Biomedical subjects

J J W Lagendijk

Publications and source records attributed to J J W Lagendijk.

17 recordsLinked to original sources

PubMed2006

Influence of the linac design on intensity-modulated radiotherapy of head-and-neck plans.

In this study, we quantify the impact of linac/MLC design parameters on IMRT treatment plans. The investigated parameters were leaf width in the MLC, leaf transmission, related to the thickness of the leaves, and penumbra related primarily to the source size. Seven head-and-neck patients with stage T1-T3N0-N2cM0 oropharyngeal cancer were studied. For each patient nine plans were made with a different set of linac/MLC parameters. The plans were optimized in Pinnacle(3) v7.6c and PLATO RTS v2.6.4, ITP v1.1.8. A hypothetical ideal linac/MLC was introduced to investigate the influence of one parameter at a time without interaction of other parameters. When any of the three parameters was increased from the ideal set-up values (leaf width 2.5 mm, transmission 0%, penumbra 3 mm), the mean dose to the parotid glands increased, given the same tumour coverage. The largest increase was found for increasing leaf transmission. The investigation showed that by changing more than one parameter of the ideal linac/MLC set-up, the increase in the mean dose was smaller than the sum of dose increments for each parameter separately. As a reference to clinical practice, we also optimized the plans of the seven patients with the clinically used Elekta SLi 15, equipped with a standard MLC with a leaf width of 10 mm. As compared to the ideal linac, this resulted in an increase of the average dose to the parotid glands of 5.8 Gy.

Dose-Response Relationship, Radiation↗

PubMed2006

Modelling the impact of blood flow on the temperature distribution in the human eye and the orbit: fixed heat transfer coefficients versus the Pennes bioheat model versus discrete blood vessels.

Prediction of the temperature distribution in the eye depends on how the impact of the blood flow is taken into account. Three methods will be compared: a simplified eye anatomy that applies a single heat transfer coefficient to describe all heat transport mechanisms between the sclera and the body core, a detailed eye anatomy in which the blood flow is accounted for either by the bioheat approach, or by including the discrete vasculature in the eye and the orbit. The comparison is done both for rabbit and human anatomies, normo-thermally and when exposed to homogeneous power densities. The first simplified model predicts much higher temperatures than the latter two. It was shown that the eye is very hard to heat when taking physiological perfusion correctly into account. It was concluded that the heat transfer coefficient describing the heat transport from the sclera to the body core reported in the literature for the first simplified model is too low. The bioheat approach is appropriate for a first-order approximation of the temperature distribution in the eye when exposed to a homogeneous power density, but the discrete vasculature down to 0.2 mm in diameter needs to be taken into account when the heterogeneity of the temperature distribution at a mm scale is of interest.

Animals↗

PubMed2006

Development of a tapping device: a new needle insertion method for prostate brachytherapy.

The purpose of this study is to develop and test a tapping device for needle insertion for prostate brachytherapy. This device will tap the needle into the prostate with a certain, well-defined, amount of momentum, instead of the currently used method of pushing the needle. Because of the high needle insertion velocity, we expect prostate motion and deformation to be less compared to current methods. We measured the momentum that is applied when manually tapping the needle into the prostate and found a mean momentum of 0.50 +/- 0.07 N s. The tapping device is pneumatically driven and we found that the delivered momentum increased linearly with the applied air pressure. The efficacy of the tapping device was tested on a piece of beef, placed on a freely moving and rotating platform. A significant correlation was found between the applied pressure and the rotation and displacement of the beef. Displacements and rotations were minimal for the highest pressure (4 bar) and amounted to only 2 mm and 6 degrees, respectively. Higher air pressures will further reduce displacements and rotations.

Brachytherapy↗

PubMed2006

Patient position verification using small IMRT fields.

