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Almhagen, Erik
Publications (6 of 6) Show all publications
Christensen, J. B., Almhagen, E., Stolarczyk, L., Vestergaard, A., Bassler, N. & Andersen, C. E. (2019). Ionization quenching in scintillators used for dosimetry of mixed particle fields. Physics in Medicine and Biology, 64(9), Article ID 095018.
Open this publication in new window or tab >>Ionization quenching in scintillators used for dosimetry of mixed particle fields
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2019 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 64, no 9, article id 095018Article in journal (Refereed) Published
Abstract [en]

Ionization quenching in ion beam dosimetry is often related to the fluence- or dose-averaged linear energy transfer (LET). Both quantities are however averaged over a wide LET range and a mixed field of primary and secondary ions. We propose a novel method to correct the quenched luminescence in scintillators exposed to ion beams. The method uses the energy spectrum of the primaries and accounts for the varying quenched luminescence in heavy, secondary ion tracks through amorphous track structure theory. The new method is assessed against more traditional approaches by correcting the quenched luminescence response from the BCF-12, BCF-60, and 81-0084 plastic scintillators exposed to a 100 MeV pristine proton beam in order to compare the effects of the averaged LET quantities and the secondary ions. Calculations and measurements show that primary protons constitute more than 92% of the energy deposition but account for more than 95% of the luminescence signal in the scintillators. The quenching corrected luminescence signal is in better agreement with the dose measurement when the secondary particles are taken into account. The Birks model provided the overall best quenching corrections, when the quenching corrected signal is adjusted for the number of free model parameters. The quenching parameter kB for the BCF-12 and BCF-60 scintillators is in agreement with literature values and was found to be kB = (10.6 +/- 0.1) x 10(-2) mu m keV(-1) for the 81-0084 scintillator. Finally, a fluence threshold for the 100 MeV proton beam was calculated to be of the order of 10(10) cm(-2), corresponding to 110 Gy, above which the quenching increases non-linearly and the Birks model no longer is applicable.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
plastic scintillator, particle dosimetry, quenching, proton therapy
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-386171 (URN)10.1088/1361-6560/ab12f2 (DOI)000466572600005 ()30909170 (PubMedID)
Available from: 2019-06-19 Created: 2019-06-19 Last updated: 2019-06-19Bibliographically approved
Almhagen, E., Boersma, D. J., Nyström, H. & Ahnesjö, A. (2018). A beam model for focused proton pencil beams. Physica medica (Testo stampato), 52, 27-32
Open this publication in new window or tab >>A beam model for focused proton pencil beams
2018 (English)In: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 52, p. 27-32Article in journal (Refereed) Published
Abstract [en]

Introduction: We present a beam model for Monte Carlo simulations of the IBA pencil beam scanning dedicated nozzle installed at the Skandion Clinic. Within the nozzle, apart from entrance and exit windows and the two ion chambers, the beam traverses vacuum, allowing for a beam that is convergent downstream of the nozzle exit. Materials and methods: We model the angular, spatial and energy distributions of the beam phase space at the nozzle exit with single Gaussians, controlled by seven energy dependent parameters. The parameters were determined from measured profiles and depth dose distributions. Verification of the beam model was done by comparing measured and GATE acquired relative dose distributions, using plan specific log files from the machine to specify beam spot positions and energy. Results: GATE-based simulations with the acquired beam model could accurately reproduce the measured data. The gamma index analysis comparing simulated and measured dose distributions resulted in > 95% global gamma index pass rates (3%/2 mm) for all depths. Conclusion: The developed beam model was found to be sufficiently accurate for use with GATE e.g. for applications in quality assurance (QA) or patient motion studies with the IBA pencil beam scanning dedicated nozzles.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Proton therapy, Monte Carlo, Beam model
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-364002 (URN)10.1016/j.ejmp.2018.06.007 (DOI)000442110000004 ()30139606 (PubMedID)
Funder
Swedish Childhood Cancer FoundationSwedish Radiation Safety Authority
Available from: 2018-10-30 Created: 2018-10-30 Last updated: 2018-10-30Bibliographically approved
Christensen, J. B., Almhagen, E., Nystrom, H. & Andersen, C. E. (2018). Quenching-free fluorescence signal from plastic-fibres in proton dosimetry: understanding the influence of Cerenkov radiation. Physics in Medicine and Biology, 63(6), Article ID 065001.
Open this publication in new window or tab >>Quenching-free fluorescence signal from plastic-fibres in proton dosimetry: understanding the influence of Cerenkov radiation
2018 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 63, no 6, article id 065001Article in journal (Refereed) Published
Abstract [en]

