Latest Posts

DC Hall, AV Trofimov, BA Winey, NJ Liebsch, and H Paganetti. In Press. “Predicting patient-specific dosimetric benefits of proton therapy for skull-base tumors using a geometric knowledge-based method.” International Journal of Radiation Oncology • Biology • Physics, 2017.Abstract

Purpose: To predict the organ-at-risk (OAR) dose levels achievable with proton beam therapy (PBT), solely based upon the geometric arrangement of the target volume in relation to the OARs. Comparison to an alternative therapy yields a prediction of the patient-specific benefits offered by PBT. This could enable a physician at a hospital without proton capabilities to make a better-informed referral decision, or aid patient selection in model-based clinical trials.

Methods and Materials: Skull-base tumors were chosen to test the method, owing to their geometric complexity and multitude of nearby OARs. By exploiting correlations between dose and distance-to-target in existing PBT plans, models were independently trained for six types of OAR: brainstem, cochlea, optic chiasm, optic nerve, parotid gland and spinal cord. Once trained, the models could estimate the feasible dose-volume histogram and generalized equivalent uniform dose (gEUD) for OAR structures of new patients. Models were trained using 20 patients and validated with a further 21 patients. Validation was achieved by comparing the predicted gEUD to that of the actual PBT plan.

Results: The predicted and planned gEUD were in good agreement: considering all OARs, the prediction error was +1.4 ± 5.1 Gy (mean ± SD) and Pearson’s correlation coefficient was 93%. When compared to an IMRT plan, the model could classify whether an OAR structure would experience a gain with a sensitivity of 93% (95% CI: 87% – 97%) and a specificity of 63% (95% CI: 38% – 84%).

Conclusions: We trained and validated models that quickly and accurately predict the patient-specific benefits of PBT for skull-base tumors. Similar models could be developed for other tumor sites. Such models are useful when an estimation of the feasible benefits of PBT is desired, but the experience and/or resources required for treatment planning are unavailable.

New TOPAS documentation website goes live!

I have moved our documentation from the old PDF document to a website hosted by ReadTheDocs: http://topas.readthedocs.org

They also host a PDF version: https://media.readthedocs.org/pdf/topas/latest/topas.pdf

From the user perspective, I hope that this will help to discover features of TOPAS more easily and find solutions to their problems more quickly. Hyperlinks now connect related sections.

Recent Publications

Predicting patient-specific dosimetric benefits of proton therapy for skull-base tumors using a geometric knowledge-based method

DC Hall, AV Trofimov, BA Winey, NJ Liebsch, and H Paganetti. In Press. “Predicting patient-specific dosimetric benefits of proton therapy for skull-base tumors using a geometric knowledge-based method.” International Journal of Radiation Oncology • Biology • Physics, 2017.Abstract

Purpose: To predict the organ-at-risk (OAR) dose levels achievable with proton beam therapy (PBT), solely based upon the geometric arrangement of the target volume in relation to the OARs. Comparison to an alternative therapy yields a prediction of the patient-specific benefits offered by PBT. This could enable a physician at a hospital without proton capabilities to make a better-informed referral decision, or aid patient selection in model-based clinical trials.

Methods and Materials: Skull-base tumors were chosen to test the method, owing to their geometric complexity and multitude of nearby OARs. By exploiting correlations between dose and distance-to-target in existing PBT plans, models were independently trained for six types of OAR: brainstem, cochlea, optic chiasm, optic nerve, parotid gland and spinal cord. Once trained, the models could estimate the feasible dose-volume histogram and generalized equivalent uniform dose (gEUD) for OAR structures of new patients. Models were trained using 20 patients and validated with a further 21 patients. Validation was achieved by comparing the predicted gEUD to that of the actual PBT plan.

Results: The predicted and planned gEUD were in good agreement: considering all OARs, the prediction error was +1.4 ± 5.1 Gy (mean ± SD) and Pearson’s correlation coefficient was 93%. When compared to an IMRT plan, the model could classify whether an OAR structure would experience a gain with a sensitivity of 93% (95% CI: 87% – 97%) and a specificity of 63% (95% CI: 38% – 84%).

Conclusions: We trained and validated models that quickly and accurately predict the patient-specific benefits of PBT for skull-base tumors. Similar models could be developed for other tumor sites. Such models are useful when an estimation of the feasible benefits of PBT is desired, but the experience and/or resources required for treatment planning are unavailable.

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Validation of nuclear models in Geant4 using the dose distribution of a 177 MeV proton pencil beam

DC Hall, A Makarova, H Paganetti, and B Gottschalk. 2016. “Validation of nuclear models in Geant4 using the dose distribution of a 177 MeV proton pencil beam.” Physics in Medicine and Biology, 1, 61: N1-10. Publisher's VersionAbstract

A proton pencil beam is associated with a surrounding low-dose envelope, originating from nuclear interactions. It is important for treatment planning systems to accurately model this envelope when performing dose calculations for pencil beam scanning treatments, and Monte Carlo (MC) codes are commonly used for this purpose. This work aims to validate the nuclear models employed by the Geant4 MC code, by comparing the simulated absolute dose distribution to a recent experiment of a 177 MeV proton pencil beam stopping in water.

