Dosimetry audit in advanced radiotherapy using in-house developed anthropomorphic head & neck phantom.

The treatment of head and neck (H&N) cancer presents formidable challenges due to the involvement of normal tissue and organs at risk (OARs) in the close vicinity. Ensuring the precise administration of the prescribed dose demands prior dose verification. Considering contour irregularity and heterogeneity in the H&N region, an anthropomorphic and heterogeneous H&N phantom was developed and fabricated locally for conducting the dosimetry audit in advanced radiotherapy treatments. This specialized phantom emulates human anatomy and incorporates a removable cylindrical insert housing a C-shaped planning target volume (PTV) alongside key OARs including the spinal cord, oral cavity, and bilateral parotid glands. Acrylonitrile Butadiene Styrene (ABS) was chosen for PTV and parotid fabrication, while Delrin was adopted for spinal cord fabrication. A pivotal feature of this phantom is the incorporation of thermoluminescent dosimeters (TLDs) within the PTV and OARs, enabling the measurement of delivered dose. To execute the dosimetry audit, the phantom, accompanied by dosimeters and comprehensive guidelines, was disseminated to multiple radiotherapy centers. Subsequently, hospital physicists acquired computed tomography (CT) scans to generate treatment plans for phantom irradiation. The treatment planning system (TPS) computed the anticipated dose distribution within the phantom, and post-irradiation TLD readings yielded actual dose measurements. The TPS calculated and TLD measured dose values at most of the locations inside the PTV were found comparable within ± 4%. The outcomes affirm the suitability of the developed anthropomorphic H&N phantom for precise dosimetry audits of advanced radiotherapy treatments.

A Simplified Approach for Determination of Inflection Points of Flattening Filter-Free Photon Beam Using In-House Developed Software and Derivation of Reference Levels.

Aim: This article aimed to present the salient features of the in-house developed Java program for the determination of inflection point and dosimetric parameters of flattening filter-free (FFF) photon beam. Reference levels for the dosimetric parameters of the FFF photon beams were also presented. Materials and Methods: Beam profiles of 6 MV FFF and 10 MV FFF photon beams for a collimator setting of 20 cm × 20 cm measured at 10 cm depth in an isocentric setup acquired from various institutions were analyzed using an in-house developed Java program and manual method. The values of reference dose value (RDV), field size, penumbra, and degree of un-flatness (defined as the lateral separation between 90% [X90%], 75% [X75%], and 60% [X60%] dose points on the profile) were calculated and compared. The reference values of field size, penumbra, and degree of un-flatness were also determined for Varian and Elekta medical electron linear accelerators (LINACs). Results: The maximum differences for RDV determined using the Java method and manual method are 2.4% and 2.7% for 6 and 10 MV FFF photon beams, respectively. The maximum difference between the values of field size, penumbra, and degree of un-flatness determined using Java and manual methods is within 1.3 mm. The reference values of field size and penumbra for Varian LINACs are 19.94 ± 0.10 cm and 0.83 ± 0.08 cm (6 MV FFF) and 19.95 ± 0.10 cm and 0.83 ± 0.08 cm (10 MV FFF). Similarly, the reference values of field size and penumbra for Elekta LINACs are 20.02 ± 0.09 cm and 0.94 ± 0.12 cm (6 MV FFF) and 20.03 ± 0.11 cm and 0.97 ± 0.16 cm (10 MV FFF). Conclusions: A software program was developed in Java for analyzing the beam profiles of FFF photon beams. The results of Java-derived values of dosimetric parameters of FFF photon beams were found in good agreement with the values determined using the manual method. The reference values of these parameters were also derived and quoted using a large cohort of the data.

Measurement of dose enhancement factor for Xoft Axxent electronic brachytherapy device using nanoparticle-embedded alginate film and radiochromic film.

