A computational study of combination HIFU-chemotherapy as a potential means of overcoming cancer drug resistance

The application of local hyperthermia, particularly in conjunction with other treatment strategies (like chemotherapy and radiotherapy) has been known to be a useful means of enhancing tumor treatment outcomes. However, to our knowledge, there has been no mathematical model designed to capture the impact of the combination of hyperthermia and chemotherapies on tumor growth and control. In this study, we propose a nonlinear Partial Differential Equation (PDE) model which describes the tumor response to chemotherapy, and use the model to study the effects of hyperthermia on the response of prototypical tumor to the generic chemotherapeutic agent. Ultrasound energy is delivered to the tumor through High Intensity Focused Ultrasound (HIFU), as a noninvasive technique to elevate the tumor temperature in a controlled manner. The proposed tumor growth model is coupled with the nonlinear density dependent Westervelt and Penne's bio-heat equations, used to calculate the net delivered energy and temperature of the tumor and its surrounding normal tissue. The tumor is assumed to be composed of two species: drug-sensitive and drug-resistant. The central assumption underlying our model is that the drug-resistant species is converted to a drug-sensitive type when the tumor temperature is elevated above a certain threshold temperature. The "in silico" results obtained, confirm that hyperthermia can result in less aggressive tumor development and emphasize the importance of designing an optimized thermal dose strategy. Furthermore, our results suggest that increasing the length of the on/off cycle of the transducer is an efficient approach to treatment scheduling in the sense of optimizing tumor eradication.

Warming the postpartum body as a form of postnatal care: An ethnographic study of medical injections and traditional health practices in Cambodia

Postpartum care is a critical element for ensuring survival and health of mothers and newborns but is often inadequate in low- and middle-income countries due to barriers to access and resource constraints. Newly delivered mothers and their families often rely on traditional forms of postnatal care rooted in social and cultural customs or may blend modern and traditional forms of care. This ethnographic study sought to explore use of biomedical and traditional forms of postnatal care. Data were collected through unstructured observation and in-depth interviews with 15 mothers. Participants reported embracing traditional understandings of health and illness in the post-partum period centered on heating the body through diet, steaming, and other applications of heat, yet also seeking injections from private health care providers. Thematic analysis explored concepts related to transitioning forms of postnatal care, valuing of care through different lenses, and diverse sources of advice on postnatal care. Mothers also described concurrent use of both traditional medicine and biomedical postnatal care, and the importance of adhering to cultural traditions of postnatal care for future health. Maternal and newborn health are closely associated with postnatal care, so ensuring culturally appropriate and high-quality care must be an important priority for stakeholders including understand health practices that are evolving to include injections.

The prognosis impact of hyperthermic intraperitoneal chemotherapy (HIPEC) plus cytoreductive surgery (CRS) in advanced ovarian cancer: the meta-analysis

BACKGROUND AND OBJECTIVE

Previous studies about the prognostic value of the HIPEC have yielded controversial results. Therefore, this study aims to assess the impact of HIPEC on patients with ovarian cancer.

RESULTS

We included 13 comparative studies, and found that the overall survival (OS) and progression-free survival (PFS) in HIPEC groups were superior to groups without HIPEC treatment in the all total population (HR = 0.54,95% CI:0.45 to 0.66, HR = 0.45, 95% CI: 0.32 to 0.62). Additionally, the subgroup analysis showed that patients with advanced primary ovarian cancers also gained improved OS and PFS benefit from HIPEC (HR = 0.59,95% CI:0.46 to 0.75, HR = 0.41,95% CI:0.32 to 0.54). With regard to recurrent ovarian cancer, HIPEC was associated with improved OS (HR = 0.45,95% CI:0.24 to 0.83), but for the PFS, no correlation was observed between HIPC group and the non-HIPEC group (HR = 0.55,95% CI:0.27 to 1.11). HIPEC also led to favorable clinical outcome (HR = 0.64,95% CI:0.50 to 0.82, HR = 0.36,95% CI:0.20 to 0.65) for stage III or IV ovarian cancer with initial diagnosis.

CONCLUSION

The review indicated that HIPEC-based regimens was correlated with better clinical prognosis for patients with primary ovarian cancers. For recurrent ovarian cancers, HIPEC only improved the OS but did not elicit significant value on the PFS.

Hospital readmission rates and risk factors for readmission following cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) for peritoneal surface malignancies

BACKGROUND

Cytoreductive surgery and Hyperthermic intra-peritoneal chemotherapy (CRS/HIPEC) for peritoneal surface malignancies is associated with high morbidity. The increased numbers of patients undergoing CRS/HIPEC in recent years mandates risk analysis and quality assurance. However, only scarce data exist regarding causative parameters for readmission. The aim of this study was to assess readmission rates and risk factors associated with readmission.

METHODS

A retrospective-cohort study including patients from two high-volume centers who underwent CRS/HIPEC surgery between the years 2007-2016 was performed. Patients' demographics, peri-operative data and readmission rates were recorded.

RESULTS

223 patients were included in the study. The 7 and 30-day readmission rates were 3.5% (n = 8) and 11% (n = 25), respectively. Late readmission rates (up to 90 days) were 11% (n = 25). The most common causes of readmission were surgical related infections (35%), small bowel obstruction (17.5%) and dehydration (14%). Post-operative complications were associated with higher readmission rates (p = 0.0001). PCI score was not associated with higher rates of readmission.

CONCLUSION

Readmissions following CRS/HIPEC occur mainly due to infectious complications and dehydrations. Patients following CRS/HIPEC should be discharged after careful investigation to a community based continuing care with access for IV fluid replacement or antibiotics administration when required.

Hyperthermic intraperitoneal chemotherapy for peritoneal surface malignancies: A single institution Indian experience

BACKGROUND

Cytoreductive surgery followed by hyper- thermic intraperitoneal chemotherapy (HIPEC) has shown better oncological outcomes in peritoneal surface malignancies (PSM). We assessed the feasibility and perioperative outcomes of this procedure in Indian patients.

METHODS

In this prospective observational study from February 2013 to April 2015, we included 56 patients (41 females, 73.2%) with PSM. They had a good performance status, were either treatment-naïve or previously treated by surgery and systemic chemotherapy. They underwent cytoreductive surgery followed by HIPEC using a hyperthermia pump, with the temperature at 42 °C for 30-90 minutes. The chemotherapy regimen was based on the primary malignancy. Perioperative outcome data were collected and analysed. We also analysed the short-term oncological outcomes.

RESULTS

Our patients included those with peritoneum confined ovarian carcinoma (32, 57.1%), colorectal carcinoma (9, 16.1%), pseudomyxoma peritonei (7, 12.5%), meso- thelioma (2, 3.6%), gastric carcinoma (2, 3.6%) and others (4, 7.1%). The median duration of surgery including HIPEC was 9 hours and the median hospital stay was 12 days. The median time for gastrointestinal recovery was 5 days. One-fifth of patients (11, 19.7%) required an extended stay in the inten- sive care unit. The most common grades 3 and 4 complications were hypocalcaemia 32.1%, hypokalaemia 32.1%, anaemia 21.4% and thrombocytopenia 7.1%. Major morbidity requiring surgical intervention occurred in 8.9% of patients. The 60-day operative mortality was 1.8%. At a median follow-up of 16 months, 7.1% developed peritoneal recurrence, 8.9% had systemic recurrence and 7.1% succumbed to the disease. Patients with platinum-resistant ovarian carcinomas had more peritoneal recurrence (3.6%).

