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Clinical Issues in Proton Radiotherapy
Clinical Issues in Proton Radiotherapy
Thomas F. DeLaney
The unequivocal evidence that higher radiation doses to the tumor result in higher rates of local tumor control in animals1 and patients2 and that higher doses to normal tissues increase the risk for complications3 have spurred technical developments in radiation oncology to optimize therapeutic ratio by maximizing tumor dose and minimizing normal tissue radiation. The physical properties of protons described in the preceding chapters made them a good choice for studies in the clinic designed to improve the therapeutic ratio. Exploratory studies outlined in Chapters 1 and 2 established an estimate of the proton relative biological effectiveness (RBE) of 1.1 that appeared to be clinically appropriate and that has been adopted in most clinics.4 The pioneering clinical studies performed at the Massachusetts General Hospital (MGH)-Harvard Cyclotron Laboratory (HCL) established that protons could be used to deliver higher and more highly localized doses to tumors in patients than had been technically possible with photons.5 The tumors selected for initial study, choroidal melanoma, base of skull and cervical spine chordomas and chondrosarcomas, and prostate cancers, were chosen because local control at conventional photon doses were suboptimal and because these anatomic sites could be reached with the 160-MeV, fixed horizontal beam available at the HCL.6
The excellent results achieved in these tumors were duplicated in other facilities around the world, often by clinicians and physicists who had the opportunity to visit or spend fellowship time at the MGH-HCL.7,8 Indeed, this sophisticated technology was not only transferable but its adoption in new facilities often yielded new technologic and clinical advances.9 The opening of multiple new facilities is expected to accelerate the rate of technologic advance in the field.
The Particle Therapy Cooperative Group (PTCOG) was formed in the 1980s10 to share ideas and advance the field, with one of its goals to develop hospital-based proton facilities that could treat tumors anywhere in the body with rotational gantries analogous to those which were standard on clinical photon linear accelerators. This goal was achieved with the opening of the hospital-based facility at Loma Linda University in 1990; multiple facilities since then that have opened around the world. A list of the 28 operational charged particle facilities (as of December 2006) and the number of patients treated by each is shown in Table 9.1. Twenty-five of these facilities are currently treating with protons, two (NIRS in Chiba, Japan and Gesellschaft für Schwerionenforschung [GSI] in Darmstadt, Germany) are treating with carbon ions, and one (in Hyogo, Japan) is using both. There are now many other proton facilities in various states of planning, construction, and commissioning. These new hospital-based facilities with rotational gantries have greatly expanded the anatomic sites and clinical scenarios for which proton delivery is now technically possible. This chapter will address some of the clinically relevant issues that will be important for optimizing the use of protons in these facilities. Chapter 10 will address similar issues for the use of heavier charged particles. Note that the clinical results and proton and heavier charged particle therapy techniques for individual anatomic sites and tumor types will be addressed in detail in Chapters 11-22.
