The dosimetric comparison between tandem-ovoid and tandemring applicator in cervical cancer brachytherapy

Abstract

Aim: The study aims to evaluate the differences in dosimetry between tandem-ovoid (TO) and tandem-ring (TR) gynecologic brachytherapy applicators using different optimizing techniques in image-based brachytherapy. Background: Conventionally, TO applicators are in use to deliver doses to tumor in intracavitary brachytherapy. Nowadays, different types of applicators are available for cervical cancer brachytherapy treatment such as TR, tandem-cylinder, hybrid intracavitary, and interstitial applicators. Materials and Methods: In the present study, we used a TR and Fletcher-style TO applicator in the same patient, in two different sessions of brachytherapy. Four plans were generated for each patient, utilizing two different optimization techniques for each applicator used. A dose of 9 Gy (Gray) was prescribed and plans were normalized to left point A, and in other techniques, the optimization is done to achieve the recommended organ at risk (OAR) dose–volume constraints. Dose–volume and dose point parameters were compared. Results: The results indicate that the (OAR doses assessed by dose–volume histogram criteria were lower than the International Commission on Radiation Units and Measurements (ICRU) point doses for bladder and rectum with both TO and TR applicators for point A normalized plans. Both bladder and sigmoid received higher doses in TO than in TR but were statistically not significant (NS), but the rectum doses are higher in TR than in TO and it was statistically significant. The isodose volumes are higher in point A normalized plans than in OAR-based optimized plans in both applicators. The ICRU point doses are lower in OAR optimized plans than in point A normalized plans in both applicators. Conclusions: TO and TR applicators are commonly used gynecological intracavitary applicators. In this present study we did not find any significant difference between doses delivered to ICRU Point and Isodose volumes, after using both applicators .Critical OAR doses were also comparable. The only advantage of the ring applicator is, it provides an additional degree of freedom to load the vaginal sources over the ovoids and easy application in cases of narrow fornices with greater reproducibility.