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D Lefkopoulos

Publications and source records attributed to D Lefkopoulos.

At least 19 recordsLinked to original sources
PubMed2006

[Present and future of the image guided radiotherapy (IGRT) and its applications in lung cancer treatment].

These last years, the new irradiation techniques as the conformal 3D radiotherapy and the IMRT are strongly correlated with the technological developments in radiotherapy. The rigorous definition of the target volume and the organs at risk required by these irradiation techniques, imposed the development of various image guided patient positioning and target tracking techniques. The availability of these imaging systems inside the treatment room has lead to the exploration of performing real-time adaptive radiation therapy. In this paper we present the different image guided radiotherapy (IGRT) techniques and the adaptive radiotherapy (ART) approaches. IGRT developments are focused in the following areas: 1) biological imaging for better definition of tumor volume; 2) 4D imaging for modeling the intra-fraction organ motion; 3) on-board imaging system or imaging devices registered to the treatment machines for inter-fraction patient localization; and 4) treatment planning and delivery schemes incorporating the information derived from the new imaging techniques. As this paper is included in the "Cancer-Radiotherapie" special volume dedicated to the lung cancers, in the description of the different IGRT techniques we try to present the lung tumors applications when this is possible.

Forecasting↗
PubMed2006

[Prostate localization systems for prostate radiotherapy].

The development of sophisticated conformal radiation therapy techniques for prostate cancer, such as intensity-modulated radiotherapy, implies precise and accurate targeting. Inter- and intrafraction prostate motion can be significant and should be characterized, unless the target volume may occasionally be missed. Indeed, bony landmark-based portal imaging does not provide the positional information for soft-tissue targets (prostate and seminal vesicles) or critical organs (rectum and bladder). In this article, we describe various prostate localization systems used before or during the fraction: rectal balloon, intraprostatic fiducials, ultrasound-based localization, integrated CT/linear accelerator system, megavoltage or kilovoltage cone-beam CT, Calypso 4D localization system tomotherapy, Cyberknife and Exactrac X-Ray 6D. The clinical benefit in using such prostate localization tools is not proven by randomized studies and the feasibility has just been established for some of these techniques. Nevertheless, these systems should improve local control by a more accurate delivery of an increased prescribed dose in a reduced planning target volume.

Humans↗
PubMed2006

[Image-guided radiotherapy by in-room CT-linear accelerator combination].

Target localization has become increasingly important in the advent of IMRT, as treatment margins are reduced and target doses are increased with high-dose gradients outside this target volume. The in-room CT on rails-LINAC system allows CT imaging while the patient remains immobilized in the treatment position just prior to treatment. The anatomic inter- and intra-fractional variations can be therefore quantified during a course of treatment. The position of the tumour can be checked and corrected before the fraction. In case of modification of tumour shape, a re-planning of the treatment is also feasible. However, several issues remain: the integration with routine clinical treatment due to a lack of software tools, the frequency of imaging, and the cost-efficiency ratio. The clinical experience is yet very limited but CT-image-guided radiotherapy appears promising for prostate, brain and spinal tumours.

Brain Neoplasms↗
PubMed2006

[Image registration for radiation therapy: Practical aspects and quality control].

The development of conformal radiotherapy techniques (CRT) and intensity modulated CRT requires an accurate delineation of target structures and organs at risk. Thus, additional information provided by anatomical and/or functional imaging modalities can be used for volume of interest determination combined with traditionally used Computed Tomography imaging (CT): for instance, functional or morphological Magnetic Resonance Imaging (f MRI or m MRI) or Positron Emission Tomography (PET). A prerequisite to the simultaneous use of this information is image registration. Due to the differences between the images and the information they provide, a quality control of image registration process for radiotherapy is mandatory. The purpose of this article is to present the difficulties in implementing such controls and to show the necessity for a clinical validation on patient's images. The last part of this work presents the possible interest in using f MRI to help radio-oncologists in the treatment planning for gliomas associated to image coregistration and quality control considerations.

Brain Neoplasms↗
PubMed2005

Risk of melanoma following adulthood cancer: a case-control study.