Aim: Inw nanoparticles-aided radiotherapy, the radiation sensitivity of tumor is increased with the infusion of nanoparticles in tumor. This therapeutic modality is capable of delivering enhanced dose to tumor, without exceeding the normal tissue tolerance dose. Further, the quantification of the enhanced dose using suitable dosimeter is important. The present study is aimed at measuring the dose enhancement factors (DEFs) using the combination of nanoparticles-embedded alginate (Alg) film and unlaminated Gafchromic EBT3 film. Materials and Methods: Gold nanoparticles (AuNPs)- and silver nanoparticles (AgNPs)-embedded Alg polymer films were synthesized and characterized using standard techniques. Further, a customized version of the Gafchromic EBT3 film, i.e., unlaminated EBT3 film, was specially fabricated. The DEFs were measured using Xoft Axxent electronic brachytherapy device. Results: The surface plasmon resonance (SPR) and particle size of AuNPs were found to be 550 and 15 ± 2 nm, respectively. In the case of AgNPs, the SPR and particle size were recorded as 400 and 13 ± 2 nm, respectively. The DEFs measured, using unlaminated EBT3 film, for Xoft Axxent electronic brachytherapy using AuNPs and AgNPs were 1.35 ± 0.02 and 1.20 ± 0.01, respectively. Conclusion: The increase in dose enhancement during nanoparticles-aided electronic brachytherapy can be attributed to dominance of photoelectric effect, due to the presence of low-energy X-rays. The investigation indicates that the Xoft Axxent electronic brachytherapy device is suitable for nanoparticles-aided brachytherapy.

Experimental method for temperature measurement on lateral planes along a Rijke tube to assess efficacy of control method.

The thermo-acoustic instabilities developed inside the combustor causes serious structural damage and reduces the life of power producing devices. The present work involves experimental investigation to assess effect of radial micro-jets air injection on thermo-acoustic instabilities and temperature in lateral planes. A co-axial pre-mixed gas burner used as the heat source inside the Rijke tube with variable location. Two types of Rijke tubes were used for experimental study, one is of steel with 75 mm internal diameter and 750 mm in length for the measurement of wall pressure, temperature and acoustics. •In the first part of the study, acoustic instability zone for different inlet mass flow rates was identified.•In the second part of study, the entire cross-sectional of Rijke tube was divided into 193 subzones and temperatures were measured at 193 locations when instability was present.•In third part, again temperatures were measured at 193 locations with implementation of control method with complete suppression of thermo-acoustic instabilities.

Hearing outcomes in children with single sided deafness: Our experience at a tertiary paediatric otorhinolaryngology unit.

INTRODUCTION: Hearing rehabilitation options for single sided deafness (SSD) include contralateral routing of sound (CROS) aids and bone conduction devices (BCDs). This study aimed to review the management of children with SSD at our tertiary paediatric otolaryngology unit over the last 15 years. MATERIAL AND METHODS: A retrospective cohort study was performed. Primary hearing outcomes were measured using the Children's Home Inventory for Listening Difficulties (CHILD) questionnaire score and secondary hearing outcomes were measured using hearing thresholds for speech in noise. Outcomes were measured pre and post bone conduction device (BCD) trial. RESULTS: 49 patients with SSD were identified. 20 children had trial of a BCD. 16 patients had pre- and post- BCD trial CHILD scores available for analysis. There was a statistically significant improvement in CHILD scores and speech in noise testing at +5 dB and +0 dB following amplification with a BCD. The mean use of BCD was 1.3 h per day. DISCUSSION: We have described the management of children with SSD in our unit. This study demonstrated a statistically significant benefit of BCD use on hearing outcomes. However, device compliance is low suggesting hearing advice choice in the population is complex and further research is warranted.

The effect on the T-14 paediatric throat disorders outcome score of delaying adenotonsillectomy surgery due to COVID-19.

INTRODUCTION: Adenotonsillectomy is commonly performed for recurrent tonsillitis and obstructive sleep apnoea. These conditions may improve with age. The COVID-19 pandemic led to all UK elective surgery being suspended. This study aimed to determine whether delaying surgery had any effect on a patient's symptoms using the validated T-14 paediatric throat disorders outcome test. METHODS: Patients completed a T-14 questionnaire when the child was listed for surgery; this was repeated on the revised surgery date and a paired t test was used to compare the responses. RESULTS: Questionnaires were completed by 29 patients a mean of 6.4 months apart. There was a significant improvement in scores (p<0.02) for five domains: eating habits, visits to a doctor/A&E, antibiotics for less than 2 weeks, chronic infections and school missed due to sore throats. CONCLUSIONS: This study demonstrates that following delays resulting from the COVID-19 pandemic, paediatric patients experienced an improvement in some aspects of their quality of life while awaiting tonsillectomy and/or adenoidectomy. This was most apparent in quality-of-life measures relating to recurrent tonsillitis, namely visits to a doctor/A&E, antibiotics for less than 2 weeks, chronic infections and school missed due to sore throats. Patients may experience an improvement in some of their individual symptoms, in particular their infective symptoms, during an observation period.

