There are lots of different techniques and methods of treatment radiotherapy in use and the language isn’t always straightforward. Below are some commonly used terminology and descriptions.
- Intensity-Modulated Radiotherapy (IMRT)
- Stereotactic body radiotherapy (SBRT) and stereotactic ablative radiotherapy (SABR)
- Stereotactic radiosurgery (SRS) and Stereotactic Radiotherapy (SRT)
- Image-guided radiotherapy (IGRT)
- Intra-operative Radiotherapy (IORT)
- Superficial Radiotherapy (SRT)
- Deep Inspiration Breath Hold (DIBH)
Intensity-Modulated Radiotherapy (IMRT)
IMRT is a newer and more sophisticated way of delivering conventional external beam radiotherapy. It can be delivered using a conventional Linear accelerator (Linac) as well as other modalities. It uses multiple beams of X-rays of varying intensity directed towards the cancer, angled from various directions around the patient. The radiotherapy beams are shaped by multi-leaf collimators (MLCs) allowing for different doses of radiation to be given to different parts of the area needing treatment.
This gives us control of the radiation enabling us to avoid or minimise exposure to surrounding healthy tissue while maximising dose to the cancer. This is particularly effective when dealing with cancers that are close to vital organs or structures within the body. This leads to higher chance of cure for some cancers (e.g., prostate cancer) and significantly reduces the risk of damage from radiation.
This effect (safely being able to give higher doses of radiation) is called dose escalation. IMRT allows treatment to be accurately delivered to unusually shaped cancers and can also create concave (hollow) areas within the high dose region. This allows the dose of radiation to a sensitive organ e.g. the rectum (lower bowel) or the spinal cord, to be kept to a minimum. IMRT is always combined with Image-Guided Radiotherapy (IGRT) see below for more details on this.
Specific examples include:
IMRT may allow the dose to the eyes and other critical parts of the brain to be reduced, hence avoiding damage. The dose to hormone-producing areas and even the memory areas of the brain can also be reduced.
Head, neck and face cancers
IMRT can significantly reduce the dose to the salivary glands reducing one of the worst long-term side effects from treating some of these cancers in the past – a dry mouth (xerostomia).
Breast and lung cancers
IMRT can be used to reduce doses to the heart and lungs. In breast cancer IMRT has been shown to reduce skin reactions from treatment. If the cancer is close to the spine, IMRT can allow a higher dose to be delivered without damaging the spinal cord.
In the past, treatment close to the spinal cord often had to be completely avoided or the dose reduced as spinal cord damage is one of the most serious rare side effects of radiation (causing paralysis or weakness). With IMRT techniques, the risk of this becomes extremely low.
Abdominal and pelvic cancers
IMRT can be very effective in reducing side effects from treatment of abdominal cancers for example in the stomach, pancreas and lower oesophagus. In the pelvis, radiotherapy for cancers of the bowel (colorectal cancers), often use IMRT to reduce the risk of damage to the bowel and bladder.
IMRT is standard treatment now for treating localised prostate cancers and is often also used after an operation where the surgery (radical prostatectomy) has not removed all the cancer cells. IMRT allows higher doses to the prostate with a higher chance of controlling the cancer (cure). It also means that the lymph nodes can be more easily treated with reduced side effects than previously.
The main organ close to the prostate that sometimes limited the dose that could safely be delivered is the rectum (lower bowel). IMRT allows the amount of rectum in the high dose area to be minimised. This means short and long-term side effects have become significantly less common.
Cervix and uterine (endometrial or womb) cancer
IMRT is commonly used to treat the cancer with or without pelvic lymph nodes. Again, IMRT increases accuracy, and reduces short-term and late effects, also relating mainly to bladder and bowel irradiation.
Depending on the circumstances, the only minor disadvantage for patients having IMRT may be a slightly increased treatment time – though still only a few minutes per treatment.
Stereotactic body radiotherapy (SBRT) and stereotactic ablative radiotherapy (SABR)
These are both an advanced form of radiotherapy that is used to treat many different types of cancer. The two terms are interchangeable. It is a type of radiotherapy where a few very high doses of radiation are delivered to relatively small, well-defined tumours. SBRT is used to treat small, isolated tumours that lie outside the brain.
It is used to treat both primary cancer (where the cancer started such as the lung or the prostate), or where a cancer may have spread (secondary cancers or metastases). Secondary cancers treated with SBRT include those in the bone, lung or liver.
