Skin Distance Research Articles

The usefulness of F-18 FDG PET/CT-mammography for preoperative staging of breast cancer: comparison with conventional PET/CT and MR-mammography

BackgroundThe objective of the study was to compare the diagnostic efficacy of an integrated Fluorine-18 fluorodeoxyglucose (F-18 FDG) PET/CT-mammography (mammo-PET/CT) with conventional torso PET/CT (supine-PET/CT) and MR-mammography for initial assessment of breast cancer patients.Patients and methodsForty women (52.0 ± 12.0 years) with breast cancer who underwent supine-PET/CT, mammo-PET/CT, and MR-mammography from April 2009 to August 2009 were enrolled in the study. We compared the size of the tumour, tumour to chest wall distance, tumour to skin distance, volume of axillary fossa, and number of meta-static axillary lymph nodes between supine-PET/CT and mammo-PET/CT. Next, we assessed the difference of focality of primary breast tumour and tumour size in mammo-PET/CT and MR-mammography. Histopathologic findings served as the standard of reference.ResultsIn the comparison between supine-PET/CT and mammo-PET/CT, significant differences were found in the tumour size (supine-PET/CT: 1.3 ± 0.6 cm, mammo-PET/CT: 1.5 ± 0.6 cm, p < 0.001), tumour to thoracic wall distance (1.8 ± 0.9 cm, 2.2 ± 2.1 cm, p < 0.001), and tumour to skin distance (1.5 ± 0.8 cm, 2.1 ± 1.4 cm, p < 0.001). The volume of axillary fossa was significantly wider in mammo-PET/CT than supine-PET/CT (21.7 ± 8.7 cm3 vs. 23.4 ± 10.4 cm3, p = 0.03). Mammo-PET/CT provided more correct definition of the T-stage of the primary tumour than did supine-PET/CT (72.5% vs. 67.5%). No significant difference was found in the number of metastatic axillary lymph nodes. Compared with MR-mammography, mammo-PET/CT provided more correct classification of the focality of lesion than did MR-mammography (95% vs. 90%). In the T-stage, 72.5% of cases with mammo-PET/CT and 70% of cases with MR-mammography showed correspondence with pathologic results.ConclusionsMammo-PET/CT provided more correct definition of the T-stage and evaluation of axillary fossa may also be delineated more clearly than with supine-PET/CT. The initial assessment of mammo-PET/CT would be more useful than MR-mammography because the mammo-PET/CT indicates similar accuracy with MR-mammography for decision of T-stage of primary breast tumour and more correct than MR-mammography for defining focality of lesion.

Outcomes of intracorporeal lithotripsy of upper tract stones is not affected by BMI and skin-to-stone distance (SSD) in obese and morbid patients

The purpose of this study is to determine if body mass index (BMI) and stone skin distance (SSD) affect stone free rate (SFR) in obese and morbid obese patients who underwent flexible URS for proximal ureteral or renal stones < 20 mm. A retrospective chart review was performed of consecutive patients that underwent flexible URS. Inclusion criteria were: proximal ureteral stones and renal stones less than 20 mm in the preoperative computed tomography (CT). SFR were then compared according to SSD and BMI. A total of 153 patients were eligible for this analysis, 49 (32.02%) with SSD < 10 cm and 104 (67.97%) with SSD ≥ 10 cm. The mean stone size was 10.5 ± 6.4 mm. The overall SFR in our study was 82.4%. The SFR for the SSD < 10 and ≥ 10 were 79.6% and 83.7% respectively (p = 0.698) and for BMI < 30, ≥ 30 and < 40 and ≥ 40 were 82.9%, 81.7% and 90.9% respectively. Regression analysis showed no affect between BMI or SSD regarding SFR. Ureteroscopy should be considered as a first-line of treatment for renal/proximal stones in obese and morbid obese patients. URS may be preferable to SWL in obese patients independently of the SSD, BMI or the location of proximal stones.

