A simplified method of four-dimensional dose accumulation using the mean patient density representation

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-guided Therapy

Background:

• Accurate 4D cumulative dose estimation is crucial for effective radiation therapy.
• Respiratory motion significantly impacts dose delivery accuracy in thoracic and abdominal treatments.
• Current 4D dose calculations can be computationally intensive, posing challenges for clinical workflows.

Purpose of the Study:

• To validate the feasibility of using an average 4DCT image set (AVG-CT) for 4D cumulative dose estimation.
• To compare dose discrepancies between the AVG-CT approach and full 4D summation in phantom and patient data.
• To assess the clinical significance of dose differences for target volumes and organs at risk.

Main Methods:

• Generation of 4DCT numerical phantoms and corresponding AVG-CTs.
• Calculation of static dose on each 4DCT phase and cumulative dose using full 4D summation.
• Calculation of AVG-CT cumulative dose using a single static dose distribution applied across all phases.
• Evaluation in four lung cancer patient cases using deformable image registration to obtain displacement vector fields (DVFs).

Main Results:

• AVG-CT approximation resulted in slightly higher cumulative doses compared to full 4D summation, with discrepancies increasing with tumor excursion.
• Clinically insignificant differences were observed for GTV parameters (min, mean, max, D99, D1) when using AVG-CT with deformable registration in patients.
• Negligible differences in dosimetric indices and dose coverage were found for the spinal cord, esophagus, and heart.

Conclusions:

• The AVG-CT approach, coupled with deformable registration, accurately accounts for respiratory tumor motion.
• This method has been validated for 4D dose accumulation, demonstrating its potential to simplify clinical practice.
• The AVG-CT method offers a promising avenue for streamlining 4D dose calculations, particularly for adaptive radiotherapy planning.