The source strength of encapsulated 60Co gamma-ray brachytherapy sources for the high dose rate remote afterloader was measured by the newly developed sandwich method. The calibrated JAPM sub-standard dosemeter whose collecting size is 6 mm in diameter and 20 mm long was used with a digital voltmeter capable of four digits. A sandwich output measuring device made of lucite which has two build-up caps and a bar to fix a guide tube for source capsule was used to achieve a precise result at a short distance from the source. A space between two build-up caps is fixed at 16.0 cm to reduce an error due to geometrical setting up, in the just middle of which the source is transfered through a thin plastic guide tube from a source container. Correction factors were calculated for finite size of the ionization chamber and multi-cells source to regard them as a point detector and a point source. The output is given in the unit of R min-1 cm2 or Gy min-1cm2. The intercomparison of the source strength was also performed with 33 source capsules in 12 radiotherapy facilities.

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Central axis tissue-air ratios (TAR) for 4 MV x rays of a large number of square, rectangular and irregular fields defined by a multi-split collimator for conformation therapy were obtained experimentally up to a depth of 25 cm. Families of TAR curves as a function of area at depth, divided by perimeter (A/P) for fixed values of depth were plotted first using the data for square fields. These were then compared with data for irregular fields. When the equivalent perimeter of the field Pe was used, rather than the real perimeter P, the A/P method for determining TAR was found to be applicable within a 2% error up to a 15 cm depth for uneven fields shaped with the multi-split collimator.

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Response characteristics of two types of thermoluminescent neutron dosimeters were studied. One is a 30 cm-diameter polyethylene-paraffin (PEP) sphere with CaSO4: Tm+6Li (UD 136N) and CaSO4+7Li (UD 137N) at the center and the other is a 5cm-diameter PEP hemisphere containing six pairs of TLDs, in which four pairs are covered with cadmium and two pairs without cadmium. Comparison of sensitivities of CaSO4: Tm+6Li, Li2B407: Cu, and TLD 600 ribbon to thermal neutrons and gamma rays was also made. The 30 cm-sphere dosimeter was found capable of measuring 0.3 mrem of neutron dose in gamma background up to 1.2 mR. The 5 cm-hemisphere dosimeter was found suitable for neutron measurement received by personnel while handling 252Cf sources. The UD 136N was found to be 7 times more sensitive to thermal neutrons than TLD 600 ribbon. The results of measurements of practical neutron fields with these thermoluminescent neutron dosimeters were described. (This work was supported in part by the U. S. Department of Energy under contract No. EY-76-C-09-0739.)

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Reciprocal visits have been made to National Institute of Radiological Sciences by the physicists from Texas A&M University, M. D. Anderson Hospital, University of Washington and Institute of Medical Sciences of Tokyo Univertity for a neutron dosimetry Intercomparison in 1976. The parameters that the usually measured are tissue dose in air, tissue dose at the depths of 5,10,15 and 20 cm in TE liquid phantom, neutron/gamma ratios in air and in phantom, and photon calibration of ionization chambers. Other parameters that are compared are kT-factor and ku-factor which are concerned in W-value, stopping power ratios and kerma ratios, and correction factor for an ion loss by recombination. After the intercomparison the measurements of ku have been made by NIRS physicists using the modified lead filtration method. The reevaluation of the data has been made for a comparison using an observed ku and theoretical kT which has been calculated using revised kerma factors by ICRU in 1977. This paper describes some of the results of the intercomparison and discusses the implications of the findings.

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A personal monitoring has been carried out using thermoluminescent dosimeter (TLD) to assess radiation exposure to nurses during the care of the patients who were treated with radium interstitial brachytherapy in the protected ward. The nursing procedures monitored were drip infusion to upper extremity, intramuscular injection to upper and lower extremity and tracheal aspiration for the patients of tongue cancer, and drip infusion to upper extremity, change of diaper and record of urine output for gynecological patients. The results measured were expressed as specific exposure in terms of mR per mg of radium to compare the exposure of each implant and to obtain difference of specific exposure between the nurses for each nursing procedure individually. The specific exposure of well experienced nurses were less than those of little experienced nurses. And, large difference of specific exposure between individual nurse indicates the necessity of improvement and standardization of nursing procedures. TLD monitoring was found to be convenient to inspect nursing procedure individually for the works with brachytherapy sources so that the reduction of radition exposure and also the reduction of apprehension felt by the nursing staff can be expected.

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