The prescribed photon energy of a TELETHERAPY TREATMENT COURSE.

National Codes:

1	Superficial (less than 160 kV)
2	Orthovoltage (less than 500 kV)
3	Megavoltage (less than 6 MV)
4	Megavoltage (equal to or greater than 6 MV)
7	Cobalt
8	Other (not Photon or Electron)

Note that TELETHERAPY ELECTRON ENERGY uses codes 5 and 6.

References:
National Cancer Data Set Version1.3_ISB October 2002 

This attribute is also known by these names:

Context	Alias
plural	TELETHERAPY PHOTON ENERGY