Pre-treatment patient-specific stopping power by combining list-mode proton radiography and x-ray CT
The relative stopping power (RSP) uncertainty is the largest contributor to the range uncertainty in proton therapy. The purpose of this work was to develop a systematic method that yields accurate and patient-specific RSPs by combining (1) pre-treatment x-ray CT and (2) daily proton radiography of...
Saved in:
| Main Authors: | , |
|---|---|
| Format: | Article (Journal) |
| Language: | English |
| Published: |
3 August 2017
|
| In: |
Physics in medicine and biology
Year: 2017, Volume: 62, Issue: 17, Pages: 1-18 |
| ISSN: | 1361-6560 |
| DOI: | 10.1088/1361-6560/aa7c42 |
| Online Access: | Verlag, Volltext: http://dx.doi.org/10.1088/1361-6560/aa7c42 Verlag, Volltext: http://stacks.iop.org/0031-9155/62/i=17/a=6836 
|
| Author Notes: | Charles-Antoine Collins-Fekete, Sébastien Brousmiche, David C. Hansen, Luc Beaulieu and Joao Seco |
| Summary: | The relative stopping power (RSP) uncertainty is the largest contributor to the range uncertainty in proton therapy. The purpose of this work was to develop a systematic method that yields accurate and patient-specific RSPs by combining (1) pre-treatment x-ray CT and (2) daily proton radiography of the patient. The method was formulated as a penalized least squares optimization problem (argmin( ##IMG## [http://ej.iop.org/images/0031-9155/62/17/6836/pmbaa7c42ieqn001.gif] $\Vert \bf A\bf x-\bf b\Vert _2^2$ )). The parameter A represents the cumulative path-length crossed by the proton in each material, separated by thresholding on the HU. The material RSPs (water equivalent thickness/physical thickness) are denoted by x . The parameter b is the list-mode proton radiography produced using Geant4 simulations. The problem was solved using a non-negative linear-solver with ##IMG## [http://ej.iop.org/images/0031-9155/62/17/6836/pmbaa7c42ieqn002.gif] $\bf x\geqslant0$ . A was computed by superposing proton trajectories calculated with a cubic or linear spline approach to the CT. The material’s RSP assigned in Geant4 were used for reference while the clinical HU-RSP calibration curve was used for comparison. The Gammex RMI-467 phantom was first investigated. The standard deviation between the estimated material RSP and the calculated RSP is 0.45%. The robustness of the techniques was then assessed as a function of the number of projections and initial proton energy. Optimization with two initial projections yields precise RSP (⩽1.0%) for 330 MeV protons. 250 MeV protons have shown higher uncertainty (⩽2.0%) due to the loss of precision in the path estimate. Anthropomorphic phantoms of the head, pelvis, and lung were subsequently evaluated. Accurate RSP has been obtained for the head ( ##IMG## [http://ej.iop.org/images/0031-9155/62/17/6836/pmbaa7c42ieqn004.gif] $\mu =0.21\pm1.63%$ ), the lung ( ##IMG## [http://ej.iop.org/images/0031-9155/62/17/6836/pmbaa7c42ieqn005.gif] $\mu=0.06\pm0.99%$ ) and the pelvis ( ##IMG## [http://ej.iop.org/images/0031-9155/62/17/6836/pmbaa7c42ieqn006.gif] $\mu=0.90\pm3.87%$ ). The range precision has been optimized using the calibration curves obtained with the algorithm, yielding a mean ##IMG## [http://ej.iop.org/images/0031-9155/62/17/6836/pmbaa7c42ieqn007.gif] $\rm R_80$ difference to the reference of 0.11 ±0.09%, 0.28 ± 0.34% and ##IMG## [http://ej.iop.org/images/0031-9155/62/17/6836/pmbaa7c42ieqn008.gif] $0.05 \pm 0.06%$ in the same order. The solution’s accuracy is limited by the assumed HU/RSP bijection, neglecting inherent degeneracy. The proposed formulation of the problem with prior knowledge x-ray CT demonstrates potential to increase the accuracy of present RSP estimates. |
|---|---|
| Item Description: | Gesehen am 15.08.2018 |
| Physical Description: | Online Resource |
| ISSN: | 1361-6560 |
| DOI: | 10.1088/1361-6560/aa7c42 |