Burnout Rates in Clinical Radiation Oncology and Variations across Professional Subgroups

PURPOSE/OBJECTIVE(S)

Physician and medical professional burnout has emerged as an important issue in clinical medicine and has been shown to negatively affect patient outcomes. The aim of this study is to determine how rates of burnout vary between different radiation oncology professional subgroups.

MATERIALS/METHODS

Participants were selected from those employed in one of the professional subgroups (radiation therapists, nurses, physicists, dosimetrists, and physicians) at two institutions that cover a total of seven sites. 126 individuals were recruited to participate. In addition to demographics, participants were asked to respond to questions regarding professional burnout utilizing the Maslach Burnout Inventory (MBI). Responses were on a seven-point Likert scale with subcategories of Exhaustion, Depersonalization, and Personal Achievement. Each participant's score per subcategory was categorized as either low, moderate, or high. For our primary outcome, frequencies and proportions were reported and Fisher's Exact Test was used to evaluate whether there was a statistically significant difference in proportions in categorized burnout scores across professional subgroups. Secondary analyses were performed comparing burnout across sex, age, and categorized years in position. An alpha level of 0.05 was used for all analyses.

RESULTS

In total, 55 participants responded to the survey: 12 nurses, 8 dosimetrists, 12 physicians, 5 physicists, and 18 radiation therapists for a response rate of 43.6%. Demographics were consistent across professional subgroups with the exception of participant sex (p = .0397), which had a greater proportion of females (72.22%) in the Radiation Therapist subgroup. Among the three subcategories, only Exhaustion had a significant difference between groups (p = .0494) with Dosimetrists (62.50%) and Physicists (40.00%) experiencing the highest level of burnout. For Depersonalization, at least one individual in each subgroup identified high burnout with higher rates among the Dosimetrists (25.00%) and Physicists (40.00%). Similarly, at least one person in each subgroup reported high burnout in Personal Achievement, but the highest response was among Dosimetrists (37.50%). In total, at least 12.75% of participants reported high burnout in at least one subcategory. No statistically significant differences in burnout were detected in our secondary analyses across sex, age, and years in position.

CONCLUSION

Our study showed that burnout rates are moderate in members of the radiation oncology team, with dosimetrists and physicists displaying the highest levels of burnout. In order to better estimate professional burnout, larger studies should be conducted to determine causes of burnout. Furthermore, wellness programs should be encouraged and incentivized to help reduce burnout and improve workplace morale, occupational fulfillment, and effective patient care.

Development and verification of the signal to noise ratio for a layer of turbulence in a multi-layer atmosphere

Wide-field image correction in systems that look through the atmosphere generally requires a tomographic reconstruction of the turbulence volume to compensate for anisoplanatism. The reconstruction is conditioned by estimating the turbulence volume as a profile of thin homogeneous layers. We present the signal to noise ratio (SNR) of a layer, which quantifies how difficult a single layer of homogeneous turbulence is to detect with wavefront slope measurements. The signal is the sum of wavefront tip and tilt variances at the signal layer, and the noise is the sum of wavefront tip and tilt auto-correlations given the aperture shape and projected aperture separations at all non-signal layers. An analytic expression for layer SNR is found for Kolmogorov and von Kármán turbulence models, then verified with a Monte Carlo simulation. We show that the Kolmogorov layer SNR is a function of only layer Fried length, the spatio-angular sampling of the system, and normalized aperture separation at the layer. In addition to these parameters, the von Kármán layer SNR also depends on aperture size, and layer inner and outer scales. Due to the infinite outer scale, layers of Kolmogorov turbulence tend to have lower SNR than von Kármán layers. We conclude that the layer SNR is a statistically valid performance metric to be used when designing, simulating, operating, and quantifying the performance of any system that measures properties of layers of turbulence in the atmosphere from slope data.

Brachytherapy for Central Serous Chorioretinopathy

Brachytherapy is widely used for the treatment of choroidal melanoma and has recently been explored for the treatment of wet age-related macular degeneration. We propose the use of low dose radiation via episcleral brachytherapy in refractory cases of central serous chorioretinopathy (CSCR). The pathogenesis of CSCR involves dilatation and hyperpermeability of large choroidal vessels. Low dose radiation can induce intimal proliferation in large choroidal vessels and decrease their hyperpermeability. Concerns about the use of brachytherapy in CSCR include damage to the choriocapillaris or the retinal vessels. This can be addressed with the use of a specialized device through which a very precise and appropriate dose can be delivered. The dose of the radiation delivered decreases exponentially at a depth of approximately 0.5–1.5 mm from the devise–sclera interface. Considering an increased choroidal thickness in cases of CSCR, delivery of a safe dose can be assured.

Two-year outcomes of episcleral brachytherapy adjunct to anti-VEGF therapy for treatment-resistant nAMD

PURPOSE

This study was designed to demonstrate the safety and feasibility of episcleral brachytherapy (ESB) for the treatment of anti-vascular endothelial growth factor (anti-VEGF) resistant neovascular age-related macular degeneration (nAMD) in a 6-subject cohort adjunct to anti-VEGF therapy.

METHODS

Six eyes of six subjects with anti-VEGF resistant nAMD (persistent fluid or hemorrhage despite frequent anti-VEGF treatment) were treated with ESB between May 2018 and July 2018 as part of a larger early feasibility trial. Baseline and follow-up exams with multi-modal imaging were conducted.

RESULTS

In this analysis, six eyes were included. The mean age was 74.7 years; 33% were female; 67% had polypoidal choroidal vasculopathy. The mean number of lifetime anti-VEGF injections received prior to the study enrollment was 33.9 injections and 10 injections in the year prior to the study enrollment. In the first and second years following ESB, the mean number of injections was 8.5 and 8, respectively. No evidence of radiation-induced toxicity through 2 years following ESB was observed. The mean baseline VA was 55.3 letters. At 1 year, the mean VA increased by 3.2 letters and 1.7 letters at year 2. At 2 years, the mean change in vascular complex on ICGA was - 18%, - 43% on OCTA, and - 5% on FA. The subjects also experienced a mean decrease in CRT on OCT of 21% after 2 years.

CONCLUSIONS

The results from this six-subject cohort with 2-year data support additional investigations of ESB for nAMD, specifically those with persistent disease activity and treatment resistant nAMD.

