, D2cc, D1cc, D0.1cc, and V100 of the bladder and the rectum were compared using the 2-sided Wilcoxon signed rank test. Using M1 as the gold standard, M2 and M3 were each compared against M1. For 22 patients who previously received postoperative HDR-VB using a vaginal cylinder and planned using M1 (creating a patient-specific plan for each fraction) for endometrial cancer, alternative plans were retrospectively created using plans M2 and M3 under institutional review board approval. The prescription ranged from 500 to 700 cGy per fraction for 3 to 4 fractions, using 25- to 35-mm diameter cylinders treating upper 35 to 55 mm. For M2, a patient-specific plan was created for each patient based on Fraction 1 CT and applied to the CT simulation acquired prior to subsequent fractions. For M3, a template plan matching the cylinder/prescription was selected from an institution-established library applied to the CT simulation acquired before each fraction. The rectum and bladder were contoured on the CTs of each fraction for dose comparison between the 3 methods. D50, D2cc, D1cc, D0.1cc, and V100 of the bladder and the rectum were compared using the 2-sided Wilcoxon signed rank test. Using M1 as the gold standard, M2 and M3 were each compared against M1. ResultsA total of 49 fractions (with distinct plans for M1 vs M2) were available for M1 versus M2 comparison, and 74 fractions for M1 versus M3 comparison. For M1 versus M2, there was no statistically significant difference (P75 cGy for only 2 fractions, in which M3 was higher than M1 in D.1cc to the bladder. A total of 49 fractions (with distinct plans for M1 vs M2) were available for M1 versus M2 comparison, and 74 fractions for M1 versus M3 comparison. For M1 versus M2, there was no statistically significant difference (P75 cGy for only 2 fractions, in which M3 was higher than M1 in D.1cc to the bladder. ConclusionM1 and M2 showed no statistically significant differences in rectal or bladder doses, while M1 led to higher rectal dose yet lower bladder dose than M3, though this difference was minor. Plan standardization in HDR-VB may result in considerable time and cost savings with minimal OAR dose differences. M1 and M2 showed no statistically significant differences in rectal or bladder doses, while M1 led to higher rectal dose yet lower bladder dose than M3, though this difference was minor. Plan standardization in HDR-VB may result in considerable time and cost savings with minimal OAR dose differences.