Computational Optimization of Irradiance and Fluence for Interstitial Photodynamic Therapy Treatment of Patients with Malignant Central Airway Obstruction

There are no effective treatments for patients with extrinsic malignant central airway obstruction (MCAO). In a recent clinical study, we demonstrated that interstitial photodynamic therapy (I-PDT) is a safe and potentially effective treatment for patients with extrinsic MCAO. In previous preclinical studies, we reported that a minimum light irradiance and fluence should be maintained within a significant volume of the target tumor to obtain an effective PDT response. In this paper, we present a computational approach to personalized treatment planning of light delivery in I-PDT that simultaneously optimizes the delivered irradiance and fluence using finite element method (FEM) solvers of either Comsol Multiphysics^® or Dosie™ for light propagation. The FEM simulations were validated with light dosimetry measurements in a solid phantom with tissue-like optical properties. The agreement between the treatment plans generated by two FEMs was tested using typical imaging data from four patients with extrinsic MCAO treated with I-PDT. The concordance correlation coefficient (CCC) and its 95% confidence interval (95% CI) were used to test the agreement between the simulation results and measurements, and between the two FEMs treatment plans. Dosie with CCC = 0.994 (95% CI, 0.953-0.996) and Comsol with CCC = 0.999 (95% CI, 0.985-0.999) showed excellent agreement with light measurements in the phantom. The CCC analysis showed very good agreement between Comsol and Dosie treatment plans for irradiance (95% CI, CCC: 0.996-0.999) and fluence (95% CI, CCC: 0.916-0.987) in using patients' data. In previous preclinical work, we demonstrated that effective I-PDT is associated with a computed light dose of ≥45 J/cm² when the irradiance is ≥8.6 mW/cm² (i.e., the effective rate-based light dose). In this paper, we show how to use Comsol and Dosie packages to optimize rate-based light dose, and we present Dosie's newly developed domination sub-maps method to improve the planning of the delivery of the effective rate-based light dose. We conclude that image-based treatment planning using Comsol or Dosie FEM-solvers is a valid approach to guide the light dosimetry in I-PDT of patients with MCAO.

Abstract 2423: Image-guided interstitial photodynamic therapy with palliative radiotherapy for ablating extrabronchial malignant central airway obstruction

Background: Patients with extrabronchial tumors that induce malignant central airway obstruction (MCAO) face dire prognoses with significant morbidity and 1-7 months overall survival. These tumors are inoperable. High-dose curative radiotherapy is associated with significant toxicity. Chemotherapy has limited localized benefits and immunotherapy cannot address the immediate need to halt tumor progression. Our preliminary data suggest that image-guided interstitial photodynamic therapy (I-PDT) with porfimer sodium is safe and potentially effective in patients with extrabronchial tumors that induce MCAO and there is a need to further improve the rate of response. Here we present results showing an improved tumor response rate by augmenting I-PDT with palliative radiotherapy (p-XRT).

Methods: We investigated the addition of p-XRT prior to I-PDT to sensitize the target tumor to subsequent photoreaction in mouse models. Eight- to twelve-week-old C3H and C57B/6 mice with locally advanced (400-600 mm3) SCC-VII or LLC tumors, respectively, were treated with I-PDT alone or with p-XRT followed by I-PDT. The p-XRT regimen was 10 Gy x2 over two days. At 24-26 h after the second 10 Gy fraction, the I-PDT was administered with 5 mg/kg porfimer sodium activated with 630-nm laser light at 5.0 mW/cm2 and 45 J/cm2 at tumor margins. Photoacoustic imaging and light dosimetry measurements were used to investigate the impact of p-XRT on the tumor microenvironment as it pertains to the response to I-PDT. Tumor progression was monitored over 60 days. Image-based treatment planning was used to translate the preclinical findings into a treatment in clinical settings (8 Gy x1 followed by I-PDT) for patients with extrabronchial MCAO.

Results: Preceding I-PDT with p-XRT increases tumor oxygenation for 1-2 days after the last radiation fraction and improves light penetration within mouse tumors. Administering p-XRT 24-48 h before I-PDT significantly (p<0.05, log-rank test) increases the rate of complete tumor response and control from 0% in p-XRT alone or 0-6% in I-PDT alone, to 31-64% for p-XRT followed by I-PDT. In patients, administration of I-PDT with porfimer sodium 48 h after 8Gy x1 p-XRT is feasible and can provide control of extrabronchial MCAO accompanied by symptomatic relief.

