A preliminary study of the role of modulated electron beams in intensity modulated radiotherapy, using automated beam orientation and modality selection.
OBJECTIVE
To develop an algorithm for optimal beam arrangement selection in intensity-modulated radiotherapy (IMRT) of mixed photon and electron beams. To apply this algorithm to study the utility of modulated electron beams in the context of IMRT planning.


METHODS
The optimization algorithm selects, for a user-specified number of beams, the optimal IMRT arrangement (beam orientations, and photon/electron modality for each orientation) using a novel fast heuristic intensity modulation procedure. The algorithm was employed to select optimal beam arrangements for breast (two, four, and six axial beams) and head-and-neck (three, four, five, and seven nonaxial beams) cases.


RESULTS
For the two cases, increasing the number of selected beams: (1) increased the number of electron beams for the breast case, but not more than one electron beam was selected for the head-and-neck case; (2) decreased critical structure doses for both cases; and (3) decreased target homogeneity for the breast case, but improved it for the head-and-neck case.


CONCLUSIONS
In the two cases analyzed using the selection algorithm, the primary role of modulated electrons differs based on treatment site-normal tissue dose reduction in breast and target homogeneity improvement in head and neck. Although this preliminary study with two cases appears to suggest that the role of intensity-modulated electrons differs based on treatment site, further investigation of large numbers of cases and varied treatment sites are required to establish a definitive conclusion.
Das
Shiva K
SK
Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA. shiva@radonc.duke.edu
Bell
Michael
M
Marks
Lawrence B
LB
Rosenman
Julian G
JG
D000465:Algorithms; D001943:Breast Neoplasms / Q000532:radiotherapy*; D004583:Electrons / Q000627:therapeutic use*; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D017785:Photons / Q000627:therapeutic use; D020266:Radiotherapy, Conformal / Q000379:methods*