National Research Tomsk Polytechnic University, Tomsk, Russia
Russian Federation
Russian Federation
Russian Federation
Russian Federation
National Research Tomsk Polytechnic University
National Research Tomsk Polytechnic University
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.
1. Syed YA, Petel-Yadav A.K, Rivers C, Singh A.K. Stereotactic radiotherapy for prostate cancer: A review and future directions. World J Clin Oncol. 2017;8(5):389-97. DOI:https://doi.org/10.5306/wjco.v8.i5.389.
2. Diot Q, Kavanagh B, Timmerman R, Miften M. Biological-based optimization and volumetric modulated arc therapy delivery for stereotactic body radiation therapy// Med. Phys. 2012;39(1:237-45. DOI:https://doi.org/10.1118/1.3668059.
3. Fiorentino A, Giaj-Levra N, Tebano U, et al. Stereotactic ablative radiation therapy for brain metastases with volumetric modulated arc therapy and flattening filter free delivery: feasibility and early clinical results. Radiol Med. 2017;122(9):676-82. DOI:https://doi.org/10.1007/s11547-017-0768-0.
4. Gafchromic. Gafchromic EBT3 film specifications. [Internet]. 2017 [cited 2019 Feb. 20]. Available from: http://www.gafchromic.com/documents/EBT3_Specifications.pdf
5. Andreo P, Burns D, Hohlfeld K, et al. Absorbed dose determination in external beam radiotherapy: An international code of practice for dosimetry based on standards of absorbed dose to water. Technical Report Series no. 398. IAEA. 2000:251.
6. Almond P, Biggs P, Coursey B, et al. AAPM’s TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams. Med. Phys. 1999;26(9:1847-70
7. Sorriaux J, Kacperek A, Rossomme S, et al. Evaluation of gafchromic ebt3 films characteristics in therapy photon, electron and proton beams. Physica Medica. 2013;29. Suppl.6:599-606. DOI: https://doi.org/10.1016/j.ejmp.2012.10.001.
8. Hartmann B. Martisikova M, Jakel O. Technical note: Homogeneity of Gafchromic EBT2 film. Med Phys. 2010;37.Suppl.4:1753-1756. DOI:https://doi.org/10.1118/1.3368601.
9. Niewald M, Fleckenstein J, Licht N, et al. Intraoperative radiotherapy (IORT) combined with external beam radiotherapy (EBRT) for soft-tissue sarcomas - a retrospective evaluation of the homburg experience in the years 1995-2007. Radiat Oncol. 2009;4. Suppl.32:1-6. DOI:https://doi.org/10.1186/1748-717X-4-32.
10. Niroomand-Rad A, Blackwell C, Coursey B, et al. Radiochromic film dosimetry: Recommendations of AAPM radiation therapy committee task group 55. Med Phys. 1998;25. Suppl.11:2093-115. DOI:https://doi.org/10.1118/1.598407.
11. Devic S, Seuntjens J, Hegyi G, et al. Dosimetric properties of improved gafchromic films for seven dierent digitizers. Med Phys. 2004;31. Suppl.9:2392-401. DOI:https://doi.org/10.1118/1.1776691.
12. Butson M, Yu P, Cheung T, Alnawaf H. Energy response of the new ebt2 radiochromic film to x-ray radiation. Radiat Measur. 2010;45. Suppl.7:836-9. DOI:https://doi.org/10.1016/j.radmeas.2010.02.016.
13. Micke A, Lewis D, Yu X. Multichannel film dosimetry with nonuniformity correction. Med Phys. 2011;38. Suppl.5:2523-34. DOI:https://doi.org/10.1118/1.3576105.
14. Devic S. Radiochromic film dosimetry: Past, present, and future. Physica Medica. 2011;27. Suppl.3:122-134. DOI:https://doi.org/10.1016/j.ejmp.2010.10.001.
15. Soares C. Radiochromic film dosimetry. Radiat Measur. 2006;41. Suppl.1:S100-S116.
16. Reinhardt S, Hillbrand M, Wilkens J, Assmann W. Comparison of gafchromic EBT2 and EBT3 films for clinical photon and proton beams. Med Phys. 2012;39 Suppl.8:5257-62. DOI:https://doi.org/10.1118/1.4737890.
17. Wolfram. [Internet]. 2019. [cited 2019, Feb. 20]. Available from: https://www.wolfram.com/mathematica.
18. IBA. Description of dosimetric system iba matrix. [Internet]. 2019. [cited 2019, Feb. 20]. Available from: http://www.iba-dosimetry.com/complete-solutions/radiotherapy/imrt-igrt-rotational-qa/matrixxes.
19. IBA, Description of clinical dosimeter dose-1. [Internet]. 2017. [cited 2019, Feb. 20]. Available from: http://www.iba-dosimetry.com/sites/default/files/resources/RT-BR-E-DOSE1_Rev.1_0211_0.pdf.
20. PTW, Description of dosimeter ptw unidos E. [Internet]. 2017. [cited 2019, February 20]. Available from: http://www.ptw.de/unidos_e_dosemeter_ad0.html.
21. PTW, Description of electron cionization chamber PTW23343. [Internet]. 2017. [cited 2019, Feb. 20]. Available from: http://www.ptw.de/advanced_markus_electron_chamber.html.
22. PTW, Description of solid state phantom ptw rw3 SLAP phantom T29672. [Internet] 2017. [cited 2019, February 20]. Available from: http://www.ptw.de/acrylic_and_rw3_slab_phantoms0.html.
23. Epson, Technical characteristics of EPSON Perfection V750 scanner. [Internet]. 2017. [cited 2019, Feb. 20]. Available from: http://epson.ru/catalog/scanners/epson-perfection-v750-pro/?page=characteristics.
