SU-E-T-412: Effect of Ingested Contrast Media On Dose Reporting for GI Malignancies Comparing Multiple Dose Calculation Algorithms

Authors


Abstract

Purpose:

Varian AcurosXB calculates dose-to-medium (Dm) as well as the clinically prevalent dose-to-water (Dw). For abdominal malignancies, ingested contrast is used during simulation to delineate the treatment volume (TV) or outline the organ at risk (OAR), but this effect is transient. The purpose of this study is to evaluate the effect of contrast media on dose reporting using AAA, Acuros(Dw) and Acuros(Dm).

Methods:

Ingested contrast was contoured and either “forced” to water density or left uncorrected. Six plans were generated for 26 patients in Eclipse using identical leaf motions and MU values. The Acuros(Dm) forced density plan was our gold standard.

Results:

For 6MV plans where contrast was in the TV, AAA underrepresented the dose to the contrast region by 3.91%±3.08% (p=0.037) and 2.51%±1.25% (p=0.005) for unforced and forced densities respectively. Acuros(Dw) plans with unforced and forced densities overrepresented the dose by 2.97%±1.23% (p=.001) and 1.66%±0.24% (p=2.5e-4). For 6MV plans where contrast was an OAR, all plans were not statistically significantly different from the Acuros(dm) plan. For 15MV plans where contrast was in the TV, AAA overrepresented the dose to the contrast region by 0.73%±0.49% (p=0.015) and 0.95%±0.39% (p=0.002) for unforced and forced densities respectively. Acuros(Dw) plans with unforced and forced densities overrepresented the dose by 2.15%±1.20% (p=0.009) and 1.00%±0.63% (p=0.007). Plans calculated with an unforced density in Acuros dm consistently showed the closest agreement to the Acuros(Dm) plan calculated with forced densities. For all 26 plans, the difference was -0.25%±0.84%.

Conclusion:

The appearance of contrast media will impact dose calculation. More clinical studies are needed to determine if dw and dm reporting shows any clinical significance. Care should be taken to force the density of contrast media in the GI region to a suitable value. As a fail safe condition, the use of Acuros(Dm) is recommended for these treatments.

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