Paraspinal volumetric modulated arc therapy.
OBJECTIVE
The processes involved in the treatment of paraspinal tumours by volumetric modulated arc therapy (VMAT) are described here by means of an illustrative case.


METHODS
Az single anticlockwise arc from gantry angle 179° to 181° was constructed using SmartArc (Philips Radiation Oncology Systems, Fitchburg, WI) with control points spaced at 2°. The dose prescription was 60 Gy in 30 fractions to cover the planning target volume (PTV) as uniformly as possible while sparing the 0.3-cm planning risk volume (PRV) around the spinal cord. The plan was verified before treatment using a diode array phantom and radiochromic film. Treatment delivery was on a Synergy linear accelerator with a beam modulator head (Elekta Ltd, Crawley, UK).


RESULTS
Homogeneous dose coverage of the PTV was achieved with a D(2%) of 62.0 Gy and D(98%) of 55.6 Gy. Maximum spinal cord dose was 49.9 Gy to 0.1 cm(3) and maximum dose to the spinal cord PRV was 55.4 Gy to 0.1 cm(3). At pre-treatment verification, the percentage of the high-dose region receiving a dose within 3% and 3 mm of the planned dose was 98.8% with the diode array and 93.4% with film. Delivery time was 2 min 15 s and the course of treatment was successfully completed.


CONCLUSIONS
VMAT was successfully planned, verified and delivered for this challenging tumour site. VMAT provides a very suitable method of treating complex paraspinal tumours, offering a high-quality conformal dose distribution with a short delivery time.
The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK. james.bedford@icr.ac.uk
J L
JL
Bedford
H M
HM
Convery
V N
VN
Hansen
F H
FH
Saran
D006801:Humans; D009364:Neoplasm Recurrence, Local / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D020069:Shoulder Pain / Q000209:etiology; D013125:Spinal Neoplasms / Q000532:radiotherapy* / Q000601:surgery