Purpose: Therapeutic radiation doses for thoracic tumors are significantly restricted to decrease the risk of nontumor tissue damage, yet radiation-induced lung injury (RILI) still occurs in over 1/3 of thoracic radiation treatment cases. Although RILI can be clinically monitored using pulmonary function measurements, the regional functional effects of the injury are not well understood. Hyperpolarized 3He magnetic resonance imaging provides measurements of regional lung function and structure with high spatial and temporal resolution; the authors use this tool longitudinally for the first time in seven subjects after clinical diagnosis of RILI in order to better understand regional changes in lung function and structure post-RILI.
Methods: All subjects underwent spirometry, plethysmography, and MRI at 3.0 T 35.1 +/- 12.2 weeks after radiation therapy commenced. Thoracic 1H, static 3He ventilation, and 3He diffusion-weighted images were acquired to generate the 3He apparent diffusion coefficient (ADC) and 3He percent ventilated volume (PVV). Four subjects returned 22.0 +/- 0.8 weeks after baseline imaging for follow-up spirometry and 3He MRI measurements of ADC and PVV.
Results: At baseline, PVV was significantly different (p = 0.025) and lower in the ipsilateral diseased lung (55 +/- 29%) compared to the contralateral nondiseased lung (88 +/- 5%). Longitudinally, significant increases were observed for 3He MRI PVV (16% +/- 6%, p = 0.012) and 3He MRI ADC (0.02 +/- 0.01 cm2/s, p = 0.003) in the contralateral lung only, in the four subjects who returned for follow-up, while no changes in the ipsilateral lung were reported.
Conclusions: Hyperpolarized 3He MRI was well tolerated in all subjects with moderate to severe RILI. Functional improvements and microstructural changes were observed in the contralateral lung, while the ipsilateral lung remained stable, suggesting that functional compensatory changes may have occurred in the contralateral lung due to ipsilateral lung radiation-induced injury.