GEC-ESTRO survey of 106Ru eye applicator practice for ocular melanoma - Physicist survey.

AIM: 106Ru eye plaque brachytherapy (BT, interventional radiotherapy) is an eye-preserving treatment for uveal melanoma performed in about 100 clinics worldwide. Despite this relatively low number, there is a considerable variation in clinical practice. In 2022, the BRAPHYQS and Head & Neck and Skin GEC-ESTRO working groups conducted a survey to map the current clinical practice. The survey consisted of a physicist and a physician part. This paper describes the physicist results. However, three physician questions with overlapping interest are included here as well. MATERIALS AND METHODS: The survey questions pertained to commissioning and quality control (QC) of the plaques, treatment planning, radiobiological correction, as well as more general questions on practice improvement. The questions overlapping with the physician survey were related to dose prescription and margins. RESULTS: Sixty-five physicist responses were included. A majority of the centres do not perform an independent measurement of the absorbed dose at reference depth, percentage depth dose (PDD) and off-axis data. A lack of calibration services and suitable equipment are the main reasons. About one third of the centres indicated that they do image based treatment planning. The use of margins and dose prescription showed a large variability, despite the availability of guidelines [1]. Many respondents expressed a strong wish for improvement in a wide range of aspects of clinical practice. CONCLUSION: The physics survey showed a wide variability regarding quality control of the 106Ru sources and treatment planning practice.

A Prognostic Score for the Prediction of Local Treatment Failure in Plaque Brachytherapy of Uveal Melanoma.

Purpose: To develop a prognostic score that correlates to a low, medium, and high incidence of treatment failure after plaque brachytherapy of uveal melanoma (UM). Methods and Materials: All patients who have received plaque brachytherapy for posterior UM at St. Erik Eye Hospital in Stockholm, Sweden from 1995 through 2019 were included (n = 1636). Treatment failure was defined as tumor recurrence, lack of tumor regression, or any other condition requiring a secondary transpupillary thermotherapy (TTT), plaque brachytherapy, or enucleation. The total sample was randomized into 1 training and 1 validation cohort, and a prognostic score for the risk for treatment failure was developed. Results: In multivariate Cox regression, low visual acuity, tumor distance to the optic disc ≤2 mm, American Joint Committee on Cancer (AJCC) stage, and a tumor apical thickness of >4 (for Ruthenium-106) or >9 mm (for Iodine-125) were independent predictors of treatment failure. No reliable threshold could be identified for tumor diameter or cancer stage. In competing risk analyses of the validation cohort, the cumulative incidence of treatment failure, as well as of secondary enucleation, increased with the prognostic score: In the low, intermediate, and high-risk classes, the 10-year incidence of treatment failure was 19, 28, and 35% and of secondary enucleation 7, 19, and 25 %, respectively. Conclusions: Low visual acuity, American Joint Committee on Cancer stage, tumor thickness, and tumor distance to the optic disc are independent predictors of treatment failure after plaque brachytherapy for UM. A prognostic score was devised that identifies low, medium, and high risk for treatment failure.

Validation of automated post-adjustments of HDR prostate brachytherapy treatment plans by quantitative measures and oncologist observer study.

PURPOSE: The aim was to evaluate a postprocessing optimization algorithm's ability to improve the spatial properties of a clinical treatment plan while preserving the target coverage and the dose to the organs at risk. The goal was to obtain a more homogenous treatment plan, minimizing the need for manual adjustments after inverse treatment planning. MATERIALS AND METHODS: The study included 25 previously treated prostate cancer patients. The treatment plans were evaluated on dose-volume histogram parameters established clinical and quantitative measures of the high dose volumes. The volumes of the four largest hot spots were compared and complemented with a human observer study with visual grading by eight oncologists. Statistical analysis was done using ordinal logistic regression. Weighted kappa and Fleiss' kappa were used to evaluate intra- and interobserver reliability. RESULTS: The quantitative analysis showed that there was no change in planning target volume (PTV) coverage and dose to the rectum. There were significant improvements for the adjusted treatment plan in: V150% and V200% for PTV, dose to urethra, conformal index, and dose nonhomogeneity ratio. The three largest hot spots for the adjusted treatment plan were significantly smaller compared to the clinical treatment plan. The observers preferred the adjusted treatment plan in 132 cases and the clinical in 83 cases. The observers preferred the adjusted treatment plan on homogeneity and organs at risk but preferred the clinical plan on PTV coverage. CONCLUSIONS: Quantitative analysis showed that the postadjustment optimization tool could improve the spatial properties of the treatment plans while maintaining the target coverage.

