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M Stasi

Publications and source records attributed to M Stasi.

17 recordsLinked to original sources
PubMed2005

D-IMRT verification with a 2D pixel ionization chamber: dosimetric and clinical results in head and neck cancer.

Dynamic intensity-modulated radiotherapy (D-IMRT) using the sliding-window technique is currently applied for selected treatments of head and neck cancer at Institute for Cancer Research and Treatment of Candiolo (Turin, Italy). In the present work, a PiXel-segmented ionization Chamber (PXC) has been used for the verification of 19 fields used for four different head and neck cancers. The device consists of a 32x32 matrix of 1024 parallel-plate ionization chambers arranged in a square of 24x24 cm2 area. Each chamber has 0.4 cm diameter and 0.55 cm height; a distance of 0.75 cm separates the centre of adjacent chambers. The sensitive volume of each single ionization chamber is 0.07 cm3. Each of the 1024 independent ionization chambers is read out with a custom microelectronics chip.The output factors in water obtained with the PXC at a depth of 10 cm were compared to other detectors and the maximum difference was 1.9% for field sizes down to 3x3 cm2. Beam profiles for different field dimensions were measured with the PXC and two other types of ionization chambers; the maximum distance to agreement (DTA) in the 20-80% penumbra region of a 3x3 cm2 field was 0.09 cm. The leaf speed of the multileaf collimator was varied between 0.07 and 2 cm s-1 and the detector response was constant to better than 0.6%. The behaviour of the PXC was measured while varying the dose rate between 0.21 and 1.21 Gy min-1; the mean difference was 0.50% and the maximum difference was 0.96%. Using fields obtained with an enhanced dynamic wedge and a staircase-like (step) IMRT field, the PXC has been tested for simple 1D modulated beams; comparison with film gave a maximum DTA of 0.12 cm. The PXC was then used to check four different IMRT plans for head and neck cancer treatment: cervical chordoma, parotid, ethmoid and skull base. In the comparison of the PXC versus film and PXC versus treatment planning system, the number of pixels with gamma parameter<or=1 was 97.7% and 97.6%, respectively.

Chordoma↗
PubMed2004

Two-dimensional and quasi-three-dimensional dosimetry of hadron and photon beams with the Magic Cube and the Pixel Ionization Chamber.

Two detectors for fast two-dimensional (2D) and quasi-three-dimensional (quasi-3D) verification of the dose delivered by radiotherapy beams have been developed at University and Istituto Nazionale di Fisica Nucleare (INFN) of Torino. The Magic Cube is a stack of strip-segmented ionization chambers interleaved with water-equivalent slabs. The parallel plate ionization chambers have a sensitive area of 24 x 24 cm2, and consist of 0.375 cm wide and 24 cm long strips. There are a total of 64 strips per chamber. The Magic Cube has been tested with the clinical proton beam at Loma Linda University Medical Centre (LLUMC), and was shown to be capable of fast and precise quasi-3D dose verification. The Pixel Ionization Chamber (PXC) is a detector with pixel anode segmentation. It is a 32 x 32 matrix of 1024 cylindrical ionization cells arranged in a square 24 x 24 cm2 area. Each cell has 0.4 cm diameter and 0.55 cm height, at a pitch of 0.75 cm separates the centre of adjacent cells. The sensitive volume of each single ionization cell is 0.07 cm3. The detectors are read out using custom designed front-end microelectronics and a personal computer-based data acquisition system. The PXC has been used to verify dynamic intensity-modulated radiotherapy for head-and-neck and breast cancers.

Calibration↗
PubMed2004

The behavior of several microionization chambers in small intensity modulated radiotherapy fields.

The aim of this work is to compare different ion chambers available for dose measurements in small fields used in intensity modulated radiotherapy. Some dosimetric aspects, related to these small radiation fields, i.e., lack of electronic lateral equilibrium and steep dose region, must be evaluated, in order to obtain an accurate technique implementation. Furthermore, the size of the sensitive volume of the chambers compared with the mapping of the beams or segments needs consideration. If the size of the chamber is too large for the flatness of the field, the measurement can deviate from the expected absorbed dose at a point. We propose a comparison of various dosimetric values between different microionization chambers with respect to a smaller dosimeter, such as the diamond detector.

