Feasibility of imaging ⁹⁰Y microspheres at diagnostic activity levels for hepatic radioembolization treatment planning

Abstract

Purpose Prior to 90Y hepatic radioembolization, a dosage of 99mTc‐macroaggregated albumin (99mTc‐MAA) is administered to simulate the distribution of the 90Y‐loaded microspheres. This pretreatment procedure enables lung shunt estimation, detection of potential extrahepatic depositions, and estimation of the intrahepatic dose distribution. However, the predictive accuracy of the MAA particle distribution is often limited. Ideally, 90Y microspheres would also be used for the pretreatment procedure. Based on previous research, the pretreatment activity should be limited to the estimated safety threshold of 100 MBq, making imaging challenging. The purpose of this study was to evaluate the quality of intra‐ and extrahepatic imaging of 90Y‐based pretreatment positron emission tomography/computed tomography (PET/CT) and quantitative single photon emission computed tomography (SPECT)/CT scans, by means of phantom experiments and a patient study. Methods An anthropomorphic phantom with three extrahepatic depositions was filled with 90Y chloride to simulate a lung shunt fraction (LSF) of 5.3% and a tumor to nontumor ratio (T/N) of 7.9. PET /CT (Siemens Biograph mCT) and Bremsstrahlung SPECT/CT (Siemens Symbia T16) images were acquired at activities ranging from 1999 MBq down to 24 MBq, representing post‐ and pretreatment activities. PET/CT images were reconstructed with the clinical protocol and SPECT/CT images were reconstructed with a quantitative Monte Carlo‐based reconstruction protocol. Estimated LSF, T/N, contrast to noise ratio of all extrahepatic depositions, and liver parenchymal and tumor dose were compared with the phantom ground truth. A clinically reconstructed SPECT/CT of 150 MBq 99mTc represented the current clinical standard. In addition, a 90Y pretreatment scan was simulated for a patient by acquiring posttreatment PET/CT and SPECT/CT data with shortened acquisition times. Results At an activity of 100 MBq 90Y, PET/CT overestimated LSF [+10 percentage point (pp)], underestimated liver parenchymal dose (−3 Gy/GBq), and could not detect the extrahepatic depositions. SPECT/CT more accurately estimated LSF (−0.7 pp), parenchymal dose (−0.3 Gy/GBq) and could detect all three extrahepatic depositions. 99mTc SPECT/CT showed similar accuracy as 90Y SPECT/CT (LSF: +0.2 pp, parenchymal dose: +0.4 Gy/GBq, all extrahepatic depositions visible), although the noise level in the liver compartment was considerably lower for 99mTc SPECT/CT compared to 90Y SPECT/CT. The patient’s SPECT/CT simulating a pretreatment 90Y procedure accurately represented the posttreatment 90Y microsphere distribution. Conclusions Quantitative SPECT/CT of 100 MBq 90Y could accurately estimate LSF, T/N, parenchymal and tumor dose, and visualize extrahepatic depositions.

Comparison of the Biograph Vision and Biograph mCT for quantitative 90Y PET/CT imaging for radioembolisation

“…The higher sensitivity of new digital PET/CT scanners may open doors to new applications. Recently, we proposed the use of a low dosage of 90 Y microspheres (~100 MBq) for a pretreatment radioembolisation procedure for therapy planning purposes [11,12]. Currently, pretreatment radioembolisation procedures are performed with technetium-99m ( 99m Tc)-labelled macro aggregated albumin (MAA).…”

“…A safe dosage for the pretreatment 166 Ho microsphere procedure is 250 MBq [17,18]. Inasmuch as the total energy absorbed per becquerel is higher for 90 Y than for 166 Ho, this dosage would translate to 100 MBq of 90 Y to avoid unintended radiation damage [11,12,19].…”

Nuclear imaging for improved radioembolization treatment planning

“…This is known to cause a positive bias in the reconstruction, especially in parts of low counts (e.g. the lungs), resulting in an overestimation of the LSF [139][140][141]. LSD was higher for the 90 Y glass microspheres than for the 90 Y resin microspheres because of the higher administered activity.…”

“…The higher sensitivity of new digital PET/CT scanners may open doors to new applications. Recently, we proposed the use of a low dosage of 90 Y microspheres (~100 MBq) for a pre-treatment radioembolization procedure for therapy planning purposes [140,141]. Currently, pre-treatment radioembolization procedures are performed with technetium-99m ( 99m Tc) labelled macroaggregated albumin (MAA).…”

“…A safe dosage for the pre-treatment 166 Ho microsphere procedure is 250 MBq [144,145]. Inasmuch as the total energy absorbed per Bq is higher for 90 Y than for 166 Ho, this dosage would translate to 100 MBq of 90 Y to avoid unintended radiation damage [29,140,141].…”