EMPATHY

Evaluation and optimization of proton arc therapy

Project objectives and goals

Radiotherapy (RT) is an established modality for cancer treatment and broadly used for every second cancer patient. In the vast majority of treatments high-energy X-rays are used. Still, photon therapy (XRT) is irremediably limited by the physics of X-rays, depositing a lot of dose upstream and downstream of the target volume. In contrast, protons focus most of the dose in a well-determined area in the target. Compared to XRT, for the same dose in the target, proton therapy (PT) deposits about 50% less dose in the patient. This is particularly interesting in pediatric cases where it is of utmost importance to minimize the irradiation of healthy tissues to lower the risk of radiation-induced secondary cancers. In certain aspects, PT still lags behind XRT, compromising its dosimetric superiority. This concerns essential hardware and software components, for example on-board imaging with quantitative image information of sufficient precision tailored to the requirements of PT and the possibility of adapting the treatment according to the anatomy of the day. While in XRT it has become standard to irradiate while continuously rotating the beam around the patient (arc therapy), in PT usually only a few fixed beam directions are used. Fortunately, technologies are rapidly evolving in PT. Proton arc therapy and online adaptive PT will become reality with commercial solutions in the next couple of years. They will allow even better restriction of the dose to the target.
However, the introduction of these technologies leads to the emergence of new challenges: the combination of adaptive PT and proton arc therapy is not obvious, due to the considerable complexity of proton arc treatment planning. In addition, the dispersion of low doses over larger volumes of tissue and the more intensive use of X-ray imaging is a challenge. The reduction of imaging dose is of particular interest for pediatric patients. Our objective is to enable a major technological and clinical leap for PT, with the association of arc delivery, online treatment adaptation, and novel imaging modalities (photon counting CT), without eluding practical and implementation considerations. With a strong focus on the expected toxicity, with a thorough optimization of all irradiation sources, we will very likely and relevantly improve treatment outcome for pediatric cases, both short and long term.

Project coordinator

Carles Gomà, Research Foundation Clínic Barcelona-August Pi i Sunyer Biomedical Research Institute (IDIBAPS), Spain