Out-of-field beam characteristics of a 6 MV photon beam: Results of a Monte Carlo study

Detailed characteristics of particles in the periphery of a 6 MV photon beam resulting from the exposure of a water phantom were analyzed. The characteristics at the periphery were determined with respect to particles’ origin and charge, using Monte Carlo simulations. Results showed that in the peripheral regions, the energy fluence and the mean energy distribution of particles are independent of depth, and the majority of charged particles originate in the irradiated volume. The results are used to examine out-of-field dosimetry factors

Design of a generally applicable abdominal shield for reducing fetal dose during radiotherapy of common malignancies in pregnant patients

Background: In most cancer cases, the treatment choice for a pregnant patient is radiotherapy. In these patients, the abdomen is usually not exposed; therefore fetus exposure is due to peripheral dose (PD). The purpose of this study was to estimate the fetal dose (the maximum PD in each pregnancy stage) for modalities available and to fabricate and evaluate a generally applicable fetal shield. Materials and Methods: PD values were measured for brain, breast and mediastinum irradiation in a whole body anthropomorphic phantom using a NE 2571 ionization chamber. An external shield was then designed to reduce the fetal dose to the standard dose limit, 5 mSv. Results: The range of PD values as a function of distance from the field’s edge were as follows 1) 9.4-259 cGy for Mantel field; 2) 6.5-95 cGy for chest wall irradiation with 10 MeV electrons, 3) 8.5- 52.5 cGy for tangential field with Co-60 and 4) 4.8-7.8 cGy for brain radiotherapy with 9 MV photon. PD values for the same setups using the fetal shield were as follows: 1) 1.4-22 cGy, 2) 0.5-4 cGy, 3) 1.5-5 cGy and 4) under 1 cGy. Conclusions: The measured PD data sets can be used to estimate fetal dose for specific treatment setups and pregnancy stages. The use of external shield designed in this research reduced the fetal dose effectively to under the threshold (a 70-90% reduction), except for the final stages of pregnancy in Hodgkin’s patients

Design and Implementation of a Monte Carlo Framework for Assessment of Spoiler Applications in Abutting Electron Fields

Background: Field matching problems in abutting electron fields can be man-aged by using spoilers. Objective: The aim of this study was to design a Monte Carlo framework for the assessment of spoiler application in abutting electron fields. Material and Methods: In this experimental study, a Siemens Primus treatment head was simulated for a 5 MeV electron beam using BEAMnrc, DOSXYZnrc and EGSnrc user codes. Validation of beam model was done by measurement using a MP3-M water tank and a Semi-flex Chamber-31010 (PTW, Freiburg, Germany). An in-house routine was developed to calculate the combined isodose curves result-ing from simulated adjacent fields. The developed framework was analyzed using PMMA and chromium spoilers. Results: The penumbra width increased from 27.5 mm for open fields to 42 mm for PMMA and 40 mm for chromium. The maximum junction dose reduced from 115% for open fields to 107% for PMMA and 108% for chromium. R90 reduced about 6 mm for PMMA and 3 mm for chromium. Uniformity index reduced from 93% to 77% for both spoilers. Surface dose increased from 79% to 89% for PMMA and 88% for chromium. Conclusion: Using spoilers, penumbra width at the surface was increased, size and depth of hot spots as well as the therapeutic range were reduced and dose homo-geneity at the junction of abutting electron fields was improved. For both spoilers, the uniformity index reduced, and surface percent dose increased. The results of this research can be used to optimize dose distribution in electron beam treatment using abutting fields

Evaluation of Therapeutic Properties of a Low Energy Electron Beam Plus Spoiler for Local Treatment of Mycosis Fungoides: A Monte Carlo Study

Background: When using low-energy electron beams for the treatment of skin lesions, such as Mycosis Fungoides (MF), a beam spoiler is used to decrease electron therapeutic depth (R90) while increasing the surface dose. Objective: The aim of this study was to evaluate the characteristics of a 5 MeV electron beam when using a spoiler for the local treatment of MF skin lesions by Monte Carlo (MC) simulation. Methods: A Siemens Primus treatment head and an acrylic spoiler, positioned at the end of applicator, were simulated using BEAMnrc, an EGSnrc user code. The modelled beam was validated by measurement using MP3-M water tank, Roos parallel plate chamber and Semi flex Chamber-31013 (all from PTW, Freiburg, Germany). For different spoiler thicknesses, dose distributions in water were calculated for 2 field sizes and were compared to those for the corresponding open fields. Results: For a 1.3 cm spoiler, therapeutic range changed from 1.5 cm (open field) to 0.5 cm and 0.4 cm for 10 × 10 cm2 and 20 × 20 cm2 field sizes, respectively. Maximum increase in penumbra width was 2.8 and 3.8 cm for 10 × 10 cm2 and 20 × 20 cm2 field sizes, respectively. Maximum increase in bremsstrahlung contamination was %2 in both field sizes. Conclusion: R90 decreased exponentially with increase in spoiler thickness. The effect of field size on penumbra was much larger for spoiled beam compared to the open beam. The results of this research can be applied to optimize the radiation treatment of MF patients in our hospital

