Radioembolization of Hepatic Lesions from a Radiobiology and Dosimetric Perspective

Abstract

Radioembolization (RE) of liver cancer with 90Y-microspheres has been applied in the last two decades with notable responses and acceptable toxicity. Two types of microspheres are available, glass and resin, the main difference being the activity/sphere. Generally, administered activities are established by empirical methods and differ for the two types. Treatment planning based on dosimetry is a prerogative of few centers, but has notably gained interest, with evidence of predictive power of dosimetry on toxicity, lesion response, and overall survival (OS). Radiobiological correlations between absorbed doses and toxicity to organs at risk, and tumor response, have been obtained in many clinical studies. Dosimetry methods have evolved from the macroscopic approach at the organ level to voxel analysis, providing absorbed dose spatial distributions and dose–volume histograms (DVH). The well-known effects of the external beam radiation therapy (EBRT), such as the volume effect, underlying disease influence, cumulative damage in parallel organs, and different tolerability of re-treatment, have been observed also in RE, identifying in EBRT a foremost reference to compare with. The radiobiological models – normal tissue complication probability and tumor control probability – and/or the style (DVH concepts) used in EBRT are introduced in RE. Moreover, attention has been paid to the intrinsic different activity distribution of resin and glass spheres at the microscopic scale, with dosimetric and radiobiological consequences. Dedicated studies and mathematical models have developed this issue and explain some clinical evidences, e.g., the shift of dose to higher toxicity thresholds using glass as compared to resin spheres. This paper offers a comprehensive review of the literature incident to dosimetry and radiobiological issues in RE, with the aim to summarize the results and to identify the most useful methods and information that should accompany future studies.

The conflict between treatment optimization and registration of radiopharmaceuticals with fixed activity posology in oncological nuclear medicine therapy

“…As in external beam radiotherapy, simulation is possible using a nontherapeutic but radioactive biodegradable simulator ( 99m Tc albumin macroaggregates). Radiationinduced toxicity to normal liver tissue is a considerable lifethreatening risk associated with this treatment [20,21]. Because dosimetry in liver radioembolization involves less work and this treatment is associated with an important risk, the number of centres in Europe currently adopting dosimetric planning of liver radioembolization is increasing (EANM survey 22]).…”

90Y Hepatic Radioembolization: An Update on Current Practice and Recent Developments

“…Nonetheless, the partition model based on pretreatment 99m Tc-MAA SPECT/CT should be preferred by nuclear physicians and interventional radiologists, because lesionbased dosimetry on pretreatment 99m Tc-MAA SPECT/CT has been shown to correlate with response and survival (39)(40)(41)(42)(43). The aim of radioembolization is to deliver the highest possible absorbed dose to tumor cells ("tumor dose") in order to induce apoptosis and tumor load reduction.…”

Impact of SPECT corrections on 3D‐dosimetry for liver transarterial radioembolization using the patient relative calibration methodology

“…16 An optimal treatment planning should include 3D voxelbased dosimetry, accounting for nonuniform absorbed dose distributions when studying dose-effect correlations. 9,[17][18][19][20][21][22][23] Image-based 3D dosimetry can be performed in several ways: direct Monte Carlo (MC) simulation, which is considered the gold standard; 9,[24][25][26][27][28][29][30] convolution calculations by voxel S-values, reliable in nearly uniform density tissue; 19,[31][32][33][34][35][36] local energy deposition method. 18,20,[36][37][38][39] Activity distribution quantification by SPECT is the major concern, due to physical and clinical degrading factors of the images.…”