Dose reduction study in vaginal balloon packing filled with contrast for HDR brachytherapy treatment.
OBJECTIVE
Vaginal balloon packing is a means to displace organs at risk during high dose rate brachytherapy of the uterine cervix. We tested the hypothesis that contrast-filled vaginal balloon packing reduces radiation dose to organs at risk, such as the bladder and rectum, in comparison to water- or air-filled balloons.


METHODS
In a phantom study, semispherical vaginal packing balloons were filled with air, saline solution, and contrast agents. A high dose rate iridium-192 source was placed on the anterior surface of the balloon, and the diode detector was placed on the posterior surface. Dose ratios were taken with each material in the balloon. Monte Carlo (MC) simulations, by use of the MC computer program DOSXYZnrc, were performed to study dose reduction vs. balloon size and contrast material, including commercially available iodine- and gadolinium-based contrast agents.


RESULTS
Measured dose ratios on the phantom with the balloon radius of 3.4 cm were 0.922 ± 0.002 for contrast/saline solution and 0.808 ± 0.001 for contrast/air. The corresponding ratios by MC simulations were 0.895 ± 0.010 and 0.781 ± 0.010. The iodine concentration in the contrast was 23.3% by weight. The dose reduction of contrast-filled balloon ranges from 6% to 15% compared with water-filled balloon and 11% to 26% compared with air-filled balloon, with a balloon size range between 1.4 and 3.8 cm, and iodine concentration in contrast of 24.9%. The dose reduction was proportional to the contrast agent concentration. The gadolinium-based contrast agents showed less dose reduction because of much lower concentrations in their solutions.


CONCLUSIONS
The dose to the posterior wall of the bladder and the anterior wall of the rectum can be reduced if the vaginal balloon is filled with contrast agent in comparison to vaginal balloons filled with saline solution or air.
Radiation Oncology, Moffitt Cancer Center, Tampa, FL, USA.
Amarjit S
AS
Saini
Geoffrey G
GG
Zhang
Steven E
SE
Finkelstein
Matthew C
MC
Biagioli
D000388:Air; D001918:Brachytherapy / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D003287:Contrast Media; D004106:Dilatation / Q000295:instrumentation / Q000379:methods; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D007455:Iodine / Q000032:analysis; D007496:Iridium Radioisotopes / Q000627:therapeutic use; D009010:Monte Carlo Method; D009942:Organometallic Compounds; D058958:Organs at Risk / Q000528:radiation effects*; D019047:Phantoms, Imaging; D011832:Radiation Injuries / Q000517:prevention & control*; D011835:Radiation Protection / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects*; D012965:Sodium Chloride; D014283:Triiodobenzoic Acids; D001743:Urinary Bladder / Q000528:radiation effects*; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy; D014621:Vagina; D014867:Water
D003287:Contrast Media; D007496:Iridium Radioisotopes; D009942:Organometallic Compounds; D014283:Triiodobenzoic Acids; C073590:gadolinium ethoxybenzyl DTPA; D014867:Water; D012965:Sodium Chloride; D007455:Iodine; D019786:Gadolinium DTPA; C054871:ioversol