Translating bed total body irradiation lung shielding and dose optimization using asymmetric MLC apertures

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Technology

Background:

• Total body irradiation (TBI) is a critical component of hematopoietic stem cell transplantation.
• Optimizing dose distribution and shielding organs at risk (OARs) during TBI is challenging.
• Current TBI techniques may result in dose uncertainties and suboptimal OAR protection.

Purpose of the Study:

• To develop and dosimetrically compare a revised translating bed TBI technique using asymmetric dynamic multileaf collimator (MLC) adjustments.
• To evaluate the effectiveness of this new technique in optimizing dose distribution and shielding the lungs to tolerance limits.
• To assess the reduction in dose uncertainties at tissue interfaces compared to a symmetric MLC-based TBI technique.

Main Methods:

• Development of a revised translating bed TBI technique employing an asymmetrically-adjusted, dynamic MLC.
• CT scanning of an anthropomorphic RANDO phantom and calculation of radiological depths (RD).
• Optimization of asymmetric MLC apertures based on RD values for uniform 3D dose distribution using the Eclipse treatment planning system.

Main Results:

• The revised asymmetric MLC technique achieved dose uniformity within 2.1% confidence limits.
• Dose uncertainties at interfaces were reduced from over ±4% to less than ±1.5%.
• Effective lung shielding was achieved, with doses reduced by 20%, 30%, and 40% of the prescribed dose, confirmed by DVH analysis.

Conclusions:

• The revised asymmetric MLC-based TBI technique offers superior dose distribution and effective lung shielding.
• This technique significantly reduces hot and cold spots at lung-tissue interfaces compared to symmetric MLC methods.
• MLC-based OAR shielding eliminates the need for cumbersome patient-specific physical blocks, streamlining radiotherapy procedures.