Supracondylar humeral fractures in children

Supracondylar humeral fractures are common in children, but there are no classification systems or radiological parameters that predict the likelihood of having to perform an open reduction. In a retrospective case-control study we evaluated the use of the medial spike angle and fracture tip-skin distance to predict the mode of reduction (closed or open) and the operating time in fractures with posterolateral displacement. A total of 21 patients (4.35%) with a small medial spike angle (< 45°) were identified from a total of 494 patients, and 42 patients with a medial spike angle of > 45° were randomly selected as controls. The medial spike group had significantly smaller fracture tip-skin distances (p < 0.001), longer operating times (p = 0.004) and more complications (p = 0.033) than the control group. There was no significant difference in the mode of reduction and a composite outcome measure. After adjustments for age and gender, only fracture tip-skin distance remained significantly associated with the operating time (β = -0.724, p = 0.042) and composite outcome (OR 0.863 (95% confidence interval 0.746 to 0.998); p = 0.048). Paediatric orthopaedic surgeons should have a lower threshold for open reduction when treating patients with a small medial spike angle and a small fracture tip-skin distance.

Pseudo-Verlet lists: a new, compact neighbour list representation

Verlet lists, or neighbour lists, are a popular device to speed up the computation of non-bonded interactions in molecular dynamics and other particle-based simulations, in which a list of interacting particles for a given geometry is computed once and reused over several time steps until the geometry changes significantly. The size of the Verlet list is generally indices in the range , where N is the total number of particles, ρN is the particle number density and rc and rs are the cutoff and skin distances, respectively. Due to their memory requirements, Verlet lists are not always an optimal choice on multi-core or graphics processing unit systems in which the memory bandwidth per core is limited. This paper introduces pseudo-Verlet lists, an alternative neighbour list representation which requires only 13N indices in the range , thus requiring less storage, and resulting in better cache reuse.

Impact of various color LED flashlights and different lighting source to skin distances on the manual and the computer‐aided detection of basal cell carcinoma borders

Quantitative analysis based on digital skin image has been proven to be helpful in dermatology. Moreover, the borders of the basal cell carcinoma (BCC) lesions have been challenging borders for the automatic detection methods. In this work, a computer-aided dermatoscopy system was proposed to enhance the clinical detection of BCC lesion borders. Fifty cases of BCC were selected and 2000 pictures were taken. The lesion images data were obtained with eight colors of flashlights and in five different lighting source to skin distances (SSDs). Then, the image-processing techniques were used for automatic detection of lesion borders. Further, the dermatologists marked the lesions on the obtained photos. Considerable differences between the obtained values referring to the photographs that were taken at super blue and aqua green color lighting were observed for most of the BCC borders. It was observed that by changing the SSD, an optimum distance could be found where that the accuracy of the detection reaches to a maximum value. This study clearly indicates that by changing SSD and lighting color, manual and automatic detection of BCC lesions borders can be enhanced.

SU‐E‐J‐51: Effect of Exactrac 6D Correction On Dose for SRT Patients with IR Body Markers

