Author(s): Sameer S. A. Natto
Article publication date: 2009-12-01
Vol. 27 No. 4 (yearly), pp. 187-194.
177
Keywords
iPlan treatment planning system, SRS/SRT, radiosensitive structures, radiotherapy, ×‑ray.
Abstract
The BrainLab iPlan Treatment Planning System (TPS) was used to model a clinac ×-ray
photon beam with the BrainLab stereotactic radiosurgery (SRS) apparatus. The head and neck
region of the anthropomorphic Rando phantom was scanned using both CT and MRI imaging
modalities. Imaged slices were fused together for better contrast using the automatic image fusion
provided with iPlan RT image software. A 1.25 cm3 tumour was assumed and defined at the back of
the brain. Nine intracranial radiosensitive structures were segmented manually and automatically
by using the atlas-based auto-segmentation tool implemented in iPlan RT image software. The
iPlan RT dose software was then employed to estimate the dose received by 50% of each of these
structures and the tumour. Volumes and doses of automatically and manually segmented structures
were then compared. Generally, it was found that iPlan RT image overestimates the volume of
intracranial structures except two of them, the right and the left eye, were underestimated. The dose
received by radiosensitive structures exposed to direct ×-ray beam were affected by segmentation
discrepancies, while the off-beam structures were not. It was found that auto-segmentation helped
in reducing the time required for segmentation by considerable amounts with acceptable accuracy.
Finally, an important recommendation is to explore the possibility of predefining the radiological
properties of different types of tumour cells in the code for quick and accurate auto-segmentation
of Gross Tumour Volume (GTV), for better dose estimation.