The origin of photons emitted in optical fibres under proton irradiation has been attributed to either entirely Cerenkov radiation or light consisting of fluorescence with a substantial amount of Cerenkov radiation. The source of the light emission is assessed in order to understand why the signal from optical fibres irradiated with protons is reportedly quenching-free. The present study uses the directional emittance of Cerenkov photons in 12 MeV and 20 MeV electron beams to validate a Monte Carlo model for simulating the emittance and transmission of Cerenkov radiation in optical fibres. We show that fewer than 0.01 Cerenkov photons are emitted and guided per 225 MeV proton penetrating the optical fibre, and that the Cerenkov signal in the optical fibre is completely negligible at the Bragg peak. Furthermore, on taking the emittance and guidance of both fluorescence and Cerenkov photons into account, it becomes evident that the reported quenching-free signal in PMMA-based optical fibres during proton irradiation is due to fluorescence.

Keywords
ionization quenching, dosimetry, fluorescence, Cerenlcov radiation, proton therapy, quenching-free
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-386315 (URN)10.1088/1361-6560/aaafad (DOI)000460106200001 ()29446760 (PubMedID)
Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-06-24Bibliographically approved
Grönlund, E., Almhagen, E., Johansson, S., Traneus, E. & Ahnesjö, A. Robust maximization of tumor control probability for radicality constrained dose painting by numbers of head and neck cancer.
Open this publication in new window or tab >>Robust maximization of tumor control probability for radicality constrained dose painting by numbers of head and neck cancer
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(English)In: Article in journal (Refereed) Submitted
Abstract [en]

Background and Purpose The aim of this study was to evaluate the potential and robustness to increase the tumor control probability (TCP) for robustly optimized dose painting plans compared to conventional homogeneous dose plans for head and neck cancers.

Material and Methods We optimized a set of dose painting plans with a robust TCP maximizing objective under different mean dose constraints for the primary clinical target volume (CTVT). These plans were optimized with the robust mini-max algorithm together with dose-responses driven by standardized uptake values (SUV) from 18F-fluorodeoxyglucose positron emission tomography (FDG-PET). The robustness in TCP was evaluated through sampling treatment scenarios with iso-center displacements. We also analyzed the impact on TCP predictions by considering dose-response uncertainties.

Results The average increase in TCP with dose painting ranged between 3 to 20 percentage points (p.p.) which depended on the allowed integral CTVT dose. The median deviation in TCP increase was below 1p.p. for all sampled treatment scenarios versus the nominal plans. Patients with large tumors and large spread of SUV gained the greatest TCP increases. By considering dose-response uncertainties, a decrease of the TCP for a homogeneous dose yielded an increasing dose painting potential.

Conclusions We have found that it is feasible to optimize FDG-PET driven dose painting plans that robustly increase the TCP compared to homogeneous dose treatments for head and neck cancers. The greatest potential TCP increases were found for patients with larger and more SUV heterogeneous tumors, which may give guidance for patient selection to further test the presented dose painting formalism.

Keywords
Dose painting; Dose painting by numbers; Head and neck cancer; 18F-FDG PET/CT
National Category
Cancer and Oncology
Research subject
Medical Radiophysics
Identifiers
urn:nbn:se:uu:diva-394216 (URN)
Funder
Swedish Cancer Society, 130632
Available from: 2019-10-05 Created: 2019-10-05 Last updated: 2019-10-14Bibliographically approved
Grönlund, E., Almhagen, E., Johansson, S., Traneus, E. & Ahnesjö, A. Robust maximization of tumor control probability for radicality constrained dose painting by numbers of head and neck cancer.
Open this publication in new window or tab >>Robust maximization of tumor control probability for radicality constrained dose painting by numbers of head and neck cancer
Show others...
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

Background and Purpose The aim of this study was to evaluate the potential and robustness to increase the tumor control probability (TCP) for robustly optimized dose painting plans compared to conventional homogeneous dose plans for head and neck cancers.