A commonly used approach to quantify and minimize patient setup errors is by using electronic portal imaging devices (EPIDs). The position of the tumor can be verified indirectly by matching the bony anatomy to a reference image containing the same structures. In this paper we present two off-line methods for detecting the position of the bony anatomy automatically, even if every single portal image of each segment of an IMRT treatment beam contains insufficient matching information. Extra position verification fields will no longer be necessary, which reduces the total dose to the patient. The first method, the stack matching method (SMM), stacks the portal image of each segment of a beam to a three dimensional (3D) volume, and this volume is subsequently used during the matching phase. The second method [the averaged projection matching method (APMM)], is a simplification of the first one, since the initially created volume is reduced again to a 2D artificial image, which speeds up the matching procedure considerably, without a significant loss of accuracy. Matching is based on normalized mutual information. We demonstrate our methods by comparing them to existing matching routines, such as matching based on the largest segment. Both phantom and patient experiments show that our methods are comparable with the results obtained from standard position verification methods. The matches are verified by means of visual inspection. Furthermore, we show that when a distinct area of 40-60 cm2 of the EPID is exposed during one treatment beam, both SMM and APMM are able to deliver a good matching result.

Humans↗

PubMed2005

Assessment of rigid multi-modality image registration consistency using the multiple sub-volume registration (MSR) method.

Registration of different imaging modalities such as CT, MRI, functional MRI (fMRI), positron (PET) and single photon (SPECT) emission tomography is used in many clinical applications. Determining the quality of any automatic registration procedure has been a challenging part because no gold standard is available to evaluate the registration. In this note we present a method, called the 'multiple sub-volume registration' (MSR) method, for assessing the consistency of a rigid registration. This is done by registering sub-images of one data set on the other data set, performing a crude non-rigid registration. By analysing the deviations (local deformations) of the sub-volume registrations from the full registration we get a measure of the consistency of the rigid registration. Registration of 15 data sets which include CT, MR and PET images for brain, head and neck, cervix, prostate and lung was performed utilizing a rigid body registration with normalized mutual information as the similarity measure. The resulting registrations were classified as good or bad by visual inspection. The resulting registrations were also classified using our MSR method. The results of our MSR method agree with the classification obtained from visual inspection for all cases (p < 0.02 based on ANOVA of the good and bad groups). The proposed method is independent of the registration algorithm and similarity measure. It can be used for multi-modality image data sets and different anatomic sites of the patient.

Algorithms↗

PubMed2005

IMRT sequencing for a six-bank multi-leaf system.

In this study, we present a sequencer for delivering step-and-shoot IMRT using a six-bank multi-leaf system. Such a system was proposed earlier and combines a high-resolution field-shaping ability with a large field size. It consists of three layers of two opposing leaf banks with 1 cm leaves. The layers are rotated relative to each other at 60 degrees . A low-resolution mode of sequencing is achieved by using one layer of leaves as primary MLC, while the other two are used to improve back-up collimation. For high-resolution sequencing, an algorithm is presented that creates segments shaped by all six banks. Compared to a hypothetical mini-MLC with 0.4 cm leaves, a similar performance can be achieved, but a trade-off has to be made between accuracy and the number of segments.

Algorithms↗

PubMed2005

Integrating a MRI scanner with a 6 MV radiotherapy accelerator: dose increase at tissue-air interfaces in a lateral magnetic field due to returning electrons.

In the framework of the development of the integration of a MRI-scanner with a linear accelerator, the influence of a lateral, magnetic field on the dose distribution has to be determined. Dose increase is expected at tissue-air boundaries, due to the electron return effect (ERE): electrons entering air will describe a circular path and return into the phantom causing extra dose deposition. Using IMRT with many beam directions, this exit dose will not constitute a problem. Dose levels behind air cavities will decrease because of the absence of electrons crossing the cavity. The ERE has been demonstrated both by simulation and experiment. Monte Carlo simulations are performed with GEANT4, irradiating a water-air-water phantom in a lateral magnetic field. Also an air tube in water has been simulated, resulting in slightly twisted regions of dose increase and decrease. Experimental demonstration is achieved by film measurement in a perspex-air-perspex phantom in an electromagnet. Although the ERE causes dose increase before air cavities, relatively flat dose profiles can be obtained for the investigated cases using opposite beam configurations. More research will be necessary whether this holds for more realistic geometries with the use of IMRT and whether the ERE can be turned to our advantage when treating small tumour sites at air cavities.

