Stationary molecules in well-defined internal states are of broad interest for physics and chemistry. In physics, this includes metrology, quantum computing and many-body quantum mechanics, whereas ...in chemistry, state-prepared molecular targets are of interest for uni-molecular reactions with coherent light fields, for quantum-state-selected bi-molecular reactions and for astrochemistry. Here, we demonstrate rotational ground-state cooling of vibrationally and translationally cold MgH+ ions, using a laser-cooling scheme based on excitation of a single rovibrational transition. A nearly 15-fold increase in the rotational ground-state population of the X 1Σ+ electronic ground-state potential has been obtained. The resulting ground-state population of 36.7±1.2% is equivalent to that of a thermal distribution at about 20 K. The obtained cooling results imply that cold molecular-ion experiments can now be carried out at cryogenic temperatures in room-temperature set-ups.
Most solid-state detectors, including 3D dosimeters, show lower signal in the Bragg peak than expected, a process termed quenching. The purpose of this study was to investigate how variation in ...chemical composition of a recently developed radiochromic, silicone-based 3D dosimeter influences the observed quenching in proton beams. The dependency of dose response on linear energy transfer, as calculated through Monte Carlo simulations of the dosimeter, was investigated in 60 MeV proton beams. We found that the amount of quenching varied with the chemical composition: peak-to-plateau ratios (1 cm into the plateau) ranged from 2.2 to 3.4, compared to 4.3 using an ionization chamber. The dose response, and thereby the quenching, was predominantly influenced by the curing agent concentration, which determined the dosimeter's deformation properties. The dose response was found to be linear at all depths. All chemical compositions of the dosimeter showed dose-rate dependency; however this was not dependent on the linear energy transfer. Track-structure theory was used to explain the observed quenching effects. In conclusion, this study shows that the silicone-based dosimeter has potential for use in measuring 3D-dose-distributions from proton beams.
A new deformable polydimethylsiloxane (PDMS) based dosimeter is proposed that can be cast in an anthropomorphic shape and that can be used for 3D radiation dosimetry of deformable targets. The new ...material has additional favorable characteristics as it is tissue equivalent for high-energy photons, easy to make and is non-toxic. In combination with dual wavelength optical scanning, it is a powerful dosimeter for dose verification of image gated or organ tracked radiotherapy with moving and deforming targets.
Abstract
Background. The increasing complexity of radiotherapy (RT) has motivated research into three-dimensional (3D) dosimetry. In this study we investigate the use of 3D dosimetry with ...polymerizing gels and optical computed tomography (optical CT) as a verification tool for complex RT: dose painting and target tracking. Materials and Methods. For the dose painting studies, two dosimeters were irradiated with a seven-field intensity modulated radiotherapy (IMRT) plan with and without dose prescription based on a hypoxia image dataset of a head and neck patient. In the tracking experiments, two dosimeters were irradiated with a volumetric modulated arc therapy (VMAT) plan with and without clinically measured prostate motion and a third with both motion and target tracking. To assess the performance, 3D gamma analyses were performed between measured and calculated stationary dose distributions. Results. Gamma pass-rates of 95.3% and 97.3% were achieved for the standard and dose-painted IMRT plans. Gamma pass-rates of 91.4% and 54.4% were obtained for the stationary and moving dosimeter, respectively, while tracking increased the pass-rate for the moving dosimeter to 90.4%. Conclusions. This study has shown that the 3D dosimetry system can reproduce and thus verify complex dose distributions, also when influenced by motion.
Purpose:
Both temporal and thermal dependencies of the dose response have been observed in radiochromic dosimeters. As these dependencies may be influenced by the dose level, the present study ...investigates the temperature dependence during irradiation and the temporal change of the optical response following irradiation of radiochromic dosimeters at a range of doses.
Methods:
Cuvette samples of the PRESAGE™ radiochromic dosimeter were irradiated within a dose range of 0–10 Gy at irradiation temperatures within 5–35 °C and postirradiation storage within 6–30 °C. The optical response due to irradiation was measured using a standard spectrophotometer and the data were analyzed in terms of thermal and temporal change.