Conclusions: Augmenting I-PDT with p-XRT improves the rate of tumor response. Murine studies show that p-XRT increases tumor blood oxygenation and light penetration which could contribute to better response to I-PDT. I-PDT with porfimer sodium preceded by p-XRT is feasible with possible benefits in patients with extrabronchial MCAO.

Citation Format: Emily Oakley, Sarah Chamberlain, Nathaniel Ivanick, Alan Hutson, Theresa Busch, Gal Shafirstein. Image-guided interstitial photodynamic therapy with palliative radiotherapy for ablating extrabronchial malignant central airway obstruction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2423.

Abstract 2420: Interstitial chemo-phototherapy for treatment of locally advanced hepatocellular carcinoma: A preclinical study

Background Patients with hepatocellular carcinoma (HCC) have a poor prognosis with a 5-year survival rate of only 35%. Patients with locally advanced HCC (single or multinodal tumors >3 cm) may not be candidates for curative treatments such as surgical resection, liver transplant or thermal ablation due to tumor size, poor liver function, or other medical co-morbidities. The objective of this study was to investigate the potential use of interstitial chemo-phototherapy (I-CPT) to treat locally advanced HCC with a porphyrin-phospholipid (PoP) liposomal formulation of doxorubicin (Dox) that combines the targeted delivery of doxorubicin with photodynamic therapy to improve local drug delivery. We aimed to identify a safe and effective light dose for the photoactivation of Dox-Pop in the treatment of locally advanced HCC tumors in two pre-clinical models.

Methods Sprague-Dawley rats were inoculated with Morris hepatoma cells directly into the left lateral liver lobe. When the tumors reached 2-2.5 cm along the longest axis, they were treated with Dox-Pop followed by light (i.e. I-CPT). For each rat, we applied our image-based treatment planning to guide the light delivery. Following treatment, tumor response was measured through weekly contrast-enhanced magnetic resonance imaging (CE-MRI). Complete response was defined as no evidence of the tumor via MRI or pathological examination. Our image-based treatment planning was used to translate the findings in the rat study to woodchucks with 1.5-4 cm hepatitis virus induced HCC. Weekly blood samples and bi-weekly CE-MRI were performed to assess tumor response up to 70 days.

Results Five out of the six rats treated with I-CPT had complete response, with three of the five surviving ≥10 weeks post treatment without tumor recurrence or progression. The other two rats with complete response died between 5-7 weeks post treatment. Death was not attributed to the original treatment. Control, untreated rats were euthanized due to tumor progression within 1-2 weeks after tumors reached 2-2.5 cm. From the rat studies, we identified that a light dose rate and dose of respectively, ≥13.4 mW/cm2 and ≥25 J/cm2 can effectively activate the Dox-Pop liposomes. Of the five woodchucks treated with I-CPT using our effective light regimen, two survived ≥ 68 days post treatment without tumor progression. Another woodchuck had a complete response, but was euthanized 55 days post treatment due to the development of a second tumor. One woodchuck had progressive disease following I-CPT. One woodchuck died unexpectedly 5 days post I-CPT. Death was attributed to high tumor necrosis.

Conclusions This study demonstrated the potential use of I-CPT as a treatment option for locally advanced HCC not candidate for standard of care therapies. Ongoing studies are being conducted in woodchucks to optimize the I-CPT light settings and improve tumor response.

Citation Format: Emily Oakley, Minhyung Kim, Sanjana Ghosh, Hilliard Kutscher, Jonathan Lovell, Leslie Curtin, Sandra Sexton, Alan Hutson, Gal Shafirstein. Interstitial chemo-phototherapy for treatment of locally advanced hepatocellular carcinoma: A preclinical study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2420.

