TY - JOUR
T1 - Megavoltage photon beam attenuation by carbon fiber couch tops and its prediction using correction factors
AU - Hayashi, Naoki
AU - Shibamoto, Yuta
AU - Obata, Yasunori
AU - Kimura, Takashi
AU - Nakazawa, Hisato
AU - Hagiwara, Masahiro
AU - Hashizume, Chisa I.
AU - Mori, Yoshimasa
AU - Kobayashi, Tatsuya
PY - 2010
Y1 - 2010
N2 - The purpose of this study was to evaluate the effect of megavoltage photon beam attenuation (PBA) by couch tops and to propose a method for correction of PBA. Four series of phantom measurements were carried out. First, PBA by the exact couch top (ECT, Varian) and Imaging Couch Top (ICT, BrainLAB) was evaluated using a water-equivalent phantom. Second, PBA by Type-S system (Med-Tec), ECT and ICT was compared with a spherical phantom. Third, percentage depth dose (PDD) after passing through ICT was measured to compare with control data of PDD. Forth, the gantry angle dependency of PBA by ICT was evaluated. Then, an equation for PBA correction was elaborated and correction factors for PBA at isocenter were obtained. Finally, this method was applied to a patient with hepatoma. PBA of perpendicular beams by ICT was 4.7% on average. With the increase in field size, the measured values became higher. PBA by ICT was greater than that by Type-S system and ECT. PBA increased significantly as the angle of incidence increased, ranging from 4.3% at 180° to 11.2% at 120°. Calculated doses obtained by the equation and correction factors agreed quite well with the measured doses between 120° and 180° of angles of incidence. Also in the patient, PBA by ICT was corrected quite well by the equation and correction factors. In conclusion, PBA and its gantry angle dependency by ICT were observed. This simple method using the equation and correction factors appeared useful to correct the isocenter dose when the PBA effect cannot be corrected by a treatment planning system.
AB - The purpose of this study was to evaluate the effect of megavoltage photon beam attenuation (PBA) by couch tops and to propose a method for correction of PBA. Four series of phantom measurements were carried out. First, PBA by the exact couch top (ECT, Varian) and Imaging Couch Top (ICT, BrainLAB) was evaluated using a water-equivalent phantom. Second, PBA by Type-S system (Med-Tec), ECT and ICT was compared with a spherical phantom. Third, percentage depth dose (PDD) after passing through ICT was measured to compare with control data of PDD. Forth, the gantry angle dependency of PBA by ICT was evaluated. Then, an equation for PBA correction was elaborated and correction factors for PBA at isocenter were obtained. Finally, this method was applied to a patient with hepatoma. PBA of perpendicular beams by ICT was 4.7% on average. With the increase in field size, the measured values became higher. PBA by ICT was greater than that by Type-S system and ECT. PBA increased significantly as the angle of incidence increased, ranging from 4.3% at 180° to 11.2% at 120°. Calculated doses obtained by the equation and correction factors agreed quite well with the measured doses between 120° and 180° of angles of incidence. Also in the patient, PBA by ICT was corrected quite well by the equation and correction factors. In conclusion, PBA and its gantry angle dependency by ICT were observed. This simple method using the equation and correction factors appeared useful to correct the isocenter dose when the PBA effect cannot be corrected by a treatment planning system.
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U2 - 10.1269/jrr.09116
DO - 10.1269/jrr.09116
M3 - Article
C2 - 20508376
AN - SCOPUS:77954967953
SN - 0449-3060
VL - 51
SP - 455
EP - 463
JO - Journal of Radiation Research
JF - Journal of Radiation Research
IS - 4
ER -