Abstract Background and purpose A substantial reduction of uncertainties in clinical brachytherapy should result in improved outcome in terms of increased local control and reduced side effects. ...Types of uncertainties have to be identified, grouped, and quantified. Methods A detailed literature review was performed to identify uncertainty components and their relative importance to the combined overall uncertainty. Results Very few components ( e.g. , source strength and afterloader timer) are independent of clinical disease site and location of administered dose. While the influence of medium on dose calculation can be substantial for low energy sources or non-deeply seated implants, the influence of medium is of minor importance for high-energy sources in the pelvic region. The level of uncertainties due to target, organ, applicator, and/or source movement in relation to the geometry assumed for treatment planning is highly dependent on fractionation and the level of image guided adaptive treatment. Most studies to date report the results in a manner that allows no direct reproduction and further comparison with other studies. Often, no distinction is made between variations, uncertainties, and errors or mistakes. The literature review facilitated the drafting of recommendations for uniform uncertainty reporting in clinical BT, which are also provided. The recommended comprehensive uncertainty investigations are key to obtain a general impression of uncertainties, and may help to identify elements of the brachytherapy treatment process that need improvement in terms of diminishing their dosimetric uncertainties. It is recommended to present data on the analyzed parameters (distance shifts, volume changes, source or applicator position, etc.), and also their influence on absorbed dose for clinically-relevant dose parameters ( e.g. , target parameters such as D90 or OAR doses). Publications on brachytherapy should include a statement of total dose uncertainty for the entire treatment course, taking into account the fractionation schedule and level of image guidance for adaptation. Conclusions This report on brachytherapy clinical uncertainties represents a working project developed by the Brachytherapy Physics Quality Assurances System (BRAPHYQS) subcommittee to the Physics Committee within GEC-ESTRO. Further, this report has been reviewed and approved by the American Association of Physicists in Medicine.
Purpose
In the absence of a 6D couch and/or assuming considerable intrafractional patient motion, rotational errors could affect target coverage and OAR‐sparing especially in multiple metastases ...VMAT‐SRS cranial cases, which often involve the concurrent irradiation of off‐axis targets. This work aims to study the dosimetric impact of rotational errors in such applications, under a comparative perspective between the single‐ and two‐isocenter treatment techniques.
Methods
Ten patients (36 metastases) were included in this study. Challenging cases were only considered, with several targets lying in close proximity to OARs. Two multiarc VMAT plans per patient were prepared, involving one and two isocenters, serving as the reference plans. Different degrees of angular offsets at various orientations were introduced, simulating rotational errors. Resulting dose distributions were evaluated and compared using commonly employed dose‐volume and plan quality indices.
Results
For single‐isocenter plans and 1⁰ rotations, plan quality indices, such as coverage, conformity index and D95%, deteriorated significantly (>5%) for distant targets from the isocenter (at> 4–6 cm). Contrarily, for two‐isocenter plans, target distances to nearest isocenter were always shorter (≤4 cm), and, consequently, 1⁰ errors were well‐tolerated. In the most extreme case considered (2⁰ around all axes) conformity index deteriorated by on‐average 7.2%/cm of distance to isocenter, if one isocenter is used, and 2.6%/cm, for plans involving two isocenters. The effect is, however, strongly associated with target volume. Regarding OARs, for single‐isocenter plans, significant increase (up to 63%) in Dmax and D0.02cc values was observed for any angle of rotation. Plans that could be considered clinically unacceptable were obtained even for the smallest angle considered, although rarer for the two‐isocenter planning approach.
Conclusion
Limiting the lesion‐to‐isocenter distance to ≤4 cm by introducing additional isocenter(s) appears to partly mitigate severe target underdosage, especially for smaller target sizes. If OAR‐sparing is also a concern, more stringent rotational error tolerances apply.
Abstract Purpose To study the effect of finite patient dimensions and tissue heterogeneities in head and neck high dose rate brachytherapy. Methods and materials The current practice of TG-43 ...dosimetry was compared to patient specific dosimetry obtained using Monte Carlo simulation for a sample of 22 patient plans. The dose distributions were compared in terms of percentage dose differences as well as differences in dose volume histogram and radiobiological indices for the target and organs at risk (mandible, parotids, skin, and spinal cord). Results Noticeable percentage differences exist between TG-43 and patient specific dosimetry, mainly at low dose points. Expressed as fractions of the planning aim dose, percentage differences are within 2% with a general TG-43 overestimation except for the spine. These differences are consistent resulting in statistically significant differences of dose volume histogram and radiobiology indices. Absolute differences of these indices are however small to warrant clinical importance in terms of tumor control or complication probabilities. Conclusions The introduction of dosimetry methods characterized by improved accuracy is a valuable advancement. It does not appear however to influence dose prescription or call for amendment of clinical recommendations for the mobile tongue, base of tongue, and floor of mouth patient cohort of this study.