Equipment Failure Analysis↗
PubMed1999

[Dosimetric characterization of a multileaf collimator].

INTRODUCTION: We studied the dosimetric characteristics of a multileaf collimator (MLC) installed on a dual energy accelerator with 6 and 18 MV photon beams in the Radiotherapy Department of Mauriziano Umberto I Hospital in Turin initiating its use in clinical practice. In particular, measurements included transmission through and between the leaves and at the junction under closed-leaves, central axis percentage depth dose, output factors and effective penumbra. MATERIAL AND METHODS: The MLC installed on the dual energy (6 and 18 MV) linear accelerator Varian Clinac 2100 C/D used in our radiotherapy department is an add-on component positioned below the standard jaws; it consists of 40 computer-controlled opposed pairs of 5 cm thick tungsten leaves, each projecting a 1 cm width at the isocenter, and it provides a maximum treatment field of 40 x 40 cm2 at 100 cm SAD. Transmission, penumbra and scalloping values were measured with the standard radiographic film routinary used in our department. A laser scanning photodensitometer (WP102, Wellhofer) with a 450 microns spot was used to obtain the optical density and the relative dose profile. Radiographic films had been calibrated with an ionization chamber, by irradiating samples to known doses; this calibration was used to correct the film scanner readings to dose. Percentage depth doses were also measured in an automatic water phantom (WP600, Wellhofer) for irregular fields defined by either MLC or alloy blocks, in order to test the differences in the build-up region due to the presence of the acrylic accessory tray. Measured and calculated output factors were compared for some irregular fields defined by the MLC. This comparison tested the algorithm accuracy of our Treatment Planning System 3D CadPlan 3.1.1 Varian-Dosetek. RESULTS AND DISCUSSION: For both energies, approximately 2% of the incident radiation on the MLC is transmitted and an additional 0.5% leakage occurs between adjacent leaves. The leakage under closed-leaves junction is remarkable: about 25-33%. Relative depth dose curves are similar for two fields shaped by either MLC or conventional jaws. Skin dose with MLC-shaped field is less (3.5%) than the one with cerrobend block-shaped fields. The monitor unit calculation procedure used in our treatment planning system can be applied to the MLC (the difference is less than 1%). Effective penumbra in MLC-shaped irregular fields is on the average 11 mm, which is slightly wider (2-3 mm) than the conventional cerrobend blocks penumbra. Effective penumbra increases with depth, field width and leaves positioning. CONCLUSIONS: The MLC, if properly used (collimator rotation, jaws and leaves position, high number of fields), can be applied to conformal radiotherapy with good results. The MLC is better than conventional cerrobend blocks both to improve the treatment reproducibility and accuracy, and relative to dosimetric characteristics like dose transmission and skin dose. The use of MLC to modulate beam fluence (IMRT) will permit to modify beam intensity for improved shaping of the treated volume and to overcome the static therapy dosimetric limitations.

Particle Accelerators↗
PubMed1997

Measurements of exit dose profiles in 60Co beams with a conventional portal film system.

