A comparison of optic nerve dosimetry in craniospinal radiotherapy planned and treated with conventional and intensity modulated techniques.
OBJECTIVE
Some CNS tumours present leptomeningeal dissemination. Craniospinal radiotherapy is complex and recurrences may occur at sites of target volume underdosage. IMRT, being highly conformal to the target, could theoretically underdose the optic nerves if they are not specifically targeted leading to optic nerve recurrences. We analyzed optic nerve dosimetry when they are not specifically targeted.


METHODS
We designed 3D-conformal and tomotherapy plans for our last five patients treated to the craniospinal axis, not including the optic nerves in the target volume. We analyzed the dose delivered to the optic nerves, to the anterior and posterior half of the optic nerves, and to a theoretical optic nerve-PTV.


RESULTS
The dose delivered to the optic nerves was similar for both plans in all patients (V95% close to 100%) except one in whom tomotherapy considerably underdosed the anterior optic nerves. The dose to the optic nerve-PTV was lower with tomotherapy in all patients.


CONCLUSIONS
Despite not intentionally targeting the optic nerves, the dose to the optic nerves with IMRT was similar to 3D-conformal plans in most cases but left no margin for setup error. In individual cases the anterior half of the optic nerves could be significantly underdosed.
Rene
Nicholas J
NJ
Department of Radiation Oncology, McGill University Health Centre, Montreal, QC, Canada.
Brodeur
Marylene
M
Parker
William
W
Roberge
David
D
Freeman
Carolyn
C
D016543:Central Nervous System Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D016371:Cranial Irradiation; D006801:Humans; D008577:Meningeal Neoplasms / Q000517:prevention & control / Q000556:secondary; D008578:Meninges / Q000528:radiation effects; D009900:Optic Nerve / Q000528:radiation effects*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal; D050397:Radiotherapy, Intensity-Modulated; D013116:Spinal Cord / Q000528:radiation effects