Effect of block trays on skin dose in radiotherapy.
Percentage dose at the surface and at 1 mm depth for megavoltage photon beams are increased through the influence of block trays. This represents a decrease in skin sparing properties for both the epidermal and dermal layers. The increase in percentage dose varies with type and thickness of block tray material. At 6MVp, 20cm x 20cm field size, the percentage surface dose is 26%, 26.5%, 33% and 35% for open, steel honeycomb tray, 6mm perspex and 10 mm perspex block trays respectively. At 1 mm depth these values are 52%, 52.5%, 61%, 60% respectively. A similar effect is seen at higher energies. Results show that care should be taken when selecting an appropriate block tray if skin sparing is of importance.
Butson
M J
MJ
Illawarra Cancer Care Centre, Department of Radiotherapy, Wollongong NSW, Australia.
Mathur
J N
JN
Metcalfe
P E
PE
D006801:Humans; D019047:Phantoms, Imaging; D011834:Radiation Monitoring; D011878:Radiotherapy / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D012867:Skin / Q000528:radiation effects*; D013499:Surface Properties