MRI-Based Evaluation of the Vaginal Cuff in Brachytherapy Planning: Are We Missing the Target?

Abstract

Purpose Although recurrences and toxicity occur after vaginal cuff (VC) brachytherapy, little is known about dosimetry due to the inability to clearly visualize the VC on computed tomography (CT). T2-weighted (T2W) magnetic resonance imaging (MRI) is superior to CT in this setting, and we hypothesized that it could provide previously unascertainable dosimetric information. Methods and Materials In a cohort of 32 patients who underwent cylinder-based brachytherapy for endometrial cancer with available MR simulation images, the VC was retrospectively contoured on T2W images, and cases were replanned to treat the upper VC to a dose of 7 Gy/fraction prescribed to 5 mm. Relevant dose-volume parameters for the VC were calculated. Results T2W MRI identified significant underdosing not observed on CT or T1-weighted imaging. Over two-thirds (69%) of patients had at least 1 cm3 of VC that received less than 75% of the prescription dose and half (50%) of patients had a least 1 cm3 of VC that received less than 50% of the prescription dose. The mean minimum point dose to the VC was 2.4 Gy, or 34% of the intended prescription dose (range: 0.53–6.4 Gy). Conclusions We identified previously unreported VC underdosing in over two-thirds of our patients, with most of these patients having volumes of undistended VC that received less than half of the prescription dose. The maximum dimension was along the craniocaudal axis in some patients or left-right/anterior-posterior axis in others, suggesting that suture material may be restricting access to the vaginal apex and that alternative applicators may be needed when the diameter of the apex is larger than the introitus. Additional follow-up will be needed to determine whether underdosing is associated with isolated VC failure or whether low failure rates across the cohort suggest that some patients are being exposed to excessive dose and unnecessary risk of toxicity.

Vaginal Cuff Brachytherapy in Endometrial Cancer

“…[73,74] Chapman et al compared magnetic resonance (MRI) and CT images of the patients, and they found that with MRI, a volume of 1 cm3 and more received less than 75% of the defined dose at least in 69% of patients. [75] Low-dose areas often located on the top of the vagina, where the cylinder could not be located exactly because of suture materials.…”

Vaginal cuff brachytherapy in endometrial cancer – a technically easy treatment?

“…Average absolute percentage dose differences for the bladder, rectum and prescription points on CT and MRI were 2.2%, 2.3% and 2.2%, respectively, and the mean central source deviation was 0.6 mm, which was associated with longer acquisition times in MRI 101. Chapman et al102 carried out sequential MRI and CT scans. They observed using MRI that 69% of the patients had at least 1 cm 3 of VC receiving <75% of the prescription dose.…”

Quantitative Analysis of Vaginal Wall Thickness in Vaginal Cuff Brachytherapy - Multichannel Balloon vs. Single-Channel Brachytherapy

“…However, little is known about the volume of tissue superior to the vaginal cuff and the thickness of proximal vaginal canal. Therefore, the true dosimetry to the target volume in vaginal cuff is not clear [6].…”