Megavoltage photon beam attenuation by carbon fiber couch tops and its prediction using correction factors

Naoki Hayashi, Yuta Shibamoto, Yasunori Obata, Takashi Kimura, Hisato Nakazawa, Masahiro Hagiwara, Chisa I. Hashizume, Yoshimasa Mori, Tatsuya Kobayashi

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)455-463
Number of pages9
JournalJournal of Radiation Research
Issue number4
Publication statusPublished - 2010

All Science Journal Classification (ASJC) codes

  • Radiation
  • Radiology Nuclear Medicine and imaging
  • Health, Toxicology and Mutagenesis


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