Mastoid obliteration versus canal wall down or canal wall up mastoidectomy for cholesteatoma: Systematic review and meta-analysis.

BACKGROUND: There is ongoing debate over the optimal surgical approach for cholesteatoma treatment1-5. The aim of this review was to determine whether canal-wall down with mastoid obliteration is associated with favourable outcomes compared to either canal-wall down without obliteration or canal-wall up. The primary outcome was cholesteatoma reoccurrence with secondary outcomes including otorrhoea, reoperation and patient-reported outcome measures. METHODS: Medline, Embase, Cochrane databases and clinicaltrials.gov were searched for studies reporting outcomes of patients undergoing primary CWD-MO for cholesteatoma and directly compared with CWD and CWU mastoidectomies. Data were collated and meta-analysis performed. RESULTS: 2379 patients were included from 12 studies that met the inclusion criteria. CWD-MO was found to be associated with significantly less risk of recurrence when compared to CWU (OR = 0.330 (95 % CI 0.191-0.570, p < 0.001). When compared to CWD, CWD-MO was associate with significantly lower incidence of persistent otorrhoea (OR 0.405 (95 % CI 0.232-0.706, p < 0.001) while the rates of recurrence were comparable (OR: 1.231 [95 % CI: 0.550-2.757] p = 0.613). Otorrhoea rates between CWD-MO and CWU were equivalent as was reoperation. Quality of life and hearing outcomes were variably reported. CONCLUSIONS: This systematic review demonstrates that CWD-MO technique achieves lower recurrence rates comparable to CWD approaches and superior to CWU, while offering improved long-term control of otorrhoea. The final procedural choice should be decided based on surgeon experience, skill set and individual patient factors. To address the risk of selection bias, a randomised controlled trial is needed to answer this important research question.

Evaluation of computed tomography dose profiler probe for computed tomography dose index and geometric efficiency measurements.

The purpose of this study was to evaluate the performance of solid-state sensor based computed tomography dose profiler (CTDP) probe for measurement of standard computed tomography dose metric CTDI100and free in air geometric efficiency for various beam widths available in a 128-slice CT scanner and also to estimate the efficiency of CTDI100metric. The response accuracy of CTDP probe was verified using a standard 100 mm long ionization chamber. The geometric efficiency measurements performed by the CTDP probe were validated using XR-QA2 radiochromic film measurements. The efficiency of CTDI100metric was assessed by calculating the ratio of CTDI100measured in the center hole position to CTDI∞measured in the same position of both head and body phantoms. The weighted CTDI values derived from CTDI100measured by the CTDP probe showed an average difference of 8% from ionization chamber measured values. The efficiency of CTDI100metric estimated using CTDP probe and 150 mm long phantoms was in the range of 82% to 86% and 76% to 80% for head and body phantom measurements respectively. The differences in the geometric efficiency values for various beam settings and tube voltages measured by the CTDP probe and films were within 7%. Taken together, the results of this study proved that unlike the 100 mm long ionization chamber, the CTDP probe can be efficiently used to determine CTDI for any length over which dose integration is desired and also measure geometric efficiency of MDCT scanners for various beam widths in helical mode of operation.

Application of unlaminated EBT3 film dosimeter for quantification of dose enhancement using silver nanoparticle-embedded alginate film.