CONCLUSION

In patients with PSM, surgical cytoreduction and HIPEC is feasible and potentially beneficial. It can be done with low mortality and acceptable morbidity. It requires a dedicated team of surgeons, anaesthetists and intensivists and proper infrastructure.

Mean-field and linear regime approach to magnetic hyperthermia of core-shell nanoparticles: can tiny nanostructures fight cancer?

The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy.

Evaluation of the charges, safety, and mortality of percutaneous renal thermal ablation using the nationwide inpatient sample

PURPOSE

To perform a national analysis of safety, charges, complications, and mortality of percutaneous image-guided renal thermal ablation and compare outcomes by hospital volume.

MATERIALS AND METHODS

Using the Nationwide Inpatient Sample, trends in the proportion of inpatient percutaneous renal thermal ablation procedures performed at high-volume centers in the United States from 2007-2011 were evaluated. In-hospital mortality, discharge to long-term care facility, length of stay, hospitalization charges, and postoperative complications were compared between high-volume and low-volume ablation centers. High volume was set at the 90th percentile for renal thermal ablation volume, which equated to seven or more patients per year. A multivariate logistic regression analysis adjusting for hospital volume, age, sex, Charlson Comorbidity Index, obesity, race, and insurance status was performed to analyze the influence of hospital volume on the above-listed outcomes.

RESULTS

This study included 874 patients. The number of hospitals ranged from 59-77 depending on year. Overall, 328 patients (37.5%) were treated at high-volume ablation centers. The proportion of patients treated at high-volume centers decreased from 42.0% in 2007-2009 to 28.5% in 2010-2011. High-volume hospitals also performed significantly more partial nephrectomies than low-volume hospitals. On multivariate logistic regression analysis, increasing hospital volume was associated with lower odds of in-hospital mortality (odds ratio [OR] = 0.31, 95% confidence interval [CI] = 0.02-0.95) and lower odds of discharge to a long-term care facility (OR = 0.00, 95% CI = 0.00-0.66). Increasing hospital volume was also associated with lower odds of blood transfusion (OR = 0.84, 95% CI = 0.72-0.94). Length of stay decreased with increasing hospital volume (P = .03).

CONCLUSIONS

Patient safety may be maximized when renal ablation is performed at high-volume centers as a result of both greater procedural experience and potentially multidisciplinary triage and periprocedural management.

[Survival rates for large choroidal melanomas]

Choosing the treatment method for patients with large choroidal melanomas remains a subject of debate. No literature data can be found on survival of such patients after either eye-preserving surgery or enucleation that takes into account the initial tumor size. The purpose of the study was to analyze the five-year survival rates for large choroidal melanomas (by J.A. Shields) in respect of the provided treatment.

MATERIAL AND METHODS

Medical records of 103 patients who had undergone treatment for choroidal melanoma (initial prominence 5.0-10.2 mm, initial diameter 7.3-20 mm) were studied. Eye-preserving surgery was performed on 60 patients, of whom 46 patients received brachytherapy (single session in 37 cases) and the other 14 patients--brachytherapy in combination with transpupillary thermotherapy (with subsequent endoresection of the tumor in one case). A total of 16 patients from this group required secondary enucleation. Primary enucleation was performed on 63 patients. Histopathological results confirming choroidal melanoma were analyzed in all 79 cases.

RESULTS AND DISCUSSION

The 5-year melanoma-specific cumulative survival rate in the group of eye-preserving surgery was 0.8146, while in the group of primary enucleation it reached 0.8951. The 8-year rate was 0.6921 and 0.7558 correspondingly. However, according to Gehan-Wilcoxon test, the differences were statistically insignificant (p = 0.11). The five-year survival of large choroidal melanoma patients who underwent eye-preserving surgery and no enucleation was 0.7708, 9-year - 0.6175.

CONCLUSION

Since the five-year melanoma-specific survival rate after primary enucleation is higher than that after eye-preserving surgery and secondary enucleation (though the difference is statistically insignificant), treatment options for large choroidal melanomas have to be chosen individually, taking into account the age and attitude of the patient as well as the size of the tumor.

National trends in surgical therapy for benign prostatic hyperplasia in the United States (2000-2008)

OBJECTIVE

To report an update of the change in usage trends for different surgical treatments of benign prostatic hyperplasia (BPH) among the United States Medicare population data from 2000-2008. The rate of usage of thermotherapy and laser therapy in the surgical treatment of BPH has been changing over the past decade in conjunction with a steady decrease of transurethral resection of the prostate (TURP).

METHODS

Using the 100% Medicare carrier file for the years 2000-2008, we calculated counts and population-adjusted rates of BPH surgery. Rates of TURP, thermotherapy, and laser-using modalities were calculated and compared in relation to age, race, clinical setting, and reimbursement.

RESULTS

After years of a steady rise, the total rate of all BPH procedures peaked in 2005 at 1078/100,000 and then declined by 15.4% to 912/100,000 in 2008. TURP rates continued to decline from 670 in 2000 to 351/100,000 in 2008. Rates of microwave thermoablation peaked in 2006 at 266/100,000 and then declined 26% in 2008. Laser vaporization almost completely replaced laser coagulation and in 2008 was the most commonly performed procedure second to TURP, with the majority performed as outpatient procedures (70%) and an increasing percentage in the office (12%). Men between ages 70 and 75 had the highest rate of procedures. Reimbursement rates correlate using some but not all procedures. Racial disparities reported previously appear to have resolved.

CONCLUSION

Surgical treatment of BPH continues to change rapidly. TURP continues to decline and laser vaporization is the fastest growing modality. There is a big shift toward outpatient/office procedures. Reimbursement rates do not appear to have a consistent effect on usage.

Thermal characteristics of microwave ablation in the vicinity of an arterial bifurcation

PURPOSE

The objective of this research was to reveal the thermal characteristics of microwave ablations in the vicinity of an arterial bifurcation.

METHODS

The temperature distribution after microwave heating of a liver-like material in the close proximity of an arterial bifurcation was simulated using the finite element method. Coupled fluid flow and solid heat transfer were taken into consideration and a three-dimensional analysis was performed. An experimentally determined SAR (specific absorption rate) generated by the absorption of microwaves in liver-like material was used in the analysis instead of utilizing electromagnetic calculations. Several different tests of time-controlled ablations with varying distances between the microwave antenna and the bifurcation were performed and detailed temperature distributions near the bifurcation were obtained.

