Dosimetric effects of air pockets around high-dose rate brachytherapy vaginal cylinders.
OBJECTIVE
Most physicians use a single-channel vaginal cylinder for postoperative endometrial cancer brachytherapy. Recent published data have identified air pockets between the vaginal cylinders and the vaginal mucosa. The purpose of this research was to evaluate the incidence, size, and dosimetric effects of these air pockets.


METHODS
25 patients receiving postoperative vaginal cuff brachytherapy with a high-dose rate vaginal cylinders were enrolled in this prospective data collection study. Patients were treated with 6 fractions of 200 to 400 cGy per fraction prescribed at 5 mm depth. Computed tomography simulation for brachytherapy treatment planning was performed for each fraction. The quantity, volume, and dosimetric impact of the air pockets surrounding the cylinder were quantified.


RESULTS
In 25 patients, a total of 90 air pockets were present in 150 procedures (60%). Five patients had no air pockets present during any of their treatments. The average number of air pockets per patient was 3.6, with the average total air pocket volume being 0.34 cm(3) (range, 0.01-1.32 cm(3)). The average dose reduction to the vaginal mucosa at the air pocket was 27% (range, 9-58%). Ten patients had no air pockets on their first fraction but air pockets occurred in subsequent fractions.


CONCLUSIONS
Air pockets between high-dose rate vaginal cylinder applicators and the vaginal mucosa are present in the majority of fractions of therapy, and their presence varies from patient to patient and fraction to fraction. The existence of air pockets results in reduced radiation dose to the vaginal mucosa.
Richardson
Susan
S
Department of Radiation Oncology, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, MO 63110, USA. srichardson@radonc.wustl.edu
Palaniswaamy
Geethpriya
G
Grigsby
Perry W
PW
D000388:Air; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods; D016889:Endometrial Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery; D004867:Equipment Design; D005260:Female; D006046:Gold; D006801:Humans; D009092:Mucous Membrane / Q000000981:diagnostic imaging; D011446:Prospective Studies; D019736:Prostheses and Implants; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed; D014621:Vagina / Q000033:anatomy & histology / Q000000981:diagnostic imaging
D006046:Gold