Marzena Rydygier

Technical Note: Improving proton stopping power ratio determination for a deformable silicone‐based 3D dosimeter using dual energy CT

PURPOSE The aim of this study was to investigate whether the stopping power ratio (SPR) of a deformable, silicone-based 3D dosimeter could be determined more accurately using dual energy (DE) CT compared to using conventional methods based on single energy (SE) CT. The use of SECT combined with the stoichiometric calibration method was therefore compared to DECT-based determination. METHODS The SPR of the dosimeter was estimated based on its Hounsfield units (HUs) in both a SECT image and a DECT image set. The stoichiometric calibration method was used for converting the HU in the SECT image to a SPR value for the dosimeter while two published SPR calibration methods for dual energy were applied on the DECT images. Finally, the SPR of the dosimeter was measured in a 60 MeV proton by quantifying the range difference with and without the dosimeter in the beam path. RESULTS The SPR determined from SECT and the stoichiometric method was 1.10, compared to 1.01 with both DECT calibration methods. The measured SPR for the dosimeter material was 0.97. CONCLUSIONS The SPR of the dosimeter was overestimated by 13% using the stoichiometric method and by 3% when using DECT. If the stoichiometric method should be applied for the dosimeter, the HU of the dosimeter must be manually changed in the treatment planning system in order to give a correct SPR estimate. Using a wrong SPR value will cause differences between the calculated and the delivered treatment plans.

Response of human lymphocytes to proton radiation of 60 MeV compared to 250 kV X-rays by the cytokinesis-block micronucleus assay

Particle radiotherapy such as protons provides a new promising treatment modality to cancer. However, studies on its efficacy and risks are relatively sparse. Using the cytokinesis-blocked micronucleus assay, we characterized response of human peripheral blood lymphocytes, obtained from health donors irradiated in vitro in the dose range: 0-4. 0 Gy, to therapeutic proton radiation of 60 MeV from AIC-144 isochronous cyclotron, by studying nuclear division index and DNA damage and compared them with X-rays. Peripheral blood lymphocytes show decreased ability to proliferate with increasing radiation doses for both radiation types, however, in contrast to X-rays, irradiation with protons resulted in a higher proliferation index at lower doses of 0.75 and 1.0 Gy. Protons are more effective in producing MN at doses above 1.75 Gy compared to X-rays. Dose-response curves for micronucleus incidence can be best described by a cubic model for protons, while for X-rays the response was linear. The differences in the energy spectrum and intracellular distribution of energy between radiation types are also apparent at the intracellular distribution of cytogenetic damage as seen by the distribution of various numbers of micronuclei in binucleated cells. Our studies, although preliminary, further contribute to the understanding of the mechanistic differences in the response of HPBL in terms of cellular proliferation and cytogenetic damage induced by protons and X-rays as well as intra-cellular distribution of energy and thus radiobiological effectiveness.

RADIOTHERAPY PROTON BEAM PROFILOMETRY WITH scCVD DIAMOND DETECTOR IN SINGLE PARTICLE MODE

Proton radiotherapy requires precise knowledge of the volumetric dose distribution. In proton beam delivery systems, based on narrow pencil beams, a contribution from small doses in low-intensity regions, consisting mainly of scattered protons, may have not negligible influence on total dose delivered to patient. Insufficient information about dose profile can cause underestimation of dose and potential delivery of inflated dose during hadrontherapy treatment. Presented work aims to verify applicability of diamond detectors, produced by Chemical Vapor Deposition method, for therapeutic proton beam profilometry at large fields. This requires the capability of measuring the core of the beam intensity profile (wide dynamic range) as well as its lateral spread (very high sensitivity) with a single device.

Chemically tuned linear energy transfer dependent quenching in a deformable, radiochromic 3D dosimeter

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 dosimeters 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.

