Electron conformal radiotherapy using bolus and intensity modulation.
OBJECTIVE
Conformal electron beam therapy can be delivered using shaped bolus, which varies the penetration of the electrons across the incident beam so that the 90% isodose surface conforms to the distal surface of the planning target volume (PTV). Previous use of this modality has shown that the irregular proximal surface of the bolus causes the dose heterogeneity in the PTV to increase from 10%, the typical dose spread of a flat-water surface to approximately 20%. The present work evaluates the ability to restore dose homogeneity by varying the incident electron intensity.


METHODS
Three patients, one each with chest wall, thorax, and head-and-neck cancer, were planned using electron conformal therapy with bolus, with and without intensity modulation. Resulting dose distributions and dose-volume histograms were compared with non-intensity-modulated bolus plans.


RESULTS
In all cases, the DeltaD(90%-10%) for the PTV was reduced; for example, for the head-and-neck case, the DeltaD(90%-10%) for the PTV was reduced from 14.9% to 9.2%. This reduction in dose spread is a direct result of intensity modulation.


CONCLUSIONS
The results showed that intensity-modulated electron beams could significantly improve the dose homogeneity in the PTV for patients treated with electron conformal therapy using shaped bolus.
Kudchadker
Rajat J
RJ
Department of Radiation Physics, M.D. Anderson Cancer Center, University of Texas, Houston, TX 77030, USA. rkudchad@mdanderson.org
Hogstrom
Kenneth R
KR
Garden
Adam S
AS
McNeese
Marsha D
MD
Boyd
Robert A
RA
Antolak
John A
JA
D000328:Adult; D001943:Breast Neoplasms / Q000532:radiotherapy*; D004583:Electrons; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008875:Middle Aged; D019047:Phantoms, Imaging; D020266:Radiotherapy, Conformal / Q000379:methods*; D013899:Thoracic Neoplasms / Q000532:radiotherapy*; D014867:Water
D014867:Water