GEC-ESTRO ACROP recommendations on calibration and traceability of HE HDR-PDR photon-emitting brachytherapy sources at the hospital level.

The vast majority of radiotherapy departments in Europe using brachytherapy (BT) perform temporary implants of high- or pulsed-dose rate (HDR-PDR) sources with photon energies higher than 50 keV. Such techniques are successfully applied to diverse pathologies and clinical scenarios. These recommendations are the result of Working Package 21 (WP-21) initiated within the BRAchytherapy PHYsics Quality Assurance System (BRAPHYQS) GEC-ESTRO working group with a focus on HDR-PDR source calibration. They provide guidance on the calibration of such sources, including practical aspects and issues not specifically accounted for in well-accepted societal recommendations, complementing the BRAPHYQS WP-18 Report dedicated to low energy BT photon emitting sources (seeds). The aim of this report is to provide a European-wide standard in HDR-PDR BT source calibration at the hospital level to maintain high quality patient treatments.

Monte Carlo characterization of high atomic number inorganic scintillators for in vivo dosimetry in 192 Ir brachytherapy.

BACKGROUND: There is increased interest in in vivo dosimetry for 192 Ir brachytherapy (BT) treatments using high atomic number (Z) inorganic scintillators. Their high light output enables construction of small detectors with negligible stem effect and simple readout electronics. Experimental determination of absorbed-dose energy dependence of detectors relative to water is prevalent, but it can be prone to high detector positioning uncertainties and does not allow for decoupling of absorbed-dose energy dependence from other factors affecting detector response . PURPOSE: To investigate which measurement conditions and detector properties could affect their absorbed-dose energy dependence in BT in vivo dosimetry. METHODS: We used a general-purpose Monte Carlo (MC) code PENELOPE for the characterization of high-Z inorganic scintillators with the focus on ZnSe ( Z ¯ = 32 $\bar{Z}=32$ ) Z. Two other promising media CsI ( Z ¯ = 54 $\bar{Z}=54$ ) and Al2 O3 ( Z ¯ = 11 $\bar{Z}=11$ ) were included for comparison in selected scenarios. We determined absorbed-dose energy dependence of crystals relative to water under different scatter conditions (calibration phantom 12 × 12 × 30 cm3 , characterization phantoms 20 × 20 × 20 cm3 , 30 × 30 × 30 cm3 , 40 × 40 × 40 cm3 , and patient-like elliptic phantom 40 × 30 × 25 cm3 ). To mimic irradiation conditions during prostate treatments, we evaluated whether the presence of pelvic bones and calcifications affect ZnSe response. ZnSe detector design influence was also investigated. RESULTS: In contrast to low-Z organic and medium-Z inorganic scintillators, ZnSe and CsI media have substantially greater absorbed-dose energy dependence relative to water. The response was phantom-size dependent and changed by 11% between limited- and full-scatter conditions for ZnSe, but not for Al2 O3 . For a given phantom size, a part of the absorbed-dose energy dependence of ZnSe is caused not due to in-phantom scatter but due to source anisotropy. Thus, the absorbed-dose energy dependence of high-Z scintillators is a function of not only the radial distance but also the polar angle. Pelvic bones did not affect ZnSe response, whereas large and intermediate size calcifications reduced it by 9% and 5%, respectively, when placed midway between the source and the detector. CONCLUSIONS: Unlike currently prevalent low- and medium-Z scintillators, high-Z crystals are sensitive to characterization and in vivo measurement conditions. However, good agreement between MC data for ZnSe in the present study and experimental data for ZnSe:O by Jørgensen et al. (2021) suggests that detector signal is proportional to the average absorbed dose to the detector cavity. This enables an easy correction for non-TG43-like scenarios (e.g., patient sizes and calcifications) through MC simulations. Such information should be provided to the clinic by the detector vendors.