Interstitial Photothermal Therapy Generates Durable Treatment Responses in Neuroblastoma

Photothermal therapy (PTT) represents a promising modality for tumor control typically using infrared light-responsive nanoparticles illuminated by a wavelength-matched external laser. However, due to the constraints of light penetration, PTT is generally restricted to superficially accessible tumors. With the goal of extending the benefits of PTT to all tumor settings, interstitial PTT (I-PTT) is evaluated by the photothermal activation of intratumorally administered Prussian blue nanoparticles with a laser fiber positioned interstitially within the tumor. This interstitial fiber, which is fitted with a terminal diffuser, distributes light within the tumor microenvironment from the "inside-out" as compared to from the "outside-in" traditionally observed during superficially administered PTT (S-PTT). I-PTT improves the heating efficiency and heat distribution within a target treatment area compared to S-PTT. Additionally, I-PTT generates increased cytotoxicity and thermal damage at equivalent thermal doses, and elicits immunogenic cell death at lower thermal doses in targeted neuroblastoma tumor cells compared to S-PTT. In vivo, I-PTT induces significantly higher long-term tumor regression, lower rates of tumor recurrence, and improved long-term survival in multiple syngeneic murine models of neuroblastoma. This study highlights the significantly enhanced therapeutic benefit of I-PTT compared to traditional S-PTT as a promising treatment modality for solid tumors.

In Vivo Models for Studying Interstitial Photodynamic Therapy of Locally Advanced Cancer

Interstitial photodynamic therapy (I-PDT) is a promising therapy considered for patients with locally advanced cancer. In I-PDT, laser fibers are inserted into the tumor for effective illumination and activation of the photosensitizer in a large tumor. The intratumoral light irradiance and fluence are critical parameters that affect the response to I-PDT. In vivo animal models are required to conduct light dose studies, to define optimal irradiance and fluence for I-PDT. Here we describe two animal models with locally advanced tumors that can be used to evaluate the response to I-PDT. One model is the C3H mouse bearing large subcutaneous SCCVII carcinoma (400-600 mm³). Using this murine model, multiple light regimens with one or two optical fibers with cylindrical diffuser ends (cylindrical diffuser fiber, CDF) can be used to study tumor response to I-PDT. However, tissue heating may occur when 630 nm therapeutic light is delivered through CDF at an intensity ≥60 mW/cm and energy ≥100 J/cm. These thermal effects can impact tumor response while treating locally advanced mice tumors. Magnetic resonance imaging and thermometry can be used to study these thermal effects. A larger animal model, New Zealand White rabbit with VX2 carcinoma (~5000 mm³) implanted in either the sternomastoid (neck implantation model) or the biceps femoris muscle (thigh implantation model), can be used to study I-PDT with image-based pretreatment planning using computed tomography. In the VX2 model, the light delivery can include the use of multiple laser fibers to test light dosimetry and delivery that are relevant for clinical use of I-PDT.

An Optical Surface Applicator for Intraoperative Photodynamic Therapy

BACKGROUND AND OBJECTIVES

Intraoperative photodynamic therapy (IO-PDT) is typically administered by a handheld light source. This can result in uncontrolled distribution of light irradiance that impacts tissue and tumor response to photodynamic therapy. The objective of this work was to characterize a novel optical surface applicator (OSA) designed to administer controlled light irradiance in IO-PDT.

STUDY DESIGN/MATERIALS AND METHODS

An OSA was constructed from a flexible silicone mesh applicator with multiple cylindrically diffusing optical fibers (CDF) placed into channels of the silicone. Light irradiance distribution, at 665 nm, was evaluated on the OSA surface and after passage through solid tissue-mimicking optical phantoms by measurements from a multi-channel dosimetry system. As a proof of concept, the light administration of the OSA was tested in a pilot study by conducting a feasibility and performance test with 665-nm laser light to activate 2-(1'-hexyloxyethyl) pyropheophorbide-a (HPPH) in the thoracic cavity of adult swine.

RESULTS

At the OSA surface, the irradiance distribution was non-uniform, ranging from 128 to 346 mW/cm2 . However, in the tissue-mimicking phantoms, beam uniformity improved markedly, with irradiance ranges of 39-153, 33-87, and 12-28 mW/cm2 measured at phantom thicknesses of 3, 5, and 10 mm, respectively. The OSA safely delivered the prescribed light dose to the thoracic cavities of four swine.

CONCLUSIONS

The OSA can provide predictable light irradiances for administering a well-defined and potentially effective therapeutic light in IO-PDT. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength: A Biomechanical Study

PURPOSE

To compare the response to cyclical loading and ultimate pull-out strength of threaded suture anchor with and without calcium phosphate bone void filler augmentation in a polyurethane foam block model and in vitro proximal humerus cadaveric model.

