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Segment Matching Optimization for Modulated Electron Radiation Therapy

G gokhroo, E Klein*, Washington University, Saint Louis, MO

MO-G-213AB-6 Monday 5:15:00 PM - 6:00:00 PM Room: 213AB

Purpose: Modulated electron radiotherapy (MERT) has been demonstrated to be an ideal treatment for lesions close to the surface in terms of dose coverage and sparing of underlying critical organs and normal tissues. The purpose of this study was to obtain the parameters and devise strategies for segment matching which are necessary for efficient MERT treatment planning.
Methods: In this study we used EGS4nrc/BEAMnrc and MCSim code for Monte Carlo calculations. The Computational Environment for Radiotherapy research (CERR) tool was used for viewing and comparing plans. A water phantom, delineated with stepped target idealized for two segments with sizes from 2 to 6 cm and electron beam energies of 6, 9, 12, 16 and 20 MeV were used for the calculations. The variation in dose distribution with different energies of abutted electron segments and change in segment size were studied. In order to obtain homogenous dose at the segment match, various gaps and smoothing between segments were introduced. Finally, a salivary gland MERT plan was executed using the segment match optimization scheme.
Results: As the energy difference between two consecutive segments increased, dose uniformity at the segment junction decreased. For small segments (< 4 cm) optimization can be improved by introducing a gap (1-2 mm) between segments. However, for larger segments, smoothing was found to be more beneficial than gapping the segments. The salivary gland case was successful in terms of dose coverage and homogeneity aided by the segment matching techniques described.
Conclusions: We conclude that use of bigger segments, and smaller differences in energy for abutting segments, should be prioritized for MERT planning. This study provides an optimization regimen of segment matching for MERT treatment planning with gaps/smoothing, depending on segment size and energy in order to provide better dose coverage and expedite the forward planning process.

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