Penumbra Measurements and Comparison of In-House and Standard Circular Cones by the Gafchoromic Film, Pinpoint Ion Chamber, and MCNPX Monte Carlo Simulation

Document Type: Original Paper

Authors

1 Radiotherapy Oncology Research Center, Cancer Institute, Tehran University of Medical Sciences,Tehran, Iran.

2 radiotherapy oncology department, cancer research centre, Tehran university of medical sciences,Tehran,Iran

3 Radiotherapeutic Oncology Department of Cancer Institute, Tehran, Iran

4 Department of Medical Physics, Tehran University of Medical Science, Tehran, Iran

5 Department of Radiotherapy Physics, Cancer Research Centre, cancer Institute, Tehran University of Medical Sciences, Tehran, Iran

6 Tehran University of Medical Sciences

7 Radiotherapy Oncology Research Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran

8 Radiotherapy Oncology Department, Cancer Research Centre, Tehran University of Medical Sciences, Tehran, Iran

Abstract

Introduction: Penumbra is an important property of the radiation beam to obtain a suitable margin surrounding the target volume. Therefore, the precise penumbra width determination in stereotactic radiotherapy is necessary for treatment planning. This study aimed to compare the obtained results of penumbra width by in-house and standard circular cones by different dosimeters, as well as evaluating the function of EBT3 for dosimetric properties of the small field radiation.
Material and Methods: Different circular cones were mounted on the head of the accelerator to produce 12, 20, and 40 mm field sizes at isocenter. Dosimetric measurements were performed with the EBT3 film, PinPoint ion chamber. Afterwards, MCNPX Monte Carlo simulation was used to evaluate the dosimetric parameters.
Results: According to the obtained results, the penumbra width was increased by larger diameters of circular cones. The obtained measured data by PinPoint ion chamber showed a larger penumbra width compared to those calculated by Monte Carlo at all field sizes. The gamma index analysis revealed  distance-to-agreement and dose-difference of 2 mm /2%/ at all points. The results of this study showed that source to diaphragm distance had a major role in penumbra size determination of small field dosimetry with PinPoint ion chamber, EBT3 film, and Monte Carlo simulation.
Conclusion: As findings of this study reported, EBT3 films are reliable detectors for relative dosimetry due to high spatial resolution for small field sizes. Furthermore, they can be used for measuring beam profile and percentage depth dose curves.

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