Signedunsigned
Inscribedon shaft: 2.5
Historical AttributesThese range modulators were used in treating cancer patients with proton beam radiation at the Harvard Cyclotron Laboratory.
The tightly-focused cyclotron beam had to be spread out to cover the tumor with a uniform dose. The hardware was grouped in a nozzle-shaped treatment head. The beam first met two scatterers, which spread protons uniformly across a circular area. Next the stepped blades of the spinning range modulator spread the dose out in depth. A fixed absorber served as range shifter to control the maximum depth of penetration in the tumor. Nearer to the patient and held in a metal snout (which stopped unwanted protons), the protons met a patient-specific brass aperture and acrylic bolus (or range compensator). The aperture defined the cross-sectional shape of the dose. The bolus determined its distal shape and compensated for inhomogeneity (such as bone) through which the protons would go.
ProvenanceHarvard Cyclotron Laboratory, Cambridge, MA, 1960s-2002; The Francis H. Burr Proton Therapy Center at Massachusetts General Hospital, Boston, 2002-2009; transfer to CHSI, 2009.