The accuracy of Acuros XB algorithm for radiation beams traversing a metallic hip implant - comparison with measurements and Monte Carlo calculations.

Jarkko Ojala,Simo Hyödynmaa,Mika Kapanen,Petri Sipilä,Maunu Pitkänen

doi:10.1120/jacmp.v15i5.4912

Abstract

In this study, the clinical benefit of the improved accuracy of the Acuros XB (AXB) algorithm, implemented in a commercial radiotherapy treatment planning system (TPS), Varian Eclipse, was demonstrated with beams traversing a high‐Z material. This is also the first study assessing the accuracy of the AXB algorithm applying volumetric modulated arc therapy (VMAT) technique compared to full Monte Carlo (MC) simulations. In the first phase the AXB algorithm was benchmarked against point dosimetry, film dosimetry, and full MC calculation in a water‐filled anthropometric phantom with a unilateral hip implant. Also the validity of the full MC calculation used as reference method was demonstrated. The dose calculations were performed both in original computed tomography (CT) dataset, which included artifacts, and in corrected CT dataset, where constant Hounsfield unit (HU) value assignment for all the materials was made. In the second phase, a clinical treatment plan was prepared for a prostate cancer patient with a unilateral hip implant. The plan applied a hybrid VMAT technique that included partial arcs that avoided passing through the implant and static beams traversing the implant. Ultimately, the AXB‐calculated dose distribution was compared to the recalculation by the full MC simulation to assess the accuracy of the AXB algorithm in clinical setting. A recalculation with the anisotropic analytical algorithm (AAA) was also performed to quantify the benefit of the improved dose calculation accuracy of type ‘c’ algorithm (AXB) over type ‘b’ algorithm (AAA). The agreement between the AXB algorithm and the full MC model was very good inside and in the vicinity of the implant and elsewhere, which verifies the accuracy of the AXB algorithm for patient plans with beams traversing through high‐Z material, whereas the AAA produced larger discrepancies.PACS numbers: 87.55.‐x, 87.55.D‐, 87.55.K‐, 87.55.kd, 87.55.Qr

Highlights

Ojala et al.: Accuracy of Acuros XB (AXB) with a hip implant expectancy has continuously increased which, in combination with improved diagnostic methods, have led to increased cancer detection rates
The phantom study The dose-to-medium converted measured values by both the Farmer ionization chamber (IC) and the IBA SFD and calculated values for both the AXB algorithm and the Monte Carlo (MC) model in both original computed tomography (CT) and artifact-corrected datasets are presented in Tables 1 and 2 and Figs. 3 and 4, respectively
The dose distributions calculated by the AXB algorithm showed small deviations, on average within 2.5%, when compared to measurements and the MC model, but the performance was considered acceptable

Summary

Introduction

Ojala et al.: Accuracy of AXB with a hip implant expectancy has continuously increased which, in combination with improved diagnostic methods, have led to increased cancer detection rates. All these factors together have resulted in increased number of radiotherapy patients having prosthetic devices implanted in their bodies.[1,2] There are three different types of hip implant materials. The most common alloy contains cobalt, chromium, and molybdenum, but there are implants made of titanium-aluminum-vanadium alloy and stainless steel Common for all these high-density and atomic number (Z) material combinations is the corrosion and fatigue resistance and mechanical strength. The extended HU value scale has been developed to allow the differentiation of high-Z materials from tissues, and even identify various metals and alloys used in implants.[4,5]

Methods

Results

Discussion

Conclusion