The use and advantages of a multichannel vaginal cylinder in high-dose-rate brachytherapy

Abstract

Purpose: This paper describes California Endocurietherapy’s (CET) high-dose-rate (HDR) multichannel cylinder, the rationale for its design, procedure for its insertion, and the dosimetry involved in its use. A study was done that compared the doses achieved using the CET multichannel cylinder to the same cylinder if it only had a central channel. Methods and Materials: The CET multichannel vaginal cylinder was inexpensively constructed, using parts from various suppliers. After insertion in the patient, the cylinder is affixed to a base plate to prevent displacement. Two sets of orthogonal films (without and with rectal barium) are taken in preparation for digitization of the catheters, bladder, rectal, and pelvic sidewall points. Using HDR brachytherapy planning software, the dose distribution is adjusted to achieve the prescribed dose (5 Gy HDR) 5 mm lateral to the cylinder surface, 5 mm lateral at the proximal parametrial tissue, and 4 mm superior to the vaginal apex. Doses to the bladder and rectum are limited to approximately 85% and 75%, respectively, of the prescribed dose. The plan is optimized on geometric parameters. For dose comparison to treatment using a central channel cylinder, the lateral channels are de-activated, leaving only the central channel activated. Dose points are placed 5 mm laterally and superiorly from the cylinder surface, and the plan is optimized to deliver a uniform dose to the defined dose points. The doses and treatment volumes are statistically compared. Results: The CET multichannel cylinder allows much better dose control than the central channel cylinder. The multichannel cylinder achieves lower bladder and rectal doses by 14% and 15%, respectively, when compared to the central channel cylinder. By increasing the dwell times of certain dwell positions, the prescription dose is achieved in the vaginal apex and proximal parametrial tissues and along the length of the cylinder. Conclusion: The multichannel cylinder enables more flexibility in isodose shaping and dose control to various points and structures when compared to the conventional central channel cylinder.