- - - PhD, Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
- - - PhD, Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
- - - MD, Department of Clinical Oncology, Faculty of Medicine, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
- - - MD, Department of Clinical Oncology, Faculty of Medicine, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
- - - PhD, Department of Medical Physics, Faculty of Medicine, Iran University of Medical Sciences, Tehran, Iran

Background: It is recommended for each set of radiation data and algorithm that subtle deliberation is done regarding dose calculation accuracy. Knowing the errors in dose calculation for each treatment plan will result in an accurate estimate of the actual dose achieved by the tumor. Objective: This study aims to evaluate the equivalent path length (EPL) and equivalent tissue air ratio (ETAR) algorithms in radiation dose calculation.Material and Methods: In this experimental study, the TEC-DOC ۱۵۸۳ guideline was used. Measurements and calculations were obtained for each algorithm at specific points in thorax CIRS phantom for ۶ and ۱۸ MVs and results were compared. Results: In the EPL, calculations were in agreement with measurements for ۲۷ points and differences between them ranged from ۰.۱% to ۱۰.۴% at ۶ MV. The calculations were in agreement with measurements for ۲۱ points and differences between them ranged from ۰.۴% to ۱۳% at ۱۸ MV. In ETAR, calculations were also in consistent with measurements for ۲۱ points, and differences between them ranged from ۰.۱% to ۹% at ۶ MV. Moreover, for ۱۸ MV, the calculations were in agreement with measurements for ۱۷ points and differences between them ranged from ۰% to ۱۱%. Conclusion: For the EPL algorithm, more dose points were in consistent with acceptance criteria. The errors in the ETAR were ۱% to ۲% less than the EPL. The greatest calculation error occurs in low-density lung tissue with inhomogeneities or in high-density bone. Errors were larger in shallow depths. The error in higher energy was more than low energy beam.

Algorithms, Dose Calculation Error, Lung Tissue, Inhomogeneities, Radiotherapy, Treatment Planning Systems, Radiation Dosage