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

Publication date: Available online 28 January 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Christina Hunter Chapman, Joann I. Prisciandaro, Katherine E. Maturen, Yue Cao, James M. Balter, Karen McLean, Shruti Jolly
Purpose/ObjectivesWhile recurrences and toxicity occur after vaginal cuff (VC) brachytherapy, little is known about dosimetry due to the inability to clearly visualize the VC on CT. T2-weighted (T2W) MRI is superior to CT in this setting, and we hypothesized that it could provide previously unascertainable dosimetric information.Methods and MaterialsIn 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 re-planned to treat the upper VC to a dose of 7Gy/fraction prescribed to 5mm. Relevant dose-volume parameters for the VC were calculated.ResultsT2W MRI identified significant underdosing not observed on CT or T1-weighted imaging. Over two thirds (69%) of patients had at least 1cc of VC that received less than 75% of the prescription dose and half (50%) of patients had a least 1cc 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 Gy - 6.4 Gy).ConclusionsWe 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 cranio-caudal 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.

Teaser

Using T2-weighted MRI, we retrospectively identified the novel finding of vaginal cuff underdosing in patients undergoing cylinder-based brachytherapy. It is unclear whether this is a new phenomenon--possibly related to modern surgical technique--that has the potential to increase failure rates, or whether this is an old phenomenon, in which case existing recommendations may lead clinicians to over-treat some patients to compensate for anatomic variation in others.


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