Pilot Study: Texture Analysis of PET Imaging Demonstrates Changes in 18F-FDG Uptake of the Brain After Prophylactic Cranial Irradiation

Prophylactic cranial irradiation (PCI) is used to decrease the probability of developing brain metastases in patients with small cell lung cancer and has been linked to deleterious cognitive effects. Although no well-established imaging markers for these effects exist, previous studies have shown that structural and metabolic changes in the brain can be detected with MRI and PET. This study used an image processing technique called texture analysis to explore whether global changes in brain glucose metabolism could be characterized in PET images. Methods: ¹⁸F-FDG PET images of the brain from patients with small cell lung cancer, obtained before and after the administration of PCI, were processed using texture analysis. Texture features were compared between the pre- and post-PCI images. Results: Multiple texture features demonstrated statistically significant differences before and after PCI when texture analysis was applied to the brain parenchyma as a whole. Regional differences were also seen but were not statistically significant. Conclusion: Global changes in brain glucose metabolism occur after PCI and are detectable using advanced image processing techniques. These changes may reflect radiation-induced damage and thus may provide a novel method for studying radiation-induced cognitive impairment.

Preliminary Clinical Evaluation of Intrafraction Prostate Displacements for Two Immobilization Systems

Immobilization systems and their corresponding set-up errors influence the clinical target volume to the planning target volume (CTV-PTV) margins, which is critical for hypofractionated prostate stereotactic body radiotherapy (SBRT). This preliminary study evaluates intrafraction prostate displacement for two immobilization systems (A and B). Six consecutive patients having localized prostate cancer and implanted prostate marker seeds were studied. Planar X-ray images were acquired pre- and post-treatment to find the intrafraction prostate displacement. The average absolute displacements (lateral, longitudinal, vertical) were 0.9 ± 0.4 mm, 1.7 ± 0.1 mm, 1.3 ± 0.3 mm (system A), and 0.5 ± 0.2 mm, 0.6 ± 0.1 mm, 0.8 ± 0.3 mm (system B), with average three-dimensional displacements of 2.6 ± 0.2 mm (system A) and 1.3 ± 0.2 mm (system B). The computed CTV-PTV margins (lateral, longitudinal, vertical) were 2.5 mm, 2.5 mm, 3.6 mm and 1.4 mm, 1.6 mm, 2.4 mm for systems A and B, respectively. This suggests that the immobilization system influences intrafraction prostate displacement and, therefore, the margins applied. However, the margins found for both systems are comparable to the margins used for hypofractionated prostate SBRT.

A simple knowledge-based tool for stereotactic radiosurgery pre-planning

We studied the dosimetry of single‐isocenter treatment plans generated to treat a solitary intracranial lesion using linac‐based stereotactic radiosurgery (SRS). A common metric for evaluating SRS plan quality is the volume of normal brain tissue irradiated by a dose of at least 12 Gy (V12), which is important because multiple studies have shown a strong correlation between V12 and incidence of radiation necrosis. Unrealistic expectations for values of V12 can lead to wasted planning time. We present a model that estimates V12 without having to construct a full treatment plan. This model was derived by retrospectively analyzing 50 SRS treatment plans, each clinically approved for delivery using circular collimator cone arc therapy (CAT). Each case was re‐planned for delivery via dynamic conformal arc therapy (DCAT), and then scaling arguments were used to extend dosimetric data to account for different prescription dose (PD) values (15, 18, 21, or 24 Gy). We determined a phenomenological expression for the total volume receiving at least 12 Gy (TV12) as a function of both planning target volume (PTV) and PD: TV12/1cc=n∗PD/1Gy+d∗PTV/1cca∗PD/1Gyc, where a,c,n,d are fit parameters, and a separate set of values is determined for each plan type. In addition, we generated a sequence of plots to clarify how the relationship between conformity index (CI) and TV12 depends on plan type (CAT vs DCAT), PTV, and PD. These results can be used to suggest realistic plan parameters and planning goals before the start of treatment planning. In the absence of access to more sophisticated pre‐planning tools, this model can be locally generated and implemented at relatively low cost with respect to time, money, and expertise.

Regional Changes in Brain 18F-FDG Uptake After Prophylactic Cranial Irradiation and Chemotherapy in Small Cell Lung Cancer May Reflect Functional Changes

Chemotherapy followed by prophylactic cranial irradiation (PCI) is associated with increased survival in patients with small cell lung cancer but is associated with fatigue and cognitive impairment. This retrospective study evaluated regional differences in ¹⁸F-FDG uptake by the brain before and after PCI. The null hypothesis was that direct toxic effects on the brain from PCI and chemotherapy are symmetric; thus, asymmetric deviations may reflect functional changes due to therapy. Methods: Electronic medical records from 2013 to 2016 were reviewed for patients with small cell lung cancer, MRI of brain negative for metastasis, and ¹⁸F-FDG PET/CT scans before and after PCI. As the standard of care, patients received first-line chemotherapy or chemoradiation to the thorax followed by PCI. The ¹⁸F-FDG PET/CT scans nearest the PCI were selected. Sixteen patients met these initial criteria. Commercially available PET software was used to register and subtract the PET scans before and after PCI to obtain difference maps. Occipital and cerebellar regions were excluded from the final statistical analysis given the known high variability and misregistration. The χ² test was used to analyze the data. Results: Two patients had ¹⁸F-FDG uptake differences only in the occipital and cerebellar regions. The software registration failed on 1 patient's scans. Therefore, 13 patients were included in the final analysis. Nine of 13 patients demonstrated significant unilateral changes in only 1 region of the brain, and 3 of 13 showed significant changes unilaterally in 2 regions. The χ² test revealed a significant unilateral regional difference on a patient level (χ² = 6.24, P = 0.025). The most commonly affected brain region was the frontal lobe. Conclusion: Significantly more patients had unilateral than bilateral regional differences (both increases and decreases) in ¹⁸F-FDG uptake in the brain before and after PCI. This finding suggests that differences in unilateral distribution are related to functional changes, since direct toxicity alone from PCI and chemotherapy would be symmetric. The frontal region was the most commonly affected, suggesting a potential contributing etiology for cognitive impairment and decreased executive function after therapy.

