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

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Computational Physics

Background:

• Conformal radiotherapy aims to precisely deliver radiation dose to tumors while sparing healthy tissues.
• Optimizing dose distribution remains a challenge in radiotherapy, particularly for complex targets and critical structures.
• External physical fields have been explored to modulate radiation dose, but their clinical application is limited.

Purpose of the Study:

• To investigate the potential of using strong transverse magnetic fields to enhance dose distributions in high-energy photon beam radiotherapy.
• To explore the effects of different magnetic field configurations (linear and dipole) and parameters (strength, gradient) on dose enhancement and reduction.
• To assess the feasibility of magnetic field-assisted radiotherapy for improving treatment efficacy and safety.

Main Methods:

• Modification of the EGS4 Monte Carlo code to simulate charged particle transport in magnetic fields.
• Calculation of dose distributions for various high-energy photon beams under the influence of hypothetical transverse magnetic fields.
• Evaluation of dose enhancement and reduction effects for linear and dipole magnetic field configurations.

Main Results:

• Strong transverse magnetic fields (> 1 T) with high longitudinal gradients (> 0.5 T/cm) can create localized regions of significant dose enhancement and reduction.
• The magnitude, extent, and location of dose modifications depend on magnetic field strength, gradient, and photon beam energy.
• A 5 T magnetic field with an infinite longitudinal gradient (solenoidal field) resulted in up to 200% dose enhancement and 40% dose reduction for a 15 MV photon beam.
• A 60% dose enhancement was observed over a 2 cm depth region for a 15 MV beam with B = 5 T and G = 2.5 T/cm.
• Similar qualitative effects were observed with dipole magnetic fields.

Conclusions:

• Strong transverse magnetic fields offer a promising method for manipulating dose distributions in high-energy photon beam radiotherapy.
• Well-designed magnetic fields can achieve substantial dose enhancement within the target volume and significant dose reduction in surrounding critical structures.
• This approach holds potential for improving the precision and effectiveness of conformal radiotherapy, warranting further investigation and development.