TheraSphere® For Treatment of Metastases in Liver

This study will acquire imaging information from 3-5 patients that will demonstrate feasibility of future implementation of personal dosimetry-based treatment planning for Trans-arterial Radio-embolization (TARE).

TARE therapy of liver neoplasia using 90Y-theraspheres has a long history. The device is FDA approved for the treatment of hepatocellular carcinoma, but has been used extensively for treatment of secondary liver neoplasia, including metastatic colorectal lesions under Humanitarian Device Exemption protocols such as this one.

As a targeted radioactive therapy, the current TARE implementation suffers from a lack of efficiency characteristic of radiopharmaceutical therapy (RPT) in general; namely, that the activity determined to treat the patient is not optimized according to normal organ tolerated absorbed dose and tumor efficacy thresholds. The amount of activity to be administered is determined from volumetrics established from associated imaging, either MRI or X-ray CT, where the total volume of irradiated tissue is considered as irrigated by the artery selected for administration, including both tumor and normal organ tissue. From this volume determination, the activity necessary to deliver an average pre-determined safe absorbed dose (120 Gy) to the entire irradiated region is calculated and administered.

In RPT, in the theranostic paradigm, a pre-therapeutic, or surrogate, quantity of activity is administered to the patient; 3D imaging (SPECT/CT or PET/CT) is then acquired at several time points and the individual patient's pharmacokinetics are determined, the normal organ and tumor dosimetry are performed and the optimal administered activity calculated that will deliver safe and efficacious treatment for the individual patient is determined, generally limited by the normal organ at risk maximum tolerated dose.

TARE presents a number of unique characteristics that enable a simpler version of this approach than is typical for most RPT. The method of administration means that only the normal liver and lungs need to be considered as potential organs at risk as the microspheres embolize and do not circulate systemically; the lack of associated photons in the 90Y decay chain means that a simple activity-to-dose-rate conversion can be used; the embolization means that only a single imaging time point is necessary as there is no redistribution of activity over time and the dose rate is converted to absorbed dose using the physical decay parameters of 90Y. These natural simplifications are already exploited in the current volumetric paradigm, where a 99mTc-macro albumin aggregate (MAA) surrogate and planar imaging are used to determine the fraction of total activity that is shunted to the lung and where a derived conversion factor is used to convert activity to absorbed dose.

The technical complication in TARE is that the surrogate (99mTc-MAA) has a different nature from the therapeutic device (90Y-theraspheres), and thus the reliability of the predictive quality of the surrogate is disputed. However, with precise and advanced imaging reconstruction and dosimetry the investigators have shown the ability to accurately and precisely predict normal liver and tumor average 90Y-therasphere uptake and absorbed dose from 99mTc-MAA.

This protocol seeks to acquire the imaging information from 3-5 patients that will demonstrate feasibility of future implementation of personal dosimetry-based treatment planning for TARE. In addition to the clinical standard of care assessments: 1. a single SPECT/CT instead of the current planar image will be acquired of the surrogate 99mTc-MAA; 2. An additional single 3D image (either SPECT/CT or PET/CT, depending on machine availability) will be acquired up to 6 hours post-administration of the therapeutic 90Y-microspheres for comparison. Informed consent will be obtained.