Experimental validation tests of fast Fourier transform convolution and multigrid superposition algorithms for dose...

Area of Science:

• Medical Physics
• Radiotherapy
• Radiation Oncology

Background:

• Accurate dose calculation is crucial for modern conformal radiotherapy, especially for challenging lung tumor treatments.
• Treatment planning systems (TPS) employ various algorithms for dose calculation, each with potential for error.

Purpose of the Study:

• To assess the accuracy of fast Fourier transform convolution (FFTC) and multigrid superposition (MGS) algorithms in dose calculation for lung radiotherapy.
• To compare the predicted dose values from these algorithms against experimental measurements.

Main Methods:

• FFTC and MGS algorithms within a FOCUS 3.0.0 TPS were used to calculate doses for photon beams (6 and 25 MV).
• Simulated lung geometries (mediastinum-lung and thoracic wall-lung-thoracic wall) were irradiated.
• Calculated doses were validated using radiographic films and ionization chamber measurements.

Main Results:

• FFTC algorithm exhibited over 10% average deviation in absolute dose and up to 8 mm discrepancies in beam fringe values.
• MGS algorithm met the 3%-3 mm accuracy criteria, with an average absolute dose deviation of approximately 1%.
• MGS showed beam fringe deviations within 3 mm and ionometric-film measurement deviations within 3%.

Conclusions:

• MGS algorithm provides accurate dose distributions and absolute dose calculations in inhomogeneous lung regions.
• MGS is suitable for routine clinical practice and dose-escalation programs in lung radiotherapy.
• FFTC algorithm is not recommended for clinical use due to significant dose calculation errors.