Jean-Yves Giraud

MRI/TRUS data fusion for prostate brachytherapy. Preliminary results.

Prostate brachytherapy involves implanting radioactive seeds (I125 for instance) permanently in the gland for the treatment of localized prostate cancers, e.g., cT1c-T2a N0 M0 with good prognostic factors. Treatment planning and seed implanting are most often based on the intensive use of transrectal ultrasound (TRUS) imaging. This is not easy because prostate visualization is difficult in this imaging modality particularly as regards the apex of the gland and from an intra- and interobserver variability standpoint. Radioactive seeds are implanted inside open interventional MR machines in some centers. Since MRI was shown to be sensitive and specific for prostate imaging whilst open MR is prohibitive for most centers and makes surgical procedures very complex, this work suggests bringing the MR virtually in the operating room with MRI/TRUS data fusion. This involves providing the physician with bi-modality images (TRUS plus MRI) intended to improve treatment planning from the data registration stage. The paper describes the method developed and implemented in the PROCUR system. Results are reported for a phantom and first series of patients. Phantom experiments helped characterize the accuracy of the process. Patient experiments have shown that using MRI data linked with TRUS data improves TRUS image segmentation especially regarding the apex and base of the prostate. This may significantly modify prostate volume definition and have an impact on treatment planning.

Quality assurance in the 22991 EORTC ROG trial in localized prostate cancer: Dummy run and individual case review

INTRODUCTIONnEORTC trial 22991 was designed to evaluate the addition of concomitant and adjuvant short-term hormonal treatments to curative radiotherapy in terms of disease-free survival for patients with intermediate risk localized prostate cancer. In order to assess the compliance to the 3D conformal radiotherapy protocol guidelines, all participating centres were requested to participate in a dummy run procedure. An individual case review was performed for the largest recruiting centres as well.nnnMATERIALS AND METHODSnCT-data of an eligible prostate cancer patient were sent to 30 centres including a description of the clinical case. The investigator was requested to delineate the volumes of interest and to perform treatment planning according to the protocol. Thereafter, the investigators of the 12 most actively recruiting centres were requested to provide data on five randomly selected patients for an individual case review.nnnRESULTSnVolume delineation varied significantly between investigators. Dose constraints for organs at risk (rectum, bladder, hips) were difficult to meet. In the individual case review, no major protocol deviations were observed, but a number of dose reporting problems were documented for centres using IMRT.nnnCONCLUSIONSnOverall, results of this quality assurance program were satisfactory. The efficacy of the combination of a dummy run procedure with an individual case review is confirmed in this study, as none of the evaluated patient files harboured a major protocol deviation. Quality assurance remains a very important tool in radiotherapy to increase the reliability of the trial results. Special attention should be given when designing quality assurance programs for more complex irradiation techniques.

Quality assurance of the EORTC trial 22911. A phase III study of post-operative external radiotherapy in pathological stage T3N0 prostatic carcinoma: the dummy run.

INTRODUCTIONnA dry run of a clinical trial (EORTC 22911) is presented in which 12 centres have participated. These are the centres which have contributed the largest number of patients to the trial.nnnMATERIAL AND METHODSnEach participating centre received data from a suitable patient. Investigators were asked to plan and treat the patient according to the protocol guidelines and return the data for evaluation of compliance.nnnRESULTSnThe results show that compliance to the protocol guidelines was generally good. There were a few minor deviations in the dose and fractionation schedule, in the volume reduction for the booster dose and in the dose prescription point. None of these deviations will affect the outcome of the study. The most important observation is the large inter-centre variation in target volumes.nnnCONCLUSIONSnThe results of this study underlines the need for a strict definition of the target volume and the adoption of the ICRU 50 recommendations in future protocols.

Patient Set-Up Using Portal Images: 2D/2D Image Registration Using Mutual Information

OBJECTIVEnConformal radiation therapy requires accurate patient set-up for each fraction delivery. Electronic portal imaging devices allow the acquisition of portal images just before and even during dose delivery. However, the quantitative interpretation of these images in determining and correcting the patients position remains uncertain, and automated methods are therefore being developed. Such methods must be usable for the different radiation therapy techniques. They must be robust and as automated as possible for use in clinical routines. This work was undertaken to establish the feasibility of 2D/2D registration for portal/portal and portal/simulator images in radiotherapy.nnnMATERIALS AND METHODSnThis paper describes an automated method based on the combination of calibration algorithms and pixel-based registration algorithms. We present experiments with the different imaging techniques, some of which use a phantom with and without a gold standard. Preliminary results obtained using patient data are also presented and discussed.nnnRESULTSnThe results obtained with a phantom demonstrated that this automated method for 2D/2D registration is fast, accurate, and robust, even in the case of blurred images for small treatment fields.nnnCONCLUSIONSnMutual information is a feasible method for 2D/2D portal/portal and portal/simulator image registration in radiotherapy.

