Appropriate Methodology for EBRT and HDR Intracavitary/Interstitial Brachytherapy Dose Composite and Clinical Plan Evaluation for Patients with Cervical Cancer

Abstract Purpose This study assessed the appropriateness of full parameter addition (FPA) methods with respect to three-dimensional deformable dose composite method for evaluating combined external beam radiotherapy (EBRT) and intracavitary brachytherapy (ICBT). Method A total of 22 patients, who received EBRT and HDR ICBT, were retrospectively evaluated. The split-ring and Tandem applicators were used for all the patients. Additional interstitial needles were used for 5 patients to supplement the implant. Deformable image registrations were performed to deform the secondary EBRT and ICBT planning CTs onto the reference CT from the third fraction of ICBT. Dice similarity coefficient was used to evaluate the quality of deformable registration. Doses were transferred to the reference CT, scaled to the equivalent dose in 2 Gy fractions (EQD2) and combined to create the dose composite. Eight different dose accumulation methods were evaluated and compared. D 2cc and D 0.1cc for OARs were investigated. Results The differences in D 2cc for rectum, bladder, sigmoid and bowel between FPA method for whole pelvis EBRT and ICBT using old ABS worksheet ( FPA_E h +I_old ) and deformable composite for EBRT with boosts and ICBT ( Def_E+B+I ) were -2.19+1.37 Gy α/β=3 , -0.64+1.13 Gy α/β=3 , -2.06+2.71 Gy α/β=3 , and -1.59+0.89 Gy α/β=3 , respectively. The differences in D 2cc for rectum, bladder, sigmoid and bowel between the new ABS worksheet ( FPA_E h +B+I_abs ) and Def_E+B+I methods were 1.21+1.22 Gy α/β=3 , 1.93+1.38 Gy α/β=3 , 0.72+1.12 Gy α/β=3 , and 1.19+1.46 Gy α/β=3 , respectively. Differences in DVH parameter values among Def_E+B+I and other FPA methods were not statistically significant (p >0.05). Conclusions Compared to FPA based method, deformable registration based dose composite demonstrated lower OAR D 2cc and D 0.1cc values, however the differences were not statistically significant. Current ABS recommended FPA based sheet can serve as an acceptable plan evaluation tool for clinical purposes.