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IC3DDose 2024 – 13^th International Conference on 3D Dosimetry

The 13^th International Conference on 3D Dosimetry was held in Aarhus, Denmark, on 17-19 June 2024.

The IC3DDose conference serves as a meeting point between scientists developing new dosimeter systems and readout methods and researchers with a clinical background and motivation. Participants included both new and more experienced researchers in the field as well as company representatives.

A total of 66 participants from 17 countries met for three days at the Aarhus University campus in order to present and discuss the latest developments in advanced radiation dosimetry, predominately with applications towards three-dimensional dose measurements. One opening address, 12 invited talks, 20 contributed talks, and 10 poster presentations were given at the conference. In addition, the optimal ways to bring the scientific results into the radiotherapy clinics, for the benefit of patients, were discussed at a panel debate. All activities took place in a single track, and the participants had good possibilities to interact during designated poster sessions, meet-the-speakers-of-the-day sessions, and breaks. The setting provided a homely campus atmosphere that inspired the participants to engage in numerous scientific discussions.

The conference also included a welcome reception at Danish Centre for Particle Therapy (DCPT), where conference participants were invited on a tour behind the scenes at the proton facility.

The 13^th edition of the IC3Ddose conference contributed to the continuous identification of new research areas of relevance for the overarching theme of three-dimensional dose measurements. It brought together scientists from the more established chemically based 3D dosimeters with scientists developing approaches based on physical processes, such as scintillation, optically stimulated luminescence, Cherenkov radiation, and charge-based technologies. This mix appeared to be a source of mutual inspiration and cross-fertilization of both scientific ideas and techniques. Several of the developments presented at the conference showed potential to become useful for the treatment verification of future cancer patients.

The associated 21 papers presented in these proceedings add to an already extensive collection of 118 review and 612 proffered papers in 10 previous volumes of the Journal of Physics Conference Series from the past conferences.

List of International Scientific Committee, Local Organizing Committee and Editors of the proceedings are availabel in this pdf.

All papers published in this volume have been reviewed through processes administered by the Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Contributors, who wished to present at the conference (oral or poster), had to submit an extended abstract (max. four pages) via a "Call for Papers" in the Morressier Proceedings Management System, which resulted in 33 submissions. These were all found acceptable for presentation by the international scientific committee of the conference.

The contributors had the option to publish their extended abstracts in the conference proceedings, and 21 out of the 33 contributors chose this option. Invited speakers were also given an opportunity to publish an extended abstract in the conference proceedings, and one speaker chose this option. In total, 22 manuscripts were thus intended for publication and sent for review.

Type of peer review: Single Anonymous

Conference submission management system: Morressier

Number of submissions received: 34

Number of submissions sent for review: 22

Number of submissions accepted: 21

Acceptance Rate (Submissions Accepted / Submissions intended for publication × 100): 95

Average number of reviews per paper: 4

Total number of reviewers involved: 18

Contact person for queries:

Name: Brian Julsgaard

E-mail: brianj@phys.au.dk

Affiliation: Aarhus University

3D dosimeters are mainly manufactured as single-phase chemical compositions in a container. In most cases, they imitate a single soft tissue, such as muscle or the brain. Research on dosimeters imitating lungs and bones is very rare. In turn, in this work we report the first experiments aimed at producing multiphase 3D dosimeters imitating different tissues in one container.

Accurate surface-dose measurements in proton therapy are challenging and often of poor spatial resolution for most dosimeter types. However, optically stimulated luminescence (OSL) based 2D dosimeters could provide the required spatial dose resolution. The aim of this study was to investigate the dosimetric precision and energy dependence of an in-house made reusable dosimeter composed of a silicone-film containing OSL-active nanoparticles. The dosimeter was irradiated with a clinical proton therapy field and the readout dose was compared to the results from a commercial dosimeter. The pixelwise noise-to-signal ratio for the OSL dosimeter remained below 2% for doses above 1 Gy, and the energy dependence was negligible in the investigated energy range.