Medical Image Computing and Computer-Aided Medical Interventions Applied to Soft Tissues: Work in Progress in Urology

Until recently, computer-aided medical interventions (CAMI) and medical robotics have focused on rigid and nondeformable anatomical structures. Nowadays, special attention is paid to soft tissues, raising complex issues due to their mobility and deformation. Mini-invasive digestive surgery was probably one of the first fields where soft tissues were handled through the development of simulators, tracking of anatomical structures and specific assistance robots. However, other clinical domains, for instance urology, are concerned. Indeed, laparoscopic surgery, new tumour destruction techniques (e.g., HIFU, radiofrequency, or cryoablation), increasingly early detection of cancer, and use of interventional and diagnostic imaging modalities, recently opened new challenges to the urologist and scientists involved in CAMI. This resulted in the last five years in a very significant increase of research and developments of computer-aided urology systems. In this paper, we propose a description of the main problems related to computer-aided diagnostic and therapy of soft tissues and give a survey of the different types of assistance offered to the urologist: robotization, image fusion, surgical navigation. Both research projects and operational industrial systems are discussed

Fiber background rejection and crystal over-response compensation for GaN based in vivo dosimetry.

For dosimetric measurements using an implantable optical fiber probe with GaN (Gallium Nitride) scintillator as radioluminescence (RL) transducer, a bi-channel method is proposed to reject the background contribution of the irradiated fiber segment. It is based on spectral differences between the narrow-band light emission from GaN and the large-band background from the irradiated optical fiber. Experimental validation of this method using 6xa0MV photon beam has shown that the remaining background contribution after subtraction is below 1.2% for square field sizes ranging from 3xa0cm to 20xa0cm. Furthermore, a compensation method for the over-response of GaN is also proposed, since GaN is not tissue equivalent. The over-response factor of GaN exhibits a linear increase with square field aperture and depends on depth from phantom surface. This behaviour is modelled to allow compensation in specific conditions. The proposed method has been evaluated and has shown a maximum deviation of 3% for a 6xa0MV photon beam and 1% for an 18xa0MV photon beam at a depth beyond the build-up region.

External radiotherapy of prostatic carcinoma: a quadratic optimization of the dose distribution

Radiation therapy uses the energy imparted by radiation in order to treat tumours: this method offers the main advantage of being non-invasive. Because all parts of the body get a dose, it requires, however, a great prudence. The dosimetric planning is necessary for concentrating the dose into the tumour and saving healthy tissues as much as possible. This task is performed by radiophysicists, who determine a treatment plan after several tests. The aim of our work, which is focused on the treatment of the prostate, is to automate this stage. We describe a new mathematical model for this optimization problem, and present some numerical results including different field shapes.

Automatic 3D seed location and orientation detection in CT image for prostate brachytherapy.

In prostate brachytherapy, the analysis of the 3D pose information of each individual implanted seed is one of the critical issues for dose calculation and procedure quality assessment. This paper addresses the development of an automatic image processing solution for the separation, localization and 3D orientation estimation of prostate seeds. This solution combines an initial detection of a set of seed candidates in CT images (using a thresholding and connected component method) with an orientation estimation using principal components analysis (PCA). The main originality of the work is the ability to classify the detected objects based on a priori intensity and volume information and to separate groups of seeds using a modified k-means method. Experiments were carried out on CT images of a phantom and a patient aiming to compare the proposed solution with manual segmentation or other previous work in terms of detection performance and calculation time.

Implantable in vivo Dosimetric Probe Based on GaN Radioluminescence

This paper presents an implantable in-vivo dosimetric probe using a small-volume GaN bulk as scintillator. The high light yield of GaN under irradiation in radiotherapy conditions is observed. Heavily-doped n-type GaN is chosen because of enhanced and dominant UV emission. The fabrication process of the probe is described. It is tested using 6 and 18MV photon beams. Measured results show reproducibility errors of less than 2% for a delivered dose of 50cGy. The linearity of the measure and its independence of the dose rate are also verified. The probe’s output light has both GaN and fiber contributions. The fiber contribution may vary with the beam incidence angle (due to dominant Cerenkov effect), while the GaN does not have such dependence.

Influence of linear energy transfer on the nucleo-shuttling of the ATM protein: a novel biological interpretation relevant for particles and radiation

PURPOSEnLinear energy transfer (LET) plays an important role in radiation response. Recently, the radiation-induced nucleo-shuttling of ATM from cytoplasm to the nucleus was shown to be a major event of the radiation response that permits a normal DNA double-strand break (DSB) recognition and repair. Here, we aimed to verify the relevance of the ATM nucleo-shuttling model for high-LET particles and various radiation types.nnnMETHODS AND MATERIALSnATM- and H2AX-immunofluorescence was used to assess the number of recognized and unrepaired DSB in quiescent fibroblast cell lines exposed to x-rays, γ-rays, 9- and 12-MeV electrons, 3- and 65-MeV protons and 75-MeV/u carbon ions.nnnRESULTSnThe rate of radiation-induced ATM nucleo-shuttling was found to be specific to each radiation type tested. By increasing the permeability of the nuclear membrane with statin and bisphosphonates, 2 fibroblast cell lines exposed to high-LET particles were shown to be protected by an accelerated ATM nucleo-shuttling.nnnCONCLUSIONSnOur findings are in agreement with the conclusion that LET and the radiation/particle type influence the formation of ATM monomers in cytoplasm that are required for DSB recognition. A striking analogy was established between the DSB repair kinetics of radioresistant cells exposed to high-LET particles and that of several radiosensitive cells exposed to low-LET radiation. Our data show that the nucleo-shuttling of ATM provides crucial elements to predict radiation response in human quiescent cells, whatever the LET value and their radiosensitivity.