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Abstract
BACKGROUND:
The aim of the present study was to verify the dosimetric accuracy of two-dimensional (2D) in vivo rectal dosimetry using an endorectal balloon (ERB) with unfoldable EBT3 films for high-dose-rate (HDR) brachytherapy for cervical cancer. The clinical applicability of the technique was discussed.

MATERIAL AND METHODS:
ERB inflation makes the EBT3 films unrolled, whereas its deflation makes them rolled. Patient-specific quality assurance (pQA) tests were performed in 20 patient plans using an Ir-192 remote afterloading system and a water-filled cervical phantom with the ERB. The dose distributions measured in ERBs were compared with those of the treatment plans.

RESULTS:
The absolute dose profiles measured by the ERBs were in good agreement with those of treatment plans. The global gamma passing rates were 96-100% and 91-100% over 20 pQAs under the criteria of 3%/3 mm and 3%/2 mm, respectively, with a 30% low-dose threshold. Dose-volume histograms of the rectal wall were obtained from the measured dose distributions and showed small volume differences less than 2% on average from the patients' plans over the entire dose interval. The positioning error of the applicator set was detectable with high sensitivity of 12% dose area variation per mm. Additionally, the clinical applicability of the ERB was evaluated in volunteers, and none of them felt any pain when the ERB was inserted or removed.

CONCLUSIONS:
The 2D in vivo rectal dosimetry using the ERB with EBT3 films was effective and might be clinically applicable for HDR brachytherapy for cervical and prostate cancers to monitor treatment accuracy and consistency as well as to predict rectal toxicity.

Author information

Jeang EH1, Goh Y1, Cho KH1, Min S1, Choi SH2, Jeong H3, Jo K4, Lee N1, Song S1, Lee SB1, Shin D1, Kim YJ1, Kim JY1, Kim DY1, Hwang UJ5, Lim YK1.
1
a Proton Therapy Center , National Cancer Center , Goyang , Korea.
2
b Department of Radiation Oncology , Korea Cancer Center Hospital , Seoul , Korea.
3
c Department of Radiation Oncology , Gyeongsang National University Hospital , Jinju , Korea.
4
d Department of Radiation Oncology , Samsung Medical Center , Seoul , Korea.
5
e Department of Radiation Oncology , National Medical Center , Seoul , Korea.