Radiation therapy of tumours is a complex matter. One the one hand you want to remove the tumour, on the other you want to do it with as few side-effects as possible. The aim is to increase the focus on the damaged organs and avoid radiation on the healthy organs in the body, so as not to damage these in the process. This means that any radiation therapy must be tailored to each individual patient and administered in daily instalments over weeks, if not months.
Chief engineer and medical physicist Liv Bolstad Hysing at Haukeland University Hospital set out to improve on the methods currently in use. In the work on her doctoral thesis that was completed earlier this autumn and entitled «Exploring and exploiting the potential of IMRT to spare the bowel», Bolstad Hysing has designed a method that improves radiation precision by exploiting new technology more fully. Using her method the dosage employed on the damaged body parts can be intensified whilst minimising the radiation of healthy tissue.
A larger dose
Current radiation limits have been set conservatively for safety reasons.
– We won’t administer a dose that may incur serious side effects. But a number of patients return to us because they are not cured. If the doctor wants to administer a higher dose, this is a method that makes this practical, Bolstad Hysing says.
Contrary to common perception, organs are not immovable. They are in constant flux. Even when you measure a carefully specified area repeatedly, it is impossible to guarantee that healthy areas are not affected. The gut is particularly vulnerable when treating patients with prostate cancer and this is the organ that Bolstad Hysing focuses on in her work.
In the past this group of patients received inadequate treatment and often suffered intestinal problems after radiotherapy. But thanks to an advanced method known as Intensity-Modulated Radiation Therapy (IMRT) treatment is now more accurate. Whereas the tumour still receives high-dosage radiation, the intestines are shielded and there are fewer side effects. This tempts the use of higher dosage so that more patients may be cured. But to achieve this there needs to be strict control of the movement of body organs of each patient.
The movement of organs
Doctors, physicists and radiation therapists view a CT scan of the patient to see the outline of the tumour and the surrounding tissue. But a single CT scan only shows the outline at one given moment and by the time the patient is treated the organ may have moved.
In Bolstad Hysing’s method a number of CT scans are performed over a period of time. This way the movement of the intestines can be tracked on a day-to-day basis. This information is then used to create a predictability map for the intestines to target the radiation, and thus ensure better safety measures. By doing so, healthy areas can if possible be avoided or targeted with lower radiation levels.
– Some patients have guts that move a lot around, other patients have guts that stay pretty still. The more CT scans administered, the less margin for error. Most patients already receive very good treatment. But if you wish a larger dose or have an illness that makes you prone to intestinal disease, these extra scans may be worth it for both patient and doctor.
A method for the future
The advantages are obvious, but so are the extra costs. And the probability matrix is based on software that is not widely available yet, at least not in Norway. It may be a while before this method is applied.
– More tailored treatment requires more resources than at present. Basic research can sometimes be ten years ahead of its time. But there is a lot of interest in this method and in time it can help to provide better treatment, Liv Bolstad Hysing says.
Liv Bolstad Hysing’s project is one of the pioneering projects at MedViz, a cross-disciplinary research cluster and collaboration between the University of Bergen, Haukeland University Hospital and Christian Michelsen Research.