Statistical evaluation of dosimetric differences changes between the Modified Batho's density correction method and the Anisotropic Analytical Algorithm for clinical practice

Abstract

Purpose: The aim of this work was to assess and to quantify, for clinical practice, the differences in computed doses using two types of dose calculation algorithm for the heterogeneity correction including target volumes and organs at risk (OARs).

Methods: 35 patients having lung, breast, spine, head & neck, brain and pelvic tumors, were studied. For each patient, 2 treatment plans were generated. In plan 1, the dose was calculated using the Modified Batho's (MB) density correction method integrated in the Pencil Beam Convolution algorithm. In plan 2, the dose was calculated using the Anisotropic Analytical Algorithm (AAA). To compare the two plans a dosimetric analysis was carried out including cumulative and differential dose volume histograms (DVH), coverage index, and conformity index. Wilcoxon signed rank and Spearman’s tests were used to calculate p-values and correlation coefficients (r), respectively. Bootstrap simulation with 1000 random samplings was used to calculate the 95% confidence interval (95% CI).

Results: The analysis of DVH showed that the AAA method calculated significantly higher doses for OARs for all cancer sites and lower doses for target volumes, especially for targets located in lung, with p < 0.05. The data demonstrated a strong correlation between MB and AAA for all cancer sites with r > 0.9.

Conclusion: This study confirms that using the AAA integrated into Eclipse^® TPS, the calculated dose will be increased to OARs, and reduced to target volumes. Thus, when changing from the MB algorithm to AAA, attention should be paid to avoid any bias of over/under estimating the dose given by AAA and to hold discussions between physicists and oncologists regarding any necessary modification in the prescription method.