RESULTS

The interaction between the recirculation flow in the bifurcation and the heat transfer in the surrounding tissue makes the temperature distribution near the bifurcation complicated. Most importantly, after a period of continuous heating with constant microwave output power, the maximum temperatures caused by the ablation did not always increase with the distance between the antenna and the bifurcation.

CONCLUSION

It can be concluded that inadequate ablations can be the result not only from a close proximity between the antenna and the blood vessel, but also from a complicated blood flow in large vessels whose structure causes recirculation flow.

Numerical analysis of temperature and thermal dose response of biological tissues to thermal non-equilibrium during hyperthermia therapy

The temperature and thermal dose response of tumor tissue to hyperthermia therapy under conditions of thermal non-equilibrium have been investigated. The thermal model considers the tissue with its blood vessel distribution as a porous medium and employs the convection term instead of the perfusion term in the energy conservation equations for both tissue and blood. By using a numerical method, the temperatures and thermal dose responses of tissues with different vessel diameters, blood velocities, and porosities were calculated. Through an accuracy comparison, the numerical results were used to compare this model with the results for the one-equation porous model under thermal equilibrium. The primary results indicate that the one-equation porous model is suitable for a distribution of blood vessels when the diameters are less than 30 microm and the blood velocities are lower than 0.4 cm s(-1).

[Hypothermia after cardiac arrest--daily trained clinical practice? A survey at northern Germany hospitals]

Hypothermia after out of hospital cardiac arrest should be clinical practice for years. But is it really meanwhile daily trained practice? A survey at northern German hospitals gives an answer to this question.

Mild therapeutic hypothermia after cardiac arrest - a nationwide survey on the implementation of the ILCOR guidelines in German intensive care units

AIM

To investigate the implementation of mild therapeutic hypothermia (MTH) after cardiac arrest into clinical practice.

METHODS AND RESULTS

A structured evaluation questionnaire was sent to all German hospitals registered to have ICUs; 58% completed the survey. A total of 93 ICUs (24%) reported to use MTH. Of those, 93% started MTH in patients after out-of-hospital resuscitation with observed ventricular fibrillation and 72% when other initial rhythms were observed. Only a minority of ICUs initiate MTH in patients after cardiac arrest with cardiogenic shock (28%), whereas 48% regarded cardiogenic shock as a contra-indication for MTH. On average, target temperature was 33.1+/-0.6 degrees C and duration of cooling 22.9+/-4.9 h. Many centres used economically priced cold packs (82%) and cold infusions (80%) for cooling. The majority of the ICUs considered infection, hypotension and bleeding as relevant complications of hypothermia which was of therapeutic relevance in less than 25% of the cases.

CONCLUSIONS

MTH is underused in German ICUs. Centres which use MTH widely follow the recommendations of ILCOR with respect to the indication and timing of cooling. In hospitals that use MTH the technique is considered to be safe and inexpensive. More efforts are needed to promote this therapeutic option and hypothermia since MTH has now been included into European advanced cardiovascular life support protocols.

Evaluation of a dual-arm Archimedean spiral array for microwave hyperthermia

PURPOSE

This effort describes a third-party performance evaluation of a novel, commercial, dual-armed Archimedean spiral array hyperthermia applicator. The applicator is analysed for its ability to couple efficiently into muscle equivalent phantom loads, operate over a broad bandwidth to help accommodate variable tissue properties and generate predictable and repeatable SAR contours that are adaptable to clinically probable disease shapes.

MATERIALS AND METHODS

Characterization of the applicator includes E-field and return-loss measurements in liquid muscle tissue-equivalent phantom, as well as comparison of 'treatment-planning' simulations of several possible array SAR patterns with measured SAR from non-coherently driven spiral array antennae.

RESULTS

The applicator demonstrates a reasonably low return loss over a large bandwidth and the ability to generate a very uniform heating pattern. Ability to adjust SAR contours spatially to fit specific shapes is also demonstrated.

CONCLUSIONS

This device should prove a welcome addition to a currently limited set of superficial heating applicators to provide controllable heating of superficial tissue disease.

Meta-Analysis of the Efficacy and Safety of Intradiscal Electrothermal Therapy (IDET)

OBJECTIVE

The objective of this study was to determine the representative outcomes of the intradiscal electrothermal therapy (IDET) procedure in terms of pain relief, reduction of disability, and risk of complications.

DESIGN

Meta-analysis, using a random-effects model. A Medline literature search was conducted using search terms associated with the IDET procedure including IDET, intradiscal electrothermal therapy, intervertebral disk, and annuloplasty.

OUTCOME MEASURES

The outcomes analyzed were the visual analog scale (VAS) assessment of pain, the bodily pain, and physical functioning subscales of the SF-36 health survey, and the Oswestry disability index.

RESULTS

From 1998 to March 2005, 62 peer-reviewed articles were identified regarding the IDET procedure. Forty-five articles were excluded, leaving a total of 17 unique published reports included in this review. The overall mean improvement in pain intensity was 2.9 points as measured by the VAS. The overall mean improvement in physical function was 21.1 points as measured by the SF-36. The overall mean improvement in bodily pain was 18.0 points as measured by the SF-36. The overall mean improvement in disability was 7.0 points as measured by the Oswestry disability index. The overall incidence of complications was 0.8%.

CONCLUSION

Although variation exists in the reported outcomes among the various studies of the IDET procedure, the pooled results of the published studies provide compelling evidence of the relative efficacy and safety of the IDET procedure.

Changes in the dielectric properties of rat prostate ex vivo at 915 MHz during heating

Changes in the tissue dielectric properties at 915 MHz of rat prostate tissue due to heating at temperatures in the range 45-75 degrees C were measured. The changes were found to be reversible with temperature and independent of the time of heating. The dielectric properties at 23 +/- 1 degrees C were measured as epsilon' = 62.8 +/- 2.7 and sigma = 1.17 +/- 0.07 S/m, while the linear temperature coefficients for reversible changes were 1.10 +/- 0.11%/ degree C for conductivity and -0.31 +/- 0.05% /degree C for relative permittivity. These properties and their temperature coefficients can be utilized in microwave treatment planning programmes to provide insight into the effects of dielectric changes that arise during microwave thermal therapy of prostate cancer.

Infrared thermographic SAR measurements of interstitial hyperthermia applicators: errors due to thermal conduction and convection

Thermal conduction and convection were examined as sources of error in thermographically measured SAR patterns of an interstitial microwave hyperthermia applicator. Measurements were performed in a layered block of muscle-equivalent phantom material using an infrared thermographic technique with varying heating duration. There was a 52.7% reduction in maximum SAR and 75.5% increase in 50% iso-SAR contour area for a 60-s heating duration relative to a 10-s heating duration. A finite element model of heat transfer in an homogeneous medium was used to model conductive and convective heat transfer during the thermographic measurement. Thermal conduction artefacts were found to significantly distort thermographically measured SAR patterns. Convective cooling, which occurs when phantom layers are exposed for thermal image acquisition, was found to significantly affect the magnitude, but not the spatial distribution, of thermographically measured SAR patterns. Results from this investigation suggest that the thermal diffusion artefacts can be minimized if the duration of the applied power pulse is restricted to 10 s or less.

