Can the AAPM Task Group 21 protocol lead to optimum ion chamber designs?

The recently published AAPM Task Group 21 protocol for high-energy dosimetry is complicated in that it requires the physicist to obtain the values of about a dozen different physical variables by looking them up in tables or graphs. This should be compared with the procedure of earlier protocols using the concept of a single multiplier C lambda. We have investigated how the physical principles outlined in the improved AAPM protocol could be utilized for the redesign of the therapy-level ion chambers in such a way that one can reduce the number of factors that need to be looked up in tables or graphs for the calibration of high-energy teletherapy photon beams.

Cardiac blood pool imaging over the complete cardiac cycle with a multiformat imager.

A new method of obtaining scintigraphic images of the cardiac blood pool for the study of ventricular wall motion is described. The method, which is based upon an inexpensive modification of a commercial multiformat imaging device, yields a set of serial gated images covering the entire cardiac cycle. These images may be converted into a film loop to yield a continuous motion picture of the mechanical cycle of the heart.

Accuracy in patient setup and its consequence in dosimetry.

Analysis of 5575 settings on a computer-monitered Theratron-80 60Co unit demonstrates that human error does occur in treating patients with radiation. The errors are due to inaccurate setting of such parameters as field size, gantry angle, collimator rotation, treatment time, etc. The error rate per parameter was found to be about 3%, and more than two-thirds of the patients monitored with the PDP 11/45 computer had at least one error at some stage during the full course of treatment.