Germline single nucleotide polymorphisms associated with response of urothelial carcinoma to platinum-based therapy: the role of the host

BACKGROUND

Variations in urothelial carcinoma (UC) response to platinum chemotherapy are common and frequently attributed to genetic and epigenetic variations of somatic DNA. We hypothesized that variations in germline DNA may contribute to UC chemosensitivity.

PATIENTS AND METHODS

DNA from 210 UC patients treated with platinum-based chemotherapy was genotyped for 80 single nucleotide polymorphisms (SNPs). Logistic regression was used to examine the association between SNPs and response, and a multivariable predictive model was created. Significant SNPs were combined to form a SNP score predicting response. Eleven UC cell lines were genotyped as validation.

RESULTS

Six SNPs were significantly associated with 101 complete or partial responses (48%). Four SNPs retained independence association and were incorporated into a response prediction model. Each additional risk allele was associated with a nearly 50% decrease in odds of response [odds ratio (OR) = 0.51, 95% confidence interval 0.39-0.65, P = 1.05 × 10(-7)). The bootstrap-adjusted area under the curves of this model was greater than clinical prognostic factors alone (0.78 versus 0.64). The SNP score showed a positive trend with chemosensitivity in cell lines (P = 0.115).

CONCLUSIONS

Genetic variants associated with response of UC to platinum-based therapy were identified in germline DNA. A model using these genetic variants may predict response to chemotherapy better than clinical factors alone.

Reproductive biology of squaretail coralgrouper Plectropomus areolatus using age-based techniques

The squaretail coralgrouper Plectropomus areolatus was identified as a fast-growing, early maturing and relatively short-lived aggregation-spawning epinephelid. Examinations of sectioned otoliths found females and males first maturing at 2 and 3 years, respectively, suggesting protogynous hermaphroditism; however, no transitionals were observed in samples. Age distribution for the two sexes was similar and both were represented in the oldest age class; however, significant sex-specific differences in size-at-age were identified. Both sexes fully recruit into the fishery at age 4 years and reach 90% of asymptotic length by age 3 years. Underwater visual assessments, combined with the gonado-somatic indices, revealed a 5 month reproductive season, with interannual variability observed in the month of highest density within the spawning aggregation. Catch restrictions on adults during spawning times and at reproductive sites, combined with gear-based management and enhanced enforcement, are recommended to maintain spawning stocks. Based on the available evidence, the sexual pattern for this species is unresolved.

Prostate cancer risk in men with prostate and breast cancer family history: results from the REDUCE study (R1)

BACKGROUND

To what degree the associations between PCa risk and family history of prostate cancer (PCa) and/or breast cancer (BCa) are attributable to screening biases is unclear. We examined these questions within the REDUCE study, where biopsies were largely independent of prostate specific antigen (PSA) minimizing screening biases.

METHODS

Data were from REDUCE, which tested dutasteride 0.5 mg daily for PCa risk reduction in men with PSA 2.5-10.0 ng mL(-1) and a negative prestudy biopsy. Among men undergoing at least one on-study biopsy with complete data (n = 6415; 78.1%), the association between family history and PCa risk was tested using multivariate logistic regression adjusting for clinicodemographic characteristics.

RESULTS

A family history of PCa alone was associated with increased PCa diagnosis (OR: 1.47, 95%CI: 1.22-1.77). In North America, PCa family history was not related to PCa diagnosis (OR: 1.02, 95%CI: 0.73-1.44), whereas outside North America, PCa family history was significantly related to diagnosis (OR: 1.72, 95%CI: 1.38-2.15) (P-interaction = 0.01). A family history of both PCa and BCa (OR: 2.54, 95%CI: 1.72-3.75) but not BCa alone (OR: 1.04, 95%CI: 0.84-1.29) was associated with increased PCa risk versus no family history and irrespective of geographical region.

CONCLUSIONS

In REDUCE, PCa family history was significantly related to PCa diagnosis, although only for men outside North America. The presence of both PCa and BCa family history significantly increased risk versus PCa family history alone, irrespective of geographical region. Ultimately, our observations may support the need for changes in how we address family history in terms of both risk of PCa diagnosis and general risk stratification.

Confidence limit variation for a single IMRT system following the TG119 protocol

PURPOSE

To evaluate the robustness of TG119-based quality assurance metrics for an IMRT system.

METHODS

Four planners constructed treatment plans for the five IMRT test cases described in TG119. All plans were delivered to a 30 cm x 30 cm x 15 cm solid water phantom in one treatment session in order to minimize session-dependent variation from phantom setup, film quality, machine performance, etc. Composite measurements utilized film and an ionization chamber. Per-field measurements were collected using a diode array device at an effective depth of 5 cm. All data collected were analyzed using the TG119 specifications to determine the confidence limit values for each planner separately and then compared.

RESULTS

The mean variance of ion chamber measurements for each planner was within 1.7% of the planned dose. The resulting confidence limits were 3.13%, 1.98%, 3.65%, and 4.39%. Confidence limit values determined by composite film analysis were 8.06%, 13.4%, 9.30%, and 16.5%. Confidence limits from per-field measurements were 1.55%, 0.00%, 0.00%, and 2.89%.

CONCLUSIONS

For a single IMRT system, the accuracy assessment provided by TG119-based quality assurance metrics showed significant variations in the confidence limits between planners across all composite and per-field evaluations. This observed variation is likely due to the different levels of modulation between each planner's set of plans. Performing the TG119 evaluation using plans produced by a single planner may not provide an adequate estimation of IMRT system accuracy.

