Document Type : Conference Proceedings
Authors
1
Department of Medical Physics and Medical Engineering, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
2
Radiotherapy Oncology Research Centre, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran. Nedaieha@sina.tums.ac.ir Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran.
3
Radiotherapy Oncology Research Centre, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran. s-gholami@sina.tums.ac.ir. Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran. The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, Trieste 34151, Italy.
4
Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran.
Abstract
Introduction: In radiation therapy, the accuracy of dose calculations by a treatment planning system (TPS) is important to achieve tumor control and to spare normal tissue. Treatment planning system calculations in the heterogeneous situation may present significant inaccuracies. In this study, three different dose calculation algorithms, pencil beam (PB), collapsed cone (CC), and Monte-Carlo (MC), provided by our planning system were compared to assess their impact on the three-dimensional planning of lung region.
Materials and Methods: The methodology was based on IAEA TEC-DOC 1583. The phantom resembling the human thorax are used and all tests were planned on three- dimensional treatment planning systems (TPSs) and irradiated with photon beams of 6, and 18 MV X-ray energies. The doses in specific points were measured with an ionization chamber. The differences between the measured and calculated doses were reported. This study was tested using different algorithms/inhomogeneity correction methods implemented in Monaco treatment planning system.
Results: The measurements were conducted for all test case datasets for two photon beam energies and calculation algorithms. The deviation between the measured and calculated values for all test cases made with advanced algorithms (MC and CC) were within the agreement criteria, while the larger deviations were observed for PB algorithm. Subsequently, there were discovered dose differences greater than 20% for some simple algorithms and high energy X-ray beams. The number of measurements with results outside the agreement criteria increased with the increase of the beam energy and decreased with TPS calculation algorithm sophistication. Also, a few errors in the basic dosimetry data in TPS were detected and corrected.
Conclusion: Differences were found when comparing the calculation algorithms. The PB algorithm actually overestimated the dose compared with those calculated by the CC and MC algorithms. The MC algorithm showed better accuracy than the other algorithms. Therefore advanced dose calculation algorithms are suitable and should be used in clinical practice
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