Pawel Olko

Particle radiotherapy with conformal beams aims to tailor the delivered radiation and dose with spatial customization. For treatments using beam shaping collimators it is desired to verify the delivered doses and examine the characteristics of the produced fields with imaging response. For this purpose, we use the semiconductor pixel detector Timepix which provides time-resolved spectral-and imaging response with high spatial resolution and particle-type resolving power. Precise measurements are performed in-field at the isocenter on selected regions (≤14 mm) of delivered beams of low intensity (≤pA). Detailed information in wide dynamic range is produced in the form of field composition (particle-type species), spectral (deposited energy, linear-energy-transfer spectra) and spatial dose distribution at the sub-mm scale (≈200 μm spatial resolution). Results are presented for measurements of two conformal beam collimators used for eye treatment with 55 MeV protons. The produced 2-D maps and 1D profile distributions can be used for experimental verification of spatially fractionated radiation therapy (grid therapy), and in particle therapy for verification of Monte Carlo transport calculation, including LET distribution at the target isocenter position.

Objective. This work investigates the use of passive luminescence detectors to determine different types of averaged linear energy transfer ( LET ― ) for the energies relevant to proton therapy. The experimental results are compared to reference values obtained from Monte Carlo simulations. Approach. Optically stimulated luminescence detectors (OSLDs), fluorescent nuclear track detectors (FNTDs), and two different groups of thermoluminescence detectors (TLDs) were irradiated at four different radiation qualities. For each irradiation, the fluence- ( LET ― f ) and dose-averaged LET ( LET ― d ) were determined. For both quantities, two sub-types of averages were calculated, either considering the contributions from primary and secondary protons or from all protons and heavier, charged particles. Both simulated and experimental data were used in combination with a phenomenological model to estimate the relative biological effectiveness (RBE). Main results. All types of LET ― could be assessed with the luminescence detectors. The experimental determination of LET ― f is in agreement with reference data obtained from simulations across all measurement techniques and types of averaging. On the other hand, LET ― d can present challenges as a radiation quality metric to describe the detector response in mixed particle fields. However, excluding secondaries heavier than protons from the LET ― d calculation, as their contribution to the luminescence is suppressed by ionization quenching, leads to equal accuracy between LET ― f and LET ― d . Assessment of RBE through the experimentally determined LET ― d values agrees with independently acquired reference values, indicating that the investigated detectors can determine LET ― with sufficient accuracy for proton therapy. Significance. OSLDs, TLDs, and FNTDs can be used to determine LET ― and RBE in proton therapy. With the capability to determine dose through ionization quenching corrections derived from LET ― , OSLDs and TLDs can simultaneously ascertain dose, LET ― , and RBE. This makes passive detectors appealing for measurements in phantoms to facilitate validation of clinical treatment plans or experiments related to proton therapy.

The radioluminescence (RL) emitted by LiMgPO₄ detector under proton beam irradiation was investigated in real time at the radiotherapy facility in the Institute of Nuclear Physics Polish Academy of Sciences in Krakow. The facility uses protons accelerated by the AIC-144 isochronous cyclotron up to the energy of 60 MeV. The measurements of RL were carried out using a remote optical fiber device with a luminophore detector and photomultiplier located at opposite ends of the optical fiber. A thin slice of LiMgPO₄ doped with Tm (1.2 mol%) crystal was exposed to the proton beam. The tested detector allowed for the measurement of proton beam current, flux fluence and determination of proton beam time structure parameters. The investigation of LiMgPO₄ crystal showed its high sensitivity, fast reaction time to irradiation and possibility of application as the detector for control of proton beam parameters.

Following the publication of the joint The International Commissions on Radiation Units and Measurements (ICRU) and on Radiological Protection (ICRP) report on new operational quantities for radiation protection, the European Dosimetry Group (EURADOS) have carried out an initial evaluation. The EURADOS report analyses the impact that the new quantities will have on: radiation protection practice; calibration and reference fields; European and national regulation; international standards and, especially, dosemeter and instrument design. The task group included experienced scientists drawn from across the various EURADOS working groups.

Objective. The Jagiellonian positron emission tomography (J-PET) technology, based on plastic scintillators, has been proposed as a cost effective tool for detecting range deviations during proton therapy. This study investigates the feasibility of using J-PET for range monitoring by means of a detailed Monte Carlo simulation study of 95 patients who underwent proton therapy at the Cyclotron Centre Bronowice (CCB) in Krakow, Poland. Approach. Discrepancies between prescribed and delivered treatments were artificially introduced in the simulations by means of shifts in patient positioning and in the Hounsfield unit to the relative proton stopping power calibration curve. A dual-layer, cylindrical J-PET geometry was simulated in an in-room monitoring scenario and a triple-layer, dual-head geometry in an in-beam protocol. The distribution of range shifts in reconstructed PET activity was visualized in the beam’s eye view. Linear prediction models were constructed from all patients in the cohort, using the mean shift in reconstructed PET activity as a predictor of the mean proton range deviation. Main results. Maps of deviations in the range of reconstructed PET distributions showed agreement with those of deviations in dose range in most patients. The linear prediction model showed a good fit, with coefficient of determination r ² = 0.84 (in-room) and 0.75 (in-beam). Residual standard error was below 1 mm: 0.33 mm (in-room) and 0.23 mm (in-beam). Significance. The precision of the proposed prediction models shows the sensitivity of the proposed J-PET scanners to shifts in proton range for a wide range of clinical treatment plans. Furthermore, it motivates the use of such models as a tool for predicting proton range deviations and opens up new prospects for investigations into the use of intra-treatment PET images for predicting clinical metrics that aid in the assessment of the quality of delivered treatment.