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Original Article

Korean Journal of Medical Physics 2013; 24(4): 271-277

Published online December 30, 2013

Copyright © Korean Society of Medical Physics.

Convolution-Superposition Based IMRT Plan Study for the PTV Containing the Air Region: A Prostate Cancer Case

Convolution-Superposition 알고리즘을 이용한 치료계획시스템에서 공기가 포함된 표적체적에 대한 IMRT 플랜: 전립선 케이스

Sei-Kwon Kang, Jai-Woong Yoon, Soah Park, Taejin Hwang, Kwang-Ho Cheong, Taejin Han, Haeyoung Kim, Me-Yeon Lee, Kyoung Ju Kim, Hoonsik Bae

강세권ㆍ윤제웅ㆍ박소아ㆍ황태진ㆍ정광호ㆍ한태진ㆍ김해영ㆍ이미연ㆍ김경주ㆍ배훈식

Department of Radiation Oncology, Hallym University College of Medicine, Seoul, Korea

한림대학교 의과대학 방사선종양학교실

Received: December 6, 2013; Accepted: December 13, 2013

Abstract

In prostate IMRT planning, the planning target volume (PTV), extended from a clinical target volume (CTV), often contains an overlap air volume from the rectum, which poses a problem inoptimization and prescription. This study was aimed to establish a planning method for such a case. There can be three options in which volume should be considered the target during optimization process; PTV including the air volume of air density (‘airOpt’), PTV including the air volume of density value one, mimicking the tissue material (‘density1Opt’), and PTV excluding the air volume (‘noAirOpt’). Using 10 MV photon beams, seven field IMRT plans for each target were created with the same parameter condition. For these three cases, DVHs for the PTV, bladder and the rectum were compared. Also, the dose coverage for the CTV and the shifted CTV were evaluated in which the shifted CTV was a copied and translated virtual CTV toward the rectum inside the PTV, thus occupying the initial position of the overlap air volume, simulating the worst condition for the dose coverage in the target. Among the three options, only density1Opt plan gave clinically acceptable result in terms of target coverage and maximum dose. The airOpt plan gave exceedingly higher dose and excessive dose coverage for the target volume whereas noAirOpt plan gave underdose for the shifted CTV. Therefore, for prostate IMRT plan, having an air region in the PTV, density modification of the included air to the value of one, is suggested, prior to optimization and prescription for the PTV. This idea can be equally applied to any cases including the head and neck cancer with the PTV having the overlapped air region. Further study is being under process.

KeywordsIMRT, Convolution-superposition, Prostate, Rectum air

Korean Society of Medical Physics

Vol.35 No.1
March 2024

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

Frequency: Quarterly

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