Melanoma is a severe skin cancer related to sun exposure. Whether this malignancy is linked to exposure to ionising radiation during adulthood is still controversial. This case-control study examined the risk of melanoma following treatment for an adulthood first malignant neoplasm (FMN). Cases were patients who presented with cutaneous melanoma after a first cancer in adulthood. Controls (3 per case) were patients free of melanoma, matched for age, duration of follow-up since the FMN, type of FMN, and followed in the same institution. A total of 57 cases and 171 controls were included. In the final multivariate analysis, no risk of melanoma was associated with radiotherapy (odds ratio (OR) for 1 Gy = 1.01, 95% confidence interval (95%CI) 0.96-1.07) nor hormonotherapy, whereas chemotherapy use (OR = 2.3, 95%CI 0.93-5.6) and having a history of familial cancer (OR = 2.8, 95%CI 1.3-5.9) exhibited a nearly significant risk. In conclusion, unlike the evidence for risk of exposure to ionising radiation during childhood, we did not substantiate a risk for association of melanoma with exposure to ionising radiation during adulthood. The risk associated with chemotherapy should justify the implementation of skin surveillance for early detection of melanoma in these patients.

Adolescent↗
PubMed2004

[Dosimetric validation of compensator for their use in clinical routine, in conformation radiotherapy].

PURPOSE: The aim of this work was to establish the acquisition, calculation and 3D compensator manufacturing optimum parameters. This methodology is based on virtual simulation and 3D dosimetry. MATERIALS AND METHODS: The material used is a helicoidal CT (PQ 5000-Marconi), a virtual simulation system (AcQsim version 4-Marconi), a Treatment Planning System (Dosigray), a linear accelerator Saturne 43 (Varian, CGR), an automated milling system for compensator filters (Autimo 2.5 D-HEK), a water tank phantom (wellhofer) and an homogeneous phantom with simple patterns in order to simulate the obliquity surface of patient body. The compensator was composed by granulate tin because this material ensures a good profile modulation. The compensation plane has been calculated at 80% to dose profile. The compensator thickness profile has been calculated with different acquisition (slice thickness, pitch factor), calculation (attenuation coefficient, bixel) and fabrication parameters (drill diameter, specification of milling system). RESULTS: After this preliminary study, we have defined the optimum parameters for the compensator realization. We have observed that the slice thickness, bixel size and drill diameter are the parameters that mainly affect the profiles homogeneity. The choice of parameters with smaller dimensions S = 3 mm; B = 3 mm, F = 3 mm, improve the profiles homogeneity. Though, for manufacture times compatible with the clinical routine, the selected parameters are S = 5 mm, B = 6 mm and F = 6 mm. Compensator can be used for any type of Linac. However, one must pay attention on their realization and their positioning on the beam central axis.

Humans↗
PubMed2003

[Quality assurance program for intensity-modulated radiotherapy (IMRT) treatments of head and neck carcinomas].

A new technique such as intensity-modulated radiotherapy needs a quality assurance program. A French cooperative group joined to define a common program for the use of this technique in the case of head and neck carcinomas. Specific controls are necessary and even mandatory, for example: leaves position, speed of the leaves and the linearity of the dose with the monitor unit number. Measurements in homogeneous phantoms will validate calculated treatment plans. Absolute and relative measurements need ionisation chambers and films. Measurements for each beam, gantry at 0 degrees, are basic measurements. If those are impossible due to the treatment planning software, they can be performed with the treatment angles, films of course positioned perpendicularly to the beam axis. A consensus must be established between members to reduce the frequency and the number of measurements. Nevertheless, it currently seems mandatory to maintain measurements for each beam. Moreover, incidents that happen during this kind of treatment have to be recorded and new verifications will have to be realised then. This program is a unique possibility to match the application of a new technique whatever the type of equipment.

Algorithms↗
PubMed2001

[Automatic definition of prescription isodose for stereotaxic radiation of arteriovenous malformations].

PURPOSE: To evaluate dosimetric consequences generated by the automatic definition based on lesion coverage of prescription isodose. A clinical series of 124 arteriovenous malformations was analysed. Plan quality was quantified by the standard deviation of the differential dose volume histogram calculated in the lesion. MATERIAL AND METHODS: We define two quantitative protocols based on lesion coverage for the automatic definition of prescription isodose using a volumetric definition of coverage (90% of lesion volume), and an isodose-based definition proposed by RTOG (prescription isodose equals minimum isodose in the lesion divided by 0.9). RESULTS: We have evaluated the plans obtained for these two protocols, calculating several dose-volume indices. These indices are presented as a function of dose-volume histogram standard deviation in order to quantify the consequences of their variations for this representative series of plans. The margin our team tolerates is such that the sum of underdosed lesion and overdosed healthy tissues factors remains lower than one. Protocol based on volumetric coverage gives results situated within this margin. Protocol based on RTOG definition produces conformation indices that could be greater than 1. CONCLUSION: The absolute dose would be decided taking into account examined dose-volume indices and clinical data. A protocol for automatic definition of prescription isodose using volumetric lesion coverage seems to be more judiciously adapted to arteriovenous malformation conformal plans in stereotactic conditions because of variations observed in the overdosage of healthy tissues.

