Technical Note: Improving proton stopping power ratio determination for a deformable silicone-based 3D dosimeter using dual energy CT.
OBJECTIVE
The aim of this study was to investigate whether the stopping power ratio (SPR) of a deformable, silicone-based 3D dosimeter could be determined more accurately using dual energy (DE) CT compared to using conventional methods based on single energy (SE) CT. The use of SECT combined with the stoichiometric calibration method was therefore compared to DECT-based determination.


METHODS
The SPR of the dosimeter was estimated based on its Hounsfield units (HUs) in both a SECT image and a DECT image set. The stoichiometric calibration method was used for converting the HU in the SECT image to a SPR value for the dosimeter while two published SPR calibration methods for dual energy were applied on the DECT images. Finally, the SPR of the dosimeter was measured in a 60 MeV proton by quantifying the range difference with and without the dosimeter in the beam path.


RESULTS
The SPR determined from SECT and the stoichiometric method was 1.10, compared to 1.01 with both DECT calibration methods. The measured SPR for the dosimeter material was 0.97.


CONCLUSIONS
The SPR of the dosimeter was overestimated by 13% using the stoichiometric method and by 3% when using DECT. If the stoichiometric method should be applied for the dosimeter, the HU of the dosimeter must be manually changed in the treatment planning system in order to give a correct SPR estimate. Using a wrong SPR value will cause differences between the calculated and the delivered treatment plans.
Department of Medical Physics, Aarhus University/Aarhus University Hospital, Aarhus 8000, Denmark.
Vicki Trier
VT
Taasti
Department of Medical Physics, Aarhus University/Aarhus University Hospital, Aarhus 8000, Denmark.
Ellen Marie
EM
Høye
Department of Medical Physics, Aarhus University/Aarhus University Hospital, Aarhus 8000, Denmark.
David Christoffer
DC
Hansen
Department of Medical Physics, Aarhus University/Aarhus University Hospital, Aarhus 8000, Denmark.
Ludvig Paul
LP
Muren
Department of Clinical Engineering and Department of Radiology, Aarhus University/Aarhus University Hospital, Aarhus 8000, Denmark.
Jesper
J
Thygesen
Department of Medical Physics, Aarhus University/Aarhus University Hospital, Aarhus 8000, Denmark.
Peter Sandegaard
PS
Skyt
Department of Physics and Astronomy, Aarhus University, Aarhus 8000, Denmark.
Peter
P
Balling
Department of Physics and Astronomy, Aarhus University, Aarhus 8000, Denmark.
Niels
N
Bassler
Department of Oncology, Aarhus University/Aarhus University Hospital, Aarhus 8000, Denmark.
Cai
C
Grau
Institute of Nuclear Physics PAN, Krakow 31-342, Poland.
Gabriela
G
Mierzwińska
Institute of Nuclear Physics PAN, Krakow 31-342, Poland.
Marzena
M
Rydygier
Institute of Nuclear Physics PAN, Krakow 31-342, Poland.
Jan
J
Swakoń
Institute of Nuclear Physics PAN, Krakow 31-342, Poland.
Pawel
P
Olko
Department of Medical Physics, Aarhus University/Aarhus University Hospital, Aarhus 8000, Denmark.
Jørgen Breede Baltzer
JBB
Petersen
D002138:Calibration; D006801:Humans; D011522:Protons; D000072232:Radiation Dosimeters; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D012828:Silicones; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*
D011522:Protons; D012828:Silicones