The dosimetric impact of heterogeneity corrections in high-dose-rate ¹⁹²Ir brachytherapy for cervical cancer: Investigation of both conventional Point-A and volume-optimized plans.

PURPOSE

To evaluate the dosimetric impact of heterogeneity corrections on both conventional and volume-optimized high-dose-rate (HDR) ¹⁹²Ir brachytherapy tandem-and-ovoid treatment plans.

METHODS AND MATERIALS

Both conventional and volume-optimized treatment plans were retrospectively created using eight unique CT data sets. In the volume-optimized plans, the clinical target volume (CTV) and organs-at-risk (rectum, bladder, and sigmoid) were contoured on the CT data sets by a single physician. For each plan, dose calculations representing homogeneous water medium were performed using the Task Group (TG-43) formalism and dose calculations with heterogeneity corrections were performed using a commercially available treatment planning system.

RESULTS

For the conventional plans, the change in dose between TG-43 and heterogeneity-corrected calculations was assessed for the following points: Point-A (left and right) and International Commission on Radiation Units and Measurements (ICRU) 38 defined rectum and bladder points. It was found that the dose to the ICRU bladder decreased the most (-2.2±0.9%), whereas ICRU rectum (-1.7±0.8%), Point-A right (-1.1±0.4%), and Point-A left (-1.0±0.3%) also showed decreases with heterogeneity-corrected calculations. For the volume-optimized plans, the change in dose between TG-43 and heterogeneity-corrected calculations was assessed for the following dose-volume histogram parameters: D(90) of the CTV and D(2cc) of the rectum, bladder, and sigmoid. It was found that D(90) of the CTV decreased by -1.9±0.7% and D(2cc) decreased by -2.6±1.4%, -1.0±0.4%, and -2.0±0.6% for the rectum, bladder and sigmoid, respectively, with heterogeneity-corrected calculations.

CONCLUSIONS

Heterogeneity corrections on high-dose rate plans were found to have only a small dosimetric impact over TG-43-based dose calculations for both conventional Point-A and volume-optimized plans.