Radiation Oncology

Radiation Oncology (XRT) refers to usage of ionizing radiation for the treatment of cancer by controlling malignant cells. It is commonly applied for the treatment of cancer as Ionizing radiation works by damaging the DNA of exposed tissue. Due to this procedure the cancerous cells become more susceptible to death as the DNA repair machinery is hampered.

During the radiation therapy, normal tissues are spared by using the shaped radiation beams from varied angles of exposure for intersection at the tumour. It results in larger absorbed dose in cancerous cells than surrounding healthy tissues. In addition to the tumour, the radiation fields may also comprise of draining lymph nodes in case they are clinically or radiological involved with malignant cells.

Effect on different types of cancer

The response of different types of cancer to radiation therapy is different depending on their

radiosensitivity.

Modest doses of radiation rapidly kill highly radiosensitive cancer cells such as germ cell tumours, Leukemias and most lymphomas.

Higher doses of radiation are required for treating majority of epithelial cancers as they are only moderately radiosensitive.

Very higher doses of radiation are required for radical cure of radioresistant cancers such as Renal cell cancer and melanoma.

Leukemias are not curable with radiation therapy as they are spread through the body.

Lymphoma can be cured with radiation if it is localised to one specific area in the body.

Early Stage Moderately radioresponsive tumors are routinely exposed to curative doses of radiation therapy such as head and neck cancer, breast cancer, non-melanoma skin cancer, cervical cancer, anal cancer, non-small cell lung cancer, and prostate cancer.

Metastatic cancers are incurable with radiation therapy as they are spread throughout the body.

The response of a tumor to radiation therapy is also related to its size with response of large tumors is less than response of smaller tumours.

Types of Radiation therapy

There are three main divisions of radiation therapy depending on the position of the radiation source used for the treatment.

External beam radiation therapy (EBRT or XRT): In this procedure, a radiation source is placed outside the body.

Ø Conventional external beam radiation therapy (2DXRT) uses linear accelerator machines for delivering the two-dimensional beams.

Ø Stereotactic radiation involves focused radiation beams for targeting a tumour that has been clearly defined by using extremely detailed imaging scans.

Ø Particle therapy involves the usage of energetic ionizing particles for targeting tumour.

Brachytherapy or sealed source radiation therapy: In this procedure, a radiation source is placed in the area or nearby the area under treatment.

Systemic radioisotope therapy or unsealed source radiotherapy: In this procedure, the radioisotopes are delivered into the body by infusion or oral ingestion. It is a type of targeted therapy that uses the properties of radioisotopes for targeting the cancerous tissues.

Acute side effects