Body Burden↗

PubMed2004

Integrating a MRI scanner with a 6 MV radiotherapy accelerator: dose deposition in a transverse magnetic field.

Integrating magnetic resonance imaging (MRI) functionality with a radiotherapy accelerator can facilitate on-line, soft-tissue based, position verification. A technical feasibility study, in collaboration with Elekta Oncology Systems and Philips Medical Systems, led to the preliminary design specifications of a MRI accelerator. Basically the design is a 6 MV accelerator rotating around a 1.5 T MRI system. Several technical issues and the clinical rational are currently under investigation. The aim of this paper is to determine the impact of the transverse 1.5 T magnetic field on the dose deposition. Monte Carlo simulations were used to calculate the dose deposition kernel in the presence of 1.5 T. This kernel in turn was used to determine the dose deposition for larger fields. Also simulations and measurements were done in the presence of 1.1 T. The pencil beam dose deposition is asymmetric. For larger fields the asymmetry persists but decreases. For the latter the distance to dose maximum is reduced by approximately 5 mm, the penumbra is increased by approximately 1 mm, and the 50% isodose line is shifted approximately 1 mm. The dose deposition in the presence of 1.5 T is affected, but the effect can be taken into account in a conventional treatment planning procedure. The impact of the altered dose deposition for clinical IMRT treatments is the topic of further research.

Computer Simulation↗

PubMed2004

A six-bank multi-leaf system for high precision shaping of large fields.

In this study, we present the design for an alternative MLC system that allows high precision shaping of large fields. The MLC system consists of three layers of two opposing leaf banks. The layers are rotated 60 degrees relative to each other. The leaves in each bank have a standard width of 1 cm projected at the isocentre. Because of the symmetry of the collimator set-up it is expected that collimator rotation will not be required, thus simplifying the construction considerably. A 3D ray tracing computer program was developed in order to simulate the fluence profile for a given collimator and used to optimize the design and investigate its performance. The simulations show that a six-bank collimator will afford field shaping of fields of about 40 cm diameter with a precision comparable to that of existing mini MLCs with a leaf width of 4 mm.

Computer Simulation↗

PubMed2004

A feasibility study of interstitial hyperthermia plus external beam radiotherapy in glioblastoma multiforme using the Multi ELectrode Current Source (MECS) system.

PURPOSE: Thermoradiotherapy has been shown in several randomized trials to increase local control compared to radiotherapy alone. The first randomized study of interstitial hyperthermia in glioblastoma multiforme showed a survival benefit for hyperthermia, though small. Improvement of the heating technique could lead to improved results. The purpose of this feasibility study is to present the clinical and thermal data of application of an improved interstitial hyperthermia system. METHODS AND MATERIALS: Six patients with a glioblastoma multiforme were treated with interstitial hyperthermia using the Multi Electrode Current Source Interstitial Hyperthermia (MECS-IHT) system. The MECS-IHT system has the capability of spatial monitoring of temperature and individually steering of heating electrodes. Three sessions were given aiming at a steady state temperature of 42 degrees C for 1 h, with an interval of 3-4 days, during an external irradiation scheme of 60 Gy in 6 weeks. Hyperthermia was delivered with a mean of 10 catheters, 18 heating electrodes and 38 thermal probes per patient. RESULTS: Sub-optimal temperatures were encountered in the first two patients leading to adjustments in technique thereafter with subsequent improvement of thermal data. With a catheter spacing of 11-12 mm, measurements yielded a mean T(90), T(50) and T(10) of 39.9, 43.7 and 45.2 degrees C, respectively, over three sessions in the last patient. The power per electrode to reach this temperature distribution varied from 25-100% of full power in each of the last four patients. Thermal data were reproducible over the three sessions. Acute toxicity was minimal. CONCLUSIONS: Despite the spatial steering capabilities of the MECS-IHT system, a large temperature heterogeneity was encountered. The heterogeneity was the reason to limit the catheter spacing to 11-12 mm, thus making only small tumour volumes feasible for interstitial heating.

