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Dosimetric evaluation of a novel electron–photon mixed beam, produced by a medical linear accelerator

Published online by Cambridge University Press:  10 January 2018

Navid Khaledi ,
Dariush Sardari ,
Mohammad Mohammadi ,
Ahmad Ameri  and
Nick Reynaert
Navid Khaledi
Affiliation:
Department of Clinical Oncology, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Dariush Sardari
Affiliation:
Department of Medical Radiation Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
Mohammad Mohammadi
Affiliation:
Department of Radiation Oncology, Royal Adelaide Hospital, Adelaide, Australia
Ahmad Ameri*
Affiliation:
Department of Clinical Oncology, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Nick Reynaert
Affiliation:
Medical Physics Department, Centre Oscar Lambret, Lille, France
*
Correspondence to: Ahmad Ameri, Department of Clinical Oncology, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Tel: +98 21 73430000. E-mail: a_ameri@sbmu.ac.ir
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Abstract

Aim

This study deals with the characteristics of simultaneous photon and electron beams in homogenous and inhomogeneous phantoms by experimental and Monte Carlo dosimetry, for therapeutic purposes. Materials and methods: Both 16 and 20 MeV high-energy electron beams were used as the original beam to strike perforated lead sheets to produce the mixed beam. The dosimetry results were achieved by measurement in an ion chamber in a water phantom and film dosimetry in a Perspex nasal phantom, and then compared with those calculated through a simulation approach. To evaluate two-dimensional dose distribution in the inhomogeneous medium, the dose–area histogram was obtained.

Results

The highest percentage of photon contribution in mixed beam was found to be 36% for 2-mm thickness of lead layer with holes diameter of 0·2 cm for a 20 MeV primary electron energy. For small fields, the percentage depth dose parameters variations were found to be similar to pure electron beam within ±2%. The most feasible flatness in beam profile was 11% for pure electron and 7% for the mixed beam. Penumbra changes as function of depth was about ten times better than in pure electron field.

Conclusions

The results present some dosimetric advantages that can make this study a platform for the production of simultaneous mixed beams in future linear accelerators (LINACs), which through redesign of the LINAC head, which could lead to setup error reduction and a decrease of intra-fractional tumour cells repair.

Keywords

electron beamfilm dosimetrymixed beamphoton beamradiation therapy
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 17 , Issue 3 , September 2018 , pp. 319 - 331
Copyright
© Cambridge University Press 2018 

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