Verification of four-dimensional photon dose calculations

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Biology

Background:

• Thoracic treatment planning aims to incorporate patient-specific organ motion into dose calculations.
• Four-dimensional (4D) dose calculation algorithms have been developed for research but require clinical validation.
• Accurate 4D dose calculations are crucial for effective and safe radiation therapy.

Purpose of the Study:

• To evaluate and validate the accuracy of a 4D dose calculation algorithm using phantom measurements.
• To assess the algorithm's performance across different motion patterns (sinusoidal, irregular) and treatment plans (single-beam, multiple-beam, IMRT).

Main Methods:

• Utilized a rigid and a deformable anthropomorphic thoracic phantom on a motion platform.
• Investigated sinusoidal and irregular motion patterns, including patient-derived breathing profiles.
• Calculated doses using the 4D algorithm and measured delivered doses with thermoluminescent dosimeters (TLDs) and film.
• Compared measured and calculated doses using TLD ratios and gamma analysis with established passing criteria (3% for TLD, 5%/3 mm for gamma).

Main Results:

• All TLD measurements in both phantoms met the clinical passing criteria.
• 42 out of 48 film evaluations passed the criteria.
• Films failing the criteria were exclusively from the rigid phantom with irregular motion.
• No statistically significant performance differences were observed across various treatment plans.

Conclusions:

• The 4D dose calculation algorithm demonstrates accuracy within clinically acceptable standards when patient breathing is reproducible.
• The algorithm's performance is consistent across different treatment plan types.
• Phantom measurements provide essential validation for the clinical application of 4D dose calculation in thoracic radiotherapy.