An on-line acquisition system for radiation therapy: external photon and electron beams.

An on-line data acquisition system for external beam treatment planning has been developed. The hardware consists of a Tektronix 4054 Computer, an SHM Nuclear 3-D scanning water phantom, interfaces for 16 channels of ADC and 32 channels of digital I/O, and two detector probes for measuring dose distribution and monitoring fluctuations in machine output. The program to control the movement of the scanning probe and to collect data is written in BASIC. Results of the measurements are plotted in real time on the Tektronix screen. The beam data format consists of a set of percentage depth doses along the central axis and five sets of off-axis ratios at five different depths. In the electron mode, when ionization chambers are used, data points are averages of two measurements, one with positive bias and the other with negative bias. The beam data are stored on disk which can be assessed by the Capintec treatment planning system.