What are radiations?
High-intensity waves which have the potential to damage cells are called radiations. There are different radiations based on the wavelength of the waves. Each one has a different working potential and extent of impact on human tissues.
The use of radiations in the destruction of cancer cells is called radiation therapy.
Radiation therapy can be used along with chemotherapy or surgery. Almost half the patients who are diagnosed with cancer undergo radiation therapy.
When radiation therapy is used for treating blood cancer, it is used along with drug therapy or chemotherapy. It is also used to relieve pain or discomfort caused by enlarged organs.
How does it work?
Radiations which are aimed at a cell will ionize the cellular particles and lead to the destruction of the DNA and thus stop their uncontrolled division. The radiation also affects normal cells. This causes damage to the healthy cells as well.
What are the types of radiation therapy?
Based on the source of radiation they can be divided into two types:
- External radiation: the source of radiation is from an external device. There are many devices which emit radiations at various intensities and frequencies.
The external beam radiation is delivered using a machine called a linear accelerator (also known as LINAC). A LINAC uses electricity to speed up subatomic particles to a very high speed. This creates the radiations which are then aimed at a tumour.
One of the commonly used radiation therapy is the 3D conformal radiation therapy (3D-CRT). Other methods that are used are:
- Intensity-modulated radiation therapy (IMRT): in this kind of therapy, there are multiple beam shaping devices called collimators. This type of radiation device allows the oncologist to regulate the intensity of radiation in different regions. The dose of radiation is chosen first. This is followed by a selection of regions or tissues to be applied to. This is why it is called inverse treatment planning.
- Image-guided radiation therapy: multiple imaging scans (using CT, MRI, PET) are taken successively to accurately estimate the size and position of a tumour. This increases the accuracy of radiation treatment and allows the oncologist to reduce the radiation exposure towards the healthy tissues.
- Tomotherapy: It is a hybrid between a CT scan and IMRT. It delivers radiation for treatment as well as imaging. This imaging can even be done right before the treatment to get accurate sizing of an ever-changing tumour. The part which is responsible for the imaging also rotates around the patient like a CT scanner.
- Stereotactic radiosurgery: A technique of radiotherapy which captured highly detailed and accurate images and sizes of a tumour. This allows high doses of radiation to be applied to the exact location of a tumour. It can only be performed on well-defined tumours. It is commonly used for tumours in the brain.
- Stereotactic body radiation therapy: this is similar to SRS. Radiations are given in fewer sessions, with higher doses. The imaging is not as accurate as in the brain or spinal cord as the movement of a tumour is more. SBRT is given for well-defined tumours which are isolated like tumours of the lung and liver. It may be referred to as Cyberknife by doctors, which is a brand name.
- Proton therapy: the radiation is delivered through protons instead of photons. The photons deposit energy throughout their path but photons deposit energy only at the end of their path. In theory, this is supposed to minimize the amount of exposure to normal tissues.
- Other charged particle beam: Electron beams may be used to emit radiation but can only be used on superficial structures like skin cancers.
- Internal radiation: devices can be placed in the patient’s body which slowly emit radiation. They may also be given through the bloodstream which has ionising properties. Internal radiation is also called brachytherapy.
Internal radiation may be given locally or systemically.
Local internal radiation: devices which release radiations are inserted near a tumour or at the site of a tumour. These radioactive devices are available in the form of seeds with radioactive isotopes within pellets. They may be inserted through needles, catheters, tubes. Once the radioactive isotope decays naturally and releases radiation which affects the surrounding cancerous tissues, the “seed” becomes inactive and can be left in the body.
The dosage can be either high dosage or low dosage treatment.
Some of the therapies done are:
- Interstitial brachytherapy: pellets are placed within the prostate.
- Episcleral brachytherapy: pellets are placed within the sclera of the eye to treat melanoma of the eye.
- Systemic internal radiation: The patient is made to swallow radioactive substance which is bound to a monoclonal antibody. The monoclonal antibody helps the drug to reach the target cells. For example:
- Ibritumomab tiuxetan is given to treat non-Hodgkin’s lymphoma of the B-cell type. The antibody recognises the protein on the b cells and binds to it.
- Some systemic drugs are given as pain relief for palliative care in some bone metastatic cancers.
What are the common side effects of radiation therapy?
Since radiation therapy does affect normal cells along with cancer cells, there are some side effects that result from it.
These are seen in most of the therapies irrespective of the type, location and intensity of treatment.
- Hair loss: if the radiation is aimed at a region that grows hair, hair loss can be expected.
- Skin problems: the exposed part of the skin may form rashes, blisters, dryness, itching and peeling. They usually go away when the patient’s treatment is over.
- Fatigue: it is one of the common side effects of radiation therapy. Exhaustion, tiredness and malaise are seen regardless of which region is being treated.
Side effects specific to the region of exposure:
- Head and neck:
Difficulty in swallowing
Shortness of breath
Breast or nipple soreness
A cough and fever
Fullness of chest
Radiation fibrosis (due to untreated radiation pneumonitis)
Reduced sperm count
Menopause or other changes in the menstrual cycle
Vaginal itching, burning, dryness