Radiation-induced lung injury - what do we know in the era of modern radiotherapy?

Radiation-induced lung injury (RILI) that is usually divided into an early radiation-induced pneumonitis (RIP) and late chronic radiation-induced lung fibrosis (RILF) remains a clinically significant toxicity in radiation oncology. Thus, a thorough understanding of underlying molecular mechanisms and risk factors is crucial. This review, focused on patients treated with modern radiotherapy (RT) techniques, describes the different clinical presentations of RIP, with most typical imaging findings and usefulness of pulmonary function tests and laboratory assessment in differential diagnosis. The most critical patient- and treatment-related predictors are summarized and discussed - age and sex, comorbidities, tumour characteristics, concomitant treatment, and RT-plan parameters. The conventional grading scales and contemporary approach to quantitative assessment (radiomics, CT density changes) is described as well as treatment methods.

Normal Lung Tissue CT Density Changes after Volumetric-Arc Radiotherapy (VMAT) for Lung Cancer.

Radiation-induced lung injury remains a significant toxicity in thoracic radiotherapy. Because a precise diagnosis is difficult and commonly used assessment scales are unclear and subjective, there is a need to establish quantitative and sensitive grading methods. The lung tissue density change expressed in Hounsfield units (HUs) derived from CT scans seems a useful numeric surrogate. The study aimed to confirm a dose-response effect on HU value changes (ΔHU), their evolution in time, and the impact of selected clinical and demographic factors. We used dedicated, self-developed software to register and analyze 120 pairs of initial and follow-up CT scans of 47 lung cancer patients treated with dynamic arc radiotherapy. The differences in HU values between CT scans were calculated within discretized dose-bins limited by isodose lines. We have proved the dose-effect relationship, which is well described with a sigmoid model. We found the time evolution of HU changes to suit a typical clinical presentation of radiation-induced toxicity. Some clinical factors were found to correlate with ΔHU degree: planning target volume (PTV), V35 in the lung, patient's age and a history of arterial hypertension, and initial lung ventilation intensity. Lung density change assessment turned out to be a sensitive and valuable method of grading post-RT lung toxicity.