Effects of a strong magnetic field on selected radiation
dosimeters (TLD, OSLD, EBT3 film, PRESAGE)
Poster No.:
R-0175
Congress:
2014 CSM
Type:
Scientific Exhibit
Authors:
M. Mathis, G. Sawakuchi, D. Flint, R. Tailor, S. Beddar, G. Ibbott,
Z. Wen; HOUSTON/US
Keywords:
Radiation physics, MR physics, Radioprotection / Radiation dose,
Experimental, Physics, Dosimetry, Quality assurance
DOI:
10.1594/ranzcr2014/R-0175
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Page 1 of 8
Aim
To study the effects that a strong magnetic field (B) may have on selected radiation
dosimeters (Fig. 1), including thermoluminescent dosimeters (TLDs), optically stimulated
luminescence dosimeters (OSLDs), EBT3 film, and PRESAGE dosimeters. This study
will help to determine which types of dosimeters are suitable to be used for quality
assurance and in-vivo dosimetry measurements in a strong B field, particularly in a
magnetic resonance imaging guided linear accelerator (MR-Linac) system.
Images for this section:
Fig. 1: Dosimeters selected for study
Page 2 of 8
Methods and materials
All four types of dosimeters were separated into two categories which were either
exposed or not exposed (control) to a strong B field. In each category a group of
dosimeters was irradiated with a dose of 2, 4, or 6 Gy.
•
•
In the first part of the experiment, dosimeters were placed inside a Bruker
animal MR system (Fig. 2) where the B field was slightly greater than 2.5
T for at least 1 hour pre-irradiation. After the dosimeters were irradiated,
they were placed back inside the MR system for least 1 hour. Results were
compared with irradiated control groups without exposure to a B field.
In the second part of the study, dosimeters were irradiated inside an MRLinac prototype (Fig. 3) in University Medical Center - Utrecht. The main
B field of MR system was 1.5 T. The control groups were irradiated with a
conventional Linac without a B field.
Images for this section:
Fig. 1: Dosimeters selected for study
Page 3 of 8
Fig. 2: Bruker small animal MR system
Page 4 of 8
Fig. 3: Dosimeters in plastic phantom irradiated with MR-Linac prototype in UMC-Utrecht
Page 5 of 8
Results
For dosimeters exposed to a B field before and after irradiation, small difference (<2%,
see Fig. 4) was observed in comparison to the control groups for all four types of
dosimeters.
For dosimeters with simultaneous exposure to a B field and radiation, OSLDs had
excellent agreement with the control groups (<1%, see Fig. 5). For TLDs, the agreement
was about 5%, which was within experiment uncertainty (~6%, due to uncertainty
in machine output, experiment set up, beam profile, dosimeter variance, etc). The
agreement for films was also within 5%. However, larger disagreement in PRESAGE
dosimeters was observed (10-12%).
Images for this section:
Fig. 4: Dosimeter response comparison between no B field exposure and with B field
exposure pre- and post-irradiation.
Page 6 of 8
Fig. 5: Dosimeter relative response comparison between no B field irradiation with a
conventional linac (0 T) vs. irradiation with simultaneous B field exposure with the MRLinac (1.5 T).
Page 7 of 8
Conclusion
Sequential exposure to a strong B field before and after irradiation does not appear to
change the dosimetric properties of TLDs, OSLDs, EBT3 films or PRESAGE dosimeters.
With simultaneous exposure to both the B field and radiation, TLDs, OSLDs, and films
seem not significantly affected by the B field within the experimental uncertainty (6%).
The disagreement in PRESAGE dosimeter data is currently under investigation. Further
study is ongoing to test reproducibility and reduce experiment uncertainty.
Personal information
References
1. Raaymakers, B.W., et al. Integrating a 1.5 T MRI scanner with a 6 MV accelerator:
proof of concept. Phys Med Biol 54, N229-237 (2009).
Page 8 of 8