Grid Block Design Based on Monte Carlo Simulated Dosimetry, the Linear Quadratic and Hug-Kellerer Radiobiological...

Area of Science:

• Medical Physics
• Radiation Oncology
• Biophysics

Background:

• Grid therapy is a technique used in radiation oncology to improve tumor targeting.
• Optimizing the physical parameters of Grid blocks is crucial for maximizing therapeutic benefit.
• Previous studies have explored Grid therapy's clinical efficacy, but optimal block design requires further investigation.

Purpose of the Study:

• To determine the optimal hole diameter and spacing for Grid blocks to achieve a therapeutic advantage.
• To identify Grid block parameters that maximize the therapeutic ratio (TR) and minimize the geometrical sparing factor (GSF).

Main Methods:

• Monte Carlo (MC) simulations using Geant4 code to model dose distributions for 25 Grid block designs.
• Calculation of therapeutic ratio (TR) and geometrical sparing factor (GSF) using linear quadratic and Hug-Kellerer radiobiological models.
• Fabrication and experimental dosimetric characterization of an optimized Grid block using ionization chambers, Gafchromic film, and TLDs.

Main Results:

• Grid blocks with 1.00–1.25 cm hole diameters and 1.7–1.8 cm spacing demonstrated optimal therapeutic parameters (TR > 1.3, GSF ≈ 0.90).
• Measured dosimetric characteristics, including dose profiles and output factors, closely matched simulated data within ±5%.
• The ratio of open to blocked area (ROTBA) was also considered in optimizing block design.

Conclusions:

• A method utilizing MC dosimetry and radiobiological models was developed to design Grid blocks for optimal therapeutic response.
• Experimental validation confirmed the accuracy of the simulation data for the optimized Grid block.
• The findings provide a basis for designing improved Grid blocks in radiation therapy.