Results:
The initial dose response was linear over the applied dose range independent of irradiation temperature. However, the optical response to a specific dose increased exponentially with irradiation temperature corresponding to an activation energy of 0.114 ± 0.007 eV. The temporal change in dose response after irradiation consisted of an offset, an auto-oxidation rate with activation energy 0.84 ± 0.03 eV, and an initial exponential increase in optical response (1.6 ± 0.2 eV) followed by an exponential decrease in optical response (0.98 ± 0.08 eV). These contributions depended on both storage temperature and the dose given, leading to a nonlinear dose response with time at low storage temperatures and a high auto-oxidation rate at high storage temperatures.
Conclusions:
Thermal equilibration is important to the radiochromic dosimeter investigated due to an exponential change in dose response with irradiation temperature and a considerable postirradiation temporal change in response. For the dosimeter version investigated in this study, a compromise in storage temperature has to be made between increasing the nonlinearity of the dose response with time and inducing a high auto-oxidation rate.
Purpose:
The dose response of radiochromic dosimeters is based on radiation-induced chemical reactions and is thus likely to be thermally influenced. In this study we have therefore investigated the ...temperature dependence of the dose response for such dosimeters, regarding both irradiation and storage conditions.
Methods:
Dosimeter samples in cuvettes were irradiated to 5 Gy. The temperature for the different cuvettes during irradiation and post-irradiation storage was varied in the range of 3–30 °C in order to quantify the temperature dependence of the dosimeter response. The optical properties of the dosimeter samples were measured using a spectrophotometer before irradiation as well as at several times after irradiation to quantify the temporal variation of dose response (expressed as the optical density change induced by irradiation) as a function of storage temperature.
Results:
The measurements show considerable temperature dependencies of dose response both during irradiation and storage. Fit to an Arrhenius equation revealed an activation energy of 1.4 ± 0.2 eV for the variation in irradiation temperature, indicating a contribution from a thermally activated process. Variation in dose response at different storage temperatures showed an exponential increase with time followed by a decrease in optical density. Exponential Arrhenius fits to rate constants gave activation energies of 1.7 ± 0.2 eV for the increase in dose response and 2.3 ± 0.5 eV for the subsequent decrease, in this case dominated by thermally activated processes.
Conclusions:
Due to the exponential dependencies, stabilization of the dosimeter during irradiation at low temperatures (e.g., 5 °C) is preferable in clinical use to optimize the accuracy of the dose response. In addition, a low storage temperature is recommended in order to minimize the post-irradiation temporal change in dose response and thereby increase the post-irradiation stability of the dosimeter. The measurements in this study show that if the observed temperature and temporal dependencies are not considered, this could potentially deteriorate the accuracy of the dosimeter.
Abstract 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.
Abstract
Background. The on-going development of both intensity-modulated radiotherapy (IMRT), including the more recent intensity-modulated arc therapy, as well as particle beam therapy, has created ...a clear need for accurate verification of dose distributions in three dimensions (3D). Presage™ is a new 3D dosimetry material that exhibits a radiochromic response when exposed to ionizing radiation. In this study we have 1) developed an improved optical set-up for measurements of changes in OD of Presage™ point dosimeters, 2) investigated the dose response of Presage™ for photons and carbon ions in the therapy range, 3) investigated the dose response of Presage™ for photons in the kGy range and 4) investigated the fading (i.e. bleaching) of Presage™ postirradiation. Materials and methods. Presage™ was examined in 1 × 1 × 4.5 cm3 optical cuvettes; a cuvette holder assured accurate repositioning, and the optical setup included a reference detector to take into account laser intensity fluctuations. The cuvettes were measured pre- and postirradiation for a two week period. Results. A linear response was observed between dose and optical response between 0 Gy and 100 Gy for γ-radiation from Co-60 and for carbon ions (both plateau and SOBP) from 0 to 20 Gy. The dosimeter was found to have a saturation dose of approximately 100 Gy for photons. A linear energy transfer (LET) effect was not observed in the dose response of different LET radiation. The postirradiation change in optical fading was found to be 0.5% ΔOD/day. Conclusions. Our study shows that Presage™ remains a dosimeter of interest for radiation therapy with other particles as well as photons in the therapy dose range.