METHODS

This controlled biomechanical study consisted of 2 parts: (1) preliminary polyurethane foam block model, and (2) in vitro cadaveric humeri model. The preliminary foam block model intended to mimic osteoporotic bone using a 0.12 g/mL foam material. Half of the foam block models were first filled with injectable calcium phosphate bone substitute material (CP-BSM), whereas the other half were not augmented with CP-BSM. Each specimen was then instrumented with a threaded suture anchor. The same technique and process was performed in a matched cadaveric humeri model. Testing then consisted of a stepwise, increasing axial load protocol for a total of 40 cycles. If the anchor remained intact after cyclic loading, the repair was loaded to failure. The number of completed cycles, failure load, and failure modes were compared between groups.

RESULTS

Average pull-out strength for suture anchor with CP-BSM in the osteoporotic foam block model was significantly higher at 332.68 N ± 47.61 compared with the average pull-out strength of suture anchor without CP-BSM at 144.38 N ± 14.58 (P = .005). In the matched cadaveric humeri model, average pull-out strength for suture anchor with CP-BSM was significantly higher at 274.07 N ± 102.07 compared with the average pull-out strength of suture anchor without CP-BSM at 138.53 N ± 109.87 (P = .029).

CONCLUSIONS

In this time zero, biomechanical study, augmentation of osteoporotic foam block and cadaveric bone with calcium phosphate bone substitute material significantly increases pull-out strength of threaded suture anchors.

CLINICAL RELEVANCE

Considering concerns about suture anchor pull-out from osteoporotic bone, augmentation with calcium phosphate bone substitute material increases load to failure resistance.

Irradiance, Photofrin® Dose and Initial Tumor Volume are Key Predictors of Response to Interstitial Photodynamic Therapy of Locally Advanced Cancers in Translational Models

The objective of the present study was to develop a predictive model for Photofrin® -mediated interstitial photodynamic therapy (I-PDT) of locally advanced tumors. Our finite element method was used to simulate 630-nm intratumoral irradiance and fluence for C3H mice and New Zealand White rabbits bearing large squamous cell carcinomas. Animals were treated with light only or I-PDT using the same light settings. I-PDT was administered with Photofrin® at 5.0 or 6.6 mg kg-1 , 24 h drug-light interval. The simulated threshold fluence was fixed at 45 J cm-2 while the simulated threshold irradiance varied, intratumorally. No cures were obtained in the mice treated with a threshold irradiance of 5.4 mW cm-2 . However, 20-90% of the mice were cured when the threshold irradiances were ≥8.6 mW cm-2 . In the rabbits treated with I-PDT, 13 of the 14 VX2 tumors showed either local control or were cured when threshold irradiances were ≥15.3 mW cm-2 and fluence was 45 J cm-2 . No tumor growth delay was observed in VX2 treated with light only (n = 3). In the mouse studies, there was a high probability (92.7%) of predicting cure when the initial tumor volume was below the median (493.9 mm3 ) and I-PDT was administered with a threshold intratumoral irradiance ≥8.6 mW cm-2 .

Irradiance controls photodynamic efficacy and tissue heating in experimental tumours: implication for interstitial PDT of locally advanced cancer

Background

Currently delivered light dose (J/cm²) is the principal parameter guiding interstitial photodynamic therapy (I-PDT) of refractory locally advanced cancer. The aim of this study was to investigate the impact of light dose rate (irradiance, mW/cm²) and associated heating on tumour response and cure.

Methods

Finite-element modeling was used to compute intratumoural irradiance and dose to guide Photofrin^® I-PDT in locally advanced SCCVII in C3H mice and large VX2 neck tumours in New Zealand White rabbits. Light-induced tissue heating in mice was studied with real-time magnetic resonance thermometry.

Results

In the mouse model, cure rates of 70–90% were obtained with I-PDT using 8.4–245 mW/cm² and ≥45 J/cm² in 100% of the SCCVII tumour. Increasing irradiance was associated with increase in tissue heating. I-PDT with Photofrin^® resulted in significantly (p < 0.05) higher cure rate compared to light delivery alone at same irradiance and light dose. Local control and/or cures of VX2 were obtained using I-PDT with 16.5–398 mW/cm² and ≥45 J/cm² in 100% of the tumour.

Conclusion

In Photofrin^®-mediated I-PDT, a selected range of irradiance prompts effective photoreaction with tissue heating in the treatment of locally advanced mouse tumour. These irradiances were translated for effective local control of large VX2 tumours.

