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J S Laughlin

Publications and source records attributed to J S Laughlin.

At least 91 records · Page 5Linked to original sources
PubMedDate not supplied

Portable tissue equivalent calorimeter.

A portable tissue equivalent calorimeter has been constructed and employed to measure absorbed dose in a mixed fast-neutron and gamma-ray field. Design details and measurement techniques are described along with the limits of precision and absolute accuracy. Experiments have been carried out with a cyclotron produced neutron beam using the 9Be(d,n)10B reaction at dose rates ranging from 3 to 25 rad/min. A series of ten measurements at a dose rate of approximately 10 rad/min were performed with a precision of +/- 2% (standard deviation about the mean). The compact design of this calorimetric dosimeter system facilitates transport to other laboratories for the measurement of absorbed dose in several complex radiation fields.

Calorimetry↗
PubMedDate not supplied

Calibration methods for measuring splenic sequestration by external scanning.

Conventional methods for measuring splenic sequestration of labeled cells rely on stationary probe counting over the liver and spleen. A quantitative spleen-scanning method is proposed as a means of performing a more accurate diagnosis of the degree of splenic sequestration. Improved methods for calibrating a rectilinear scanner employing "constant resolutions" collimators, designed for the in vivo measurement, are reported, Clinical evaluation of this method was performed by scanning several patients scheduled for splenectomy. Good correlation between in vivo and in vitro measurements of splenic radioactivity for 29 patients was obtained. A least-squares fit to the data yielded a coefficient of determination r2=0.93.

Chromium Radioisotopes↗
PubMedDate not supplied

Dosimetric measurements in the neutron field produced by a deuterium gas target with a compact medical cyclotron.

Several dosimetric measurements have been carried out in the neutron field produced by accelerated deuterons incident upon a pressurized deuterium gas target. A significant improvement has been achieved in central-axis depth dose when compared to the 9Be(3He,n)11C interaction previously studied . Designs for a target with a high-power dissipation capability are currently underway.

Deuterium↗
PubMedDate not supplied

Design for a multiple target system for a medical cyclotron.

A novel target system has been designed for a compact cyclotron. The system permits one of three or more targets to be selected remotely for bombardment, permits all target and chemical operations to be controlled remotely, causes no change in beam energy or beam current, occupies a limited space, and is simple to construct and maintain. The targets are mounted to a flexible bellows-multiple port manifold assembly, supported on a fan-shaped turntable. A motor moves the system to align the target to be bombarded with the main beam axis. Designs for two subassemblies are also presented. These are a retractable target chamber for water and a remotely controlled variable collimator.

Particle Accelerators↗
PubMedDate not supplied

"Nonisolated-sensor" solid polystyrene absorbed dose measurements.

A "nonisolated-sensor" solid polystyrene calorimeter was constructed to test the role of thermal diffusion in limiting the length of irradiation time during which temperature measurements with nonisolated sensors could be made sufficiently free of drift for determining dose with radiation fields such as gamma rays, x rays, and high-energy electrons. From measured ratios of dose at 5.0 and 0.5 cm in polystyrene and comparisons to dose measurements with a polystyrene parallel-plate (pancake) ion chamber, it was shown that thermal diffusion is sufficiently small in polystyrene to permit accurate measurements for irradiation periods of less than 20 min. Comparison of the absorbed dose measurements and depth dose ratios with pancake ion chambers and calorimeter showed, that within the precision and accuracy of the two measuring systems, there is close agreement. The nonisolated-sensor solid polystyrene calorimeter has the interesting features of (i) simplicity of construction, (ii) simplicity of operation without vacuum or feedback for temperature control, (iii) capability of simultaneous measurements at several depths and off-axis positions, (iv) the very small thermal defect correction with polystyrene, and (v) operation with the calorimeter in any orientation.

Calorimetry↗
PubMedDate not supplied

Phosphorus activation neutron dosimetry and its application to an 18-MV radiotherapy accelerator.

