Lung Dose Measured on Postradioembolization <sup>90</sup>Y PET/CT and Incidence of Radiation Pneumonitis
Martina Stella, Rob van Rooij, Marnix G. E. H. Lam, Hugo W. A. M. de Jong, Arthur J. A. T. Braat
Abstract
Radiation pneumonitis is a rare but possibly fatal side effect of Yttrium-90 (<sup>90</sup>Y) radioembolization. It may occur 1 to 6 months after therapy, in case a significant part of the <sup>90</sup>Y microspheres shunt to the lungs. In current clinical practice, a predicted value of lung dose greater than 30Gy is considered a criterion to exclude patients from treatment. However, contrasting findings regarding the occurrence of radiation pneumonitis and lung dose were previously reported in literature. In this study, the relationship between the lung dose value and the eventual occurrence of radiation pneumonitis after <sup>90</sup>Y radioembolization was investigated. <b>Methods</b>: A total of 317 <sup>90</sup>Y liver radioembolization procedures performed during an 8-years period (Feb.2012–Sep.2020) were retrospectively analyzed. Predicted lung mean dose using <sup>99m</sup>Tc-MAA planar scintigraphy (LMD<sub>MAA</sub>) acquired during the planning phase and left lung mean dose (LMD<sub>Y-90</sub>) using the <sup>90</sup>Y PET/CT acquired after the treatment were calculated. For the lung dose computation, it was chosen to use the left lung as representative lung volume, to compensate for the scatter from the liver moving in the cranial-caudal direction due to breathing and mainly affecting the right lung. <b>Results</b>: Two hundred and seventy-two patients underwent <sup>90</sup>Y procedures, of which 63% performed with glass microspheres and 37% with resin microspheres. Median injected activity was 1974MBq (range: 242-9538MBq). Median LMD<sub>MAA</sub> was 3.5Gy (range: 0.2–89.0Gy). For 14 procedures LMD<sub>MAA</sub> was >30Gy. Median LMD<sub>Y-90</sub> was 1Gy (range: 0.0–22.1Gy). No patients had a LMD<sub>Y-90</sub> >30Gy. Of the three patients with a LMD<sub>Y-90</sub> >12Gy, two patients (LMD<sub>Y-90</sub> = 22.1Gy, LMD<sub>MAA</sub> = 89Gy and LMD<sub>Y-90</sub> = 17.7Gy, LMD<sub>MAA</sub> = 34.1Gy, respectively) developed radiation pneumonitis and consequently died. A third patient with a LMD<sub>Y-90</sub> equal to 18.4Gy (LMD<sub>MAA</sub> = 29.1Gy) died 2 months after treatment, before imaging evaluation, due to progressive disease. <b>Conclusion</b>: The occurrence of radiation pneumonitis as a consequence of lung shunt following <sup>90</sup>Y radioembolization is rare (<1 %). No radiation pneumonitis developed in cases with a measured LMD<sub>Y-90</sub> lower than 12Gy.