Caren van Roekel

30 Chapter 2 4.3. Lung shunt calculation Lung shunting is caused by arteriovenous anastomoses or shunts in the liver parenchyma or in a tumor. Excessive activity deposition in the lungs can result in radiation pneumonitis after radioembolization. Based on experience with external beam radiation therapy (EBRT), the highest tolerable lung shunt was defined as 30 Gy after a single treatment and a cumulative dose of 50 Gy after repeated treatments (2). The lung shunt fraction (LSF) is defined as: = √ ∗ √ ∗ ) + √ ∗ = 0.2024 ∗ ℎ ℎ ( ) 0,725 ∗ ℎ ( ) 0,425 ( ) = ( − 0,2) + ( + ) ( ) = ( ( ) ∗ ( )) 50 ( ) = ( ) ( ) ( ) ( ) ⁄ ( ) = ( ) ∗ ([ ∗ ( )] + ( )) 49,670 ∗ (1 − ℎ ) ( ) = ℎ ( ) ∗ 3780 ( ) (1, 46). Planar imaging can be used to calculate the lung shunt after administration of 99m Tc-MAA (Figure 5). However, Elschot et al. and Yu et al. have demonstrated that the lung absorbed doses are significantly overestimated by pretreatment 99m Tc-MAA imaging (53, 55). FIGURE 5. Figure 5 shows a planar scan with lung and liver ROIs to calculate lung shunt. In this example, there was visually no lung shunt and calculation showed 9%.