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Biomedical subjects

D Pontvert

Publications and source records attributed to D Pontvert.

At least 19 recordsLinked to original sources
PubMed2006

[Brachytherapy for prostate cancer: old concept, new techniques].

Whereas it has been proposed almost one century ago, brachytherapy for prostate cancer has only recently emerged, especially thanks to endorectal echography, allowing to visualize seed implantation, to the development of seeds for permanent delivery and of micro-sources for high-dose rate delivery, and also to the development of three-dimension dosimetry programs allowing real-time implantations. For selected patients with localized prostate cancer (PSA < 10, Gleason < 7, no extracapsular extension, volume < 50-60 g), prostate brachytherapy with permanent implants (iodine 125 or, less frequently, palladium 103) gives results which appear at 10-15 years comparable to those of surgery. Incontinence and impotence rates appear lower than those of classical surgery. However, the first post-implant months are usually accompanied by urinary toxicity that should not be minimized. High-dose rate brachytherapy (HDR) could find its indications, in combination with conformal radiotherapy, in the treatment of more advanced forms, presenting an intermediate risk. It could also be an alternative to brachytherapy with permanent implants for the low-risk forms mentioned above, especially in developing countries where the cost of radioactive seeds slows down the use of this technique. Brachytherapy for prostate cancer should, therefore, find more and more indications, because of the increased incidence of prostate cancer, due to population ageing, of the increased proportion of localized forms, due to better detection, of the patient's request for less toxicity, and of the expecting lowering of the costs, which are now equivalent to those of surgery and should further lower.

Brachytherapy↗
PubMed2004

[Constraints and dosage for prostate cancer patients treated with conformal radiotherapy and intensity modulated radiation therapy].

PURPOSE: Intensity modulated radiation therapy (IMRT) is based on a methodology called inverse planning. Starting from dosimetric objectives, constraints of optimization are fixed and given to the inverse planning system, which in turn calculates the modulated intensity to apply to each beam. Since the algorithms allow the constraints to be violated, the results of optimization may differ from the initial dosimetric objectives. Consequently, the user is compelled to adapt the choice of the constraints according to the type of modulation and until satisfactory results are found. The purpose of this work is to present our experience in the choice of these constraints for prostate cancer treatments, as we moved from conformal radiotherapy to IMRT. Treatments were performed with a Varian 23EX linac and calculations were realized with the Varian CadPlan-Helios planning system. PATIENTS AND METHODS: The approach used for the first 12 patients treated at institut Curie with IMRT from June 2002 was analysed. The treatment always consisted of a combination of conformal radiotherapy with and without intensity modulation. RESULTS AND CONCLUSION: Results showed that, a larger fraction of the treatment performed with IMRT induced a better sparing of the organs at risk for the same homogeneous dose distribution to the target volume. Apart from the dose-volume constraint for the rectum, a fixed set of constraints, slightly more restrictive than the dosimetric objectives, could be used for all patients. Compared with conformal radiotherapy, the conformation factor for IMRT increased up to 16%. A specific study was undertaken in view of treatments completely performed with IMRT. The optimal technique consisted in performing separated IMRT plans for the two target volumes, the prostate volume and the prostate plus seminal vesicles volume respectively. Another satisfactory possibility was to define new constraints on two separated planning target volumes, prostate and seminal vesicles. This last approach is now routinely implemented for our IMRT patients.

Humans↗
PubMed2002

Predictive factors of radiation therapy for patients with prostate specific antigen recurrence after radical prostatectomy.

OBJECTIVE: To assess the efficacy of salvage/adjuvant radiation therapy (RT) for patients with prostate-specific antigen (PSA) recurrence after radical prostatectomy (RP). PATIENTS AND METHODS: Between 1997 and 2001, 52 patients were treated in our institution with RT for PSA recurrence after RP. The mean (range) delay between RP and RT was 30.5 (0.16-105.6) months. Eighteen patients received no hormonal therapy before RT. The failure of RT was defined as three consecutive increases in PSA levels with intervals of > or = 6 weeks. RESULTS: Within a mean (range) follow-up of 27.7 (6-69) months, 18 patients presented with biochemical progression. The 3-year biochemical progression-free survival was 51%. Using univariate analysis, an age < 65 years (P = 0.0262), a Gleason score on the RP specimen of > or = 8 (P = 0.0024), stage pT3 (P = 0.02), a detectable nadir PSA after RT (P < 0.001) and the absence of hormonal therapy (P = 0.0359) were associated with a lower biochemical progression-free survival. However, only the Gleason score (P = 0.0395) and nadir serum PSA after RT (P = 0.028) remained independent predictive factors on multivariate analysis. CONCLUSION: Half of the present patients treated with RT for an isolated high serum PSA level after RP were free of biochemical relapse at 3 years of follow-up. RT may be proposed to selected patients with mild morbidity. However, definitive evidence of the beneficial effect of adjuvant RT for patients with PSA recurrence after RP awaits the conclusion of randomized clinical trials.

