Organs at risk dose constraints in carbon ion radiotherapy at MedAustron: Translations between LEM and MKM RBE models and preliminary clinical results.

BACKGROUND: Carbon ion radiotherapy (CIRT) treatment planning is based on relative biological effectiveness (RBE) weighted dose calculations. A large amount of clinical evidence for CIRT was collected in Japan with RBE estimated by the modified microdosimetric kinetic model (MKM) while all European centres apply the first version of the local effect model (LEM). Japanese schedules have been used in Europe with adapted prescription dose and organs at risk (OAR) dose constraints. Recently, less conservative adapted LEM constraints have been implemented in clinical practice. The aim of this study was to analyse the new set of LEM dose constraints for brain parenchyma, brainstem and optic system considering both RBE models and evaluating early clinical data. MATERIAL AND METHODS: 31 patients receiving CIRT at MedAustron were analysed using the RayStation v9A planning system by recalculating clinical LEM-based plans in MKM. Dose statistics (D1cm3, D5cm3, D0.1cm3, D0.7cm3, D10%, D20%) were extracted for relevant critical OARs. Curve fitting for those values was performed, resulting in linear quadratic translation models. Clinical and radiological toxicity was evaluated. RESULTS: Based on derived fits, currently applied LEM constraints matched recommended MKM constraints with deviations between -8% and +3.9%. For particular cases, data did not follow the expected LEM vs MKM trends resulting in outliers. Radiological (asymptomatic) toxicity was detected in two outlier cases. CONCLUSION: Respecting LEM constraints does not automatically ensure that MKM constraints are met. Constraints for both RBE models need to be fulfilled for future CIRT patients at MedAustron. Careful selection of planning strategies is essential.

Catalogue of dose rate constants for more than 400 radionuclides in terms of ambient dose H∗ and comparison of figures to ambient dose equivalent H∗(10).

In 2020, the International Commission on Radiation Units & Measurements ICRU has released Report 95 on "Operational Quantities for External Radiation Exposure". This publication introduced a new measurand, namely ambient dose H∗, as the operational quantity for external exposure to be applied in the future replacing ambient dose equivalent H∗(10). It should be noted that this change will make it necessary to adjust previously used constants and coefficients or at least to review them with regard to the new measurand. Therefore, this recommendation represents a significant cut in implementation of radiation protection systems. The revision of all previously valid factors makes it possible to develop a consistent data set. The combination of experience gained in the last decades with more extensive data sets (e.g. on the spectra of individual radionuclides) with comparatively large computing power allows the definition of optimized data collections serving as input for Monte Carlo methods. Therefore, this publication is intended to lay a suitable foundation consisting of dose rate constants for more than 400 radionuclides concerning the future measurand ambient dose H∗ and to indicate differences to values related to the ambient dose equivalent H∗(10) used nowadays.

A novel approach towards the calculation of dose rate constants for ambient dose equivalent H∗(10) by including low energy x-rays.

The nuclide-specific dose rate constant, formerly called gamma ray constant, is one of the most important quantities in practical radiation protection dosimetry. For radiation sources with known radionuclide composition and activity, the expected dose rates at various distances can easily be calculated with reasonable approximations. In addition, they serve as a planning basis for the design of shielding of radiation application rooms and facilities. In this study, dose rate constants were calculated using the most recent conversion coefficients and the most suitable spectral data for more than 400 radionuclides using different calculation approaches. In addition this paper provides a critical review of currently published dose rate constants for the ambient dose equivalent H∗(10).

Computationally Efficient Combination of Multi-channel Phase Data From Multi-echo Acquisitions (ASPIRE).

PURPOSE: To develop a simple method for combining multi-echo phase information from a number of coils in an array that requires no volume coil or additional scans and yields signal-to-noise ratio-optimal images that reflect only ΔB0-related phase. THEORY AND METHODS: Two SNR optimal coil combination methods were developed which retrieve the ΔB0-related phase by determining the coil-dependent phase offsets. The first variant, MCPC-3D-S, requires the unwrapping of one phase image; the second variant, ASPIRE, allows unwrapping to be avoided if two echoes j and k satisfy the echo time relation m⋅TEk=(m+1)⋅TEj, where m is an integer, making this a particularly fast and robust approach. Both developed methods constitute improvements over a prior method, MCPC-3D, in terms of robustness and computational expense. RESULTS: In the brain at 7 T, phase matching and contrast-to-noise ratio were higher with MCPC-3D-S and ASPIRE than with phase difference reconstruction, and similar to the reference coil-dependent Roemer combination. Unlike the Roemer and virtual reference coil methods, the proposed approaches also eliminated all non- ΔB0-related phase. CONCLUSION: MCPC-3D-S is an improvement over prior multi-echo methods, which is useful if the ASPIRE echo time condition cannot be fulfilled. ASPIRE is a particularly fast and robust approach that runs on the scanner's reconstructor in a small fraction of the acquisition time. Magn Reson Med 79:2996-3006, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Optimized conformal paraaortic lymph node irradiation is not associated with enhanced renal toxicity.

