High-dose-rate interstitial brachytherapy for gynecologic malignancies—dosimetric changes during treatment period

Abstract

To overcome cranio-caudal needle displacement in pelvic high-dose-rate interstitial brachytherapy (HDRIB), we have been utilizing a fullystretched elastic tape to thrust the template into the perineum. The purpose of the current study was to evaluate dosimetric changes during the treatment period using this thrusting method, and to explore reproducible planning methods based on the results of the dosimetric changes. Twenty-nine patients with gynecologic malignancies were treated with HDRIB at the Cancer Institute Hospital. Pre-treatment and post-treatment computed tomography (CT) scans were acquired and a virtual plan for post-treatment CT was produced by applying the dwell positions/times of the original plan. For the post-treatment plan, D90 for the clinical target volume (CTV) and D2cc for the rectum and bladder were assessed and compared with that for the original plan. Cranio-caudal needle displacement relative to CTV during treatment period was only 0.7 ± 1.9 mm. The mean D90 values for the CTV in the pre- and post-treatment plans were stable (6.8 Gy vs. 6.8 Gy) and the post-treatment/pre-treatment D90 ratio was 1.00 ± 0.08. The post-/pre-treatment D2cc ratio was 1.14 ± 0.22 and the mean D2cc for the rectum increased for the post-treatment plan (5.4 Gy vs. 6.1 Gy), especially when parametrial infiltration was present. The mean D2cc for the bladder was stable (6.3 Gy vs. 6.6 Gy) and the ratio was 1.06 ± 0.20. Our thrusting method achieved a stable D90 for the CTV, in contrast to previous prostate HDRIB reports displaying reductions of 35–40% for D90 during the treatment period.

Proton Arc Therapy vs Interstitial HDR Brachytherapy in Gynecologic Cancer with Parametrial/pelvic Side Wall Extension

“…Dosimetric effects of interfractional displacement of source or needle positions is often ignored in iHDR treatment. Tambas et al [24] reported that 68% of needles shifted 2 6 2.3 mm, and other researchers have reported shifts up to 5 mm [25][26][27]. Such shifts alter dose distribution and are comparable to the typical robustness range of a proton plan of 3 mm/3.5%.…”

Inter-Fraction and Intra-Fraction Variation in the Absorbed-Dose Delivery during Interstitial High Dose Rate Brachytherapy—A Study Using MicroMOSFET <i>In-Vivo</i> Dosimeter

“…Onoe et al [16] found the solution to overcome the cranio-caudal displacement of needles with the help of fully stretched elastic tape. They pasted the tape with the template assembly on the patient.…”

An <i>In-Vivo</i> Study during Combined Intracavitary and Interstitial Brachytherapy of Gynaecological Malignancies Using microMOSFET

“…Consequently, the variation in dose measurements owing to the healing of tissue oedema is substantial during first and subsequent fractions. Onoe et al [6] reported that oedema in perineal area pushes the applicators towards the caudal direction. This results in moving the measuring point close to the ring applicator in most of the incidences.…”

“…During multisession brachytherapy, there is a likelihood of changes in the position and orientation of the catheters [6] [7]. Reimaging and re-planning may reduce these inter-fractional variations to certain extent, but intra-fractional uncertainty still remains.…”