PO-0794: First proton irradiation experiments with a deformable radiochromic 3D dosimeter

S373 ________________________________________________________________________________ Iopromide and gadolinium sulfate solutions were introduced into standard Fricke dosimeter solution for final concentrations of iodine from 2.5 mg I/ml to 50 mg I/ml and gadolinium from 5 mg Gd/ml to 10 mg Gd/ml. Detection of iron (III) ions was performed with spectrophotometer Varian Cary 50. For measurement of iron (III) ions concentration in the presence of iopromide ammonium tiocianate (Panreac) was used as an indicator because optical spectrum of iopromide interfere with optical spectrum of iron (III) ions. Irradiation of Fricke solutions was performed with 110 kVp Xrays through 3.5 mm Al filter at 0.7 Gy/min dose rate.

Application of the micronucleus assay performed by different scorers in case of large-scale radiation accidents

Abstract Mass casualty scenarios of radiation exposure require high throughput biological dosimetry techniques for population triage, in order to rapidly identify individuals, who require clinical treatment. Accurate dose estimates can be made by biological dosimetry, to predict the acute radiation syndrome (ARS) within days after a radiation accident or a malicious act involving radiation. Timely information on dose is important for the medical management of acutely irradiated persons [1]. The aim of the study was to evaluate the usefulness of the micronuclei (MNi) scoring procedure in an experimental mode, where 500 binucleated cells were analyzed in different exposure dose ranges. Whole-body exposure was simulated in an in vitro experiment by irradiating whole blood collected from one healthy donor with 60 MeV protons and 250 keV X-rays, in the dose range of 0.3-4.0 Gy. For achieving meaningful results, sample scoring was performed by three independent persons, who followed guidelines described in detail by Fenech et al. [2, 3]. Compared results revealed no significant differences between scorers, which has important meaning in reducing the analysis time. Moreover, presented data based on 500 cells distribution, show that there are significant differences between MNi yields after 1.0 Gy exposure of blood for both protons and X-rays, implicating this experimental mode as appropriate for the distinction between high and low dose-exposed individuals, which allows early classification of exposed victims into clinically relevant subgroups.

Application of alanine dosimetry in dose assessment for ocular melanoma patients undergoing proton radiotherapy – preliminary results

Abstract Basing on alanine solid state/electron paramagnetic resonance (EPR) dosimetry, a supplementary method of cumulatively recording the therapeutic dose received by ocular cancer patients undergoing fractionated proton radiotherapy is proposed. By applying alanine dosimetry during the delivery of consecutive fractions, the dose received within each fraction can be read out by EPR spectrometry and a final permanent cumulative record of the total dose delivered obtained. The dose response of the alanine detector was found to be practically independent on its position within the extended proton Bragg peak region. Dose measurements based on entrance dose recorded in proton beams individually formed for each patient are presented. The described method will be applied as a complementary Quality Assurance procedure for patients undergoing proton radiotherapy at the Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland (IFJ PAN).

Studies of scintillator response to 60 MeV protons in a proton beam imaging system

Abstract A Proton Beam Imaging System (ProBImS) is under development at the Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN). The ProBImS will be used to optimize beam delivery at IFJ PAN proton therapy facilities, delivering two-dimensional distributions of beam profiles. The system consists of a scintillator, optical tract and a sensitive CCD camera which digitally records the light emitted from the proton-irradiated scintillator. The optical system, imaging data transfer and control software have already been developed. Here, we report preliminary results of an evaluation of the DuPont Hi-speed thick back screen EJ 000128 scintillator to determine its applicability in our imaging system. In order to optimize the light conversion with respect to the dose locally deposited by the proton beam in the scintillation detector, we have studied the response of the DuPont scintillator in terms of linearity of dose response, uniformity of light emission and decay rate of background light after deposition of a high dose in the scintillator. We found a linear dependence of scintillator light output vs. beam intensity by showing the intensity of the recorded images to be proportional to the dose deposited in the scintillator volume.