Modulated electron beams using multi-segmented multileaf collimation.

E E Klein

doi:10.1016/s0167-8140(98)00050-4

Home/Archive/PubMed

PubMed · 9925250

Modulated electron beams using multi-segmented multileaf collimation.

E E Klein

View original source ↗Export metadata ↓

Abstract

BACKGROUND AND PURPOSE: Conformal radiation therapy by modulation of photon and electron beams has been described for many techniques. Modulation of electron beams with the use of either bolus or altered scanned beams is reported. Our institution previously investigated the use of MLC for fixed static electron fields. The results were dismal due to the wide penumbra associated with multileaf collimated electrons scattered from foils. The purpose of this study was to decipher whether multi-segmented electron beams using MLC would provide a useful and practical modulated beam by taking advantage of matching the diffuse beam edges. MATERIALS AND METHODS: We started by planning simple target shapes, such as wedged and parabolic shapes. We optimized the segment widths, weights, gaps between segments and energies. We then irradiated phantoms using film to confirm the calculations. The study was limited to single-plane irradiation. We also planned and measured isodoses for a parotid target volume that possessed varying depths from surface to medial aspect. RESULTS: We found that we could optimize distributions by using the treatment depth and points of inflection to derive optimal segments. The planned treatments using a simple CET (coefficient of equivalent thickness) algorithm were confirmed with reasonable success. A 24 cm wide target was treated with nine segments in under 5 min, while most cases, including the parotid volume, were treated in under 3 min. CONCLUSIONS: We have developed a technique to complement a photon modulation program by treating lesions close to the surface. The debate as to whether this technique is optimal and more efficient than a bolus technique continues. We are currently devising methods for optimizing modulated electron MLC beams in multiple planes.

Explore related subjects

Electrons Humans Phantoms, Imaging Radiotherapy Planning, Computer-Assisted Radiotherapy, Conformal Journal Article

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

E E Klein. 1998. Modulated electron beams using multi-segmented multileaf collimation.. https://doi.org/10.1016/s0167-8140(98)00050-4

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2026

Technical note: reconstructing dose distributions from manually planned electron boosts in breast radiotherapy.

PURPOSE: In breast radiotherapy, delivery of manually-calculated electron boosts limits retrospective dose-response analyses as dose distribution is unavailable. This work evaluates the feasibility of reconstructing dose distributions from manually planned electron boosts in breast-conserving radiotherapy. METHODS: Only 72 out of 198 breast cancer patients had complete stored dose distributions from sequential electron boosts in the REQUITE study. Arbitrary data from 70/72 patients were used to develop and validate dose reconstruction method. Twenty patients were used to determine optimal parameters for Monte-Carlo-based (MC) electron dose reconstruction on RayStation (v.11B-R), considering CT-calibration curve, MC-history number, andcalculation grid resolution. Remaining 50 patients were used to quantify dose reconstruction accuracy. The similarity between reconstructed and stored dose was evaluated using 3D-gamma index and dosimetric parameters extracted from breast and tumour bed contours. Dose difference location was evaluated using dose-location histogram. RESULTS: Calculation grid resolution significantly impacted electron dose distribution (p < 0.01), where the finest grid (0.15 cm) showed highest similarity to stored doses. CT-calibration curve and MC-history number had a negligible influence on dose reconstruction. Dosimetric difference between reconstructed and stored doses was < 1 Gy for breast and tumour bed. Reconstructed dose was achieved > 90% gamma passing rate in the validation set. However, around 2.5 Gy dose differences were observed at the skin and tissue interface regions. CONCLUSIONS: Retrospective electron boost dose reconstruction is feasible with acceptable accuracy, and could increase data completeness in large cohort studies. Caution is advised when assessing dose near tissue interface and further validation is needed outside the REQUITE dataset.

Electrons↗

PubMed2001

Core molecular orbital contribution to N2O isomerization as studied using theoretical electron momentum spectroscopy.

Core molecular orbital contribution to the electronic structure of N2O isomers has been studied using quantum mechanical density functional theory combined with a plane wave impulse approximation method. Momentum distributions of wave functions for inner shell molecular orbitals of the linear NNO, cyclic and linear NON isomers of N2O are calculated through the (e, 2e) differential cross sections in momentum space. This is possible because this momentum distribution is directly proportional to the modulus squared of the momentum space wave function for the molecular orbital in question. While the momentum distributions of the NNO and cyclic N2O isomers demonstrate strong atomic orbital characteristics in their core space, the outer core molecular orbitals of the linear NON isomer exhibit configuration interactions between them and the valence molecular orbitals. It is suggested that the frozen core approximation breaks down in the prediction of the electronic structure of such an isomer. Core molecular orbital contributions to the electronic structure can alter the order of total energies of the isomers and lead to incorrect conclusions of the stability among the isomers. As a result, full electron calculations should be employed in the study of N2O isomerization.

Electrons↗

PubMed2001

Structure-property relationships in dendritic encapsulation.

Several molecular structure-property relationships are presented and compared to illustrate our current understanding of macromolecular encapsulation using dendrimers. Specifically, the effect that dendrimer architectures have on encapsulating photoactive and redox-active units fixed at the molecular core is considered.

Electrons↗