Document Type : Original Paper
Radiotherapy Oncology Research Center, Cancer Institute, Tehran University of Medical Sciences,Tehran, Iran.
radiotherapy oncology department, cancer research centre, Tehran university of medical sciences,Tehran,Iran
Radiotherapeutic Oncology Department of Cancer Institute, Tehran, Iran
Department of Medical Physics, Tehran University of Medical Science, Tehran, Iran
Department of Radiotherapy Physics, Cancer Research Centre, cancer Institute, Tehran University of Medical Sciences, Tehran, Iran
Tehran University of Medical Sciences
Radiotherapy Oncology Research Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran
Radiotherapy Oncology Department, Cancer Research Centre, Tehran University of Medical Sciences, Tehran, Iran
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.