Vaginal dose de-escalation in cervix brachytherapy
Aldred, Gillian Hallett, Lisa
Aldred, Gillian
Hallett, Lisa
Citations
Altmetric:
Abstract
Purpose or Objective
Vaginal toxicity post cervix brachytherapy is well documented [1]. The EMBRACE 2 protocol specifies dose points which can
be used to measure dose to the vagina. The vaginal TRAK gives the percentage of dwell time being delivered via the
ring/ovoids and can also be used to measure vaginal dose. This study aims to reduce the dose to the vaginal dose points
and TRAK through changes to our plan optimisation process, whilst keeping changes to target and OAR doses minimal, as
reported by S. Mohamed et al [2].
Since Feb 2018, we have had the option of using the Venezia applicator with interstitial needles. This may help to reduce
the vaginal dose in patients with larger tumours, as dose can be delivered laterally via the needles rather than the ovoids.
However, significantly larger CTV volumes are now being referred for brachytherapy rather than external beam boosts.
Prior to Feb 2018, 6.2% of brachytherapy patients had a HR-CTV >30cm3. Since then, 41.8% of patients have had an HR-CTV
> 30cm3. This is likely to have an effect on the outcome of this study as larger volumes may require higher vaginal TRAK
to achieve coverage.
Materials and Methods
Twenty plans using either Rotterdam or Venezia applicators (with or without interstitial needles) were retrospectively
replanned with the aim of reducing the vaginal TRAK whilst maintaining original EQD2 doses to targets and OAR. The vaginal
TRAK and vaginal dose points were compared between the original plans and the new plans.
Results
The vaginal TRAK was reduced by an average of 18%. This resulted in a reduction to the PIBS point doses of between 22%
and 31% and a reduction in the RV point dose of 24%. Target doses remained within 5% of the original plans and OAR doses
were reduced apart from bowel which increased by an average of 1.4%.
Conclusion
Reduction of vaginal TRAK during plan optimisation results in a reduction to vaginal point doses. This has been shown to
reduce vaginal side effects [3], therefore vaginal TRAK should be minimised in the optimisation process whilst meeting
target and OAR dose limits. The current planning protocol limits vaginal TRAK to the EMBRACE recommendations of 30-40%,
however much lower values can be easily achieved in most cases.
Authors
Description
Date
2021
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Aldred G, Hallett L. PP-0142 Vaginal dose de-escalation in cervix brachytherapy. Radiotherapy and Oncology . 2021 May;158:S107.