An important step in the verification of the reliability of portal films as in vivo dosemeters is the evaluation of the agreement between exit dose profiles and optical density profiles measured on the portal film. To test the possibilities of a conventional portal film system in 60Co beams suitable for head and neck irradiation, we verified the agreement between relative exit doses (measured by ionization chamber) and relative optical densities, on cubic homogeneous phantoms, on an homogeneous "step" phantom and on a cubic phantom including air and aluminium inhomogeneities. The optical density profiles were corrected with the appropriate sensitometric curves. For an homogeneous phantom 10.8 cm thick and with the film in contact with the phantom, the agreement was found to be excellent with a mean deviation of 0.8% and a maximum deviation of 1.5%. The agreement was worse when the air gap between the exit surface of the phantom and the portal film was increased (with an air gap equal to 15 cm the maximum deviation was 4%), and when the thickness of the phantom was increased (for a thickness of 14.4 cm the maximum deviation was 3.1%). The agreement was found to be acceptable for the "step" phantom too, with a mean deviation around 1% and a maximum deviation within 2% (air gap equal to zero). When air and aluminium inhomogeneities were incorporated into the phantom a maximum deviation of 6% and a mean deviation less than 3% were found. Furthermore, the relative optical density profiles show an underestimate of measured off-axis exit dose values under a high density inhomogeneity and a small overestimate under a low density inhomogeneity. Results suggest the possibility of using conventional portal films for exit relative dosimetry in head and neck irradiation with 60Co beams if the air gap is kept as small as possible.

Air↗
PubMed1997

[Factors affecting the contralateral dose for the non-treated breast in irradiation following quadrantectomy].

We evaluated, with a treatment planning system, the maximum and the mean contralateral breast doses, and, with thermoluminescent dosemeters LiF100; the skin dose during radiation therapy after conservative surgery. The doses were correlated with technical parameters through statistical analysis. Since 1995, 100 patients have been considered, all of them treated with two 60Co tangential beams after quadrantectomy. The mean dose to the contralateral breast exhibited a statistically significant correlation with the gantry angle of the lateral (Pearson, p < .02) and medial beams (p < .01); the maximum dose was correlated with the gantry angle of the lateral (p < .002) and the medial beams (p < .002). In the last 50 patients, the skin dose (measured with TLDs) was correlated with: distance from beam edge (Pearson, p < .02), breast thickness (p < .01), gantry angle of the lateral beam (p < .005), gantry angle of the medial beam (p < .002). Furthermore, only the gantry angle of the lateral (p < .02) and of the medial beams (p < .01) exhibited statistically significant Spearman's correlation with skin dose. Wilcoxon's signed rank sum test for paired data was performed to study wedge dependence. The average contralateral breast dose using two wedges was statistically reduced with respect to the dose without wedges (p < .02). These results suggest that the dose to the contralateral breast could be significantly decreased by careful attention to the treatment details, which implies that the procedures related to the technical aspects of the therapy should be submitted to careful quality control.

Breast Neoplasms↗
PubMed1996

Protein kinase C inhibitors enhance G-protein induced phospholipase A2 activation in intact human platelets.

Washed intact human platelets were prelabelled with [3H]arachidonic acid ([3H]AA) and stimulated with thrombin or with AlF4-, a known unspecific activator of G-proteins. Both stimuli induced the liberation of [3H]AA, the release of beta-thromboglobulin (beta-TG) and platelet aggregation. PMA did not induce liberation of [3H]AA although it induced beta-TG release and aggregation; preincubation with PMA did not modify significantly the amounts of [3H]AA and beta-TG released by thrombin or AlF4-. Different inhibitors of PKC (staurosporine, H-7 and calphostin C) increased the release of [3H]AA and inhibited beta-TG release and aggregation induced by AlF4- but they had no effect when platelets were stimulated with thrombin (0.5 U/ml). Calphostin C was able to release [3H]AA by itself without inducing aggregation of beta-TG release. Okadaic acid (a serine/threonine phosphoprotein phosphatase inhibitor) greatly inhibited the release of [3H]AA, beta-TG and aggregation in AlF4--stimulated platelets. These results indicate the presence of a G-protein mediated mechanism for the activation of a platelet phospholipase A2 which is negatively affected by a protein kinase, sensible to putative inhibitors of protein kinase C, and it is activated by a protein phosphatase, sensible to okadaic acid.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

[The results of sandwich adjuvant radiotherapy in 2nd- and 3rd-stage rectal adenocarcinoma. The authors' personal experience].

