Development and characterisation of a high-sensitivity X-ray CT polymer gel dosimeter

Area of Science:

• Medical Physics
• Radiotherapy
• Polymer Science

Background:

• Clinical 3D dosimetry is crucial for radiotherapy but limited by polymer gel dosimeter sensitivity and MRI dependence.
• Existing dosimeters often lack the sensitivity required for accurate dose measurement in complex clinical scenarios.

Purpose of the Study:

• To optimize a Poly AMPS Sodium Salt And Gelatin (PASSAG) polymer gel dosimeter for enhanced performance with X-ray computed tomography (CT).
• To improve the sensitivity and clinical feasibility of polymer gel dosimetry for 3D dose distribution measurements.

Main Methods:

• Increased total monomer concentration and tested cosolvents to improve solubility of N, N'-methylenebisacrylamide.
• Identified n-propanol as the optimal cosolvent, leading to an 18.3% monomer concentration and 30% crosslinker ratio.
• Formulated PASSAG-N with specific concentrations of deionised water, n-propanol, 2-acrylamido-2-methylpropane sulfonic acid sodium salt, crosslinker, gelatin, and initiator.

Main Results:

• The optimized PASSAG-N formulation demonstrated a 250% increase in Hounsfield Unit (HU) change compared to cosolvent-free versions, indicating significantly enhanced sensitivity.
• PASSAG-N exhibited a linear dose response from 1-12 Gy with an average sensitivity of 1.072 ± 0.041 HU Gy⁻¹ and a dose resolution of ≤ 0.31 Gy.
• Theoretical calculations confirmed the dosimeter's equivalence to water, soft tissue, brain, and muscle, supporting its clinical applicability.

Conclusions:

• The optimized PASSAG-N polymer gel dosimeter offers a highly sensitive and practical alternative for clinical X-ray CT-based dosimetry.
• This advancement addresses the limitations of previous gel dosimeters, paving the way for improved 3D dosimetry in radiotherapy.