Lung tumor tracking in fluoroscopic video based on optical flow

Respiratory gating and tumor tracking for dynamic multileaf collimator delivery require accurate and real-time localization of the lung tumor position during treatment. Deriving tumor position from external surrogates such as abdominal surface motion may have large uncertainties due to the intra- and interfraction variations of the correlation between the external surrogates and internal tumor motion. Implanted fiducial markers can be used to track tumors fluoroscopically in real time with sufficient accuracy. However, it may not be a practical procedure when implanting fiducials bronchoscopically. In this work, a method is presented to track the lung tumor mass or relevant anatomic features projected in fluoroscopic images without implanted fiducial markers based on an optical flow algorithm. The algorithm generates the centroid position of the tracked target and ignores shape changes of the tumor mass shadow. The tracking starts with a segmented tumor projection in an initial image frame. Then, the optical flow between this and all incoming frames acquired during treatment delivery is computed as initial estimations of tumor centroid displacements. The tumor contour in the initial frame is transferred to the incoming frames based on the average of the motion vectors, and its positions in the incoming frames are determined by fine-tuning the contour positions using a template matching algorithm with a small search range. The tracking results were validated by comparing with clinician determined contours on each frame. The position difference in 95% of the frames was found to be less than 1.4 pixels (approximately 0.7 mm) in the best case and 2.8 pixels (approximately 1.4 mm) in the worst case for the five patients studied.

PATIENT POSITIONING USING IMPLANTED GOLD MARKERS WITH THE NOVALIS BODY SYSTEM IN THE THORACIC SPINE

OBJECTIVE

To evaluate the effectiveness of implanted gold marker registration compared with bony fusion alignment for patient positioning using the Novalis Body system.

METHODS

Eighteen treatment fractions of stereotactic spinal radiotherapy were analyzed for three patients who each had three implanted gold seeds placed near their spinal lesions before radiotherapy. At each treatment session, the registration was first performed using bony fusion and then verified by another bony fusion, followed by registration with implanted markers. The software reported the calculated shifts for both methods. In addition, the actual three-dimensional coordinate positions of the markers were read using PTDReader software. Implanted marker positions were analyzed for variations in individual maker coordinate displacement, interseed distances, and area transcribed by them. Measured positional differences between the two fusion methods were applied to actual treatment plans to assess the resulting dosimetric differences in the treatment plans.

RESULTS

Both fusion algorithms were shown to localize the patient well, within 1.5 mm, but the implanted marker fusion consistently related less deviation from the planned isocenter, by approximately 0.5 mm, than did the bony fusion. Exceptions to this localization occurred when the average interseed distances were less than 3.0 cm and resulted in the two registration methods being equivalent. Implanted spine markers were also shown to have less than 0.7 mm deviation from the planned marker coordinates, indicating no migration of the seeds. Dose distributions were found to be highly dependant on differences in fusion method, with spinal cord doses up to 350% greater with bony fusion than with implanted markers.

CONCLUSION

Implanted markers used with the Novalis Body system have been shown to be more effective in patient positioning than the bony fusion method in the thoracic spine.

A deformable lung tumor tracking method in fluoroscopic video using active shape models: a feasibility study

A dynamic multi-leaf collimator (DMLC) can be used to track a moving target during radiotherapy. One of the major benefits for DMLC tumor tracking is that, in addition to the compensation for tumor translational motion, DMLC can also change the aperture shape to conform to a deforming tumor projection in the beam's eye view. This paper presents a method that can track a deforming lung tumor in fluoroscopic video using active shape models (ASM) (Cootes et al 1995 Comput. Vis. Image Underst. 61 38-59). The method was evaluated by comparing tracking results against tumor projection contours manually edited by an expert observer. The evaluation shows the feasibility of using this method for precise tracking of lung tumors with deformation, which is important for DMLC-based real-time tumor tracking.

Psychometric properties of the BASIS-24© (Behaviour and Symptom Identification Scale-Revised) Mental Health Outcome Measure

Objective. Outcome measurement in mental health services is an area of considerable clinical interest and policy priority. This study sought to assess the Behaviour and Symptom Identification Scale-24 (BASIS-24©), a brief, patient self-reported measure of psychopathology and functioning, in a UK sample, including establishing population norms for comparative purposes. Methods. Participants were 588 adults recruited from psychiatric inpatient, outpatient and primary care settings; and 630 adults randomly sampled from primary care lists who completed the BASIS-24©, and the Brief Symptom Inventory (BSI) at two time points. Results. BASIS-24© demonstrated adequate reliability (coefficient α values for combined clinical sample across subscales ranged from 0.75 to 0.91), validity and responsiveness to change (effect size for change of the BASIS-24© was 0.56 compared with 0.48 for BSI Global Severity Index). Population norms were established for the general population and adult in-patients (at in-take). The scale proved straightforward to complete across clinical settings. Variable rates of questionnaire distribution across clinical settings highlighted the ongoing challenge of incorporating outcome measures in clinical settings. Conclusion. BASIS-24© is a brief, easily administered, self-complete measure of mental well-being and functioning that adequately meets the requirements of reliability, validity and responsiveness to change required of an outcome measure.

Postprostatectomy target-normal structure overlap volume differences using computed tomography and radioimmunoscintigraphy images for radiotherapy treatment planning

PURPOSE

The purpose of this study was to analyze regions of uptake in normal structures on postprostatectomy radioimmunoscintigraphy (RIS) images by evaluating differences in the overlap volumes of prostate fossa clinical target volume (CTV) and planning target volume (PTV) using correlative computed tomography (CT) images.

MATERIALS AND METHODS

The electronic records of 13 patients who received external beam radiotherapy postprostatectomy and who underwent a vessel-based RIS/CT registration were reviewed. For each patient, the RIS-defined CTV (CTV(RIS)) was compared (in terms of the overlap volume with the surrounding bladder, rectum, pubic symphysis, and penile bulb) with the CT-defined CTV(pre) before this registration and also with CTV(post) (the final target volume used for treatment). Similar analyses were done for PTV(RIS), PTV(pre), and PTV(post) defined in each case to be the corresponding CTV + 1-cm margin.

RESULTS

CTV(RIS) overlapped significantly more with the bladder, rectum, and symphysis, but not with the penile bulb, than did either the CTV(pre) or CTV(post). However, the corresponding PTV analyses revealed no significant differences between any of the overlap volumes of any of the PTVs with the bladder, rectum, and penile bulb, but did reveal a significant difference between the PTV(RIS) and PTV(post) overlap volumes with the symphysis compared with PTV(pre) overlap volumes with the symphysis.

CONCLUSIONS

On RIS images, there appear to be areas of uptake in the bladder, rectum, and pubic symphysis but not the penile bulb; however, the dosimetric consequences of this uptake for radiation treatment planning are minimal on the bladder, rectum, and penile bulb, but require segmentation for dose reduction to the pubic symphysis.

