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Biomedical subjects

A Mazal

Publications and source records attributed to A Mazal.

At least 19 recordsLinked to original sources
PubMed2003

[Treatment of uveal melanoma with iodine 125 plaques or proton beam therapy: indications and comparison of local recurrence rates].

INTRODUCTION: This retrospective study compared the rate of local recurrence after irradiation of uveal melanoma treated with iodine 125 plaques or proton beam therapy. PATIENTS AND METHODS: Iodine 125 plaques were used to treat all uveal melanomas between the end of 1989 and 1991. Since 1991, we have used iodine plaques for small anterior tumors and proton beam for other tumors. We use a plaque with a larger diameter than the tumor diameter (2-4mm) with a dose of 90Gy at the apex. Proton beam therapy is used for all tumors at the equator or posterior to the equator not thicker than 12mm. The dose given is 60Gy cobalt equivalent in four fractions. For each patient, the initial size and location of the tumor were noted as well as the follow-up each year: the outcome for the eye (local recurrence, ocular conservation, and functional results), the occurrence of metastasis, and survival. A statistical analysis was performed. RESULTS: Between December 1989 and September 1998, 1272 patients were treated: 926 (72.8%) were treated with proton beam irradiation and 346 (27.8%) with iodine 125 plaques. The median follow-up was 5 years (60 months). For the patients treated with proton beam therapy, the mean age was 58 years, the tumor location was anterior to the equator for 3.8%, at the equator for 43.6%, and posterior to the equator for 52.6%. The mean tumor diameter was 13.4mm and the mean tumor thickness was 5.69mm. For the patients treated with iodine 125 plaques, the mean age was 61.5 years. The location of the tumor was anterior to the equator for 34.4%, at the equator for 46.5%, and posterior to the equator for 19.1%. The mean tumor diameter was 11.5mm and the mean tumor thickness was 5.12mm. The recurrence rate was 4% for the proton beam treatment and 3.75% for iodine plaques. There was no statistical difference. DISCUSSION: In the literature, the rate of local recurrence is usually higher with iodine 125 plaques than proton beam therapy. We discuss the risk factors for local recurrence after iodine 125 plaques: tumor diameter, lower dose to the tumor apex and lower dose rate, and posterior location of the tumor. We found a higher mortality rate in patients who presented local recurrence. CONCLUSION: When we use iodine 125 plaques for anterior tumors with the proper dose and dose rate to the apex of the tumor, we do not find more recurrence than with proton beam therapy.

Adolescent↗
PubMed2002

[Results of proton beam irradiation for treatment of choroidal melanoma].

PURPOSE: To evaluate the results of proton beam irradiation of choroidal melanomas on a large series of patients. PATIENTS AND METHODS: Retrospective analysis of a series of patients treated with proton beam irradiation between 1991 and December 1998. The data were analyzed to evaluate the local tumor control as well as the general progression and metastatic rate of the patients. Statistical analysis served to isolate risk factors for relapse or metastasis. RESULTS: We treated 1062 patients during the study period, with a median follow-up of 38 months. Local control was obtained for 97.1% of the patients. Tumors anterior to the equator were at risk for relapse. The survival rate was 92% at 2 years and 78% at 5 years. 73.1% of the 1062 patients died from metastasis, 6.1% of living patients presented with metastatic disease. The risk factors for death were the initial diameter, the age of the patient, and large tumor volume at diagnosis. Metastasis were essentially hepatic (94.6%). Risk factors for metastasis were: a large tumor volume, a lesion anterior or straddling the equator and the age of the patient. Ocular complications may induce a visual loss of 0.1 and less in 47% of the patients, due to optic nerve head and macular ischemia. 6% of the patients required secondary enucleation due to local complications (neovascular glaucoma). CONCLUSION: Proton beam irradiation of choroidal melanoma allows good tumor control and eye retention. The survival prognosis is associated with the initial volume of the tumor. The functional results may be improved and new therapeutics are needed to treat metastatic disease.

Adolescent↗
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↗
PubMed2001

Experimental determination and verification of the parameters used in a proton pencil beam algorithm.

We present an experimental procedure for the determination and the verification under practical conditions of physical and computational parameters used in our proton pencil beam algorithm. The calculation of the dose delivered by a single pencil beam relies on a measured spread-out Bragg peak, and the description of its radial spread at depth features simple specific parameters accounting individually for the influence of the beam line as a whole, the beam energy modulation, the compensator, and the patient medium. For determining the experimental values of the physical parameters related to proton scattering, we utilized a simple relation between Gaussian radial spreads and the width of lateral penumbras. The contribution from the beam line has been extracted from lateral penumbra measurements in air: a linear variation with the distance collimator-point has been observed. Analytically predicted radial spreads within the patient were in good agreement with experimental values in water under various reference conditions. Results indicated no significant influence of the beam energy modulation. Using measurements in presence of Plexiglas slabs, a simple assumption on the effective source of scattering due to the compensator has been stated, leading to accurate radial spread calculations. Dose measurements in presence of complexly shaped compensators have been used to assess the performances of the algorithm supplied with the adequate physical parameters. One of these compensators has also been used, together with a reference configuration, for investigating a set of computational parameters decreasing the calculation time while maintaining a high level of accuracy. Faster dose computations have been performed for algorithm evaluation in the presence of geometrical and patient compensators, and have shown good agreement with the measured dose distributions.

