A system for three-dimensional dosimetric verification of treatment plans in intensity-modulated radiotherapy with heavy ions

Karger, Christian P.; Jäkel, Oliver; Hartmann, Günther H.; Heeg, Peter

doi:10.1118/1.598728

Cited by 107 publications

(95 citation statements)

References 19 publications

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“…The use of a single-element dosimeter, requiring delivery of the whole 3D treatment field for each point, would be highly time-consuming, and multiple measurement points would be preferable. 18 The pretreatment verification measurements of patient-specific plans by scanned high energy pencil ion beams are routinely performed by simultaneous measurements of the dose at a representative sample of points, by means of a limited number of pinpoint ionization chambers (24, typically) arranged in a 3D stack, 19 calibrated in terms of dose to water. 17 Such ionization chamber arrays are considered as a suitable instrument for 3D dosimetry in scanning ion beam radiotherapy, thanks to their energy independence and small detector size.…”

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confidence: 99%

Dosimetric characterization of a microDiamond detector in clinical scanned carbon ion beams

et al. 2015

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Purpose: To investigate for the first time the dosimetric properties of a new commercial synthetic diamond detector (PTW microDiamond) in high-energy scanned clinical carbon ion beams generated by a synchrotron at the CNAO facility. Methods: The detector response was evaluated in a water phantom with actively scanned carbon ion beams ranging from 115 to 380 MeV/u (30-250 mm Bragg peak depth in water). Homogeneous square fields of 3 × 3 and 6 × 6 cm 2 were used. Short-and medium-term (2 months) detector response stability, dependence on beam energy as well as ion type (carbon ions and protons), linearity with dose, and directional and dose-rate dependence were investigated. The depth dose curve of a 280 MeV/u carbon ion beam, scanned over a 3 × 3 cm 2 area, was measured with the microDiamond detector and compared to that measured using a PTW Advanced Markus ionization chamber, and also simulated using  Monte Carlo code. The detector response in two spread-out-Bragg-peaks (SOBPs), respectively, centered at 9 and 21 cm depths in water and calculated using the treatment planning system (TPS) used at CNAO, was measured. Results: A negligible drift of detector sensitivity within the experimental session was seen, indicating that no detector preirradiation was needed. Short-term response reproducibility around 1% (1 standard deviation) was found. Only 2% maximum variation of microDiamond sensitivity was observed among all the evaluated proton and carbon ion beam energies. The detector response showed a good linear behavior. Detector sensitivity was found to be dose-rate independent, with a variation below 1.3% in the evaluated dose-rate range. A very good agreement between measured and simulated Bragg curves with both microDiamond and Advanced Markus chamber was found, showing a negligible LET dependence of the tested detector. A depth dose curve was also measured by positioning the microDiamond with its main axis oriented orthogonally to the beam direction. A strong distortion in Bragg peak measurement was observed, confirming manufacturer recommendation on avoiding such configuration. Very good results were obtained for SOBP measurements, with a difference below 1% between measured and TPS-calculated doses. The stability of detector sensitivity in the observation period was within the experimental uncertainty. Conclusions: Dosimetric characterization of a PTW microDiamond detector in high-energy scanned carbon ion beams was performed. The results of the present study showed that this detector is suitable for dosimetry of clinical carbon ion beams, with a negligible LET and dose-rate dependence. C 2015 American Association of Physicists in Medicine. [http://dx

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Dosimetric characterization of a microDiamond detector in clinical scanned carbon ion beams

et al. 2015

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“…MRI gel dosimetry (Ramm et al 2000, Maryansky et al 1993, Olsson et al 1990 provides 3D dose information but it has the disadvantage that a magnetic resonance imaging unit is needed for evaluation. 3D arrays of ionization chambers (Karger et al 1999) present reliable dosimetric properties, but do not have satisfactory spatial resolution (∼5-6 mm). Stacks of ionization chambers with strip-segmented cathodes for 2D readout have a better spatial response in a plane perpendicular to the beam, but they do not provide full 2D dose information in that plane (only two projections of the beam profile in that plane) (Bonazzola et al 1998, Brusasco et al 2000.…”

Section: Introductionmentioning

confidence: 99%

A scintillating gas detector for 2D dose measurements in clinical carbon beams

Seravalli¹,

Boer²,

Geurink

et al. 2008

Phys. Med. Biol.

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A two-dimensional position sensitive dosimetry system based on a scintillating gas detector has been developed for pre-treatment verification of dose distributions in hadron therapy. The dosimetry system consists of a chamber filled with an Ar/CF 4 scintillating gas mixture, inside which two cascaded gas electron multipliers (GEMs) are mounted. A GEM is a thin kapton foil with copper cladding structured with a regular pattern of sub-mm holes. The primary electrons, created in the detector's sensitive volume by the incoming beam, drift in an electric field towards the GEMs and undergo gas multiplication in the GEM holes. During this process, photons are emitted by the excited Ar/CF 4 gas molecules and detected by a mirror-lens-CCD camera system. Since the amount of emitted light is proportional to the dose deposited in the sensitive volume of the detector by the incoming beam, the intensity distribution of the measured light spot is proportional to the 2D hadron dose distribution. For a measurement of a 3D dose distribution, the scintillating gas detector is mounted at the beam exit side of a water-bellows phantom, whose thickness can be varied in steps. In this work, the energy dependence of the output signal of the scintillating gas detector has been verified in a 250 MeV/u clinical 12 C ion beam by means of a depth-dose curve measurement. The underestimation of the measured signal at the Bragg peak depth is only 9% with respect to an airfilled ionization chamber. This is much smaller than the underestimation found for a scintillating Gd 2 O 2 S:Tb ('Lanex') screen under the same measurement conditions (43%). Consequently, the scintillating gas detector is a promising device for verifying dose distributions in high LET beams, for example to check hadron therapy treatment plans which comprise beams with different energies.

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“…During the irradiation the actual beam information (lateral position x, y, number of particles N and longitudinal displacement dz) and the motion signal dX are recorded in a time resolved manner (Saito, Bert, Chaudhri, Gemmel, Schardt, & Rietzel 2009b). As quality assurance phantom, a static water tank equipped with an array of 24 small ionization chambers (ICs) can be used as it had been performed for plan verification in therapy of static tumours at GSI (Karger et al 1999). In the static water phantom, the dose distribution of the beam tracking case is different from that for a static target case due to the position adaptation to the virtual target, as it is illustrated in figure 7. shows distribution without beam tracking that corresponds to the reference plan, and the lower panel corresponds to the ideal beam tracking case.…”

Section: Qa Measurementsmentioning

confidence: 99%