Poster - Thurs Eve-32: Dose errors related to the treatment couch
M Niedbala1, B Nyiri1,2, L Gerig1,2,3
1Ottawa Hospital Cancer Centre, Ottawa, ON.
Medical Physics
|May 18, 2017
Summary
Carbon fibre radiotherapy couches significantly affect patient dose and skin sparing. Treatment planning systems can accurately account for this couch attenuation, improving radiation therapy accuracy.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Equipment
Background:
- Modern radiotherapy linear accelerators (linacs) utilize carbon fibre couch tops for their radio-translucent properties.
- Beam attenuation and its impact on dose calculations are often overlooked in radiotherapy planning.
Purpose of the Study:
- To investigate beam attenuation and loss of skin sparing caused by different carbon fibre radiotherapy couches (Siemens MedTec and Elekta Medical Intelligence).
- To compare measured dose data with predictions from the CMS treatment planning system (XiO).
Main Methods:
- Examined beam attenuation and skin sparing for various photon beams passing through Siemens and Elekta couches.
- Compared measured surface doses with predictions from the CMS treatment planning system (XiO version 4.33.02).
- Assessed couch attenuation as a function of gantry angle and beam characteristics.
Main Results:
- The Siemens and Elekta couches exhibited different attenuation signatures due to structural variations, with radiological thicknesses of 4.5 mm and 6.0 mm, respectively, at normal incidence.
- Surface dose after couch transmission for a 6MV beam was 93% (Elekta) vs. 83% (Siemens).
- The CMS TPS accurately predicted couch attenuation (within 1% of measurement) and loss of skin sparing, except at the Siemens couch's lateral edge.
Conclusions:
- Different carbon fibre radiotherapy couches have distinct attenuation properties that significantly influence patient dose.
- The CMS treatment planning system can effectively model couch attenuation and its impact on dose, enhancing radiotherapy accuracy.
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