Algorithms↗
PubMed2001

Intraocular inflammation after proton beam irradiation for uveal melanoma.

AIM: To describe the inflammatory reaction that can occur following proton beam irradiation of uveal melanomas based on a large series of patients and to try to determine the risk factors for this reaction. METHODS: Data from a cohort of patients with uveal melanoma treated by proton beam irradiation between 1991 and 1994 were analysed. The presence of inflammation was recorded and evaluated. Kaplan-Meier estimates and statistical analysis of general and tumour related risk factors were performed. RESULTS: 28% of patients treated during this period presented with ocular inflammation (median follow up 62 months). Risks factors were essentially tumour related and were correlated with larger lesions (height > 5 mm, diameter > 12 mm, volume > 0.4 cm(3)). Multivariate analysis identified initial tumour height and irradiation of a large volume of the eye as the two most important risk factors. Ocular inflammation usually consisted of mild anterior uveitis, resolving rapidly after topical steroids and cycloplegics. The incidence of inflammation after proton beam irradiation of melanomas seems higher than previously reported and is related to larger lesions. Evidence of inflammation associated with uveal melanoma has been described and seems to be associated with tumour necrosis (spontaneous or after irradiation). The appearance of transient inflammation during the follow up of these patients may be related to the release of inflammatory cytokines during tumour necrosis. CONCLUSION: Inflammation following proton beam irradiation is not unusual. It is correlated with larger initial tumours and may be related to tumour necrosis.

Analysis of Variance↗
PubMed2000

[Optic neuropathy after proton-beam therapy for malignant choroidal melanoma].

Proton-beam irradiation is a conservative therapy commonly used for the treatment of uveal malignant melanomas. Some adverse effects such as optic neuropathy can compromise the visual outcome. We were interested in determining the risk factors for radiation papillopathy. Since there is currently no effective therapy, this is an interesting way to improve prevention of optic neuropathy. Six hundred sixty-two eyes had more than 24 month follow-up after proton-beam irradiation for uveal melanoma. In five hundred twenty-two cases, the clinical examination of the optic nerve head by ophthalmoscopy was possible. One-hundred eleven optic discs were pathologic, whereas 411 remained disease-free. Retrospective study of these two groups allowed to quantify the risk factors for optic neuropathy. The irradiation of more than 2mm of optic nerve at 30 Grays-equivalents appeared to be the major risk factor for optic neuropathy. For a given irradiation dose, the observed pattern of clinical responses was heterogeneous. These results are discussed and compared to the previous published reports. Visual results and life prognosis are also discussed, considering the optic nerve head status. Proton-beam therapy can preserve the optic nerve when the tumor location allows to keep it away from the irradiation-field. Patients must be informed about the risk of optic neuropathy after proton-beam irradiation.

Choroid Neoplasms↗
PubMed1999

Proton dosimetry intercomparison based on the ICRU report 59 protocol.

BACKGROUND AND PURPOSE: A new protocol for calibration of proton beams was established by the ICRU in report 59 on proton dosimetry. In this paper we report the results of an international proton dosimetry intercomparison, which was held at Loma Linda University Medical Center. The goals of the intercomparison were, first, to estimate the level of consistency in absorbed dose delivered to patients if proton beams at various clinics were calibrated with the new ICRU protocol, and second, to evaluate the differences in absorbed dose determination due to differences in 60Co-based ionization chamber calibration factors. MATERIALS AND METHODS: Eleven institutions participated in the intercomparison. Measurements were performed in a polystyrene phantom at a depth of 10.27 cm water equivalent thickness in a 6-cm modulated proton beam with an accelerator energy of 155 MeV and an incident energy of approximately 135 MeV. Most participants used ionization chambers calibrated in terms of exposure or air kerma. Four ionization chambers had 60Co-based calibration in terms of absorbed dose-to-water. Two chambers were calibrated in a 60Co beam at the NIST both in terms of air kerma and absorbed dose-to-water to provide a comparison of ionization chambers with different calibrations. RESULTS: The intercomparison showed that use of the ICRU report 59 protocol would result in absorbed doses being delivered to patients at their participating institutions to within +/-0.9% (one standard deviation). The maximum difference between doses determined by the participants was found to be 2.9%. Differences between proton doses derived from the measurements with ionization chambers with N(K)-, or N(W) - calibration type depended on chamber type. CONCLUSIONS: Using ionization chambers with 60Co calibration factors traceable to standard laboratories and the ICRU report 59 protocol, a distribution of stated proton absorbed dose is achieved with a difference less than 3%. The ICRU protocol should be adopted for clinical proton beam calibration. A comparison of proton doses derived from measurements with different chambers indicates that the difference in results cannot be explained only by differences in 60Co calibration factors.

