O15. Modelling of the Siemens Linac couch in the Monaco planning system. (September 2016)

• Record Type: Journal Article
• Authors: Rall, C.
• Is Part Of: Physica medica. Volume 32(2016)Supplement 2
• Page Start: 145
• Publication Date: 2016-09
• Subjects: Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2016.07.023
• Languages: English
• ISSNs: 1120-1797

Abstract

Abstract : Introduction: Carbon fibre material is used for the Linac couch since it is light, strong and rigid. It is presumed to be radio-transparent for mega-voltage photons. Literature has indicated that the attenuation properties of carbon fibre couches may not be negligible, especially with intensity modulated radiotherapy (IMRT) treatments where more beams intersect the couch. According to Spezi et al. (Radiother Oncol, 89:114-122, 2008), inclusion of the Siemens couch in head and neck IMRT can lead to a target dose reduction of 2% and organ at risk (OAR) dose increase of 5% and might be more pronounced if heavily weighted posterior beams are used. This study investigates the influence of the couch on treatment plans in the Monaco planning system. Materials and Methods: The couch was computed tomography (CT) scanned and imported into the Monaco planning system in the treatment couch library. Appropriate densities were assigned to the delineated contours of the couch (carbon fibre and inner foam) and were validated by absolute dosimetric measurements. Treatment plans calculated with and without the couch model were compared. Results: Point dose measurements were done in a circular phantom, 10 × 10 cm 2 field size and 6 MV beam. Measurements indicated attenuation of the beam of up to 4.03 ± 0.28% due to the influence of the couch. After appropriate densities of the couch were assigned, measured, compared to planned values, where within a range of 0.15 ± 0.11% to 0.97 ± 0.20%, excluding two angles which had partial interception of the central axis with the couch edge. Conclusion: This study showed that the presence of the couch does affect dosimetry. Protocols will be adjusted to include the couch in patient treatment planning, if this study's outcome is comparable to literature.