Twin machines validation for VMAT treatments using electronic portal-imaging device: a multicenter study

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Technology

Background:

• Volumetric Arc Therapy (VMAT) with RapidArc™ is a precise radiotherapy technique.
• Ensuring treatment consistency across different linear accelerators (linacs) is crucial for patient safety and care continuity.
• Switching patients between linacs without re-optimization requires verification of plan accuracy.

Purpose of the Study:

• To verify the accuracy of Volumetric Arc Therapy (VMAT) plans delivered by RapidArc™ when patients are switched between identical "twin" linear accelerators (linacs).
• To assess if re-optimization is necessary when transferring a VMAT plan from one linac to another with the same energy and mechanical parameters.

Main Methods:

• Four institutions and eight linacs were involved, analyzing 242 measurements from 74 patients treated with 6MV RapidArc™.
• Treatment plans created on linac A were verified on both linac A and its "twin" linac B using an electronic portal imager (EPID).
• Gamma index analysis (3%/3mm threshold) was employed to compare measured and computed doses, assessing plan accuracy.

Main Results:

• High agreement was observed between measured and computed doses, with 94.79% (linac A) and 94.61% (linac B) of points passing the gamma criteria.
• Smoothed measurement analysis showed even higher agreement, with 98.67% (linac A) and 98.59% (linac B) passing the threshold.
• The dose difference between the two linacs was minimal, with 99.92% of points passing the criteria, indicating excellent consistency.

Conclusions:

• The study suggests that patients can be safely transferred between linacs with identical mechanical and energy parameters for VMAT treatment.
• The same VMAT plan can be used on a "twin" linac without the need for re-optimization, simplifying patient management.
• This finding supports the clinical feasibility of seamless patient workflow across matched linacs in radiotherapy centers.