Purpose.The paper describes the application of unlaminated Gafchromic EBT3 film dosimeter for quantification of dose enhancement using locally synthesized silver nanoparticle-embedded alginate film (AgNPs-Alg film) for nanoparticles-aided radiotherapy.Materials and Methods.AgNPs-Alg film was synthesized and characterized using standard techniques. The unlaminated Gafchromic EBT3 film was specially customized for dosimetric measurement. The dose enhancements due to AgNPs-Alg film was experimentally determined for ISO wide spectrum x-rays series (average energy ranging from 57-137 keV) and 6 and 10 MV x-rays using laminated and unlaminated Gafchromic EBT3 film. The radiation dose of 1 Gy was delivered to a combination of AgNPs-Alg films and EBT3 film.Results.Ultraviolet-Visible spectroscopy of silver nanoparticles shows a surface plasmon resonance peak at 400 nm. The average particle size of 13 ± 2 nm was measured using Atomic Force Microscopy. For unlaminated film, the dose enhancements of 29%, 23%, 14% and 2% was observed for ISO wide spectrum x-rays having average energy of 57, 79, 104 and 137 keV, respectively. The dose enhancement was negligible for 6 and 10 MV x-rays. In the case of laminated film, no significant dose enhancement was measured for all the x-ray energies.Conclusion.The unlaminated Gafchromic EBT3 film can be a suitable choice for the measurement of dose enhancement. Further, silver nanoparticles can be used during nanoparticle-aided radiotherapy when irradiated at low x-ray energy.

Probability Distribution of Pixel Intensities of EBT3 Films and its Application in the Correction of Uncertainty Budget.

BACKGROUND AND AIM: Modern radiotherapy modalities, such as Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy involve complex dose delivery. The dose delivery is complex as it involves beam modulation, hence, manual dose calculations for these techniques are not possible. Film dosimetry is commonly used method of dose verification for these modalities because of the advantages associated with it. The quantification of uncertainty associated with a film dosimetry system under clinical use becomes important for accurate dosimetry. The spread in the distribution of the pixel values (PV) of the irradiated film contributes to the uncertainty. The probability distribution (PD) of the PV was studied for the clinical photon beam energies of 6, 10, and 15 MV. METHODS AND MATERIALS: Gafchromic EBT3 film and EPSON 10000XL flatbed scanner were used for this purpose and using the resulting PD, the uncertainty budgets for these energies in the red, green and blue color channels were estimated. RESULTS: The PV of exposed films for the energies studied follows t-distribution, the sum of the squares of the deviation of the measured data from the fitted value was of the order of 10-7, this indicates the goodness of fit. The "t" value corrected combined standard uncertainty (CSU) at 1σ confidence level for exposed film and dose measurement at 200 cGy were 1.42%, 1.48%, and 1.63% and 1.99%, 3.23%, and 5.08% for 6, 10, and 15 MV energies, respectively, in the red colour channel. CONCLUSION: In the case of the limited number of measurements of a quantity, the SU values must be corrected using the "t" value to get the correct CSU.

Increased incidence of idiopathic paediatric facial palsy during the coronavirus disease 2019 pandemic.

BACKGROUND: Bell's palsy is a lower motor neurone facial weakness of unknown aetiology, although reactivation of a virus within the facial nerve has been proposed. METHODS: A prospective study was conducted of Bell's palsy cases presenting to our paediatric ENT unit over a 19-week period, from February to June 2020. Patients were invited for severe acute respiratory syndrome coronavirus-2 antibody testing. A text-message questionnaire was sent to other ENT centres to determine their observational experience. RESULTS: During the study period, 17 children presented with Bell's palsy, compared with only 3 children in the same time period in the previous year (p < 0.0001). Five patients underwent severe acute respiratory syndrome coronavirus-2 antibody testing, the results of which were all negative. Four out of 15 centres questioned perceived an increased incidence in paediatric Bell's palsy. CONCLUSION: Clinicians are encouraged to be vigilant to the increase in paediatric Bell's palsy seen during the coronavirus disease 2019 pandemic, which may represent a post-viral sequela of coronavirus disease 2019.

Computation of epistemic uncertainty due to limited data samples in small field dosimetry using Fuzzy Set Theory.

