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Monte Carlo Corrected DVHs for Retrospective Dose-Volume ModelingPowerPoint Presentation

Monte Carlo Corrected DVHs for Retrospective Dose-Volume Modeling

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Monte Carlo Corrected DVHs for Retrospective Dose-Volume Modeling

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Monte Carlo Corrected DVHs for Retrospective Dose-Volume Modeling

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Monte Carlo Corrected DVHs for Retrospective Dose-Volume Modeling

Patricia Lindsay, Joseph Deasy,

Issam El Naqa, Milos Vicic

Department of Radiation Oncology

Washington University, St. Louis

Partially supported by NIH grant R01 CA 90445 and a grant from Computerized Medical Systems, Inc.

- Retrospective analyses of tumor control and complications of lung cancer
- Need accurate 3-D dose distributions
- Archived dose distributions typically calculated without accounting for tissue heterogeneity (or using a very simple heterogeneity correction)
- More accurate dose distributions may lead to different correlations between dose-volume factors and complication rates

Match Monte Carlo to Water-based archived dose distribution

Recalculate MC using full CT

Determine beamlet weights and wedge effects

Predict actual dose received by patient

Computation Time – about 2 hours per plan

(10 nodes on cluster of 1.6 GHz AMD processors)

- VMC++ Monte Carlo code (Kawrakow†)
- Monte Carlo model of patient transport only
- Nominal input spectra (6 or 18 MV)
- Not accounting for scatter from beam modifiers (blocks, MLCs, wedges)

† Kawrakow I., VMC++, Electron and Photon Monte Carlo Calculations Optimized for Radiation Treatment Planning, Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation and Applications: Proceedings of the Monte Carlo 2000 Conference.

- 3-D treatment plan archives (RTOG format) imported into in-house software (CERR†)
- Information in CERR plan:
- Beam energy
- Gantry angles
- MLC or block field shapes
- Original 3-D dose distributions
- CT scan
- Not beam weights

†CERR(A Computational Environment for Radiotherapy Research) can be obtained from http://radium.wustl.edu/CERR

- Dose distributions prospectively generated with commercial TPS using Clarkson or Superposition/convolution algorithm, with or without heterogeneity corrections
- Compared with MC with and without heterogeneity corrections
- 6 and 18 MV plans
- Five different patient geometries

- 4 fields
- AP-PA, RPO-LAO
- No wedges or compensators
- MLC shaped
- 6 MV
Beam Weights:

TPS: 35, 25, 24, 16

MC: 34, 26, 24, 16

(Plan review using CERR)

- Small differences between Clarkson and Superposition/Convolution (S/C) DVHs when heterogeneity is included
- MC agrees very well with S/C dose distributions in water and with heterogeneity

- 3 Fields
- AP-PA wedged pair, LAT field
- MLC shaped
- 18 MV
Beam Weights:

TPS: 45, 46, 9

MC: 44, 43, 13

Water-Based

Heterogeneity Corrected

TPS (S/C)

Monte Carlo

- Large differences between Clarkson and S/C DVHs when heterogeneity is included
- Again MC agrees very well with S/C dose distributions both in water and with heterogeneity

- A novel method has been introduced to recompute Monte Carlo dose distributions from treatment planning system data.
- Monte Carlo recomputation of 3D dose distributions accounting for patient heterogeneity accurately reproduce superposition/convolution dose distributions.
- Using inaccurate heterogeneity corrections may lead to significant errors.
- Dose distributions which accurately account for heterogeneity may have an impact on predictions of tumor control and normal tissue complication rates.