Pelvic dose accumulation accuracy in a CBCT based online adaptive radiotherapy system

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Accurate dose accumulation is critical for online adaptive radiotherapy (OART).
• Evaluating dose accumulation accuracy and errors in pelvic treatments is essential.
• The Ethos v1.1 and v2.0 systems are used for OART dose accumulation.

Purpose of the Study:

• Quantify dose accumulation accuracy of Ethos v1.1 and v2.0 systems.
• Assess the clinical significance of dose accumulation errors in pelvic OART.
• Compare Ethos system performance against true dose accumulation.

Main Methods:

• Simulated OART sessions using modified pelvic CTs with realistic deformation vector fields (DVF).
• Dose accumulation using Ethos system (D(fx)Ethos) and true DVF (D(fx)True).
• 3D gamma analysis and comparison of clinical goals between methods.

Main Results:

• Significant discrepancies noted between applied DVF and Ethos-calculated DVF for both versions.
• Ethos v1.1 met 90% gamma pass rate; Ethos v2.0 did not consistently meet this benchmark.
• Dose accumulation errors affected 6% of clinical goals, misrepresenting their achievement status.

Conclusions:

• Ethos v1.1 demonstrated acceptable dose accumulation performance for tested pelvic CTs.
• Ethos v2.0 exhibited substantial discrepancies in dose accumulation.
• Dose accumulation inaccuracies in OART can impact treatment plan evaluation.