Measurement of Collimator Scatter Factor for Photon Fields Using Gafchromic EBT2 Film and Ion Chamber

Background and Objective: In radiotherapy, measurement of the output factor in the air is one of the input parameters for Implementation of treatment planning systems and beam modeling. The aim of this study is to design a mini-phantom and select the appropriate detector for measuring the output factor. Subjects and Methods: In-air output factor was measured for Siemens linear accelerator 6 MV energy and field sizes of 4, 6, 8, 10, 15, 2 cm irradiated by 200MU. Measurements were performed using a Gafchromic film EBT2 and 0.6 cc Farmer ion chamber and then the results were compared with Report of AAPM Therapy Physics Committee Task Group 74. For lateral electron equilibrium and electron contamination removal, two top of the water and Cerrobend were designed for film dosimetry and plexiglass buildup cap for Farmer chamber was applied. Results: The output factor increases with field size, and this increase in Cerrobend top is less than water top and Farmer dosimeter. In comparison between the results reported by TG74 and this study shows that film dosimetry with water top and Farmer chamber have 0.35 and 0.68 mean percentage differences with TG74 respectively and meanwhile the film dosimetry with Cerrobend top presents 1.48 mean percentage differences. Conclusion: EBT2 film with mini phantom made of water as a good alternative to ion chamber dosimeters known as a standard dosimeter especially the film can be used for a wider range of field size

Differential MicroRNA Expression Levels in Cutaneous Acute Graft-versus Host Disease

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) is a curative treatment for numerous haematological malignancies. However, acute graft-versus-host disease (aGvHD) is a major complication affecting 40-70% of all transplant patients, whereby the earliest and most frequent presentation is in the skin. MicroRNAs play a role in varied biological process and have been reported as potential biomarkers for aGvHD. More recently, microRNAs have received added attention as circulatory biomarkers that can be detected in biofluids. In the present study we performed global microRNA expression profiling using a discovery cohort of diagnostic cutaneous aGvHD biopsies (n=5, stage 1-3) and healthy volunteers (n=4), in order to identify a signature list of microRNAs that could be used as diagnostic biomarkers for cutaneous aGvHD. Candidate microRNAs (n=8) were then further investigated in a validation cohort of post-HSCT skin biopsies (n=17) for their association with aGvHD. Expression of miR-34a-5p (p<0.001), miR-34a-3p (p=0.013), miR-503-5p (p=0.021) and let-7c-5p (p=0.037) was elevated in cutaneous aGvHD and significantly associated with survival outcome (miR-34a-3p ROC AUC=0.93, p=0.003, Log Rank p=0.004; miR-503-5p ROC AUC=0.83 p=0.021, Log Rank p=0.003). There was no association with relapse. A statistical interaction between miR-34a-3p and miR-503-5p (p=0.016) was diagnostic for aGvHD. Expression levels of the miR-34a-5p protein target p53 were assessed in the epidermis of the skin, and an inverse correlation was identified (r2=0.44, p=0.039). Expression of the validated candidate microRNAs was also assessed at day 28 post-HSCT in the sera of transplant recipients, in order to investigate their potential as circulatory microRNA biomarkers. Expression of miR-503-5p (p=0.001), miR-34a-5p (p=0.005) and miR-34a-3p (p=0.004) were significantly elevated in the sera of patients who developed aGvHD vs. no-aGvHD (n=30) and miR-503-5p was associated with overall survival (ROC AUC=0.80, p=0.04, Log Rank p=0.041). In conclusion, this investigation reports that microRNA expression levels in clinical skin biopsies, obtained at the time of cutaneous aGvHD onset, show potential as diagnostic biomarkers for aGvHD and as predictive biomarkers for overall survival. Additionally, the same microRNAs can be detected in the circulation and show predictive association with post-HSCT outcomes

Research of changes of the instability of phase frequency characteristic of high-voltage divider of the pressure, connected with non-identity its elements

