Gemma Busuttil
Crown Princess Mary Cancer Centre, Westmead
Radiation Therapist

Emma-Rae Parker
Radiation Therapist
Crown Princess Mary Cancer Centre, Westmead

Background and Purpose:

Moderate vaginal morbidity and associated patient distress is common following cervix high dose rate (HDR) brachytherapy however limited data is available regarding appropriate vaginal dose aims. Recent results from the EMBRACE study has established a vaginal stenosis dose-response curve using the recto-vaginal ICRU point resulting in a recommended planning aim of ≤65Gy, while ICRU 89 recommends observation of upper vaginal point doses in advanced planning.

This study aims to retrospectively observe doses to vaginal points of cervix HDR brachytherapy patients treated at the Crown Princess Mary Cancer Centre (CPMCC) and establish if assessment of vaginal points at the time of planning could potentially reduce vaginal dose.

Method:

53 cervix brachytherapy patients were treated between January 2014 and April 2018 at CPMCC. A planning aim of 80-90Gy to 90% of the high risk clinical target volume (HR-CTV) was initially used until dose escalation to 90-95Gy was introduced in Jan 2016. At the time of planning, rectal D2cc dose was limited to <75Gy with an aim to achieve <65Gy. Vaginal isodoses were visually inspected on the planning CT/MRI scans.

Doses to the recto-vaginal ICRU point and upper vaginal points were retrospectively reported from BrachyVision and the biological weighted equivalent dose in 2Gy fractions (EQD2) calculated. These doses were then compared against planning aims extracted from the EMBRACE results.

Results:

All brachytherapy plans recorded an EQD2 dose to the recto-vaginal ICRU point of <75Gy, of which 77% were <65Gy. This remained stable despite escalation of the planning aim dose to the HR-CTV in 2016 and correlated well with the rectal D2cc.

The left and right upper vaginal points achieved 75% and 81% <95Gy respectively, of which 62% and 72% received <85Gy. However there was significant variation in those that did not meet the aims and greater outliers were present when the HR-CTV received over 90Gy.

Conclusion:

Recto-vaginal ICRU point dose is adequately restricted by limiting the rectal D2cc in the majority of patients. Observation of the upper vaginal points at the time of planning should be considered due the potential for significantly high dose in a quarter of patients, especially when prescribed over 90Gy to the HR-CTV.


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