Intensity modulation with photons for benign intracranial tumours: A planning comparison of volumetric single arc, helical arc and fixed gantry techniques

Background and purpose: 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. Materials and 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 (RAHD120 with the new High Definition MLC with 2.5 mm leaf width at isocentre and RAM120 with the standard Millennium with 5 mm 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. V95% (in %) was higher than 99% for all techniques, minimum significant dose (D99%) was 95.5 ± 1.4 for IMRT, 96.2 ± 1.4 and 97.0 ± 1.2 for the RAHD120 and RAM120 approaches and 96.8 ± 1.7 for HT, maximum significant dose (D1%, 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 (CI95%) 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: V10Gy (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 ± 4.2 103 Gy cm3, 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