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KMID : 1164220170290020043
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Journal of Korean Society for Radiotherapeutic Technology
2017 Volume.29 No. 2 p.43 ~ p.51
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Dosimetric effects of couch attenuation and air gaps on prone breast radiation therapy
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Kim Min-Seok
Jeon Soo-Dong
Bae Sun-Myeong
Back Geum-Mun
Song Heung-Kwon
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Abstract
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Purpose: The purpose of this study is to evaluate the dosimetric effects of couch attenuation and air gaps using 3D phantom for prone breast radiation therapy.
Materials and method: A 3D printer(Builder Extreme 1000) and computed tomography (CT) images of a breast cancer patient were used to manufacture the customized breast phantom. Eclipse External Beam Planning 13.6 (Varian Medical Systems Palo Alto, CA, USA) was used to create the treatment plan with a dose of 200 cGy per fraction with 6 MV energy. The Optically Stimulated Luminescence Detector(OSLD) was used to measure the skin dose at four points (Med 1, Med 2, Lat 1, Lat 2) on the 3D phantom and ion-chamber (FC65-G) were used to perform the in-vivo dosimetry at the two points (Anterior, Posterior). The Skin dose and in-vivo dosimetry were measured with reference air gap (3 cm) and increased air gaps (1, 2, 3, 4, 5, 6 cm) from reference distance between the couch and 3D phantom.
Results: As a result, measurement for the skin dose at lateral point showed a similar value within ±4% compared to the plan. While the air gap increased, skin dose at medial 1 was reduced. And it was also reduced over 7 % when the air gap was more than 3 cm compared to radiation therapy plan. At medial 2 it was reduced over 4 % as well. The changes of dose from variety of the air gap showed similar value within ±1 % at posterior. As the air gap was increased, the dose at anterior was also increased and it was increased by 1 % from the air gap distance more than 3 cm.
Conclusion: Dosimetrical measurement using 3D phantom is very useful to evaluate the dosimetric effects of couch attenuation and air gaps for prone breast radiation therapy. And it is possible to reduce the skin dose and increase the accuracy of the radiation dose delivery by appling the optimized air gap.
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KEYWORD
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carbon fiber couch , prone position breast , skin dose , air gap
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