§ 228.65. Electron beam quality.

 The licensee shall determine that the following beam quality requirements are met:

   (1)  The absorbed dose resulting from X-rays in a useful electron beam at a point on the central axis of the beam 10 centimeters greater than the practical range of the electrons may not exceed the values in Table I. Linear interpolation shall be used for values not stated.

Table I

	X-Ray Absorbed Dose as a
Maximum Energy of	Fraction of Maximum
Electron Beam in MeV	Absorbed Dose
1	0.03
15	0.05
35	0.10
50	0.20

   (2)  Compliance with paragraph (1) shall be determined using:

     (i)   A measurement within a phantom with the incident surface of the phantom at the normal treatment distance and normal to the central axis of the beam.

     (ii)   The largest field size available which does not exceed 15 centimeters by 15 centimeters.

     (iii)   A phantom whose cross-sectional dimensions exceed the measurement radiation field by at least 5 centimeters and whose depth is sufficient to perform the required measurement.

   (3)  The licensee shall determine, or obtain from the manufacturer, the maximum percentage absorbed dose due to stray neutrons in the useful beam for specified operating conditions.

Source

   The provisions of this §  228.65 adopted October 2, 1998, effective October 3, 1998, 28 Pa.B. 4894.

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