Aktueller Stand der Radiofrequenzablation von Lebertumoren

INTRODUCTION

Radio frequency ablation (RFA) represents a new technique for local destruction of liver tumors. Indication and procedure are poorly validated at present.

METHOD

To record the actual nationwide RFA application in Germany, a survey of 2026 hospitals with standardized questionnaires was conducted.

RESULTS

With a respond rate of 17.5%, results from 58 hospitals covering 1700 ablated patients were analyzed. In 25.9% of them, RFA is already used in potentially curative resectable tumors, in 22.4% even when incomplete ablation for tumor mass reduction is expected. Of the 58 hospitals, 75% combine resection and RFA to reach a so-called R-0 situation. The maximal tumor sizes they quoted for achieving complete ablation ranged from <3 cm to 11 cm. In contraindications for RFA, the tumor size, number of tumors, critical localization of the tumor, and disorders of liver function were mentioned the most.

CONCLUSION

This survey documents significant discrepancies in indication, application, procedure, and results in RFA for liver tumors. The lack of general standards and an overestimation of the method may lead to uncritical application, neglect of standard therapy, or unsatisfying results.

Outcomes of workers' compensation claimants with low back pain undergoing intradiscal electrothermal therapy

STUDY DESIGN

Case series.

OBJECTIVE

To describe the outcomes of workers' compensation (WC) claimants who have had a lumbar intradiscal electrothermal therapy (IDET) procedure.

SUMMARY OF BACKGROUND DATA

IDET was developed as a less invasive treatment alternative to fusion after failure of conservative treatment for discogenic low back pain (LBP). Initial IDET case series from single practices have reported improved pain, function, and return to work outcomes. Little is known about results when performed by a variety of providers or in WC populations.

MATERIALS AND METHODS

LBP cases that underwent IDET between December 1, 1998 and February 29, 2000 were identified from WC records. Data sources included hardcopy claim files, administrative medical billing data, and computerized claim file narrative reports. Outcomes included narcotic use 6 months or more after IDET, additional invasive treatment after IDET (low back injections or surgery), and improved work status 24 months after IDET.

RESULTS

One hundred forty-two cases from 23 states were identified, with 97 different providers performing the procedure. Mean duration of symptoms before IDET was 26 months. Mean follow-up duration after IDET was 22 months. Ninety-six (68%) of the cases did not meet one or more of the published inclusion criteria. Seventy-eight cases (55%) received at least two narcotic prescriptions 6 months or more after IDET. Fifty-three (37%) had at least one lumbar injection and 32 (23%) had lumbar surgery after IDET. A total of 55 (39%) were working at 24 months after IDET; of these, 28 (20%) were not working and 27 (19%) were working before IDET. Narcotic use after IDET was associated with narcotic use before IDET, the same provider performing discography and IDET (provider self-referral), and positive signs of radiculopathy (C = 0.80). Need for invasive lumbar procedures after IDET were associated with provider self-referral, narcotic use before IDET, and older age (C = 0.73). Continued work absence after IDET was associated with provider self-referral, male gender, litigation, narcotic use before IDET, and older age (C = 0.83). Conformance with published selection criteria for IDET was not associated with provider self-referral or outcomes, nor was duration before IDET associated with outcomes.

CONCLUSION

The procedure may be less effective when performed by a variety of providers than suggested by initial case series performed by single providers or practices in work-related LBP cases. Provider self-referral and narcotic use before IDET are significant risk factors for poor outcomes. Randomized controlled trials are needed to determine whether there is a subset of patients with discogenic back pain who derive substantial and sustained benefit from this procedure.

Assessment of prognostic factors in severe traumatic brain injury patients treated by mild therapeutic cerebral hypothermia therapy

This study analyzed the predictable factors of outcome such as neuro-parameters and systemic complications to elucidate the indications for therapeutic hypothermia. In our institute, 35 patients with severe head injury (Glasgow Coma Scale 3-7) were treated with mild hypothermia therapy (33 degrees-35 degrees C). Twenty-two of these 35 patients underwent complete neuromonitoring and outcome assessments by Glasgow Outcome Scale (GOS) at three months after injury. GOS of hypothermia group was significantly better than another patient group which was treated without mild hypothermia therapy. The hypothermia group was divided into two groups: good outcome (GOOD) (good recovery or moderate disability; n = 9, 40.9%) and poor outcome (POOR) (severe disability, vegetative state, or death; n = 13, 59.1%). The mean age (mean 30.2 years, range 9-46) was significantly lower in GOOD than in POOR (mean 45.2 years, range 17-62). Patients aged over 50 years had poor outcome. CPP was significantly higher in GOOD during hypothermia. All patients with thrombocytopenia had poor outcome. Hypothermia therapy can improve outcome in patients with traumatic brain injury who are younger than 50 years old, without severe brain damage, and if improvement of cerebral perfusion is expected. Systemic complications must be prevented as far as possible by combination with other therapies.

SAR pattern perturbations from resonance effects in water bolus layers used with superficial microwave hyperthermia applicators

This study examines the effect of various thickness water bolus coupling layers on the SAR (Specific Absorption Rate) patterns from Dual Concentric Conductor (DCC) based Conformal Microwave Array (CMA) superficial hyperthermia applicators. Previous theory has suggested that water bolus coupling layers can be considered as a dielectric resonator; therefore, it is possible for the impinging electric field to stimulate volume oscillations and surface wave oscillations inside the water bolus. These spurious oscillations will destructively or constructively interact with the impinging electric field to cause a perturbation of the applicator SAR pattern. An experiment was designed which consisted of mapping the electric field produced by a four element DCC CMA applicator in liquid muscle phantom at depths of 5 and 10mm in front of four different thickness water boli; 0 (no bolus) 4, 9 and 13mm. Using the Finite Difference Time Domain (FDTD) method, SAR distributions were calculated for similar test cases. It was found that for water bolus thicknesses of 9mm or greater, there is a marked perturbation of both experimental and theoretical SAR distributions. It is believed that this perturbation is experimental confirmation of the volume and surface wave oscillation theory described by previous investigators.

Risk factors for early failure after thermal capsulorrhaphy

Thermal capsular shrinkage has rapidly become a common procedure for a variety of shoulder conditions usually associated with instability, although clinical data on outcomes are limited. The objective of this study was to identify risk factors for poor outcome after thermal capsulorrhaphy. Of 106 patients who underwent thermal shrinkage, 15 patients with treatment failures were identified. The mean time to failure after the procedure was 6.3 months (range, 1 to 16). Previous operations and multiple recurrent dislocations were associated with poor outcome at a highly significant level. Multidirectional instability and participation in contact sports did not attain statistical significance as risk factors. However, statistical power in these two comparisons was insufficient to exclude them as potential risk factors. A concomitant procedure at the time of thermal capsulorrhaphy was not associated with poor outcome. The data from early treatment failures can be useful in guiding patient selection for thermal capsulorrhaphy. This procedure may be of limited value for patients who have had prior operations or have a history of multiple dislocations. The data also suggest that thermal capsulorrhaphy should be used cautiously in patients with multidirectional instability or in those who are involved in contact sports.

