Total body irradiation dose optimization based on radiological depth.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Previous aperture modulated translating bed total body irradiation (TBI) techniques relied on Eclipse fluence optimization for aperture definition.
• Sources of error in the prior technique were identified, necessitating characterization and correction.

Purpose of the Study:

• To identify, characterize, and correct errors in the previous fluence optimization technique for translating bed TBI.
• To develop a clinically viable fluence optimization module for the translating bed TBI technique.

Main Methods:

• Calculated radiological depths along divergent ray lines through CT slices of a RANDO phantom.
• Defined beam apertures using a dynamic multileaf collimator (DMLC) based on radiological depths and calibration factors.
• Modified apertures to account for intra-patient scatter and imported MLC files into Eclipse for dose calculation and dynamic delivery.

Main Results:

• Achieved dose homogeneity within ± 4% in the head and neck region of the RANDO phantom, an improvement over the previous technique's -5% to +7%.
• The new technique demonstrated a ten-fold reduction in planning time.
• Significantly reduced the likelihood of user error during the planning process.

Conclusions:

• A clinically viable aperture modulated translating bed TBI technique has been developed.
• The technique employs dynamically shaped MLC-defined beam apertures derived from radiological depth calculations.
• This advancement offers improved accuracy and efficiency in TBI delivery.