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Modelling of a proton spot scanning system using MCNP6
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
2017 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 860, article id 012025Article in journal (Refereed) Published
Abstract [en]

The aim of this work was to model the characteristics of a clinical proton spot scanning beam using Monte Carlo simulations with the code MCNP6. The proton beam was defined using parameters obtained from beam commissioning at the Skandion Clinic, Uppsala, Sweden. Simulations were evaluated against measurements for proton energies between 60 and 226 MeV with regard to range in water, lateral spot sizes in air and absorbed dose depth profiles in water. The model was also used to evaluate the experimental impact of lateral signal losses in an ionization chamber through simulations using different detector radii. Simulated and measured distal ranges agreed within 0.1 mm for R90 and R80 , and within 0.2 mm for R50 . The average absolute difference of all spot sizes was 0.1 mm. The average agreement of absorbed dose integrals and Bragg-peak heights was 0.9%. Lateral signal losses increased with incident proton energy with a maximum signal loss of 7% for 226 MeV protons. The good agreement between simulations and measurements supports the assumptions and parameters employed in the presented Monte Carlo model. The characteristics of the proton spot scanning beam were accurately reproduced and the model will prove useful in future studies on secondary neutrons.

Place, publisher, year, edition, pages
2017. Vol. 860, article id 012025
National Category
Other Physics Topics
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-161042DOI: 10.1088/1742-6596/860/1/012025ISI: 000412324300025OAI: oai:DiVA.org:su-161042DiVA, id: diva2:1255847
Conference
International Nuclear Science and Technology Conference (INST), Bangkok, Thailand, August 4-6, 2016
Available from: 2018-10-15 Created: 2018-10-15 Last updated: 2018-10-19Bibliographically approved
In thesis
1. Out-of-field doses from proton therapy and doses from CBCT imaging: Risk of radiation-induced second cancer from modern radiotherapy
Open this publication in new window or tab >>Out-of-field doses from proton therapy and doses from CBCT imaging: Risk of radiation-induced second cancer from modern radiotherapy
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of ionizing radiation for treatment of cancer diseases is continuously increasing as patient survival is improving and new treatment techniques are emerging. While this development is beneficial for curing primary tumors, concerns have been raised regarding the unwanted dose contribution to healthy tissues of patients and the associated risk of radiation-induced second cancer (RISC). This is especially important for younger patients receiving radiotherapy more often than before and for whom the risk of developing RISC is elevated in comparison to the typical adult radiotherapy patient. In order to estimate the risk of RISC associated with modern radiotherapy and imaging, the associated radiation doses must be determined.

Patients undergoing radiotherapy receive in-field doses from the primary beam but also out-of-field doses originating from secondary radiation produced in the beamline and within the patient. Over the last years, the use of proton pencil beam scanning (PBS) therapy has rapidly increased due to its potential to reduce the in-field doses to healthy tissues in comparison to photon therapy. One of the drawbacks with proton therapy is the production of neutrons capable of travelling large distances and depositing out-of-field doses to organs located far from the primary treatment field. The dose reduction associated with proton PBS therapy could consequently be affected by the out-of-field doses originating from secondary radiation.

The sharp dose gradients associated with modern treatment techniques, such as photon intensity-modulated radiotherapy (IMRT) and proton PBS therapy require more frequent and accurate patient imaging in comparison to conventional treatment techniques such as three-dimensional conformal radiotherapy (CRT). Setup verification images could be acquired with cone-beam computed tomography (CBCT) producing three-dimensional patient images at the cost of an increased patient dose in comparison to planar x-ray imaging. Concerns have been raised regarding the cumulative patient doses from repeated CBCT imaging versus the dose-saving benefits associated with modern radiotherapy techniques like IMRT and proton PBS.

In this thesis, a study on the in-field and out-of-field doses to healthy tissues from photon IMRT and CRT treatments of head and neck tumors showed that the risk of RISC was unaffected by the employed treatment technique and indicated that the lifetime risk of cancer induction was of the order of 1-2%.

Results from measurements and Monte Carlo simulations showed that the out-of-field absorbed doses and equivalent doses associated with proton PBS treatments of brain tumors were up to 60 µGy/Gy and 150 µSv/Gy, respectively. The risk of RISC associated with these out-of-field doses was in the range of approximately one induced cancer in ten thousand treated patients. A simulation study on the doses from a proton gantry-mounted CBCT system showed that repeated CBCT imaging could result in cumulative organ doses of almost 2 Gy. The conclusion from these studies is that the dose-sparing effects of proton PBS therapy are not overshadowed by the out-of-field doses originating from secondary radiation for brain tumor treatments, but that the cumulative doses from repeated CBCT imaging could have a relevant impact on the overall dose reduction.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2018. p. 55
National Category
Other Physics Topics
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-161044 (URN)978-91-7797-470-3 (ISBN)978-91-7797-471-0 (ISBN)
Public defence
2018-11-30, Rehabsalen, Norrbacka, S2 plan 01, Karolinska Universitetssjukhuset, Solna, Stockholm, 09:00 (English)
Opponent
Supervisors
Available from: 2018-11-07 Created: 2018-10-16 Last updated: 2018-11-02Bibliographically approved

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