Lung shunting and radiation pneumonitis after holmium-166 TARE: a case study.

Purpose: The assessment of the lung shunting fraction (LSF) in yttrium-90 (⁹⁰Y) or holmium-166 (¹⁶⁶Ho) transarterial radioembolization (TARE) is customary in order to reduce the risk of radiation pneumonitis (RP). Lung shunting detected through a test dose is considered a relative contraindication, and it is generally advised to keep the predicted lung dose below 30 Gy. Few cases of RP have been reported in the literature. We present two cases of RP after treatment with ¹⁶⁶Ho TARE.

Methods: Two patients with hepatocellular carcinoma received ¹⁶⁶Ho TARE, respectively as part of a clinical trial and a re-treatment according to standard clinical practise. LSF and lung dose measurements were performed both after the work-up and after the therapeutic dose using planar imaging and SPECT. At follow up, CT imaging and pulmonary evaluation including lung function testing were performed.

Results: Two patients without any pulmonary medical history received a lung dose of 13 Gy and 18 Gy due to a LSF of 9.8% and 7.1% based on SPECT after therapy. The patients showed both clinical and radiological signs of RP which resolved 3-4 months after TARE. Lung function testing showed no restriction or obstruction, but did show lowered diffusion.

Conclusion: We present two relatively mild cases of RP after ¹⁶⁶Ho TARE, with a lung dose under the advised lung dose threshold of 30 Gy. Although no definite conclusions can be drawn based on these isolated cases of RP, it warrants caution in pre-treatment dosimetry in case of objectified lung shunt.