Hippocampal-sparing whole-brain radiotherapy: a "how-to" technique using helical tomotherapy and linear accelerator-based intensity-modulated radiotherapy.
OBJECTIVE
Sparing the hippocampus during cranial irradiation poses important technical challenges with respect to contouring and treatment planning. Herein we report our preliminary experience with whole-brain radiotherapy using hippocampal sparing for patients with brain metastases.


METHODS
Five anonymous patients previously treated with whole-brain radiotherapy with hippocampal sparing were reviewed. The hippocampus was contoured, and hippocampal avoidance regions were created using a 5-mm volumetric expansion around the hippocampus. Helical tomotherapy and linear accelerator (LINAC)-based intensity-modulated radiotherapy (IMRT) treatment plans were generated for a prescription dose of 30 Gy in 10 fractions.


RESULTS
On average, the hippocampal avoidance volume was 3.3 cm(3), occupying 2.1% of the whole-brain planned target volume. Helical tomotherapy spared the hippocampus, with a median dose of 5.5 Gy and maximum dose of 12.8 Gy. LINAC-based IMRT spared the hippocampus, with a median dose of 7.8 Gy and maximum dose of 15.3 Gy. On a per-fraction basis, mean dose to the hippocampus (normalized to 2-Gy fractions) was reduced by 87% to 0.49 Gy(2) using helical tomotherapy and by 81% to 0.73 Gy(2) using LINAC-based IMRT. Target coverage and homogeneity was acceptable with both IMRT modalities, with differences largely attributed to more rapid dose fall-off with helical tomotherapy.


CONCLUSIONS
Modern IMRT techniques allow for sparing of the hippocampus with acceptable target coverage and homogeneity. Based on compelling preclinical evidence, a Phase II cooperative group trial has been developed to test the postulated neurocognitive benefit.
Gondi
Vinai
V
Department of Human Oncology, University of Wisconsin Comprehensive Cancer Center, Madison, WI 53792, USA.
Tolakanahalli
Ranjini
R
Mehta
Minesh P
MP
Tewatia
Dinesh
D
Rowley
Howard
H
Kuo
John S
JS
Khuntia
Deepak
D
Tomé
Wolfgang A
WA
D000679:Amygdala / Q000000981:diagnostic imaging; D001932:Brain Neoplasms / Q000532:radiotherapy / Q000556:secondary; D003072:Cognition Disorders / Q000517:prevention & control*; D016371:Cranial Irradiation / Q000379:methods*; D006624:Hippocampus / Q000166:cytology / Q000000981:diagnostic imaging / Q000528:radiation effects*; D006801:Humans; D010315:Particle Accelerators; D011832:Radiation Injuries / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013234:Stem Cells / Q000166:cytology / Q000528:radiation effects; D036542:Tomography, Spiral Computed / Q000379:methods*