A novel respiratory detection method based on automated analysis of ultrasound diaphragm video

This paper proposes a novel respiratory detection method based on diaphragm motion measurements using a 2D ultrasound unit. The proposed method extracts a respiratory signal from an automated analysis of the internal diaphragm motion during breathing. The respiratory signal may be used for gating. Ultrasound studies of diaphragm breathing motion were performed on four volunteers. The ultrasound video stream was captured and transferred to a personal computer and decomposed into individual image frames. After straightforward image analysis, region of interest selection, and filtering, the mutual information (MI) and correlation coefficients (CCs) between a selected reference frame and all other frames were computed. The resulting MI and CC values were discovered to produce a signal corresponding to the respiratory cycle in both phase and magnitude. We also studied the diaphragm motion of two volunteers during repeated deep inspiration breath holds (DIBH) and found a slight relaxation motion of the diaphragm during the DIBH, suggesting that the residual motion may be important for treatments delivered at this breathing phase. Applying the proposed respiratory detection method to these ultrasound studies, we found that the MI and CC values demonstrate the relaxation behavior, indicatingthat our method may be used to determine the radiation triggering time for a DIBH technique.

Spectrum reconstruction from dose measurements as a linear inverse problem

There are three ways to determine the spectrum of a clinical photon beam: direct measurement, modelling the source and reconstruction from ion-chamber measurements. We focus on reconstruction because the necessary equipment is readily available and it provides independent confirmation of source models for a given machine. Reconstruction methods involve measuring the dose in an ion chamber after the beam passes through an attenuator. We gain information about the spectrum from measurements using attenuators of differing compositions and thicknesses since materials have energy dependent attenuation. Unlike the procedures used in other papers, we do not discretize or parametrize the spectrum. With either of these two approximations, reconstruction is a least squares problem. The forward problem of going from a spectrum to a series of dose measurements is a linear operator, with the composition and thickness of the attenuators as parameters. Hence the singular value decomposition (SVD) characterizes this operator. The right singular vectors form a basis for the spectrum, and, at first approximation, only those corresponding to singular values above a threshold are measurable. A more rigorous error analysis shows with what confidence different components of the spectrum can be measured. We illustrate this theory with simulations and an example utilizing six sets of dose measurements with water and lead as attenuators.

Evaluation of the long intra-medullary hip screw

There have been many publications about second generation femoral nails, such as the Russell-Taylor nail (Smith & Nephew Richards, Memphis, TN, USA) and Long Gamma Nail (Howmedica, Rutherford, NJ, USA), but little work has been published on the Long Intra-medullary Hip Screw (IMHS, Smith & Nephew). We set out to evaluate the effectiveness of the Long IMHS as a device for the fixation of proximal femoral fractures. We retrospectively reviewed 30 patients who had a Long IMHS inserted for a sub-trochanteric or proximal femoral fracture. Of the 30 patients, three had died and six were lost to follow up, leaving 21, whom we reviewed. Of the 21 patients reviewed the mean age was 67 years and the mean follow up was 31 weeks. Mean time to union was 15.65 weeks, with one non-union. There were three superficial wound infections. In one patient there was loosening of the distal locking screws, requiring removal and there was one case of intra-operative femoral shaft fracture. We conclude that, the Long IMHS is an effective device for the treatment of sub-trochanteric and proximal femoral fractures with a high rate of union achieved and a low complication rate.

Optimization of tumour control probability for heterogeneous tumours in fractionated radiotherapy treatment protocols

We find the dose distribution that maximizes the tumour control probability (TCP) for a fixed mean tumour dose per fraction. We consider a heterogeneous tumour volume having a radiation response characterized by the linear quadratic model with heterogeneous radiosensitivity and repopulation rate that may vary in time. Using variational calculus methods a general solution is obtained. We demonstrate the spatial dependence of the optimal dose distribution by explicitly evaluating the solution for different functional forms of the tumour properties. For homogeneous radiosensitivity and growth rate, we find that the dose distribution that maximizes TCP is homogeneous when the clonogen cell density is homogeneous, while for a heterogeneous initial tumour density we find that the first dose fraction is inhomogeneous, which homogenizes the clonogen cell density, and subsequent dose fractions are homogeneous. When the tumour properties have explicit spatial dependence, we show that the spatial variation of the optimized dose distribution is insensitive to the functional form. However, the dose distribution and tumour clonogen density are sensitive to the value of the repopulation rate. The optimized dose distribution yields a higher TCP than a typical clinical dose distribution or a homogeneous dose distribution.

Sparing of the penile bulb and proximal penile structures with intensity-modulated radiation therapy for prostate cancer

Quality of life is an important consideration in the treatment of early prostate cancer. Laboratory and clinical data suggest that higher radiation doses delivered to the bulb of penis and proximal penile structures correlates with higher rates of post-radiation impotence. The goal of this investigation was to determine if intensity-modulated radiation therapy (IMRT) spares dose to the penile bulb while maintaining coverage of the prostate. 10 consecutive patients with clinically organ confined prostate cancer were planned with 3D conformal radiation therapy (3D-CRT) or IMRT to give a dose of 74 Gy without specifically constraining the plans to spare the penile bulb. All 10 patients were ultimately treated with IMRT. Dose-volume histograms were evaluated and the doses to prostate, rectum, bladder and penile bulb were compared. IMRT reduced the mean penile bulb doses compared with 3D-CRT (33.2 Gy vs 48.9 Gy, p<0.001), the percentage of penile bulb receiving over 40 Gy (37.7% vs 67.2%, p<0.001) and the dose received by >95% of penile bulb (5.3 Gy vs 11.7 Gy, p=0.003). Maximum penile bulb doses were higher with IMRT (81.2 Gy vs 73.1 Gy, p<0.001) although the volume of this high dose region was small. Both methods resulted in similar coverage of the prostate. The volume of rectum receiving 70 Gy was significantly reduced with IMRT (18.4% vs 21.9%, p=0.003) but the volumes of bladder receiving 70 Gy were similar (p=0.3). IMRT may potentially reduce long term sexual morbidity by reducing the dose to the majority of the penile bulb.