Purpose: To study the 6D correction efficacy on dose to the target due to infrared(IR) body marker localization for stereotactic radiotherapy(SRT) patients Methods: Commercially available laboratory skull phantom, made of plastic is used in this study.It is filled with physiotherapy wax and a provision is made to insert CC13 ion‐chamber(0.13cc). The dose at a point in skull phantom is measured by CC13 ion‐chamber.An ordinary thermoplastic mould is prepared for skull phantom and 5 infrared body markers are placed at different places for localization as shown in figA. CT scan of the phantom is obtained using Siemens PET‐CT scanner with and without ion‐chamber. Treatment Planning is done on images which are without ion chamber .In the absence of ion chamber to fill the cavity a wax insert is inserted during the CT scan. 3mm slice thickness are obtained and imported to Eclipse treatment planning system(TPS) for contouring and planning.Treatment plans of 3D CRT/IMRT are planned in Eclipse on skull phantom images with isocenter placed at the chamber sensitive volume.The plan is exported to Exactrac imaging system for localization and verification. After setup of skull phantom imaging is done with exactrac stereoscopic imaging system and the 6D shifts (Vertical,logitudenal,lateral,yaw,pitch,roll) are applied. The focus to skin distance(FSD) is noted‐Table1.The radiation dose is delivered in Varian Novalis Tx.The charge collected /dose in CC13 ion chamber is noted from the DOSE1 electrometer‐Table2.The planned FSD and dose are noted from TPS. Results: The mean difference between planned and measured FSD and Dose are 0.55cm and 2.7% respectively. The mean SD of FSD and Dose are 0.383 and 1.58% respectively. Conclusion: Even though Exactrac‐6D couch shifts introduce change in FSD by 1–1.5cm the dose difference is within the range of 3% and is reasonable to treat frame less SRT treatments with IR body markers with ordinary mask.

SU-E-P-18: Patient Dose Assessment for Common Digital Diagnostic Radiology Examination in Qatar

Purpose: The aim of this study was to estimate radiation doses to patients undergoing standard radiographic examinations using Computed Radiography and Direct Digital Radiography in two hospitals within Hamad Medical Corporation in Qatar and compared with regional and international DRLs. Methods: Data on 3391 patients were recorded from deferent X‐ray HMC hospital to provide information on Qatar patient demographic information. Entrance Skin Dose (ESD) was measured for 1046 patients for the most five common X‐ray examinations (a total of 7 projections) namely: Skull, Chest, Abdomen, Lumbar Spine and Pelvis. Exposure factors such as kV, mAs and Focal to Skin Distance (FSD) were recorded for each patient. Tube Output was measured for a range of selected kV values. ESD for each individual patient was calculated using the tube output and the technical exposure factors for each examination. Results: HMC patient demographic data evaluated from this study were: average age of 39 years, mean weight of 74 kg and mean height of 165 cm. in Qatar state. The most performed procedure during the time of this study was chest PA (52%), and the least procedure performed was skull AP/LAT (1%) examination. The mean ESD values found to be generally lower than the published values. With exception of abdomen examinations at HGH hospital, mean ESD values were found to be within the established IAEA (DRL). Conclusion: The mean ESD values at HGH were found to be much higher than that at AKH for abdomen, Lumber spine AP, Lumber Spine LAT and pelvis. The mean ESD values obtained in this was compared with values from the literature and found to be generally lower than the published values. The results will be used to optimize patient doses in all HMC and can be used with more data from other private clinics to establish national dose reference levels for Qatar.

SU‐E‐T‐219: Illustration of Electron Beam Loss of Field Edge Fidelity (Beam Shape) and Uniformity with Air Gap

Purpose: Clinical use of electron beams frequently involves elaborate field shapes and/or matching of edges with adjacent poton fields. Treatment on accasion requires an extended Source Skin Distance (SSD). The optical projection of the field shape on the patient at the extended SSD does not depict the impact of the increased distance on shape and uniformity. The purpose of this presentation is to illustrate some examples of the impact Methods: Shape and dosimetric quantities measured on films exposed cross‐beam at 1 cm depth in plastic water at standard and extended SSD are compared with optical projections of shape and TPS calculations of dosimetric quantities. Results: Small field sizes of low energy electron beams have a small Effective SSD or f‐air and show a greater impact of extended distance on field shape and uniformity. For example, an f‐air value of 0.9 indicates that a net 10 percent of the beam directed towards the measurement point at the standard SSD is scattered away at the extended SSD. The scattering causes an outward bowing of straight edges, a rounding of sharp corners, loss of shape detail and a loss of uniformity of dose. Conclusion: When substantial departure from Inverse Square Law (ISL) is evident in extended SSD Electron Beam calculations it is advisable to evaluate the altered shape and uniformity so that clinical relevance can be judged. Substantial departure from ISL may mean more than a 5 or 10 percent departure from ISL or an air gap of more than 5 or 6 cm. Facilities ought to establish acceptable f‐air and air gap limits or action levels. Careful attention to minimizing air gaps as much as possible minimizes discrepancy between optically projected and actual shape and uniformity.

