Title: | Biological effect of dose distortion by fiducial markers in spot-scanning proton therapy with a limited number of fields: A simulation study |
Authors: | Matsuura, Taeko Browse this author →KAKEN DB |
Maeda, Kenichiro Browse this author |
Sutherland, Kenneth Browse this author |
Takayanagi, Taisuke Browse this author |
Shimizu, Shinichi Browse this author |
Takao, Seishin Browse this author |
Miyamoto, Naoki Browse this author |
Nihongi, Hideaki Browse this author |
Toramatsu, Chie Browse this author |
Nagamine, Yoshihiko Browse this author |
Fujimoto, Rintaro Browse this author |
Suzuki, Ryusuke Browse this author →KAKEN DB |
Ishikawa, Masayori Browse this author →KAKEN DB |
Umegaki, Kikuo Browse this author |
Shirato, Hiroki Browse this author |
Keywords: | proton spot-scanning therapy |
tumor tracking |
fiducial marker |
prostate cancer |
tumor-control probability |
Issue Date: | Sep-2012 |
Publisher: | American Association of Physicists in Medicine |
Journal Title: | Medical Physics |
Volume: | 39 |
Issue: | 9 |
Start Page: | 5584 |
End Page: | 5591 |
Publisher DOI: | 10.1118/1.4745558 |
PMID: | 22957624 |
Abstract: | Purpose: In accurate proton spot-scanning therapy, continuous target tracking by fluoroscopic X-ray during irradiation is beneficial not only for respiratory moving tumors of lung and liver but also for relatively stationary tumors of prostate. Implanted gold markers have been used with great effect for positioning the target volume by a fluoroscopy, especially for the cases of liver and prostate with the targets surrounded by water-equivalent tissues. However, recent studies have revealed that gold markers can cause a significant underdose in proton therapy. This paper focuses on prostate cancer and explores the possibility that multiple-field irradiation improves the underdose effect by markers on Tumor-Control Probability (TCP). Methods: A Monte Carlo simulation was performed to evaluate the dose distortion effect. A spherical gold marker was placed at several characteristic points in a water phantom. Markers were with two different diameters of 2 mm and 1.5 mm, both visible on fluoroscopy. Three beam arrangements of SFUD (single-field uniform dose) were examined: one lateral field, two opposite lateral fields, and three fields (two opposite lateral fields + anterior field). The Relative Biological Effectiveness (RBE) was set to 1.1 and a dose of 74 Gy (RBE) was delivered to the target of a typical prostate size in 37 fractions. The ratios of TCP to that without the marker (TCPr) were compared with the parameters of the marker sizes, number of fields, and marker positions. To take into account the dependence of biological parameters in TCP model, α/β values of 1.5, 3, and 10 Gy (RBE) were considered. Results: It was found that the marker of 1.5 mm diameter does not affect the TCPs with all α/β values when two or more fields are used. On the other hand, if the marker diameter is φ2 mm, more than two irradiation fields are required to suppress the decrease in TCP from TCPr by less than 3%. This is especially true when multiple (two or three) markers are used for alignment of a patient. Conclusions: It is recommended that φ1.5 mm markers be used to avoid the reduction of TCP as well as to spare the surrounding critical organs, as long as the markers are visible on X-ray fluoroscopy. When φ2 mm markers are implanted, more than two fields should be used and the markers should not be placed close to the distal edge of any of the beams. |
Type: | article (author version) |
URI: | http://hdl.handle.net/2115/50429 |
Appears in Collections: | 医学院・医学研究院 (Graduate School of Medicine / Faculty of Medicine) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)
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