Aged↗

PubMed2004

Radiotherapy and hyperthermia in the treatment of patients with locally advanced prostate cancer: preliminary results.

OBJECTIVE: To report an interim clinical evaluation of combined external beam irradiation (EBRT) and interstitial or regional hyperthermia in the treatment of locally advanced prostate cancer. PATIENTS AND METHODS: From 1997 to 2001, 26 patients with T3-4/NX/0M0 prostate carcinoma were treated with a combination of conformal EBRT and hyperthermia. Fourteen patients received five weekly regional hyperthermia treatments within an optimization (phase II) study, using the coaxial transverse electrical magnetic system. Twelve patients received one interstitial hyperthermia treatment within a feasibility study (phase I), using the multi-electrode current source system. Irradiation was delivered using a conformal three-field technique, administering 70 Gy in 2-Gy fractions in 7 weeks. RESULTS: The mean initial prostate-specific antigen level was 26 ng/mL. Three patients had a T4 and 23 a T3 tumour; the tumours were classified as well (four), moderately (16) and poorly (six) differentiated. The mean follow-up was 36 months. In the combined treatments there was no toxicity of more than grade 2. In regional hyperthermia the mean index temperature (T90 and T50, i.e. exceeded by 90% and 50% of the measurements) was 40.2 degrees C and 40.8 degrees C, and for interstitial hyperthermia 39.4 degrees C and 41.8 degrees C, respectively. All patients survived; seven patients had a biochemical relapse (27%), three in the regional and four in the interstitial group. The actuarial probability of freedom from biochemical relapse was 70% at 36 months for all patients together, 79% for regional and 57% for interstitial. No factors were found that could be used to predict relapse. CONCLUSIONS: The clinical outcome in these patients with advanced localized prostate cancer seems to compare favourably with most series using irradiation alone, and the treatment caused no severe complications.

Aged↗

PubMed2002

Computation of high-resolution SAR distributions in a head due to a radiating dipole antenna representing a hand-held mobile phone.

SAR distributions in a healthy female adult head as a result of a radiating vertical dipole antenna (frequency 915 MHz) representing a hand-held mobile phone have been computed for three different resolutions: 2 mm, 1 mm and 0.4 mm. The extremely high resolution of 0.4 mm was obtained with our quasistatic zooming technique, which is briefly described in this paper. For an effectively transmitted power of 0.25 W, the maximum averaged SAR values in both cubic- and arbitrary-shaped volumes are, respectively, about 1.72 and 2.55 W kg(-1) for 1 g and 0.98 and 1.73 W kg(-1) for 10 g of tissue. These numbers do not vary much (<8%) for the different resolutions, indicating that SAR computations at a resolution of 2 mm are sufficiently accurate to describe the large-scale distribution. However, considering the detailed SAR pattern in the head, large differences may occur if high-resolution computations are performed rather than low-resolution ones. These deviations are caused by both increased modelling accuracy and improved anatomical description in higher resolution simulations. For example, the SAR profile across a boundary between tissues with high dielectric contrast is much more accurately described at higher resolutions. Furthermore, low-resolution dielectric geometries may suffer from loss of anatomical detail, which greatly affects small-scale SAR distributions. Thus. for strongly inhomogeneous regions high-resolution SAR modelling is an absolute necessity.

Adult↗

PubMedDate not supplied

CT-resolution regional hyperthermia treatment planning.