Algorithms↗
PubMed1998

A preliminary comparative treatment planning study for radiotherapy of age-related maculopathy.

PURPOSE: We present a comparative planning of different approaches for external radiotherapy in age-related maculopathies. MATERIALS AND METHODS: Calculated dose distributions and dose-volume histograms for (a) bilateral irradiation with 6 MV photons, (b) a single lateral-oblique beam using either photons, electrons or protons and (c) an anterior circular proton beam. RESULTS: For lateral photon or electron beams the dose to the lens is usually lower than 10% of the dose to the macula. The entrance doses for bilateral photon beams are about 50% which increase up to 100% at the orbital bone. About 5 mm of optic nerves are irradiated at the maximal dose while the optic chiasma is spared. A single photon beam gives 50% of the dose to the fellow eye. The electron beam spares the fellow eye but gives a rather inhomogeneous dose to the target volume. For a lateral proton beam, 4 mm of optic nerve receives 90% of the dose, the skin dose is at least 70% of the dose to the macula and the lens and the fellow eye are spared. An anterior proton beam gives 90% of the dose to 1 mm of optic nerve and the 50% isodose approaches the periphery of the lens. CONCLUSION: Doses to the critical structures can be dramatically diminished for all the techniques by reducing the beam size, but only if very precise set-up techniques are used. Proton beams are an attractive solution, but the impact of such a choice on the use of proton facilities and on the national health system should be carefully evaluated, as well as the risk of radio-induced secondary neoplasias.

Humans↗
PubMed1998

Effectiveness of protons and argon ions in initiating lipid peroxidation in low-density lipoproteins.

In this study, human low-density lipoprotein (LDL) vesicles were irradiated with 73 MeV protons (LET of 1 keV/microm) and 11.4 MeV/nucleon argon ions (LET of 1.52 MeV/pm) and the effectiveness of charged particles in initiating peroxidation of LDLs was investigated. The LDL suspension (6 g/l) was exposed to protons and to argon ions in a dose range of 24 Gy to 2.4 kGy. Irradiations were carried out at the synchrocyclotron at the CPO and at the UNILAC of the GSI. After irradiation three chemical assays were used to study the progression of peroxidation of LDLs: the formation of conjugated dienes, the formation of thiobarbituric acid-reactive substances (TBARS) and the increase in the relative electrophoretic mobility of the LDLs. The results were compared with those obtained after gamma irradiation. For protons the yields of the peroxidation products were 10 times lower than after gamma irradiation. However, for doses below 200 Gy, protons appeared to be more effective than gamma rays in damaging the protein moiety, as deduced from the observed increase in the relative electrophoretic mobility of the LDLs. The irradiation with argon ions led to a negligible formation of peroxidation products, but an increase in the relative electrophoretic mobility of the LDLs was observed. The results are indicative of a lower yield of lipid peroxidation after irradiation with high-LET particles. In contrast, protons and argon ions appear to be more effective in inducing bulk protein and phospholipid damage than gamma rays.

Argon↗
PubMed1997

Proton dosimetry comparison involving ionometry and calorimetry.

A comparison of the absorbed dose to tissue determined by various ionization chambers, Faraday cups, and an A-150 plastic calorimeter was performed in the 200 MeV proton beam of Orsay, France. Four European proton-therapy centers (Clatterbridge, UK, Louvain la Neuve, Belgium, and Nice and Orsay, France) participated in the comparison. An agreement of better than 1% was observed in the absorbed dose to A-150 measured with the different chambers of the participating groups. The mean ratio of the absorbed dose to A-150 determined with the calorimeter to that determined by the different ionization chambers in the different irradiation conditions was found to be 0.952 +/- 0.007 [1 standard deviation (SD)] according to the code of practice used by all the participating centers, based on Janni's tables of stopping powers and a value of 35.2 J/Coulomb for (W(air)/e)p. A better agreement in the mean ratio calorimeter/chamber, 0.985 +/- 0.007 (1 SD) is observed when using the proton stopping power ratio values recently published by the International Commission on Radiation Units and Measurements in Report no. 49. The mean ratio of these doses determined in accordance with the American Association of Physicists in Medicine protocol and using the new recommended stopping power tables becomes 1.002 +/- 0.007 (1 SD). Two Faraday cups agree in measured charge to within 0.8%; however, the calculation of dose is underestimated by up to 17%; compared with ion chamber measurements and seems to be very sensitive to measurement conditions, particularly to the distance to the collimator.