Negative effect of seroma on breast balloon brachytherapy dosimetry

PurposeBalloon brachytherapy is commonly used to deliver Accelerated Partial Breast Irradiation (APBI). Seroma interference is a relatively common phenomenon during APBI. The negative effect of seroma accumulation on the planning target volume evaluation (PTV_Eval) coverage is not well understood. Methods and MaterialsThis is a dosimetric replanning study on 10 patients with evidence of seroma collection at time of initial computed tomographic simulation around the catheter. Total dose was 34 Gy given at 3.4 Gy twice a day over 5 treatment days. A total of 20 plans were generated, 10 plans without accounting for and 10 after subtracting the seroma. We then compared the changes seen in PTV_Eval between plans as a factor of the seroma volume. ResultsMedian age was 62 years (51-83). Histology was invasive in 7/10 cases and in situ in 3/10. Median balloon to skin distance was 8.5 mm (3-14). Median balloon volume was 39 cc (30-104). Median seroma volume was 3.34 cc (1.13-13.71). For every 1 cc of accumulated seroma the percentage of PTV_Eval coverage by the 90% isodose line (V90) was found to decrease by 2.45% (P < .0001; confidence interval [CI], 1.87-3.03) and coverage by the 100% isodose line (V100) was decreased by 1.11% (P < .0001; CI, 0.81-1.41). Fifty percent (5/10) of previously acceptable plans with seroma not accounted for failed to meet the V90 ≥90% requirement after subtracting the seroma. ConclusionsAccumulation of seroma was associated with a considerable negative impact on PTV_Eval dosimetry with a greater impact on V90 compared with the V100. Clinicians must be careful in detecting and accounting for such accumulation in treatment plans to prevent underdosing of the at risk target breast tissue.

Monte Carlo optimization of total body irradiation in a phantom and patient geometry

The objective of this work is to apply a Monte Carlo (MC) accelerator model, validated by experimental data at isocentre distances, to a large-field total body irradiation (TBI) technique and to develop a strategy for individual patient treatment on the basis of MC dose distributions. Calculations are carried out using BEAMnrc/DOSXYZnrc code packages for a 15 MV Varian accelerator. Acceptable agreement is obtained between MC data and measurements in a large water phantom behind a spoiler at source–skin distances (SSD) = 460 cm as well as in a CIRS® thorax phantom. Dose distributions in patients are studied when simulating bilateral beam delivery at a distance of 480 cm to the patient central sagittal plane. A procedure for individual improvement of the dose uniformity is suggested including the design of compensators in a conventional treatment planning system (TPS) and a subsequent update of the dose distribution. It is demonstrated that the dose uniformity for the simple TBI technique can be considerably improved. The optimization strategy developed is straightforward and suitable for clinics where the TPS available is deficient to calculate 3D dose distributions at extended SSD.

Image-Guided Preoperative Intracavitary Brachytherapy and Taxan–Platinum Based Postperative Chemoradiation In Endometrial Cancer Patients with Poor Prognosis

This scan showedacceptable criterionofbeing less than 10%air of the PTVeval. Comparisons were then made in an attempt to correlate why there was increasing air during treatment. The following is the observed criterion for patient 1: left breast, balloon volume of 49.78cc, surgeon A, skin distance of 8.1mm, rib distance of 15.7mm, anteriorly angled lateral catheter placement, breast density of -93HU, 9 o’clock balloon position. The following is the observed criterion for patient 2: right breast, balloon volume of 43.2cc, surgeon B, skin distance of 5.0mm, rib distance of 10.2mm, straight lateral catheter placement, breast density of -105HU, 12 o’clock balloon position. From this criterion, there was no clear correlation between the two patients. Conclusions: Despite this study containing only two of twenty-two patients, it still provides insight as to how important the daily CT scan is before each treatment. It determines the air pocket volume andwhether or not to continue with the treatment. This study will be continued with other patients that accumulate more than 10% of air within the PTVeval and will be evaluated with the same format, hoping to determine some common factors.