This technique differs from other external beam radiotherapy as it involves the delivery of higher doses of radiation to the cancer. This is why the word ‘ablative’ is part of the name sometimes given for this type of treatment. These higher doses are given to the patient from X-ray beams directed from outside the body and using a small number of treatments (also called fractions). Typically, one to five treatments are used over a few days. As with all external beam radiotherapy the delivery of this technique is extremely precise which is what the term ‘stereotactic’ refers to. There are several technologies available that can be used to deliver this technique including Linac based, Cyberknife, and Tomotherapy.
The ability to deliver SBRT has been made possible by several technological advances including keeping patients comfortably still during treatment, tracking the movement of the tumour, better tumour identification and more precise and accurate delivery of the radiotherapy. As this type of treatment requires millimetre accuracy, it also requires significantly improved methods to ensure that the radiation is focused on a small area of cancer within the patient.
With modern radiotherapy, it is now possible to take a live scan at the time of treatment using built in CT equipment to ensure accuracy of the treatment delivery. When the radiotherapy is given to the cancer, the dose is high at this point but falls off rapidly outside the target. This means there is a low risk of damaging adjacent normal healthy tissues or organs. Often limiting or adjusting for movement of the cancer (for instance in the lung as the patient breathes) is done to make sure the cancer is not missed and the surrounding tissue (in this case the lung) does not get too much radiation.
More can be found on this subject on the SBRT Consortium website.
The UK SABR Consortium was created in 2008 with the specific aim of developing a SABR service across the UK. It is now a multi-disciplinary network of over 300 radiotherapy clinicians, medical physicists and radiographers who have produced guidelines, training and quality assurance programs that have been instrumental in introduction of SABR and other innovative radiotherapy techniques to the UK.
In many situations where SBRT is recommended or is now considered to be a treatment option, this is as an alternative to surgery (radiosurgery) for removal of small to moderately sized cancers. This avoids the need for an anaesthetic and the risks of an operation, especially for patients who are elderly, frail or have other health issues that might make surgery risky or impossible.
At some cancer sites e.g. bone, an operation is not feasible or may be extremely difficult. This is why sometimes SBRT is called a ‘minimally invasive’ cancer treatment technique. This special type of radiotherapy is becoming more prevalent and available as the evidence for its use continues to grow.
Stereotactic radiosurgery (SRS) and Stereotactic Radiotherapy (SRT)
For areas within the brain as well as the SBRT \ SABR equipment already mentioned (e.g. Linear Accelerator Based, Cyberknife and Tomotherapy) stereotactic radiosurgery (SRS) can also be delivered by a machine known as a GammaKnife. The GammaKnife is not a knife in the conventional sense but uses a focused array of intersecting beams of gamma to treat lesions within the brain. Usually a single high dose (SRS) of radiation is delivered to the tumour with the assistance of highly accurate imaging and planning or it can be up to 5 fractions \ doses (SRT). A head frame is usually required for brain treatments to ensure the patient stays completely still, this treatment session can take up to an hour. The technique provides an alternative method of treatment for a number of conditions, for which open neurosurgery may be either not practicable or carry a high risk of complications.
Delivery of SRS / SRT is not painful. It is usually well tolerated by patients. The potential side effects of treatment vary depending on the area being treated. These will be discussed by the radiotherapy treatment team. Some patients may experience side-effects following treatment including tiredness, mild nausea or headache. These are usually only temporary and mild in nature. Other rarer side-effects may occur months or years after treatment but are not common. The meticulous planning and treatment processes used in SRS / SRT minimise these side-effects.
The expected results of treatment vary according to the condition being treated and cannot therefore be easily summarised. Your radiotherapy treatment team will give you more details about this and all aspects of the process before a final decision is made about treatment with this specialised technique.
Image-guided radiotherapy (IGRT)
This describes the use of a variety of advanced imaging modalities (X-rays, Cone beam CT scans, MRI) taken throughout the course of radiotherapy treatment to accurately identify and localise the treatment area before the radiation is delivered. Many different modalities are used and this will depend on what is available in the radiotherapy department and the type of treatment machines that are being used. Sometimes small markers made of metal (e.g. gold) or other materials seen well on X-rays, are placed inside a cancer or organ. Images are taken prior to and sometimes during treatment delivery so finer adjustments can be made to ensure sub-millimetre accuracy. The images taken are used not only to verify the treatment positioning but can also identify changes in a cancers location to enable adjustments to be made during treatment, such as the positioning of the patient or the planned radiation dose.
For example, cancers located in the lung, the therapeutic radiographers can take images during the delivery of the actual treatment so that they can compensate for the movement occurring during normal breathing. This is known as 4-dimensional radiotherapy (4D-RT) where the fourth dimension is ‘time’.
