employee
National Research Tomsk Polytechnic University, Tomsk, Russia
Russian Federation
employee
Russian Federation
employee
employee
Russian Federation
employee
Russian Federation
employee
National Research Tomsk Polytechnic University
graduate student
employee
National Research Tomsk Polytechnic University
graduate student
GRNTI 76.03 Медико-биологические дисциплины
GRNTI 76.33 Гигиена и эпидемиология
OKSO 14.04.02 Ядерные физика и технологии
OKSO 31.06.2001 Клиническая медицина
OKSO 31.08.08 Радиология
OKSO 32.08.12 Эпидемиология
BBK 51 Социальная гигиена и организация здравоохранения. Гигиена. Эпидемиология
BBK 534 Общая диагностика
TBK 5708 Гигиена и санитария. Эпидемиология. Медицинская экология
TBK 5712 Медицинская биология. Гистология
TBK 5734 Медицинская радиология и рентгенология
TBK 6212 Радиоактивные элементы и изотопы. Радиохимия
Purpose: Investigation of the relative errors of absorbed dose measurement based on polymer films Gafchromic EBT3 for clinical electron and photon beams of medical accelerators. Material and methods: Polymer Gafchromic EBT3 films were calibrated using different radiation beams, namely photon and electron beams of Elekta Axesse medical accelerator with beam energy equal to 10 MV and 10 MeV, correspondingly, and electron beam of a betatron for intraoperative radiotherapy with beam energy equal to 6 MeV. The film pieces were irradiated by the uniform dose field in the dose range from 0.5 to 40 Gy. The dose value was controlled by cylindrical ionization chamber in the case of Elekta Axesse accelerator and by the Markus parallel chamber in the case of betatron. The irradiated films were scanned using Epson Perfection V750 Pro flatbed scanner in 16 bit RGB color mode with 150 dpi resolution. The red and green channels were used for further analysis. The central part of each film was used for calculation of average values of net optical density and its root-mean-square. As a result, the calibration curves, i.e. dependence on the reference absorbed dose measured by ionization chamber on the net optical density were constructed taking into account uncertainties of dose measurement and optical density measurement. Results: The relative uncertainty for the dose measurement lies within 7 % for low doses (less than 1 Gy) and within 4 % for higher doses. The green channel is less sensitive to the radiation, but its relative uncertainty values are in general 1–2 % lower than the ones for the red channel. The use of different calibration sources results in different calibration curves with difference up to ±6 % for the green channel. Conclusion: The polymer Gafchromic EBT3 films could be used for absorbed dose measurement for the doses not less than 0.5 Gy. For lower dose values the dose measurement uncertainty caused by statistical reasons amounts 15 %. For dose values of about 1 Gy and higher the dose measurement uncertainty amounts 5 % that allows to use the films for transverse and longitudinal prescription treatment dose distribution measurement with very high spatial resolution.
radiation therapy, Gafchromic EBT3 film, clinical dosimetry, medical accelerators, absorbed dose, uncertainties
Introduction
Radiation therapy is widely used for treatment of malignant tumors all over the world. The development of radiation therapy is based on the development of dose delivery techniques that include Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Therapy. These techniques allow high-quality dose delivery that results in possibility to carry out hypofractionated radiation therapy. This fractionation type is effective for example in the cases of prostate carcinomas [1] or lung cancer [2]. IMRT and VMAT techniques are also effective in the case of irradiation of brain [3] or liver metastases [2]. Each dosimetric treatment plan which use high gradient dose fields should be verified before implementation and patient treatment. One of the widely used ways to check the treatment plan quality is based on the using of radiochromic polymer films that have the best spatial resolution among all dosimeters used in the medical physics. The typical spatial resolution of the polymer films is about 0.1 mm. That is why radiochromic dosimetric films are widely used in clinical dosimetry of photon, electron and proton beams mainly for obtaining of dose spatial distributions of a radiotherapy device. Such films are not exposed by the visible light that makes them more reliable in routine operation. In 2011 third generation of radiochromic film GAFCHROMIC EBT3 was presented. The film is a tissue-equivalent dosimeter with the dose measurement range 0.1–20 Gy according to the manufacture specification [4]. The film has low energy dependence and could be used for dosimetry of both electron and photon beams.
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