Calibration↗
PubMed1997

[Initial results of proton therapy in choroidal melanoma at the d'Orsey Center for Proton Therapy; the first 464 cases].

PURPOSE: Retrospective analysis of the treatment of choroidal melanoma with protontherapy at the Centre de protonthérapie d'Orsay, France. PATIENTS AND METHODS: Between September 1991 and September 1995, 612 patients presenting with choroidal melanoma were treated by protontherapy in Orsay. Following initial management of the first 464 patients, results were analyzed, as were results after a 1-year follow-up for 305 patients, a 2-year follow-up for 169 patients, and a 3-year follow-up for 59 patients. RESULTS: Univariate analysis showed that the actuarial local recurrence rate was 5%, the 3-year survival rate 88%, and the overall metastasic rate 5%. The initial tumor volume was the most significant predictive factor for visual results and metastases. Multivariate analysis revealed that visual results were significantly related to the initial tumor volume, initial retinal detachment, and total dose delivered to the optic nerve and macula. CONCLUSION: Protontherapy of choroidal melanoma allows in most cases conservation of the eye without modification of survival. Visual results mainly depend on the site and size of the tumor.

Choroid Neoplasms↗
PubMed1997

A model for the lateral penumbra in water of a 200-MeV proton beam devoted to clinical applications.

An experimental approach for modeling the lateral penumbra of a proton beam has been investigated. Measurements were made with a silicon diode in a water tank. Several geometrical configurations (phantom position, collimator-to-surface distance, collimator diameter, bolus thickness, air gap, etc.) and beam characteristics (range, modulation, etc.) have been studied. The results show that the lateral penumbra is almost independent of the beam modulation and the diameter of the collimator. The use of scaled variables for depth and penumbra allows us to represent the increase in penumbra with depth for any configuration with a second order polynomial function, provided that the penumbra at the entrance of the medium and at the depth of the range are known.

Biophysical Phenomena↗
PubMed1996

[Quality assurance in protontherapy: a systematic approach in progress at Orsay].

The degree of accuracy and reliability required in proton therapy can only be guaranteed if a comprehensive quality assurance (QA) programme is established. Such a programme obviously has common features with general QA in radiotherapy, but some aspects are specific to the use of protons and particularly to the characteristics of each facility. A study is in progress at Orsay to convert a series of quality controls into a systematic quality assurance programme. It includes some basic steps on organisation, setting up a QA committee and QA task groups, organising meetings, policies, procedures, records, qualifications, and determining some examples of tolerance in controls. Among some critical and specific points identified in this process are the combined treatment with photons at different institutions, the specificity of a non-hospital-based and complex facility, the high degree of precision required for the patient setup, and the need to develop in-house basic tools such as the treatment planning system. The inclusion of all the patients in prospective well-defined clinical trials, the comparison with alternative techniques and the radiobiological studies are considered as fundamentals for the QA programme. Present dosimetric and radiobiological intercomparisons between protontherapy centres are considered as partial audits. A study is in progress to establish common dosimetric and clinical protocols, radiobiological models and dose and volume specifications. In spite of the differences between the existing facilities, it should also be possible to obtain international consensus on general guidelines for a QA programme in proton therapy.

Clinical Competence↗
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↗
PubMed1995

An experimental approach to the design of a scattering system for a proton therapy beam line dedicated to ophthalmological applications.

PURPOSE: The development of a scattering system for a proton therapy beam line dedicated to ophthalmological applications. METHODS AND MATERIALS: A protontherapy beam line has been developed for the treatment of uveal melanoma at the Orsay synchrocyclotron. The original 200 MeV proton beam is degraded to 76 MeV and the final beam characteristics (range, modulation, flatness, collimation) are obtained with beam modifiers in the treatment room. A passive scattering system is used to obtain a uniform dose distribution in the beam cross-section throughout 30 mm in diameter, with minimal losses in energy and dose rate. We have used an experimental approach for the scattering study. RESULTS: An elliptical ring shaped from 0.1-mm thick lead is the solution we have adopted for the scattering system. For a modulated beam, a flatness of 1% is obtained on transverse profiles. The energy loss introduced by this scatterer is only 0.5 MeV, with no appreciable change in the range over the treatment field. For an unmodulated beam, 21% of intensity is lost when the scatterer is used. The distal and the lateral dose fall-off (90-10%) for a modulated beam are 2.6 mm. These last values are independent of the range and the modulation currently used for the ophthalmic applications. CONCLUSION: A specific passive scattering system can be adapted to a particular beam emittance. A systematic experimental approach can easily be undertaken to obtain the scatterer adapted for small irradiation fields in proton therapy.

Equipment Design↗