AbstractID: 6796 Title: Clinical use of a micro-IMRT system
A micro-IMRT system for stereotactic radiotherapy (SRT) has been in clinical use at
the Prince of Wales Hospital since November 2000, with five patients either
undergoing or completed treatment by March 2001. Beam collimation is via a
Radionics MMLC (projected leaf width at isocentre 4 mm) attached to a Siemens
Primus linear accelerator. MMLC field settings are auto-sequenced using the
Primelink system which interfaces the Primeview R&V interface to the MMLC
controller. Delivery of a coplanar plan with seven beams and 50 field segments
requires about 15 minutes including automated gantry rotations. Treatment planning
is performed using the Radionics XPlan SRT planning system with an integrated
inverse planning module based on the KonRad program. Optimisation is fast
(typically about one minute) due to the deterministic, gradient-based algorithm.
For IMRT treatment of small lesions, conformality of the dose distribution is
enhanced by the high-resolution of the MMLC. Equivalent target coverage with a
standard MLC (leaf width 10 mm) can be achieved by treating an expanded tumour
volume as the target, but at the cost of increased involvement of adjacent normal
tissues. DVH information can be exported and used for quantitative comparisons
between plans.
Field sequences and intensity maps for a patient treatment are applied to a phantom
for comparison of planned and delivered dose distributions. Dosimetry is via TLDs
placed along the AP and lateral directions in the axial plane through the isocenter.
Three sets of TLDs are exposed and the profiles plotted against those from the plan.