Utilization of an Applicator System Including a Tandem with Multi-Directional Interstitial Needle-Guide Ring and Perineal Template for High Dose Rate Brachytherapy Boost Treatments of Large-Volume Cervical Adenocarcinoma

Abstract

To study the ability of a gynecological applicator system of a tandem with a pair of lunar ovoids with multi-directional needle guides and a perineal template to appropriately provide large-volume boost High Dose Rate Brachytherapy (HDR) treatment to cervical adenocarcinoma. Three HDR boost plans of patients with large target volumes (121 – 224 cm3) were used for dosimetric performance evaluation. All patients used an applicator with a tandem and a pair of needle-guide lunar ovoids, and two patients used the perineal template additionally for some fractions. The investigated applicator is different from other integrated needle-guide applicators because the ovoids have needle guides that curve the interstitial needles out 30-degrees relative to the direction of the tandem, thus allowing dwell locations farther from midline. The number of needles loaded depended on the extension of the target volume and ranged from 10 to 21 needles. Based on patient anatomy, the needles were placed and pushed as far as it was necessary under ultrasound guidance. On average, the straight channels were inserted 6.5 cm and flared channels 4.6 cm from the ring. Plans were optimized to the high-risk target volume (HRCTV) using inverse optimization to an expanded planning volume HRCTV-OPTI, which included the HRCTV and the area around the lunar ovoids with standard constraints based on GEC-ESTRO recommendations. For each patient, coverage of the HRCTV was achieved with 90% of the volume receiving at least 100% of the prescription dose (Mean 106.3%). Target conformity was 0.69 on average. The total reference dose volume for the three patients in this study ranged from 156 to 289 cm3. The typical total reference dose volume when treating with a standard loading to point A with no needles was 83 to 93 cm3 depending on the applicator size. Average dose as percentage of the prescription dose to the 2 cm3 volume of the Bladder, Rectum, Sigmoid, and Bowel were 78.9%, 68.2%, 70.6%, and 50.9% respectively. Dose to Point A on average was over 204%. Patient tolerance of repeated interstitial needle placement was reported to be good, with low to moderate bleeding and pain post-procedure. All patients showed response to treatment, with one showing total pelvic control on follow-up. Planning time per fraction increased to a mean of 1.7 hours, from an average of 1 hour for a standard tandem and ring treatment, with total average procedure time of 4 hours (2 hr. 19 min. - 5 hr. 54 min.). Multi-directional needle-guide applicators for cervical HDR are useful in creating high quality plans that meet target and organ constraints for volumes that are much larger than the standard, without substantial sacrifice of patient comfort or time in spite of the added treatment planning complexity.