Emerging technologies in brachytherapy.

Brachytherapy is a mature treatment modality. The literature is abundant in terms of review articles and comprehensive books on the latest established as well as evolving clinical practices. The intent of this article is to part ways and look beyond the current state-of-the-art and review emerging technologies that are noteworthy and perhaps may drive the future innovations in the field. There are plenty of candidate topics that deserve a deeper look, of course, but with practical limits in this communicative platform, we explore four topics that perhaps is worthwhile to review in detail at this time. First, intensity modulated brachytherapy (IMBT) is reviewed. The IMBT takes advantage ofanisotropicradiation profile generated through intelligent high-density shielding designs incorporated onto sources and applicators such to achieve high quality plans. Second, emerging applications of 3D printing (i.e. additive manufacturing) in brachytherapy are reviewed. With the advent of 3D printing, interest in this technology in brachytherapy has been immense and translation swift due to their potential to tailor applicators and treatments customizable to each individual patient. This is followed by, in third, innovations in treatment planning concerning catheter placement and dwell times where new modelling approaches, solution algorithms, and technological advances are reviewed. And, fourth and lastly, applications of a new machine learning technique, called deep learning, which has the potential to improve and automate all aspects of brachytherapy workflow, are reviewed. We do not expect that all ideas and innovations reviewed in this article will ultimately reach clinic but, nonetheless, this review provides a decent glimpse of what is to come. It would be exciting to monitor as IMBT, 3D printing, novel optimization algorithms, and deep learning technologies evolve over time and translate into pilot testing and sensibly phased clinical trials, and ultimately make a difference for cancer patients. Today's fancy is tomorrow's reality. The future is bright for brachytherapy.

Source strength determination in iridium-192 and cobalt-60 brachytherapy: A European survey on the level of agreement between clinical measurements and manufacturer certificates.

BACKGROUND AND PURPOSE: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

OPTIMAL SELECTION OF BASE MATERIALS FOR ACCURATE DUAL-ENERGY COMPUTED TOMOGRAPHY: COMPARISON BETWEEN THE ALVAREZ-MACOVSKI METHOD AND DIRA.

The choice of the material base to which the material decomposition is performed in dual-energy computed tomography may affect the quality of reconstructed images. The aim of this work is to investigate how the commonly used bases (water, bone), (water, iodine) and (photoelectric effect, Compton scattering) affect the reconstructed linear attenuation coefficient in the case of the Alvarez-Macovski method. The performance of this method is also compared with the performance of the Dual-energy Iterative Reconstruction Algorithm (DIRA). In both cases, the study is performed using simulations. The results show that the Alvarez-Macovski method produced artefacts when iodine was present in the phantom together with human tissues since this method can only work with one doublet. It was shown that these artefacts could be avoided with DIRA using the (water, bone) doublet for tissues and the (water, iodine) doublet for the iodine solution.

ACCURACY OF CT NUMBERS OBTAINED BY DIRA AND MONOENERGETIC PLUS ALGORITHMS IN DUAL-ENERGY COMPUTED TOMOGRAPHY.