Algorithms↗
PubMed2001

[Physical and methodological aspects of multimodality imaging and principles of treatment planning in 3D conformal radiotherapy].

The recent evolutions of the imaging modalities, the dose calculation models, the linear accelerators and the portal imaging permit to improve the quality of the conformal radiation therapy treatment planning. With DICOM protocols, the acquired imaging data coming from different modalities are treated by performant image fusion algorithms and yield more precise target volumes and organs at risk. The transformation of the clinical target volumes (CTV) to planning target volumes (PTV) can be realised using advanced probabilistic techniques based on clinical experience. The treatment plans evaluation is based on the dose volume histograms. Their precision and clinical relevance are improved by the multi-modality imaging and the advanced dose calculation models. The introduction of the inverse planning systems permitting to realise modulated intensity radiation therapy generates highly conformal dose distributions. All the previously cited complex techniques require the application of rigorous quality assurance programs.

Dose Fractionation, Radiation↗
PubMed2001

[Comparison of biological functional assessment in intensity-modulated radiotherapy: two-dimensional study].

Modulated intensity dose distributions are obtained by inverse planning. It requires an inversion algorithm and an objective function that can be physical or biological. The biological objective functions aim at quantifying the probability of the favourable end of the treatment. The inversion algorithm used is analytical and is based on the mathematical analysis of the singular values decomposition. It proposes as many solutions as there are elementary beams. From the Tumour Control Probability, Normal Tissue Complication Probabilities and complication free tumour control, three biological assessment functions of the proposed solutions are compared with the least square difference between the prescribed and obtained dose distributions. We used a simplified irradiation configuration: Brahme's dose prescription (2D modelling of a prostate) and 9 beams (1D). The choice by mean of biological criterion of the optimal solution makes it possible to increase the average dose in the tumour, so as its homogeneity compared to physical optimisation. Conversely, the organs at risk are then less protected. The laying down of relevant constraints makes it possible to obtain satisfactory dose distributions. Concerning the validity of the models and data used, some limitations appear. At present time, it seems to exclude the use in clinical routine of an only biological optimisation. The future availability of new biological data will allow the development and in particular the clinical use of biological optimisation.

Algorithms↗
PubMed2001

[Importance of quantitative evaluation in the planning of the stereotactic irradiation of complex cAVMs].

BACKGROUND AND PURPOSE: The purpose was to present the successive steps of dosimetric planning and the different means used to allow the choice of the best solution among several planning projects considering the anatomical and clinical features of arteriovenous malformation. Method. Four successive steps were: A study of these factors for 5 different plannings of a clinical case using different isocenters is presented and the results are discussed. CONCLUSION: For complex arteriovenous malformations several hours are often necessary to permit physicians/radiotherapists to elaborate planning which is often a compromise among several solutions.

Cerebral Angiography↗
PubMed2001

[Radiosurgery of cerebral arteriovenous malformations: methodology of the dose prescription and its implications for dosimetric results. Retrospective study of 408 cases].

PURPOSE: To study dosimetric implications of our group dose prescription methodology on a series of 408 cerebral arteriovenous malformations. MATERIAL: and method. Between January 1990 and July 1998, 408 patients with cerebral arteriovenous malformations that had never been irradiated before, were treated radiosurgically in a single fraction at Tenon Hospital. 223 patients were treated with a single isocentre and 185 with multiple isocenters. Dosimetric characteristics have been studied as a function of the global quality index of planning, defined our group as the standard deviation of the differential dose volume histogram calculated in the lesion. RESULTS: One percent correlation obtained between some dosimetric data and the global quality index of planning allowed to modelize by linear equations the connection between this quality index and minimum isodose in the lesion, mean doses and isodoses in the underdosed part of the lesion and in the complete lesion. This was done for mono isocentric cases and multi isocentric cases. CONCLUSION: Before the choice of the therapeutic dose and prescription isodose, it is therefore possible from the global quality index of planning to foresee isodoses modelized by the defined equations. So, the radiotherapist can compensate using the prescription since conformity is not perfect and thus attenuate healthy tissues overdosage.

