Abstract
To compare the dosimetric effects of American Association of Physicists in Medicine (AAPM) TG43 dose formalism and AcurosBV (grid-based Boltzmann solver, GBBS) formalism on high-dose-rate (HDR) brachytherapy planning for cervical cancer patients irradiated using three different applicators.
A TG43 plan and a AcurosBV plan were generated for each of the 30 patients. Twenty patients who had undergone whole pelvic radiotherapy followed by cervical HDR brachytherapy and the remaining 10 patients who underwent total hysterectomy only gave HDR brachytherapy also were enrolled in this study. The patients were divided into three groups according to the types of applicators used: tandem and ovoid (T & O), tandem and ring (T & R), and cylinder. To compare the dosimetric parameters, the cumulative dose-volume histograms (DVHs) were measured. We also compared the doses at 90% of the volume (D90%), the volume receiving 100% and 150% of the prescribed dose (V100% and V150%) for the clinical target volume (CTV-HR), and the doses of point A, the dose receiving 0.1 and 2 cc of the volume (D0.1cc and D2cc) for the organs-at-risk (OARs).
Compared with the AcurosBV plans, TG43 plans predicted higher D90%, V100%, and V150% of CTV-HR, dose of point A, and D0.1cc and D2cc of OARs in three types of applicators. Except D2cc of sigmoid in T & R and cylinder applicators, the D90%, V100%, and V150% of CTV-HR; the dose of point A and the D0.1cc and D2cc of bladder, rectum, and small bowel exhibited significant discrepancies (all p < 0.05). The effects of the three types of applicators on the dose distribution were quite different due to the differences in the materials: The dose difference of CTV-HR and OARs was greatest (around 10%) for T & O applicators but only 1–5% for T & R and cylinder applicators.
AcurosBV was more accurate in calculating the doses in the air cavity and high-density substance than TG43. In the clinical setting, AcurosBV exhibited different dosimetric distributions in the cervix plans for HDR brachytherapy, especially in treatment planning when using T & O applicators. The AcurosBV algorithm should be considered when using T & O applicators or other materials with a much higher or lower density (metal or air) than soft tissue. However, If the density is close to that of soft tissue, considering AcurosBV algorithm requires more calculation time, TG43 could still be selected when using applicators in clinical.