Dual-energy computed tomography (CT) can be used in radiotherapy treatment planning for the calculation of absorbed dose distributions. The aim of this work is to evaluate whether there is room for improvement in the accuracy of the Monoenergetic Plus algorithm by Siemens Healthineers. A Siemens SOMATOM Force scanner was used to scan a cylindrical polymethyl methacrylate phantom with four rod-inserts made of different materials. Images were reconstructed using ADMIRE and processed with Monoenergetic Plus. The resulting CT numbers were compared with tabulated values and values simulated by the proof-of-a-concept algorithm DIRA developed by the authors. Both the Monoenergetic Plus and DIRA algorithms performed well; the accuracy of attenuation coefficients was better than about ±1% at the energy of 70 keV. Compared with DIRA, the worse performance of Monoenergetic Plus was caused by its (i) two-material decomposition to iodine and water and (ii) imperfect suppression of the beam hardening artifact in ADMIRE.

ON THE POSSIBILITY TO RESOLVE GADOLINIUM- AND CERIUM-BASED CONTRAST AGENTS FROM THEIR CT NUMBERS IN DUAL-ENERGY COMPUTED TOMOGRAPHY.

Cerium oxide nanoparticles with integrated gadolinium have been proved to be useful as contrast agents in magnetic resonance imaging. Of question is their performance in dual-energy computed tomography. The aims of this work are to determine (1) the relation between the computed tomography number and the concentration of the I, Gd or Ce contrast agent and (2) under what conditions it is possible to resolve the type of contrast agent. Hounsfield values of iodoacetic acid, gadolinium acetate and cerium acetate dissolved in water at molar concentrations of 10, 50 and 100 mM were measured in a water phantom using the Siemens SOMATOM Definition Force scanner; gadolinium- and cerium acetate were used as substitutes for the gadolinium-integrated cerium oxide nanoparticles. The relation between the molar concentration of the I, Gd or Ce contrast agent and the Hounsfield value was linear. Concentrations had to be sufficiently high to resolve the contrast agents.

Impact of theI-value of diamond on the energy deposition in different beam qualities.

Diamond detectors are increasingly employed in dosimetry. Their response has been investigated by means of Monte Carlo (MC) methods, but there is no consensus on what mass densityρ, mean excitation energyIand number of conduction electrons per atomnceto use in the simulations. The ambiguity occurs due to its seeming similarity with graphite (both are carbon allotropes). Except for the difference inρbetween crystalline graphite (2.265 g cm-3) and diamond (3.515 g cm-3), their dielectric properties are assumed to be identical. This is incorrect, and the two materials should be distinguished: (ρ= 2.265 g cm-3,I= 81.0 eV,nce= 1) for graphite and (ρ= 3.515 g cm-3,I= 88.5 eV,nce= 0) for diamond. Simulations done with the MC codepenelopeshow that the energy imparted in diamond decreases by up to 1% with respect to 'pseudo-diamond' (ρ= 3.515 g cm-3,I= 81.0 eV,nce= 0) depending on the beam quality and cavity thickness. The energy imparted changed the most in cavities that are small compared with the range of electrons. The difference in the density-effect term relative to graphite was the smallest for diamond owing to an interplay effect thatρ,Iandncehave on this term, in contrast to pseudo-diamond media when eitherρorIalone were adjusted. The study also presents a parameterized density-effect correction function for diamond that may be used by MC codes like EGSnrc. Theestarprogram assumes thatnce= 2 for all carbon-based materials, hence it delivers an erroneous density-effect correction term for graphite and diamond. Despite the small changes of the energy imparted in diamond simulated with two differentIvalues and expected close-to-negligible deviation from the published small-field output correction data, it is important to pay attention to material properties and model the medium faithfully.

Experimental assessment of a phosphor model for estimating the relative extrinsic efficiency in radioluminescent detectors.

