Presentation Evaluation of three-dimensional organ doses using polymer gel dosimeter in radiotherapy for uterine cervical cancer

青天目, 州晶  ,  米内, 俊祐  ,  小原, 哲  ,  佐野, ひろみ  ,  砂岡, 正良  ,  玉川, 学  ,  若月, 優  ,  唐澤, 久美子  ,  赤羽, 恵一  ,  島田, 義也

1. IntroductionRecent progresses on radiotherapy can provide benefits to patients, and survive for a long period. On the other hand, undesired irradiation to non-target healthy tissue adjacent to the target is theoretically unavoidable, secondary cancer risk is of interest to the survivors. In practice, the treatment planning system (TPS) plays an important role for reducing doses in organ at risk. However, it is doubtful whether the TPS can give accurate doses in the low dose region far from the target organ, in which the acute effects rarely occur but secondary cancers may occur. Therefore, in this study, non-target organ doses of pelvic field in 3D using anthropomorphic phantom and polymer gel dosimeter were acquired in radiotherapy for uterine cervical cancer, and compared to the TPS calculation. 2. Materials and methodsTo evaluate 3D dose distribution directly in uterine cervical radiotherapy, the anthropomorphic phantom of a female pelvis was developed. Containers filled with polymer gel in the phantom simulate organs. Additionally, 4 or 5 glass dosimeters were set in each organ for the dose calibration. The standard treatment plan in Japan was created for the phantom as a patient by using the TPS in each external beam radiotherapy (EBRT) or intra-cavitary brachytherapy (ICBT). The 10Gy of EBRT was delivered to the whole pelvis with or without center shielding using a 10MV x-ray beam from CLINAC21EX. In ICBT, It was irradiated with Ir-192 sources using microSelectron-HDR. Gel dosimeters after irradiations were read with MRI, and the reading values were calibrated by the absorbed dose measured with glass dosimeters set in each organ. The measured 3D dose distributions compared with the TPS calculations.3. ResultIn case 30Gy of EBRT and 20Gy of center shielding EBRT were delivered, the dose of uterine corpus, bladder, and rectum, or sigmoid colon and ovary were exposed approximately total 30Gy or 50Gy as the average absorbed dose. In case 24Gy of ICBT at A point were delivered uterine corpus, bladder, and rectum, or sigmoid colon and ovary were exposed approximately total from10Gy to 20Gy or a few Gy as the average absorbed dose 4. ConclusionThis study shows the 3D dose distributions in the uterine cervical cancer radiotherapy by using the female phantom and gel dosimeters. These results could be the basis for the second cancer incidence.

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