Evaluating dose distributions of high dose rate 60Co brachytherapy in an asymmetric tumor: A comparison of different designs of vaginal cylindrical applicators.

The aim of this study is to evaluate organ-at-risk (OAR) doses obtained from different designs of intracavitary cylinder applicators during high-dose-rate (HDR) brachytherapy of an asymmetric vaginal tumor. Dose distributions around five cylinder applicators were obtained using the Geant4 toolkit. Three of these applicators are commercially available: single-channel, multi-channel, and shielded. Additionally, two proposed sub-configurations were evaluated: (I) a combination of the multichannel applicator with a central shield and (II) a dynamically modulated cylinder (DMC). The dose distributions of the proposed applicators were compared to those of the single-channel cylinder applicator. The results showed that using a cylindrical applicator with a higher degree of freedom in plan optimization can improve OAR, sparing up to 60% for the rectum and 20% for the bladder. In conclusion, this work suggests using a new design of a cylindrical applicator to enhance the therapeutic ratio of brachytherapy for asymmetric and irregularly shaped vaginal tumors.

A Dosimetric evaluation of a high dose rate cobalt-60 brachytherapy source using shielded, single and multi-channel cylinder applicators for gynecological cancers.

Vaginal brachytherapy is a standard method for preventing the recurrences of malignancies in the treatment of gynecological cancers. Cylindrical applicators are usually employed in high dose rate cobalt-60 source brachytherapy after abdominal hysterectomy or bilateral salpingo-oophorectomy treatment. The aim of this study is to conduct an assessment of dosimetric properties of single channel, multichannel, and shielded cylinder applicators. This study utilizes a pelvis phantom with three different volumes of bladder and rectum to perform dose measurement around the cylindrical applicators. GAFCHROMIC EBT3 model film was used to measure dose distributions in water phantom around the bladder, rectum, applicator, and CTV. In order to properly compare the performance of the shielded applicator with multichannel and single channel applicators, we consider the both cases of a one-sided CTV and two CTVs placed on both sides of the vagina. Dose-volume histograms analysis shows no statistically significant difference in tumoral region for the two types of CTV between cylindrical applicators. The V120%, V100% and D95% values of target volume were 47.36%. 91.46%, and 3.99Gy for multi-channel cylinder applicator, 60.2%, 95.02%, and 3.99Gy for single channel cylinder applicator, respectively. Statistical analysis reports D0.1cc, D1cc, and D2cc for the multichannel applicator demonstrates a significant dose reduction in bladder compared with single channel. The V120%, V100%, and D95% values of target volume were 55.50%. 97.90%, and 3.91Gy for multi-channel cylinder applicator with four active channels (MCC-4), 41.56%, 92.10%. and 4.13Gy for shielded cylinder applicator, respectively. Statistical analysis reports D0.1cc, D1cc and D2cc for the MCC-4 demonstrates a noticeable dose reduction in bladder and rectum compared with Shielded channel. The results indicate that employing multichannel applicator in vaginal high dose rate cobalt-60 source brachytherapy can reduce the received dose to organs at risk without any significant loss of received dose in CTV, which is contributed to its asymmetric or symmetric dose distribution that depend on which channels are activated.