Model 670
Head Scatter Mini-phantom
The Model 670 water-equivalent, cylinder mini-phantom improves the dosimetric accuracy and reliability of the linear accelerator beam MU calculation by taking into account stray scatter radiation and electron contamination when determining the total radiation dose given. Head scatter, the stray radiation that bounces around inside the head of a linear accelerator, occurs with each machine. Some of this radiation is scattered forward and hits the patient to become a contributing factor to the total radiation dose.
Application of this phantom is described in ESTRO Booklet March 1997, "Monitor unit calculation for high energy photon beams" for output, volume scatter and scatter primary ratio measurements. By making a measurement with the Miniphantom at a reference depth of 10cm, the physicist can investigate and isolate the influence of scatter radiation on a reference dose measured in a slab phantom.
The Mini-phantom consists of a cylinder, 4cm in diameter, 17.5cm long, made of water-equivalent Plastic Water®. An alignment groove scribed at 10cm serves to indicate the isocenter and coincides with the ion chamber reference point. The standard chamber cavity, parallel to the phantom axis, is for the classic Farmer-type chamber, but it can be made for any commercially-available cylindrical chamber at no additional cost. The Mini-phantom may be used with the CNMC Model AL-CSSP chamber stand equipped with a special vertical adaptor or any suitable chamber stand that allows vertical chamber orientation.
Model AL-CSSP
Identical to the Model AL-CSS chamber stand, but it includes an additional 90° quick-release clamp to vertically position a Farmer-type chamber or any cylindrical chamber with a stem of up to 12.7mm diameter. It retains the ability of the Model AL-CSS to hold ion chambers in a horizontal orientation for in-air measurements.
Plastic Water® is a registered trademark of Computerized Imaging Reference Systems, Inc. (C.I.R.S.)