Intensity modulated radiation therapy with electrons using algorithm based energy/range selection methods.
OBJECTIVE
In recent years photon intensity modulated radiation therapy (IMRT) has gained attention due to its ability to improve conformity of dose distributions. A potential advantage of electron-IMRT is that the dose fall off in the depth dose curve makes it possible to modulate the dose distribution in the direction of the beam by selecting different electron energies. This paper examines the use of a computer based energy selection in combination with the IMRT technique to optimise the electron dose distribution.


METHODS
One centimetre square electron beamlets ranging from 2.5 to 50 MeV were pre-calculated in water using Monte Carlo methods. A modified IMRT optimisation tool was then used to find an optimum mix of electron energies and intensities. The main principles used are illustrated in some simple geometries and tested on two clinical cases of post-operated ca. mam.


RESULTS
It is clearly illustrated that the energy optimisation procedure lowers the dose to lung and heart and makes the dose in the target more homogeneous. Increasing the energy at steep gradients compensates for lack of target coverage at beam edges and steep gradients. Comparison with a clinically acceptable four segment plan indicates the advantage of the used electron IMRT technique.


CONCLUSIONS
Using an intensity optimised mix of computer selected electron energies has the potential to improve electron treatments for mastectomy patients with good target coverage and reduced dose to normal tissue such as lung and heart.
Olofsson
Lennart
L
Department of Radiation Sciences, Radiation Physics, Umeå University, SE-901 87 Umeå, Sweden.
Mu
Xiangkui
X
Nill
Simeon
S
Oelfke
Uwe
U
Zackrisson
Björn
B
Karlsson
Mikael
M
D000465:Algorithms; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D003131:Combined Modality Therapy; D004307:Dose-Response Relationship, Radiation; D004583:Electrons; D005260:Female; D006801:Humans; D020714:Maximum Tolerated Dose; D011832:Radiation Injuries / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods; D012680:Sensitivity and Specificity; D016896:Treatment Outcome