Aged↗
PubMed2001

Combination of photon and proton radiation therapy for chordomas and chondrosarcomas of the skull base: the Centre de Protonthérapie D'Orsay experience.

PURPOSE: Prospective analysis of local tumor control, survival, and treatment complications in 44 consecutive patients treated with fractionated photon and proton radiation for a chordoma or chondrosarcoma of the skull base. METHODS AND MATERIALS: Between December 1995 and December 1998, 45 patients with a median age of 55 years (14-85) were treated using a 201-MeV proton beam at the Centre de Protonthérapie d'Orsay, 34 for a chordoma and 11 for a chondrosarcoma. Irradiation combined high-energy photons and protons. Photons represented two-thirds of the total dose and protons one-third. The median total dose delivered within the gross tumor volume was 67 cobalt Gray equivalent (CGE) (range: 60-70). RESULTS: With a mean follow-up of 30.5 months (range: 2-56), the 3-year local control rates for chordomas and chondrosarcomas were 83.1% and 90%, respectively, and 3-year overall survival rates were 91% and 90%, respectively. Eight patients (18%) failed locally (7 within the clinical tumor volume and 1 unknown). Four patients died of tumor and 2 others of intercurrent disease. In univariate analysis, young age at time of radiotherapy influenced local control positively (p < 0.03), but not in multivariate analysis. Only 2 patients presented Grade 3 or 4 complications. CONCLUSION: In skull-base chordomas and chondrosarcomas, the combination of photons with a proton boost of one-third the total dose offers an excellent chance of cure at the price of an acceptable toxicity. These results should be confirmed with a longer follow-up.

Adolescent↗
PubMed1999

Proton beam therapy (PT) in the management of CNS tumors in childhood.

At the Centre de Protontherapie d'Orsay, nine children with intra-cranial malignancies were treated between July 1994 and January 1998. Immediate and late tolerances were excellent in all cases (follow-up 2 to 50 months). Two patients recurred locally (marginal failures), seven are alive and doing well. At Loma Linda, 28 children were treated between 1991 and 1994, 16 for a benign tumor of the brain and twelve for a malignant one. With a follow-up of seven to 49 months, three patients died (grade 2 to 4 gliomas), one is living with a persistent disease. Four children had treatment-related toxicity (one cataract, two hormonal failures and two seizures). The other children are doing well. At MGH Boston, 18 children with skull base-cervical spine chordomas have been reported. At five years, actuarial survival and disease-free survival have been 68 and 63%, respectively. Children with cervical sites had a worse prognosis (p = 0.008). Four children had radiation-related morbidity: two pituitary failures, one temporal lobe necrosis, one temporal muscle fibrosis. In this experience, such rare tumors seemed to behave in children like in adults.

Adolescent↗
PubMed1998

[Localized or metastatic cancer of the prostate: review of new treatment modalities].

Amongst men, prostatic adenocarcinoma is the most common cancer and the second most frequent cause of deaths. Widespread PSA measurement have led to earlier diagnosis. Recent clinical trials have tried to show an improvement in the prognosis. Early stages are mainly treated surgically even if local control results are similar with radiotherapy. Radiotherapy is the main stay of treatment for more locally advanced disease, either conventionally or conformational. Adjuvant hormonotherapy has been shown to improve survived as opposed to neoadjuvant hormonotherapy which only has local effects. The treatment of metastatic disease is palliative with the use of antiandrogens. In case of relapse, a second line of hormonotherapy or a chemotherapy is given. However the problem is the lack of effective drugs. Response rates to the main drug treatment are around 10 to 20%. New therapeutic approaches are now based on antimicrotubules agents but it is difficult to evaluate their efficacity. Further clinical trials will provide more information about improvement in survival rates and in quality of life.

Humans↗
PubMed1997

Automatic three-dimensional expansion of structures applied to determination of the clinical target volume in conformal radiotherapy.