NMR evidence of pentaoxo organosilicon complexes in dilute neutral aqueous silicate solutions

Silicon-29 NMR spectra of a neutral, dilute aqueous silicic acid solution, with a pH and Si concentration typical of soil solutions, reveal that a significant fraction of the silicon is incorporated in two five-coordinated organosilicon complexes when sodium gluconate is present.

A model for optimizing normal tissue complication probability in the spinal cord using a generalized incomplete repair scheme

The purpose of this study was to determine the treatment protocol, in terms of dose fractions and interfraction intervals, which minimizes normal tissue complication probability in the spinal cord for a given total treatment dose and treatment time. We generalize the concept of incomplete repair in the linear-quadratic model, allowing for arbitrary dose fractions and interfraction intervals. This is incorporated into a previously presented model of normal tissue complication probability for the spinal cord. Equations are derived for both mono-exponential and bi-exponential repair schemes, regarding each dose fraction and interfraction interval as an independent parameter, subject to the constraints of fixed total treatment dose and treatment time. When the interfraction intervals are fixed and equal, an exact analytical solution is found. The general problem is nonlinear and is solved numerically using simulated annealing. For constant interfraction intervals and varying dose fractions, we find that optimal normal tissue complication probability is obtained by two large and equal doses at the start and conclusion of the treatment, with the rest of the doses equal to one another and smaller than the two dose spikes. A similar result is obtained for bi-exponential repair. For the general case where the interfraction intervals are discrete and also vary, the pattern of two large dose spikes is maintained, while the interfraction intervals oscillate between the smallest two values. As the minimum interfraction interval is reduced, the normal tissue complication probability decreases, indicating that the global minimum is achieved in the continuum limit, where the dose delivered by the "middle" fractions is given continuously at a low dose rate. Furthermore, for bi-exponential repair, it is seen that as the slow component of repair becomes increasingly dominant as the magnitude of the dose spikes decreases. Continuous low-dose-rate irradiation with dose spikes at the start and end of treatment yields the lowest normal tissue complication probability in the spinal cord, given a fixed total dose and total treatment time, for both mono-exponential and bi-exponential repair. The magnitudes of the dose spikes can be calculated analytically, and are in close agreement with the numerical results.

A descriptive study of an epidemic of poisoning caused by heroin adulterated with scopolamine

OBJECTIVE

Adulterants, contaminants, and diluents are all examples of additives to street drugs. Some of these additives may be pharmacologically active; however, it is unusual for them to cause toxic side effects. In the spring of 1995, a new form of heroin appeared in New York City, spreading to other East Coast cities, that was adulterated with scopolamine. It caused severe anticholinergic toxicity in heroin users with patients often presenting to emergency departments in great numbers. This is a report of the demographics and clinical characteristics of the epidemic.

METHODS

A combination of prospective and retrospective data collection from the New York City, New Jersey, Delaware Valley, and Maryland Poison Centers. The primary measurements were age, sex, route of drug use, vital signs, signs and symptoms, disposition, and treatment.

RESULTS

Of the 370 cases reported to the participating poison centers, 129 were excluded from the final analysis because of insufficient data. Of the patients who used this product, 55% presented with signs and symptoms of heroin toxicity but then became severely agitated with anticholinergic symptoms when naloxone was used to reverse respiratory depression. Nasal insufflation was the route of administration in 34% of the cases. Seizures were rare (3%). Ninety percent required admission, and half were admitted to a critical care unit.

CONCLUSIONS

Adulteration of street drugs can lead to toxic epidemics. Poison centers are essential for identification of these trends and are the primary source of information on diagnosis and treatment.

Asymmetric preference of serine proteases toward phosphonate and phosphinate esters

We have previously reported the asymmetric synthesis of (alpha-aminoalkyl) diphenylphosphonate and phosphinate derivatives designed as inhibitors of chymotrypsin- and elastase-like proteases. This paper reports the first kinetic evaluation of individual epimers of the (alpha-aminoalkyl) diphenylphosphonates as inactivators of chymotrypsin, cathepsin G and neutrophil elastase (HNE). Results show that the (R)-epimers consistently function as more potent irreversible inactivators of their respective target proteases than the corresponding (S)-epimers. Additionally, phosphinate analogues were found to be consistently superior to their diphenylphosphonate counterparts. For example, Cbz. Phe(P)(OPh)-(CH(2))(2)-CO(2)Et inactivates cathepsin G approximately 45-fold more rapidly (k(i)/K(i) = 1.2 x 10(5) M(-1). min(-1)) than the analogous Cbz.Phe(P)(OPh)(2) (2.6 x 10(3) M(-1). min(-1)). Similarly, Cbz.Val(P)(OPh)-(CH(2))(2)-CO(2)Et was found to inactivate HNE some 3-fold more efficiently than Cbz.Val(P)(OPh)(2) (6.5 x 10(3) and 2.0 x 10(3) M(-1). min(-1), respectively).

Volume rendering quantification algorithm for reconstruction of CT volume-rendered structures: Part I. Cerebral arteriovenous malformations

Volume rendering is a visualization technique that has important applications in diagnostic radiology and in radiotherapy but has not achieved widespread use due, in part, to the lack of volumetric analysis tools for comparison of volume rendering to conventional visualization techniques. The volume rendering quantification algorithm (VRQA), a technique for three-dimensional (3-D) reconstruction of a structure identified on six principal volume-rendered views, is introduced and described. VRQA involves three major steps: 1) preprocessing of the partial surfaces constructed from each of six volume-rendered images; 2) merging these processed partial surfaces to define the boundaries of a volume; and 3) computation of the volume of the structure from this boundary information. After testing on phantoms, VRQA was applied to CT data of patients with cerebral arteriovenous malformations (AVM's). Because volumetric visualization of the cerebral AVM is relatively insensitive to operator dependencies, such as the choice of opacity transfer function, and because precise volumetric definition of the AVM is necessary for radiosurgical treatment planning, it is representative of a class of structures that is ideal for testing and calibration of VRQA. AVM volumes obtained using VRQA are intermediate to those obtained using axial contouring and those obtained using CT-correlated biplanar angiography (two routinely used visualization techniques for treatment planning for AVM's). Applications and potential expansions of VRQA are discussed.