Optimal wrist position for long and short axis ultrasound guided radial artery cannulation.

The radial artery is the most common site for arterial cannulation. Procedures for improving radial artery cannulation have involved direct visualization of the vessel with ultrasonography (US). The aim of this study evaluate the short axis and long axis radial artery measurements at 0º, 45º, 60º wrist joint angle and find out the optimal wrist joint angle for long and short axis US guided radial artery cannulation. This study was approved by the Institutional Ethical Committee and the study was performed in accordance with the ethical principles for human investigations, as outlined by the Second Declaration of Helsinki. One hundred fifty-two (90 men and 62 women, 18-48 years of age, mean age: 32.9 ± 6.1) healthy volunteers were recruited. The radial artery distance between skin and height, width, area in short axis and radial artery distance between skin and height was measured in long axis at 0º, 45º, 60º wrist joint angle were measured. Results. Short axis radial artery distance between skin, width, height, area and long axis radial artery distance between skin, height were statistically significantly different among 0º, 45º, 60º (p< 0.05; for all comparisons). Short axis width was statistically significantly increased at 45º compared to at 0º (p< 0.001;). Short axis radial artery distance between skin and height at 45º were statistically significantly decreased than at 0º (p< 0.001; for all comparisons) and long axis skin distance and height at 45º were also statistically significantly decreased than at 0º (p< 0.001; for both comparisons). Short axis radial artery skin distance and area at 60º is statistically significantly decreased than at 45º (p< 0.001; for both comparisons) and also long axis height of radial artery at 60º is statistically significantly decreased than at 45º (p< 0.001;). Angle increment up to 45º might help clinicians for radial artery cannulation in short axis plane whereas this angle increment maneuver decreased the arterial height in long axis which might be a potential disadvantage for cannulation.

Mono-Isocentric Technique in the Breast Cancer and Organ at Risk Tolerance

Purpose: To investigate the impact of the single-isocentre technique on the volumetric dose of lung and heart for adjuvant radiation in breast cancer with regional nodal. Methods and materials: Thirty patients treated for breast cancer with supraclavicular fossa irradiation; two techniques of treatment TMT (Traditional Matching Technique) and MIT (Mono-Isocentric Technique) are compared, TMT (tangents in SAD and supraclavicular (SCL) in SSD: Source Skin Distance) and MIT (the all fields in SAD: Source Axe Distance) (Chart 1). Techniques were compared according to dose volume histograms (DVHs) analysis in terms of PTV homogeneity and as OARs (Organs at Risk) dose and volume parameters. Results: The dose distribution in PTV is similar in the both techniques TMT and MIT but with hot spots in the junction of the three fields for the TMT (average 120% for TMT and 110% for MIT). The analysis of DVHs shows a decrease in the mean OARs. Lung and heart dose is improved using the MIT and with significant difference in the V20 and V30 for the lung and in the V10 and V40 for the heart. Conclusions: The results of our study demonstrated that the target volumes were sufficiently irradiated with the MIT and the lung and heart volumes irradiated were small. Furthermore, it should not be over or under dose in the supraclavicular and tangential junction.

