Online 3D EPID-based dose verification: Proof of concept

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Radiation Oncology

Background:

• Radiotherapy delivery errors can cause significant patient harm and reduced life expectancy.
• Online dose verification during irradiation allows for immediate intervention, such as halting the linear accelerator (linac), to prevent overdosing or underdosing.
• Existing offline Electronic Portal Imaging Device (EPID)-based 3D in vivo dosimetry systems have the potential for online verification if processing time is reduced.

Purpose of the Study:

• To adapt and optimize an existing EPID-based 3D in vivo dosimetry system for online treatment verification.
• To demonstrate that the system can achieve the necessary speed for real-time dose reconstruction and verification within the linac acquisition time.
• To validate the system's capability in detecting significant radiotherapy delivery errors during treatment.

Main Methods:

• Accelerated the dose verification system through a new software package for non-real-time computations and a multithreaded algorithm for 3D dose reconstruction.
• Implemented dose verification by comparing planned and reconstructed 3D dose distributions in the target and non-target volumes.
• Tested the real-time dosimetry system using an anthropomorphic phantom with three VMAT plans (head-and-neck, rectum, prostate) and introduced delivery errors, including linac halting functionality.

Main Results:

• The complete processing time for a single portal frame, including dose verification, was reduced to 266 ± 11 ms.
• Introduced delivery errors were detected within 5-10 seconds of irradiation time.
• Precomputation time was approximately 180 seconds per treatment arc.

Conclusions:

• A prototype online 3D dose verification tool utilizing portal imaging has been successfully developed and validated.
• The system demonstrated technological feasibility for online 3D dose verification in radiotherapy.
• The developed tool can detect significant delivery errors, enhancing patient safety during radiation therapy.