Radiation-Induced Lung Diseases: Risk Factors, Symptoms, and Treatment

Introduction

Cancer is one of the most dangerous disorders of modern times. Around 18 million people around the world are suffering from various forms of cancer. Almost 1 lakh people are losing lives every year due to this fatal disorder. Over the years, researchers have introduced several treatment modalities for curing cancer. Radiation therapy is one of the most popular treatments used in cancer therapy, but the potential complication of radiation therapy is damage to normal tissue. Radiation therapy during the treatment of intrathoracic malignancies, including lung, breast, and esophageal cancer, may cause damage to the lung tissue. This may lead to different complications. That is why understanding radiation-induced lung changes is important.

What Is the Role of Radiation?

Radiation is a high-energy ray that is used to kill cancer cells. Different types and doses of radiation are used for the treatment of different cancers. Sometimes it is used in combination with chemotherapy and surgical therapy.

There are two types of radiation therapy. In external beam radiation therapy (EBRT), radiation is given from outside the body; in internal radiation therapy, a small source of radiation is placed inside the body in close proximity to the malignant tissue.

Previously for external beam radiation therapy, two-dimensional techniques such as chest radiographs are used to determine the amount of radiation. But internal structures are three-dimensional. As a result, errors like miscalculation in dosing and improper placement of radiation sources used to happen. To overcome these shortcomings, various techniques are used nowadays. These are:

1. Three-Dimensional Conformal Radiation Therapy (3D-CRT): Computerized tomography-based simulations are used for accurate positing of the radiation source and calculation of the doses.

2. Intensity Modulated Radiation Therapy (IMRT): This is also a three-dimensional radiation therapy that is used to modulate the intensity of the radiation. This is done for better orientation of radio waves and for protecting other internal structures.

3. Stereotactic Body Radiation Therapy (SBRT): In this technique, a concentrated amount of radiation is given to multiple body sites over a short period of time.

In spite of using all these modern methods, radiation-induced damage to the surrounding lung tissues is common. Various factors determine the extent of damage to the lung tissues during radiation therapy.

What Are the Risk Factors?

The potential risk doctors for the development of radiation-induced lung changes are:

1. Tumor Location: Tumor location and its proximity to other healthy vital structs are potential risk factors for radiation-induced lung injury. Such healthy tissues may be exposed to radiation because of lung movement during radiation therapy. Sometimes tumors are responsible for perfusion, which increases the chances of radiation-induced damage to other structures.

2. Tumor Volume: Large size of the tumors is related to increased incidence of radiation-induced lung injury. Also, the large size of the tumor is responsible for the increased radiation dose.

3. Comorbid Conditions: Different lung pathological conditions like COPD (chronic obstructive pulmonary disease; a group of disorders responsible for constrictions of airways), interstitial lung disease (ILD- disorders responsible for fibrosis of lungs) are associated with more damage of the lung structures during radiation therapy.

4. Smoking: Smoking is considered an irritant to the lung tissues. This causes pathological changes and inflammation in the lung tissues and lining of the respiratory tract. This increases the probability of damage to the radiation process.

5. Age and Genetics: The process of regeneration and repair is affected by the aging process. Also, the amount of inflammation, DNA repair, and regeneration is affected by the genetics of the person. That is why the extent of the radiation-induced damage is not equal for everyone.

What Is the Clinical Effect of Radiation?

The effect of the radiation on the lung tissues is known as radiation pneumonitis. The effect on the lung tissues is based on symptoms and clinical findings of the patients.

A. Symptoms of Radiation Pneumonitis:

The clinical symptoms are:

1. Low-grade fever.

2. Breathing difficulty.

3. Dry cough.

4. Chest pain and heaviness in the chest.

Following diagnostic tests are done to confirm the diagnosis of Radiation pneumonitis.

B. Diagnostic Tests:

1. Haziness in the chest and ground glass appearance are the features of early radion-induced changes in chest X-rays. Features like pleural effusion and lung nodules can also be seen in these cases.

2. For advanced cases, computerized tomography (CT) of the lung is done. Ground glass appearance, homogenous consolidations, parenchymal distortion, and lung fibrosis can also be diagnosed through this method.

Apart from this, other tests like positron emission tomography-computed tomography, bronchoscopy, and lung function tests can also be done. Laboratory tests for serum Surfactant protein-D (SP-D) and Krebs von den Lungen-6 (KL-6) are done. In the case of radiation pneumonitis, these factors are elevated.

On the basis of symptoms and clinical grading, the following grading of radion pneumonitis is followed.

1. Grade 1: Asymptomatic or mild symptoms are present. Slight radiographic changes can be seen.

2. Grade 2: Moderate symptomatic with the presence of heavy cough and fever. A patchy radiographic appearance can be seen.

3. Grade 3: Severe symptoms are present. Focal consolidations are suggestive of lung fibrosis and can be observed in radiographs.

4. Grade 4: Severe respiratory distress. The patient needs oxygen support or ventilation.

5. Grade 5: Death due to adverse effects.

How to Manage Such Conditions?

• Oral application of Prednisone is advised for patients with mild symptoms (up to Grade 2). The preferred dose is one to two milligrams per kilogram per day, and the tapering dose is followed for three to four weeks.

• For patients with severe symptoms (Grade 3 and Grade 4), intravenous corticosteroids like methylprednisolone are prescribed. The dose recommendation is two four milligrams per kilogram per day, and the tapering dosing method is followed for the next six weeks.

• The function of steroids is to reduce the amount of inflammatory mediators and prevent oxidative damage to the lung tissues. For additional action, inhalation of steroids is advised.

• For prophylactic purposes, several drugs can be used. Amifostine acts as a radioprotector drug. Angiotensin-converting enzyme inhibitors prevent the accumulation of collagen fibers and reduce the chance of lung fibrosis. Pentoxifylline helps in the reduction of the amount of inflammatory substances. Four hundred milligrams of Pentoxifylline is taken orally three times a day for eight weeks.

Conclusion:

Radiation is an effective tool in the treatment of cancer. Radiation-induced damage of the lung tissues depends upon several factors the extent of cancer, age, and habit. Severe damage to the lung tissues may even cause death. With the use of modern radiation methods, scientists can now reduce lung damage through proper positioning of the radiation sources. Also, different drugs like steroids can reduce the amount of lung tissue damage.’