Matching photon and electron fields with dynamic intensity modulation

A technique was developed to reduce the size and magnitude of the hot and cold spots in the abutting regions of photon and electron fields. The photon and electron fields were set up such that the photon field extended approximately 2 cm into the electron field in the abutting region. The region of the photon beam that overlapped the electron field was modulated using a multileaf collimator, effectively broadening the photon penumbra to make it complimentary to the electron penumbra. The computer calculations were verified using film measurements for abutting a 6 MV photon beam with a 9 MeV electron beam. A uniform dose was achieved at a prespecified depth of 2 cm, and dose uniformity was improved at the specified depth and beyond compared with unmodulated photon beams. A slight increase in dose inhomogeneity was seen at shallower depths. The overall areas of the hot and cold spots were significantly reduced. The technique also reduced the sensitivity of dose homogeneity to setup errors such that the magnitudes of the hot and cold spots were about half of those produced with unmodulated photon beam when an overlap or gap of 4 mm was introduced. The technique was applied to the treatment of a head and neck cancer and a lymphoma involving the right pleura with markedly reduced dose inhomogeneity in the abutting regions.

Using vascular structure for CT-SPECT registration in the pelvis

The authors outline a method for three-dimensional registration of pelvic CT and 111In-labeled monoclonal antibody capromab pendetide (111In MoAb 7E11.C5) images using 99mTc-labeled red blood cell SPECT data.

METHODS

This method of CT-SPECT registration relies on the identification of major blood vessels in the CT and 99mTc SPECT images. The vessels are segmented from the image datasets by outlining them on transverse planar slices using a mouse-based drawing tool. Stacking the transverse outlines provides a three-dimensional representation of the vascular structures. Registration is performed by matching the surfaces of the segmented volumes. Dual isotope acquisition of 111In and 99mTc activities provides precise SPECT-SPECT registration so that registration in three dimensions of the 111In MoAb and CT images is achieved by applying the same transformation obtained from the 99mTc SPECT-CT registration.

RESULTS

This method provided accurate registration of pelvic structures and significantly improved interpretation of 111In MoAb 7E11.C5 exams. Furthermore, sites of involvement by prostate cancer suggested by the 111In MoAb examination could be interpreted with the bony and soft tissue (nodal) anatomy seen on CT.

CONCLUSION

This method is a general clinical tool for the registration of pelvic CT and SPECT imaging data. There are immediate applications in conformal radiation therapy treatment planning for certain prostate cancer patients.

A three-dimensional algorithm for optimizing beam weights and wedge filters

An essential step towards optimizing and automating radiation therapy treatment planning is to develop an effective algorithm to find the optimal beam weights and wedge filters for a given set of beam directions and modalities. This problem is solved by introducing a variable transformation based on the universal and omni wedge principles. Instead of directly optimizing an objective function with respect to wedge angles and orientations, each field is first decomposed into a superposition of an open field and two orthogonal wedged fields. This transforms the problem of finding J beam weights, wedge angles, and orientations to that of optimizing a system with 3J beam weights (J open beams and 2J nominal wedged beams), where J is the total number of incident beam directions. An iterative algorithm based on a method originally developed for image reconstruction is used to find the 3J beam weights. The technique is applied to a few clinical cases. Treatment plans are improved compared to those obtained through the conventional manual trial and error planning process. In addition, planning time and effort are greatly reduced.

Fast iterative algorithms for three-dimensional inverse treatment planning

Three types of iterative algorithms, algebraic inverse treatment planning (AITP), simultaneous iterative inverse treatment planning (SIITP), and iterative least-square inverse treatment planning (ILSITP), differentiated according to their updating sequences, were generalized to three dimension with true beam geometry and dose model. A rapid ray-tracing approach was developed to optimize the primary beam components. Instead of recalculating the dose matrix at each iteration, the dose distribution was generated by scaling up or down the dose matrix elements of the previous iteration. This significantly increased the calculation speed. The iterative algorithms started with an initial intensity profile for each beam, specified by a two-dimensional pixel beam map of M elements. The calculation volume was divided into N voxels, and the calculation was done by repeatedly comparing the calculated and desired doses and adjusting the values of the beam map elements to minimize an objective function. In AITP, the iteration is performed voxel by voxel. For each voxel, the dose discrepancy was evaluated and the contributing pencil beams were updated. In ILSITP and SIITP, the iteration proceeded pencil beam by pencil beam instead of voxel by voxel. In all cases, the iteration procedure was repeated until the best possible dose distribution was achieved. The algorithms were applied to two examples and the results showed that the iterative techniques were able to produce superior isodose distributions.

Verification of the omni wedge technique

The optimal field shape achieved using a multileaf collimator (MLC) often requires collimator rotation to minimize the adverse effects of the scalloped dose distribution the leaf steps produce. However, treatment machines are designed to deliver wedged fields parallel or perpendicular to the direction of the leaves. An analysis of cases from our clinic showed that for 25% of the wedged fields used to treat brain and lung tumors, the wedge direction and optimal MLC orientation differed by 20 degrees or more. The recently published omni wedge technique provides the capability of producing a wedged field with orientation independent of the orientation of the collimator. This paper presents a comparison of the three-dimensional (3D) dose distributions of the omni wedged field with distributions of wedged fields produced using both the universal and dynamic wedge techniques. All measurements were performed using film dosimetry techniques. The omni wedge generated fields closely matched the conventional wedged fields. Throughout 95% of the irradiated volume (excluding the penubra), the dose distribution of the omni wedged field ranged from +5.5 to -3.5 +/- 1.5% of that of the conventionally wedged fields. Calculation of the omni wedged field is as accurate as conventional wedged field calculation when using a 3D treatment planning systems. For two-dimensional treatment planning systems, where one must assume that the omni wedged field is identical to a conventional field, the calculated field and the delivered field differs by a small amount.

Declining rate of cricothyrotomy in trauma patients with an emergency medicine residency: implications for skills training

OBJECTIVE

To report the change in cricothyrotomy rate with emergency medicine (EM) residency development and to address the implications for training in this skill.

METHODS

A retrospective chart review was used to determine the cricothyrotomy rate at a 1,000-bed urban Level-1 trauma center with EM, surgery, and anesthesiology residencies. All adult trauma patient visits to the ED between July 1, 1985, and June 30, 1995, were reviewed. The cricothyrotomy rate was defined as the total number of cricothyrotomies per trauma admissions during a study phase.

