Presentation on theme: "Pencil-Beam Redefinition Algorithm Robert Boyd, Ph.D."— Presentation transcript:
1 Pencil-Beam Redefinition Algorithm Robert Boyd, Ph.D.
2 Pencil Beam Algorithms central axis ofbroad beam (Z)Xpixel bounding pencil beams(2x2 mm2 at isocenter)YZX-Y plane normal to beam axis (Z)
3 Pencil Beam Redefinition DXZZ+DZX-Y planes are spaced 5 mm apart on Z axis
4 PBRA 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
5 PBRA 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
29 Ethmoid Sinus - Profile at Y = 13.0 cm Varian 2100, 16 MeV, 10x10-cm2 applicator, 100 cm SSD
30 Clinical 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.
38 Pencil-Beam Divergence Current PBRA virtual source distance is equal to distance to broad beam virtual sourcemathematics assume “parallel”point beamsintegration performed over projected areasvirDxDz
39 Pencil-Beam Divergence divPBRA virtual source distance is a pencil beam-specific parametermathematics assume divergent point beamsintegration performed over normal pixel widthsvirDxDz
41 20-MeV Horizontal Air Slab Varian Clinac 2100, 15x15-cm2 open applicator, 100 cm SSD
42 Pencil-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
44 Future 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