As Cherenkov emissions are related to dose, they can be used as signal for dosimetric purposes using polarized imaging. However, when using this method, angular corrections must be applied because of Cherenkov anisotropy. Several Cherenkov light source-to-camera distances were tested to characterize its impact on the deviations from reference values of the calculated dose distributions. Average relative differences ranging from −1.6% to −11% between Cherenkov-based results and scintillation results were extracted. It is observed that an increase in Cherenkov light source-to-camera distance decreases the difference between the Cherenkov optical signal and the dose. This reduces the importance of angular corrections at higher distances (4 m and beyond).

The dose response of materials used in radiochromic three-dimensional (3D) dosimeters is often characterised via spectrophotometry of small cuvette samples as it is less time-consuming and cheaper. However, spatially-resolved dose measurements for clinical purposes are obtained using 3D optical computed tomography (CT). Hence, the link between the method of characterisation and the method for extracting 3D dose information must be established. The aim of this study was to investigate if spectrophotometry-based dose-response characterisation using cuvette-sized samples is valid for calibration of 3D optical CT readout systems using a silicone-based radiochromic dosimeter. Additionally, the uniformity of 3D optical CT dose-response readout of larger samples was investigated. We found the dose response of cuvette-sized samples read out by spectrophotometry to agree with the averaged dose response across cuvette-sized samples read out by optical CT and with the response near the edges of larger samples scanned using the same apparatus. Thus, cuvette-based dose-response spectrophotometry can be used to calibrate 3D optical CT readout using silicone-based radiochromic dosimeters. However, caution should be taken when considering larger samples as they exhibit a gradual radial increase in dose response from the centre and outwards.

This work presents the first use of a cable robot for 3D dosimetry. Its design was optimized to operate in water and offer five degrees of freedom. It was equipped with a plastic scintillation detector. The cables and the end effector were made of plastic, thus making all components inside the phantom water equivalent. Feasibility and reproducibility was demonstrated using a 6MV beam. The cable robot prototype had a usable workspace of 40 cm in each direction and could rotate over 90 degrees in both the polar and azimuthal directions. It was tested at speeds of up to 120.8 mm/s. Position precision was within 2.5 mm for translation and within 1.1 mm for rotations about a fixed point. This new robotic dosimetry system is more versatile and can address limitations of current water phantoms that are constrained to only 3 translation axes.

The paper concerns a bone-imitating dosimeter called BoneGel (PAGAT2–Pluronic F–127 with hydroxyapatite). The addition of inorganic salt (MgCl₂) to the composition increased the dose sensitivity of the dosimeter.

This work presents a new elastic radiochromic gel containing a radiation-sensitive nitro blue tetrazolium chloride (NBT) embedded in a poly(vinyl alcohol) (PVA) matrix, which can simultaneously function as a bolus and a dosimeter in radiotherapy.

This work presents a 2D Fricke dosimeter with xylenol orange (XO), gelatine matrix and addition of sorbitol. The dosimeter was irradiated with various monitor units ranging from 500 to 10000 MU (3.6-72 Gy). The addition of sorbitol significantly reduced the diffusion coefficient of Fe³⁺ ions and improved the mechanical properties of the gel, while the chemical stability of the dosimeter decreased.

As a method for three-dimensional quality assurance in boron neutron capture therapy (BNCT), micelle gel dosimeters are focused on. We are investigating dose-component discrimination method by using multiple gel dosimeters which have each different radiation quality specificity. In this study, the characteristics of each gel dosimeter for neutrons and gamma-rays were evaluated, and a dose-component discrimination method was suggested.

Despite the rapid development of new technologies, 4D dose assessment related to the breathing movement of target organs during radiotherapy treatment is still a challenge. This study aimed to investigate the feasibility of polymer gel dosimeters to assess 4D dose distribution accuracy in VMAT radiotherapy treatment under dynamic conditions and to compare assessment results with the data obtained using a cylindrical water-equivalent phantom with a three-dimensional diode array (ArcCheck). For this purpose, several homemade polymer gels were filled in cylindrical containers and placed within the ArcCheck phantom. The entire system was mounted on rotating wheels and periodically moved by a connected robotic platform during irradiation. Generally, good agreement was found between measurement results of the 4D dose distribution obtained in the bulk of volume using homemade polymer gel dosimeters and diode detector system, indicating the potential to address the remaining small errors in further experiments. The latter implies the applicability of polymer gel dosimeters for the validation of high-dose stereotactic treatment plans under realistic 4D dose distribution conditions.

