Microdosimetric specification of the radiation quality of a d(48.5)+Be fast neutron therapy beam produced by a superconducting cyclotron

The proportional counter microdosimetric technique has been employed to quantify variations in the quality of a d(48.5)+Be fast neutron beam passing through a homogeneous water phantom. Single event spectra have been measured as a function of spatial location in the water phantom and field size. The measured spectra have been separated into component spectra corresponding to the gamma, recoil proton and alpha plus heavy recoil ion contribution to the total absorbed dose. The total absorbed dose normalized to the "monitor units" used in daily clinical use has been calculated from the measured spectra and compared to the data measured with calibrated ion chambers. The present measurements agree with the ion chamber data to within 5%. The RBE of the neutron beam is assumed to be proportional to the microdosimetric parameter y* for the dose ranges pertinent to fractionated neutron therapy. The relative variations in y*, assumed to be representative of variations in the RBE are mapped as a function of field size and spatial location in the phantom. A variation in the RBE of about 4% for points within and 8% for points outside a 10 cm x 10 cm field is observed. The variations in the RBE within the beam are caused by an increase in the gamma component with depth. An increase in the RBE of about 4% is observed with increasing field size which is attributed to a change in the neutron spectrum. Compared to the uncertainties in the prescribed dose, associated with uncertainties in the clinically used RBE, variation in the RBE between various tissues, and other dosimetric uncertainties caused by factors such as patient inhomogeneities, patient setup errors, patient motion, etc., the measured spatial RBE variations are not considered significant enough to be incorporated into the treatment planning scheme.     

Acceleration of ageing processes by ionizing radiation (author''s transl)]

The dynamics of arterial, venous, and lymphatic flow in the mesentery were studied in dogs, using an electromagnetic flowmeter for the blood and cannulation and gravimetric measurement for the lymph. Ligation of veins caused an increased venous outflow in adjacent veins and a marked increase in lymph flow. When marginal vessels were ligated, eliminating the major collateral flow, venous flow decreased, but elevated lymph flow persisted. Simultaneous ligation of arteries and veins resulted in increases of both arterial and venous flow in adjacent vessels. Lymph flow decreased unless excessive arterial collateral flow persisted. When collateral marginal vessel flow was occluded, adjacent venous and arterial blood flow decreased to control levels. With arterial ligation, collateral arterial blood flow increased slightly, but venous and lymph flow decreased sharply. When collateral marginal vessels were eliminated, adjacent arterial blood flow decreased to control levels and venous flow virtually stopped. As a result of these studies, the technic of early primary arterial ligation followed by marginal vessel ligation appears to be the most satisfactory procedure for decreasing venous and lymphatic outflow and hopefully avoiding dissemination of cancer cells during the operation. This technic is now being used as a modification of the "no touch" technic for cancer of the colon.     

Study of dental materials by laser beam scanning

Several properties of dental materials are characterized by dimensional variation induced by different parameters. In this work a non-contact method used for measurement of linear dimensional variation is shown. The accuracy is +/- 1 micron for sample length ranging from 1 to 70 mm.