Future options: the potential role of proton irradiation

Because of its physical properties, proton irradiation should be the treatment of choice for loco regional irradiation of breast cancer patients. Conventional irradiation usually with photons has improved in the past decades reducing the dose to the organs at risk like the heart and the lungs. Still due to the properties of photons the organs at risk get unintended dose. Protons are charged particles and are able to deliver the dose to a specified depth where they stop and therefore no exit dose like in photon irradiation. This is the so-called Bragg Peak. Although in recent years there has been a clear increase in the number of proton facilities, the availability remains scarce and the costs high. The increased availability and improvement in delivery techniques have let to more interest in the applicability for breast cancer patients. The most important challenge is how to select patients that most benefit from this new technique. Irradiated breast cancer patients are at increased risk to develop cardiac and pulmonary toxicity and have more chance to develop secondary tumors. The advantages of dose reduction achieved by using proton irradiation or any other technique can be quantified by using data on dose effects relation for the toxicity of interest. Patients that most benefit from proton irradiation can be selected by the model based approach (the Dutch model). This model based approach quantifies the risk reduction based on the difference in dose to the organ of interest between photon and proton irradiation.