A method of MRI-based thermal modelling for a RF phased array

Magnetic Resonance Imaging (MRI) is an attractive method of temperature monitoring in vivo due to its non-invasive nature. The natural extension of this temperature monitoring is to implement temperature control. This work outlines a method of MRI-based thermal modelling for multi-source phased array heating systems that can potentially be employed, in the future, for real time temperature prediction and control. This method is based on Pennes bioheat equation. It employs the superposition of an empirically acquired basis set of temperature distributions that define the heating system's temperature response. MR thermal images based on the proton resonance frequency shift (PRFS) technique are used to acquire this basis set. The feasibility of this approach is tested in phantom using a radiofrequency (RF) heating system. The results show that this method can accurately reproduce measured temperature distributions outside of the basis set.

A hybrid equation for simulation of perfused tissue during thermal treatment

Bio-heat equations (BHEs) are necessary for predicting tissue temperature during thermal treatment. For some applications, however, existing BHEs describe the convective heat transfer by the blood perfusion in an unsatisfactory way. The two most frequently used equations, the BHE of Pennes and the k(eff) equation, use for instance either a heat sink or an increased thermal conductivity in order to account for the blood perfusion. Both these methods introduce modelling inaccuracies when applied to an ordinary tissue continuum with a variety of vessel sizes. In this study, a hybrid equation that includes both an increased thermal conductivity and a heat sink is proposed. The equation relies on the different thermal characteristics associated with small, intermediate and large sized vessels together with the possibilities of modelling these vessels using an effective thermal conductivity in combination with a heat sink. The relative importance of these two terms is accounted for by a coefficient beta. For beta = 0 and beta = 1, the hybrid equation coincides with the BHE of Pennes and the k(eff) equation, respectively. The hybrid equation is used here in order to simulate temperature fields for two tissue models. The temperature field is greatly affected by beta, and the effect is dependent on, e.g. the boundary conditions and the power supply. Since the BHE of Pennes and the k(eff) equation are included in the hybrid equation, this equation can also be useful for evaluation of the included equations. Both these heat transfer modes are included in the proposed equation, which enables implementation in standard thermal simulation programmes.

The significance of accurate dielectric tissue data for hyperthermia treatment planning

For hyperthermia treatment planning, dielectric properties of several tissue types are required. Since it is difficult to perform patient specific dielectric imaging, default values based on literature data are used. However, these show a large spread (approximately 50%). Consequently, it is important to know what limit this spread imposes on the accuracy of the SAR and subsequently on the temperature distributions. Hyperthermia treatment plans performed with different values for the dielectric properties were compared. This showed that a spread of 50% resulted in the average absolute difference of approximately 20% in both SAR and temperature distributions (heat sink approach) for regional hyperthermia. For interstitial hyperthermia, a spread of 25% resulted in the averaged absolute difference of approximately 10% in the SAR distributions and 5% in the temperature distributions (heat sink approach). Considering other problems that hamper hyperthermia treatment planning, it can be concluded that default values for the dielectric properties suffice.

Planning of hyperthermic treatment for malignant glioma using computer simulation

Interstitial hyperthermia was applied using a radiofrequency generator in the treatment of four malignant glioma patients who had especially deep seated brain tumours or were at high risk. Prior to heating tumours, treatment planning based on an accurate prediction of temperature distribution is essential. The present paper introduces a novel treatment planning method and discusses its clinical efficacy. The two-dimensional finite element method was used for simulation of temperature distribution, which was calculated using the bioheat transfer equation. This technique was applied to plan treatment. Temperature was measured at two points during heating and these values were compared with those estimated by the simulation. In addition, the area of the contrast enhanced (CE) rim on the pre-heating computed tomography (CT) image was compared with the low density area of the CE rim on the post-heating CT image, which was obtained within 2 months after heating. The optimal position and number of radiofrequency (RF) electrodes to include the outside of the CE rim in the simulated area above 42 degrees C contour could be easily determined using this planning system in all cases. The temperature estimated by the simulation was in good agreement with the actual values obtained (within 0.4 degrees C). The post-heating CT image revealed that the hyperthermic procedure described herein achieved more than an 80% low density area within the CE rim in all cases (mean 86.0%). These results demonstrate that this novel treatment planning method may prove to be a clinically valuable tool in the treatment of malignant glioma with RF electrodes.

Calibrated electro-optic E-field sensors for hyperthermia applications

E-field measurements are an important task for the investigation of newly developed hyperthermia applicators as well as for online control of hyperthermia treatments. Compact and non-perturbing integrated optical E-field sensors based on LiNbO3 as well as optical E-field sensors based on infrared emitting diodes and light bulbs are suitable for nearfield measurements of hyperthermia antennas. In order to investigate their properties a calibration cell with transverse electromagnetic (TEM) waves has been constructed. By using this cell, calibration curves and directional patterns for all sensors have been measured. Due to the threshold behaviour of the IRED and light bulb sensor, only the LiNbO3 sensor is capable of measuring weak fields inside an applicator or a homogeneous phantom.

An on-line phase measurement system for quality assurance of the BSD 2000. Part II: results of the phase measurement system

Phase constancy and accuracy are significant for regional hyperthermia with phased array radiofrequency hyperthermia systems. They are both necessary for a precise target steering in therapy. For the BSD 2000 system (BSD Medical Corp. Salt Lake City, Utah, USA), the phase values of all channels are checked with a self-developed automatic on-line phase measurement system. On different days the phases are measured under identical conditions, where the output paths are cut off with 50 ohm dummy loads to suppress the influence of the radiation conditions of the antennae on the measurement values. The results show how the phase values of the four channels change in the first 30 min and from day to day. During this time interval after the start the phases drop down by up to 15 degrees. For the time later changes are very slight and the differences from day to day are negligible. The phase shift that occurs in the first 30 min is as high as a change of the target point by 1 cm. Earlier switching on of the amplifiers prevents this shift occurring during the treatment. The measurement system provides a good tool for determination of phase accuracy and is easy to realize.

An on-line phase measurement system for quality assurance of the BSD 2000. Part I: technical description of the measurement system

The hyperthermia system BSD 2000 with the ring applicator Sigma 60 utilizes the principle of a phase controlled group radiation source. The accuracy of the phase relationship between the four receiving HF signals is crucial for the position of the electric field inside the applicator. Therefore, essential significance falls to the phase control of the system. An automatic phase measuring technique has been developed to register immediately the phase position of the four channels of the BSD 2000 with respect to a reference signal. The system improves the insurance of the technical safeguarding. In the first part of this work, the technical realization of the measurement system is described and first measurements with the system are given. In the second part, results with respect to the quality assurance of the BSD 2000 system are presented.

