Evaluation of the accuracy of calculated dose with the EPL and ETAR algorithms using thorax CIRS phantom.

Introduction: Each treatment planning algorithm has some errors in dose calculation. Particularly these errors are more pronounced in the heterogeneous regions. It is recommended for each set of radiation data and algorithm subtle deliberation done regarding dose calculation accuracy. Knowing the amount of error in dose calculation will result in a fairly accurate estimate of the actual absorbed dose to the tumor. Also, if the errors have a certain trend, the correction coefficients can be applied to emend the dose. There are limited reports that have examined the algorithm in their health center. This study aimed to evaluate the EPL and ETAR algorithms in radiation dose calculation using thorax CIRS phantom.   Materials and Methods: In this empirical study TEC-DOC 1583 guideline provided by IAEA was used. Experimental measurements were obtained using an ionization chamber at the recommended points according to above instructions for 6 and 18 MV energies. The values of the measurements were compared with the values obtained from the calculation of the EPL and ETAR algorithms using acceptance criteria specified in the instruction. A total of 31 measurements and calculations were obtained for each algorithm with a specific energy. Due to the small number of measurable points in the phantom, for each test, difference between the measurement and calculation was normalized to the reference point of each test. Results: In the EPL algorithm for 6 MV energy, the calculations were in agreement with measurements for 27 dose points and differences between measurements and calculations ranged from 0.1% to 10.4%. For 18 MV energy, the calculations were in agreement with measurements for 21 dose points and differences between measurements and calculation ranged from 0.4% to 13%. In ETAR algorithm for 6 MV, calculations were in agreement with measurements for 21 dose points, and differences between measurements and calculations ranged from 0.1% to 9%. For 18 MV, the calculations were in agreement with measurements for 17 dose points and differences between calculations and measurements ranged from 0% to 11%. Conclusion: For the EPL algorithm, compared with the ETAR algorithm, more dose points were agreed with acceptance criteria. Although the numerical values of the errors in the ETAR algorithm were 1 to 2 percent less than the EPL algorithm. The greatest error occurs when calculations made in low density lung tissue with inhomogeneities or in high density bone. Errors were larger in shallow depths. Overall, the error in higher energy was more than low energy beam.