Journal of Biomedical Physics and Engineering

An Update of Couch Effect on the Attenuation of Megavoltage Radiotherapy Beam and the Variation of Absorbed Dose in the Build-up Region

Document Type : Original Research

Authors

T Sedaghatian 1, 2
M Momennezhad 3, 4
S H Rasta 2, 5, 6
Y Makhdoomi 4
S Abdollahian 4

1 Department of Medical Physics, Faculty of Medicine, Tabriz University of Medical Science, Tabriz, Iran

2 Immunology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran

3 Department of Medical Physics, Faculty of Medicine, Mashhad University of Medical Sciences, Iran

4 Radiotherapy and Oncology Reza Center, Mashhad, Iran

5 Department of Medical Bioengineering, Tabriz University of Medical Sciences, Iran

6 Faculty of Medical Sciences, University of Aberdeen, UK

Abstract
Purpose: Fiber carbon is the most common material used in treating couch as it causes less beam attenuation than other materials. Beam attenuation replaces build-up region, reduces skin-sparing effect and causes target volume under dosage. In this study, we aimed to evaluate beam attenuation and variation of build-up region in 550 TxT radiotherapy couch.
Materials and Methods: In this study, we utilized cylindrical PMMA Farmer chamber, DOSE-1 electrometer and set PMMA phantom in isocenter of gantry and the Farmer chamber on the phantom. Afterwards, the gantry rotated 10°, and attenuation was assessed. To measure build-up region, we used Markus chamber, Solid water phantom and DOSE-1 electrometer. Doing so, we set Solid water phantom on isocenter of gantry and placed Markus chamber in it, then we quantified the build-up region at 0° and 180° gantry angels and compared the obtained values.
Results: Notable attenuation and build-up region variation were observed in 550 TxT treatment table. The maximum rate of attenuation was 5.95% for 6 MV photon beam, at 5×5 cm2 field size and 130° gantry angle, while the maximum variation was 7 mm for 6 MV photon beam at 10×10 cm2 field size.
Conclusion: Fiber carbon caused beam attenuation and variation in the build-up region. Therefore, the application of fiber carbon is recommended for planning radiotherapy to prevent skin side effects and to decrease the risk of cancer recurrence.

Keywords

Beam Attenuation
Carbon Fiber
Couch Insert
Surface Dose
Megavoltage Radiotherapy
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Journal of Biomedical Physics and Engineering
Volume 7, Issue 3 - Serial Number 3
25
September and October 2017
Pages 279-288

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