NEW THERMOLUMINESCENT BASO4-EU SHEET FOR IN-VIVO MEASUREMENT OF SPATIAL DOSE DISTRIBUTION IN RADIATION-THERAPY

A new highly sensitive thermoluminescent (TL) sheet has been studied a s a means of in vivo measurement of spatial dose distribution of radia tion therapy. This TL sheet (40 cm x 50 cm x 0.2 mm), which is compose d of teflon mixed with BaSO4:Eu doped powder, is very flexible and can be cut to the desired size. The TL sheet was found to have a linear r esponse with a very wide dynamic range of at least 0.002 cGy to 5000 c Gy absorbed dose. In addition, this sheet does not need be shielded, b ecause of its insensitivity to room light, and therefore the sheet can detect low-energy electrons decreased by a few millimeter thick air f or H-3(maximum beta-ray energy: 18 KeV). The spatial dose distribution was printed out with a newly developed digital readout system. In add ition, another high-resolution dosimetry system, which exposes X-ray f ilm with TL photons emitted from the irradiated TL sheet at constant r oom temperature, is reported. Clinically, the in vivo dose distributio n on the surface of the rectal cancer for intracavitary radiation ther apy was determined. The applicability of TL sheet for in vivo measurem ent of dose distribution is discussed.