Breast Cancer Recurrence after Inadvertent Malpositioning of a Partial Breast Radiation Catheter

Accelerated partial breast irradiation (APBI) is an alternative to receiving whole breast radiation in carefully selected patients. Because breast cancer local recurrence rates are low and follow-up has been short-term, the exact cause of recurrences after APBI has been difficult to evaluate. We report the first case of documented radiation balloon catheter malpositioning that resulted in local recurrence. Patients undergo CT imaging of the breast after radiation balloon catheter placement for radiotherapy treatment planning, which evaluates adequate conformance of the balloon to the surrounding breast parenchyma and confirms a >7 mm distance between the balloon surface and the skin surface. Although true local recurrences are rare in appropriately selected partial breast irradiation candidates, inadvertent malpositioning of the radiation treatment catheter can increase the risk. This case is presented to illustrate the importance of comparing CT radiation planning images, with treatment catheter in place, to the original diagnostic breast imaging studies to confirm proper catheter positioning (in addition to measuring balloon to skin distance and conformance) prior to initiating radiotherapy.

Development and optimization of a beam shaper device for a mobile dedicated IOERT accelerator

The aim of this study was to design and build a prototype beam shaper to be used on a dedicated mobile accelerator that protects organs at risk within the radiation field and conforms the beam to the target geometry during intraoperative electron radiotherapy (IOERT). A dosimetric characterization of the beam shaper device was performed based on Monte Carlo (MC) simulations, as well as experimental data, at different energies, field sizes, and source to skin distances. A mobile light intraoperative accelerator (LIAC(®), Sordina, Italy) was used. The design of the beam shaper prototype was based on MC simulations (BEAMnrc∕OMEGA and DOSXYZnrc code) for a selection of materials and thicknesses, as well as for dosimetric characterization. Percentage depth dose (PDD) and profile measurements were performed using a p-type silicon diode and a commercial water phantom, while output factors were measured using a PinPoint ion chamber in a PMMA phantom. Planar doses in planes of interest were carried out using radiochromic films (Gafchromic(TM) EBT and EBT2) in PMMA and in a Solid Water(®) phantom. Several experimental set-ups were investigated with the beam shaper device fixed on the top of the phantom, varying both the short side of the rectangular field and the air gap between the device and the phantom surface, simulating the clinical situation. The output factors (OFs) were determined using different geometrical set-ups and energies. The beam shaper prototype consists of four blades sliding alongside each other and mounted on a special support at the end of the 10 cm diameter PMMA circular applicator. Each blade is made of an upper layer of 2.6 cm of Teflon(®) and a lower layer of 8 mm of stainless steel. All rectangles inscribed in a 5 cm diameter can be achieved in addition to any "squircle-shaped" field. When one side of the rectangular field is held constant and the second side is reduced, both R(50) and R(max) move towards the phantom surface. Comparing the PDDs obtained with the 5 cm circular applicator and with a 4.4 × 4.4 cm(2) square field (that is the equivalent square of the 5 cm circular field) obtained with the beam shaper, a different behavior was observed in the region extending from the surface to a depth of 50% of the maximum dose. Isodoses measured for rectangular fields used for clinical cases (i.e., 4 × 9 cm(2) 8 MeV) are shown, with different air gaps. For each energy investigated, the normalized OFs slowly increase, when the length of the side decreases down to about 4 cm, and then rapidly decreases for smaller field widths. MC simulation showed an excellent agreement with experimental data (<2%). The beam shaper device is able to provide square∕rectangular∕squircle fields with adequate dose homogeneity for mobile dedicated accelerators, thus allowing conformal treatment with IOERT. Monte Carlo simulation can be a very useful tool to simulate any clinical set up and can be used to create a data set to calculate MUs, thereby increasing the accuracy of the delivered dose during IOERT procedures.

