EBT GAFCHROMIC^TM film dosimetry in compensator-based intensity modulated radiation therapy

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• 作者：Seyedali Vaezzadeh ; Ph.D.^? ; Mahmoud Allahverdi ; Ph.D.^? ; ^&dagger ; ; ^{alahverdi@sina.tums.ac.ir} ; Hasan A. Nedaie ; Ph.D.^&dagger ; ; Mohammadreza Ay ; Ph.D.^? ; ^&Dagger ; ; Alireza Shirazi ; Ph.D.^? ; Mehran Yarahmadi ; Ph.D.^?
• 关键词：EBT GAFCHROMIC films ; Compensator-based IMRT ; Ionization chamber ; Monte Carlo simulation
• 刊名：Medical Dosimetry
• 出版年：2013
• 出版时间：Summer, 2013
• 年：2013
• 卷：38
• 期：2
• 页码：176-183
• 全文大小：1665 K

文摘

The electron benefit transfer (EBT) GAFCHROMIC films possess a number of features making them appropriate for high-quality dosimetry in intensity-modulated radiation therapy (IMRT). Compensators to deliver IMRT are known to change the beam-energy spectrum as well as to produce scattered photons and to contaminate electrons; therefore, the accuracy and validity of EBT-film dosimetry in compensator-based IMRT should be investigated. Percentage-depth doses and lateral-beam profiles were measured using EBT films in perpendicular orientation with respect to 6 and 18 MV photon beam energies for: (1) different thicknesses of cerrobend slab (open, 1.0, 2.0, 4.0, and 6.0 cm), field sizes (5¡Á5, 10¡Á10, and 20¡Á20 cm²), and measurement depths (D_max, 5.0 and 10.0 cm); and (2) step-wedged compensator in a solid phantom. To verify results, same measurements were implemented using a 0.125 cm³ ionization chamber in a water phantom and also in Monte Carlo simulations using the Monte Carlo N-particle radiation transport computer code. The mean energy of photons was increased due to beam hardening in comparison with open fields at both 6 and 18 MV energies. For a 20¡Á20 cm² field size of a 6 MV photon beam and a 6.0 cm thick block, the surface dose decreased by about 12 % and percentage-depth doses increased up to 3 % at 30.0 cm depth, due to the beam-hardening effect induced by the block. In contrast, at 18 MV, the surface dose increased by about 8 % and depth dose reduced by 3 % at 30.0 cm depth. The penumbral widths (80 % to 20 % ) increase with block thickness, field size, and beam energy. The EBT film results were in good agreement with the ionization chamber dose profiles and Monte Carlo N-particle radiation transport computer code simulation behind the step-wedged compensator. Also, there was a good agreement between the EBT-film and the treatment-planning results on the anthropomorphic phantom. The EBT films can be accurately used as a 2D dosimeter for dose verification and quality assurance of compensator-based C-IMRT.