Acute radiodermatitis is the most common side effect in non-melanoma skin cancer patients undergoing radiotherapy. Nonetheless, despite the ongoing progress of clinical trials, no effective regimen ...has been found yet. In this study, a non-woven patch, comprised of electrospun polymeric micro/nanofibers loaded with an aqueous extract of Pinus halepensis bark (PHBE), was fabricated and clinically tested for its efficacy to prevent radiodermatitis. The bioactivity of the PHBE patch was evaluated in comparison with a medical cream indicated for acute radiodermatitis. Twelve volunteer patients were selected and randomly assigned to two groups, applying either the PHBE patch or the reference cream daily. Evaluation of radiation-induced skin reactions was performed during the radiotherapy period and 1 month afterwards according to the Radiation Therapy Oncology Group (RTOG) grading scale, photo-documentation, patient-reported outcomes (Visual Analog Scale, questionnaire), biophysical measurements (hydration, transepidermal water loss, erythema, melanin), and image analysis. In contrast with the reference product, the PHBE patch showed significant anti-inflammatory activity and restored most skin parameters to normal levels 1 month after completion of radiation therapy. No adverse event was reported, indicating that the application of the PHBE patch can be considered as a safe medical device for prophylactic radiodermatitis treatment.
The effect of the reportedly low ionizing radiation doses, such as those very often delivered to patients in interventional cardiology, remains ambiguous. As interventional cardiac procedures may ...have a significant impact on total collective effective dose, there are radiation protection concerns for patients and physicians regarding potential late health effects. Given that very low doses (<100 mSv) are expected to be delivered during these procedures, the purpose of this study was to assess the potency and suitability of current genotoxicity biomarkers to detect and quantitate biological effects essential for risk estimation in interventional cardiology. Specifically, the biomarkers γ-H2AX foci, dicentric chromosomes, and micronuclei, which underpin radiation-induced DNA damage, were studied in blood lymphocytes of 25 adult patients before and after interventional cardiac procedures. Even though the mean values of all patients as a group for all three endpoints tested show increased yields relative to baseline following medical exposure, our results demonstrate that only the γ-H2AX biomarker enables detection of statistically significant differences at the individual level (
p
< 0.001) for almost all patients (91%). Furthermore, 24 h after exposure, residual γ-H2AX foci were still detectable in irradiated lymphocytes. Their decline was found to vary significantly among the individuals and the repair kinetics of γ-H2AX foci was found to range from 25 to 95.6% of their maximum values obtained.
Brachytherapy treatment outcomes depend on the accuracy of the delivered dose distribution, which is proportional to the reference air-kerma rate (RAKR). Current societal recommendations require the ...medical physicist to compare the measured RAKR values to the manufacturer source calibration certificate. The purpose of this work was to report agreement observed in current clinical practice in the European Union.
A European survey was performed for high- and pulsed-dose-rate (HDR and PDR) high-energy sources (192Ir and 60Co), to quantify observed RAKR differences. Medical physicists at eighteen hospitals from eight European countries were contacted, providing 1,032 data points from 2001 to 2020.
Over the survey period, 77% of the 192Ir measurements used a well chamber instead of the older Krieger phantom method. Mean differences with the manufacturer calibration certificate were 0.01% ± 1.15% for 192Ir and –0.1% ± 1.3% for 60Co. Over 95% of RAKR measurements in the clinic were within 3% of the manufacturer calibration certificate.
This study showed that the agreement level was generally better than that reflected in prior societal recommendations positing 5%. Future recommendations on high-energy HDR and PDR source calibrations in the clinic may consider tightened agreements levels.
We report the experimental observation and theoretical analysis of a novel beam-steering effect in periodic waveguide arrays that arises from the interplay between discrete diffraction, Kerr ...nonlinearity and any mechanism that effectively weakens the nonlinear part of the beam. In this regime the propagation direction shows increased sensitivity to the input angle and for a certain angular range around normal incidence a nonlinear beam may be guided to a direction opposite to that initially inserted. For continuous wave beams the role of this mechanism is played by absorption of any kind, such as three photon absorption, two photon absorption or even linear absorption. For pulsed beams we show that the same dynamics can arise due to strong normal temporal dispersion, while absorption is not necessary and can be a further enhancing or alternative factor. This observation falls under a more general dissipation-assisted beam velocity control mechanism in nonlinear optical lattices, which is also theoretically predicted by the effective particle approach.
. To investigate the potential of 2D ion chamber arrays to serve as a standalone tool for the verification of source strength, positioning and dwell time, within the framework of
Ir high-dose rate ...brachytherapy device quality assurance (QA).
A commercially available ion chamber array was used. Fitting of a 2D Lorentzian peak function to experimental data from a multiple source dwell position irradiation on a frame-by-frame basis, facilitated tracking of the source center orthogonal projection on the array plane. For source air kerma strength verification, Monte Carlo simulation was employed to obtain a chamber array- and source-specific correction factor of calibration with a 6 MV photon beam. This factor converted the signal measured by each ion chamber element to air kerma in free space. A source positioning correction was also applied to lift potential geometry mismatch between experiment and Monte Carlo simulation.
