PMID- 35124798
OWN - NLM
STAT- MEDLINE
DCOM- 20220310
LR  - 20220311
IS  - 2473-4209 (Electronic)
IS  - 0094-2405 (Linking)
VI  - 49
IP  - 3
DP  - 2022 Mar
TI  - An initial systematic study of the linear energy transfer distributions of a 
      proton beam under a transverse magnetic field.
PG  - 1839-1852
LID - 10.1002/mp.15478 [doi]
AB  - PURPOSE: To evaluate the biological effectiveness of magnetic resonance 
      (MR)-guided proton beam therapy, comprehensively characterizing the dose and 
      dose-averaged linear energy transfer (LET(d) ) distributions under a magnetic 
      field is necessary. Although detailed analysis has characterized curved beam 
      paths and distorted dose distributions, the impact of a magnetic field on LET(d) 
      should also be explored to determine the proton relative biological effectiveness 
      (RBE). Hence, this initial study aims to present a basic analysis of LET(d) 
      distributions in the presence of a magnetic field using Monte Carlo simulation 
      (MCS). METHODS: Geant4 MCS (version 10.1.p01) was performed to calculate the 
      LET(d) distribution of proton beams. The incident beam energies were set to 70.2, 
      140.8, and 220 MeV, and both zero- and finite-emittance pencil beams as well as 
      scanned field were simulated. A transverse magnetic field of 0-3 T was applied 
      within a water phantom placed at the isocenter, and the three-dimensional dose 
      and LET(d) distributions in the phantom were calculated. Then, the depth profiles 
      of LET(d) along the curved trajectory and the lateral LET(d) profile at the Bragg 
      peak (BP) depth were analyzed under changing energies and magnetic fields. In 
      addition, for zero- and finite-emittance beams, the correlation of the lateral 
      asymmetries between the dose and LET(d) distributions were analyzed. Finally, 
      spread-out Bragg peak (SOBP) fields were simulated to assess the depth-dependent 
      asymmetry of the LET(d) distributions. RESULTS: A transverse magnetic field 
      distorted the lateral LET(d) distribution of a pencil beam at close to the BP, 
      and the magnitude of the distortion at the BP increased for higher energy beams 
      and larger magnetic fields. For a zero-emittance beam, the differences in LET(d) 
      between the left and right D(20) positions were relatively large; the difference 
      in LET(d) was 1.5 and 2.3 keV/mum at 140.8 and 220 MeV, respectively, at a 
      magnetic field of 1.5 T. These asymmetries were pronounced at positions where the 
      dose asymmetries were large. The size of the asymmetry was less substantial for a 
      finite-emittance beam and even less for a scanned field. However, a 1.5-keV/mum 
      difference still remained between the left and right D(20) positions of a scanned 
      field penumbra for a 220 MeV beam under the same magnetic field. For the SOBP 
      field, it was found that the distal region of SOBP had the highest LET(d) 
      distortions, followed by the central and proximal regions for the middle-sized 
      SOBP (5 x 5 x 5 cm(3) ), whereas the degree of LET(d) distortion did not vary 
      much with depth for the 10 x 10 x 10-cm(3) SOBP field. CONCLUSION: Our results 
      indicate that not only the dose but also LET(d) distortions should be considered 
      to accurately evaluate the biological effectiveness of MR-guided proton beam 
      therapy.
CI  - (c) 2022 American Association of Physicists in Medicine.
FAU - Fujii, Yusuke
AU  - Fujii Y
AD  - Graduate School of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan.
AD  - Hitachi Ltd., Hitachi, Ibaraki, Japan.
FAU - Ueda, Hideaki
AU  - Ueda H
AD  - Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan.
FAU - Umegaki, Kikuo
AU  - Umegaki K
AD  - Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan.
AD  - Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Hokkaido, 
      Japan.
AD  - Department of Medical Physics, Hokkaido University Hospital, Sapporo, Hokkaido, 
      Japan.
FAU - Matsuura, Taeko
AU  - Matsuura T
AD  - Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan.
AD  - Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Hokkaido, 
      Japan.
AD  - Department of Medical Physics, Hokkaido University Hospital, Sapporo, Hokkaido, 
      Japan.
LA  - eng
GR  - 21H02859/JSPS KAKENHI/
GR  - JPMJFR200X/JST FOREST/
PT  - Journal Article
DEP - 20220211
PL  - United States
TA  - Med Phys
JT  - Medical physics
JID - 0425746
RN  - 0 (Protons)
SB  - IM
MH  - *Linear Energy Transfer
MH  - Magnetic Fields
MH  - Monte Carlo Method
MH  - *Proton Therapy/methods
MH  - Protons
MH  - Relative Biological Effectiveness
OTO - NOTNLM
OT  - MR-guided proton therapy
OT  - Monte Carlo method
OT  - linear energy transfer
EDAT- 2022/02/07 06:00
MHDA- 2022/03/11 06:00
CRDT- 2022/02/06 20:40
PHST- 2022/01/11 00:00 [revised]
PHST- 2021/07/28 00:00 [received]
PHST- 2022/01/12 00:00 [accepted]
PHST- 2022/02/07 06:00 [pubmed]
PHST- 2022/03/11 06:00 [medline]
PHST- 2022/02/06 20:40 [entrez]
AID - 10.1002/mp.15478 [doi]
PST - ppublish
SO  - Med Phys. 2022 Mar;49(3):1839-1852. doi: 10.1002/mp.15478. Epub 2022 Feb 11.