From January, 1985, to June, 1993, 125 patients with stages B2-C adenocarcinomas of the rectum were submitted to pre- and postoperative irradiation according to Thomas Jefferson University protocol guidelines. Five hundred cGy were administered as a single preoperative dose 24 hours before surgery using parallel opposed (AP-PA) treatment fields including the whole pelvis. Pathologic samples were classified following the Astler-Coller staging criteria. Forty-seven patients had no postoperative treatment because their disease stage was A, B1 or D, 11 for refused consent and 9 postoperative complications preventing any further therapy. Seventy-eight patients concluded the treatment schedule and are assessable for response. Radiotherapy total dose consisted of 4400-5000 cGy administered over 5-6 weeks: the patients were treated with megavoltage photons (15-MeV photons) and one dose fraction of 2 Gy was delivered daily, 5 days a week, with the "box" or the "three-field" technique. Median follow-up time was 50.2 months from the beginning of treatment for all the patients in our series (range: 18-120 months). Radiation therapy was well tolerated: 5 patients had severe diarrhea and 2 had small bowel obstruction which required surgery. Local recurrences were observed in 13 of 78 patients (16.7%). Overall actuarial survival at 5 years was 66.8%. Our results confirm the efficacy of this treatment, which is in agreement with international literature data. However, no difference was seen relative to the results obtained with postoperative irradiation alone. We conclude that sandwich radiotherapy can be an effective tool for the local control of rectal adenocarcinoma, with acceptable morbidity, even though it fails to prevent metastases.

Adenocarcinoma↗
PubMed1993

Cloricromene inhibits leukotriene formation by human polymorphonuclear leucocytes by suppressing arachidonate release from membrane phospholipids.

Cloricromene, an antithrombotic agent known to inhibit the release of arachidonic acid (AA) in stimulated human platelets, was tested for its effects on arachidonate release and metabolism in human polymorphonuclear leucocytes (PMNs). Cloricromene dose-dependently suppressed the release of leukotriene B4 (LTB4), as assessed by radioimmunoassay, from both isolated PMNs and human whole blood stimulated with the calcium ionophore A23187 or with serum-treated zymosan (STZ). The inhibitory effect was higher when the concentration of the stimulating agent was weaker. Cloricromene also inhibited dose-dependently the liberation of LTB4, LTC4, LTD4 and 5-hydroxy-6,8,11,14-eicosatraenoic acid as assessed by HPLC in the supernantant of A23187-stimulated PMNs. Finally, the drug was able to suppress the release of [3H]AA from purified human PMNs prelabeled with the radioactive fatty acid and stimulated with either A23187 or with STZ. The A23187-induced decrease in the radioactivity of phosphatidylinositol, the phospholipid class mainly involved in AA release in stimulated PMNs, was also inhibited by cloricromene. Cloricromene suppresses leukotriene formation in human PMNs by reducing AA release from membrane phospholipids, possibly through interference with phospholipase A2 activation; this activity may contribute to the leucocyte-inhibitory effects reported previously for cloricromene.

Arachidonic Acid↗
PubMed1993

Cloricromene inhibits G-protein-mediated activation of phospholipase A2 in human platelets.

The coumarin derivative, cloricromene, an antithrombotic drug previously indicated as AD6, is known to inhibit the release of radioactive arachidonic acid from human platelets prelabelled with arachidonic acid and stimulated with thrombin. This effect might be due to the drug itself or to its catabolite, cloricromene acid. When added to platelet lysates neither compound inhibited phospholipase A2 activity assayed either with endogenous or with exogenous substrates. However, some inhibition was instead shown when intact platelets were first exposed to cloricromene and then enzyme activity was assayed in the lysate. Preincubation of platelets with the drug caused a dose-dependent inhibition of arachidonic acid mobilization in fluoroaluminate-stimulated platelets. beta-Thromboglobulin (beta-TG) release, a phenomenon previously shown to share common steps with phospholipase A2 activation, was also dose-dependently inhibited by cloricromene. Cloricromene also reduced the radioactivity associated with phosphatidic acid in fluoroaluminate-stimulated platelets but not in platelets stimulated with thrombin. These results are consistent with the hypothesis that cloricromene, or its catabolite, inhibits the production of arachidonic acid in stimulated platelets by interfering with a G-protein mediated activation of phospholipase A2 that is independent from the receptor-activated phosphoinositide phospholipase C.

