The use of high density metal foils to increase surface dose in low-energy clinical electron beams.
OBJECTIVE
This paper describes a practical method of elevating the surface dose of clinical electron beams in the energy range 3-12 MeV using thin high density metal foils (tin and lead) as an alternative to tissue equivalent bolus. Because, relative to water, these materials exhibit a high scattering power to stopping power ratio, the desired dose elevation may be achieved with less energy loss than conventional bolus and consequently a gain in therapeutic interval.


METHODS
The foil thickness required to raise the surface dose to 90% off peak, for a given electron energy, was calculated using published scattering and stopping power data. An empirical expression is derived to facilitate calculation of foil thickness (tin or lead) to produce a given surface dose.


CONCLUSIONS
Measurements were made to confirm the predictions of the derived expression and were found to be in good agreement.
Lambert
G D
GD
Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, Tyne and Wear, UK.
Richmond
N D
ND
Kermode
R H
RH
Porter
D J
DJ
D004583:Electrons; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000295:instrumentation* / Q000379:methods; D013679:Technology, Radiologic