Optimizing field patching in passively scattered proton therapy with the use of beam current modulation

Area of Science:

• Medical Physics
• Radiation Oncology
• Particle Therapy

Background:

• Patched-field proton therapy aims to deliver precise radiation doses but can suffer from dose heterogeneity.
• Combining dose distributions from separate fields in proton therapy can lead to unacceptable variations in the target dose.

Purpose of the Study:

• To investigate methods for improving dose homogeneity in patched-field proton therapy.
• To evaluate the effectiveness of beam current modulation in reducing dose non-uniformity (DNU) in patched proton therapy plans.

Main Methods:

• MCNPX simulations were used to model Mevion S250 beamline configurations.
• Spread-out Bragg peak dose distributions were generated for depths between 5.0 and 30.0 cm.
• Dose non-uniformity (DNU) was assessed using standard and optimized beam current modulation techniques.

Main Results:

• Standard patched-field deliveries showed DNU of 10% or less only for lateral profiles between 12.5-17.5 cm deep.
• Outside this range, standard deliveries exhibited DNU exceeding 35% in some cases.
• Optimized distal profiles using beam current modulation reduced DNU to 10% or less for all lateral profiles deeper than 15.0 cm.

Conclusions:

• Optimizing beam current modulation creates more gradual distal dose falloff, enhancing dose summation homogeneity.
• This method effectively mitigates hot and cold spots in patched dose distributions, improving clinical acceptability.
• The technique is applicable to various proton therapy systems beyond the Mevion system for better dose homogeneity.