Cohort Studies↗
PubMed2001

[Technologic developments in radiotherapy and stereotactic radiosurgery].

We present a review of current technological progress enabling improvement in the quality of stereotactic irradiations: imaging fusion; individual adaptation of dosimetric planning to the shape of the target thanks to several collimation systems, spatial modulation of the beam with the use of multileaf microcollimators, beam intensity modulation, robotisation of the materials, owing to hardware and software developments.

Brain Neoplasms↗
PubMed2001

[Cerebral arteriovenous malformations treated by radiosurgery: a series of 705 cases].

BACKGROUND AND PURPOSE: After a review of the main radiosurgical published series, to evaluate our own series of 705 patients with cerebral arteriovenous malformations treated by radiosurgery alone or in combination with embolization or surgery. PATIENTS: and method. From January 1984 to December 1998, 705 patients were treated by a multidisciplinary team including neurosurgeons, neuroradiologists, radiophysicians and radiotherapists. Age of revelation of the cerebral arteriovenous malformations ranged between birth to 73 years (mean 27, median 25). Age at time of radiosurgery ranged between 7 and 75 years (mean 33, median 31). There were 410 males for 295 females (sex- ratio 1.4). Symptoms of revelation were hemorrhage for 59%, seizures for 23%, headaches for 14% and progressive deficits for 4%. Discovery of cerebral arteriovenous malformation was fortuitous in 4% of cases. Repartition following Spetzler's grading was 12% in grade I, 36% in grade II, 40% in grade III, 12% in grade IV and 0% in grade V. Maximal size ranged between 4 and 60 mm (mean 23, median 20). Volume ranged between 0.2 and 24.3 cc (mean 3.8, median 2.8). Majority of cerebral arteriovenous malformations were large size (42% with size higher than 25 mm) and large volume (54% higher than 10 cc. 54% of patients had treatment prior radiosurgery: 38% had embolization, 10% were operated, 4% were treated by radiosurgery (reirradiation) and 3% were operated and embolized. RESULTS: Overall complete obliteration rate was 55%. The obliteration rate was correlated with size (77% for cAVMs lower than 15 mm, 62% for cerebral arteriovenous malformations between 15 and 25 mm, and 44% for cerebral arteriovenous malformations higher than 25 mm), with volume (94% for cerebral arteriovenous malformations lower than 1 cc, 64% between 1 and 4 cc, 48% between 4 and 10 cc, and 62% for cerebral arteriovenous malformations higher than 10 cc), dose at reference isodose, minimal dose, morphological parameters (presence of dural components, arteriolovenous fistula, plexiform angioarchitecture, arterial steal, arterial recruitment, deep exclusive drainage, venous plicature, venous confluence, venous ectasia, venous reflux), sectional topography and good recovery of the target. Embolization was a confusion factor not associated with obliteration rate. After multivariate analysis, only Dmin and complete coverage of the cerebral arteriovenous malformations were correlated with obliteration rate. Delay of obliteration was significantly correlated after multivariate analysis with Dmin, complete coverage, arteriolovenulary angioarchitecture (positive correlation) and venous ectasia (negative correlation). CONCLUSION: Overall complete obliteration rate is unreliable data to assess efficacy of radiosurgical method in the tretment of cerebral arteriovenous malformations. The obliteration rate must be interpretated after stratification on several morphological and dosimetric parameters.

Adolescent↗
PubMed2001

[Retrospective analysis of failures in radiosurgery treatment of cerebral arteriovenous malformations].

The aim of this paper is to analyze retrospectively the reasons for the failure in cerebral arteriovenous malformations radiosurgery. Several factors are evoked and discussed mainly: inaccurate target, intentional partial irradiation, repermeabilization of a previously embolized cerebral arteriovenous malformation. The results suggest the necessity of a complete irradiation of the nidus. The strategy of partial volume irradiation should be avoided, even if it necessitates lowering of the doses in large cerebral arteriovenous malformations. Accuracy in the target determination is required and a complete stereoangiography is necessary.

Adolescent↗
PubMed2001

[Re-irradiation of cerebral arteriovenous malformations. Experience of the Sainte-Anne-Tenon Group].

