ESTRO 36 Abstract Book

S132 ESTRO 36 2017 _______________________________________________________________________________________________

Conclusion

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.

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 2. Film and profile results for the 6MV beam.