PMID- 30822764
OWN - NLM
STAT- MEDLINE
DCOM- 20200312
LR  - 20200312
IS  - 1361-6560 (Electronic)
IS  - 0031-9155 (Linking)
VI  - 64
IP  - 11
DP  - 2019 May 23
TI  - Influence of cone beam CT (CBCT) scan parameters on size specific dose estimate 
      (SSDE): a Monte Carlo study.
PG  - 115002
LID - 10.1088/1361-6560/ab0bc8 [doi]
AB  - The CT dose index (CTDI(vol)) is the dosimetric quantity used for multi-slice CT 
      (MSCT) with beams  ⩽4 cm. Conversion factors (f (size)) based on patient size are 
      applied to CTDI(vol) to adjust for differences in patient size and derive 
      size-specific dose estimates (SSDE) relating to patient dose. The aim of this 
      study is to: (1) investigate use of a similar technique to provide SSDE values 
      for cone beam CT (CBCT) scans, (2) determine whether factors derived for narrow 
      beam MSCT are suitable for CBCT, and (3) investigate the influence of CBCT 
      parameters on f (size) values. Monte Carlo simulations were used to model an 
      on-board imager system integrated into a Varian Truebeam linear accelerator, and 
      to assess doses for imaging. The CTDI(vol) is unsuitable for CBCT dosimetry, thus 
      the assessments were applied to the modification CTDI(IEC), recommended by the 
      international electrotechnical commission (IEC). Conversion factors 
      (f (size,CBCT)) were derived for CBCT to allow adjustment of values for the 
      absorbed dose in water (AD) averaged over the beam width in the middle of the 
      phantoms. Values of AD were evaluated as for CTDI(300) measured with a 30 cm long 
      chamber in centres and peripheries of long water phantoms with diameters of 
      10-40 cm for head and body protocols. Three beam widths 8, 16, and 24 cm were 
      used with tube potentials ranging from 80-140 kV, for full and partial rotation 
      modes. In order to derive f (size,CBCT) values, calculated values for AD were 
      normalized with respect to the weighted CTDI(IEC) assessed in standard CTDI 
      phantoms and free-in-air. Variations in f (size,CBCT) with beam width were 
      minimal, 1%-5%, but those with tube potential were greater for 80 kV at small 
      diameters reaching 11%. Acquisition mode affected f (size,CBCT) values by up to 
      7%. Best-fit curves were derived from the f (size,CBCT) values and compared to 
      those reported by AAPM TG-204 for MSCT. Conversion factors estimated from these 
      curves for 120 kV were within  +/-8% and  +/-13% of the MSCT values over head and 
      body diameters, respectively, representing the majority of the adult population. 
      Therefore, the use of MSCT factors to convert CTDI(IEC) for CBCT scans may lead 
      to under/overestimation of doses to patients by 5% and 6%, on average, for the 
      head and body protocols, respectively. Best-fit curves of the results from this 
      study provide values that could be used to convert CTDI(IEC) for specific 
      water-equivalent diameter (D (w)) to a SSDE.
FAU - Abuhaimed, Abdullah
AU  - Abuhaimed A
AD  - The National Centre for Applied Physics, King Abdulaziz City for Science and 
      Technology (KACST), Riyadh, Saudi Arabia. Department of Biomedical Physics, King 
      Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia. Author to 
      whom any correspondence should be addressed.
FAU - Martin, Colin J
AU  - Martin CJ
FAU - Demirkaya, Omer
AU  - Demirkaya O
LA  - eng
PT  - Journal Article
DEP - 20190523
PL  - England
TA  - Phys Med Biol
JT  - Physics in medicine and biology
JID - 0401220
SB  - IM
MH  - Adult
MH  - *Algorithms
MH  - Cone-Beam Computed Tomography/*methods
MH  - Head/*diagnostic imaging/radiation effects
MH  - Humans
MH  - Infant, Newborn
MH  - *Monte Carlo Method
MH  - Particle Accelerators/*instrumentation
MH  - *Phantoms, Imaging
MH  - Radiation Dosage
MH  - *Radiography, Abdominal
MH  - Radiometry/methods
EDAT- 2019/03/02 06:00
MHDA- 2020/03/13 06:00
CRDT- 2019/03/02 06:00
PHST- 2019/03/02 06:00 [pubmed]
PHST- 2020/03/13 06:00 [medline]
PHST- 2019/03/02 06:00 [entrez]
AID - 10.1088/1361-6560/ab0bc8 [doi]
PST - epublish
SO  - Phys Med Biol. 2019 May 23;64(11):115002. doi: 10.1088/1361-6560/ab0bc8.