Parametrizing the collimator scatter factor, Sc (or head scatter factor), of a linear accelerator by the side of the equivalent square of the collimator setting at the isocenter does not accurately predict the change in Sc when the width and length of a rectangular field are exchanged. We have studied two methods based on measurements of square fields to predict Sc's of rectangular fields more accurately. The first method parametrizes Sc by the side of the equivalent square of the flattening filter region visible from the point of calculation. The Sc's of rectangular fields were predicted to an accuracy of 1% from measurements with square fields. The second method computes Sc of rectangular configurations by integrating radiation that can reach the point of calculation from a point source at the target and a second extended source at the flattering filter. The radial distribution of the extended source at the level of the flattering filter is computed from Sc of square fields measured at the isocenter. Effects of extended distance are modeled by separately performing inverse square law corrections for the two sources. This method also predicted the measured values to within 1% accuracy.

A simple noninvasive method is described for determining the backscatter to a monitor chamber of a medical accelerator based on the measurement of charge deposited in the target. This method is compared quantitatively to the more elaborate telescopic method for photon beams of 6 MV and 15 MV on linear accelerators having mica and Kapton monitor chambers. The new target charge method gives results consistent with the telescopic method to within 0.3%.

We present measurements of the pion transverse momentum (p t ) spectra in central Si-nucleus collisions in the rapidity range 2.0 < y < 5.0 for p t down 1

At the time of treatment planning it would be useful to know whether part of the treatment beam passes through the patient/couch support assembly before it passes through the patient. In the previous work of Yorke, the range of gantry angles leading to beam-couch intersection was found as a function of couch translation for symmetric field sizes and for zero couch rotation. Yorke's method has been extended to include couch rotation, dual independent jaws, and multi-leaf collimator (MLC) field shapes. In addition, the new method is also applicable in the situation of the couch top located above the isocenter. For a clinically treatable, 20 x 20 cm field configuration in a linac, the range of gantry angles leading to beam-couch intersection are different by 6.7 degrees for a couch rotation angle of 25 degrees when compared to no couch rotation. The new method agrees with data within the setup and measurement uncertainties for a variety of field sizes including an oval shaped MLC field, and various couch locations, couch, and collimator rotation angles.

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