Recent development of quasistatic zooming has enabled the computation of mm-resolution SAR distributions within reasonable computation times. These high-resolution SAR distributions proved to be completely dissimilar from the cm-resolution distributions. To study the impact of high-resolution SAR modelling on regional hyperthermia treatment planning (HTP), a conventional, low-resolution treatment plan is compared to an high-resolution plan. This comparison shows that the high-resolution plan yields totally different SAR and temperature distributions when compared to the conventional plan. Both SAR and temperature maxima predicted by the low-resolution plan are not predicted by the high-resolution plan and, even worse, the low-resolution plan fails to predict maxima that are predicted by the high-resolution plan. Furthermore, it appears that small-scale SAR maxima can result in temperature maxima which may cause treatment-limiting hot spots. These small-scale SAR maxima appear to be highly determined by the dielectric geometry of the patient. This demonstrates the need for an accurate, high-resolution description of this dielectric geometry. Moreover, it suggests that it may be very difficult to reduce potential treatment-limiting hot spots in clinical practice. This study demonstrates the need for high-resolution regional hyperthermia treatment planning.

Hyperthermia, Induced↗

PubMedDate not supplied

Treatment planning for capacitive regional hyperthermia.

Capacitively coupled hyperthermia devices are widely in use, mainly in Asian countries. In this paper, a comprehensive treatment planning system, including a Specific Absorption Rate (SAR) and thermal model for capacitively coupled hyperthermia, is described and demonstrated using a heterogeneous patient model. In order to accurately model a hyperthermia treatment, simulation at high resolution is mandatory. Using the quasi-static approximation, the electromagnetic problem can be solved at high resolution with acceptable computational effort. The validity of the quasi-static approximation is demonstrated by comparing the Maxwell solution of a phantom problem to the quasi-static approximation. Modelling of capacitive hyperthermia of the prostate reveals the difficulty of heating deep-seated tumours in the pelvic area. Comparison of the SAR distribution in the heterogeneous patient model and a patient shaped agar phantom shows a shielding effect of the pelvic bone and the influence of the fat-muscle distribution. It is shown that evaluation of capacitive hyperthermia with agar phantoms leads to overly optimistic conclusions. Therapeutic relevant tumour temperatures can only be obtained by permitting temperature extrema in normal tissue. This concurs with clinical practice, where treatment-limiting hot spots restrict the tumour temperature. It is demonstrated that the use of very cold overlay bolus bags has only a very superficial effect. The presented model can be used for individual treatment planning and optimization, for the evaluation of capacitive applicator modifications and comparison with other devices.

Electromagnetic Fields↗

PubMedDate not supplied

A prospective quality of life study in patients with locally advanced prostate cancer, treated with radiotherapy with or without regional or interstitial hyperthermia.

INTRODUCTION: The aim of this prospective study was to describe quality of life (QoL) in patients with locally advanced prostate carcinoma treated with conventional radiotherapy and to evaluate the influence of adding regional or interstitial hyperthermia. MATERIALS AND METHODS: All patients were irradiated using a CT-planned conventional three field technique, administering 70 Gy to prostate and vesicles. In two different phase I studies, hyperthermia was added to the radiotherapy. Twelve patients were treated with one interstitial hyperthermia treatment, lasting 60 min. Fourteen patients have been treated with five regional hyperthermia treatments, lasting 75 min each. In both hyperthermia studies, the body, bladder and rectum temperatures remained below safety limits. Patients treated with radiotherapy alone (n = 58) or combined with regional (n = 8) or interstitial hyperthermia (n = 12) completed the European Organization for Research and Treatment of Cancer (EORTC) core questionnaire (C30 + 3), the EORTC prostate cancer module (PR25) and the Rand 36 health survey before treatment and 1 and 6 months after completion of treatment. Analysis of Variance (ANOVA) for repeated measurements has been performed to describe the data. RESULTS: All patient groups were comparable concerning patient characteristics. No significant interaction or difference in QoL has been noticed between the two hyperthermia patient groups and the patient group without hyperthermia. Therefore, all groups were analysed together (n = 78) to detect QoL changes in time. A deterioration of QoL has been measured from baseline to 1 month after treatment. Fatigue, pain, urinary symptoms, bowel symptoms and financial difficulties increased significantly. Social, physical and role functioning worsened significantly. No differences in QoL were measured 6 months after treatment compared to the baseline measurement, except for a decrease in sexual activity. CONCLUSIONS: After radiotherapy with or without hyperthermia only a temporary deterioration of QoL occurs, concerning social, psychological and disease related symptoms. Additional hyperthermia does not seem to decrease QoL.