Aluminum↗
PubMed1993

Post-operative analgesia with tramadol: a controlled study compared with an analgesic combination.

The analgesic action of tramadol in the post-operative period was compared with that of an analgesic combination (Nisidin) in a sample of 60 patients (31 male, 29 female) aged between 20 and 70 years undergoing surgical operations on the abdomen involving opening of the peritoneum. The study was carried out according to a controlled and randomized experimental design. Tramadol in 100 mg/2 ml vials and Nisidin in 2 ml vials were administered parenterally at a dosage of three vials a day during the first three days of the post-operative period. The analgesic action of tramadol was shown to be more effective than that of Nisidin both after the first dose and during the three days of observation (p < 0.01). Local and general safety were good in both groups, and respiratory and heart rates did not undergo clinically significant modifications. In conclusion, tramadol proves to be particularly indicated in the treatment of post-operative pain, given that it has analgesic action combined with good local and general safety.

Adult↗
PubMed1992

Activation of phospholipase A2 and beta-thromboglobulin release in human platelets: comparative effects of thrombin and fluoroaluminate stimulation.

Several reports have suggested that the activity of platelet phospholipase A2 is modulated by GTP-binding protein(s) whose nature and properties need to be defined. Fluoroaluminate is known to activate G-proteins and this leads to a number of cellular responses including the activation of phospholipases. This paper demonstrates that human platelets, prelabelled with [3H]arachidonic acid, produce free arachidonic acid when stimulated with fluoroaluminate and this effect is time- and dose-dependent. The production of arachidonic acid is not inhibited by neomycin, a PI-cycle inhibitor, but is completely abolished by mepacrine, an inhibitor of both phospholipase A2 and C. At low concentration of fluoroaluminate (10 mM NaF) phospholipase A2 but not phospholipase C is activated. In addition, fluoroaluminate treatment releases beta-thromboglobulin (beta-TG) and this effect is not inhibited by acetylsalicylic acid. Under identical conditions both neomycin and mepacrine suppress the release of arachidonic acid and beta-TG induced by thrombin. Sodium nitroprusside, which increases cGMP levels in platelets, inhibits arachidonic acid liberation and beta-TG release in thrombin-stimulated platelets but has no effect in fluoroaluminate-treated platelets; cGMP was reported to suppress phospholipase C activation. These results are consistent with the hypothesis that, in thrombin-stimulated platelets, the liberation of arachidonic acid and beta-TG are strictly dependent on the activation of phospholipase C. We have also provided evidence for the existence of a phospholipase A2 activated by a G-protein which is independent from the degradation of phosphoinositides and, contrary to phospholipase C, it is not down regulated by cGMP.

Aluminum↗
PubMed1990

The coumarin derivative AD6 inhibits the release of arachidonic acid by interfering with phospholipase A2 activity in human platelets stimulated with thrombin.

AD6 is a coumarin derivative which is able to inhibit platelet aggregation and release due to various agonists as adrenaline, PAF, Ca++ ionophore and others. It has been demonstrated that this compound reduces the production of free arachidonate and diglyceride from human platelets pulse-labeled with radioactive arachidonic acid thus suggesting a possible interference with the activity of phospholipase A2 and/or phospholipase C. The present report indicates that the drug has no effect on the increase of the labeling of phosphatidic acid which takes place when platelets pulse-labeled with arachidonic acid are stimulated with thrombin. Furthermore, AD6 is not able to cause changes on the metabolism of phosphoinositides monitored using platelets pre-labeled with [3H] inositol. These observations exclude the possibility that AD6 interferes with phospholipase C activity. Experiments with platelets pulse-labeled with arachidonate suggest that AD6 inhibits phospholipase(s) A2 activity or modulate negatively one or more processes involved in its activation.

