145 / 1082
S132
ESTRO 36 2017
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Conclusion
These results show that T1 and T2 mapping, DCE and DWI
are robust over different imaging platforms. The quality
of T1 and T2 mapping on the MR-Linac has been
demonstrated using a scan of a healthy volunteer.
OC-0260 Experimental verification of dose
enhancement effects in a lung phantom from inline
mag netic fields
B.M. Oborn
1
, M. Gargett
2
, T. Causer
1
, N. Hardcastle
2
, P.
Metcalfe
3
, P. Keall
4
1
Illawarra Cancer Care Centre, Medical Physics,
Wollongong NSW, Australia
2
Royal North Shore Hospital, Medical Physics, Sydney,
Australia
3
University of Wollongong, Centre for Medical Radiation
Physics, Wollongong, Australia
4
Universityof Sydney, School of Medicine, Sydney,
Australia
Purpose or Objective
To present for the first time experimental evidence of lung
dose enhancement effects caused by stro ng inline
magnetic fields. Such fields will be typical of future inline
MRI-linac systems.
Material and Methods
A permanent magnet device was utilized to generate a 1.2
T magnetic field that encompassed a small lung-
equivalent phantom of 0.3 g/cm
3
. 6MV and 10 MV photon
beams with 0.5 x 3 cm
2
field size were incident parallel
with the magnetic field direction and EBT3 film was placed
inside the lung phantom (Fig 1 shows a schematic setup).
Monte Carlo simulations were also performed of the
identical setup, and of larger field sizes.
Figure 1. Schematic diagram of the lung phantom setup
and magnetic field orientation.
Results
Inclusion of the 1.2 T inline magnetic field induced a 12%
(6MV) and 14% (10MV) increase in the dose along the beam
central axis as compared to the 0 T reference case (Fig 2).
This increase arises from a relative reduction in the
amount of lateral secondary electron scatter in the low
density lung medium. Monte Carlo modeling matched well
(+/- 2%) to the experimentally observed results. For
simulated larger field sizes the enhancement effect drops
off to around 3% at 5x5 cm
2
, which is a natural result of
charged particle equilibrium being restored at larger field
sizes. This dose enhancement effect will be expected to
compliment the precise treatment of small tumors
embedded in lung tissue using real-time inline MRI-linac
systems.
Figure 2. Film and profile results for the 6MV beam.