Material and Methods We optimized a set of dose painting plans with a robust TCP maximizing objective under different mean dose constraints for the primary clinical target volume (CTVT). These plans were optimized with the robust mini-max algorithm together with dose-responses driven by standardized uptake values (SUV) from 18F-fluorodeoxyglucose positron emission tomography (FDG-PET). The robustness in TCP was evaluated through sampling treatment scenarios with iso-center displacements. We also analyzed the impact on TCP predictions by considering dose-response uncertainties.

Results The average increase in TCP with dose painting ranged between 3 to 20 percentage points (p.p.) which depended on the allowed integral CTVT dose. The median deviation in TCP increase was below 1p.p. for all sampled treatment scenarios versus the nominal plans. Patients with large tumors and large spread of SUV gained the greatest TCP increases. By considering dose-response uncertainties, a decrease of the TCP for a homogeneous dose yielded an increasing dose painting potential.

Conclusions We have found that it is feasible to optimize FDG-PET driven dose painting plans that robustly increase the TCP compared to homogeneous dose treatments for head and neck cancers. The greatest potential TCP increases were found for patients with larger and more SUV heterogeneous tumors, which may give guidance for patient selection to further test the presented dose painting formalism.

Keywords
Dose painting; Dose painting by numbers; Head and neck cancer; 18F-FDG PET/CT
National Category
Cancer and Oncology
Research subject
Medical Radiophysics
Identifiers
urn:nbn:se:uu:diva-395142 (URN)
Funder
Swedish Cancer Society, 130632
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-18Bibliographically approved
Grönlund, E., Almhagen, E., Johansson, S., Traneus, E., Nyholm, T., Thellenberg, C. & Ahnesjö, A.Robust treatment planning of dose painting for prostate cancer based on ADC-to-Gleason score mapping: what is the potential to increase the tumor control probability?.
Open this publication in new window or tab >>Robust treatment planning of dose painting for prostate cancer based on ADC-to-Gleason score mapping: what is the potential to increase the tumor control probability?
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background and Purpose

We have in this study evaluated our earlier published dose painting formalism for prostate cancer that is driven by dose-responses of Gleason scores mapped from apparent diffusion coefficient (ADC) image data. The aim of this study is to evaluate the ability to actualize increases of the tumor control probability (TCP) with optimization of “dose painting by numbers” (DPBN) plans in a treatment planning system (TPS) compared to uniform dose treatments for patients with high-risk prostate cancer.

Material and Methods

We have evaluated the potential to actualize TCP increases with realistic DPBN plans as compared to uniform dose treatments for a test set of 17 patients diagnosed with high-risk prostate cancer and pre-RT ADC image data. This potential was evaluated through calculating the DPBN efficiency, defined as the ratio of TCP increases for realistic DPBN plans by TCP increases for ideal DPBN prescriptions. Both the ideal DPBN prescriptions and the realistic DPBN plans were optimized with the objective to maximize the TCP for the target prostate volumes (CTVT) while retaining the same average dose as for conventional uniform dose treatments. For the realistic DPBN plan optimization we tested the impact on the TCP by applying different photon energies, different levels of precision of the mapping of ADC data into Gleason score driven dose-responses, and with respect to different levels of iso-center positioning uncertainties through optimizing with robust minimax optimization.

Results

The median DPBN efficiency for the most conservative planning scenario optimized with 15MV photons, a low precision ADC-to-Gleason mapping, and a robustness distance of 0.6 cm was 10%, meaning that more than half of the patients had a gain in TCP of at least 10% of the TCP for an ideal DPBN prescription. By using 6MV photons, increasing the precision of the ADC-to-Gleason mapping, and decreasing the robustness distance the median of the DPBN efficiency increased by up to 40%.

Conclusions

Optimization of DPBN plans in a TPS can according to our formalism yield TCP increases compared to conventional uniform dose treatments for prostate cancer. These TCP increases are more likely when there is a high precision on the mapping of image data into dose-responses and a high certainty of the tumor position during treatment. These findings motivate further development to ensure accurate and precise mappings of image data into dose-responses and to ensure a high spatial certainty of the tumor position when implementing DPBN in a TPS.

Keywords
Dose painting; Dose painting by numbers; Prostate cancer;
National Category
Cancer and Oncology
Research subject
Medical Radiophysics
Identifiers
urn:nbn:se:uu:diva-394217 (URN)
Funder
Swedish Cancer Society, 130632
Available from: 2019-10-05 Created: 2019-10-05 Last updated: 2019-10-14Bibliographically approved
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