Figure 4 - uploaded by Andreas Peters
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Three consecutive synchrotron cycles. For each energy a new cycle has to be initiated. All synchrotron devices are ramped down and up again to a slightly different energy level. The phases with dose delivery to the patient are shown in green, those needed for preparation and acceleration phases in red.
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![Figure 1: The rasterscan technique used at HIT [1]. The energy of the...](profile/Andreas-Peters-3/publication/289567101/figure/fig5/AS:668452805148679@1536382976823/The-rasterscan-technique-used-at-HIT-1-The-energy-of-the-ion-beam-defines-the_Q320.jpg)
At the Heidelberg Ion-Beam Therapy Centre (HIT) more than 2000 cancer patients have been treated with ions using the raster-scanning method since 2009. The synchrotron provides pencil beams in therapy quality for more than 250 energy steps for each ion species allowing to vary the penetration depth and thus to irradiate the tumour slice-by-slice. S...
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... By doing so, the WET limits could already be implemented during the imaging process rather than during post-processing. This dynamic energy painting could also accelerate the image acquisition due to the multi-energy operation currently being implemented at HIT (Schömers et al 2014(Schömers et al , 2017. ...
xD; Objective. Compact ion imaging systems based on thin detectors are a promising prospect for the clinical environment since they are easily integrated into the clinical workflow. Their measurement principle is based on energy deposition instead of the conventionally measured residual energy or range. Therefore, thin detectors are limited in the water-equivalent thickness range they can image with high precision. This article presents our energy painting method, which has been developed to render high precision imaging with thin detectors feasible even for objects with larger, clinically relevant WET ranges.
Approach . A detection system exclusively based on pixelated silicon Timepix detectors was used at the Heidelberg ion-beam therapy center to track single helium ions and measure their energy deposition behind the imaged object. Calibration curves were established for five initial beam energies to relate the measured energy deposition to water-equivalent thickness (WET). They were evaluated regarding their accuracy, precision and temporal stability. Furthermore, a 60 mm × 12 mm region of a wedge phantom was imaged quantitatively exploiting the calibrated energies and five different mono-energetic images. These mono-energetic images were combined in a pixel-by-pixel manner by averaging the WET-data weighted according to their single-ion WET precision (SIWP) and the number of contributing ions.
Main result. A quantitative helium-beam radiograph of the wedge phantom with an average SIWP of (1.82 ± 0.05) % over the entire WET interval from 150 mm to 220 mm was obtained. Compared to the previously used methodology, the SIWP improved by a factor of 2.49 ± 0.16. The relative stopping power value of the wedge derived from the energy-painted image matches the result from range pullback measurements with a relative deviation of only 0.4 %.
Significance. The proposed method overcomes the insufficient precision for wide WET ranges when employing detection systems with thin detectors. Applying this method is an important prerequisite for imaging of patients. Hence, it advances detection systems based on energy deposition measurements towards clinical implementation.
... The particle beam would first be accelerated to the desired energy. After completion of an iso-energy slice irradiation, the remaining particles would be re-accelerated [4,5] or decelerated [3,[6][7][8] to the adjacent energy, allowing the particles to be delivered at different energies in a single synchrotron cycle. ...
... and extract remaining particles to the next following energies given by a patient's treatment plan in a consecutive sequence. Within this scenario the time consuming synchrotron phases of injection, acceleration from injection to extraction energy, the ramping down after one extraction phase, and preparation for a subsequent cycle are avoided several times yet reducing treatment time tremendously [3]. A similar approach, but yet different in detail, has been implemented at the HIMAC facility [4]. ...
At the Heidelberg ion beam therapy center (HIT) cancer patients are treated with the raster-scanning dose delivery method of heavy ion pencil beams. The beams are provided by a synchrotron which allows for a variation of the ion penetration depth by changing the ion beam energy for each synchrotron cycle. In order to change the beam energy within one synchrotron cycle the accelerator and its data supply model within the control system have been extended extensively. In this extended data supply model beam re-acceleration or deceleration between two arbitrary extraction energies is defined. The model defines an additional transition phase, i.e. current and-more generally-set value patterns between extraction and the re-acceleration yet giving the possibility of setting the beam properties suitable for further acceler-ation/deceleration. This includes the dipoles, correctors, quadrupoles, sextupoles, KO-Exciter (spill break), and RF. This allows for the survey and optimisation of the beam properties including possible beam losses of the re-accelerated, transversally blown up beam for arbitrary energy levels.
... Estimations regarding the time reduction have already been presented in [3]. The benefit and requirements have now been analysed again in detail using the data of more than 1000 patients treated at HIT in a period of 18 months [4]. ...
... This device permits a relative measurement of ionisation events in two ionisation chambers as a function of depth in water. Figure 5 clearly shows two different depth dose curves 3 . In one series of multi energy carbon spills the depth dose profile has been measured in the first part of the spill (blue circles). ...
In the active raster scanning method performed at HIT since 2009, tumours are irradiated slice-by-slice by changing the extraction energy. The synchrotron provides a library of 255 different extraction energy levels per ion type, according to the aimed penetration depth. So far, a new synchrotron cycle is started for each iso energy slice resulting in a non-optimal duty cycle. In order to reduce treatment time and to increase the number of patients treated per day, synchrotron cycles with several extraction flattops on different energy levels are planned. After completing one iso energy slice, remaining particles will be re-accelerated to the adjacent level. As a first test a new data supply model generating patterns for power supplies and RF devices with two different extraction flattops has been implemented recently. The properties of the re-accelerated beam are now under detailed examination. The re-accelerated beam was successfully extracted and guided to the experimental area. Ionisa-tion chambers along the beam line clearly show two spills on two different extraction flattops. The desired change of beam energy has been verified by range measurements in a water column.
