Particle Therapy 2017

medicalphysicsweb.org/cws/article/opinion/32466 and other sources

The fall: toxicity

The rise: tumor control

• Rela)vely small installa)ons - spread of neutron therapy facili)es • Demonstra)on of tumor control in radio-resistant tumors • Salivary gland • Prostate • Pancreas

• Neutron beams produced by protons or deuterons with energies greater than about 50 MeV could produce tumor control with side effects no worse than low LET radia)on. For this reason facili)es which had performed clinical trials using rela)vely low energy beams either stopped trea)ng pa)ents or upgraded their accelerators to a higher energy.

• Computa)ons of absorbed dose did not include addi)onal neutron capture in hydrogen-rich )ssues, which results in higher energy release in hydrogen-rich )ssues. Such )ssues include white ma=er in the brain and the fat that surrounds most important organs, which is closely associated with their blood supply

• Neutron therapy using the 2-D techniques of the 1970s irradia)ng large volumes normal )ssue • The well-established finding that RBE varies in different )ssues was dismissed, along with the important fact that RBE increases with falling dose/frac)on, which mi)gates the effect of a reduc)on in physical dose beyond the region of cancer • The fact that RBE also varies with cell prolifera)on rate, so that slow-growing cells have higher values, was not appreciated. It is the slow-growing cells that make up the majority of normal )ssue and which contribute to severe )ssue damage at extended )me periods aRer irradia)on

The 1970s rise and fall of neutron beam therapy