Optimising phosphor screens in dose detectors or imaging sensor designs is a cumbersome and time- consuming work normally involving specialised measuring equipment and advanced modelling. It is known that crucial optical parameters of the same phosphor may vary within a wide range of values. The aim of this work was to experimentally assess a simple previously published model where the case specific optical parameters (scattering and absorption) are instead represented by a fixed, single parameter, the light extinction factor, ξ. The term extrinsic efficiency, N, of a phosphor is also introduced, differing from the common denotation "absolute efficiency", after noting that unknown factors (such as temperature dependence) can have an influence during efficiency estimations and hence difficult to claim absoluteness. N is expressed as the ratio of light energy emitted per unit area at the phosphor surface to incident x-ray energy fluence. By focusing on ratios and relative changes in this study, readily available instruments in a Medical Physics Department (i.e. a photometer) could be used. The varying relative extrinsic efficiency for an extended range of particle sizes (7.5 and 25 µm) and layer thicknesses (220 to 830 µm) were calculated in the model from the input parameters: the mean particle size of the phosphor, the layer thickness, the light extinction factor and the calculated energy imparted to the layer. In-house manufactured screens (Gd2O2S:Tb) were used for better control of design parameters. The model provided good qualitative agreement to experiment with quantitative deviations in relative extrinsic efficiency within approximately 2%.

Segmentation of bones in medical dual-energy computed tomography volumes using the 3D U-Net.

Deep learning algorithms have improved the speed and quality of segmentation for certain tasks in medical imaging. The aim of this work is to design and evaluate an algorithm capable of segmenting bones in dual-energy CT data sets. A convolutional neural network based on the 3D U-Net architecture was implemented and evaluated using high tube voltage images, mixed images and dual-energy images from 30 patients. The network performed well on all the data sets; the mean Dice coefficient for the test data was larger than 0.963. Of special interest is that it performed better on dual-energy CT volumes compared to mixed images that mimicked images taken at 120 kV. The corresponding increase in the Dice coefficient from 0.965 to 0.966 was small since the enhancements were mainly at the edges of the bones. The method can easily be extended to the segmentation of multi-energy CT data.

Investigation of a synthetic diamond detector response in kilovoltage photon beams.

PURPOSE: An important characteristic of radiation dosimetry detectors is their energy response which consists of absorbed-dose and intrinsic energy responses. The former can be characterized using Monte Carlo (MC) simulations, whereas the latter (i.e., detector signal per absorbed dose to detector) is extracted from experimental data. Such a characterization is especially relevant when detectors are used in nonrelative measurements at a beam quality that differs from the calibration beam quality. Having in mind the possible application of synthetic diamond detectors (microDiamond PTW 60019, Freiburg, Germany) for nonrelative dosimetry of low-energy brachytherapy (BT) beams, we determined their intrinsic and absorbed-dose energy responses in 25-250 kV beams relative to a 60 Co beam, which is usually the reference beam quality for detector calibration in radiotherapy. MATERIAL AND METHODS: Three microDiamond detectors and, for comparison, two silicon diodes (PTW 60017) were calibrated in terms of air-kerma free in air in six x-ray beam qualities (from 25 to 250 kV) and in terms of absorbed dose to water in a 60 Co beam at the national metrology laboratory in Sweden. The PENELOPE/penEasy MC radiation transport code was used to calculate the absorbed-dose energy response of the detectors (modeled based on blueprints) relative to air and water depending on calibration conditions. The MC results were used to extract the relative intrinsic energy response of the detectors from the overall energy response. Measurements using an independent setup with a single ophthalmic BEBIG I25.S16 125 I BT seed (effective photon energy of 28 keV) were used as a qualitative check of the extracted intrinsic energy response correction factors. Additionally, the impact of the thickness of the active volume as well as the presence of extra-cameral components on the absorbed-dose energy response of a microDiamond detector was studied using MC simulations. RESULTS: The relative intrinsic energy response of the microDiamond detectors was higher by a factor of 2 in 25 and 50 kV beams compared to the 60 Co beam. The variation in the relative intrinsic energy response of silicon diodes was within 10% over the investigated photon energy range. The use of relative intrinsic energy response correction factors improved the agreement among the absorbed dose to water values determined using microDiamond detectors and silicon diodes, as well as with the TG-43 formalism-based calculations for the 125 I seed. MC study of microDiamond detector design features provided a possible explanation for inter-detector response variation at low-energy photon beams by differences in the effective thickness of the active volume. CONCLUSIONS: MicroDiamond detectors had a non-negligible variation in the relative intrinsic energy response (factor of 2) which was comparable to that in the absorbed-dose energy response relative to water at low-energy photon beams. Silicon diodes, in contrast, had an absorbed-dose energy dependence on photon energy that varied by a factor of 6, whereas the intrinsic energy dependence on beam quality was within 10%. It is important to decouple these two responses for a full characterization of detector energy response especially when the user and reference beam qualities differ significantly, and MC alone is not enough.