Arachidonic Acid↗
PubMedDate not supplied

Effective penumbra and scalloping effect: a dosimetric study in multifield radiotherapy with multileaf collimator for prostate cancer treatment.

AIMS AND BACKGROUND: The aim of the study was to test whether the multileaf collimator can be used to replace divergent alloy blocks for field shaping and to evaluate the dosimetric impact of the scalloping effect and the effective penumbra in multifield isocentric configurations routinely used at our department to treat early stage prostate tumor in supine patients. Deviations between measurements and treatment planning system calculations are also discussed in order to estimate the accuracy of effective penumbra calculations carried out by the software in the presence of blocks or a multileaf collimator. METHODS: The multileaf collimator installed on a dual energy (6 and 18 MV) linear accelerator Varian CLINAC 2100 C/D is an add-on component positioned below the standard jaws, with 40 computer-controlled opposed pairs of tungsten leaves. Transmission, effective penumbra and scalloping measurements were performed with films placed at different depths in a (30 x 30 x 20 cm3) acrylic phantom. A laser scanning photodensitometer was used to obtain the optical density and the relative dose profile. Effective penumbra and scalloping effect measured data were tested on a software phantom; the phantom, automatically performed with the treatment planning system, was a regular parallelepiped measuring 30 x 30 x 20 cm3 and the acrylic electronic density value. RESULTS: For one multileaf collimator-shaped field, the width of effective penumbra was about 2 mm wider than penumbra for cerrobend blocks, at a 45 degrees angle between leaf motion direction and the field edge. Collimator rotation, automatically performed by the treatment planning system, by minimizing the sum of over- and underblocked areas, reduces the differences between the multileaf collimator and blocks. The differences between measured and treatment planning system calculated data were within the treatment planning system dose calculation accuracy limits, as recommended in ICRU Report No. 42. CONCLUSIONS: Penumbra and, for the multileaf collimator, scalloping effect values seem to depend on the gantry angle, i.e., on the fields path of entry. The values for even fields are higher than the those for odd fields, because the dose gradient at the target edges is steeper for a single field than for two opposite fields, and the interplay of doses from the individual beams increases the distance between the isodose levels. Therefore, in order to reduce scalloping and effective penumbra values, it would be better to rotate the collimators, above all in even-number field techniques. In particular, the six-field technique, used mostly in prostate treatment, shows the same effective penumbra values with the multileaf collimator, with proper collimator rotation, and in blocked fields.

Humans↗
PubMedDate not supplied

Does concomitant chemoradiotherapy influence cosmetic outcome in conservative treatment of breast cancer?

PURPOSE: To evaluate retrospectively factors influencing the cosmetic outcome after conservative treatment for breast cancer. MATERIAL AND METHODS: From 1988 until 1992, 164 patients were treated with conservative surgery (quadrantectomy) and radiotherapy with 60Co (50 Gy on the whole breast) plus 10 Gy on the surgical bed (300 kV photons) for T1-T2 breast cancers; 46 patients (28%) received concomitant adjuvant chemotherapy (CMF schedule). Cosmesis evaluation was carried out after 24 to 108 months (median, 38 months). A logistic regression analysis was performed to identify independent variables influencing the aesthetic outcome. P values of 0.05 or less were considered significant. RESULTS: Univariate analysis showed that T2 versus T1 (P = 0.0102), lower quadrants site (P = 0.0002) and concomitant adjuvant chemotherapy (P = 0.0009) produced a worse aesthetic outcome. Multivariate analysis confirmed the same factors: tumor size (P = 0.0020), tumor site (P = 0.0150) and concomitant chemotherapy (P = 0.0024). CONCLUSIONS: The significant negative influence on the cosmetic outcome of concomitant adjuvant chemotherapy implies questions about the timing of radiotherapy and chemotherapy in breast cancer conservative treatment.

Adult↗