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Spatial Fractionation of the Dose in Heavy Ion Therapy

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Y Prezado

G Fois1, Y Prezado2*, (1) University of Cagliari, Monserrato, Cagliari, (2) IMNC-CNRS, Orsay, Ile de France

SU-E-T-531 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the possible gain in tissue sparing in heavy ion therapy when a spatial fractionation of the dose is used.

Methods: Monte Carlo simulations (GATE v.6) have been used as a method to calculate the dose distributions in a cylindrical water phantom (16 cm height and 16 cm of diameter). The phantom was irradiated with carbon and oxygen minibeams of 0.7 mm of beam width and 1.4, 2.1, 2.8 and 3.5 mm center-to-center distances. The ratio of the peak-to-valley doses (PVDR), that is considered to be a very relevant dosimetric parameter, was evaluated at different depths. The beam penumbras were also assessed as an important parameter for tissue sparing.

Results: Very high values of PVDR, significantly superior than the ones achieved in other spatial fractionated radiotherapy techniques, like in synchrotron minibeam radiation therapy were obtained. In addition, the penumbras are much more smaller than in the case of MV Grid therapy and of Gamma Knife radiosurgery. Of the two types of ions studied, oxygen is the one that provides the more advantageous dose distributions.

Conclusion: A gain in tissue sparing might be expected in this new radiotherapy approach thanks to the high PVDR obtained, the small penumbras and the absence of deposited dose after the Bragg Peak. This could be used to treat radioresistant tumors or non-cancer diseases, like epilepsy.

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