Intensity modulation with photons for benign intracranial tumours: a planning comparison of volumetric single arc, helical arc and fixed gantry techniques.
OBJECTIVE
The potential benefits and limitations of the new RapidArc treatment concept compared to Helical Tomotherapy and fixed gantry intensity modulation techniques have been assessed at treatment planning level on 12 patients presenting with 'benign' brain tumours.


METHODS
Plans for five acoustic neurinomas, five meningiomas and two pituitary adenomas were computed for an Helical Tomotherapy (HT) unit, for RapidArc delivery (RA) on a linac equipped with two types of MLC (RA_HD120 with the new High Definition MLC with 2.5mm leaf width at isocentre and RA_M120 with the standard Millennium with 5mm resolution) and for fixed beam IMRT with the High Definition MLC. Analysis was mostly performed on physical quantities derived from Dose-Volume Histograms (DVHs).


RESULTS
Target coverage resulted basically equivalent among techniques. V(95%) (in %) was higher than 99% for all techniques, minimum significant dose (D(99%)) was 95.5+/-1.4 for IMRT, 96.2+/-1.4 and 97.0+/-1.2 for the RA_HD120 and RA_M120 approaches and 96.8+/-1.7 for HT, maximum significant dose (D(1%), in %) was 102.2+/-0.8, 102.7+/-0.5, 102.4+/-0.5 and 103.0+/-1.1, respectively, standard deviation (in %) was 1.4+/-0.4, 1.3+/-0.3, 1.1+/-0.2 and 0.8+/-0.3, respectively. Conformity Index (CI(95%)) was 0.47+/-0.12, 0.46+/-0.12, 0.43+/-0.11 and 0.38+/-0.11, respectively. For organs at risk all techniques respected planning objectives. Concerning the healthy tissue: V(10 Gy) (in %) was 9.4+/-5.5, 9.9+/-6.1, 9.2+/-6.1 and 12.1+/-8.8, respectively. Integral dose measured on the healthy tissue was 7.5+/-3.3, 9.7+/-3.4, 8.7+/-3.4, 10.4+/-4.2 10(3) Gy cm(3), respectively.


CONCLUSIONS
For the class of tumours investigated in this report, HT and RA and IMRT proved to be adequate to properly treat patients. Further studies on more complex cases need to be investigated in order to assess the effectiveness of this new technique in a broader clinical perspective.
Fogliata
Antonella
A
Oncology Institute of Southern Switzerland, Radiation Oncology Department, Bellinzona, Switzerland.
Clivio
Alessandro
A
Nicolini
Giorgia
G
Vanetti
Eugenio
E
Cozzi
Luca
L