A revised model for electron dosimetry in the human small intestine

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Gastroenterology

Background:

• Accurate absorbed dose calculation to the small intestine (SI) wall is essential for radiation therapy and understanding gastrointestinal toxicity.
• Previous dosimetry studies often reported interface dose as

Purpose of the Study:

• To calculate the absorbed dose to the adult human small intestine (SI) wall from electrons originating in the lumen contents.
• To investigate the impact of lumen radius and wall thickness variations on dose distribution.
• To determine the actual dose delivered to SI stem cells.

Main Methods:

• A computational model of the adult human SI was developed using concentric cylinders.
• The Monte Carlo N-Particle (MCNP) code was employed to simulate electron transport and energy deposition.
• Detailed physics treatments for secondary photons and variance reduction techniques were utilized for precise calculations.

Main Results:

• Energy-specific depth dose curves were constructed, showing limited energy deposition in deep stem cell layers.
• The fraction of energy reaching stem cells varied significantly with electron energy (1.66 x 10(-6) to 1.21 x 10(-1) for 10-500 keV).
• Interface dose is a substantial overestimate of the actual stem cell dose; lumen radius variation significantly impacts depth doses.

Conclusions:

• The study highlights that the commonly reported SI wall dose is an overestimate of the true dose to critical stem cells.
• Variations in lumen radius have a notable effect on dose distribution, which can be approximated by the inverse square of the radius.
• Accurate dosimetry requires considering the depth of stem cells and geometric parameters like lumen radius.