Particle Therapy Practice. Sixty Years' Experience and Visions for the Next Century.

The history of particle therapy practice started when fast neutron treatment was performed at LBL in 1938. Thereafter, hope and despair followed repeatedly. Based on the initial malpractice at LBL, fast neutron therapy was re-introduced into clinical trial at Hammersmith Hospital, which resulted in an amazingly hopeful outcome. Hammersmith's results encouraged the practice of particle therapy worldwide. Though numbers of huge accelerators were constructed and many extensive clinical trials were undertaken, little absolute gain for fast neutron therapy was demonstrated. The clinical results of boron neutron capture therapy (BNCT) using thermal neutrons from atomic reactors are still far from satisfactory and negative pion therapy failed to show appreciable benefits as expected. Particle therapy practice fell into a temporary depression in the late 1980's. Proton therapy coming after those failures have carefully established its efficacy by demonstrating superb results in limited diseases such as intraocular melanomas and skull base tumors. Recent advances in technology along with evolving needs of society have highlighted particle therapy again. Many new proton treatment facilities have been constructed around the world since the first dedicated proton treatment facility was built at Loma Linda University Medical Center in 1990. Heavy ion therapy has been expected to have superior biological effects to proton therapy. HIMAC at NIRS is the first dedicated heavy ion medical facility which started treatment in 1994 to clarify its use in clinical oncology. Particle therapy has now become eligible in a hospital-based setting and surrounding situations are dramatically changing. Clinical efficacy of particle therapy should be demonstrated in appropriate manners based on the reflection of past history, while its relative cost should not be extremely unequaled to other modalities to justify its existence as an open medical practice in the future.