Retrospective Dosimetric Comparison of Low-Dose-Rate and Pulsed-Dose-Rate Intracavitary Brachytherapy Using a Tandem and Mini-Ovoids

The purpose of this study was to compare the dose distribution of Iridium-192 (¹⁹²Ir) pulsed-dose-rate (PDR) brachytherapy to that of Cesium-137 (¹³⁷Cs) low-dose-rate (LDR) brachytherapy around mini-ovoids and an intrauterine tandem. Ten patient treatment plans were selected from our clinical database, all of which used mini-ovoids and an intrauterine tandem. A commercial treatment planning system using AAPM TG43 formalism was used to calculate the dose in water for both the ¹³⁷Cs and ¹⁹²Ir sources. For equivalent system loadings, we compared the dose distributions in relevant clinical planes, points A and B, and to the ICRU bladder and rectal reference points. The mean PDR doses to points A and B were 3% ± 1% and 6% ± 1% higher than the LDR doses, respectively. For the rectum point, the PDR dose was 4% ± 3% lower than the LDR dose, mainly because of the ¹⁹²Ir PDR source anisotropy. For the bladder point, the PDR dose was 1% ± 4% higher than the LDR dose. We conclude that the PDR and LDR dose distributions are equivalent for intracavitary brachytherapy with a tandem and mini-ovoids. These findings will aid in the transfer from the current practice of LDR intracavitary brachytherapy to PDR for the treatment of gynecologic cancers.