Evaluation of dose distribution algorithms sensitivity for a range of random/systematic transitional and rotational displacement occurred in twodimensional dose map comparisons

Composite analysis and gamma function are two algorithms used to assess the agreement between a reference and an evaluated two-dimensional dose maps. Two criteria are defined dose distribution in high and low dose gradient regions. The Composite analysis is a binary map and in contrast, the response of gamma function algorithm is continuous values. Although the both algorithms enable to identify agreed and disagreed areas for two-dimensional maps, the sensitivity of their response is not reported yet. Several EDR2 films are exposed in an open field for a range of radiation field sizes. The acquired portal images are then converted into dose using an appropriate method and registered as reference images. Two in-house codes are written in MATLAB based on the Composite analysis and gamma function algorithms. The reference images were then manipulated from 1 to 5 mm and 1 to 5 degree to evaluate transitional and rotational displacements. In order to extract more information from the gamma function, an extra sentence was added to the Composite analysis and Gamma function algorithms to find the overdose/lowerdose areas between evaluated and reference dose maps. The agreement percentages between two dose maps compared were generally larger for the composite analysis than those obtained from gamma function analysis. The same results were also found with the variation of Distance To Agreement (DTA) and Dose tolerance (%ΔD) criteria from 1 to 4 pixels and 1 to 3% deviation from the reference point, respectively. It sounds that the agreement percentage obtained from the composite algorithm is closer to the idea of two-dimensional dose verification proposed protocol proposed by van Dyk. However, the composite model only displays the passed or failed regions of dose maps, while the gamma function provides more information about the agreeing and disagreeing regions of compared maps. The Gamma function algorithm enables to generate more information and details compared to Composite algorithm. This algorithm can also be upgraded with an extra sentence to recognize overdose/lowerdose regions.

Evaluation of dose distribution algorithms sensitivity for a range of random/systematic transitional and rotational displacement occurred in twodimensional dose map comparisons Keywords:

Composite analysis , gamma function , Distance To Agreement , Dose tolerance