PURPOSE: A method is provided for the automatic calculation of the Clinical Target Volume (CTV) by automatic three dimensional (3D) expansion of the Gross Tumor Volume (GTV), keeping a constant margin M in all directions and taking into account anatomic obstacles. METHODS AND MATERIALS: Our model uses a description of the GTV from contours (polygons) defined in a series of parallel slices obtained from Computed Tomography (CT) or Magnetic Resonance Imaging (MRI). Each slice is considered sequentially, including those slices located apart from the GTV at a distance smaller than M. In the current slice a two-dimensional (2D) expansion is performed by transforming each vertex of the polygon into a circle with a radius equal to M, and each segment into a rectangle with a height equal to 2M. A cartesian millimetric grid is then "projected" onto the slice and a specific value is assigned at each point depending if the point is internal to the 2D expansion. The influence in the current slice of any slice located at a distance delta z smaller than M is taken into account by applying a 2D expansion using a margin [formula: see text]. Additional contours representative of various "barriers" stopping the expansion process can also be defined. RESULTS: The method has been applied to cylindrical and spherical structures and has proven to be successful, provided that the slice thickness is small enough. For usual slice thicknesses and margins, it gives a slight overestimation of the additional volume (around 5%) due to the choice that the calculated target volume would not be less than the expected volume. It has been shown that for a spherical volume, a 2D expansion performed slice by slice leads to a volume up to 80% smaller than that obtained by 3D expansion. CONCLUSIONS: This tool, which mimics the tumor cell spreading process, has been integrated in our treatment-planning software and used clinically for conformal radiotherapy of brain and prostatic tumors. It has been found to be extremely useful, not only saving time but also allowing a precise determination of the CTV which would be impossible to do manually.

Algorithms↗
PubMed1996

Clinical applications of proton therapy.

Proton therapy offers considerable potential advantages in the management of poorly resectable, radio-resistent tumors close to critical anatomical structures. So far over 15,000 patients have been treated worldwide with two major indications: conservative management of ocular melanomas in which local control exceeds 95% at 5 years and curative irradiation of sarcomas at the base of the skull and cervical canal, with a survival rate between 84 and 94% at 5 years. The different protocols tested currently worldwide are discussed.

Adolescent↗
PubMed1996

Potential of T2 relaxation time measurements for early detection of radiation injury to the brain: experimental study in pigs.

PURPOSE: To investigate the MR T2 relaxation time and histologic changes after a single-fraction 25-Gy dose of radiation to the brain of pigs. METHODS: The right hemisphere of 10 Meishan pigs was irradiated with a single dose of 25 GY at the 90% isodose, using a 12-MeV electron beam. T2 relaxation time was measured within three regions of interest in the brain: those that had received 90%, 70%, and 40% of the total dose, respectively. T2 kinetics over time was compared with histologic studies. RESULTS: Brain T2 values were noted to increase within the irradiated areas. T2 kinetics were analyzed in three phases: an immediate transient phase and two long-lasting phases. These two long-lasting phases were correlated with the detection of ventricular compression and necrosis, respectively. The T2 increase within the 90% region of interest was 19%, 22%, and 26% for phases I, II, and III, respectively. T2 measurements within other regions of interest were not significant. CONCLUSION: Although our results suggest a dose threshold for T2 variations, brain T2 values increased after irradiation at a level at which disease could not be seen on conventional MR images. This illustrates the value of using conventional MR imaging in a quantitative manner to assess molecular tissue abnormalities at earlier stages of developing diseases.

Animals↗
PubMed1995

Quantitative magnetic resonance and isotopic imaging: early evaluation of radiation injury to the brain.

PURPOSE: Using magnetic resonance (MR) and isotopic imaging to investigate the cerebral alterations after highdose single-fraction irradiation on a pig model. We assessed the nuclear magnetic resonance (NMR) relaxation times as early markers of radiation injury to the healthy brain. METHODS AND MATERIALS: A total of 17 animals was studied; 15 irradiated and 2 unirradiated controls. Pigs were irradiated with a 12 MeV electron beam at a rate of 2 Gy/min. Ten animals received 40 Gy at the 90% isodose, five animals received 60 Gy, and two animals were unirradiated. The follow-up intervals ranged from 2 days to 6 months. T1-weighted scans, T2-weighted scans, and scintigrams were performed on all animals to study neurological abnormalities, cerebral blood flow, and blood-brain barrier (BBB) integrity. T1 and T2 relaxation times were measured in selected regions of interest (ROIs) within the irradiated and contralateral hemispheres. A ratio T1 after irradiation/T1 before irradiation, and a ratio T2 after irradiation/T2 before irradiation, were calculated, pooled for each dose group, and followed as a function of time after irradiation. RESULTS: Scintigraphy visualized the brain perfusion defect and BBB disruption in all irradiated brains. The ratio T2 after irradiation/T2 before irradiation was proportional to the effective dose received. The T2 ratio kinetics could be analyzed in three phases:an immediate and transient phase, two long-lasting phases, which preceded compression of the irradiated lateral ventricle, and edema and necrosis at later stages of radiation injury, respectively. The magnetic resonance imaging (MRI) observations correlated well with histological analysis. CONCLUSION: The results show that quantitative imaging is a sensitive in vivo method for early detection of cerebral radiation injury. The reliability and dose dependence of T2 relaxation time may offer new opportunities to detect and understand brain pathophysiology after high-dose single-fraction irradiation.

