A dosimetric evaluation of conventional helmet field irradiation versus two-field intensity-modulated radiotherapy technique.
OBJECTIVE
To compare dosimetric differences between conventional two-beam helmet field irradiation (external beam radiotherapy, EBRT) of the brain and a two-field intensity-modulated radiotherapy (IMRT) technique.


METHODS
Ten patients who received helmet field irradiation at our institution were selected for study. External beam radiotherapy portals were planned per usual practice. Intensity-modulated radiotherapy fields were created using the identical field angles as the EBRT portals. Each brain was fully contoured along with the spinal cord to the bottom of the C2 vertebral body. This volume was then expanded symmetrically by 0.5 cm to construct the planning target volume. An IMRT plan was constructed using uniform optimization constraints. For both techniques, the nominal prescribed dose was 3,000 cGy in 10 fractions of 300 cGy using 6-MV photons. Comparative dose-volume histograms were generated for each patient and analyzed.


RESULTS
Intensity-modulated radiotherapy improved dose uniformity over EBRT for whole brain radiotherapy. The mean percentage of brain receiving >105% of dose was reduced from 29.3% with EBRT to 0.03% with IMRT. The mean maximum dose was reduced from 3,378 cGy (113%) for EBRT to 3,162 cGy (105%) with IMRT. The mean percent volume receiving at least 98% of the prescribed dose was 99.5% for the conventional technique and 100% for IMRT.


CONCLUSIONS
Intensity-modulated radiotherapy reduces dose inhomogeneity, particularly for the midline frontal lobe structures where hot spots occur with conventional two-field EBRT. More study needs to be done addressing the clinical implications of optimizing dose uniformity and its effect on long-term cognitive function in selected long-lived patients.
Yu
James B
JB
Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520-8040, USA.
Shiao
Stephen L
SL
Knisely
Jonathan P S
JP
D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000556:secondary; D016371:Cranial Irradiation / Q000379:methods*; D006801:Humans; D011859:Radiography; D011879:Radiotherapy Dosage / Q000592:standards; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*