Predicting radiotoxic effects after BNCT for brain cancer using a novel dose calculation model

Area of Science:

• Radiation Oncology
• Medical Physics
• Neuro-oncology

Background:

• The normal brain is a critical dose-limiting organ in radiotherapy for brain tumors.
• Accurate dose assessment is crucial for predicting normal tissue complication probability (NTCP) after radiotherapy, particularly Boron Neutron Capture Therapy (BNCT).
• Somnolence syndrome (SS≥2) is a common adverse event following brain radiotherapy.

Purpose of the Study:

• To develop a model for calculating photon isoeffective doses (D_IsoE) to the normal brain.
• To correlate D_IsoE with the incidence of grade 2 or higher somnolence syndrome (SS≥2) after BNCT.
• To establish a dose-response relationship for SS≥2 in BNCT patients.

Main Methods:

• Constructed a D_IsoE model to equate BNCT absorbed dose NTCP with reference photon dose NTCP.
• Utilized rat spinal cord irradiation data to parameterize Lyman's NTCP model for both conventional and BNCT.
• Calculated D_IsoE for BNCT treatments and introduced an equivalent uniform dose (EUD) model incorporating peak and average brain doses.

Main Results:

• The D_IsoE model indicated higher-than-anticipated photon-equivalent doses in the brain.
• Neither peak nor average whole-brain dose alone predicted SS≥2.
• A combined D_IsoE and EUD dose-response model effectively explained the incidence of SS≥2 after BNCT.

Conclusions:

• The developed D_IsoE and EUD models successfully predict somnolence syndrome incidence post-BNCT.
• Presented the first dose-response relationship for SS≥2 derived exclusively from BNCT-treated brain tumor patients.
• The findings suggest consistency between BNCT and photon radiotherapy responses for SS≥2.