Effects of combined treatment with coffee cherry and whole-body hyperthermia on the growth of spontaneous mammary tumours in SHN mice

Based on findings that free access in drinking water of the extract of coffee cherry (CC), the residue left after the removal of coffee beans, and whole-body hyperthermia (WBH) induced by far-infrared ray (FIR) can markedly inhibit the growth of spontaneous mammary tumours of SHN mice, the effects of the combined treatment with these agents were examined in this study. The significant inhibition of tumour growth by single treatment with either CC or WBH was not enhanced by their combination. Meanwhile, the body weight loss during WBH was significantly decreased by CC. Normal and preneoplastic growth of mammary glands and plasma component levels were affected little by either treatment. The findings confirmed the "normalization effects" of CC usually obtained with natural products and stress the need for prudence in the choice of any agent, natural or synthetic, to be applied simultaneously to increase the efficacy of WBH.

Hyperthermia treatment planning

The development of hyperthermia, the treatment of tumours with elevated temperatures in the range of 40-44 degrees C with treatment times over 30 min, greatly benefits from the development of hyperthermia treatment planning. This review briefly describes the state of the art in hyperthermia technology, followed by an overview of the developments in hyperthermia treatment planning. It particularly highlights the significant problems encountered with heating realistic tissue volumes and shows how treatment planning can help in designing better heating technology. Hyperthermia treatment planning will ultimately provide information about the actual temperature distributions obtained and thus the tumour control probabilities to be expected. This will improve our understanding of the present clinical results of thermoradiotherapy and thermochemotherapy, and will greatly help both in optimizing clinical heating technology and in designing optimal clinical trials.

Effect of complex bolus-tissue load configurations on SAR distributions from dual concentric conductor applicators. Specific absorption rate

Power deposition [specific absorption rate (SAR)] distributions from a two-element array configuration of 4-cm-square 915-MHz dual concentric conductor (DCC) microwave antennas were characterized theoretically for several clinically realistic complex bolus-tissue load models using the finite difference time domain (FDTD) numerical method. The purpose of this effort was to determine the perturbing effects on SAR of three often unavoidable heterogeneities in the bolus-tissue load. The three cases studied in this work consist of bone (two ribs spaced 1 cm apart) embedded 5-mm or 1-cm deep in muscle or layered fat-muscle tissue, small air bubbles trapped between the coupling bolus and tissue surface, and variable thickness water bolus layer due to sharply contoured anatomy. Results of the FDTD simulations demonstrate rather small effects on SAR distribution for both rib-sized bones > or = 5-mm deep in muscle and small air pockets < or = 1-mm thick. Larger air bubbles > 1-cm diameter by 3-mm depth showed a distinct concentration of SAR near the lateral sides of the air bubbles, and a blocking effect under the bubbles when located directly under the center of a DCC aperture where there is a higher normal E-field component. Variation from 2.5- to 7.5-mm bolus thickness under the two aperture array produced only minor perturbation of the uniformity and penetration of SAR, along with minor reduction in SAR under the thicker bolus which should be accommodated sufficiently by changes in applied power to the array elements.

Whole body hyperthermia: a secure procedure for patients with various malignancies?

OBJECTIVE

To establish the safety of systemic Cancer Multistep Therapy (sCMT) including whole body hyperthermia, by means of hemodynamic, laboratory and clinical investigations.

DESIGN

Prospective study.

SETTING

University clinic.

PATIENTS

12 patients with various cancers (with sCMT), a second group of 20 patients with colorectal carcinoma treated with chemotherapy (without sCMT).

INTERVENTIONS

25 treatments with sCMT for 60 min at 41.8 degrees C (including chemotherapy) were given in addition to induced hyperoxemia and hyperglycemia under general anesthesia.

MEASUREMENTS AND RESULTS

Invasive monitoring of systemic and pulmonary hemodynamics as well as pulmonary gas exchange was used at 37 degrees C, 40 degrees C, 41.8 degrees C and 39 degrees C. In addition, laboratory parameters were measured before and within 4 days of therapy. At 41.8 degrees C, invasive monitoring showed characteristic signs of hyperdynamic circulation. In addition, right-to-left shunt, oxygen consumption, oxygen delivery and lactate levels were significantly different from pretreatment values. At the end of therapy, lactate levels and the extravascular lung water index increased, whereas all other parameters showed a clear tendency to return to initial values. Within the first day after sCMT, we measured a slight but significant reversible increase in serum creatinine compared to pretreatment values, but found no significant alterations of other chemical parameters. Between the sCMT group and controls, there was only a temporary significant difference in aspartate aminotransferase levels 2 days after therapy.

CONCLUSIONS

sCMT, including whole body hyperthermia, accompanied by suitable anesthesiological management and monitoring, does not lead to any serious or sustained organ dysfunction and can therefore be regarded as a safe therapy.

Experimental evaluation of two simple thermal models using transient temperature analysis

Thermal models are used to predict temperature distributions of heated tissues during thermal therapies. Recent interest in short duration high temperature therapeutic procedures necessitates the accurate modelling of transient temperature profiles in heated tissues. Blood flow plays an important role in tissue heat transfer and the resultant temperature distribution. This work examines the transient predictions of two simple mathematical models of heat transfer by blood flow (the bioheat transfer equation model and the effective thermal conductivity equation model) and compares their predictions to measured transient temperature data. Large differences between the two models are predicted in the tissue temperature distribution as a function of blood flow for a short heat pulse. In the experiments a hot water needle, approximately 30 degrees C above ambient, delivered a 20 s heating pulse to an excised fixed porcine kidney that was used as a flow model. Temperature profiles of a thermocouple that primarily traversed the kidney cortex were examined. Kidney locations with large vessels were avoided in the temperature profile analysis by examination of the vessel geometry using high resolution computed tomography angiography and the detection of the characteristic large vessel localized cooling or heating patterns in steady-state temperature profiles. It was found that for regions without large vessels, predictions of the Pennes bioheat transfer equation were in much better agreement with the experimental data when compared to predictions of the scalar effective thermal conductivity equation model. For example, at a location r approximately 2 mm away from the source, the measured delay time was 10.6 +/- 0.5 s compared to predictions of 9.4 s and 5.4 s of the BHTE and ETCE models, respectively. However, for the majority of measured locations, localized cooling and heating effects were detected close to large vessels when the kidney was perfused. Finally, it is shown that increasing flow in regions without large vessels minimally perturbs temperature profiles for short exposure times; regions with large vessels still have a significant effect.

