Direct dose mapping versus energy/mass transfer mapping for 4D dose accumulation: fundamental differences and...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Treatment Planning

Background:

• Accurate dose accumulation is crucial in radiation therapy, particularly with organ motion or tissue deformation.
• Direct Dose Mapping (DDM) and Energy/Mass Transfer (EMT) are key algorithms for dose accumulation.
• DDM's interpolation method can lack rigor with complex deformations, while EMT relies on fundamental physics principles.

Purpose of the Study:

• To implement and compare the clinical dosimetric differences between DDM and EMT algorithms.
• To evaluate the accuracy of dose accumulation for lung cancer patients undergoing stereotactic radiosurgery.
• To determine the suitability of DDM versus EMT for cumulative dose calculations in the reference phase.

Main Methods:

• Implemented DDM and EMT algorithms within the Eclipse treatment planning system.
• Compared dose accumulation for ten lung cancer patients, mapping doses from respiratory phases to the end-of-exhale (EE) phase.
• Utilized Demons-based registration for displacement vector fields to transfer dose and energy, with dose calculated per phase and accumulated.

Main Results:

• DDM and EMT algorithms produced significant differences in cumulative dose, particularly in regions with sharp mass density variations and high dose gradients.
• Differences in minimum dose for the Planning Target Volume (PTV) reached up to 11%, and for the Internal Target Volume (ITV) up to 4%.
• The study observed noticeable discrepancies between the two algorithms, highlighting potential inaccuracies with DDM.

Conclusions:

• Energy/Mass Transfer (EMT) mapping provides a more physically sound and accurate method for dose accumulation compared to Direct Dose Mapping (DDM).
• DDM may not be adequate for precise cumulative dose distribution calculations in complex scenarios like stereotactic radiosurgery with motion.
• EMT should be considered for accurate dose accumulation in radiotherapy planning to ensure reliable treatment delivery.