SU-E-T-553: Dose-Mass Vs. Dose-Volume Optimization: A Phantom Study

Area of Science:

• Medical Physics
• Radiotherapy Planning
• Radiation Dosimetry

Background:

• Current radiotherapy planning often relies on dose-volume-histogram (DVH) based optimization.
• DVH optimization assumes uniform density, which can lead to inaccuracies in heterogeneous tissues.

Purpose of the Study:

• To compare the merits of mass-based optimization against volume-based optimization.
• To demonstrate the advantages of dose-mass-histogram (DMH) optimization in heterogeneous media using a simple phantom.

Main Methods:

• DVH-based objective functions were converted to DMH-based functions by incorporating voxel densities.
• A digital phantom with varying densities (0.2 g/cm³ and 0.8 g/cm³) was used.
• Monitor units were calculated for DVH- and DMH-based optimizations to achieve a target dose.

Main Results:

• Irradiating through lower density material (0.2 g/cm³) resulted in approximately 23% lower dose compared to higher density material (0.8 g/cm³).
• When DVH and DMH optimizations matched target dose-volume histograms, DMH delivered a higher proportion of dose through the lower density region (70% vs. 60%).

Conclusions:

• DMH optimization is more general and accurate than DVH optimization in heterogeneous media.
• DMH accounts for density variations, leading to improved dose deposition and reduced dose to critical structures.
• Mass-based optimization offers a more physically accurate approach to radiotherapy planning.