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Related Experiment Video

Updated: Jul 16, 2025

Evaluating Targeting Accuracy in the Focal Plane for an Ultrasound-guided High-intensity Focused Ultrasound Phased-array System

Evaluating Targeting Accuracy in the Focal Plane for an Ultrasound-guided High-intensity Focused Ultrasound Phased-array System

Published on: March 6, 2019

Beam Focal Spot Offset Determination for Linear Accelerators: A Phantom less Method.

Silpa AjayKumar^1,2, Arathi C¹, Resmi K B¹

¹Radiation Oncology Department, Malabar Cancer Centre, Kerala, India.

The Gulf Journal of Oncology

|September 21, 2023

Summary

This summary is machine-generated.

Accurate radiotherapy requires verifying the beam focal spot. This study presents an electronic portal imaging device (EPID)-based method to measure beam focal spot offset, ensuring treatment accuracy and safety.

Keywords:

ClinaciX Versa HD.QA focal spot. EPID

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Area of Science:

Medical Physics
Radiation Oncology
Radiotherapy Quality Assurance

Background:

Radiotherapy effectiveness depends on precise beam focal spot positioning.
Periodic verification of the beam focal spot is crucial for patient safety and treatment efficacy.
Existing methods for beam focal spot offset measurement can be complex.

Purpose of the Study:

To develop and validate an electronic portal imaging device (EPID)-based technique for measuring beam focal spot offset.
To assess the accuracy and reproducibility of the proposed EPID-based method.
To provide a reliable tool for routine quality assurance in radiotherapy.

Main Methods:

Utilized a combination of jaws and multileaf collimator (MLC) to create symmetric fields.
Employed collimator rotations (180° or 360°) to determine radiation isocenters.
Correlated the difference between isocenters with beam focal spot offset for linear accelerators (Varian ClinaciX, Elekta Versa HD).

Main Results:

The EPID-based method demonstrated agreement with the co-rotational penumbra modulation (CPM) technique within 0.00923±0.009360 mm (SD).
The method exhibited excellent reproducibility, with variations within 0.0365 mm (SD).
A modified approach was successfully implemented for linear accelerators lacking dual jaw sets (e.g., Elekta Agility® head).

Conclusions:

The developed EPID-based technique is accurate and reproducible for measuring beam focal spot offset.
This method is suitable for routine quality assurance (QA) protocols.
Ensuring beam focal spot offset is within tolerance enhances radiotherapy treatment precision.