6-MV small field output factors: intra-/intermachine comparison and implementation of TRS-483 using various detectors and several linear accelerators.

PURPOSE: To investigate the applicability of output correction factors reported in TRS-483 on 6-MV small-field detector-reading ratios using four solid-state detectors. Also, to investigate variations in 6-MV small-field output factors (OF) among nominally matched linear accelerators (linacs). METHODS: The TRS-483 Code of Practice (CoP) introduced and provided output correction factors to be applied to measured detector-reading ratios to obtain OFs for several small-field detectors. Detector readings for 0.5 cm × 0.5 cm to 8 cm × 8 cm fields were measured and normalized to that of 10 cm × 10 cm field giving the detector-reading ratios. Three silicon diodes, IBA PFD, IBA EFD (IBA, Schwarzenbruck, Germany), PTW T60017, and one microdiamond, PTW T60019 (PTW, Freiburg, Germany), were used. Output correction factors from the CoP were applied to measured detector-reading ratios. Measurements were performed on six Clinac and six TrueBeam linacs (Varian Medical Systems, Palo Alto, USA). An investigation of the relationship between the size of small fields and corresponding detector-reading ratio among the linacs was performed by measuring lateral dose profiles for 0.5 cm × 0.5 cm fields to determine the full width half maximum (FWHM). The relationship between the linacs' focal spot size and the small-field detector-reading ratio was investigated by measuring 10 cm × 10 cm lateral dose profiles and determining the penumbra width reflecting the focal spot size. Measurement geometry was as follows: gantry angle = 0°, collimator angle = 0°, source-to surface distance (SSD) = 90 cm, and depth in water = 10 cm. RESULTS: For a given linac and 0.5 cm × 0.5 cm field, the deviations in detector-reading ratios among the detectors were 9%-15% for the Clinacs and 4%-5% for the TrueBeams. Use of output correction factors reduced these deviations to 6%-12% and 3%-4%, respectively. For field sizes equal to or larger than 0.8 cm × 0.8 cm, the deviations were corrected to 1% using output correction factors for both Clinacs and TrueBeams. For a given detector and 0.5 cm × 0.5 cm field, the deviations in detector-reading ratios among the linacs were 11%-17% for the Clinacs and 5-6% for the TrueBeams. For 1 cm × 1 cm the deviations were 1%-2% for Clinacs and 1% for TrueBeams. For field sizes larger than 1 cm × 1 cm the deviations were within 1% for both Clinacs and TrueBeams. No relationship between FWHMs and detector-reading ratios for 0.5 cm × 0.5 cm was observed. For Clinacs, larger 10 cm × 10 cm penumbra width yielded lower 0.5 cm × 0.5 cm detector-reading ratio indicating an effect of the focal spot size. For TrueBeams, the spread of penumbra widths was lower compared to Clinacs and no similar relationship was observed. CONCLUSIONS: Output correction factors from the TRS-483 CoP are not sufficient for accurate determination of OF for 0.5 cm × 0.5 cm fields but are applicable for 0.8 cm × 0.8 cm to 8 cm × 8 cm fields. Nominally matched Clinacs and TrueBeams show large differences in detector-reading ratios for fields smaller than 1 cm × 1 cm.

