Comparative study of brachytherapy using ring and ovoid applicators in treatment of advanced cervical cancer

BackgroundImage-guided brachytherapy became essential to cervical cancer treatment following chemo-radiotherapy. A variety of applicators including Tandem-Ring (TR) and Tandem-Ovoid (TO) applicators are used to apply brachytherapy.ObjectiveThis study aims to dosimetrically compare TR versus TO applicators by using two different optimization techniques.MethodsBoth applicator sets were applied to the 24 patients. The prescribed dose was 7 Gy/fraction, and the treatment plans were normalized to HR-CTV. Two different optimization techniques are applied, along the four treatment fractions. The first optimization technique was a theoretical assumption that aimed to deliver 7 Gy to 90 % of the volume of the HR-CTV. While the second was the clinical situation which aimed to preserve the organs at risk (OARs) according to the ICRU 89 dose-volume constraints, considering that, 90% of HR-CTV is covered by not less than 90% of the prescribed dose. DVHs were generated, and dosimetric parameters including point A, and D2cc of rectum, bladder, and sigmoid, as well as the dose at different volumes of HR-CTV and IR-CTV, were recorded and compared.ResultsThe results demonstrate that using Ovoid-Tandem applicators achieved significantly higher dose at point A, significantly higher coverage to both HR-CTV and IR-CTV, in addition to significantly better protection to the mean D2cc of the rectum in both optimization techniques. On the other hand, using Ring-Tandem applicators give significantly more protection to the mean D2cc of the bladder, but HR-CTV and IR-CTV have significantly lower coverage.ConclusionOvoid-Tandem and Ring-Tandem applicators are the most common interchangeable intracavitary gynecological applicators. In this study, the results demonstrated that Ovoid-Tandem applicators have the advantages of significantly higher coverage for HR-CTV, and IR-CTV, in addition to more protection for D2cc of the rectum. On the contrary, Ring-Tandem applicators can provide higher protection for D2cc of the bladder, and more comfort to the patients.