Caren van Roekel

270 Chapter 10 resulting in more homogeneous distribution of the microspheres in the tumors and healthy liver tissue, regardless of the number of microspheres infused. With 90 Y glass microspheres, it is possible to increase or decrease the number of microspheres per dose, by varying the specific activity: the twelve-day shelf-life post-calibration allows for a wide range. At 16 days post-calibration, the activity per microsphere is only 70 Bq, whereas at four days post-calibration, the activity per sphere is 1532 Bq (76). In a preclinical study, the risk of complications to the healthy liver tissue was low up to eight days post-calibration (76). There are no guidelines on when to use which type of microsphere. For so- called radiation segmentectomy (i.e. a high radiation dose to one or two segments), the risk of stasis should be kept in mind, which is higher with a high number of microspheres injected in a limited target volume. Therefore, 90 Y glass microspheres are the type of choice, which was proven to be safe and effective for this purpose (77). Since conclusive comparative data is lacking, no other recommendations can be provided. Which treatment planning methods are currently used? For resin microspheres, the so-called body surface area (BSA) method is mostly used. This method adjusts the prescribed activity for the patient’s BSA and the fractional tumor burden. The formula for the injected activity (IA) is: = √ ∗ √ ∗ ) + √ ∗ = 0.2024 ∗ ℎ ℎ ( ) 0,725 ∗ ℎ ( ) 0,425 ( ) = ( − 0,2) + ( + ) ( ) = ( ( ) ∗ ( )) 50 ( ) = ( ) ( ) ( ) ( ) ⁄ ( ) = ( ) ∗ ([ ∗ ( )] + ( )) 49,670 ∗ (1 − ℎ ) (54, 78). The prescribed activity is reduced in case of lung shunting (79). The BSA method assumes a correlation between BSA and liver weight. However, this is not necessarily true and may result in an undertreatment of small patients with large livers, and an overtreatment of large patients with small livers. Another limitation of this method is that it does not take the degree of tumor uptake into account (54, 78). For glass microspheres, the Medical Internal Radiation Dose (MIRD) method was developed (72). The prescribed activity is determined by calculating the activity required to achieve a desired average absorbed dose in the perfused or target volume (i.e. between 80-150 Gy). The MIRD method assumes a homogenous