An extended dose-volume model in high dose-rate brachytherapy - Using mean-tail-dose to reduce tumor underdosage.

PURPOSE: High dose-rate brachytherapy is a method of radiotherapy for cancer treatment in which the radiation source is placed within the body. In addition to give a high enough dose to a tumor, it is also important to spare nearby healthy organs [organs at risk (OAR)]. Dose plans are commonly evaluated using the so-called dosimetric indices; for the tumor, the portion of the structure that receives a sufficiently high dose is calculated, while for OAR it is instead the portion of the structure that receives a sufficiently low dose that is of interest. Models that include dosimetric indices are referred to as dose-volume models (DVMs) and have received much interest recently. Such models do not take the dose to the coldest (least irradiated) volume of the tumor into account, which is a distinct weakness since research indicates that the treatment effect can be largely impaired by tumor underdosage even to small volumes. Therefore, our aim is to extend a DVM to also consider the dose to the coldest volume. METHODS: An improved DVM for dose planning is proposed. In addition to optimizing with respect to dosimetric indices, this model also takes mean dose to the coldest volume of the tumor into account. RESULTS: Our extended model has been evaluated against a standard DVM in ten prostate geometries. Our results show that the dose to the coldest volume could be increased, while also computing times for the dose planning were improved. CONCLUSION: While the proposed model yields dose plans similar to other models in most aspects, it fulfils its purpose of increasing the dose to cold tumor volumes. An additional benefit is shorter solution times, and especially for clinically relevant times (of minutes) we show major improvements in tumour dosimetric indices.

GEC-ESTRO ACROP recommendations on calibration and traceability of LE-LDR photon-emitting brachytherapy sources at the hospital level.

Prostate brachytherapy treatment using permanent implantation of low-energy (LE) low-dose rate (LDR) sources is successfully and widely applied in Europe. In addition, seeds are used in other tumour sites, such as ophthalmic tumours, implanted temporarily. The calibration issues for LE-LDR photon emitting sources are specific and different from other sources used in brachytherapy. In this report, the BRAPHYQS (BRAchytherapy PHYsics Quality assurance System) working group of GEC-ESTRO, has developed the present recommendations to assure harmonized and high-quality seed calibration in European clinics. There are practical aspects for which a clarification/procedure is needed, including aspects not specifically accounted for in currently existing AAPM and ESTRO societal recommendations. The aim of this report has been to provide a European wide standard in LE-LDR source calibration at end-user level, in order to keep brachytherapy treatments with high safety and quality levels. The recommendations herein reflect the guidance to the ESTRO brachytherapy users and describe the procedures in a clinic or hospital to ensure the correct calibration of LE-LDR seeds.

Suitability of microDiamond detectors for the determination of absorbed dose to water around high-dose-rate 192 Ir brachytherapy sources.

