4D radiation therapy is a cancer treatment method that employs high-energy radiation beams to destroy cancer cells by damaging the ability of these cells to reproduce. The need for normal tissue sparing is of increasing importance as there is clinical evidence that technologies allow an increased dose to the tumor while sparing healthy tissue will improve the balance between complications and cure.

This form of radiation therapy is used to treat tumors that are located too close to vital organs and structures for other types of radiation therapy. Lung cancer radiation therapy uses powerful, high-energy X-rays to kill cancer cells or keep them from growing. The radiation is aimed at the lung cancer tumor and kills the cancer cells only in that area of the lungs.

Lung cancer is a condition that causes cells to divide in the lungs uncontrollably. This causes the growth of tumors that reduce a person’s ability to breathe. It is the leading cause of cancer-related death in the world and likely to remain so in the foreseeable future.

According to the GLOBACON report 2018, lung cancer affected about 2.1 million persons (11.6% of all cancers) and caused 1.8 million deaths (which comprised 18.4% of all cancer-related deaths. The above report also estimated that in India, a total of 67,795 new lung cancer cases occurred (5.9% of all cancers) in 2018, of which 48,698 (8.5%) occurred in males. Although global mortality due to lung cancer has started to decline, probably reflecting the decrease in smoking habits, the prevalence in India appears to be increasing.

Radiation is used before lung cancer surgery to shrink the tumor or after the surgery to kill any cancer cells left in the lungs. Sometimes external radiation is used as the main type of lung cancer treatment. This is often the case for people who may not be healthy enough to have surgery or whose cancer has spread too far to have surgery. Radiation therapy for lung cancer also can be used to relieve symptoms caused by cancer, such as pain, bleeding, or blockage of airways by the tumor.

Radiation therapy delivers high-energy x-rays that can destroy rapidly dividing cancer cells or palliate symptoms. It has many uses in lung cancer:

· As a primary treatment

· Before surgery to shrink the tumor

· After surgery to eliminate any cancer cells that remain in the treated area

· To treat lung cancer that has spread to the brain or other areas of the body or to palliate symptoms

4D radiation therapy is performed on an X-ray table with each treatment taking approximately 30 minutes. Beams of radiation are precisely matched to the shape of the tumor. During treatment, a linear accelerator moves in a circular fashion to target the tumor.

Tools Used in 4D imaging are as follows:

· 4D-CT Imaging: This advanced imaging method makes CT scans much faster and more accurate than ever before. 4D CT uses a new technology that captures the location and movement of your tumor and the movement of your body's organs over time.

· 4D PET-CT Imaging: Captures the movement of your organs and tumor over time, while also recording the metabolism of the tumor. It creates the most complete and accurate imaging data of the tumor and critical organs and also makes it possible to see the makeup and function of the tumor.

· 4D-MRI: It is a leading-edge imaging technique that offers a more comprehensive picture of the heart and the aorta. The fourth dimension is movement, allowing clinicians to better visualize blood flow through the cardiovascular system and potentially identify areas that warrant closer follow up.

4-D Radiation therapy (4DRT) provides a major therapeutic advance in the management of lung lesions. While minimizing exposure to the surrounding normal tissue or adjacent vital structure, it achieves high levels of local disease control with limited toxicity. In many cases, it might be curative or at least beneficial for patients in whom surgery is not an option. Its practical advantages include a short treatment course as well as the preservation of physical and emotional quality of life during and after treatment.

The major advantage of 4DRT is its additional normal tissue synchronizing the radiation beams with the moving target in real-time. 4DRT can be implemented differently depending upon how the time information is incorporated and utilized. The most common approach is the use of gating techniques in both imaging and treatment so that the planned and treated target localizations are identical.

4D radiation therapy is still in its early stages of development, but it will continue to advance as associated technologies improve and new approaches become available, including 4D deformable image registration, automated 4D treatment planning, and 4D treatment delivery mechanisms. Certainly, radiotherapy still plays an important role in lung cancer treatment. In recent years, new sophisticated techniques have been developed and propelled themselves into different stages of the treatment. 4D radiation therapy is a valid means for treating patients with located tumors, as it presents surprising results and minimal side effects.