A comprehensive 3D dosimetry system consisting of the ClearView^™ 3D dosimeter, VistaScan^™ optical CT scanner, and VistaAce^™ analysis software is commercially available and has the potential to be a strong verification tool with widespread applications. The clinical utility of this system (termed ClearView/Vista) has yet to be determined, and this work presents our first investigation. Clinical utility was evaluated using real patients' treatment plans: spine, head and neck, Single Isocenter Multi-Targets SRS (SIMT-SRS), and prostate cases. Independent validation was performed with a Monte Carlo-based dose calculation algorithm that was previously commissioned for clinical independent dose calculation. The analysis included line profile comparison (1D), isodose line comparison (2D), and global gamma analysis (3D). Results indicated a remarkable agreement between ClearView/Vista, the treatment planning system, and Monte Carlo, where gamma pass rates for all cases exceeded 94% even while using 2%2mm and a dose threshold of 10%. The ClearView/Vista 3D dosimetry system showed clinically acceptable accuracy and robust measurement and analysis in clinical settings.

To meet the needs of modelling small-sized detectors of orthovoltage X-rays, for spatially fractionated radiotherapy, we propose a model to determine responses of the detectors in cases of highly heterogeneous cavity. The model was applied to a detector whose cavity features a sparse high-Z perovskite scintillation layer embedded in an epoxy resin. Irradiations were carried out using the Small Animal Radiation Research Platform. Local photon and electron spectra were computed by the SpekPy toolbox and Penelope Monte Carlo simulations, respectively. The detector model considers that X-ray photons mainly interact with medium surrounding the scintillation layer, and that the output of the detector mainly results from secondary electrons in this layer. Results from model computations are compared with measurement data, showing differences less than 16% for beam energies in the 60 kVp −220 kVp range.

Scintillation imaging has been shown to provide high spatio-temporal surface dose information for delivery verification of ultra-high dose rate (UHDR) beams. To obtain higher dose rates, modified clinical machines are often utilized, requiring extensive re-characterization and treatment validation. The goal of this work was to demonstrate the utility of 1.) projecting surface images to depth and 2.) quinine-doped water tank imaging for 3D beam verification across different UHDR treatment modalities.

A dose enhancement in tumors can in principle be achieved using an enrichment of elements with high atomic number ("High-Z therapy"). The proof of dose enhancement at low non-toxic concentrations remains difficult with standard dosimeters due to the small distance of secondary electrons of X-ray photon energies. We investigated within an exploratory research approach the dose enhancement in tissue equivalent environment using MRI analysis of polymer gel dosimeters doped with molecules containing high-Z elements: bismuth, silver iodide and iopromide, a radio-diagnostic contrast agent for X-ray imaging, in photon fields of low (200 kV X-ray) and high energy (6 MV) and in an electron field (6 MeV). An enhancement of the dose response up to a relative dose enhancement factor rDE_exp≌1.4 was observed for low concentrations (w/w=0.006) of iopromide, already approved for vascular angiography with X-rays. Experimental limitations and challenging interpretations are outlined.

The application of Cherenkov radiation in radiation therapy dosimetry has been limited by the anisotropic nature of the signal. Recently, polarization imaging was investigated as a method to correct Cherenkov anisotropy and allow precise dose measurements directly in a water tank. The aim of this study is to present polarization imaging as method for the measurement of ultra-high dose rate (UHDR) intra-operative electron beams. In this new approach, the polarized Cherenkov signal was isolated and utilized as a surrogate to evaluate the quality and consistency of both UHDR and conventional electron beams. Percent depth Cherenkov signal were measured for different energies, field sizes and dose rates. The results demonstrate high linearity (R² > 0.99) of the Cherenkov signal with the number of pulses and pulse width. The wide dynamic range of the device enabled measurement for both conventional and UHDR radiation beams making it a promising candidate for real-time quality assurance devices.