Animals↗
PubMed1995

Clinical applications of proton therapy. Experiences and ongoing studies.

Proton therapy offers potentially considerable advantages in the management of slow-growing, poorly resectable or non-resectable tumors resistant to x-rays and located close to critical radiosensitive anatomical structures, such as the brain stem of the spinal cord. Among over 13,000 irradiated patients in the USA, Europe, and Japan, two major clinical indications have been documented: 1. The conservative management of choroidal melanomas, in which 98% 5-year local control can be expected at the price of low toxicity and visual preservation in approximately half of them. 2. The curative management of low-grade chondrosarcomas and chordomas of the base of the skull and cervical spine, leading to, in combination with maximal tumor resection, 84%-94% long-term survival. Other ongoing studies concern prostate, head and neck carcinomas as well as various intracranial tumors. Radiosurgical programs are being conducted generally with single fractions and under stereotactic conditions.

Bone Neoplasms↗
PubMed1995

Experimental MR study of cerebral radiation injury: quantitative T2 changes over time and histopathologic correlation.

PURPOSE: To use the pig brain as a large-animal model to examine the effects of high-dose single-fraction irradiation on MR images, T2 relaxation time, and histologic integrity. METHODS: A total of 24 Meishan pigs were studied: 20 irradiated animals and 4 unirradiated controls. A high dose was delivered to the right hemisphere of the animals, using a 12-MeV electron beam. Ten animals received 40 Gy at the 90% isodose, and 10 animals received 60 Gy. Quantitative measurement of T2 relaxation time was compared with qualitative analysis of T2-weighted images and histologic studies. RESULTS: Quantitative analysis revealed a reproducible increase of the T2 parameter within the irradiated areas. The T2 kinetic could be analyzed in two phases, which appeared before the visualization of ventricle compression, necrosis, and edema. The first is characterized by vascular inflammation and the latter by radiation necrosis and edema. Both are dose dependent. CONCLUSION: These results underline the ability of quantitative MR for early diagnosis of brain radiation lesions in vivo.

Animals↗
PubMed1993

Is reseeding from the primary a plausible cause of node failure?

In a previous analysis of node failures in 1251 consecutive patients with node positive oropharyngeal and pharyngolaryngeal squamous cell carcinomas treated by external radiotherapy alone at the Institut Curie, the main reasons for patient exclusion were node recurrence associated with primary failure (N+T failures) and doses less than 55 Gy. These exclusions reduced the number of node failures from 399/1251 (32%) to 77/798 (10%). Multivariate analysis of node recurrence indicated that node size and fixity, treatment duration, and T stage of primary were significant (higher probability of isolated node failure for the T1-T2 primaries). In the present analysis, it is noted that 60% of the N+T failures were observed less than 1 month after the completion of the irradiation and, therefore, were not likely the result of reseeding from the primary tumor. When all 1251 patients were included in the analysis, the probability of nodal failure increased for larger nodes, T4 primaries, lower nodal doses, presence of contralateral node metastases, and nodal fixation to the surrounding structures. No influence of the primary site was found. Treatment duration was closely associated with total dose to the nodes. The best description of the data was obtained with a model including total dose and not treatment time. However, as in the previous analysis, the exclusion of low-dose (less than 55 Gy) treatments resulted in the loss of a significant dose-control relationship. We conclude that the majority of node failures is unlikely to result from reseeding from the primary tumor, and therefore should not be excluded from local-control analyses. From a more radiobiological point of view, the exclusion of palliative treatments is questionable when studying the effect of dose on local control.

Adult↗
PubMed1992

Quality control of radiotherapeutic treatment of medulloblastoma in a multicentric study: the contribution of radiotherapy technique to tumour relapse. The French Medulloblastoma Group.

Between 06.86 and 11.89, 88 medulloblastoma or primitive neuroectodermic tumour (PNET) localised in the posterior fossa have been included in the M7 multicentric protocol, 82 received the totality of the radiotherapy treatment and were evaluable for this study. Twenty-two of these 82 patients relapsed: their radiotherapy treatment is analysed in the present study. In 10 cases out of the 22 relapses treatment failure was probably due to a radiotherapeutic imperfection. This study confirms the necessity of a strict radiotherapy control, particularly in multicentric study.

Adolescent↗