Room: Karl Dean Ballroom C
Purpose: We introduce modulated electron arc therapy (MEAT) using 3D bolus and a photon MLC (pMLC) for superficial and curved PTVs like chest wall patients. An automatic 3D bolus generation method and intensity modulation for MEAT is developed.
Methods: pMLC and 100 cm source-to-axis distance (SAD) are used in MEAT. The EGSnrc Monte Carlo code was used to calculate dose distributions. Electron beam energy was determined by the average thickness of the PTV along the radial direction. The bolus was initialized by the radiological-equivalent difference of the depth of 90% of the maximum dose (dâ‚‰â‚€) and the PTV distal edge along the radial direction. The bolus thickness is update via shifting and smoothing iteratively based on dâ‚‰â‚€ of the intensity modulated dose distribution along the radial direction until the desired dose distribution is achieved. Two chest wall patients are quantitatively studied with MEAT planning and compared to tangential photon beams.
Results: Only one iteration of bolus shifting and intensity modulation was done for both patients. The beam energy is 9 and 6 MeV and the arc range is 59Ëš and 86Ëš for patient 1 and patient 2, respectively. Comparing the left lung dose of electron to photon plans, the volume receiving 30 Gy (Vâ‚ƒâ‚€) and 40 Gy (Vâ‚„â‚€) is decreased by about 10% while Vâ‚‚â‚€ is decreased by 2% - 9%. Around 10% - 20% of the PTV received more than 110% of the prescription dose. Vâ‚… of the right lungs is about 7%.
Conclusion: This work shows that MEAT is an effective modality for the treatment of chest wall patients with a decrease in the maximum lung dose. Additionally, dose homogeneity can be improved using energy modulation and isocenter optimization. Lower dose in left lungs and hearts can be obtained by adding more bolus at the arc edge.