Aged↗

PubMedDate not supplied

Comparison of intra-luminal versus intra-tumoural temperature measurements in patients with locally advanced prostate cancer treated with the coaxial TEM system: report of a feasibility study.

A study was performed on regional hyperthermia for patients with locally advanced prostate carcinoma. The primary objective was to analyse the thermometry data with an emphasis on the possibility of replacing invasive thermometry by tumour-related intra-luminal thermometry. Fourteen patients were treated with a combination of conformal external beam radiotherapy (70 Gy) and hyperthermia. Hyperthermia was delivered using the Coaxial TEM system, one treatment per week, to a total of five treatments. Thermometry was performed in bladder, urethra, rectum and esophagus. Invasive thermometry in the prostate was carried out during one or two treatments for each patient by placing transperineally a central and a peripheral catheter. Heterogeneous temperature distributions were measured in the prostate. The mean average invasive temperature range was 1.1 degrees C. Due to the temperature heterogeneity and a limited number of thermometry sensors (mean 7, range 2-13), large variability between treatments and patients existed regarding achieved temperatures and dose. The mean invasive T90 was 40.2 +/- 0.6 degrees C and T50 was 40.8 +/- 0.6 degrees C. The mean Cum min T90>40.5 degrees C per treatment was 22 (range 0-50). Importantly, intra-luminal temperatures did not reliably predict invasively measured temperatures. Invasive thermometry, therefore, remains compulsory to calculate a thermal dose for an individual patient. Changes in temperature during treatment, measured by the urethral sensors, corresponded well with changes in temperature measured by the individual invasive sensors. Similar comparison of rectal temperature changes with intra-prostatic temperature changes was not as predictive. The similarity in temperature changes between the urethral and interstial sites, suggests that urethral temperatures are sufficient for treatment optimization. The SAR profile did not correspond with the temperature profile indicating heterogeneous perfusion. Although regional hyperthermia in combination with external beam radiotherapy for locally advanced prostate carcinoma is clinically feasible, the question on the importance of invasive thermometry remains.

Aged↗

PubMedDate not supplied

Increasing the systemic temperature during regional hyperthermia: effect of a cooling strategy on tumour temperatures and side-effects.

In the application of regional hyperthermia, optimization of the temperature distribution remains necessary. One of the tools that might be used is a modest increase in the systemic temperature to diminish cooling by blood perfusion. This study investigates (1) if it is feasible to increase the systemic temperature by applying other cooling strategies, without inducing unacceptable systemic stress, and (2) whether a rise in systemic temperature results in improvement of tumour temperatures. Eleven patients with locally advanced cervical carcinoma and 12 patients with locally advanced prostate carcinoma were treated with our Coaxial TEM regional hyperthermia system. In this system, the temperature of the open water bolus can be easily adjusted. Two cooling methods were applied alternately, one with a relatively low water temperature (method A), the other with a higher water bolus temperature in combination with extensive head/chest cooling by a hand shower (method B). Method B resulted in significantly higher systemic temperatures, for both patient groups separately (0.8, respectively, 0.5 degrees C) and for the total patient group (0.7 degrees C). Additionally, all tumour index temperatures were higher. For the combined group (for T50: 0.4 degrees C) and for the cervix group (for T50: 0.7 degrees C), it reached statistical significance. The raise in core temperature led to a significantly higher increase in heart rate. For the group of cervix patients, higher systemic temperatures resulted in more treatment-limiting systemic stress. For the prostate patients, systemic stress was not an important issue. Since the raise in systemic temperature did not influence the overall tolerance of treatment, method B could be applied to this group. However, the increases in tumour temperatures were small, and potential hazards of systemic temperature increase should be considered.

Adult↗