Reconstruction of a Deformed Tumor Based on Fiducial Marker Registration: A Computational Feasibility Study

Interstitial photodynamic therapy has shown promising results in the treatment of locally advanced head and neck cancer. In this therapy, systemic administration of a light-sensitive drug is followed by insertion of multiple laser fibers to illuminate the tumor and its margins. Image-based pretreatment planning is employed in order to deliver a sufficient light dose to the complex locally advanced head-and-neck cancer anatomy, in order to meet clinical requirements. Unfortunately, the tumor may deform between pretreatment imaging for the purpose of planning and intraoperative imaging when the plan is executed. Tumor deformation may result from the mechanical forces applied by the light fibers and variation of the patient’s posture. Pretreatment planning is frequently done with the assistance of computed tomography or magnetic resonance imaging in an outpatient suite, while treatment monitoring and control typically uses ultrasound imaging due to considerations of costs and availability in the operation room. This article presents a computational method designed to bridge the gap between the 2 imaging events by taking a tumor geometry, reconstructed during preplanning, and by following the displacement of fiducial markers, which are initially placed during the preplanning procedure. The deformed tumor shape is predicted by solving an inverse problem, seeking for the forces that would have resulted in the corresponding fiducial marker displacements. The computational method is studied on spheres of variable sizes and demonstrated on computed tomography reconstructed locally advanced head and neck cancer model. Results of this study demonstrate an average error of less than 1 mm in predicting the deformed tumor shape, where 1 mm is typically the order of uncertainty in distance measurements using magnetic resonance imaging or computed tomography imaging and high-quality ultrasound imaging. This study further demonstrates that the deformed shape can be calculated in a few seconds, making the proposed method clinically relevant.

Endobronchial ultrasound-guidance for interstitial photodynamic therapy of locally advanced lung cancer-a new interventional concept

Recent advances in interventional pulmonology led to a significant expansion of the diagnostic and therapeutic role of endobronchial ultrasound. In this paper, we describe a new concept for using endobronchial ultrasound to guide interstitial photodynamic therapy (PDT). For this purpose, we conducted in vitro and in vivo experiments using a phantom and animal models, respectively. A new 0.5 mm optical fiber, with cylindrical diffuser end, was used to deliver the therapeutic light through the 21-gauge endobronchial ultrasound needle. The animal experiments were performed under real-time ultrasonography guidance in mice and rabbits' tumor models. Safe and effective fiber placements and tumor illumination was accomplished. In addition, computer simulation of light propagation suggests that locally advanced lung cancer tumor can be illuminated. This study demonstrates the potential feasibility of this new therapeutic modality approach, justifying further investigation in the treatment of locally advanced lung cancers.

Quantum dot light emitting devices for photomedical applications

While OLEDs have struggled to find a niche lighting application that can fully take advantage of their unique form factors as thin, flexible, lightweight and uniformly large-area luminaire, photomedical researchers have been in search of low-cost, effective illumination devices with such form factors that could facilitate widespread clinical applications of photodynamic therapy (PDT) or photobiomodulation (PBM). Although existing OLEDs with either fluorescent or phosphorescent emitters cannot achieve the required high power density at the right wavelength windows for photomedicine, the recently developed ultrabright and efficient deep red quantum dot light emitting devices (QLEDs) can nicely fit into this niche. Here, we report for the first time the in-vitro study to demonstrate that this QLED-based photomedical approach could increase cell metabolism over control systems for PBM and kill cancerous cells efficiently for PDT. The perspective of developing wavelength-specific, flexible QLEDs for two critical photomedical fields (wound repair and cancer treatment) will be presented with their potential impacts summarized. The work promises to generate flexible QLED-based light sources that could enable the widespread use and clinical acceptance of photomedical strategies including PDT and PBM.

Surface markers for guiding cylindrical diffuser fiber insertion in interstitial photodynamic therapy of head and neck cancer

BACKGROUND AND OBJECTIVES

Image-based treatment planning can be used to compute the delivered light dose during interstitial photodynamic therapy (I-PDT) of locally advanced head and neck squamous cell carcinoma (LA-HNSCC). The objectives of this work were to evaluate the use of surface fiducial markers and flexible adhesive grids in guiding interstitial placement of laser fibers, and to quantify the impact of discrepancies in fiber location on the expected light dose volume histograms (DVHs).

