Determination of effective electron source size using multislit and pinhole cameras

Area of Science:

• Medical Physics
• Radiation Oncology
• Accelerator Physics

Background:

• Accurate determination of electron beam source characteristics is crucial for precise radiation therapy planning.
• Understanding effective source size and position impacts dose distribution and treatment efficacy.
• Varian 2100C linear accelerators are widely used, necessitating characterization of their electron beam properties.

Purpose of the Study:

• To determine the effective source sizes of 6, 12, and 20 MeV electron beams from a Varian 2100C linear accelerator.
• To compare the results obtained from two independent imaging methods: a multislit camera and a pinhole camera.
• To derive the effective source position using output measurements and the inverse square law.

Main Methods:

• Construction and utilization of a multislit camera with parallel aluminum plates and plastic spacers.
• Implementation of pinhole imaging using a lead plate with energy-dependent hole diameter and thickness.
• Positioning cameras at the movable photon collimator exit and measuring source distribution full width at half-maximum (FWHM).
• Fitting output measurements at varying source-to-surface distances (SSD) to the inverse square law for source position determination.

Main Results:

• Multislit camera FWHM: 6 MeV (6.3 ± 0.4 cm), 12 MeV (3.6 ± 0.4 cm), 20 MeV (2.7 ± 0.4 cm).
• Pinhole camera FWHM: 6 MeV (7.9 ± 0.6 cm), 12 MeV (4.5 ± 0.4 cm), 20 MeV (3.0 ± 0.4 cm).
• Measured FWHM values differed between the two cameras due to distinct imaging principles.

Conclusions:

• Both multislit and pinhole imaging methods provide valuable data on electron beam source characteristics.
• The effective source size decreases with increasing electron beam energy.
• The effective source position can be accurately determined through output measurements and inverse square law fitting.