The Effect of Contrast Agents on Dose Calculations of Volumetric Modulated Arc Radiotherapy Plans for Critical Structures

A A Elawadi,Reham Algendy,Safa Almohsen,Andrew Nisbet,Hossam Alassaf,Reham A Mohamed,Mukhtar Alshanqity,Hosam Allazkani

doi:10.3390/app11188355

Abstract

Radiotherapy dose calculation requires accurate Computed Tomography (CT) imaging while tissue delineation may necessitate the use of contrast agents (CA). Acquiring these two sets is a common practice in radiotherapy. This study aims to evaluate the effect of CA on the dose calculations. Two hundred and twenty-six volumetric modulated arc therapy (VMAT) patients that had planning CT with contrast (CCT) and non-contrast CT (NCCT) of different cancer sites (e.g., brain, head, and neck (H&N), chest, abdomen, and pelvis) were evaluated. Treatment plans were recalculated using CCT, then compared to NCCT. The variation in Hounsfield units (HU) and dose distributions for critical structures and target volumes were analyzed using mean HU, mean and maximum relative dose values, D2%, D98%, and 3D gamma analysis. HU variations were statistically significant for most structures. However, this was not clinically significant as the difference in mean HU values was within 30 HU for soft tissue and 50 HU for lungs. Variation in target volumes’ D2% and D98% were insignificant for all sites except brain and nasopharynx. Dose maximum differences were within 2% for the majority of critical structures and target volumes. 3D gamma analysis results revealed that majority of plans satisfied the 2% and 2 mm criteria. CCT may be acquired for VMAT radiotherapy planning purposes instead of NCCT, since there is no clinically significant difference in dose calculations based on either image set.

Highlights

In clinical radiation therapy, the accuracy of radiotherapy treatment planning and dose calculations requires high-quality medical images to delineate and define planning target volumes (PTV) and critical structures of interests, or organs at risk (OAR)
Computed Tomography (CT) data is essential for the treatment planning dose calculation algorithms, as these are dependent on the electron density information embedded in CT images
The longitudinal study presented in this work aims to answer the question: Is CT with contrast (CCT) imaging an acceptable alternative to non-contrast CT (NCCT) for TPS dose calculations? This will be carried out by investigating and evaluating the effect of the CCT on the treatment planning dose calculations for all concerned critical structures and target volumes using volumetric modulated arc therapy (VMAT) technique for different anatomical sites: brain, Head and Neck (H&N), chest, abdomen, and pelvis

Summary

Introduction

The accuracy of radiotherapy treatment planning and dose calculations requires high-quality medical images to delineate and define planning target volumes (PTV) and critical structures of interests, or organs at risk (OAR). CT is the most suitable modality for radiotherapy treatment planning and dose calculation algorithms due to its geometrical accuracy and tissue density information. CT data is essential for the treatment planning dose calculation algorithms, as these are dependent on the electron density information embedded in CT images. CT, may suffer imaging artifacts due to the presence of high-density materials such as dental fillings, prosthetic implants, and contrast agents. The latter are iodine-based agents introduced intentionally to opacify vascular structures and other organs. Contrast agents may alter the apparent Hounsfield Unit (HU) values

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