TU-G-BRCD-02: Do Uncertainties in Proton Therapy Limit Its Clinical Potential?

To discuss uncertainties in proton therapy and to outline how these might impact the widespread use of proton therapy.

This presentation will outline some of the differences in treatment planning for proton therapy as compared to photon therapy, in particularly related to the finite range of proton beams. The source of range uncertainties (e.g. dose calculation and treatment delivery) and some methods to address them will be presented. As examples we will discuss uncertainties in dose calculation in highly heterogeneous media (head and neck). Examples for in-vivo dose verification using dosimetric and imaging techniques in proton therapy will be outlined. Planning strategies to address uncertainties will be presented. Uncertainties due to the difference in biological effectiveness between proton and photon therapy will be addressed briefly.

The difference in physics between photon and proton interactions causes proton therapy to be associated with different type of uncertainties than photon therapy. These affect treatment planning decisions and can influence whether proton therapy does show a significant clinical advantage. Theoretical advantages in proton dose distributions as compared to photon therapy do not necessarily translate in clinical gains. Exceptions are, for example, pediatric patients where the reduction in integral dose causes significant improvements in treatment outcome as compared to conventional radiation Conclusions: Proton therapy is being used increasingly in radiation therapy. Due to inherent uncertainties in proton therapy delivery, its full potential advantage cannot yet be reached for all sites. Proton therapy personnel needs to be aware of the subtleties of proton therapy.

1. To understand how treatment planning decisions in proton therapy differs from photon therapy 2. To understand the source and the magnitude of proton range uncertainties 3. To understand how uncertainties in proton therapy affect the acceptance and spread of this modality.