Presentation on theme: "Pencil-Beam Redefinition Algorithm Robert Boyd, Ph.D."— Presentation transcript:
1Pencil-Beam Redefinition Algorithm Robert Boyd, Ph.D.
2Pencil Beam Algorithms central axis ofbroad beam (Z)Xpixel bounding pencil beams(2x2 mm2 at isocenter)YZX-Y plane normal to beam axis (Z)
3Pencil Beam Redefinition DXZZ+DZX-Y planes are spaced 5 mm apart on Z axis
4PBRA Physics Primary electron transport only delta-rays not modeledMultiple Coulomb scattering approximated with a Gaussian distributionlarge-angle scattering not modeledMean collisional energy loss onlycatastrophic energy losses not modeled
5PBRA Physics Approximations PBRA requires measured central-axis depth dose curvePBRA uses an energy-dependent correction factor C(E) to match calculated and measured central axis depth dose curve
29Ethmoid Sinus - Profile at Y = 13.0 cm Varian 2100, 16 MeV, 10x10-cm2 applicator, 100 cm SSD
30Clinical Evaluation - Results Accuracy criteria was not achieved for entire irradiated volume, albeit only a small volume (< 3.5%) had dose differences greater than 4% and greater than 2 mm DTA.PBRA showed good agreement with Monte Carlo in matching isodose lines.Better modeling of physics will improve the accuracy of PBRA-calculated dose.
4120-MeV Horizontal Air Slab Varian Clinac 2100, 15x15-cm2 open applicator, 100 cm SSD
42Pencil-Beam Divergence Results divPBRA was more accurate than PBRA for most data pointsdivPBRA was not able to achieve 4% or 2 mm accuracy for all data pointsCalculation times were approximately 30% longer
44Future Work Dosimetry studies using PBRA Tomotherapy vs. conventional electron therapyField matching for chest wall treatmentsElectron arc therapy planning using divPBRARealistic dose deposition kernels using Monte CarloAutomated custom bolus/skin collimation planning using PBRATranslating PBRA to commercial system