Neutron fluxes and dose rates in and near the 18-MV x-ray beam of a Therac-20 accelerator were determined with measured activities from the nuclear reactions 31P(n, rho)31Si (fast neutrons) and 31P(n, gamma)32P (thermal neutrons), published cross sections, and neutron energy spectra from Monte Carlo calculations. Measurements were made in the patient plane in air and at a 10-cm depth in a tissue-similar phantom, and in a plane containing the x-ray target. Orthophosphoric acid solution was identified as a suitable and convenient phosphorus dosimeter material. In the 31P activation method, fluxes and dose rates are determined as the product of measured saturation activity per 31P atom and a conversion factor, which depends on the shape of the assumed neutron spectrum. For fast neutrons, which deliver most of the dose, the accuracy error in the saturation activity determinations was shown to be approximately less than 25%. An inconsistency resulting from neglect of the accelerator's adjustable collimator in the Monte Carlo calculations was demonstrated between the measured saturation activities and the theoretical neutron spectra. The maximum neutron dose equivalent rate observed was 5.9 mSv/Gy of x-ray absorbed dose at the accelerator calibration point. Surface dose equivalent rates of the present study are less than those of fluxmeter and remmeter studies at sites outside Therac-20 treatment fields by as much as factors of 2.4 and 2.8, respectively. The phantom study showed that at 18 MV internally produced neutrons have a negligible effect on the neutron field within the patient.

Neutrons↗
PubMedDate not supplied

Neutrons from high-energy x-ray medical accelerators: an estimate of risk to the radiotherapy patient.

The problem of neutrons produced by many of the high-energy x-ray therapy machines (10 MV and above) is reviewed, and the possible risk their presence poses to radiotherapy patients is estimated. A review of the regulatory background containing a summary of the recommendations of the U.S. Council of State Governments (USCSG), and of the International Electro-Technical Commission (IEC), as well as an indication that recommendations will be forthcoming from the National Council on Radiation Protection (NCRP) and the International Commission of Radiological Protection (ICRP) is presented. The neutrons in question are produced by high-energy photons (x rays) incident on the various materials of the target, flattening filter, collimators, and other essential components of the equipment. The neutron yield (per treatment dose) increases rapidly as the megavoltage is increased from 10 to 20 MV, but remains approximately constant above this. Measurements and calculations of the quantity, quality, and spatial distribution of these neutrons and their concomitant dose are summarized. Values of the neutron dose are presented as entrance dose, midline dose (10-cm depth), and integral dose, both within and outside of the treatment volume. These values are much less than the unavoidable photon doses which are largely responsible for treatment side effects. For typical equipment, the average neutron integral dose from accelerator-produced neutrons is about 4-7 g cGy (per treatment cGy), depending on the treatment plan. This translates into an average dose of neutrons [averaged over the body of a typical 70-kg (154 lb) patient] of 0.06-0.10 cGy for a treatment of 1000 cGy. Using these neutron doses and the best available neutron risk coefficients, it is estimated that 50 X 10(-6) fatal malignancies per year due to the neutrons may follow a typical treatment course of 5000 rads of 25-MV x rays. This is only about 1/60th of the average incidence of malignancies for the general population. Thus, the cancer risk to the radiotherapy patient from accelerator-produced neutrons poses an additional risk to the patient that is negligible in comparison.

Abnormalities, Radiation-Induced↗
PubMedDate not supplied

Tumor imaging with carbon-11 labeled alpha-aminoisobutyric acid (AIB) in patients with malignant melanoma.

The potential usefulness of [C-11]-labeled alpha-aminoisobutyric acid (AIB) for tumor imaging has been demonstrated previously in our findings of increased tumor uptake with C-14-labeled AIB in human melanoma heterotransplants in nude mice, and subsequently, in a single case study using C-11 AIB to demonstrate the extent of metastases in patient with widespread malignant melanoma. We report here on the use of C-11 AIB in ten patients with metastatic or unresectable malignant melanoma. Five patients had intense tracer uptake at all known sites of tumor involvement. A sixth patient had good uptake in metastatic lesions in the shoulder and the pelvis, but did not demonstrate uptake within metastatic lesions in the lungs. Two patients had only minimal uptake over the tumor lesions while the two other patients had essentially normal studies. Further studies with C-11 AIB in patients with melanoma and other tumors are warranted.

Adult↗