На основі проведення багаторазових вимірювань визначено реальний розподіл значень ємності конденсаторів високовольтного плеча подільника напруги з допуском відхилення від номіналу, рівним ±5%. Показано, що даний розподіл є асиметричним по відношенню до номінального значення (22нФ). Проведено перенормування отриманого розподілу по відношенню до середнього значення ємності конденсаторів. Досліджується вплив реального розподілу ємностей конденсаторів на нестабільність фазочастотної характеристики високовольтного подільника напруги. Показано, що вплив реального розподілу ємностей конденсаторів з допуском ± 5% на нестабільність ФЧХ подільника є менш вираженим по відношенню до закону нормального розподілу з середнім квадратичним відхиленням, що дорівнює ±5% . Обгрунтовується як прийнятний допуск на відхилення ємності конденсаторів високовольтного плеча ±5%. Зазвичай заданий допуск на відхилення ємностей ±10% призводить до значної нестабільності ФЧХ високовольтного подільника напруги.On the basis of repeated measurements a real distribution of capacity values of condensers of a high-voltage shoulder of a potential divider is defined with the assumed deviation from the nominal, which is equal to ±5%. It is shown that the given distribution is asymmetric in the relation to rating value (22nF). The renormalization of the received distribution was done in the relation to the average capacity value of condensers. The influence of real distribution of condensers capacities on instability of the phase frequency characteristic (PFC) of a high-voltage potential divider is being researched. It is shown that the influence of the real distribution of condensers capacities with the deviation ±5% on instability of PFC of a divider is less expressed in the relation to the law of normal distribution with an average quadratic deviation, equal to ±5%. A deviation of condensers capacity of a high-voltage shoulder ±5% is proved to be acceptable. Usually the set deviation of capacities ±10% leads to unacceptably high instability of PFC of a high-voltage potential divider.На основе проведения многократных измерений определено реальное распределение значений емкости конденсаторов высоковольтного плеча делителя напряжения с допуском отклонения от номинала, равным ±5%. Показано, что данное распределение является асимметричным по отношению к номинальному значению (22нФ). Проведена перенормировка полученного распределения по отношению к среднему значению емкости конденсаторов. Исследуется влияние реального распределения емкостей конденсаторов на нестабильность фазочастотной характеристики высоковольтного делителя напряжения. Показано, что влияние реального распределения емкостей конденсаторов с допуском ±5% на нестабильность ФЧХ делителя является менее выраженным по отношению к закону нормального распределения со средним квадратическим отклонением равным ±5%. Обосновывается в качестве приемлемого допуск на отклонение емкости конденсаторов высоковольтного плеча ±5%. Обычно задаваемый допуск на отклонение емкостей ±10% приводит к значительной нестабильности ФЧХ высоковольтного делителя напряжения

DOES IN VIVO LIGAMENT FORCE PASS THROUGH LIGAMENT INSERTIONS?: A ROBOTIC STUDY

INTRODUCTION Post traumatic osteoarthritis (PTOA) is a subset of osteoarthritis that arises after traumatic joint injury. Approximately half of patients suffering from anterior cruciate ligament (ACL) injuries have been shown to progress towards PTOA within fifteen years[1]. One of the areas of research for PTOA is examining the biomechanical changes following an ACL injury. A recent study[2] examined the effects of ACL transection (ACLx) in an ovine model. In vivo stifle joint motions were recorded, and recreated in vitro using a novel robotic testing platform. Joint and tissue loads were simultaneously recorded during reproduction of in vivo joint motion[2]. This novel approach was shown to be able to reproduce in vivo motions within less than 0.1° and 0.1mm[2].   The main objective of the present study was to determine if in vivo ligament forces, obtained using the principle of superposition, pass through respective ligament insertional footprints. This study evaluated the accuracy of the measured ligament forces, as they should pass through their bony insertions. This accuracy was examined for medial and lateral collateral ligaments (MCL and LCL), and posterior cruciate ligament (PCL) in ACLx sheep.   METHODS Stifle joints from N=4 sheep that had been previously examined in ACLx kinematics studies were digitized using a coordinate measuring machine. The ligament insertional areas were thoroughly recreated in 3D space, along with the spatial position of the kinematic measurement device. Anatomic coordinate systems were defined on the femur and the tibia. These data were then exported to MATLAB scripts for further analysis. The ligament insertional areas were approximated as planes using least squares regression technique. The intersection of the ligament force vectors with the plane approximations were then calculated. The direction of a ligament force was deemed accurate if the distance between the calculated intersection and footprint centroid was within a determined threshold. A preliminary threshold was calculated as the maximum distance between the centroid and measured points of the footprint. RESULTS Analysis of the data indicated that the technique increases in accuracy for high ligament loads (Figure 1). That is to say as the ligament loads increase, the intersection-centroid distance is reduced. For lower ligament loads (mainly within the “toe” region of the ligament force-displacement behavior), however, the method requires further refinement. DISCUSSION AND CONCLUSIONS This study indicated that the method requires further refinement based on the limitations induced currently. Preliminary data shows that accuracy increases as ligament load magnitudes increase as well. Finding the intersections on plane approximations of the insertional footprints can lead to very large error when the planes approach a parallel state. In these states, a small angular change in force direction can cause a very large change in intersection-centroid distance. Each ligament and its insertions have different functions and geometries, and as such require separate limitations. Future studies would require modifications to the analysis method to account for the limitations involved with the current method