Radiopathology of the lung: experimental and clinical observations

Evolving Role of Novel Quantitative PET Techniques to Detect Radiation-Induced Complications

Radiation-induced normal tissue toxicities vary in terms of pathophysiologic determinants and timing of disease development, and they are influenced by the dose and radiation volume the critical organs receive, and the radiosensitivity of normal tissues and their baseline rate of cell turnover. Radiation-induced lung injury is dose limiting for the treatment of lung and thoracic cancers and can lead to fibrosis and potentially fatal pneumonitis. This article focuses on pulmonary and cardiovascular complications of radiation therapy and discusses how PET-based novel quantitative techniques can be used to detect these events earlier than current imaging modalities or clinical presentation allow.

Radiotherapy toxicity

Radiotherapy is used in >50% of patients with cancer, both for curative and palliative purposes. Radiotherapy uses ionizing radiation to target and kill tumour tissue, but normal tissue can also be damaged, leading to toxicity. Modern and precise radiotherapy techniques, such as intensity-modulated radiotherapy, may prevent toxicity, but some patients still experience adverse effects. The physiopathology of toxicity is dependent on many parameters, such as the location of irradiation or the functional status of organs at risk. Knowledge of the mechanisms leads to a more rational approach for controlling radiotherapy toxicity, which may result in improved symptom control and quality of life for patients. This improved quality of life is particularly important in paediatric patients, who may live for many years with the long-term effects of radiotherapy. Notably, signs and symptoms occurring after radiotherapy may not be due to the treatment but to an exacerbation of existing conditions or to the development of new diseases. Although differential diagnosis may be difficult, it has important consequences for patients.

Animal models and medical countermeasures development for radiation-induced lung damage: report from an NIAID Workshop

Since 9/11, there have been concerns that terrorists may detonate a radiological or nuclear device in an American city. Aside from several decorporation and blocking agents for use against internal radionuclide contamination, there are currently no medications within the Strategic National Stockpile that are approved to treat the immediate or delayed complications resulting from accidental exposure to radiation. Although the majority of research attention has focused on developing countermeasures that target the bone marrow and gastrointestinal tract, since they represent the most acutely radiosensitive organs, individuals who survive early radiation syndromes will likely suffer late effects in the months that follow. Of particular concern are the delayed effects seen in the lung that play a major role in late mortality seen in radiation-exposed patients and accident victims. To address these concerns, the National Institute of Allergy and Infectious Diseases convened a workshop to discuss pulmonary model development, mechanisms of radiation-induced lung injury, targets for medical countermeasures development, and end points to evaluate treatment efficacy. Other topics covered included guidance on the challenges of developing and licensing drugs and treatments specific to a radiation lung damage indication. This report reviews the data presented, as well as key points from the ensuing discussion.

Chronic diffuse interstitial fibrosis of the lung in uranium miners

Many uranium miners have been disabled by and died of pulmonary fibrosis that was not recognized as an occupational disease. A review of animal studies, complications from whole body irradiation, pulmonary function, and mortality studies of uranium miners led us to suspect radiation-induced chronic diffuse interstitial fibrosis in miners who had inhaled excessive radon progeny. A selected group of uranium miners (22) with severe respiratory disease (but no rounded nodules in chest films) were studied. Lung tissue from five disclosed severe diffuse interstitial fibrosis, with "honeycomb lung" in all. Some also had small anthrasilicotic nodules and birefringent crystals. Although quartz crystals probably contributed, we concluded that the predominant injurious agent in these cases was alpha particles from radon progeny. This disease, after a long latent period, usually results in pulmonary hypertension, shortness of breath, and death by cardiopulmonary failure.

Effect of irradiated volume on lung damage in pigs

BACKGROUND AND PURPOSE

The volume dependence of radiation induced lung damage is of important clinical concern. The aim of the present study was to investigate the effect of irradiated volume on radiation pneumonitis and lung fibrosis in pigs after fractionated irradiation.

MATERIALS AND METHODS

Twenty-five animals were irradiated with 10 x 14 cm2 fields to the whole right lung (about 530 cm3), while 19 animals received irradiation only to the lower part of the right lung (10 x 8 cm2 fields, about 260 cm3). The irradiations were given in five fractions over 5 days with total doses ranging from 14.3-38.0 Gy (whole lung) or 21.3-31.2 Gy (half lung) using a 60cobalt unit and an isocentric technique. Early lung damage was assessed during the first 8 weeks after the start of treatment by weekly chest radiographs and by twice weekly determinations of the breathing rate in resting animals. Fibrosis was quantified at autopsy (after 8 weeks or after 5-8 months) by histological evaluation and by determination of the hydroxyproline content of the lung tissue. Based on reference values obtained in 17 untreated control animals the experimental data were converted to quantals for probit analysis.

RESULTS

The data did not indicate any significant differences for the incidence of lung damage after half lung and whole lung irradiation when injury was assessed by radiography, histology, or hydroxyproline content. However, using an increase in breathing rate as experimental endpoint, significant differences of radiation induced morbidity were observed. While none of the animals after half lung irradiation showed pathological breathing rates even after doses of 29 Gy and 31 Gy, a clear if shallow dose-response relationship with an ED50-value of 27 +/- 11 Gy (SD) was obtained after whole lung irradiation (P < 0.01).

CONCLUSIONS

A volume effect can only be demonstrated for functional lung morbidity whereas induction of structural lung damage is independent of the volume irradiated.