Semi-conductor detectors in output factor measurements.
OBJECTIVE
Output factors are generally measured with cylindrical ionization chambers. It was investigated if Si-diodes of p-type instead could be used. The advantage would be the small detector size and the robust construction of the detector.


METHODS
Two types of diodes were studied, one with a shielding layer of tungsten specially made to reduce the excess response for scattered photons and one standard diode without any extra shielding. The measurements were performed at accelerating potentials between 4 and 50 MV and beam sizes between 4 cm x 4 cm and 40 cm x 40 cm.


RESULTS
The results showed that both types of diodes are suitable for measurements of head scatter factors in mini-phantoms. However, the diodes were found inappropriate for measurement of output factors for large fields in extended water phantoms. For small fields (<10 cm x 10 cm) a small detector is advantageous and no errors due to the scatter contribution were seen.


CONCLUSIONS
An cylindrical ionization chamber is the best choice for output factor measurements in extended water phantoms for large field sizes while diodes are an alternative in small fields. There were negligible differences between the detectors in head scatter measurements in mini phantoms.
Karlsson
M G
MG
Radiation Physics Department, Umeå University, Sweden.
Karlsson
M
M
Sjögren
R
R
Svensson
H
H
D006801:Humans; D011835:Radiation Protection; D011878:Radiotherapy / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D012542:Scattering, Radiation; D014414:Tungsten
D014414:Tungsten