Body mass index, dose to organs at risk during vaginal brachytherapy, and the role of three-dimensional CT-based treatment planning.
OBJECTIVE
To assess the effect of body mass index (BMI) on dose to organs at risk (OARs) during high-dose-rate vaginal brachytherapy and evaluate the role of three-dimensional dose evaluation during treatment planning.


METHODS
Three-dimensional dosimetric data for rectum, bladder, sigmoid colon, and small bowel for 125 high-dose-rate vaginal brachytherapy fractions were analyzed. Dose-volume histograms were generated for D0.1 cc and D2 cc of each OAR. Contributing factors including the use of urinary catheter and cylinder size were also recorded. As different dose fractionations were used, the OAR doses were tabulated as a percent dose prescribed to 0.5cm. All patients were treated to 4cm of the vaginal length.


RESULTS
Median BMI in this cohort was 31.7kg/m(2). The BMI values had a weak inverse correlation with D0.1 cc to sigmoid colon (rs=-0.18, p=0.047) and D0.1 cc to bladder (rs=-0.19, p=0.038). There was a strong inverse correlation of D2 cc and increasing BMI (rs=-0.64, p=0.003). The median D2 cc was 25.1% for BMI higher than 31 and 61.9% for BMI of 31 or lower. For D0.1 cc, there was also a strong inverse correlation with increasing BMI (rs=-0.57, p<0.001). Median D1 cc was 33.5% for BMI >31 and 84.4% for BMI ≤ 31. On multivariate analysis higher BMI remained a significant predictor of lower small bowel D2 cc (p<0.001) and D0.1 cc (p<0.001).


CONCLUSIONS
Women with a lower BMI receive higher doses to the bladder and small bowel compared with those with a higher BMI. Three-dimensional dose evaluation should be considered in patients with low BMI, particularly when combined with external beam radiation.
Department of Radiation Oncology, Duke University, Durham, NC. Electronic address: john.m.boyle@duke.edu.
John M
JM
Boyle
Department of Radiation Oncology, Duke University, Durham, NC.
Oana
O
Craciunescu
Department of Radiation Oncology, Duke University, Durham, NC.
Beverley
B
Steffey
Department of Radiation Oncology, Duke University, Durham, NC.
Jing
J
Cai
Department of Radiation Oncology, Duke University, Durham, NC; Duke Cancer Institute, Durham, NC.
Junzo
J
Chino
D015992:Body Mass Index; D001918:Brachytherapy / Q000379:methods*; D012809:Colon, Sigmoid; D016889:Endometrial Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007421:Intestine, Small; D015999:Multivariate Analysis; D058958:Organs at Risk; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D018714:Radiotherapy, Adjuvant; D012007:Rectum; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder; D014621:Vagina
Body mass index; Dosimetry; High-dose rate; Three-dimensional planning; Vaginal brachytherapy