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Original Article

Korean Journal of Medical Physics 2008; 19(4): 209-218

Published online December 25, 2008

Copyright © Korean Society of Medical Physics.

Geometric Calibration of Cone-beam CT System for Image Guided Proton Therapy

영상유도 양성자치료를 위한 콘빔 CT 재구성 알고리즘: 기하학적 보정방법에 관한 연구

Jin Sung Kim, Min Kook Cho, Young-bin Cho, Han Bean Youn, Ho Kyung Kim, Myounggeun Yoon, Dongho Shin, Sebyeung Lee, Re-Na Lee, Sung Yong Park, Kwan Ho Cho

김진성*ㆍ조민국ㆍ조영빈ㆍ윤한빈ㆍ김호경ㆍ윤명근*ㆍ신동호*ㆍ이세병*ㆍ이레나§ㆍ박성용*ㆍ조관호*

*Proton Therapy Center, National Cancer Center, Goyang, School of Mechanical Engineering, Pusan National University, Busan, Princess Margaret Hospital, Toronto, Canada, Department of Radiation Oncology, Mokdong Hospital, §Ewha Womans University School of Medicine, Korea

*국립암센터 양성자치료센터, 부산대학교 기계공학부, Princess Margaret Hospital, Toronto, Canada, §이화여자대학교 의과대학 목동병원 방사선종양학과

Abstract

According to improved radiation therapy technology such as IMRT and proton therapy, the accuracy of patient alignment system is more emphasized and IGRT is dominated research field in radiation oncology. We proposed to study the feasibility of cone-beam CT system using simple x-ray imaging systems for image guided proton therapy at National Cancer Center. 180 projection views (2,304×3,200, 14 bit with 127 Ռm pixel pitch) for the geometrical calibration phantom and humanoid phantoms (skull, abdomen) were acquired with 2° step angle using x-ray imaging system of proton therapy gantry room (360° for 1 rotation). The geometrical calibration was performed for misalignments between the x-ray source and the flat-panel detector, such as distances and slanted angle using available algorithm. With the geometrically calibrated projection view, Feldkamp cone-beam algorithm using Ram-Lak filter was implemented for CBCT reconstruction images for skull and abdomen phantom. The distance from x-ray source to the gantry isocenter, the distance from the flat panel to the isocenter were calculated as 1,517.5 mm, 591.12 mm and the rotated angle of flat panel detector around x-ray beam axis was considered as 0.25°. It was observed that the blurring artifacts, originated from the rotation of the detector, in the reconstructed toomographs were significantly reduced after the geometrical calibration. The demonstrated CBCT images for the skull and abdomen phantoms are very promising. We performed the geometrical calibration of the large gantry rotation system with simple x-ray imaging devices for CBCT reconstruction. The CBCT system for proton therapy will be used as a main patient alignment system for image guided proton therapy.

KeywordsProton therapy, Cone-beam CT, Geometric calibration, Image guided radiotherapy

Korean Society of Medical Physics

Vol.35 No.2
June 2024

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

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