Effect of contrast‐enhanced CT scans on heterogeneity corrected dose computations in the lung

Nichola A Burridge,Paul A Burt,Carl G Rowbottom

doi:10.1120/jacmp.v7i4.2240

Nichola A Burridge, Paul A Burt + Show 1 more

Open Access

https://doi.org/10.1120/jacmp.v7i4.2240

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Abstract

The aim of this study was to investigate and, if possible, compensate for the effect of intravenous contrast‐enhanced CT scans on the treatment planning dose distributions for lung patients. The contrast and noncontrast CT scans of 3 patients were registered, and the effect of contrast on the Hounsfield units (HU) was assessed. The effect of contrast was then simulated in the CT scans of 18 patients receiving radiotherapy of the lung by modification of the CT numbers for relevant sections of noncontrast‐enhanced CT scans. All treatment planning was performed on the Pinnacle 3 planning system. The dose distributions computed from simulated contrast CT scans were compared to the original dose distributions by comparison of the monitor units (MUs) for each beam in the treatment plan required to deliver the prescribed dose to the isocenter as well as a comparison of the total MUs for each patient, a percentage change in required MUs being equivalent to a percentage change in the dose. A correction strategy to enable the use of contrast‐enhanced CT scans in treatment planning was developed, and the feasibility of applying the strategy was investigated by calculating dose distributions for both the original and simulated contrast CT scans. A mean increase in the overall patient MUs of 1.0 ± 0.8% was found, with a maximum increase of 3.3% when contrast was simulated on the original CT scans. The simulated contrast scans confirmed that the use of contrast‐enhanced CT scans for routine treatment planning would result in a systematic change in the dose delivered to the isocenter. The devised correction strategy had no clinically relevant effect on the dose distribution for the original CT scans. The application of the correction strategy to the simulated contrast CT scans led to a reduction of the mean difference in the overall MUs to 0.1 ± 0.2% compared to the original scan, demonstrating that the effect of contrast was eliminated with the correction strategy. This work has highlighted the problems associated with using contrast‐enhanced CT scans in heterogeneity corrected dose computation. Contrast visible in the CT scan is transient and should not be accounted for in the treatment plan. A correction strategy has been developed that minimizes the effect of intravenous contrast while having no clinical effect on noncontrast CT scans. The correction strategy allows the use of contrast without detriment to the treatment plan.PACS number: 87.53.Tf

Highlights

Three-dimensional conformal radiotherapy has led to a more accurate delivery of radiotherapy and the possibility for dose escalation and lower toxicity
If this is not corrected for in the dose calculation, the delivered dose can be as much as 15% greater than expected.[3] if the CT dataset is an inaccurate representation of the tissue density due to artifacts resulting from markers, prosthetic hips, or contrast media, calculation errors may be introduced when a heterogeneity correction is applied.[4]
Because the soft tissue showed no significant increase in Hounsfield units (HU) in the contrast-enhanced scan, the soft tissue density of the radiotherapy treatmentplanning (RTP) scan was not altered in the investigation

Summary

Introduction

Three-dimensional conformal radiotherapy has led to a more accurate delivery of radiotherapy and the possibility for dose escalation and lower toxicity. The accurate definition of the GTV in this case is important in minimizing the overall treatment volume. Modern 3D treatment-planning systems use the density information within the CT scan to account for the different tissue densities within the body This is to ensure that the dose calculated will be a true representation of the dose distribution within the body. The physical density allows the attenuation of the fluence to be based on the mass attenuation of the specific material within a given voxel. This correction is important in lung cancer treatment planning due to the low density of lung tissue. If the CT dataset is an inaccurate representation of the tissue density due to artifacts resulting from markers, prosthetic hips, or contrast media, calculation errors may be introduced when a heterogeneity correction is applied.[4]

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