METHODS

Seven gel-based phantoms were made to mimic geometries of LA-HNSCC. Clinical flexible grids and fiducial markers were used to guide the insertion of optically transparent catheters, which are used to place cylindrical diffuser fibers within the phantoms. A computed tomography (CT) was used to image the markers and phantoms before and after catheter insertion and to determine the difference between the planned and actual location of the catheters. A finite element method was utilized to compute the light DVHs. Statistical analysis was employed to evaluate the accuracy of fiber placement and to investigate the correlation between the location of the fibers and the calculated DVHs.

RESULTS

There was a statistically significant difference (P = 0.018) between all seven phantoms in terms of the mean displacement. There was also statistically significant correlation between DVHs and depth of insertion (P = 0.0027), but not with the lateral displacement (P = 0.3043). The maximum difference between actual and planned DVH was related to the number of fibers (P = 0.0025) and the treatment time.

CONCLUSIONS

Surface markers and a flexible grid can be used to assist in the administration of a prescribed DVH within 15% of the target dose provided that the treatment fibers are placed within 1.3 cm of the planned depth of insertion in anatomies mimicking LA-HNSCC. The results suggest that the number of cylindrical diffuser fibers and treatment time can impact the delivered DVHs. Lasers Surg. Med. 49:599-608, 2017. © 2017 Wiley Periodicals, Inc.

Interstitial Photodynamic Therapy-A Focused Review

Multiple clinical studies have shown that interstitial photodynamic therapy (I-PDT) is a promising modality in the treatment of locally-advanced cancerous tumors. However, the utilization of I-PDT has been limited to several centers. The objective of this focused review is to highlight the different approaches employed to administer I-PDT with photosensitizers that are either approved or in clinical studies for the treatment of prostate cancer, pancreatic cancer, head and neck cancer, and brain cancer. Our review suggests that I-PDT is a promising treatment in patients with large-volume or thick tumors. Image-based treatment planning and real-time dosimetry are required to optimize and further advance the utilization of I-PDT. In addition, pre- and post-imaging using computed tomography (CT) with contrast may be utilized to assess the response.

A new finite element approach for near real-time simulation of light propagation in locally advanced head and neck tumors

Background and Objectives

Several clinical studies suggest that interstitial photodynamic therapy (I‐PDT) may benefit patients with locally advanced head and neck cancer (LAHNC). For I‐PDT, the therapeutic light is delivered through optical fibers inserted into the target tumor. The complex anatomy of the head and neck requires careful planning of fiber insertions. Often the fibers' location and tumor optical properties may vary from the original plan therefore pretreatment planning needs near real‐time updating to account for any changes. The purpose of this work was to develop a finite element analysis (FEA) approach for near real‐time simulation of light propagation in LAHNC.

Methods

Our previously developed FEA for modeling light propagation in skin tissue was modified to simulate light propagation from interstitial optical fibers. The modified model was validated by comparing the calculations with measurements in a phantom mimicking tumor optical properties. We investigated the impact of mesh element size and growth rate on the computation time, and defined optimal settings for the FEA. We demonstrated how the optimized FEA can be used for simulating light propagation in two cases of LAHNC amenable to I‐PDT, as proof‐of‐concept.

Results

The modified FEA was in agreement with the measurements (P = 0.0271). The optimal maximum mesh size and growth rate were 0.005–0.02 m and 2–2.5 m/m, respectively. Using these settings the computation time for simulating light propagation in LAHNC was reduced from 25.9 to 3.7 minutes in one case, and 10.1 to 4 minutes in another case. There were minor differences (1.62%, 1.13%) between the radiant exposures calculated with either mesh in both cases.

Conclusions

Our FEA approach can be used to model light propagation from diffused optical fibers in complex heterogeneous geometries representing LAHNC. There is a range of maximum element size (MES) and maximum element growth rate (MEGR) that can be used to minimize the computation time of the FEA to 4 minutes. Lasers Surg. Med. 47:60–67, 2015. © 2015 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Limited analgesic efficacy of nitrous oxide for painful procedures in children

STUDY OBJECTIVE

Nitrous oxide (N(2)O) is an attractive agent for procedural analgesia and sedation of children in the emergency department (ED). Despite increasing use, efficacy data for painful procedures are limited. This study aimed to determine pain scores during ED procedural sedation with N(2)O in the ED setting.

METHODS

Prospective observational study of N(2)O use as a sole agent for procedural analgesia at a tertiary children's hospital ED. Pain scores were obtained from patients and parents using visual analogue or faces scales, as appropriate. Parent and staff satisfaction with sedation and analgesia were assessed.

