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Dosimetric Evaluation of An Endorectal Balloon with Radiochromic Film for Two-Dimensional in Vivo Rectal Dosimetry During Cervical Cancer Brachytherapy

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Y Goh

Y Goh1*, E Jeang1 , K Cho1 , S Min1 , U Hwang2 , S Choi3 , N Lee1 , S Song1 , S Lee1 , D Shin1 , Y Kim1 , J Kim1 , D Kim1 , Y Lim1 , (1) National Cancer Center, Goyang-si, Gyeonggi-do, (2) National Medical Center in Korea, Seoul, (3) Korea Institute of Radiological & Medical Sciences, Seoul


SU-I-GPD-T-7 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Two-dimensional (2D) in vivo rectal dosimetry using an endorectal balloon (ERB) with an unfoldable EBT3 film was aimed to verify the dosimetric effectiveness for high-dose-rate (HDR) brachytherapy for cervical cancer and was discussed its clinical applicability.

Methods: The ERB with an unfoldable radiochromic film was used for in vivo rectal dosimetry to measure the 2D dose distribution on the anterior rectal wall of cervical cancer patient. The radiochromic film has a special feature, combined with 7 pieces of EBT3 films, to be unrolled or rolled as the balloon inflates or deflates. This film with 60(L) x 64(W) mm² size is installed on the balloon. The balloon outer diameter reaches up to about 42 mm when 100 ml water is filled. The water phantom including Fletcher and ring CT/MR applicators was used for the patient-specific quality assurance. Ten patient dose distributions for each applicator from the treatment plans were delivered by Ir-192 remote afterloading system to the ERB. The dose interpolation on measured dose distributions was performed to suppress the abnormal distribution caused by gaps between film pieces. The improved dose distributions on ERBs were compared with those of treatment plans.

Results: The absolute dose profiles measured on EBT3 films agreed well with those of plans in the parallel and perpendicular directions. The gamma passing rates were estimated as 96-100% (median=96%) for 20 patients under the criteria of 3% dose difference and 3 mm distance-to-agreement. The dose-volume histograms of the rectal wall could be obtained from the measured dose distributions, which also agreed well with the patient’s plans.

Conclusion: The 2D in vivo rectal dosimetry using the ERB with an unfoldable radiochromic film is effective and may be applicable for HDR brachytherapy for cervical cancer.

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