Volumetric modulated arc radiotherapy for vestibular schwannomas.
OBJECTIVE
To evaluate volumetric modulated arc radiotherapy (RapidArc [RA]), a novel approach allowing for rapid treatment delivery, for the treatment of vestibular schwannoma (VS).


METHODS
The RA plans were generated for a small (0.5 cm(3)), intermediate (2.8 cm(3)), and large (14.8 cm(3)) VS. The prescription dose was 12.5 Gy to the encompassing 80% isodose. The RA plans were compared with conventional radiosurgery plans using both a single dynamic conformal arc (1DCA) and five noncoplanar dynamic conformal arcs (5DCA). Conformity indices (CI) and dose-volume histograms of critical organs were compared. The RA plan for the medium-sized VS was measured in a phantom using Gafchromic EBT films and compared with calculated dose distributions.


RESULTS
The RA planning was completed within 30 min in all cases, and calculated treatment delivery time (after patient setup) was 5 min vs. 20 min for 5DCA. A superior CI was achieved with RA, with a substantial decrease in low-dose irradiation of the normal brain achieved relative to 5DCA plans. Maximum doses to critical organs were similar for RA and 5DCA but were higher for 1DCA. Film measurements showed the differences between calculated and measured doses to be smaller than 1.5% in the high-dose area and smaller than 3% in the low-dose area.


CONCLUSIONS
The RA plans consistently achieved a higher CI and decrease in areas of low-dose irradiation. This, together with shorter treatment delivery times, has led to RA replacing our conventional five-arc radiosurgery technique for VS.
Department of Radiation Oncology, VU University Medical Center, Amsterdam, The Netherlands. fj.lagerwaard@vumc.nl
Frank J
FJ
Lagerwaard
Otto W M
OW
Meijer
Elles A P
EA
van der Hoorn
Wilko F A R
WF
Verbakel
Ben J
BJ
Slotman
Suresh
S
Senan
D000465:Algorithms; D006801:Humans; D009381:Neoplasms, Radiation-Induced / Q000517:prevention & control; D016609:Neoplasms, Second Primary / Q000517:prevention & control; D009464:Neuroma, Acoustic / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D019047:Phantoms, Imaging; D016634:Radiosurgery; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014276:Trigeminal Nerve / Q000528:radiation effects; D047368:Tumor Burden