Energy modulated electron therapy using a few leaf electron collimator in combination with IMRT and 3D‐CRT: Monte Carlo‐based planning and dosimetric evaluation

Abstract

Energy modulated electron therapy (EMET) based on Monte Carlo dose calculation is a promising technique that enhances the treatment planning and delivery of superficially located tumors. This study investigated the application of EMET using a novel few-leaf electron collimator (FLEC) in head and neck and breast sites in comparison with three-dimensional conventional radiation therapy (3D-CRT) and intensity modulated radiation therapy (IMRT) techniques. Treatment planning was performed for two parotid cases and one breast case. Four plans were compared for each case: 3D-CRT, IMRT, 3D-CRT in conjunction with EMET (EMET-CRT), and IMRT in conjunction with EMET (EMET-IMRT), all of which were performed and calculated with Monte Carlo techniques. For all patients, dose volume histograms (DVHs) were obtained for all organs of interest and the DVHs were used as a means of comparing the plans. Homogeneity and conformity of dose distributions were calculated, as well as a sparing index that compares the effect of the low isodose lines. In addition, the whole-body dose equivalent (WBDE) was estimated for each plan. Adding EMET delivered with the FLEC to 3D-CRT improves sparing of normal tissues. For the two head and neck cases, the mean dose to the contralateral parotid and brain stem was reduced relative to IMRT by 43% and 84%, and by 57% and 71%, respectively. Improved normal tissue sparing was quantified as an increase in sparing index of 47% and 30% for the head and neck and the breast cases, respectively. Adding EMET to either 3D-CRT or IMRT results in preservation of target conformity and dose homogeneity. When adding EMET to the treatment plan, the WBDE was reduced by between 6% and 19% for 3D-CRT and by between 21% and 33% for IMRT, while WBDE for EMET-CRT was reduced by up to 72% when compared with IMRT. FLEC offers a practical means of delivering modulated electron therapy. Although adding EMET delivered using the FLEC results in perturbation of target conformity when compared to IMRT, it significantly improves normal tissue sparing while offering enhanced target conformity to the 3D-CRT planning. The addition of EMET systematically leads to a reduction in WBDE especially when compared with IMRT.

Direct aperture optimization for IMRT using Monte Carlo generated beamlets

“…The latchbit modification software ͑written in C code͒ converts the 23 independent latch bit tags into one single 23 bit binary number. The number of beamlets that a phase space can be divided into has now increased from 23 to 2 23 . The open-field phase space is converted into n individual phase space files-one per beamlet.…”

“…Al-Yahya et al calculate predefined geometric "fieldlet" doses using Monte Carlo data and optimize the fieldlet selection and electron energy ͑EMRT-energy modulated radiation therapy͒. 23 The technique proposed in this paper implements a novel method for segmenting a uniform phase space output from a BEAMnrc linear accelerator simulation into individual phase space beamlets. 24 These individual beamlets of phase space are projected onto a patient-specific phantom and the dose deposition distribution is simulated using DOSXYZnrc.…”

Part 2: Dynamic mixed beam radiotherapy (DYMBER): Photon dynamic trajectories combined with modulated electron beams

“…The DoF have also been extended for electron therapy, for example, modulated electron radiotherapy (MERT) [14][15][16][17][18][19][20][21][22] combines intensity and energy modulation. The typically available electron beam energies of 6-22 MeV offer a large variety of different particle ranges.…”

Delivery validation of an automated modulated electron radiotherapy plan

“…15 The efficacy of MERT in combination with 3D-CRT and IMRT was tested with results showing reduced whole body dose over the photon modalities alone. 16 Gauer et al 17 have showed superior MERT plans of whole breast and chest wall irradiations when compared to helical photon IMRT, while Salguero et al 18 showed MERT to be superior to conventional electrons for postmastectomy chest wall irradiations.…”