Vaginal Dose Surface Maps and Morbidity in Cervical Cancer Brachytherapy

Abstract

To develop a methodology for generating vagina dose-surface maps (DSMs) in cervix cancer patients. To investigate the association of dose level and spatial distribution with vaginal stenosis (St) and mucositis (Muc). A mono-institutional series of 31 patients, enrolled in the EMBRACE I study, with no vaginal St/Muc (CTCAE v3) at baseline were selected for this analysis. Patients were divided in 3 morbidity groups: 16 had St/Muc G0/1, 8 had St G≥2 (3 also had Muc G≥2), 10 had Muc G≥2 (3 also had St G≥2) within 24 months after treatment. 16 patients had vaginal involvement at diagnosis and 10 at BT. Patients received EBRT and 2 insertions and 4 fractions of HDR BT using tandem and ovoids. DSMs were generated from delineated contours of the vagina surface (VS). VS contours were unfolded by cutting them anteriorly through the urethra and inferiorly through the posterior–inferior border of the symphysis (PIBS). DSMs of EBRT and each BT fraction, converted to Gy EQD2 (α/β = 3), were added based on a system of homologous points, to generate cumulative DSMs. Dose D20cm2 (Gy), surface S60Gy (%), including their spatial location on the VS, rectovaginal (ICRU-RV) point dose, vaginal lateral 5 mm point dose and vagina length (VL measured from the vagina top to the PIBS) were compared between morbidity groups. Average/difference VS DSMs and one-way ANOVA statistical testing were used to compare between groups. A total of 96 DSMs (31 EBRT and 62 BT) were generated. Table shows mean/difference values for each parameter, according to morbidity groups. Patients in the St G≥2 and Muc G≥2 groups had significantly higher D20cm2 and ICRU-RV point doses compared to St/Muc G0/1 group. Moreover, average/difference DSMs showed that the most irradiated 20 cm2 in the St G≥2 group (mean dose 103 Gy EQD23) was spatially distributed over entire upper 1-2 cm VS circumference. St G≥2 vs St/Muc G0/1 patients had also larger S60Gy (by 27%) and shorter VL (by 9 mm). Muc G≥2 vs St/Muc G0/1 patients had significantly higher vaginal lateral 5mm point doses (by 14 Gy EQD23), while average/difference DSMs showed significant dose differences mainly in the latero-posterior area of the VS. Vaginal dose reporting is currently based on dose points. A novel method was developed to generate vaginal DSMs that incorporate 3D spatial information and new spatial dose descriptors for a more comprehensive view on vaginal doses and correlation with morbidity. St G≥2 patients had significantly higher doses over the whole VS circumference. Muc G≥2 patients showed higher D20cm2, ICRU-RV point and vagina lateral 5mm point doses. Generally, ventral vagina received lower dose than the dorsal and lateral vagina, in the majority of patients.Tabled 1Abstract 3029; TableSt/Muc G0/1 MeanSt G≥2 MeanMuc G≥2 MeanSt G≥2 - St/Muc G0/1Muc G≥2 - St/Muc G0/1Diff.pDiff.pD20cm2 (Gy)7910396240.0000*170.0031*S60Gy (%)376451270.0018*140.0176*ICRU-RV Point (Gy)637678130.0041*150.0015*Vag LAT-5mm (Gy)85909850.2465140.0085*VL (mm)595053-90.0501-60.1427 Open table in a new tab