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Home » EU Health, Health, Prostate Cancer

Image Guided Adaptive Radiotherapy

Submitted by on 14 Jul 2017 – 10:00

Image Guided Adaptive Radiotherapy combines state of the art imaging and radiotherapy techniques. Dr Ben Pais, Vice President Medical Affairs, Elekta, says it will contribute to better, more efficient and cost-effective treatment of patients with prostate cancer

Radiotherapy is one of the cornerstones in the treatment of men with prostate cancer, but also of many other patients. It can be used as monotherapy or together with surgery, chemotherapy, hormone therapy or any combination of these therapies. Interestingly the clinical outcomes do not vary a lot for any type of prostate cancer patient for either therapy. And patients with “low risk” prostate cancer are usually not actively treated anymore but monitored over time in “Watchful Waiting” or “Active Surveillance” programs. The development of radiotherapy techniques in combination with the improvement of imaging techniques has substantially contributed to improved treatment results which is the basis for the inclusion of radiotherapy in all international treatment guidelines for prostate cancer.

In the past two decades the use of imaging has become instrumental and has resulted in Image Guided RT (IGRT) becoming the standard of care whereby the accuracy of the radiation is optimised. Initially IGRT has been done with CT (Computed Tomography) but more and more CT is replaced by MRI (Magnetic Resonance Imaging) because of its advantages over CT. Soft tissue visualisation is much better with MRI.

Many anatomic structures can be better visualised with MRI than with CT which enables the radiation being delivered more precisely and accurately. Also, the generation of CT images needs a bit of radiation which makes it less suitable for frequent use. MRI does not need radiation for image generation. And, finally, CTs cannot provide anatomical data during radiation delivery which makes it impossible to use CT for real-time imaging when the patient is irradiated. MRI can be used in real-time procedures.

Image Guided Adaptive Radiotherapy (IGART), especially with MRI, has a number of advantages. The most important advantage is that it allows for real-time target visualisation during radiation. The target represents the tumour and the area around the tumour that is supposed to be irradiated. As a result the irradiation can be interrupted when the target moves outside the treatment field. Without the possibility to visualise the target radiation would continue and healthy tissue would be irradiated. But there are more advantages. In RT there are always margins around the tumours that must be irradiated and these margins also include healthy tissue.

IGART allows to reduce the margins and thereby reduce the volume of healthy tissue that is exposed to radiation. As a result the toxicity of the treatment is being reduced. At the same time it is anticipated that using IGART allows an increase of the dose to the target and higher doses are associated to better local (tumour) control, i.e. higher efficacy. This combination of higher efficacy and lower toxicity implies that the overall benefit-risk ratio of radiotherapy will improve.

Another aspect is the number fractions of a treatment. Radiotherapy is applied in a number of fractions, each used to administer a sub-dose of the overall, planned treatment dose. In the past two decades new RT-techniques have made it already possible to substantially reduce the number fractions from roughly over 30 fractions to around 20 or less fractions per treatment. IGART will most likely allow to further reduce the number of fractions. This process is referred to as hypofractionation.

It is generally known that in the upcoming decade the total number of patients with cancer will substantially increase which implies also a need for more radiotherapy treatments. In an era with limited growth possibilities for healthcare budgets this trend will demand more efficient treatment possibilities. Stereotactic Body Radiation Therapy (SBRT) is a form of RT combining a limited number of fractions (maximum 5 per treatment) with higher doses per fraction. SBRT reduces the overall treatment time of a patient without compromising the quality of the treatment. IGART makes it possible to treat more and more patients with SBRT so that more patients can be treated on one RT system, i.e. increase the efficiency of the treatment.

Prostate and thus its cancers typically move. IGART will help increasing the benefit-risk ratio of RT in the treatment of prostate cancer. There are potentially even further advantages. RT of prostate cancer currently irradiates the glad, mainly because it is difficult to precisely identify the tumour in the prostate. With the latest MRI innovations it is already possible to better diagnose the actual tumour in the prostate and it is likely that in the nearby future with real-time use of this type of MRI will allow to only that part of the prostate that contains the tumour.

Of course this require a state-of-the-art MRI with diagnostic quality combined a state-of-the-art linear accelerator, a so called “MR-Linac.”