Three-dimensional (3D) conformal radiation therapy (3D-CRT) uses 3D images on a computer.
The 3D images allow clinicians to shape beams of radiation around the shape and size of the tumour in a focused (conformed) way. This allows high doses of radiation to be given with greater accuracy, while reducing the amount of radiation damage to the surrounding healthy tissue.
This treatment increases the chances of recovery as higher levels of radiation are more effective for shrinking and killing tumours.
Compared to 2D conventional radiation therapy, 3D-CRT delivers a higher dose of radiation to a more targeted area.
In 2D radiation therapy, radiotherapy beams are directed at the tumour only from one direction, which causes all the normal tissue in front of and behind the tumour to get the full radiation dose.
In 3D conformal radiation therapy, radiotherapy beams enter from more than one direction (such as from the front and side), such that only the tumour which is at the point of focus of all the beams, gets the full dose. Normal tissues get only a fraction of the dose, hence reducing normal tissue injury. 3D CRT allows higher doses to be delivered safely.
2D radiation therapy is mostly reserved for lower dose treatments such as palliative whole brain radiotherapy, or radiotherapy for bone pain.
3D-CRT is suitable both for curative high dose treatment as well as palliative lower dose treatments.
Compared to 3D-CRT, intensity modulated radiotherapy (IMRT) and volumetric arc therapy (VMAT) further improve the shaping of the radiation dose to match the tumour.
In 3D-CRT, the shape of the radiation dose is essentially limited to simple squares or rectangles because of uniform intensity across each radiation field.
IMRT and VMAT use of a greater number of radiation fields combined with variation of beam intensity within each radiation field. This approach allows the oncologist to create any shape to match the tumour and spare normal organs.
For example, where a tumour wraps round a normal organ, IMRT/VMAT can create a C-shaped radiation dose to treat the tumour and spare the normal organ in the centre.
3D conformal radiation therapy is most useful for tumours that are close to important organs and structures in the body.
This method prevents the healthy body tissues and organs from radiation damage.
This therapy can be used to treat cancers such as:
Radiation therapy can cause side effects. They may be the result from the treatment itself or from radiation damage to the healthy cells around the treatment area. Side effects may vary depending on the kind of tissue structures near the tumour being irradiated.
In rare instances, a new cancer different from the first one being treated may develop years later. After treatment, your doctor will regularly check for complications and recurrent or new cancers.
Find out more about the risks of radiation therapy.
There are several steps to planning 3D-CRT treatment:
- Your doctor will conduct a physical examination and review your medical history.
- There will be a treatment simulation session, which includes computerised tomography (CT) scanning. Your doctor will use this scan to make an individual plan for you.
- During the session, a small mark or tattoo may be placed on your skin to help align and target the equipment.
In some cases you may need to:
- Wear a special mask or mould to keep you still during treatment.
- Follow certain bowel and bladder preparation regimen or fast prior to the simulation and treatment.
- Receive an intravenous contrast material injection during the CT scan to help define the tumour better.
- Undergo additional scanning procedures, such as positron emission tomography (PET) and magnetic resonance imaging (MRI). These diagnostic images can be merged with the planning CT and help your doctor determine the precise location of the tumour target.
- Have radio dense markers inserted into the target (tumour) for more accurate positioning.
Radiotherapy usually begins a few days after simulation.
3D conformal radiation therapy often requires multiple (fractionated) treatment sessions spread over different days. To decide the number of treatments, your doctor will consider:
- Doses to normal tissue structures
- The location, type and size of the tumour, and the objective of radiation
- Your health
Typically, patients are scheduled for sessions 5 days a week for 5 – 8 weeks.
Estimated duration
Treatment sessions usually take between 15 – 60 minutes.
Before the procedure
At the beginning of the treatment session, you will be positioned on the treatment table, guided by the marks on the skin (tattoos) defining the treatment area.
If moulded masks or devices were made, they will be used to help you maintain the proper position.
You may be repositioned during the procedure.
Your doctor or radiologist will use imaging systems on the treatment machine such as X-ray or CT to check positioning and marker location.
During the procedure
Once you are in the right position, the medical staff will leave you alone in the room. This is so they are not exposed to the radiation.
You will be able to communicate with your doctor or the staff through an intercom. They may ask you to take shallow breaths or to hold your breath during the treatment.
You should not experience any pain or discomfort during the actual treatments. However, if you experience discomfort, do inform the staff so that they can stop the machine.
After the procedure
As treatment progresses and you have undergone a few sessions, you may experience treatment-related side effects.
The type and severity of side effects will depend on the type of radiation, dosage and body part under treatment.
Early side effects happen during or right after treatment and are usually gone within a few weeks. They include:
- Diarrhoea
- Eating and digestion problems
- Fatigue
- Hair loss in the treatment area
- Headaches
- Mouth problems and difficulty swallowing
- Nausea and vomiting
- Skin problems - skin in the treatment area may become sensitive, red, irritated, or swollen. Other changes include dryness, itching, peeling, and blistering
- Soreness and swelling in the treatment area
- Urinary and bladder changes
Talk to your doctor or nurse so they can help to manage them.
Late side effects may occur months or years following treatment. While late effects may be permanent, severe side effects are rare. They include:
- Brain changes
- Colon and rectal changes
- Infertility
- Joint changes
- Kidney changes
- Lung changes
- Lymphedema
- Mouth changes
- Secondary cancer
- Spinal cord changes
Your doctor will discuss with you the potential side effects and how they will be managed.
After your treatment, you may have to go for regular follow-up appointments with your doctor to check on your recovery and look out for any side effects, which may occur well after the procedure.
Contact your doctor if notice any new symptoms so that they can help you manage them.
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