BACKGROUND AND PURPOSE: For patients with gynecologic carcinomas, irradiation of paraaortic lymph nodes (PLNs) is a routine treatment concept. Planning target volumes (PTVs) individually optimized by radiation field delineations along the big vessels permit the inclusion of at least 97% of potentially involved PLNs. However, this novel treatment technique might increase radiation-induced nephrotoxicity. Therefore, the actual incidence of kidney damage after PLN irradiation has to be assessed in order to validate the safety of this treatment concept. PATIENTS AND METHODS: 19 patients were treated with irradiation alone (50.4 Gy; 5 x 1.8 Gy/week) and monitored for up to 90 months. Functional renal parameters, namely renal plasma flow (RPF) and glomerular filtration rate (GFR), were assessed by dynamic renal scintigraphy. Additionally, patients were clinically observed (i.e., hypertension, proteinuria) and calculations of normal-tissue complication probability (NTCP) values for nonuniform kidney irradiation were performed using the Lyman-Wolbarst algorithm. RESULTS: Two patients with anticipated moderate NTCP values (12.6% and 8.7%) showed slightly impaired RPF rates at 12, 24, and after 48 months of follow-up. Only one patient in the subgroup showing NTCP values > 50% (n = 9) developed a notable impairment of renal RPF. However, all patients including those with elevated complication probabilities exhibited neither impaired GFR nor clinically apparent symptoms related to a loss of functioning renal tissue from 12 to > 48 months post irradiation. CONCLUSION: Conformal irradiation of retroperitoneal lymph nodes with individual PTV delineation appears not to be associated with clinically relevant functional impairment of the kidneys.

Beyond low-level activity: on a "non-radioactive" gas mantle.

Gas mantles for camping gas lanterns sometimes contain thorium compounds. During the last years, the use of thorium-free gas mantles has become more and more popular due to the avoidance of a radioactive heavy metal. We investigated a gas mantle type that is declared to be "non-radioactive" and that can be bought in Austria at the moment. Methods used were Instrumental Neutron Activation Analysis (INAA), gamma-spectroscopy, and Liquid Scintillation Counting (LSC). We found massive thorium contents of up to 259 mg per gas mantle. Leaching experiments showed that only 0.4% of the Th but approximately 90% of the decay products of (232)Th can be leached under conditions simulating sucking and chewing with human saliva. In this paper, the investigation of these gas mantles including the consideration of the environmental hazard caused by disposed mantles and the health hazard for unsuspecting consumers is presented and legal consequences are discussed for this fraud.

Trace elements in rock salt and their bioavailability estimated from solubility in acid.

In this study, 18 partly commercially available samples of rock salt from Austria, Germany, Pakistan, Poland, Switzerland, and Ukraine were investigated with respect to their content of trace elements using instrumental neutron activation analysis. Elements detected were Al, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Eu, Fe, Hf, La, Mn, Na, Rb, Sb, Sc, Sm, Sr, Ta, Tb, Th, and Zn, some of them only in individual cases. An estimation of the bioavailability of these trace elements was performed by dissolving an equivalent of the sodium chloride samples in diluted hydrochloric acid (simulating stomach acid), filtering off the insoluble components, and analyzing the evaporated filtrate. It could be shown that in most cases bioactive trace elements like Fe can be found in rock salt in the form of almost insoluble compounds and are therefore not significantly bioavailable, whereas thorium, for example, was partly bioavailable in two cases. A significant contribution to the recommended daily intake of metal trace elements by using rock salt for nutrition can be excluded.

Investigating the accuracy of the FLUKA code for transport of therapeutic ion beams in matter.

In-beam positron emission tomography (PET) is currently used for monitoring the dose delivery at the heavy ion therapy facility at GSI Darmstadt. The method is based on the fact that carbon ions produce positron emitting isotopes in fragmentation reactions with the atomic nuclei of the tissue. The relation between dose and beta(+)-activity is not straightforward. Hence it is not possible to infer the delivered dose directly from the PET distribution. To overcome this problem and enable therapy monitoring, beta(+)-distributions are simulated on the basis of the treatment plan and compared with the measured ones. Following the positive clinical impact, it is planned to apply the method at future ion therapy facilities, where beams from protons up to oxygen nuclei will be available. A simulation code capable of handling all these ions and predicting the irradiation-induced beta(+)-activity distributions is desirable. An established and general purpose radiation transport code is preferred. FLUKA is a candidate for such a code. For application to in-beam PET therapy monitoring, the code has to model with high accuracy both the electromagnetic and nuclear interactions responsible for dose deposition and beta(+)-activity production, respectively. In this work, the electromagnetic interaction in FLUKA was adjusted to reproduce the same particle range as from the experimentally validated treatment planning software TRiP, used at GSI. Furthermore, projectile fragmentation spectra in water targets have been studied in comparison to available experimental data. Finally, cross sections for the production of the most abundant fragments have been calculated and compared to values found in the literature.

