Studies of physiology and the morphology of the cat LGN following proton irradiation

Generation and Characterization of a Proton Microbeam for Experimental Radiosurgery

A proton microbeam has been developed to support various research endeavors. Test subjects may be irradiated from any angle with respect to the vertical because the beamline is contained within a rotating gantry used for human patients. Converting from the treatment to experimental arrangement is quick and straightforward as is the reverse. Using a series of collimators, the final beam diameter at the surface of the subject is 1 mm. The depth from the surface to the Bragg peak in water is 15 mm. Fluence distributions perpendicular to the beam axis were determined by scanning radiographic film exposed at various depths with a scanner having a pixel size of 84.7 μm. The depth dose integrated over the beam area was measured using a parallel plate ionization chamber. Central axis depth doses were calculated by multiplying the ionization chamber signal by the ratio of film doses for the central axis pixels to the integrated beam doses at each depth. A Faraday cup was used to confirm the dose at the surface while TLDs, diodes, and film were used to verify the dose at depth. The usefulness of this beamline for experimental situations has been demonstrated in a feline neurological study. The dosimetry techniques are useful for narrow beams such as used for functional radiosurgery treatments of humans.

Ion beam radiobiology and cancer: time to update ourselves

High-energy protons and carbon ions exhibit an inverse dose profile allowing for increased energy deposition with penetration depth. Additionally, heavier ions like carbon beams have the advantage of a markedly increased biological effectiveness characterized by enhanced ionization density in the individual tracks of the heavy particles, where DNA damage becomes clustered and therefore more difficult to repair, but is restricted to the end of their range. These superior biophysical and biological profiles of particle beams over conventional radiotherapy permit more precise dose localization and make them highly attractive for treating anatomically complex and radioresistant malignant tumors but without increasing the severe side effects in the normal tissue. More than half a century since Wilson proposed their use in cancer therapy, the effects of particle beams have been extensively investigated and the biological complexity of particle beam irradiation begins to unfold itself. The goal of this review is to provide an as comprehensive and up-to-date summary as possible of the different radiobiological aspects of particle beams for effective application in cancer treatment.

Late effects from hadron therapy

Successful cancer patient survival and local tumor control from hadron radiotherapy warrant a discussion of potential secondary late effects from the radiation. The study of late-appearing clinical effects from particle beams of protons, carbon, or heavier ions is a relatively new field with few data. However, new clinical information is available from pioneer hadron radiotherapy programs in the USA, Japan, Germany and Switzerland. This paper will review available data on late tissue effects from particle radiation exposures, and discuss its importance to the future of hadron therapy. Potential late radiation effects are associated with irradiated normal tissue volumes at risk that in many cases can be reduced with hadron therapy. However, normal tissues present within hadron treatment volumes can demonstrate enhanced responses compared to conventional modes of therapy. Late endpoints of concern include induction of secondary cancers, cataract, fibrosis, neurodegeneration, vascular damage, and immunological, endocrine and hereditary effects. Low-dose tissue effects at tumor margins need further study, and there is need for more acute molecular studies underlying late effects of hadron therapy.

Radiosurgery of the Rat Hippocampus: Magnetic Resonance Imaging, Neurophysiological, Histological, and Behavioral Studies

OBJECTIVE

To explore the histological, electrophysiological, radiological, and behavioral effects of radiosurgery using a new model of proton beam radiosurgery (PBR) of the rodent hippocampus.

METHODS

Forty-one rats underwent PBR of the right hippocampus with nominal doses of 5 to 130 cobalt Gray equivalents (CGE). Three control animals were untreated. Three months after PBR, 41 animals were evaluated with the Morris water maze, 23 with T2-weighted magnetic resonance imaging, and 22 with intrahippocampal microelectrode recordings. Animals that were studied physiologically were killed, and their brains were examined with Nissl staining and immunocytochemical staining for glutamic acid decarboxylase, heat shock protein 72 (HSP-72), parvalbumin, calmodulin, calretinin, calbindin, and somatostatin.

RESULTS

Ninety and 130 CGE resulted in decreased performance in the Morris water maze, increased signal on T2-weighted magnetic resonance imaging, diminished granule cell field potentials, and tissue necrosis, which was restricted to the irradiated side. These doses also resulted in ipsilateral up-regulation of calbindin and HSP-72. Parvalbumin was down-regulated at 130 CGE. The 30 and 60 CGE animals displayed a marked increase in HSP-72 staining on the irradiated side but no demonstrable cell loss. No asymmetries were noted in somatostatin, calretinin, and glutamic acid decarboxylase staining. Normal physiology was found in rats receiving up to 60 CGE.

CONCLUSION

This study expands our understanding of the effects of radiosurgery on the mammalian brain. Three months after PBR, the irradiated rat hippocampus demonstrates necrosis at 90 CGE, but not at 60 CGE, with associated abnormalities in magnetic resonance imaging, physiology, and memory testing. HSP-72 was up-regulated at nonnecrotic doses.