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AN AUTOMATIC PATIENT-CONTOUR MEASURING APPARATUS

LAWRENCE H. LANZL PH.D., THOMAS J. AHRENS , MARTIN ROZENFELD M.S., and LEON BESS PH.D.1

1 NASA, Electronics Research Center, 575 Technology Square, Cambridge, Massachusetts.

All optical-electronic system has been developed as a new approach to the task of measuring and recording patient contours. The system projects 2 slightly convergent light beams onto the patient. The resultant light spots are detected by a photomultiplier tube that is located behind a rotating slit wheel. The photomultiplier produces pulses that are analyzed to generate a voltage proportional to distance. An extremely stable system results from the use of time-dependent pulsed circuitry. The voltage generated by the system is used to drive the pen of a polar-coordinate recorder, while its table is synchronized to the rotation of the cobalt 6o unit in which the optical portion of the system is mounted.

The polar recorder has 2 channels, one of which is used to plot patient contours, while the other is used in conjunction with a transmission ionization chamber to record transmission dose or the "equivalent" homogeneous contour. The recorder is mounted in a portable utility cabinet and can be used in the therapy room prior to treatment or at the control console prior to or during treatment.

Because of the ease of operation, the 30 second recording time, and accuracy of the order of 1 mm., this system has been readily accepted by the medical personnel of our institution. Although our installation of the system restricts its use in a vertical plane, an alternate mounting would permit its use in a horizontal or even an oblique plane. It could also be mounted in a fixed position, in which case the patient would rotate about his own axis.

Because the output of the system is in electronic form and has relatively fast response, it could be used as an input for either analog or digital computers. Here the polar plotter could record the contour as well as the complete isodose distribution calculated by the computer.

The system so far has been used primarily in the medical field, but it could be adapted for numerous other applications.


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