Intra-operative Radiotherapy (IORT)
This is a single dose of radiotherapy delivered at the time of breast conserving cancer surgery and can eliminate the need for External Beam Radiotherapy (EBRT), which is typically administered five days a week, over the course of three weeks. Breast conserving surgery involves the removal of the tumour and a small area of surrounding tissue from the breast.
Intraoperative radiotherapy (IORT) is an intensive radiation treatment that’s administered during surgery. It is most commonly used for breast cancers but can be used on any part of the body where the likelihood of an incomplete excision of the disease during surgery is a concern.
IORT allows direct radiation to the target area while sparing normal surrounding tissue. IORT is used to treat cancers that are difficult to remove during surgery and when there is a concern that microscopic amounts of cancer may remain.
IORT allows higher effective doses of radiation to be used compared with conventional radiotherapy. It’s not always possible to use very high doses during conventional radiotherapy, since sensitive organs could be nearby. IORT also allows doctors to temporarily move nearby organs or shield them from radiation exposure.
Superficial Radiotherapy (SRT)
This is often referred to, as Superficial X-Ray Therapy or Kilovoltage (kV) Radiotherapy is the use of low energy X-ray’s to treat cancer and other conditions that occur either on or close to the skin surface.
Superficial Radiotherapy (SRT) is a non-surgical treatment for skin cancers such as basal cell carcinoma, squamous cell carcinoma, and Bowen’s carcinoma. It is a painless alternative to surgical removal of skin cancer, and allows patients the freedom to maintain an active lifestyle during treatment.
During SRT a patient will visit for a 3 minute treatment 3-5 times a week for about 2 or 3 weeks. Depending on the size and location of the skin cancer, the appropriate cone-shaped attachment will be placed on the SRT machine, and a few X-rays will be applied to the skin.
The patient will not feel the X-rays at the time of treatment. The skin cancer cells will become damaged and eventually fall off. This process may result in some reddening and irritation of the skin, but it will eventually heal, returning to its normal, healthy state.
Deep Inspiration Breath Hold (DIBH)
Deep Inspiration Breath Hold (DIBH) is a technique used most commonly in radiotherapy to the breast it is designed to reduce any incidental radiation dose to the heart. More information
Ultra-high dose rate (FLASH) radiotherapy is a way of treating cancer. Higher doses of radiotherapy are associated with trauma to the healthy tissue surrounding the tumour, whereas FLASH radiotherapy demonstrates a sparing effect of the healthy tissues without compromising the anti-tumour action.
Treatment success is dependent on delivering a high enough dose of radiation to destroy the tumour cells without causing severe trauma to the surrounding healthy tissues. FLASH radiotherapy (FLASH-RT) is a new technique, involving treatment of tumours at ultra-high dose rates of radiation. This actually reduces the trauma to healthy tissue around the tumour site, whilst equalling the anti-tumour effect of conventional dose rate radiotherapy (CONV-RT).
While its mechanism of action is likely to involve oxygen depletion, it is not fully understood and therefore requires further study. The doses required to achieve the FLASH effect make it unsuitable for many clinical cases. Furthermore, the availability of radiation sources capable of producing these higher doses for treatment is a limiting factor in clinical trials. If further study yields more understanding of the biological mechanisms of the FLASH effect, it may be possible to achieve it at lower doses, increasing its clinical viability.
The biological effects of radiation dose to organs at risk surrounding tumour target volumes are a major dose-limiting constraint in radiotherapy. This can mean that the tumour cannot be completely destroyed, and the efficacy of radiotherapy will be decreased. Thus, ways to reduce damage to healthy tissue has always been a topic of particular interest in radiotherapy research. Modern radiotherapy technologies such as Helical Tomotherapy (HT), intensity-modulated radiotherapy (IMRT), and proton radiotherapy can reduce radiation damage to healthy tissues. Recent outcomes of animal experiments show that FLASH radiotherapy (FLASH-RT) can reduce radiation-induced damage in healthy tissue without decreasing antitumor effectiveness. The very short radiotherapy time compared to that of conventional dose-rate radiotherapy is another advantage of FLASH-RT. The first human patient received FLASH-RT in Switzerland in 2018. FLASH-RT may become one of the main radiotherapy technologies in clinical applications in the future.
FLASH radiotherapy (FLASH-RT) is a novel radiotherapy technology defined as a single ultra-high dose-rate radiotherapy. Compared with conventional dose-rate irradiation, FLASH irradiation is 400-fold more rapid than conventional irradiationThe mechanism behind the differential responses of healthy and tumour tissues to FLASH-RT remains unclear and the various explanatory hypotheses require more experimental verification. Much more research is needed here to prove that FLASH-RT can provide more protection to healthy tissues.