PURPOSE: Experimental dosimetry of high-dose-rate (HDR) 192 Ir brachytherapy (BT) sources is complicated due to high dose and dose-rate gradients, and softening of photon energy spectrum with depth. A single crystal synthetic diamond detector microDiamond (PTW 60019, Freiburg, Germany) has a small active volume, high sensitivity, direct readout, and nearly water-equivalent active volume. The purpose of this study was to evaluate the suitability of microDiamond detectors for the determination of absorbed dose to water around HDR 192 Ir BT sources. Three microDiamond detectors were used, allowing for the comparison of their properties. METHODS: In-phantom measurements were performed using microSelectron and VariSource iX HDR 192 Ir BT treatment units. Their treatment planning systems (TPSs), Oncentra (v. 4.3) and BrachyVision (v. 13.6), respectively, were used to create irradiation plans for a cubic PMMA phantom with the microDiamond positioned at one of three source-to-detector distances (SDDs) (1.5, 2.5, and 5.5 cm) at a time. The source was stepped in increments of 0.5 cm over a total length of 6 cm to yield absorbed dose of 2 Gy at the nominal reference-point of the detector. Detectors were calibrated in 60 Co beam in terms of absorbed dose to water, and Monte Carlo (MC) calculated beam quality correction factors were applied to account for absorbed-dose energy dependence. Phantom correction factors were applied to account for differences in dimensions between the measurement phantom and a water phantom used for absorbed dose calculations made with a TPS. The same measurements were made with all three of the detectors. Additionally, dose-rate dependence and stability of the detectors were evaluated in 60 Co beam. RESULTS: The percentage differences between experimentally determined and TPS-calculated absorbed doses to water were from -1.3% to +2.9%. The values agreed to within experimental uncertainties, which were from 1.9% to 4.3% (k = 2) depending on the detector, SDD and treatment delivery unit. No dose-rate or intrinsic energy dependence corrections were applied. All microDiamonds were comparable in terms of preirradiation dose, stability of the readings and energy response, and showed a good agreement. CONCLUSIONS: The results indicate that the microDiamond is potentially suitable for the determination of absorbed dose to water around HDR 192 Ir BT sources and may be used for independent verification of TPS's calculations, as well as for QA measurements of HDR 192 Ir BT treatment delivery units at clinical sites.

Experience of using MOSFET detectors for dose verification measurements in an end-to-end 192Ir brachytherapy quality assurance system.

PURPOSE: Establishment of an end-to-end system for the brachytherapy (BT) dosimetric chain could be valuable in clinical quality assurance. Here, the development of such a system using MOSFET (metal oxide semiconductor field effect transistor) detectors and experience gained during 2 years of use are reported with focus on the performance of the MOSFET detectors. METHODS AND MATERIALS: A bolus phantom was constructed with two implants, mimicking prostate and head & neck treatments, using steel needles and plastic catheters to guide the 192Ir source and house the MOSFET detectors. The phantom was taken through the BT treatment chain from image acquisition to dose evaluation. During the 2-year evaluation-period, delivered doses were verified a total of 56 times using MOSFET detectors which had been calibrated in an external 60Co beam. An initial experimental investigation on beam quality differences between 192Ir and 60Co is reported. RESULTS: The standard deviation in repeated MOSFET measurements was below 3% in the six measurement points with dose levels above 2 Gy. MOSFET measurements overestimated treatment planning system doses by 2-7%. Distance-dependent experimental beam quality correction factors derived in a phantom of similar size as that used for end-to-end tests applied on a time-resolved measurement improved the agreement. CONCLUSIONS: MOSFET detectors provide values stable over time and function well for use as detectors for end-to-end quality assurance purposes in 192Ir BT. Beam quality correction factors should address not only distance from source but also phantom dimensions.

On the Monte Carlo simulation of small-field micro-diamond detectors for megavoltage photon dosimetry.

Monte Carlo (MC) calculated detector-specific output correction factors for small photon beam dosimetry are commonly used in clinical practice. The technique, with a geometry description based on manufacturer blueprints, offers certain advantages over experimentally determined values but is not free of weaknesses. Independent MC calculations of output correction factors for a PTW-60019 micro-diamond detector were made using the EGSnrc and PENELOPE systems. Compared with published experimental data the MC results showed substantial disagreement for the smallest field size simulated ([Formula: see text] mm). To explain the difference between the two datasets, a detector was imaged with x rays searching for possible anomalies in the detector construction or details not included in the blueprints. A discrepancy between the dimension stated in the blueprints for the active detector area and that estimated from the electrical contact seen in the x-ray image was observed. Calculations were repeated using the estimate of a smaller volume, leading to results in excellent agreement with the experimental data. MC users should become aware of the potential differences between the design blueprints of a detector and its manufacturer production, as they may differ substantially. The constraint is applicable to the simulation of any detector type. Comparison with experimental data should be used to reveal geometrical inconsistencies and details not included in technical drawings, in addition to the well-known QA procedure of detector x-ray imaging.