Striking agreement is observed over five orders of magnitude, with both the shape and normalisation well modelled. The normalisations of two depth dose curves are lower than experiment, though this could be explained by an experimental positioning error. The Geant4 neutron production model is also verified in the distal region. The entrance dose is poorly modelled, suggesting an unaccounted upstream source of low-energy protons. Recommendations are given for a follow-up experiment which could resolve these issues.

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Measurement of fiducial differential cross sections of gluon-fusion production of Higgs bosons decaying to WW→eνμν with the ATLAS detector at √s=8 TeV

ATLAS Collaboration. 2016. “Measurement of fiducial differential cross sections of gluon-fusion production of Higgs bosons decaying to WW→eνμν with the ATLAS detector at √s=8 TeV.” Journal of High Energy Physics, 8, 2016: 104. Publisher's VersionAbstract

This paper describes a measurement of fiducial and differential cross sections of gluon-fusion Higgs boson production in the HWWeνμν channel, using 20.3 fb1 of proton-proton collision data. The data were produced at a centre-of-mass energy of √s=8 TeV at the CERN Large Hadron Collider and recorded by the ATLAS detector in 2012. Cross sections are measured from the observed HWWeνμν signal yield in categories distinguished by the number of associated jets. The total cross section is measured in a fiducial region defined by the kinematic properties of the charged leptons and neutrinos. Differential cross sections are reported as a function of the number of jets, the Higgs boson transverse momentum, the dilepton rapidity, and the transverse momentum of the leading jet. The jet-veto efficiency, or fraction of events with no jets above a given transverse momentum threshold, is also reported. All measurements are compared to QCD predictions from Monte Carlo generators and fixed-order calculations, and are in agreement with the Standard Model predictions.

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Observation and measurement of Higgs boson decays to WW* with the ATLAS detector

ATLAS Collaboration. 2015. “Observation and measurement of Higgs boson decays to WW* with the ATLAS detector.” Physical Review D, 92: 012006. Publisher's VersionAbstract

We report the observation of Higgs boson decays to WW based on an excess over background of 6.1 standard deviations in the dilepton final state, where the Standard Model expectation is 5.8 standard deviations. Evidence for the vector-boson fusion (VBF) production process is obtained with a significance of 3.2 standard deviations. The results are obtained from a data sample corresponding to an integrated luminosity of 25fb1 from √s=7 and 8 TeV pp collisions recorded by the ATLAS detector at the LHC. For a Higgs boson mass of 125.36 GeV, the ratio of the measured value to the expected value of the total production cross section times branching fraction is 1.09+0.160.15(stat)+0.170.14(syst). The corresponding ratios for the gluon fusion and vector-boson fusion production mechanisms are 1.02±0.19(stat)+0.220.18(syst) and 1.27+0.440.40(stat)+0.300.21(syst), respectively. At √s=8TeV, the total production cross sections are measured to be σ(ggHWW)=4.6±0.9(stat)+0.80.7(syst)pb and σ(VBHWW)=0.51+0.170.15(stat)+0.130.08(syst)pb. The fiducial cross section is determined for the gluon-fusion process in exclusive final states with zero or one associated jet.

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Discovery and measurement of the Higgs boson in the WW decay channel

D Hall. 2015. Discovery and measurement of the Higgs boson in the WW decay channel. Switzerland: Springer International Publishing. Publisher's VersionAbstract

In the Standard Model of particle physics, the non-zero masses of the W and Z bosons and the fermions are generated through interactions with the Higgs field, excitations of which correspond to Higgs bosons. Thus, the experimental discovery of the Higgs boson is of prime importance to physics, and would confirm our understanding of fundamental mass generation.

This thesis describes a search for the ggHWWlνlν process of Higgs boson production and decay. It uses the LHC Run I dataset of pp collisions recorded by the ATLAS detector, which corresponds to an integrated luminosity of 4.5 fb−1 at 7TeV and 20.3 fb-1 at 8 TeV. An excess of events is observed with a significance of 4.8 standard deviations, which is consistent with Higgs boson production. The significance is extended to 6.1 standard deviations when the vector boson fusion production process is included. The measured signal strength is 1.11+0.23-0.21 at mH = 125 GeV. A cross section measurement of WW production, a major background to this search, is also presented using the 7 TeV dataset only.

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Measurement of W+W production in pp collisions at √s = 7 TeV with the ATLAS detector and limits on anomalous WWZ and WWγ couplings

ATLAS Collaboration. 2013. “Measurement of W+W production in pp collisions at √s = 7 TeV with the ATLAS detector and limits on anomalous WWZ and WWγ couplings.” Physical Review D, 87: 112001. Publisher's VersionAbstract

This paper presents a measurement of the W+W production cross section in pp collisions at √s=7TeV. The leptonic decay channels are analyzed using data corresponding to an integrated luminosity of 4.6fb1 collected with the ATLAS detector at the Large Hadron Collider. The W+W production cross section σ(ppW+W+X) is measured to be 51.9±2.0(stat)±3.9(syst)±2.0(lumi)pb, compatible with the Standard Model prediction of 44.7+2.11.9pb. A measurement of the normalized fiducial cross section as a function of the leading lepton transverse momentum is also presented. The reconstructed transverse momentum distribution of the leading lepton is used to extract limits on anomalous WWZ and WWγ couplings.

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