Competing irradiation techniques for para-aortic lymph nodes: dose distribution and NTCP for the kidney.

PURPOSE: Partial coirradiation of both kidneys is an unavoidable consequence of adequate dose delivery in radiation therapy of para-aortic lymph nodes (PLN). Depending on total dose anteroposterior/posteroanterior (AP/PA), opposed-fields or multifield techniques are used. To optimize the treatment of potentially tumor-affected PLN with minimal kidney involvement, we calculated normal tissue complication probabilities (NTCPs) of coirradiated kidneys for four common irradiation techniques used in the PLN area. METHODS AND MATERIALS: Planning target volume (PTV) delineation was performed in computed tomography scans of 21 patients with a lateral safety margin of 3 cm from the aorta and 2 cm aside the vena cava. Ventral and dorsal margins of the PTV were delineated 2 cm from the vessels. As previously shown (Nevinny-Stickel M, et al. Int J Radiat Oncol Biol Phys 2000;48:147-151), PTVs optimized by these altered delineations permit inclusion of at least 97% of potentially involved PLN in contrast to standard delineations based on bony structures that are more likely to miss affected lymph nodes. The present study compared NTCPs for individual PTV-based treatment planning with NTCPs for standard planning based on bony structures. For each patient, four hypothetical treatment plans were created: (A) standard AP/PA opposed fields technique with lateral field margins along the tips of the transverse processes of the vertebral bodies; (B) individually planned AP/PA opposed fields with lateral field margins according to the optimized PTV; (C) standard four-field box technique with lateral width as described for (A), with dorsal borders at the center of the vertebral bodies and ventral margins 3 cm in front of the vertebrae; and (D) individually planned four-field box with lateral field margins according to the optimized PTV. Calculation of irradiation-induced complication probability values for nonuniform kidney irradiation was performed for model doses 19.8 Gy, 30.6 Gy, and 50.4 Gy according to the Lyman-Wolbarst model. RESULTS: No dose showed a statistically significant difference (p < 0.00833, corrected for six multiple interrelated comparisons) in the median of total organ kidney NTCPs between techniques A, C, and D, with technique D intermediately ranging between technique A and C (e.g., for 50.4 Gy: A: median, 0.39; range, 0.01-0.83; C: median, 0.27 range; 0.05-0.68; D: 0.36; range, 0.03-0.72). In comparison to techniques A, C, and D, the individually planned AP/PA opposed-fields technique (B) was accompanied by significantly higher and intolerable overall kidney NTCP rates (e.g., for 50.4 Gy: median, 0.68; range, 0.01-0.99). CONCLUSION: Conformal four-field planning with individually optimized PTVs (D) resulted in only moderate tissue complication probabilities in both kidneys with the advantage of providing significantly greater inclusion of potentially involved PLNs in comparison to accepted standard procedures (A and C).

Application of commercial MOSFET detectors for in vivo dosimetry in the therapeutic x-ray range from 80 kV to 250 kV.

The purpose of this study was to investigate the dosimetric characteristics (energy dependence, linearity, fading, reproducibility, etc) of MOSFET detectors for in vivo dosimetry in the kV x-ray range. The experience of MOSFET in vivo dosimetry in a pre-clinical study using the Alderson phantom and in clinical practice is also reported. All measurements were performed with a Gulmay D3300 kV unit and TN-502RDI MOSFET detectors. For the determination of correction factors different solid phantoms and a calibrated Farmer-type chamber were used. The MOSFET signal was linear with applied dose in the range from 0.2 to 2 Gy for all energies. Due to fading it is recommended to read the MOSFET signal during the first 15 min after irradiation. For long time intervals between irradiation and readout the fading can vary largely with the detector. The temperature dependence of the detector signal was small (0.3% degrees C(-1)) in the temperature range between 22 and 40 degrees C. The variation of the measuring signal with beam incidence amounts to +/-5% and should be considered in clinical applications. Finally, for entrance dose measurements energy-dependent calibration factors, correction factors for field size and irradiated cable length were applied. The overall accuracy, for all measurements, was dominated by reproducibility as a function of applied dose. During the pre-clinical in vivo study, the agreement between MOSFET and TLD measurements was well within 3%. The results of MOSFET measurements, to determine the dosimetric characteristics as well as clinical applications, showed that MOSFET detectors are suitable for in vivo dosimetry in the kV range. However, some energy-dependent dosimetry effects need to be considered and corrected for. Due to reproducibility effects at low dose levels accurate in vivo measurements are only possible if the applied dose is equal to or larger than 2 Gy.