Very High Energy Electrons (VHEE) that can theoretically treat deep-seated tumours and be delivered at ultra-high dose rates (UHDR) could be the solution to translate FLASH radiotherapy into the clinic. Standard dosimeters have limited application in those extreme conditions, but dose-rate independent and fast-response plastic scintillation detectors (PSDs) are a potential alternative to overcome this. In this work, response of a 4-channel PSD to the 200 MeV VHEE UHDR beam delivered with doses and dose rates in pulse up to 90 Gy and 4.6 × 10⁹ Gy/s, respectively, at the CLEAR facility in CERN was characterized, using the Hyperscint RP200 platform. Scintillation light linearity with dose was observed for three scintillators from ∼5-50 Gy, while clear eiber output was linear up to 90 Gy. While linearity on this dose range was conserved even after radiation damage by exposure to 37.2 kGy total accumulated dose, light output signieicantly decreased. This work proves the potential of plastic scintillators for real-time dosimetry of UHDR VHEE beams.

Fiber coupled luminescence detectors based on organic plastic scintillators or inorganic materials such as Al₂O₃:C are suitable for dosimetry in strong magnetic fields as found in MR-linacs. The main finding of this work was that field-output factor measurements at the maximum dose point are less variable than if measured at the central beam axis (CAX). In contrast to plastic scintillators, Al₂O₃:C was found to have a yield of radioluminescence per dose that (within uncertainty) is independent of the magnetic field strength.

The occurrence of significant implant shifts between CT simulation planning and first fraction delivery is a frequent challenge for HDR prostate brachytherapy treatment. Here, we present evidence supporting the viability of a first-order adaptation strategy as a viable alternative to the conventional practice of re-scanning and re-planning. Our findings underscore the potential of this approach to enhance workflow efficiency in HDR prostate brachytherapy.

Fiducial markers are necessary for some tumor sites to ensure safe and accurate delivery of radiotherapy including proton therapy (PT). However, the high metal content of the markers may lead to shadowing of the proton beam. The aim of this study was to investigate the dose degradations around three fiducial marker types implanted in different configurations into a 3D dosimeter. The dosimeters were irradiated with a clinically relevant prostate cancer PT plan. Gamma comparisons (2%-2mm) between the control (no marker) and marker dosimeters resulted in a pass rate of 97%, and no significant differences were observed in the isodoses, indicating that markers did not affect dose coverage to the target. However, due to optical artifacts, the 3D dosimeter was unable to resolve the regions within a few millimeters from the markers.

The amorphous-silicon based design of electronic portal imaging device (a-Si EPID) is commonly available on medical linear accelerators, and thus presents enormous potential as a radiotherapy dosimetry tool. One of the recognized technical challenges with using the device is it's lack of water equivalency when measuring dose. In this work a radiation transport model, previously used to predict dose to the phosphor of an a-Si EPID, was modified to predict dose to a water-equivalent planar detector as well as to a 3D water-tank. Initial testing was performed for a 6MV beam using a variety of simple square fields and clinically relevant intensity modulated fields. Using a 2% criterion, the predicted versus measured image comparisons had pass rates between 95.9-98.2% for the square fields, and 89.2-96.3% for the modulated fields. The predicted 3D dose distribution showed a percentage depth dose agreement within 1% of that measured in a water tank (beyond 5 mm depth). These initial validation results provide confidence that the radiation transport model could be used for water-equivalent dosimetric applications in clinical radiotherapy.

In this work, we developed a three-dimensional (3D) scintillation system, whose fast response and high sensitivity allow the measurement of pencil beam (PB) characteristics (position, energy and intensity in terms of monitor units - MU) for pencil beam scanning proton therapy. The system consists of a 10 × 10 × 10 cm³ scintillator cube that produces visible light when irradiated with PBs. A high-speed camera records the scintillation distribution and a mirror positioned at 45° to the cube allows visualization of two orthogonal faces of the cube. The measurements demonstrated the ability of our system to measure beam characteristics for intensities as low as 2·10⁻³ MU in a single irradiation. Standard deviations of less than 300 μm were found for the X and Y PB positions, of approximately 150 keV for energy and of less than 5·10⁻³ MU for intensity. These measurements were then successfully used to verify the compliance of the PBs delivery with the treatment plan, thus making our system a fast and efficient verification tool.