Spatial and temporal accuracy of source movement was verified within 0.5 mm and 0.02 s, respectively, in compliance with the test endpoints recommended by international professional societies. The source air kerma strength was verified experimentally within method uncertainties estimated as 1.44% (
= 1). The source positioning correction method employed did not introduce bias to experimental results of irradiations where source positioning was accurate. Development of a custom jig attachable to the chamber array for accurate and reproducible experimental set up would improve testing accuracy and obviate the need for source positioning correction in air kerma strength verification.
Delivery of a single irradiation plan, optimized based on results of this work, to a 2D ion chamber array can be used for concurrent testing of source position, dwell time and air kerma strength, and the procedure can be expedited through automation. Chamber arrays merit further study in treatment planning QA and real time,
dose verification.
•Dose to eye lenses in intracranial CyberKnife applications.•Spatial distribution of the imaging dose in CyberKnife applications.•Image degradation due to scatter radiation in CyberKnife ...radiosurgery.
The imaging dose for intra- and extra-cranial CyberKnife radiosurgery applications was calculated and the scattered radiation reaching the digital detectors was quantified and analyzed with regard to its origin.
The image guidance subsystem of the CyberKnife was modeled based on vendor-provided information. The emitted X-ray energy spectrum for 120 kV was estimated using the SpekPy software tool. Monte Carlo (MC) image acquisition simulations were performed to calculate the total, primary and scattered photon fluences reaching each detector as a function of the imaged object dimensions. MC calculations of the imaging dose were performed for intra- and extra-cranial applications assuming 120 kV and 10 mAs acquisition settings.
The amount of scattered radiation reaching each detector was found to depend on the dimensions of the imaged anatomical region, contributing more than 40 % to the total photon fluence for regions more than 20 cm thick. More than 20 % of this scattered radiation originates from the contralateral imaging field. A maximum organ dose of 1.5 mGy at the nasal bones and an average dose of 0.37 mGy to the eye lenses per image pair acquisition was calculated for head applications. An entrance imaging dose of 0.4 mGy was calculated for extracranial applications.
Scattered radiation reaching each detector in the skull and spine tracking applications can be reduced by acquiring the pair of radiographs sequentially instead of simultaneously. A dose of 3.7 cGy to the eye lenses is estimated assuming 100 image pair exposures required for treatment completion.
Background
In Magnetic Resonance‐Linac (MR‐Linac) dosimetry formalisms, a new correction factor, kB,Q, has been introduced to account for corresponding changes to detector readings under the beam ...quality, Q, and the presence of magnetic field, B.
Purpose
This study aims to develop and implement a Monte Carlo (MC)‐based framework for the determination of kB,Q correction factors for a series of ionization chambers utilized for dosimetry protocols and dosimetric quality assurance checks in clinical 1.5 T MR‐Linacs. Their dependencies on irradiation setup conditions are also investigated. Moreover, to evaluate the suitability of solid phantoms for dosimetry checks and end‐to‐end tests, changes to the detector readings due to the presence of small asymmetrical air gaps around the detector's tip are quantified.
Methods
Phase space files for three irradiation fields of the ELEKTA Unity 1.5 T/7 MV flattening‐filter‐free MR‐Linac were provided by the manufacturer and used as source models throughout this study. Twelve ionization chambers (three farmer‐type and nine small‐cavity detectors, from three manufacturers) were modeled (including their dead volume) using the EGSnrc MC code package. kB,Q values were calculated for the 10 × 10 cm2 irradiation field and for four cardinal orientations of the detectors’ axes with respect to the 1.5 T magnetic field. Potential dependencies of kB,Q values with respect to field size, depth, and phantom material were investigated by performing additional simulations. Changes to the detectors’ readings due to the presence of small asymmetrical air gaps (0.1 up to 1 mm) around the chambers’ sensitive volume in an RW3 solid phantom were quantified for three small‐cavity chambers and two orientations.
Results
For both parallel (to the magnetic field) orientations, kB,Q values were found close to unity. The maximum correction needed was 1.1%. For each detector studied, the kB,Q values calculated for the two parallel orientations agreed within uncertainties. Larger corrections (up to 5%) were calculated when the detectors were oriented perpendicularly to the magnetic field. Results were compared with corresponding ones found in the literature, wherever available. No considerable dependence of kB,Q with respect to field size (down to 3 × 3 cm2), depth, or phantom material was noticed, for the detectors investigated. As compared to the perpendicular one, in the parallel to the magnetic field orientation, the air gap effect is minimized but is still considerable even for the smallest air gap considered (0.1 mm).
Conclusion
For the 10 × 10 cm2 field, magnetic field correction factors for 12 ionization chambers and four orientations were determined. For each detector, the kB,Q value may be also applied for dosimetry procedures under different irradiation parameters provided that the orientation is taken into account. Moreover, if solid phantoms are used, even the smallest asymmetrical air gap may still bias small‐cavity chamber response. This work substantially expands the availability and applicability of kB,Q correction factors that are detector‐ and orientation‐specific, enabling more options in MR‐Linac dosimetry checks, end‐to‐end tests, and quality assurance protocols.
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