Evaluation of segmentation algorithms for generation of patient models in radiofrequency hyperthermia

Time-efficient and easy-to-use segmentation algorithms (contour generation) are a precondition for various applications in radiation oncology, especially for planning purposes in hyperthermia. We have developed the three following algorithms for contour generation and implemented them in an editor of the HyperPlan hyperthermia planning system. Firstly, a manual contour input with numerous correction and editing options. Secondly, a volume growing algorithm with adjustable threshold range and minimal region size. Thirdly, a watershed transformation in two and three dimensions. In addition, the region input function of the Helax commercial radiation therapy planning system was available for comparison. All four approaches were applied under routine conditions to two-dimensional computed tomographic slices of the superior thoracic aperture, mid-chest, upper abdomen, mid-abdomen, pelvis and thigh; they were also applied to a 3D CT sequence of 72 slices using the three-dimensional extension of the algorithms. Time to generate the contours and their quality with respect to a reference model were determined. Manual input for a complete patient model required approximately 5 to 6 h for 72 CT slices (4.5 min/slice). If slight irregularities at object boundaries are accepted, this time can be reduced to 3.5 min/slice using the volume growing algorithm. However, generating a tetrahedron mesh from such a contour sequence for hyperthermia planning (the basis for finite-element algorithms) requires a significant amount of postediting. With the watershed algorithm extended to three dimensions, processing time can be further reduced to 3 min/slice while achieving satisfactory contour quality. Therefore, this method is currently regarded as offering some potential for efficient automated model generation in hyperthermia. In summary, the 3D volume growing algorithm and watershed transformation are both suitable for segmentation of even low-contrast objects. However, they are not always superior to user-friendly manual programs for contour generation. When the volume growing algorithm is used, the contours have to be postprocessed with suitable filters. The watershed transformation has a large potential if appropriately developed to 3D sequences and 3D interaction features. After all, the practicality and feasibility of every segmentation method critically depend on various details of the user software as pointed out in this article.

The influence of vasculature on temperature distributions in MECS interstitial hyperthermia: importance of longitudinal control

The quality of temperature distributions that can be generated with the Multi Electrode Current Source (MECS) interstitial hyperthermia (IHT) system, which allows 3D control of the temperature distribution, has been investigated. For the investigations, computer models of idealised anatomies containing discrete vessels, were used. A 7-catheter hexagonal implant geometry with a nearest neighbour distance of 15 mm was used. In each interstitial catheter with a diameter of 2.1 mm a number of 1 up to 4 electrodes were placed along an 'active section' with a length of 50 mm. The electrode segments had lengths of 50, 20, 12 and 9 mm respectively. Both single vessel and vessel network situations were analysed. This study shows that even in situations with discrete vasculature and perfusion heterogeneity it remains possible to obtain satisfactory temperature distributions with the MECS IHT system. Due to its 3D spatial control the temperature homogeneity in the implant can be made quite satisfactory.

[A phase-I/II study on the local hyperthermia of cervical N2/N3 lymph node metastases]

BACKGROUND

Patients with advanced lymph node metastases from head and neck tumors at stage N2/N3 (i.e. UICC IV) present a difficult therapeutic problem. Despite combined radio-chemotherapy and hyperfractionated and/or accelerated fractionation regimens, local control of these tumors remains unsatisfactory. For this reason, the value of local radio wave/microwave hyperthermia was examined for this patient group in a phase I/II study.

A description of discrete vessel segments in thermal modelling of tissues

In hyperthermia treatment planning vessels with a diameter larger than 0.5 mm must be treated individually. Such vessels can be described as 3D curves with associated diameters. The temperature profile along the vessel is discretized one dimensionally. Separately the tissue is discretized three dimensionally on a regular grid of voxels. The vessel as well as the tissue are positioned in one global space. Methods are supplied to describe the tissue-vessel interaction, the shift of the blood temperature profile describing the flow of blood along the vessel and the calculation of the vessel wall temperature. The calculation of the interaction is based on tissue temperature samples and the blood temperature together with the distance between the centre of the vessel and the tissue temperature sample. An analytical expression for a vessel inside a coaxial tissue cylinder is then used for the calculation of the heat flow rate across the vessel wall. The basic test system is a vessel segment embedded inside a coaxial tissue cylinder. All the tests use this setup while the following simulation parameters are varied: position and orientation of the vessel relative to the tissue grid, vessel radius, sample density of the blood temperature and power deposition inside the tissue cylinder. The blood temperature profile is examined by calculation of the local estimate of the equilibration length. All tests show excellent agreement with the theory.

Evaluation of inductively heated ferromagnetic alloy implants for therapeutic interstitial hyperthermia

Ferromagnetic alloys heated by magnetic induction have been investigated as interstitial hyperthermia delivery implants for over a decade, utilizing low Curie temperatures to provide thermal self-regulation. The minimally invasive method is attractive for fractionated thermal treatment of tumors which are not easily heated by focused microwave or ultrasound techniques. Past analyses of ferromagnetic seeds by other authors depict poor experimental correlation with theoretical heating predictions. Improvements in computer hardware and commercially available finite element analysis software have simplified the analysis of inductively heated thermal seeds considerably. This manuscript examines end effects of finite length implants and nonlinear magnetic material properties to account for previous inconsistencies. Two alloys, Ni-28 wt% Cu (NiCu) and Pd-6.15 wt% Co (PdCo), were used for comparison of theoretical and experimental calorimetric results. Length to diameter (L/d) ratios of over 20 for cylindrical seeds are necessary for minimization of end effects. Magnetic properties tested for alloys of NiCu and PdCo illustrate considerable nonlinearity of these materials in field strength ranges used for induction heating. Field strength dependent magnetic permeabilities and calorimetric data illustrate that more detailed material information must be included to accurately estimate induction power loss for these implants.

Experimental investigation of an adaptive feedback algorithm for hot spot reduction in radio-frequency phased-array hyperthermia

A computer-controlled adaptive phased array radiofrequency hyperthermia system for improved therapeutic tumor heating is experimentally investigated. Adaptive array feedback techniques are used to modify the electric-field in hyperthermia experiments with a homogeneous saline phantom target. A hyperthermia phased-array antenna system has been modified to implement adaptive nulling and adaptive focusing algorithms. The hyperthermia system is a ring phased-array antenna applicator with four independently controlled RF transmitter channels operating at a CW frequency of 100 MHz. The hyperthermia phased array is made adaptive by software modifications which invoke a gradient-search feedback algorithm that controls the amplitude and phase of each transmitter channel. The gradient-search algorithm implements the method of steepest descent for adaptive nulling (power minimization) and the method of steepest ascent for adaptive focusing (power maximization). The feedback signals are measured by electric-field short-dipole probe antennas. The measured data indicate that with an adaptive hyperthermia array it may be possible to maximize the applied electric field at a tumor position in a complex scattering target body and simultaneously minimize or reduce the electric field at target positions where undesired high-temperature regions (hot spots) occur.

Dose uniformity in MECS interstitial hyperthermia: the impact of longitudinal control in model anatomies

The quality of temperature distributions that can be generated with the multi-electrode current source (MECS) interstitial hyperthermia system, which allows 3D control of the spatial SAR distribution, has been investigated. For the investigations, computer models of idealized anatomies were used. These anatomical models did not contain discrete vessels. Binary-media anatomies, containing media interfaces oriented parallel, perpendicular or oblique with respect to the long axis of the implant, represent simple anatomies which can be encountered in the clinic. The implant volume was about 40 cm3. A seven-catheter hexagonal implant geometry with a nearest-neighbor distance of 15 mm was used. In each interstitial probe between one and four electrodes with a diameter of 2.1 mm were placed along an "active section' with a length of 50 mm. The electrode segments had lengths of 50, 20, 12 and 9 mm. This study shows that even with high contrasts in electrical and thermal conductivity in the implant it remains possible to obtain satisfactory temperature distributions with the MECS system. Due to its 3D spatial control the temperature homogeneity in the implant can be made quite satisfactory, with T10-T90 of the order of 2-3 K. Treatment planning must ensure that the placement of the current source electrodes is compatible with the media configuration.

