Real-time dose reconstruction for wedged photon beams: a generalized procedure

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• Accurate dose reconstruction is crucial for effective 3D conformal radiotherapy (3DCRT).
• Existing in vivo dosimetry methods using electronic portal imaging devices (EPIDs) often require extensive commissioning and analysis time.
• Adapting these methods for wedged beams presents additional challenges due to wedge attenuation.

Purpose of the Study:

• To extend a generalized procedure for isocenter dose reconstruction to include wedged X-ray beams.
• To develop a simplified and rapid in vivo dosimetry method for 3DCRT using aSi EPIDs.
• To validate the accuracy of the reconstructed doses against treatment planning system (TPS) calculations.

Main Methods:

• Developed a generalized procedure for reconstructing isocenter dose D(iso) for open and wedged beams from linacs of different manufacturers.
• Utilized water-equivalent solid phantoms and aSi EPIDs to determine generalized midplane doses and transit signals for various beam configurations.
• Fitted generalized data using surface equations and integrated with 'record & verify' network information for rapid D(iso) reconstruction.

Main Results:

• The generalized procedure was successfully extended to wedged beams, characterized by wedge attenuation factor W(AF).
• Isocenter dose reconstruction was achieved in approximately 25 seconds per beam post-treatment.
• In vivo dosimetry tests on pelvic treatments showed agreement within ±5% between reconstructed D(iso) and TPS-calculated D(iso,TPS).

Conclusions:

• The proposed procedure simplifies the dosimetric commissioning process for in vivo dosimetry with aSi EPIDs.
• It enables quasi-real-time in vivo dosimetry for both open and wedged 3DCRT fields across Varian, Elekta, and Siemens linacs.
• This method offers a practical and accurate solution for quality assurance in radiotherapy.