Planning tools for modulated electron radiotherapy.
OBJECTIVE
To develop tools to plan modulated electron radiotherapy (MERT) and to compare the MERT plans to conventional or intensity modulated radiotherapy (IMRT) treatment plans.


METHODS
Monte Carlo dose calculations of electron fields shaped with the inherent photon multileaf collimators (MLCs) were investigated in this study. Treatment plans for four postmastectomy breast cancer patients were generated using MERT. The distances from the patient skin surfaces to the distal planning target volume surfaces were computed along the beam axis direction to determine the physical depth. Electron beam energies were selected to provide target coverage at these depths and energy bins were generated. A custom built MERT treatment planning graphical user interface (MERTgui) was used to shape the electron bins into deliverable electron segments. Monte Carlo dose distribution simulations were performed using the MLC-defined segments generated from the MERTgui. A custom built superposition gui was used to combine doses for each segment using relative weights and final MERT treatment plans were compared to the conventional or IMRT treatment plans. In addition, a demonstration of combined MERT and IMRT treatment plans was performed.


RESULTS
The MERT treatment plans provided acceptable target organ coverage in all cases. Relative to 3D conventional or IMRT treatment plans, the MERT plans predicted lower heart doses in all cases; average of the heart D20 of all plans was reduced from 14.1 to 3.3 Gy. The contralateral breast and contralateral lung doses decreased substantially with MERT planning compared to IMRT (on average, contralateral breast heart D20 was reduced from 8.7 to 0.7 Gy and contralateral lung D20 was reduced from 8.4 to 1.2 Gy with MERT). Ipsilateral lung D20 was lower with MERT than with the conventional plans (44.6 vs 29.2 Gy with MERT), but greater when compared against IMRT treatment plans (25.4 vs 28.9 Gy with MERT). A MERT and IMRT combination plan was generated to benefit from the complementary advantages of MERT and IMRT, resulting in satisfactory target coverage and reduced organ at risk doses.


CONCLUSIONS
MERT tools can facilitate treatment planning and provide plans for treatment of shallow targets such as the postmastectomy chest wall.
Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri 63110, USA. msurucu@radonc.uchicago.edu
Murat
M
Surucu
Eric E
EE
Klein
Maria
M
Mamalui-Hunter
David B
DB
Mansur
Daniel A
DA
Low
D004583:Electrons / Q000627:therapeutic use*; D006801:Humans; D021621:Imaging, Three-Dimensional; D011878:Radiotherapy / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated