ABSTRACT
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 1583 guideline was used. Measurements and calculations were obtained for each algorithm at specific points in thorax CIRS phantom for 6 and 18 MVs and results were compared. RESULTS: In the EPL, calculations were in agreement with measurements for 27 points and differences between them ranged from 0.1% to 10.4% at 6 MV. The calculations were in agreement with measurements for 21 points and differences between them ranged from 0.4% to 13% at 18 MV. In ETAR, calculations were also in consistent with measurements for 21 points, and differences between them ranged from 0.1% to 9% at 6 MV. Moreover, for 18 MV, the calculations were in agreement with measurements for 17 points and differences between them ranged from 0% to 11%. CONCLUSION: For the EPL algorithm, more dose points were in consistent with acceptance criteria. The errors in the ETAR were 1% to 2% 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.
ABSTRACT
Dose calculation algorithm is one of the main sources of uncertainty in the radiotherapy sequences. The aim of this study was to compare the accuracy of different inhomogeneity correction algorithms for external photon beam dose calculations. The methodology was based on International Atomic Energy Agency TEC-DOC 1583. The phantom was scanned in every center, using computed tomography and seven tests were planned on three-dimensional treatment planning systems (TPSs). The doses were measured with ion chambers and the deviation between measured and TPS calculated dose was reported. This methodology was tested in five different hospitals which were using six different algorithms/inhomogeneity correction methods implemented in different TPSs. The algorithms in this study were divided into two groups: Measurement-based algorithms (type (a)) and model-based algorithms (type (b)). In type (a) algorithms, we saw 7.6% and 11.3% deviations out of agreement criteria for low- and high-energy photons, respectively. While in type (b) algorithms, these values were 4.3% and 5.1%, respectively. As a general trend, the numbers of measurements with results outside the agreement criteria increase with the beam energy and decrease with advancement of TPS algorithms. More advanced algorithm would be preferable and therefore should be implanted in clinical practice, especially for calculation in inhomogeneous medias like lung and bone and for high-energy beams calculation at low depth points.
