Spect perfusion imaging versus CT for predicting radiation injury to normal lung in lung cancer patients

OBJECTIVES: In non-small cell lung cancer (NSCLC) patients, to establish whether the fractional volumes of irradiated anatomic or perfused lung differed between those with and without deteriorating lung function or radiation associated lung injury (RALI). METHODS: 48 patients undergoing radical radiotherapy for NSCLC had a radiotherapy-planning CT scan and singlephoton emission CT lung perfusion imaging ((99m)Tc-labelled macroaggregate albumin). CT defined the anatomic and the singlephoton emission CT scan (co-registered with CT) identified the perfused (threshold 20 % of maximum) lung volumes. Fractional volumes of anatomic and perfused lung receiving more than 5, 10, 13, 20, 30, 40, 50 Gy were compared between patients with deteriorating (>median decline) vs stable (<median decline) forced expiratory volume in 1 s (FEV1) and between those with and without RALI (assessed by Common Toxic Criteria for Adverse Events) radiation pneumonitis and pulmonary fibrosis scores. RESULTS: Fractional volumes of anatomic and perfused lung receiving more than 10, 13 and 20 Gy were significantly higher in patients with deteriorating vs stable FEV1 ( p = 0.005, 0.005 and 0.025 respectively) but did not differ for higher doses of radiation (>30, 40, 50 Gy). Fractional volumes of anatomic and perfused lung receiving > 10 Gy best predicted decline in FEV1 (Area under receiver operating characteristic curve (Az = 0.77 and 0.76 respectively); sensitivity/specificity 75%/81 and 80%/71%) for a 32.7% anatomic and 33.5% perfused volume cut-off. Irradiating an anatomic fractional volume of 4.7% to > 50 Gy had a sensitivity/specificity of 83%/89 % for indicating RALI (Az = 0.83). CONCLUSION: A 10–20 Gy radiation dose to anatomic or perfused lung results in decline in FEV1. A fractional anatomic volume of >5% receiving >50 Gy influences development of RALI. ADVANCES IN KNOWLEDGE: Extent of low-dose radiation to normal lung influences functional respiratory decline.