Volume 2, Issue 2, March 1975
Index of content:
Boron neutron capture therapy for the treatment of cerebral gliomas. I: Theoretical evaluation of the efficacy of various neutron beams2(1975); http://dx.doi.org/10.1118/1.594168View Description Hide Description
The technique of boronneutron capture therapy in the treatment of cerebral gliomas depends upon the selective loading of the tumor with a 10B‐enriched compound and subsequent irradiation of the brain with low‐energy neutrons. The charged particles produced in the 10B (n,α) 7Li reaction have ranges in tissue of less than 10 μm so that the dose distribution closely follows the 10B distribution even to the cellular level. The effectiveness of this therapy procedure is dependent not only on the 10B compound but on the spectral characteristics of the neutron source as well. Hence, an optimization of these characteristics will increase the chances of therapeutic success. Transport calculations using a neutral particle transport code have been made to determine the dose–depth distributions within a simple head phantom for five different incident neutron beams. Comparison of these beams to determine their relative therapeutic efficacy was made by the use of a maximum useable depth criterion. In particular, with presently available compounds, the MIT reactor (MITR) therapy beam (a) is not inferior to a pure thermal neutron beam, (b) would be marginally improved if its gamma‐ray contamination were eliminated, (c) is superior to a partially 10B‐filtered MITR beam, and (d) produces a maximum useable depth which is strongly dependent upon the tumor‐to‐blood ratio of 10B concentrations and weakly dependent upon the absolute 10B concentration in tumor. A pure epithermal neutron beam with a mean energy of 37 eV is shown to have close to the optimal characteristics for boronneutron capture therapy. Furthermore, these optimal characteristics can be approximated by a judiciously D2O moderated and 10B‐filtered 252Cf neutron source. This tailored 252Cf source would have at least a 1.5 cm greater maximum useable depth than the MITR therapy beam for realistic 10B concentrations. However, at least one gram of 252Cf would be needed to make this a practical therapy source. If the moderated 252Cf source is not 10B filtered, the resultant neutron beam has characteristics similar to those of the MITR beam with no gamma‐ray contamination. For such a beam, 100 mg of 252Cf would produce a flux of 2.4×108 neutrons/(cm2 sec), which is an intensity suitable for therapy applications.
2(1975); http://dx.doi.org/10.1118/1.594167View Description Hide Description
There is renewed interest in diagnostic radiology in electrostatic methods of imaging, such as xeroradiography and ionography. This is due to the fact that edge contrast can be achieved, aiding in the visualization of soft tissue tumors. In analyzing the image forming properties of these systems, we chose to solve the electrostatic problems by the method of images. We present methods and recursion formulas for calculating electrostatic fields due to (a) any charge distribution on a slab of dielectric (the solution involves a single infinite series) or (b) the same as the above with the introduction of an additional ground plane parallel to the dielectricsurface (the solution now involves double infinite series). Analysis of these fields suggests new methods of controlling edge contrast and development configurations where the field which penetrates through the foil is used to produce the final image rather than the field above the charged surface.
Simple method for the generation of organ and vessel contours from roentgenographic or fluoroscopic images2(1975); http://dx.doi.org/10.1118/1.594169View Description Hide Description
A simple method is described for outlining or contouring any area defined by a change in film density or fluorscopic screen intensity. The entire process, except for the positioning of an electronic window, is accomplished using a small computer having appropriate software. The electronic window is operator positioned over the area to be processed. The only requirement is that the window be large enough to encompass the total area to be considered.
2(1975); http://dx.doi.org/10.1118/1.594170View Description Hide Description
Atomic Energy of Canada Limited 60Co teletherapy units have adjustable collimator hinges to adapt to source diameters from 0.75 to 2.50 cm. Adjustment of the collimator hinge to the manufacturer’s settings can cause a loss of radiation field flatness as high as 20% for large fields. The recommended settings appear to clip the top corners of tall source capsules. Opening the hinge adjustment restores field flatness, without changing penumbra or the inverse square law behavior of the teletherapy unit.
Laser modification to an x‐ray collimator: An aid in positioning patients for neurosurgical and radiographic procedures2(1975); http://dx.doi.org/10.1118/1.594171View Description Hide Description
In high‐ambient‐light levels such as are found in operating rooms, and at long target‐to‐patient distances, the cross lines and light field projected from conventional x‐ray collimators are not easily visible and proper patient positioning is difficult. The collimators on two mutually perpendicular x‐ray units have been modified by replacing the incandescent bulbs with lasers and adjusting the lasers to be coaxial with the x‐ray beams. These modifications have been coupled with a third wall‐mounted laser to facilitate patient positioning for stereotaxic thermal hypophysectomy. The use of the laser‐modified collimators has resulted in considerable saving of time for the operating team and has markedly reduced patient anesthesia time. The laser‐modified collimator has also been found useful in positioning patients for other radiographic procedures in the operating room and has virtually eliminated retakes due to malpositioning.
2(1975); http://dx.doi.org/10.1118/1.594173View Description Hide Description