Radiotherapy

Radiation therapy or radiotherapy is the use of high-energy x-rays to kill cancer cells. Over half of all cancer patients will need radiotherapy at some point during the course of their illness. Radiotherapy nowadays is often combined with other treatments to achieve the best results such as chemotherapy, targeted therapy and immunotherapy.

The energy of the x-rays used in radiotherapy are in the order of mega-voltage (10⁶) compared to diagnostic  x-rays used in CT scans or normal x-ray which are kilo-voltage (10³). At these high doses, the x-rays will damage the DNA in cancer cells which trigger them to die. This process can take up to weeks and months to completely accomplish. When the damaged cells die, they are broken down and removed by the body.

To minimize the effect of radiotherapy on the normal cells in the body, radiotherapy is delivered using sophisticated technology such as intensity modulated radiotherapy and image guided radiotherapy to focus the beams on the tumour and avoid normal tissue. Each body organ has a limit to the amount of radiotherapy dose it can receive and this should be calculated for every patient each time they receive treatment. Radiotherapy dose is measured in Gray (Gy) and to completely cure a nasopharyngeal cancer we typically use 70Gy but to control but not cure a metastases for example we would use 8 to 20Gy.

The Radiation Team

As with all treatments, you will have a specifically designed medical team working towards creating a treatment plan for you. This team will likely consist of:

• A clinical or radiation oncologist is the doctor who specializes in radiation therapy. This doctor will oversee all treatments and work with other members of the team to create a specialized treatment plan.
• A medical radiation physicist is an expert in operating radiation equipment.
• A dosimetrist calculates the perfect dose of radiation for your treatment.
• A radiation therapist or radiographer operates the treatment machines.
  
  

External-beam Radiation Therapy (EBRT)

External-beam radiation therapy is the most common type of radiation therapy used. It is delivered using a machine known as a “linear accelerator (linac)”. The machine works by accelerating electrons to create a beam of radiation, a miniature version of particle accelerators found in nuclear physics labs. They are highly specialized machines that take a whole team of engineers and physicists to maintain in top working order. Examples of companies that produce linacs and the names of the machines produced are Varian (Truebeam, Novalis, Halcyon, Trilogy), Elekta (Versa HD, Infinity, Synergy), Tomotherapy (Cyberknife, Radixact). Advanced computer software is needed to control the linear accelerator to ensure they deliver radiotherapy correctly.

The different types of external-beam radiation therapies are (in ascending order of complexity):

• Two-dimensional radiation therapy (2D-RT): The process where a 2D image of a cancer is created eg. simple x-rays images, allowing oncologists to create a treatment plan. This is the least accurate form of radiotherapy.
• Three-dimensional conformal radiation therapy (3D-CRT): The process where a CT Scan allows a 3D image of a cancer to be obtained. This allows the oncologist to visualize the tumour and surrounding normal tissue better. However the technology used to deliver the treatment is still basic, although better than 2D-RT.

• Intensity modulated radiation therapy (IMRT). CT Scan or PET-CT or MRI is used to visualize the tumour similar to the 3D-CRT, but in IMRT a more sophisticated form of radiation therapy delivery is used. Rather than using the same intensity in each beam such as with 3D-CRT, IMRT varies the intensity within each of its beams allowing for more accuracy during treatment.

• Stereotactic radiation therapy: This uses IMRT to deliver large and precise doses of radiation to a small tumour area. Stereotactic radiation is often limited to 1-5 Additional measures are usually taken to prevent the patient and tumour from moving during the treatment such as breathing control, abdominal compression and techniques described in Image Guided Radiation Therapy (IGRT)
  

EBRT Treatment Process

• discuss with your oncologist options and the pro and cons.
• sign a consent form indicating that you understand the process and accept the risks.
• undergo scanning procedures to locate the tumour such as a CT scan, PET-CT scan, MRI.
• customized immobilization device to hold you still during your treatment will be made.
• mark your skin to allow reproducible positioning on a day to day basis.
  
  

For those undergoing external-beam radiation therapy, sessions are short and painless, only lasting on average 2-10 minutes usually. This treatment type is typically carried out 5 times a week for up to 9 weeks, depending on your treatment plan.

Image Guided Radiation Therapy (IGRT)

Whilst it is good to plan radiotherapy using the best imaging eg. PET-CT however the tumour and parts of the body may move during radiotherapy making delivery troublesome. For example a patient may not lie down in exactly the same position every day or the tumour in the lung would move during breathing. Even being off position by a few millimeters may make a big difference and we are in danger of missing the tumour and not curing the patient or hitting normal tissue and causing unintended damage.

IGRT is the use of imaging during radiation therapy so that your team can visualise the tumour immediately before, immediately after and sometimes during radiotherapy. This leads to a much lower chance of missing the target. In general kilovoltage (kV) imaging using a CT scan attached to the linac is the most precise method and is better than megavoltage (MV) imaging especially for internal organs excluding bone.

Other forms of IGRT include fiducial markers – which are placement of gold seeds or clips in the tumour so they are more easily seen on a scan and the use of surface guided imaging which the computer uses a 3D body surface mapping,

Brachytherapy

Also known as internal radiation therapy,  this is when radioactive material is placed inside your body, either permanently or temporarily.  Brachytherapy allows delivery of higher doses of radiation to more focused areas in the body. It is commonly used to treat gynaecological cancers such as cervical, uterine and vaginal cancers and prostate cancer.

Intraoperartive Radiotherapy (IORT)

IORT is the delivery of low dose radiation directly to the area where the tumour has been removed during surgery. This is commonly used during lumpectomy (not mastectomy) breast cancer surgery.

Will I Become Radioactive?

It is a misconception that following standard EBRT therapy, a patient becomes radioactive. This is untrue.

However for brachytherapy that is implanted permanently into the body the sources remain radioactive for some time and can cause a patient to emit radiation from their body. Therefore, your level of radiation will to be monitored by your team and you will need to take precautions for some time. This may include:

• Not to come into contact with children under 16
• Not come into contact with pregnant women
• Be a safe distance from people eg. 6 feet
• Allow visitors to stay for a limited time a day eg. up to 30 minutes
  
  

Radiation Therapy and Side Effects

The effects of radiation will be focused only on the area being treated. While side effects have become fewer due to more precise treatments being developed by researchers, patients may still find that they have side effects usually starting in the second or third week of treatment, while others experience no side effects at all. Those who do experience treatments are typically found in areas located near the treatment site.

Some side effects can include:

Full body:

• Skin problems
• Fatigue
• Radiation recall – a rare rash that resembles severe sunburn
  
  

Head and neck:

• Hair loss
• Dry mouth
• Mouth sores
• Difficulty swallowing
• Nausea
• Tooth decay
  
  

Chest:

• Shortness of breath
• Sore breasts
• Stiff shoulders
• Radiation pneumonitis
• Radiation fibrosis
  
  

Stomach:

• Nausea
• Diarrhea
  
  

Pelvis:

• Diarrhea
• Bleeding of the rectum
• Bladder irritation or incontinence
  
  

In women:

• Menstrual changes
• Infertility
• Menopausal symptoms
  
  

In men:

• Erectile dysfunction
• Lower sperm count

Side effects can be treated and/or minimized through palliative care.

Following Your Treatment

Upon the conclusion of your treatment, you can expect to have regular check-ups with your radiation oncologist. These check-ups will ensure that your recovery is on track, and to diagnose and treat any side effects that you may begin to develop. As time passes and if your recovery is going well, you will need fewer check-ups.