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Dosimetric effect of modelling non-homogeneous LINAC couch using cone-beam computed tomography on quality assurance (QA) results

Published online by Cambridge University Press:  14 July 2022

Amin Banaei Open the ORCID record for Amin Banaei [Opens in a new window] ,
Mohsen Bakhshandeh Open the ORCID record for Mohsen Bakhshandeh [Opens in a new window]  and
Mohammad Rasa Golrokh-Nodehi
Amin Banaei
Affiliation:
Department of Medical physics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
Mohsen Bakhshandeh*
Affiliation:
Department of Radiology Technology, Faculty of Allied Medical Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Mohammad Rasa Golrokh-Nodehi
Affiliation:
Department of Medical Radiation Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
*
Author for correspondence: Mohsen Bakhshandeh, Department of Radiology Technology, Faculty of Allied Medical Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Email: Mbakshandeh@sbmu.ac.ir
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Abstract

Aim:

To evaluate the dosimetric effect of modelling a non-homogeneous couch on patients’ quality assurance (QA) gamma pass rates for intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques.

Materials and Methods:

A non-homogeneous treatment couch (TxT 550 TTM, CIVCO, USA) was imaged using the LINAC mounted cone-beam computer tomography (CBCT) system. Modelling this couch in different situations, including incomplete (homogeneous model), correct model and not defined situations in the treatment planning system (TPS), was performed based on the geometrical and material densities data extracted from the CBCT images. Calculated gamma pass rates between TPS dose calculations and the measurements in a phantom for different couch models were obtained and compared at two gamma criteria (2%-2 mm and 3%-3 mm).

Results:

Comparing TPS calculations for the correct modelled couch and the measurements showed high gamma pass rates for both the IMRT and VMAT techniques (96·5 ±  0·9%, 99·2 ±  0·5% for IMRT in 2%-2 mm and 3%-3 mm criteria; 97·5 ±  0·8%, 99·4 ±  0·5% for VMAT). The overall gamma pass rate of the IMRT plan QAs was reduced by about 2% and 3% on average for incomplete and no couch modelling, respectively. These reductions for VMAT techniques were 2·5% and 4·3%, respectively.

Conclusions:

Non-homogeneous couches have different parts with different attenuations, which can be correctly defined using LINAC CBCT. Modelling of treatment couch has a significant effect on patient QA results for VMAT and IMRT plans, especially in radiation fields/subfield transmitting from the couch. We suggest using LINAC CBCTs as an appropriate device for couch modelling in modulated radiotherapy techniques.

Keywords

intensity-modulatedquality assuranceradiotherapyvolumetric modulated arc therapytreatment couch
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 22 , 2023 , e31
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Copyright
© The Author(s), 2022. Published by Cambridge University Press

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