Inter‐ and intra‐fraction motion during radiation therapy to the whole breast in the supine position: A systematic review

Inter- and intra-fraction motion during radiation therapy for breast cancer has been a widely researched topic. Recently, however, with the emergence of new technologies and techniques such as intensity modulated radiation therapy (IMRT), field in field, volumetric modulated arc therapy (VMAT), tomotherapy and partial breast irradiation (PBI), the magnitude of this movement has become more important. The aim of this study is to provide a comprehensive summary of the literature relating to the magnitude of motion during radiation therapy for a breast cancer patient. A systematic review of the literature was conducted using Medline, Cinhal, Embase, Scopus and Web of Science. Studies included were limited to women having radical radiation therapy to the whole breast in the supine position. Studies needed to report quantitatively on the magnitude of inter- and intra-fraction motion using electronic portal imaging, port films or kilovoltage imaging techniques. Eighteen articles fitted the selection criteria. The averages of random and systematic error for inter- and intra-fraction movement were reported using central lung distance, central irradiated width, central beam edge to skin distance and cranio-caudal distance measurements, or isocentric matching techniques. Inter-fraction motion was consistently larger than intra-fraction motion but, on average, within a 5 mm tolerance. There were, though, large maximum inter- and intra-fraction variations observed in the measurements of individual patients, which indicate the need for daily inter- and intra- fraction motion management before implementing IMRT, VMAT, tomotherapy or PBI techniques.

Characterization of a cable‐free system based on p‐type MOSFET detectors for “in vivo” entrance skin dose measurements in interventional radiology

During radiological interventional procedures (RIP) the skin of a patient under examination may undergo a prolonged x-ray exposure, receiving a dose as high as 5 Gy in a single session. This paper describes the use of the OneDose(TM) cable-free system based on p-type MOSFET detectors to determine the entrance skin dose (ESD) at selected points during RIP. At first, some dosimetric characteristics of the detector, such as reproducibility, linearity, and fading, have been investigated using a C-arc as a source of radiation. The reference setting (RS) was: 80 kV energy, 40 cm × 40 cm field of view (FOV), current-time product of 50 mAs and source to skin distance (SSD) of 50 cm. A calibrated PMX III solid state detector was used as the reference detector and Gafchromic(®) films have been used as an independent dosimetric system to test the entire procedure. A calibration factor for the RS and correction factors as functions of tube voltage and FOV size have been determined. Reproducibility ranged from 4% at low doses (around 10 cGy as measured by the reference detector) to about 1% for high doses (around 2 Gy). The system response was found to be linear with respect to both dose measured with the PMX III and tube voltage. The fading test has shown that the maximum deviation from the optimal reading conditions (3 min after a single irradiation) was 9.1% corresponding to four irradiations in one hour read 3 min after the last exposure. The calibration factor in the RS has shown that the system response at the kV energy range is about four times larger than in the MV energy range. A fifth order and fourth order polynomial functions were found to provide correction factors for tube voltage and FOV size, respectively, in measurement settings different than the RS. ESDs measured with the system after applying the proper correction factors agreed within one standard deviation (SD) with the corresponding ESDs measured with the reference detector. The ESDs measured with Gafchromic(®) films were in agreement within one SD compared to the ESDs measured using the OneDose(TM) system, as well. The global uncertainty associated to the OneDose(TM) system established in our experiments, ranged from 7% to 10%, depending on the duration of the RIP due to fading. These values are much lower than the uncertainty commonly accepted for general diagnostic practices (20%) and of about the same size of the uncertainty recommended for practices with high risk of deterministic side effects (7%). The OneDose(TM) system has shown a high sensitivity in the kV energy range and has been found capable of measuring the entrance skin dose in RIP.

