Radiation Pneumonitis after Yttrium-90 Radioembolization: A Systematic Review

Purpose: To evaluate the available evidence of lung dosimetry and radiation pneumonitis (RP). Materials and Methods: The guideline regarding the maximum tolerated lung dose for yttrium-90 (90Y) radioembolization is an expert opinion (Level 5 evidence) based on a case series of 5 patients and recommends keeping the absorbed radiation dose to the lungs below 30 Gy per treatment and 50 Gy in a lifetime to prevent RP. The current understanding of the risks of RP is minimal despite its debilitating nature and high mortality rate. A systematic literature review was conducted in PubMed, Embase, Cochrane database, and Google Scholar for reported cases of RP. A database of 48 RP cases was compiled and analyzed. Results: Thirty patients were treated with resin and 16 patients with glass 90Y microspheres. The treatment device was not reported in 2 cases. RP developed a median of 3 months after radioembolization. The mortality rate was 40%. The hepatopulmonary shunt was not significantly different between the glass and the resin groups (21.2% [SD +/- 14%] vs 15.6% [SD +/- 7.5%]; P = .24). The radiation dose to the lungs was significantly higher in patients treated with glass compared with those with resin 90Y microspheres (41.4 Gy [SD +/- 18.4] vs 21.5 Gy [SD +/- 9.9]; P = .003). Conclusions: The dose toxicity threshold for resin microspheres is lower than that of glass microspheres. The established 30-Gy dose limit may not be uniformly applicable in all cases and for both devices. The maximum tolerable lung doses should be reevaluated, and the shortcomings of the hepatopulmonary shunt calculation need to be corrected.