[Field-integrated dosage modification (FIDM). 2. The physical principles of the procedure]

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Context:

• Photon irradiation fields often require precise customization for effective cancer treatment.
• Conventional methods may lack the flexibility to create complex, irregular irradiation zones.
• Accurate dose delivery is paramount in radiotherapy to maximize tumor control and minimize side effects.

Purpose:

• To describe a novel method for introducing irregular field stops into photon irradiation fields.
• To detail the calculation and manufacturing basis for these custom field stops, incorporating dose modification blocks.
• To present an iterative algorithm for calculating dose distributions within irregularly shaped irradiation volumes.

Summary:

• The method utilizes computed tomography or conventional radiographs to define irregular field stops with integrated dose modification.
• Input parameters include field dimensions, positions, depth, material absorption, dose modification proportions, and radiation quality.
• An iterative algorithm based on differential sector addition and an equivalent TAR scheme is used for dose distribution calculations.
• Quality assurance involves standard dosimetric methods, with planned dose deviations within +/- 5% for 60Co gamma and 15 MeV bremsstrahlung.

Impact:

• Enables more precise and conformal radiation delivery in complex anatomical sites.
• Offers enhanced flexibility in treatment planning for photon therapy.
• Contributes to improved therapeutic ratios in radiation oncology through accurate dose sculpting.