Proton Therapy Congress 2016
A model-based selection approach to identify suitable indications for proton therapy
Prof Johannes Langendijk - University of Groningen, Groningen, Netherlands
My talk in this conference was about the model-based approach. The model-based approach is a methodology which allows us to select patients for proton therapy that will benefit most from this new technology. What we expect, at least in the Netherlands, that 85% of the future indications for proton therapy will be to prevent side effects from radiation therapy, especially late side effects that can be persistent but also progressive. We also know that these side effects have a major impact on the quality of life of cancer survivors so therefore we think it’s clinically relevant. This methodology uses a so-called planning comparative study, so what we do there is that we make a treatment plan using the current technique, which is normally IMRT, then we make a treatment plan using the new technique, in this case IMPT, we compare the dose distributions and based on the dose distributions we can also produce a toxicity profile, an expected toxicity profile, for both plans. If you compare these you can calculate the difference in expected toxicities between the current technique and proton therapy.
So what we do with this methodology is that we first make a treatment plan using the current technology which is photons then we make another treatment plan using the new technology which is protons, then we compare the dose distributions between the two technologies, especially with regard to the dose in the critical healthy tissues. Then we use that information to estimate the risks on radiation-induced side effects in the future. Based on the differences in expected side effects we can then make a decision whether these patients will benefit from protons, yes or no.
Have these models matched patients’ responses?
At present we did not use already this methodology in the Netherlands so this is just what we developed in order to select patients in a proper way because the accessibility for patients and the capacity that we will create in the Netherlands will be very limited - in the beginning only for less than 1% and it will increase to a capacity which can treat about 3% of all patients that are currently treated with external beam radiotherapy in the Netherlands. So we need a kind of method to select those patients that will benefit most from this new technology.
What is your take- home message?
In summary, I think that this methodology is important to select patients that will have the most benefit from the new technology and therefore it’s also the most cost-effective way of selecting patients for new technologies in general. In addition to that, I also think that if you want to design randomised controlled trials comparing two technologies in a randomised fashion that also this model-based selection method is required to indeed select the patients for the new technology that may potentially benefit from it. It does not make sense to enter a patient into a randomised controlled trial from which you already know that the dose distributions with IMRT and IMPT are exactly the same, you will not expect a difference then.