OBJECTIVE: To estimate the epistemic (or fuzzy) uncertainty, arising due to limited data samples in the measurement of the output factors (OFs) of the small fields using Fuzzy Set Theory (FST). METHODS: EBT3 film samples of size 50 × 50 mm2 were used for the measurement of the OF of stereotactic radiosurgery (SRS) cones of size 4, 6, 7.5, 10, 12.5 and 15 mm diameter, normalized with respect to the output of 100 × 100 mm2 open field size. Three measurements were done per cone/field size. Red color channel was chosen for the dosimetry purpose, net optical density (NOD) was converted to the dose using non-linear relation. To estimate the epistemic uncertainty associated with the measured OFs due to limited number of data samples, a triangular fuzzy number (TFN) was assumed as the fuzziness in the dose delivered by the individual SRS cone/field. Uncertainty in the OF was estimated by applying the Fuzzy Vertex Method (FVM). The membership functions of the OF were constructed for each cone size and the nature of the uncertainty in the OF of the cones was expressed in the terms of its fuzziness. For the sake of completeness of the study, the statistical uncertainty involved in the procedure has also been calculated. RESULTS: The statistical and fuzzy uncertainties in the measurement of OF of cones range from 3.28 to 6.25% and 2.58 to 5.44% respectively. The smallest cone of 4 mm has the largest values of statistical and fuzzy uncertainties. The membership functions of the OF for the studied cones were triangular in nature. CONCLUSION: The epistemic uncertainty arising due to limited number of data samples holds a significant fraction of the prescribed dose, and therefore, should not be ignored in the total uncertainty estimation. ADVANCES IN KNOWLEDGE: This study highlights the significance of epistemic component of measurement uncertainty arising out due to the insufficient/limited number of measurements of a quantity.

Use of the KTP laser in totally endoscopic cholesteatoma surgery.

OBJECTIVE: This paper reviews our experience of potassium titanyl phosphate (KTP) laser in transcanal totally endoscopic cholesteatoma surgery. METHODS: A prospective cohort study was conducted in a tertiary referral centre, involving a consecutive series of children with cholesteatoma who underwent totally endoscopic cholesteatoma surgery with a KTP laser. RESULTS: The patients' mean age was 10.5 years (range, 1.8-18 years). A KTP laser was used in 70 of the 83 cases (84 per cent). The laser was not used in 13 'clean' cases, in which disease was removed more easily. Residual disease was detected in five cases (6 per cent), of which the KTP laser had been used in four (5 per cent). No complications were associated with KTP laser use. CONCLUSION: The combination of KTP laser use with endoscopic visualisation is effective for minimising the risk of residual disease using a minimally invasive surgical approach. The thin, semi-flexible fibre carrier of the KTP laser is ideally suited to work alongside the endoscope within the narrow confines of the ear canal.

Spectroscopic analyses reveal radiotherapy-induced variations in elemental composition and crystallite properties of human permanent teeth enamel.

OBJECTIVE: To study the effect of radiation therapy on the structural and elemental composition of permanent teeth enamel in vitro. METHODS: Sections from 21 noncarious healthy human teeth were exposed to a cumulative radiation dose of 20-80 Gy. The sections were subjected to electron dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis to study the elemental composition, the ratio of inorganic and organic content, and the mineralization and crystalline properties of the hydroxyapatite crystal structure respectively. All measures were taken on specified areas of enamel surface before and after radiation exposure and compared. RESULTS: In FTIR and EDS studies, the calcium to phosphorus (Ca/P) and carbonate to phosphate (CO32-/PO3-4) ratios were significantly different (P < 0.05) in teeth sections exposed to 80 Gy, indicating the deterioration of inorganic calcium and phosphorous content. The XRD spectrum data showed loss of peaks at seven specific 2θ coordinate areas, flattened peaks and an increase in the crystallite size in the radiation-exposed groups due to mineralization loss and alteration of the hydroxyapatite crystal matrix in the tooth enamel. CONCLUSIONS: Radiotherapy can induce significant variations in the inorganic and organic functional groups constituting the tooth enamel surface; and these variations are dose dependent. The mechanism responsible for delamination and radiation caries needs to be explored by studying the protein lysis pattern, which might be a leading factor causing the enamel degradation and radiation caries.

Performance Validation of In-House Developed Four-dimensional Dynamic Phantom.

