PMID- 38469437
OWN - NLM
STAT- PubMed-not-MEDLINE
LR  - 20240313
IS  - 1044-677X (Print)
IS  - 2165-7254 (Electronic)
IS  - 1044-677X (Linking)
VI  - 126
DP  - 2021
TI  - Calorimetry in Computed Tomography Beams.
PG  - 126054
LID - 10.6028/jres.126.054 [doi]
LID - 126054
AB  - A portable calorimeter for direct realization of absorbed dose in medical 
      computed tomography (CT) procedures was constructed and tested in a positron 
      emission tomography (PET) CT scanner. The calorimeter consists of two small 
      thermistors embedded in a polystyrene (PS) cylindrical "core" (1.5 cm diameter) 
      that can be inserted into a cylindrical high-density polyethylene (HDPE) phantom 
      (30 cm diameter). The cylindrical design of core and phantom allows coaxial 
      alignment of the system with the scanner rotation axis, which is necessary to 
      minimize variations in dose that would otherwise occur as the X-ray source is 
      rotated during scanning operations. The core can be replaced by a cylindrical 
      ionization chamber for comparing dose measurement results. Measurements using the 
      core and a calibrated thimble ionization chamber were carried out in a beam of 6 
      MV X-rays from a clinical accelerator and in 120 kV X-rays from a CT scanner. 
      Doses obtained from the calorimeter and chamber in the 6 MV beam exhibited good 
      agreement over a range of dose rates from 0.8 Gy/min to 4 Gy/min, with negligible 
      excess heat. For the CT beam, as anticipated for these X-ray energies, the 
      calorimeter response was complicated by excess heat from device components. 
      Analyses done in the frequency domain and time domain indicated that excess heat 
      increased calorimetric temperature rise by a factor of about 15. The 
      calorimeter's response was dominated by dose to the thermistor, which contains 
      high-atomic-number elements. Therefore, for future construction of calorimeters 
      for CT beams, lower-atomic-number temperature sensors will be needed. These 
      results serve as a guide for future alternative design of calorimeters toward a 
      calorimetry absorbed dose standard for diagnostic CT.
FAU - Chen-Mayer, H Heather
AU  - Chen-Mayer HH
AD  - National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
FAU - Tosh, Ronald E
AU  - Tosh RE
AD  - National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
FAU - Bateman, Fred B
AU  - Bateman FB
AD  - National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
FAU - Bergstrom, Paul M
AU  - Bergstrom PM
AD  - National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
FAU - Zimmerman, Brian E
AU  - Zimmerman BE
AD  - National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
LA  - eng
PT  - Journal Article
DEP - 20220310
PL  - United States
TA  - J Res Natl Inst Stand Technol
JT  - Journal of research of the National Institute of Standards and Technology
JID - 8912688
PMC - PMC10046824
OTO - NOTNLM
OT  - CT dose
OT  - absorbed dose
OT  - calorimeter
OT  - medium energy X-rays
OT  - polystyrene
OT  - thermistor
EDAT- 2022/03/10 00:00
MHDA- 2022/03/10 00:01
PMCR- 2022/03/10
CRDT- 2024/03/12 03:57
PHST- 2022/02/04 00:00 [accepted]
PHST- 2022/03/10 00:01 [medline]
PHST- 2022/03/10 00:00 [pubmed]
PHST- 2024/03/12 03:57 [entrez]
PHST- 2022/03/10 00:00 [pmc-release]
AID - 126054 [pii]
AID - 10.6028/jres.126.054 [doi]
PST - epublish
SO  - J Res Natl Inst Stand Technol. 2022 Mar 10;126:126054. doi: 10.6028/jres.126.054. 
      eCollection 2021.