Determination of surface dose in pencil beam scanning proton therapy

Kern, A.; Bäumer, Christian; Kroeninger, K.; Mertens, L. E.; Timmermann, Beate; Walbersloh, J.; Wulff, Jörg

doi:10.1002/mp.14086

Cited by 7 publications

(20 citation statements)

References 43 publications

(85 reference statements)

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“…The depth dose profile at low depth is determined by the interplay of four different effects: (1) in the first millimeters of the target, there is a steep dose build-up until a δ electron equilibrium is reached [38,39]. Its extension depends on the maximum δ electron energy and therefore on the velocity of the primary ions.…”

Section: Heavy Ion Depth Dose Profiles: Robustness Of the Dose Deliverymentioning

confidence: 99%

Beam Monitor Calibration for Radiobiological Experiments With Scanned High Energy Heavy Ion Beams at FAIR

et al. 2020

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Section: Heavy Ion Depth Dose Profiles: Robustness Of the Dose Deliverymentioning

confidence: 99%

Beam Monitor Calibration for Radiobiological Experiments With Scanned High Energy Heavy Ion Beams at FAIR

et al. 2020

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“…The PTW (Physikalisch-Technische Werkstätten, Freiburg, Germany) extrapolation ionization chamber type 23391 was validated in our previous study for the determination of surface doses in proton therapy. 2,11,27 The vented IC can be equipped with three exchangeable entrance windows consisting of Kapton ® (polyimide) foils surrounded by aluminum. The Kapton ® foils have physical thicknesses of 25, 50, and 75 μm.…”

Section: B Ionization Chambers: Ptw Extrapolation Chamber Type 233mentioning

confidence: 99%

“…The first one contributes to the systematic uncertainty U b,Dose resulted from the chamber geometry, which does not allow direct RW3 embedding due to the mechanical structure of the reverse side of the IC, and the second one due to the normalization at the gradient at a 3 cm reference depth for 100 MeV. 2 For both ICs the systematic uncertainty U b,Depth was specified with AE1.6%. The skin dose D 0:07 at a 70 μm depth was interpolated by a linear fit using the three percentage doses obtained from the three entrance windows.…”

Section: B Ionization Chambers: Ptw Extrapolation Chamber Type 233mentioning

confidence: 99%

“…In our previous study we were able to contribute to the data for surface doses, including the skin dose. 2 The skin dose was defined according to the ICRU Report No. 39 (International Commission on Radiation Units and Measurements) recommendation at a skin depth of 70 μm.…”

Section: Introductionmentioning

confidence: 99%

“…[4][5][6][7] By determining the skin dose more accurately, a relation between absorbed dose and skin toxicity may be achieved. 2 Further investigation of the clinical aspects of proton therapy may improve the modeling of dose-effect relationships retrospectively and in upcoming studies. [8][9][10][11] Dutz et al found a significant correlation between the skin dose-volume parameters such as D2% (dose to 2% of the volume) for erythema and alopecia.…”

Section: Introductionmentioning

confidence: 99%

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Impact of air gap, range shifter, and delivery technique on skin dose in proton therapy

