Micro X-Ray Irradiator Dosimetry Using Partial-Volume Techniques with Thermoluminescent Dosimeters (TLD-100)
Abstract
Purpose
To quantify dose delivered from a scanning microbeam x-ray irradiator using partial-volume techniques with thermoluminescent dosimeters (TLD-100) chips and to improve dosimetry in systems with small fields.
Methods
TLD-100 chips were irradiated using a non-stationary partial-volume technique where an x-ray microbeam was scanned across the 3.2 mm surface of the TLD chip to deliver 3 or 5 stripes. Uniform exposure was achieved by starting irradiation above and below the dosimeter. Various velocities were used to deliver estimated doses of 2, 4, and 6 Gy per stripe. TLDs were read using an automatic nitrogen gas reader (Harshaw 5500) equipped with a photomultiplier tube. A time-temperature profile was generated as each TLD was heated. The integrated charge was obtained from the area under the glow curve and corrected for background reading. The readings were normalized to the mass of the TLDs used for the stripes compared with the average mass of the calibrated TLDs.
Results
Comparisons between the 3- and 5-stripe deliveries were made. At high doses (i.e. 6 Gy), the differences between the integral charge reading from each became more pronounced. The ratio of the 5-stripe to the 3-stripe charge output is about 0.5% for 2 and 4 Gy and about 5% for 6 Gy.
Conclusion
Despite TLD’s large size in comparison to the microbeam, these results show promise for initial characterization of x-ray microbeams by using the partial-volume TLD correction method. This work emphasizes the importance of addressing nontrivial volume averaging in future microbeam dosimetry work.