Mohammad Taghi Bahreyni Toossi1, Nastaran Mohamadian1, Mohammad Mohammadi2,3, Mahdi Ghorbani4, Mohsen Hassani5, Benyamin Khajetash6, Farideh Khorshidi1, Courtney Knaup7. 1. Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran. 2. Department of Medical Physics, Royal Adelaide Hospital, Adelaide, South Australia. 3. School of Physical Sciences, The University of Adelaide, Adelaide, South Australia. 4. Biomedical Engineering and Medical Physics Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 5. Department of Radiotherapy Physics, Cancer Research Centre, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran. 6. Medical Physics Department, Faculty of Medicine, Iran University of Medical Sciences, Tehran, Iran. 7. Comprehensive Cancer Centers of Nevada, Las Vegas, Nevada, USA.
Abstract
AIM: The main purpose of the present study is assessment of skin dose in breast cancer radiotherapy. BACKGROUND: Accurate assessment of skin dose in radiotherapy can provide useful information for clinical considerations. MATERIALS AND METHODS: A RANDO phantom was irradiated using a 6 MV Siemens Primus linac with medial and tangential radiotherapy fields for simulating breast cancer treatment. Dosimetry was also performed on various positions across the fields using an EBT3 radiochromic film. Similar conditions of measurement on the RANDO phantom including field size, irradiation angle, number of fields, etc. were subsequently simulated via the Monte Carlo N-Particle Transport code (MCNP). Ultimately, dose values for corresponding points from both methods were compared. RESULTS: Considering dosimetry using radiochromic films on the RANDO phantom, there were points having underdose and overdose based on the prescribed dose and skin tolerance levels. In this respect, 81.25% and 18.75% of the points had underdose and overdose, respectively. In some cases, several differences were observed between the measurement and the MCNP simulation results associated with skin dose. CONCLUSION: Based on the results of the points which had underdose, it was suggested that a bolus should be used for the given points. With regard to overdose points, it was advocated to consider skin tolerance dose in treatment planning. Differences between the measurement and the MCNP simulation results might be due to voxel size of tally cells in simulations, effect of beam's angle of incidence, validation time of linac's head, lack of electronic equilibrium in the build-up region, as well as MCNP tally type.
AIM: The main purpose of the present study is assessment of skin dose in breast cancer radiotherapy. BACKGROUND: Accurate assessment of skin dose in radiotherapy can provide useful information for clinical considerations. MATERIALS AND METHODS: A RANDO phantom was irradiated using a 6 MV Siemens Primus linac with medial and tangential radiotherapy fields for simulating breast cancer treatment. Dosimetry was also performed on various positions across the fields using an EBT3 radiochromic film. Similar conditions of measurement on the RANDO phantom including field size, irradiation angle, number of fields, etc. were subsequently simulated via the Monte Carlo N-Particle Transport code (MCNP). Ultimately, dose values for corresponding points from both methods were compared. RESULTS: Considering dosimetry using radiochromic films on the RANDO phantom, there were points having underdose and overdose based on the prescribed dose and skin tolerance levels. In this respect, 81.25% and 18.75% of the points had underdose and overdose, respectively. In some cases, several differences were observed between the measurement and the MCNP simulation results associated with skin dose. CONCLUSION: Based on the results of the points which had underdose, it was suggested that a bolus should be used for the given points. With regard to overdose points, it was advocated to consider skin tolerance dose in treatment planning. Differences between the measurement and the MCNP simulation results might be due to voxel size of tally cells in simulations, effect of beam's angle of incidence, validation time of linac's head, lack of electronic equilibrium in the build-up region, as well as MCNP tally type.
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