The aim in radiotherapy treatment planning is to have sufficient target coverage and as low a dose to the Organs at Risk (OARs) as possible, adhering to the relevant guidelines. A high and consistent ...radiotherapy plan quality is vital when treatment plans are used as the foundation for patient selection in clinical trials. Proton therapy, being a substantially newer treatment modality than conventional photon therapy, is at risk of having a steeper learning curve in treatment planning. This inequality is important to investigate in a clinical study comparing the two, as this could influence the trial results.
This study aims to evaluate the development of radiotherapy treatment plan quality for head and neck cancer patients receiving photon and proton therapy over time in the context of the DAHANCA 35 trial.
From May 2019 to June 2023,189 patients were included in the ongoing DAHANCA 35 trial, with 63 patients in the pilot phase and 126 in the subsequent randomisation phase. In the pilot phase, all included patients were offered proton treatment, and in the randomisation phase, patients were randomised 1:2 (photon:proton). Patients were first seen at a local treatment centre, where a photon and comparative proton plan were prepared. If patients were offered proton treatment, a new clinical proton plan was made at the proton treatment centre and subsequently used for treatment. This study analysed 189 photon plans, 189 comparative proton plans, and 140 clinical proton plans.
The treatment plans were prepared conforming to the DAHANCA guidelines 1 to ensure the clinical relevance of all treatment plans
The plan quality was assessed separately for photon plans, comparative proton plans, and clinical proton plans in three time intervals.
The mean dose was investigated individually for 13 OARs relevant for head and neck cancer: oesophagus, glottic larynx, supraglottic larynx, mandible, extended oral cavity, left and right parotid glands, upper-, middle-, and lower pharyngeal constrictor muscles, left and right submandibular glands, and thyroid gland.
Furthermore, treatment plan quality was analysed using a new metric called Normalised Toxicity Index (NTI), calculated as a normalised average of the mean dose to the OARs compared to the threshold mean dose recommended by the DAHANCA guidelines.
An NTI > 1 indicated that the OARs, on average, received a dose higher than the recommended thresholds, and an NTI < 1 indicated that the OARs received a dose below the thresholds. Hence, a lower NTI indicated better plan quality concerning OAR doses.
The Kruskal-Wallis test was used to investigate a potential difference in the intervals for mean dose and NTI for each treatment type. The significance level was Bonferroni adjusted to account for multiple testing.
The three time intervals were defined with 63 patients in the pilot phase constituting one interval (Pilot phase), the subsequent 64 patients from the randomisation phase in the next interval (Randomisation 1), and the remaining 62 patients from the randomisation phase in the third interval (Randomisation 2). The periods were 22 months for the Pilot phase, 19 months for Randomisation 1, and 14 months for Randomisation 2.
Across the 13 OARs, the mean dose to individual OARs did not show a general time-dependent change, except for the right parotid gland in the clinical proton plans. Figure 1 shows a box plot with samples overlaid for the mean dose to the extended oral cavity as an example of the OARs. Display omitted
The NTI was not significantly different for the photon plans, comparative proton plans, and clinical proton plans in the three consecutive intervals, as shown in Figure 2. The median NTI for the clinical proton plans was 0.88 (interquartile range 0.70,1.00) for the Pilot phase, 0.83 0.75,0.89 for Randomization 1, and 0.79 0.67,0.98 for Randomization 2. The plan quality of the clinical proton plans appears stable from this new NTI metric. Display omitted
The analyses conducted in this study did not show a general time-dependent change in plan quality in any of the three types of plans. This could be caused by the nationally developed proton treatment planning template.
A stable treatment plan quality can help ensure a consistent selection for clinical trials, thus providing transparency for analysis of the outcome of the trials. The plan quality will continuously be followed to ensure consistency.
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