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ORIGINAL ARTICLE
Year : 2013  |  Volume : 9  |  Issue : 3  |  Page : 402-409

Dosimetric comparison between three dimensional treatment planning system, Monte Carlo simulation and gel dosimetry in nasopharynx phantom for high dose rate brachytherapy


1 Department of Nuclear Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
2 Agricultural, Medical and Industrial Research School, Nuclear Science and Technology Research Institute, Karaj, Iran
3 Department of Medical Physics, Novin Medical Radiation Institute, Tehran, Iran
4 Department of Medical Physics, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran
5 Department of Energy Science, Sung Kyun Kwan University, Suwon, Korea

Correspondence Address:
Mahdi Sadeghi
Agricultural, Medical and Industrial Research School, Nuclear Science and Technology Research Institute, P.O. Box 31485-498, Karaj
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-1482.119316

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Purpose: For the treatment of nasopharnx carcinoma (NPC) using brachytherapy methods and high-energy photon sources are common techniques. In the common three dimensional (3D) treatments planning, all of the computed tomography images are assumed homogeneous. This study presents the results of Monte Carlo calculations for non-homogeneous nasopharynx phantom, MAGICA normoxic gel dosimetry and 3D treatment planning system (TPS). Materials and Methods: The head phantom was designed with Plexiglas cylinder, head bone, and nasopharynx brachytherapy silicon applicator. For the simulations, version 5 of the Monte Carlo N-particle transport code (MCNP5) was used. 3D treatment planning was performed in Flexiplan software. A normoxic radiosensitive polymer gel was fabricated under normal atmospheric conditions and poured into test tubes (for calibration curve) and the head phantom. In addition, the head phantom was irradiated with Flexitron afterloader brachytherapy machine with 192 Ir source. To obtain calibration curves, 11 dosimeters were irradiated with dose range of 0-2000 cGy. Evaluations of dosimeters were performed on 1.5T scanner. Results: Two-dimensional iso-dose in coronal plan at distances of z = +0.3, –0.3 cm was calculated. There was a good accordance between 3D TPS and MCNP5 simulation and differences in various distances were between 2.4% and 6.1%. There was a predictable accordance between MAGICA gel dosimetry and MCNP5 simulation and differences in various distances were between 5.7% and 7.4%. Moreover, there was an acceptable accordance between MAGICA gel dosimetry and MCNP5 data and differences in various distances were between 5.2% and 9.4%. Conclusion: The sources of differences in this comparison are divided to calculations variation and practical errors that was added in experimental dosimetry. The result of quality assurance of nasopharynx high dose rate brachytherapy is consistent with international standards.


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