Florian-Emanuel Brack, Florian Kroll, Lennart Gaus, Constantin Bernert, Elke Beyreuther, Thomas Cowan, Leonhard Karsch, Stephan Kraft, Elisabeth Lessmann, Josefine Metzkes-Ng, Jörg Pawelke, Martin Rehwald, Marvin Reimold, Hans-Peter Schlenvoigt, Ulrich Schramm, Manfred Sobiella, Marvin Umlandt, Tim Ziegler, Karl Zeil
Laser-driven proton pulse provide unique properties in terms of pulse structure (ns) and instantaneous dose rate (10^9 Gy/s) but - inherently broadband and highly divergent - pose a challenge to established beamline concepts on the path to application-adapted irradiation field formation, particularly for three-dimensional cases. We present the successful implementation and characterisation of a highly efficient and tuneable dual pulsed solenoid beamline at the Draco PW facility[1] to generate volumetric dose distribution tailored to specific applications[2].
The vast experimental scope and already successfully performed studies range from systematic volumetric in-vivo tumour irradiations in a dedicated mouse model (with a stable mean dose delivery of ±10 % and a spatial dose homogeneity of ±5 % over a cylindrical volume of 5 mm diameter and height) to high-dose-rate irradiations in the FLASH regime (using proton peak dose rates of up to 10^9 Gy/s with about 20 Gy/shot homogeneously over a cylindrical sample volume of 4.5 mm diameter and 3 mm height) as well as particle diagnostics commissioning (with a multitude of spatial and spectral dose distributions).
The beamline setup is complemented by a complex beam monitoring and dosimetry detector suite adapted to the ultra-high dose rate pulses and is in its unique synergy and redundancy capable of %-level precision dose delivery to samples as required for systematic irradiation studies. In addition to established radiochromic film dosimetry, the detector suite includes saturation-corrected (transmission) ionisation chambers [3] as well as screen and bulk scintillator setups, partly with tomographic reconstruction capabilities for 3D dose distribution retrieval. Moreover, non-invasive, single-shot-capable online time-of-flight-based spectral characterisation of filtered proton pulses has proven a powerful tool for beam monitoring as well as dosimetric purposes.
In this presentation the complex and versatile dose delivery system of laser-driven protons at the Draco PW using pulsed solenoids will be discussed. Its characterisation, technological development and improvement as well as the dosimetry suite as a vital part of the precise dose delivery will be addressed, while the presentation by U. Schramm covers recent experimental activities in detail.
[1] T. Ziegler, et al., Proton beam quality enhancement by spectral phase control of a PW-class laser system, https://arxiv.org/abs/2007.11499 (2020)
[2] Brack, et al., Spectral and spatial shaping of laser-driven proton beams using a pulsed high-field magnet beamline, SciRep, 10:9118, (2020)
[3] Gotz M, et al., A new model for volume recombination in plane‐parallel chambers in pulsed fields of high dose‐per‐pulse. Phys Med Biol., 62: 8634, (2017)
After the rediscovery of the normal tissue sparing effect of high dose rate radiation, i.e. the so-called FLASH effect, by Favaudon et al. in 2014, research activities on this topic have been revived and are flourishing ever since. Yet, the exact biological mechanism as well as the required boundary conditions and radiation qualities to reach said sparing remain mostly unclear.
We present a laser-based irradiation platform at the Draco PW facility that enables systematic studies into the FLASH regime using proton peak dose rates of up to 10^9 Gy/s. Besides the PW class laser acceleration source, a key component is a pulsed high-field beamline to transport and shape the laser driven proton bunches spectrally and spatially in order to generate homogeneous dose distributions tailored to match the irradiation sample.
Making use of the diverse capabilities of the laser driven irradiation platform a pilot experiment of highest complexity has been conducted – a systematic in-vivo tumor irradiation in a specifically developed mouse model.
A plethora of online particle diagnostics, including Time-of-Flight, bulk scintillators and screens as well as ionization chambers, in conjunction with diagnostics for retrospective absolute dosimetry (radiochromic films) allowed for an unprecedented level of precision in mean dose delivery (±10 %) and dose homogeneity (±5 %) for the challenging beam qualities of a laser accelerator. The tailored detector suite is complemented by predictive simulations.
The talk addresses how our interdisciplinary team overcame all hurdles from animal model development, over enhancing the laser and laser acceleration stability, to dose delivery and online dose monitoring. Results on radiation induced tumor growth delay by laser driven as well as conventionally accelerated proton beams are critically discussed.
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