RESULTS

124 children aged 1-17 years (mean 8.1) underwent procedural analgesia with N(2)O for 131 procedures. Most procedures were orthopaedic (44%) or laceration repair (30%). In 51% of patients (95% CI 42% to 60 to 23%) pain scores remained unchanged and in 34% (95% CI 26% to 43%) pain scores increased. Overall, 34% (95% CI 26% to 43%) patients had intraprocedural scores of 50 mm or greater and 21% (95% CI 14% to 29%) had pain scores of 70 mm or greater. Some procedures such as fracture reduction had a larger proportion of patients with high pain scores or 50 mm or greater (45%) and 70 mm or greater (29%). Staff rated both sedation and analgesia as "adequate" in 92%. Parents contacted in follow-up were satisfied or very satisfied with procedures in 96% and sedations in 93%.

CONCLUSION

Data indicate that parents and staff are generally satisfied with N(2)O for procedural use in the ED. The efficacy of N(2)O as a sole agent in very painful procedures is limited.

Reduction of paediatric in-patient cardiac arrest and death with a medical emergency team: preliminary results

AIMS

To determine the impact of a paediatric medical emergency team (MET) on cardiac arrest, mortality, and unplanned admission to intensive care in a paediatric tertiary care hospital.

METHODS

Comparison of the retrospective incidence of cardiac arrest and death during 41 months before introduction of a MET service with the prospective incidence of these events during 12 months after its introduction. Comparison of transgression of MET call criteria in patients who arrested and died before and after introduction of MET.

RESULTS

Cardiac arrest decreased from 20 among 104 780 admissions (0.19/1000) to 4 among 35 892 admissions (0.11/1000) (risk ratio 1.71, 95% CI 0.59 to 5.01), while death decreased from 13 (0.12/1000) to 2 (0.06/1000) during these periods (risk ratio 2.22, 95% CI 0.50 to 9.87). Unplanned admissions to intensive care increased from 20 (SD 6) to 24 (SD 9) per month. The incidence of transgression of MET call criteria in patients who arrested decreased from 17 to 0 (risk difference 0.16/1000, 95% CI 0.09 to 0.24), and in those who died, decreased from 12 to 0 (risk difference 0.11/1000, 95% CI 0.05 to 0.18) after introduction of MET.

CONCLUSIONS

Introduction of a medical emergency team service was coincident with a reduction of cardiac arrest and mortality and a slight increase in admissions to intensive care.

Management of suspected cervical spine injuries--the paediatric perspective

Paediatric cervical spine immobilisation and management is one of the most difficult tasks to master in the paediatric trauma population. The Royal Children's Hospital--Melbourne has admitted 54 patients with diagnosed cervical spine injuries since January 1999. The management of such patients admitted to acute care facilities with suspected cervical spine injuries is inconsistent and at times sub-optimal. Management controversies centre around, application of cervical collars, clearance of the c-spine, patient movement and general care principles. In an endeavour to address these issues, the Royal Children's Hospital Trauma Service, in conjunction with the Emergency Department developed cervical spine guidelines. Teams consulted in the formulation of these guidelines included, Emergency Department, Intensive Care Unit, Orthopaedics, Neurosurgery, Radiology and General Surgery. These guidelines were developed as a clinical tool to guide management and standardise the approach of care for these patients. Specifically, the guidelines address: immobilisation of the paediatric cervical spine; radiology; clearing the cervical spine of injury; suspected or proven cervical spine injury; guidelines for times to fitting Philadelphia collar; ongoing care.

Evaluation of a coagulation analyzer

The CA-6000 compared favorably to the well-established 1600C in terms of clinical utility. Its enhanced reagent capacity and open nature make it a wise instrument selection option.

Formation of the biologic width following crown lengthening in nonhuman primates

The purpose of this study was to determine if and how the biologic width is reestablished following surgical crown lengthening. Crown-lengthening surgery was performed on the right or left maxillary and mandibular central and lateral incisors of three adult monkeys, with contralateral teeth serving as unoperated controls. Twelve weeks after surgery, tissue blocks were removed for histologic analysis. The results of a histometric evaluation indicate that the biologic width is reestablished following surgical crown lengthening. The junctional epithelium generally migrates to the apical level of root planing. Space for the supracrestal connective tissue fiber groups is created by crestal resorption of alveolar bone.