SAR optimization in a phased array radiofrequency hyperthermia system. Specific absorption rate

RF deep hyperthermia systems make use of phased arrays of applicators in order to heat tumors selectively while maintaining healthy tissue at normal temperatures. A new method for the array synthesis is proposed based on the identification of targets to be heated (tumors) and targets to be prevented from excess electromagnetic radiation. The best array feed for each target is found from the solution of the eigenvector problem for a positive definite Hermitian matrix defined for that target. The optimal feed in a global sense then results from a trade-off of the best feeds of individual targets enforced through minimization of an objective function aimed at weighting the distances of the globally optimal feed from the feed vectors optimized for each target separately. An application to the heating of a pelvis is provided as an example.

A mathematical model for predicting the temperature distribution in laser-induced hyperthermia. Experimental evaluation and applications

A time-dependent mathematical model for the heat transfer in laser-induced hyperthermia has been developed. The model calculates the temperature distribution in surface-irradiated tissues. Good agreement was found between the predictions of the model and in vitro experimental results obtained for bovine liver irradiated with an expanded beam from a Nd:YAG laser. Surface evaporation of water was included in the model and experimentally verified. The discrepancy between the measured and the calculated rise in temperature at three different depths on the axis of symmetry of the irradiating beam was found to be less than 5% after 15 min of irradiation. When irradiating in air and not accounting for the surface evaporation in the model, the accuracy of the model predictions was only 75-80%. The model was then used to investigate the influence of surface evaporation of water on the total temperature distribution theoretically in a clinically relevant case. From the numerical simulations, it was shown that, simply by providing a moistened liver surface, the maximum steady-state temperature could be forced into the tissue to a depth of 4 mm. It was also shown that, by employing the numerical model during the initial phase of hyperthermia treatment, overshooting of the temperature during the transient thermal build-up time could be prevented.

FDTD simulations of Clini-Therm applicators on inhomogeneous planar tissue models

A finite-difference time-domain (FDTD) algorithm was used to compute SAR distributions in planar fat-muscle phantom exposed to the Clini-Therm microwave applicators. The models consisted of a 30 X 30 X 7.5 cm phantom and a 15 X 15 cm, 10 X 10 cm or 7.5 X 7.5 cm aperture dielectric slab loaded applicator. The phantom was either filled with muscle material or with 1.0 cm fat on 6.5 cm muscle. A mineral oil bolus was placed on the fat-muscle model with its integrated water channels parallel to the electric or magnetic field. The FDTD resolution was 3 mm and the applicators were excited with a Gaussian pulse. The computations required 6000-8000 time steps to reach steady state, with 45-48 Mwords on a Cray Y-MP C-90 in 1000-1200 CPU seconds. The electric field components at 915 MHz were obtained by summing the Fourier coefficients at each grid point during each time step and SAR was determined. The results were qualitatively compared to existing and published thermographic heating patterns with good agreement. The computed electric field distributions had provided a three dimensional view into the problem space to investigate and understand wave propagation phenomena in complex inhomogeneous configurations that were not feasible with experimental models.

An active microwave imaging system for reconstruction of 2-D electrical property distributions

The goal of this work is to develop a microwave-based imaging system for hyperthermia treatment monitoring and assessment. Toward this end, a four transmit channel and four receive channel hardware device and concomitant image reconstruction algorithm have been realized. The hardware is designed to measure electric fields (i.e., amplitude and phase) at various locations in a phantom tank with and without the presence of various heterogeneities using standard heterodyning principles. Particular attention has been paid to designing a receiver with better than 115 dB of linear dynamic range which is necessary for imaging biological tissue which often has very high conductivity, especially for tissues with high water content. A calibration procedure has been developed to compensate for signal loss due to three-dimensional radiation in the measured data, since the reconstruction process is only two-dimensional at the present time. Results are shown which demonstrate the stability and accuracy of the measurement system, the extent to which the forward computational model agrees with the measured field distribution when the electrical properties are known, and image reconstructions of electrically unknown targets of varying diameter. In the latter case, images of both the reactive and resistive component of the electrical property distribution have been recoverable. Quantitative information on object location, size, and electrical properties results when the target is approximately one-half wavelength in size. Images of smaller objects lack the same level of quantitative information, but remain qualitatively correct.

FDTD electromagnetic and thermal analysis of interstitial hyperthermic applicators. Finite-difference time-domain

In this paper, the electromagnetic and thermal behavior of interstitial applicators was analyzed by using the Finite-Difference Time-Domain method. Two configurations were considered: a simple insulated dipole antenna radiating in a layered tissue, and an air cooled applicator radiating in a tissue-equivalent phantom. The proposed approach allows a detailed modeling of the complete structure of the applicator. Furthermore, Specific Absorption Rate and temperature distributions can be determined considering real clinical or experimental conditions. The temperature distribution for the air cooled applicator has been compared with experimental results.

Optimizing ultrasound focus distributions for hyperthermia

A method is described for generating ultrasound focus patterns for ultrasound hyperthermia treatment planning for steady state and transient hyperthermia. The solution for placement and intensity of ultrasound focus points is based on two types of temperature constraints: 1) equality constraints on the tumor boundary (temperature is held at maximum safe level) and 2) inequality constraints in the tumor interior (in a therapeutic range of temperatures). The method employs a simplex algorithm to solve a series of linear equations which approximate the heating distribution in tissue. Examples are given for field conjugate acoustic lens applicators capable of generating multiple foci simultaneously.

Finite element simulation of Sigma 60 heating in the Utah phantom: computed and measured data compared

An initial series of comparisons are made between finite element computations and laboratory measurements obtained during heterogeneous phantom heating with the Sigma 60 applicator. The phantom is a relatively complex, though still idealized, rendering of the pelvic area which has been used to study the deep heating characteristics of the Sigma 60 in this anatomy. Direct electric field measurements as well as inferred SAR through transient temperature analysis are plotted against computed results along 11 one-dimensional tracks through the phantom. Quantitative comparisons provided through the track-by-track analysis show generally good agreement between computation and measurement. The finite element method is found to predict well the jumps in the electric field when polarized perpendicularly to a muscle/fat interface. Visualizations of the complete three-dimensional distributions are also highlighted and correlate well with physical reasoning about the expected behaviour of the fields produced. Some discrepancies in the data persist and are discussed and analysed in depth. They underscore the difficulties that can arise in performing comparisons between measured and computed results and stress the need for careful and thorough investigations when attempting these types of model validation studies.