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SU‐FF‐I‐16: Calibration of TLD Chips to Maximize Accuracy in Radiographic Phantom Dosimetry
Author(s) -
Ogden K,
Lavallee R,
Huda W,
Roskopf M,
Scalzetti E
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1997496
Subject(s) - thermoluminescent dosimeter , dosimetry , imaging phantom , nuclear medicine , calibration , protocol (science) , radiography , medicine , biomedical engineering , materials science , mathematics , dosimeter , surgery , statistics , alternative medicine , pathology
Purpose: To develop an efficient annealing/readout protocol for TLD dosimetry that will maximize the accuracy and precision in radiographic dosimetry measurements. Method and Materials: 500 TLD chips were grouped in batches of 100 and subjected to varying annealing protocols and then irradiated to varying exposure levels. Three different annealing/readout protocols were tested. In protocol ♯1, the chips were annealed at 400 C for 1 hour followed by 2 hours at 100 C. The chips were exposed, and then allowed to rest for 24 hours before reading. In protocol ♯2, the anneal cycle was 400 C for 1 hour followed with a 30 minute cool‐down, followed by 20 hours at 80 C. Immediately after exposure, the TLD's were heated to 120 C for 10 minutes, then read. In protocol ♯3, the anneal cycle was 400 C for 1 hour followed by a 30 minute cool‐down, then 100 C for 2 hours. After exposure, the TLDs were pre‐heated and read as in protocol ♯2. Results: For protocol ♯1, the inter‐exposure uncertainty in the response (nC/mR) was approximately 4.2%. Using protocol ♯2, the intra‐batch uncertainty was reduced to 4.0%, and for protocol ♯3 the uncertainty was reduced to ∼3.7%. By using individual chip calibrations, the intra‐batch uncertainty for estimating consecutive exposures was reduced to 3.5%, 1.8%, and 1.7% for protocols ♯1, 2, and 3, respectively. By binning TLD signals over groups of 3 chips, the uncertainty in estimating exposures was reduced to ∼1.1% for protocol ♯3. Conclusion: With careful calibration and binning of results, an accuracy approaching 1% is readily obtained. The anneal/readout protocol that yielded the highest accuracy also required the least time for a complete cycle, with a batch of 100 chips being processed in <1 working day using a single furnace for annealing and a single‐chip reader.