Understanding stereotactic radiotherapy
Radiotherapy is one of the methods employed to treat cancer and tumours, but there are possible side effects. In this article, a consultant clinical oncologist explains the advantages of an alternative technique, called stereotactic radiotherapy, and the mechanics behind it.
What is radiotherapy?
Radiotherapy, short for radiation therapy, is when high doses of radiation are used to kill cancerous cells, reduce the size of tumours, relieve symptoms of cancer, and prevent future cancer. The type of radiation used typically consists of X-rays, and it works by altering the actual DNA of cells.
Radiotherapy is often employed in conjunction with surgery or chemotherapy to amplify the effects of other treatments and to ease the destruction or removal of tumours. Radiotherapy can be administered externally from a machine, internally (brachytherapy) where a radioactive material is placed inside the body close to the area of cancer, or via injections and capsules (radioisotope therapy).
What are the side effects of radiotherapy?
While radiotherapy aims to deliver the brunt of the radiation to the cancer, healthy cells near the cancer also become damaged or affected to a degree. This will cause side effects during the course of treatment, such as:
- Skin sensitivity and discolouration
- Chronic fatigue
- Hair loss, particularly in the area of treatment
- Nausea and dizziness
- Loss of appetite
- Mouth sores
- Diarrhoea
Upon cessation of radiotherapy, these side effects will fade as the patient recovers, but it can take some time as their cells regenerate.
What is stereotactic radiotherapy?
Stereotactic radiotherapy (SRT) is a technique of external radiotherapy that can minimise the risk of the above side effects. With SRT, high-powered doses of radiation are precisely applied to a tumour, while the tissues nearby receive a much lower amount of radiation. It is mostly used for brain cancers, but studies and trials are looking into its utilisation for other cases where surgery may be in areas prone to movement, difficult to operate, and risky for the patient, such as lung cancer and prostate cancer.
This technique is possible due to the integration of magnetic resonance imaging (MRI) with linear accelerator (linac) technology, which has revolutionised the delivery of radiotherapy. The MR-Linac system provides real-time imaging during treatment, allowing clinicians to visualise the tumour's position and adjust the radiation delivery accordingly. This capability is particularly advantageous for prostate cancer treatment, where organ motion can lead to inaccuracies in radiation delivery.
Some centres now also offer further innovations such as MRIdian, an MR-Linac system that combines high-resolution MRI with precise radiotherapy beams. This system enables clinicians to monitor and adapt to prostate movement during treatment, enhancing the accuracy and effectiveness of the therapy
What are the benefits of stereotactic radiotherapy using MR-Linac?
What happens during stereotactic radiotherapy?
The course of SRT is usually between one to 10 treatments, and each session can last around three hours, but they can also be as short as 10 minutes – it will depend on the type and extent of the patient’s cancer. Before initiating treatment, the patient will undergo CT or MRI scans so that their doctors can map out where the cancerous cells are and create a programme for the therapy to avoid healthy tissue. They may make marks, out of pen or metal pellets or rods, in order to create a clear boundary of the treatment area for the radiographer to reference during treatment.
During a SRT session, the patient is secured to a bed so that they move as little as possible while receiving treatment. This is because the machine that emits the radiation does so from multiple different angles, which are beamed directly at the specific area where the cancer is, concentrating the dose. This high commitment to precision means that healthy tissue is not also receiving the radiation in full force, and may be marginally dosed with minimal side effects.
What are the benefits of stereotactic radiotherapy?
The use of MR-Linac technology for SRT in offers several advantages:
- Real-time imaging: Continuous MRI guidance allows for immediate adjustments to the radiation beam, ensuring it targets the tumour accurately despite any movement.
- Reduced treatment duration: MR-Linac-based SBRT typically requires fewer treatment sessions, often completed within five days, compared to traditional methods that may span several weeks.
- Enhanced precision: The ability to visualise the tumour during treatment increases the precision of radiation delivery, potentially improving treatment outcomes and reducing side effects.
- Simultaneous integrated boost (SIB): The MRIdian system allows for the delivery of higher doses to aggressive tumour areas within the prostate, enhancing the likelihood of tumour control without increasing the risk to surrounding healthy tissues.
SRT can be a preferable option for patients as it is minimally invasive, has fewer and milder side effects with less overall damage, and a shorter duration of treatment as compared to other forms of radiotherapy. It is an outpatient treatment, and the recovery time after the programme is projected to be short. The results have been comparable to cancer surgery with positive outcomes and a low risk of complications.
As technology continues to evolve, it is crucial for patients to discuss all available treatment options with their oncologist to determine the most appropriate approach for their individual circumstances.