Correlation between injection moulding processing parameters and mechanical properties of microcellular polycarbonate

Since many decades, microcellular foamed materials have been produced basically to reduce the density of the materials in order to get lightweight parts. Meanwhile, it is well known that microcellular foaming by injection moulding offers many more advantages compared to compact injection moulding. Those are, e.g. lower shrinkage and warpage, shorter cycle times, lower clamp forces, reduced viscosity but improved properties of the foamed material in contrast to the compact material. These arguments are all known, but to improve the properties of the material, it is necessary to understand the interrelationship between the morphology and the mechanical properties. Furthermore, it is important to know how the processing parameters influence the morphology and the properties of the produced part. By understanding the relation between processing parameters and the consequential properties, it has become possible to create microcellular foamed parts with exactly defined properties. Through the variation of different processing parameters such as blowing agent concentration, injection velocity, mass temperature, mould temperature, weight reduction and different moulding processes like gas counter pressure injection moulded test, samples were produced to characterise the morphology and the mechanical properties. The experiments were performed with a polycarbonate type from Bayer MaterialScience. The cell size, thickness of the skin layer and distance between the cells were correlated to the processing parameters by means of nonlinear regression equations. Based on these equation, 3D graphs were created by variation of two parameters by fixing the remaining parameters to illustrate the relationships. Furthermore, the relation between the morphology and the mechanical properties was correlated, which makes it possible to produce parts through injection moulding with a well-defined Young’s modulus or flexural strength.

SU-E-I-108: Simple Approach to Determine Patient's Entrance Skin Exposure for Radiographic.

To evaluate a model which can predict patient's Entrance Skin Exposure (ESE) from height and weight and a single kVp mR/mAs measurement for radiographic. Patient height, weight and post exposure mAs are obtained to assess ESE based on IAEA model. Patient's thickness is obtained by assuming a cylindrical geometry. The validity of this assumption is tested against actual measurements. Source to Skin Distance (SSD) is computed from patient's thickness and the Source-Image receptor Distance (SID) used during exposure. Entrance Skin Exposure is calculated as a product of post exposure mAs and a single 80 kVp mR/mAs obtained at a reference distance corrected inversely for SSD. Values of mR/mAs at other kVp's are obtained by quadratic variation of output with kVp. The validity of predicting patient thickness will be presented based on numerous measurements performed on test subjects. Deviation between the ESE values using of single kVp, mR/mAs measurement and the ones obtained by the conventional multiple kVp mR/mAs will be presented as well. This work indicates a simple approach to determine the patient's ESE based on the patient's height and weight for radiographic units, which will be very useful for institutions that do not have a dedicated physicist.

SU-E-T-554: PTV to Skin Proximity for Head and Neck IMRT Treatment Planning.

The goal of this work was to evaluate measured vs. calculated surface dose as a function of PTV-to-skin proximity and calculation matrix oxel size, determine effects on plan quality, and provide parameters and levels of uncertainty for clinical use. A right-sided CTV with the lateral border 5mm from the surface was delineated on the CT data of a head and neck phantom. A 5mm PTV was generated except laterally where distances of 0-5mm were used. A 7-field IMRT plan was generated using the Eclipse TPS. Optimization was performed where 95% of the PTV receives the prescription dose using a matrix size of 2mm3 . Dose calculations were repeated for grid sizes of 1, 3 and 5mm3 . For each plan nine point dose values were obtained just inside the phantom surface, corresponding to a 2cm2 grid near the central target region. Nine ultra-thin TLDs were placed on the phantom surface corresponding to the grid. Measured and calculated dose values were compared. Conformality, homogeneity and target coverage were compared. Surface dose is over-estimated by the TPS by 21 and 8% for 5 and 3mm3 voxels, respectively and accurately predicted for 2mm3 voxels. A voxel size of 1mm3 results in underestimation of 13%. Conformality improves with increasing PTV to skin distance and a CI of unity results for grid sizes of 1-3mm3 between 4 and 4.5mm. Hot spot decreases as the PTV moves away from the surface and falls below 110% at 4mm. Underdosage worsens as the PTV approaches the skin. For decreasing PTV-to-skin distance with this TPS, isodose conformality decreases, 'hot spot' increases, and target coverage degrades. Surface dose is accurately predicted for a 2mm3 voxel size, while choosing a finer or coarser grid results in underestimation or overestimation, respectively. All of the above appear to hold for VMAT.