Conformal photon-beam therapy with transverse magnetic fields: Monte Carlo study

This work studies the use of strong transverse magnetic (B) fields with high-energy photon beams to enhance dose distributions for conformal radiotherapy. EGS4 Monte Carlo code is modified to incorporate charged particle transport in B fields and is used to calculate effects of B fields on dose distributions for a variety of high-energy photon beams. Two types of hypothetical B fields are studied, The major results are: (1) strong transverse B fields (>1 T) with high longitudinal gradients (G) (>0.5 T/cm) can produce dramatic dose enhancement as well as dose reduction in localized regions for high-energy photon beams; (2) the magnitude of the enhancement (reduction) and the geometric extension and the location of this enhancement (reduction) depend on both strength and gradient of the B field; (3) for a given B field, the dose enhancement generally increases with photon-beam energy; (4) for a 5-T B field with infinite longitudinal gradient (solenoidal field), up to 200% of dose enhancement and 40% of dose reduction were obtained along the central axis of a 15 MV photon beam; and (5) a 60% of dose enhancement was observed over a 2-cm depth region for the 15 MV beam when B=5 T and G=2.5 T/cm. Calculations for a variety of B fields and beam configurations show that, by employing a well designed B field In photon-beam radiotherapy, it is possible to achieve a significant dose enhancement within the target, while obtaining a substantial dose reduction over critical structures.