RESULTS

The study period was divided into 3 phases. Phase 1 (academic years 1985-1989): prior to the inception of the EM residency; phase 2 (academic years 1990-1992): initiation and establishment of the residency; and phase 3 (academic years 1993-1994): full implementation of the EM residency. The cricothyrotoiny rate during phase 1 was 1.8% (95% CI: 1.6 to 2.0), vs 1.1% (95% CI: 0.0 to 2.8) and 0.2% (95% CI: 0.0 to 0.2) during phases 2 and 3, respectively.

CONCLUSIONS

The cricothyrotomy rate decreased with the full implementation of the EM residency. Whether this trend was an effect of the presence of an EM faculty and residency training program, a parallel approach to airway management nationwide, or another unidentified factor will require further investigation. Nonetheless, given the increasing rarity of this procedure, it is likely that many EM, surgical, and anesthesiology residents will not acquire clinical experience with this technique during training.

An intraoral positioning appliance for stereotactic radiotherapy

Stereotactic radiotherapy provides the most accurate and effective therapy and protects the adjacent, normal tissues. The head must be positioned the same for all treatments. This article describes the fabrication and application of a noninvasive intraoral appliance that verifies the position of the head to deliver more accurate radiotherapy and protect the adjacent, normal tissues.

The case of Baby M: nursing care in an ethical wilderness

This is a reflective case study of an infant with Down Syndrome and a potentially fatal cardiac defect. It is a story of hope and loss, of silence and learning to speak, and of relinquishing space and standing ground. The purpose of this article is to explore the conflicting claims a neonatal intensive care (NICU) nurse faces in caring for critically ill infants. The questions of "Who speaks?" and "Who listens?" are addressed. The concepts of women's moral development and a nursing definition of voice are included. It is proposed that the conventional feminine voice and the embodied knowledge so integral to expert nursing actually draw strength away from the voice that needs to be permitted into the circle of decision makers when ethical issues are raised in the NICU.

Effects of Three Types of Elaboration on Learning Concepts from Text

Two experiments were performed to evaluate the effects of three different elaborative activities on concept learning. Experiment 1 consisted of 60 undergraduates, while Experiment 2 consisted of 54 undergraduates. In both experiments, subjects studied a passage which asked them to create personal examples of the target concepts, contrast the target concepts, or expand on the effects of the target concepts. Subjects took a criterion test which consisted of recall of concept definitions and teaching examples, classification of novel examples, and problem solving scenarios. In both experiments, the condition which asked subjects to contrast the target concepts produced significantly better performance than the other two conditions. Possible explanations focus on: (1) the degree to which the different elaborative activities influence the richness and/or distinctiveness of the encoded information, and (2) the relation among the focus of the elaborative activity, the experimental text, and the measured criterion outcomes.

Performance of a video-image-subtraction-based patient positioning system

PURPOSE

We have developed and tested an interactive video system that utilizes image subtraction techniques to enable high precision patient repositioning using surface features. We report quantitative measurements of system performance characteristics.

METHODS AND MATERIALS

Video images can provide a high precision, low cost measure of patient position. Image subtraction techniques enable one to incorporate detailed information contained in the image of a carefully verified reference position into real-time images. We have developed a system using video cameras providing orthogonal images of the treatment setup. The images are acquired, processed and viewed using an inexpensive frame grabber and a PC. The subtraction images provide the interactive guidance needed to quickly and accurately place a patient in the same position for each treatment session. We describe the design and implementation of our system, and its quantitative performance, using images both to measure changes in position, and to achieve accurate setup reproducibility.

RESULTS

Under clinical conditions (60 cm field of view, 3.6 m object distance), the position of static, high contrast objects could be measured with a resolution of 0.04 mm (rms) in each of two dimensions. The two-dimensional position could be reproduced using the real-time image display with a resolution of 0.15 mm (rms). Two-dimensional measurement resolution of the head of a patient undergoing treatment for head and neck cancer was 0.1 mm (rms), using a lateral view, measuring the variation in position of the nose and the ear over the course of a single radiation treatment. Three-dimensional repositioning accuracy of the head of a healthy volunteer using orthogonal camera views was less than 0.7 mm (systematic error) with an rms variation of 1.2 mm. Setup adjustments based on the video images were typically performed within a few minutes. The higher precision achieved using the system to measure objects than to reposition them suggests that the variability in repositioning is dominated by the ability of the therapist to make small, controlled changes in the position of the patient.

CONCLUSION

Using affordable, off-the-shelf technology, we have developed a patient positioning system that achieves repositioning accuracy normally associated with fractionated stereotactic systems. The technique provides real-time guidance and can be used to easily and quickly correct patient setup before every treatment, thus significantly reducing overall random positioning error. This improved positioning capability provides the precision required to realize the potential gains of conformal radiotherapy.

Functional imaging in treatment planning of brain lesions

PURPOSE

Explore the use of functional imaging data in radiation treatment planning of brain lesions.

METHODS AND MATERIALS

Compare the treatment-planning process with and without the use of functional brain imaging for clinical cases where functional studies using either single photon emission computed tomography or magnetic resonance imaging are available.

RESULTS

A method to register functional image data with planning image studies is needed for functional treatment planning. Functional volumes are not simply connected regions. One activation study may produce many isolated functional areas. After finding the functional volumes and registering the functional information with the planning imaging data, the tools used for conventional three-dimensional treatment planning are sufficient for functional treatment planning. However, the planning system must provide dose-volume histograms for volumes of interest that consist of isolated pieces. Treatment plans that spare functional brain while providing identical target coverage can be constructed for lesions situated near the functional volume. However, the dose to other areas of the brain may be increased.

CONCLUSIONS

Functional imaging will make determination of dose response of eloquent areas of the brain possible when combined with volumetric dose information and neuropsychological evaluation prior to and after radiation therapy. Realizing the full potential of functional imaging studies will require improved delineation of activated volumes and determination of the uncertainties in functional volume delineation. Optimization of treatment plans by minimizing dose to volumes activated during functional imaging studies should be used cautiously, because the dose to "silent," but possibly eloquent, brain may be increased.