OBJECTIVE: The objective of this study was to validate the performance characteristics of in-house developed four-dimensional (4D) dynamic phantom (FDDP). MATERIALS AND METHODS: There are three target inserts of 1.0, 1.5 and 2.0 cm diameter. The targets were driven in sinusoidal pattern in the longitudinal direction, using the combinations of amplitudes of 0.5, 1.0, and 1.5 cm with frequencies of 0.2 and 0.25 Hz. The amplitude and frequency of motion were measured manually, and by using Real-Time Position Management (RPM) system also. The static, free-breathing, and 4D computed tomography (CT) scans of the phantom were acquired with 1.0 mm slice thickness. The 4DCT scans were sorted into 0%-90% phase, and the maximum intensity projection (MIP) images were also generated. The static, free-breathing, and 4DCT data sets and MIP images were contoured to get VStatic, VFB, V00......V90, and internal target volume ITV MIP, respectively. The individual phase volumes were summed to obtain V4D. The length of the target in the motion was measured using MIP image and compared with theoretical length (TL). The variation of 3D displacement vector of individual phase volume with respect to V00 with the phase of motion was studied at amplitude and frequency of 1.0 cm and 0.25 Hz, respectively. The degree of similarity between VFB and V4D and VFB and ITVMIP was also studied for all the target sizes at amplitude and frequency of 1.0 cm and 0.2 Hz and 1.0 cm and 0.25 Hz, respectively. RESULTS: The amplitude and frequency of motion agreed within the limits of uncertainty with the manually and RPM measured values. The length of target in the motion matched within 1.0 mm with TL. The 3D displacement of individual phase volume showed no target size dependence, and the degree of similarity between VFB and V4D and VFB and ITVMIP decreases with increase in the displacement between the two volumes. CONCLUSIONS: The mechanical and imaging performances of FDDP were found within the acceptable limits. Therefore, this phantom can be used for quality assurance of 4D imaging process in radiotherapy.

Phantom-Based Feasibility Studies on Phase-Contrast Mammography at Indian Synchrotron Facility Indus-2.

INTRODUCTION: Use of synchrotron radiation (SR) X-ray source in medical imaging has shown great potential for improving soft-tissue image contrast such as the breast. The present study demonstrates quantitative X-ray phase-contrast imaging (XPCI) technique derived from propagation-dependent phase change observed in the breast tissue-equivalent test materials. MATERIALS AND METHODS: Indian synchrotron facility (Indus-2, Raja Ramanna Centre of Advanced Technology [RRCAT]) was used to carry out phantom feasibility study on phase-contrast mammography. Different phantoms and samples, including locally fabricated breast tissue-equivalent phantoms were used to perform absorption and phase mode imaging using 12 and 16 keV SR X-ray beam. Edge-enhancement index (EEI) and edge enhancement to noise ratio (EE/N) were measured for all the images. Absorbed dose to air values were calculated for 12 and 16 keV SR X-ray beam using the measured SR X-ray photon flux at the object plane and by applying the standard radiation dosimetry formalism. RESULTS AND CONCLUSION: It was observed in case of all the phantoms and test samples that EEI and EE/N values are relatively higher for images taken in the phase mode. The absorbed dose to air at imaging plane was found to be 75.59 mGy and 28.9 mGy for 12 and 16 keV SR energies, respectively. However, these dose values can be optimized by reducing the image acquisition time without compromising the image quality when clinical samples are imaged. This work demonstrates the feasibility of XPCI in mammography using 12 and 16 keV SR X-ray beams.

Analysis of intensive care admissions among paediatric obstructive sleep apnoea referrals.

Introduction The aim of this study was to identify the proportion of children referred to a paediatric tertiary referral centre who required admission to the paediatric intensive care unit (PICU) following surgery for obstructive sleep apnoea (OSA) and to establish risk factors for these admissions. Methods Retrospective review of case notes and the operative database was performed for all children undergoing adenotonsillectomy for sleep disordered breathing and OSA symptoms in Great Ormond Street Hospital over a 10-year period. Results Overall, 1,328 children underwent adenotonsillectomy for sleep disordered breathing and OSA. The mean age was 3.1 years (standard deviation [SD]: 1.7 years). A total of 37 (2.8%) were admitted to the PICU postoperatively (mean length of PICU stay: 1.2 days, standard deviation [SD]: 0.6 days) and 282 (21.2%) required nasopharyngeal airway (nasal prong) insertion intraoperatively. The mean length of stay on the ward following surgery was 1.4 days (SD: 0.8 days). Patients with severe OSA (apnoea-hypopnoea index [AHI] >10) and ASA (American Society of Anesthesiologists) grade ≥3 were more likely to require postoperative PICU admission (22/37 vs 381/1,291 [p<0.001] and 29/37 vs 660/1,291 [p=0.001] respectively). Severe OSA was also more common in children who required nasal prong insertion intraoperatively (186/282 vs 217/1,046, p<0.001). Conclusions Very few children referred to a paediatric tertiary referral centre actually require PICU admission following surgery. This may be in part due to the use of a nasopharyngeal airway in patients where postoperative obstruction is anticipated. In children with severe OSA (AHI >10) and an ASA grade of ≥3, nasopharyngeal airway insertion and potential admission to the PICU should be considered.

