The Actual Interest in Radiotherapy for the Utilization of Proton Beam, Highlighting Physics Basis, Technology and Common Clinical Indications

Abstract

Managing expensive technology is a debated issue in modern radiation oncology. Proton beam therapy (PBT) represents, considering its cost and its foreseen benefits, a typical case of discussion waiting for more robust results demonstrating the presumable clinical gains against the available radiation therapy (XRT) treatment alternatives based on the use of photons. The treatment with particles utilizes many different beams (neutrons, protons, pions, or helium, neon, argon, and carbon ions) that represent a distinct entity respect conventional XRT which uses photons. PBT is the most common form of heavy-particle radiation therapy used so far; it is not a new invention, being its clinical use proposed in a seminal article by R. Wilson in 1946[1] and the first patients treated in 1954 at the Lawrence Berkeley National Laboratory in California[2]. Since cyclotron or synchrotron, used to accelerate protons to therapeutic energies, were used primarily for research in particle or nuclear physics, the initial clinical activity in proton therapy was carried out in research facilities and the use of protons in clinical practice has grown slowly for several years in non-clinical setting. More than fifty years later, after a long period of seminal work in a limited number of Institutions, PBT has gained public attention in recent years because of the rapidly increasing number of centers around the world, regardless of their high cost. Hospital-based proton beam facilities have been in operation since 1990 after the opening of the first dedicated clinical center at Loma Linda Medical University Center in California - US. Since that years, commercial entities began to build cyclotrons and synchrotrons for clinical purposes. Over the last 10 years, PBT has gathered more interest in the scientific community and more media and patient attention and is now flourishing in the US and abroad. As of December, 2015, 57 proton therapy centers are in operation worldwide, others are under construction and many more in a planning phase[3]. Most patients who have been treated with heavy-particle therapy were treated with protons: PTCOG (Particle Therapy Co-Operative Group) reports that between 1954 and 2014, 137 000 patients globally received part or all of their radiation therapy with particles, and in particular 86% of them with protons[4]. The generation of these particles and the building of dedicated centers, however, requires large investments and operational costs and big infrastructure. Only relatively few studies have demonstrated the effectiveness of proton therapy and the effects are surrounded with uncertainty[5] being the cost-effectiveness still the core of the controversy around the use of PBT.