et al. 2020

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Objective: Side effects of radiation therapy may include skin damage. The surface dose is of great interest and contains the buildup effect. In particular, the proton therapy community requires further experimental data to quantify doses in the surface region. This specification includes the skin dose, which is defined according to ICRU Report No. 39 at 70 μm water equivalent depth. The aim of this study is to gather more knowledge of the skin dose by varying key parameters defined by the patient treatment plan. This consists of clinical aspects such as the influence of the air gap, the application of a range shifter (RS), or the proton delivery technique. Material/methods: Skin doses were determined with a PTW 23391 extrapolation chamber with three thin Kapton ® entrance windows operated as a conventional ionization chamber. The impact on the skin dose for quasi-monoenergetic pencil beam scanning (PBS) proton beams was evaluated for clinical air gaps between 3.5 and 51.1 cm. The differences in skin dose were assessed by irradiating equivalent fields with an RS of 51 mm water equivalent thickness (RS51) and without. Furthermore, the delivery techniques PBS, uniform scanning (US), and double scattering (DS) were compared by defining a spread-out Bragg peak (SOBP). TOPAS (V.3.1.2) was used to model an IBA nozzle with PBS and to score dose to water at the surface of a water phantom. Results: For the monoenergetic fields without the application of the RS the skin dose was constant down to an air gap of 6.2 cm. A lower air gap of 3.5 cm showed a variation in skin dose by up to 2.4% compared to the results obtained with larger air gaps. With the inserted RS51 an increase in the skin dose was found for air gaps smaller than 11.3 cm. Experimentally, a dose difference of 1.4% was recorded for an air gap of 6.2 cm by inserting an RS and none. With the Monte Carlo calculations the largest dose increase was observed at the air gap of 3.5 cm with 1.7% and 4.0% relative to the skin dose results without the RS and to the largest evaluated air gap of 51.1 cm, respectively. The SOBP comparison of the beam modalities at the measuring plane at the isocenter revealed higher skin doses without RS (including RS) by up to +1.9% (+1.5%) for DS and +1.3% (+1.1%) for US compared to PBS. For all three techniques an approx. 2% rise in skin dose was observed for the largest evaluated air gap of 37.7 cm to an air gap of 6.2 cm when using an RS51. Conclusion: The study investigated aspects of skin dose of a water equivalent phantom by varying key parameters of a proton treatment plan. Parameters like the RS, the air gap, and the delivery modality have an impact on the order of 4.0% for the skin dose at the depth of 70 μm. The increases 831

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Technical note: Providing proton fields down to the few‐MeV level at clinical pencil beam scanning facilities for radiobiological experiments

et al. 2021

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The adequate performance of radiobiological experiments using clinical proton beams typically requires substantial preparations to provide the appropriate setup for specific experiments. Providing radiobiologically interesting low-energy protons is a particular challenge, due to various physical effects that become more pronounced with larger absorber thickness and smaller proton energy. This work demonstrates the generation of decelerated low-energy protons from a clinical proton beam. Methods: Monte Carlo simulations of proton energy spectra were performed for energy absorbers with varying thicknesses to reduce the energy of the clinical proton beam down to the few-MeV level corresponding to μm-ranges. In this way, a setup with an optimum thickness of the absorber with a maximum efficiency of the proton fluence for the provisioning of low-energy protons is supposed to be found. For the specific applications of 2.5-3.3 MeV protons and 𝛼-particle range equivalent protons, the relative depth dose was measured and simulated together with the dose-averaged linear energy transfer (LETd) distribution. Results:The resulting energy spectra from Monte Carlo simulations indicate an optimal absorber thickness for providing low-energy protons with maximum efficiency of proton fluence at an user-requested energy range for experiments. For instance, providing energies lower than 5 MeV, an energy spectrum with a relative total efficiency of 38.6% to the initial spectrum was obtained with the optimal setup. The measurements of the depth dose, compared to the Monte Carlo simulations, showed that the dosimetry of low-energy protons works and protons with high LETd down to the range of 𝛼-particles can be produced. Conclusions: This work provides a method for generating all clinically and radiobiologically relevant energies -especially down to the few-MeV levelat one clinical facility with pencil beam scanning. Thereby, it enables radiobiological experiments under environmentally uniform conditions.

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Determination of surface dose in pencil beam scanning proton therapy

Cited by 7 publications

References 43 publications

Beam Monitor Calibration for Radiobiological Experiments With Scanned High Energy Heavy Ion Beams at FAIR

Beam Monitor Calibration for Radiobiological Experiments With Scanned High Energy Heavy Ion Beams at FAIR

Impact of air gap, range shifter, and delivery technique on skin dose in proton therapy

Technical note: Providing proton fields down to the few‐MeV level at clinical pencil beam scanning facilities for radiobiological experiments

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