BACKGROUND AND PURPOSE: Between 20 to 50% of cerebral arteriovenous malformations treated with radiosurgery (RS) fail to obliterate 2 to 5 years after irradiation. Patients are not protected against the risks leading to treatment. Two therapeutic options can be used to eradicate the persisting nidus: micro-surgery and a second irradiation. Our group has reirradiated 39 such patients. MATERIAL: From 1989 to 2000, 39 patients have been reirradiated (14 females and 25 males; median age 31 years). There were more left lesions: 59% than right (35%) and 5% on midline. The most frequent locations were: temporal 12 cases; parietal 8 cases; frontal 7 cases; thalamus 7 cases. The predominant first symptoms were hemorrhage (68.5%) and seizure (15.8%). Prior RS, 21/39 patients had embolization (53.8%) and 3 surgery. Method. Treatment has been performed with the same system for the first and the second radiosurgery for 37 patients. Planification and dosimetry improved during that period. The level of dose was similar for the 2 RS. MRI has been used as a non invasive follow-up tool. RESULTS: Only 28 patients were evaluable because 7/39 patients had the second radiosurgery in 1999 or in 2000 and data were lacking at the time of writing for 4 patients. Obliteration rate was 17/28 (60.7%). Nine patients bled between the two radiosurgery procedures. COMPLICATIONS: 4 new regressive deficits occurred after the second radiosurgery. The rate of parenchymal changes were higher, after the second radiosurgery. Except one patient who died of a non-related affection 2 years after obliteration of his cerebral arteriovenous malformation, thus 38/39 patients were alive. CONCLUSION: This series was small compared to the potential number of candidates suffering from failure of the first radiosurgery, but the results are promising.

Adolescent↗
PubMed2000

Linac radiosurgery for cerebral arteriovenous malformations: results in 169 patients.

PURPOSE: To present the SALT group results using Linac radiosurgery (RS) for AVM in 169 evaluable patients treated from January 1990 thru December 1993. METHODS AND MATERIALS: Median age was 33 years (range 6-68 years). Irradiation was the only treatment in 55% patients. Other treatment modalities had been used prior to RS in 45%: one or more embolizations in 36%, surgery in 6%, and embolization and surgery in 3% patients. Nidus were supratentorial in 94% patients, infratentorial in 6% patients. Circular 15 MV x-ray minibeams (6-20 mm) were delivered in coronal arcs by a GE-CGR Saturne 43 Linac. Patient set-up included a Betti arm-chair, a Talairach frame. Prescribed peripheral dose was 25 Gy on the 60%-70% isodose (max dose 100%). Arteriographic results were reassessed in December 1997 at 48 to 96 months follow-up. RESULTS: The overall obliteration rate (OR) was 64% (108/169). AVM volumes ranged from 280 to 19,920 mm(3), median 2460 mm(3). OR was 70% for AVM </= 4200 mm(3) 4200 mm(3) (p 25 mm (p = 0.04). OR was 71%, in the absence of embolization, vs. 54% for previously embolized nidus (p = 0.03). OR was 71% for monocentric RS vs. 54% for multi-isocenters (p 28 Gy vs. 55% for values </= 28 Gy (p 79% vs. 57% for lower values (p 17 Gy, vs. 59% for mLd </= 16 Gy (p 40%, vs. 54% for mLi </= 40% (p 85% vs. 60% for CR </= 84% (NS). For patients treated according to our protocol, i.e., 24-26 Gy on the 60%-70% isodoses, OR was higher (68%) than for other patients (47%) (p = 0.02). After multivariate analysis, absence of previous embolization and mono isocentric-irradiation were independent factors predicting obliteration. Complications were: recurrent hemorrhage, 4 patients (1 patient died); brain necrosis on MRI, 2 patients; subsequent epilepsy, 4 patients; other subsequent neurologic deficits, 3 patients. CONCLUSION: Overall OR was 64% (48-96 months follow-up). After monovariate analysis higher ORs were associated with smaller volumes </= 4200 mm(3), smaller nidus size </= 25 mm, absence of prior embolization, monoisocentric RS, higher values for mean and minimum lesion doses and compliance to our protocol. Higher values for the peripheral dose and isodose tended to give better results. Multivariate analysis showed that the absence of prior embolization and monoisocentric irradiation were independent factors predicting successful irradiation.

Adolescent↗