A Novel Design For Rectal Dose Reduction And Applicator Immobilizations For Hdr Treatment Of Cervical Carcinoma

Image guided high-dose-rate (HDR) brachytherapy has been extensively used as a boost treatment for cervical cancer. Its efficacy, however, is severely limited by the clumsy rectal sparing devices available commercially and the potential applicator movement. To tackle these two critical issues for Tandem & Ring (T&R) HDR treatment, we developed a novel device using a balloon and a bracket system, serving for both rectal dose reduction and applicator immobilization purposes. The balloon catheter was constructed by gluing a short inflatable tube to a long regular open-end catheter. While the open end of the catheter connects to a syringe for contrast agent injection, the other end (inflatable tube) is affixed to the inferior-posterior side of the ring applicator. Once the T&R applicator sets were inserted in place, 10 cm3 of IV contrast was injected to the inflatable tube of the balloon catheter in order to push the posterior vaginal wall away from the ring applicator. The bracket system consists of a special designed bracket, which can hold and fix itself to the T&R applicator set, a diaper-like Velcro fastener package used for connecting the patient pelvis structure to the bracket, and a buckle that holds the fasteners to stabilize the whole system. The treatment data for 21 cervical cancer patients treated with 27.5 Gy in 5 fractions were retrospectively analyzed. For each patient, CT and MRI images, acquired about 30 min apart, were registered to evaluate the effectiveness of the immobilization system. The translational and rotational displacements of the applicator sets between the two images were calculated. Patients were also surveyed for the comfort level during the treatments. Compared to the commercial solution of rectal blade, the rectal point dose when using the balloon was decreased by 34±4.2%, corresponding to an extra sparing distance of 7.9±1.1 mm. The maximum sparing distance variation per patient is 1.4±0.6 mm, indicating the high interfractional reproducibility. Half of the patients had a translational and rotational displacements of <2 mm and <1 degree, respectively, in all directions. The mean translational and rotational displacements were <3 mm and <1.5 degree, respectively, in all directions. All patients indicated minor or no difference in comfort level with or without the balloon. The rectum balloon provides significant dose reduction compared to commercial solution while minimizing patient discomfort. The immobilization system permits almost no movement of applicator during the treatment. This work can be promoted as a standardized solution for HDR treatment of cervix cancer.