Imaging and Dosimetric Study on Direct Flat-Panel Detector-Based Digital Mammography System.

INTRODUCTION: Image quality of digital mammography system is generally defined by three primary physical parameters, namely, contrast, resolution, and noise. Quantification of these metrics can be done by measuring objective image quality parameters defined as contrast-to-noise ratio (CNR), modulation transfer function (MTF), and noise power spectra (NPS). MATERIALS AND METHODS: In the present study, various imaging metrics such as CNR, contrast detail resolution, MTF, and NPS were evaluated for a direct flat-panel detector-based digital mammography system following the European Guidelines. Furthermore, system performance relating to both image quality and doses were evaluated using figure of merit (FOM) in terms of CNR2/mean glandular dose (MGD) under automatic exposure control (AEC) and clinically used OPDOSE operating mode. RESULTS AND CONCLUSION: Under AEC mode, FOM values for the 4.5 cm thick BARC polymethyl methacrylate (PMMA) phantom were found to be 15.02, 15.88, and 19.82 at Mo/Mo, Mo/Rh, and W/Rh target/filter (T/F), respectively. Under OPDOSE mode, FOM values were found to 65.32, 11.80, and 1.14 for the BARC PMMA phantom thickness of 2, 4.5, and 8 cm, respectively. Under OPDOSE mode, the calculated MGD values for three Computerized Imaging Reference Systems slab phantoms having total thickness of 7 cm were observed to be 3.03, 2.32, and 1.75 mGy with glandular/adipose tissue compositions of 70/30, 50/50, and 30/70, respectively, whereas for the 2-8-cm thick BARC PMMA phantom, the calculated MGDs were found to be in the range of 0.57-3.32 mGy. All the calculated MGDs values were found to be lower than the acceptable level of dose limits provided in European Guidelines.

Interferometric focal length measurement of positive and negative lenses using a lateral-shearing cyclic path optical configuration setup and polarization phase-shifting interferometry.

We present a simple interferometric focal length measurement technique for measuring the focal length of positive and negative lenses using a lateral-shearing cyclic path optical configuration (CPOC) setup and polarization phase-shifting interferometry (PPSI). The technique requires an auxiliary lens, whose focal length need not be known accurately, for generating a focused point source at its focal plane. The focal point of the test lens is adjusted to be in the vicinity of the focus of the auxiliary lens. The radii of the resulting spherical wave fronts emerging from the test lens, due to the defocus, for two different longitudinal shifted positions of the test lens are measured using the lateral-shearing CPOC setup and PPSI. Focal length of the test lens is determined from the known longitudinal shift and from the measured radii of the spherical wave fronts. Results obtained for 200.0 mm convex and 100.0 mm concave test lenses are presented.

Generation and application of LET calibration curve for neutron dosimetry using CR-39 detector and microwave induced chemical etching.

Microwave induced chemical etching (MICE) has been established as a faster and improved technique compared to other contemporary etching techniques for the development of tracks in a CR-39 detector. However, the methodology could not be applied for LET (linear energy transfer) spectrometry due to lack of a calibration curve using this method. For this purpose, a new LET calibration curve in the range of 12 keV/µm-799 keV/µm was generated considering different ions such as H, Li, C, O, and F on CR-39 having different LETs in water. An empirical relation was established from the obtained calibration curve for determining the value of LET (in water) from the value of V, the ratio of track etch rate to bulk etch rate. For application of this calibration curve in neutron dosimetry, CR-39 detectors were irradiated to neutrons generated from 120 and 142 MeV 16O+27Al systems followed by a similar MICE procedure. The absorbed dose (DLET) and the dose equivalent (HLET) were obtained from the LET spectra and were found to be 13% and 10% higher for 142 MeV 16O+27Al system than those for 120 MeV 16O+27Al system, respectively. The outcome of the study demonstrates the possibility of using the MICE technique for neutron dose estimation by CR-39 via LET spectrometry.