Cobalt Unit Research Articles

Radiosurgery for pituitary adenomas

Radiosurgery for pituitary adenomas

Synthesis, crystal structure, and magnetic property of a novel 2D polymer [Co(PDC)(4,4-bpy)](CH 3OH)

A novel cobalt complex {[Co(PDC)(4,4-bpy)] · (CH 3OH)} n (H 2PDC = pyridine-2,6-dicarboxylic acid; 4,4′-bpy = 4,4′-bipyridine) was synthesized and its crystal structure has been determined by X-ray diffraction. The complex has a two-dimensional (2D) layer polymeric structure, consisting of six-coordinated cobalt(II) units. Magnetic properties have been investigated in the range of 18–302 K assuming isolated Co(II) ions (without any coupling, J = 0).

Multinational assessment of some operational costs of teletherapy

Background and purposeDecisions in planning radiotherapy facilities in countries with limited financial resources require information on economic factors to make provision for sustainability. This study aims at acquiring data on some of these factors involved in delivery of teletherapy in 11 countries of different economic status. Patients and methodsRepresentatives of three European, one African, three Latin American and four Asian countries, were identified from radiation oncology institutions that operated both cobalt and linac teletherapy machines. Productivity data were prospectively collected for the year 2002. A detailed log was recorded for each machine over an arbitrary two-week period. Data on quality assurance (QA), maintenance, the capital costs of each machine, and the source replacement costs for the cobalt units were also recorded. ResultsBoth linear accelerators and cobalt machines treat more than 10,000 fractions per year per machine with 2.5 and 2.3 fields per fraction, respectively. The capital costs of the machines vary considerably, with a factor of more than 10 for linear accelerators. Cobalt sources show a huge variation in price. The median costs of QA and maintenance of a linac was US$ 41,000 compared to US$ 6000 for cobalt machines. This results for the economic factors considered in median costs per fraction of US$ 11.02 for linear accelerators and US$ 4.87 for cobalt machines. These figures do not include the costs for physicians. ConclusionsThe variation of the costs per fraction is more due to the result of differences in machine usage and costs of equipment than of national economic status. A treatment fraction on a linac with functionality comparable to cobalt, costs 50% more than cobalt therapy. This project shows that it is possible to collect data on economic factors prospectively as well as retrospectively.

222 poster Conformal radiotherapy of prostate lesions using a cobalt unit with customised beam portals and adjacent MSCT imaging: a feasibility study

222 poster Conformal radiotherapy of prostate lesions using a cobalt unit with customised beam portals and adjacent MSCT imaging: a feasibility study

Long-term safety of orbital radiotherapy for Graves' ophthalmopathy.

We investigated the long-term side-effects of orbital radiotherapy (OR) in 204 patients with Graves' ophthalmopathy (GO), irradiated from 1972-1996 [44 by cobalt unit (CU) and 160 by linear accelerator (LA), mostly combined with glucocorticoids], with a 5- to 25-yr follow-up (median, 11 yr). Cataract was observed in 21 patients (10%) 3-21 yr after OR, with a higher (not significant) prevalence in CU-treated patients (18% vs. 8% in LA-treated patients). The prevalence of cataract was higher, although not significantly, in CU-treated patients aged less than 60 yr, but not in LA-treated patients, compared with the general population. Mild, asymptomatic retinopathy was observed in 1 of 7 patients (14%) with diabetes and hypertension, in 1 of 31 patients (3%) with hypertension alone, and in 0 of 11 patients with diabetes alone. No tumors were observed in 157 patients submitted to computed tomography scan of orbital and adjacent regions. In conclusion, OR is a safe treatment, not associated with an increased frequency of cataract, provided a high voltage apparatus is used. Hypertension, especially if associated with diabetes, may represent a relative contraindication, as it may cause retinopathy. Although no secondary tumors were detected, due to the long latency of radiation-induced tumors, OR should be restricted to patients older than 35 yr.

Synthesis and characterization of porphyrin-trisbenzimidazole dinucleating ligand and its heterodinuclear complex as CcO active site model

A new dinucleating ligand having two metalbinding sites has been designed and synthesized as model ligand for Cytochrome c Oxidase. The corresponding heterodinuclear complex, as an active site model of Cytochrome c Oxidase, consisting of a porphyrinatocobalt compound covalently linked with a copper derivative of tris(2-benzimidazylmethyl) amine bearing three benzimidazole ligands for copper was synthesized and spectroscopically characterized. The spectra data suggest that there are interactions between the cobalt and copper coordination units. The cobalt is coordinated to four central nitrogens of the porphyrin and the copper has pentacoordinate geometry with the four tertiary amine nitrogens and a chloride.

Infrastructure of radiotherapy in Spain: A minimal standard of radiotherapy resources

Purpose To assess the state of our specialty, the Spanish Society of Radiotherapy and Oncology ordered a survey of all Spanish services of radiation oncology. Methods and materials In June 1999, the Society ordered an analysis of the state of radiation oncology. It created a survey that was sent to all radiotherapy units in Spain. A database was created in which 230 variables were analyzed. Results Eighty-four centers were analyzed, and 157 external beam irradiation, megavoltage units were counted, of which 67 were cobalt units and 90 were linear accelerators. The cobalt units worked an average of 11.4 h daily and the linear accelerators 11.6 h. The number of patients/unit/y was 472 for the cobalt units and 442 for the linear accelerators. The number of patients by physician and year was 179. Each center received a mean of 958 new patients annually. The average between the reception and start of treatment was 25.52 days (maximum 60), and it was estimated that only 38.1% of cancers were irradiated. The number of radiation oncologists working was 392. Spain has a deficit of 297 radiation oncologists. Conclusion There is a need for 44 MV units and for the replacement of 67 cobalt units. The present lack of units has had an impact on palliative treatment, which has resulted in pharmacy costs. As long as these instrumental deficiencies are not solved, waiting lists will continue to be inherent to the system. There are also important staff deficiencies, in that about 297 radiation oncologists would be needed to cover the needs.

Organometallic dendrimers based on (tetraphenylcyclobutadiene)cyclopentadienylcobalt modules.

The synthesis and characterization of novel organometallic polyphenylene dendrimers containing 24 or 44 phenyl rings and one cyclobutadiene(cyclopentadienyl)cobalt unit is reported. The dendrimers are made by the convergent CpCo(CO)(2)-mediated dimerization of di- or tetraethynyltolanes followed by a divergent core extension utilizing tetraphenylcyclopentadienone. The obtained dendrimers are air and water stable, soluble materials that show interesting differences in their hydrodynamic properties as evidenced by gel permeation chromatography. Scanning pulse voltammetry in solution shows that the dendrimers are oxidized at potentials ranging from 0.8 to 0.83 V. The more sterically encumbered the dendrimer, the higher its oxidation potential, that is, the more difficult oxidation is.

Dependence of the Risk of Encephalopathy on the Radiotherapy Volume after Combined Surgery and Radiotherapy of Invasive Pituitary Tumours

The effectiveness of radiotherapy in reducing tumour recurrence of pituitary adenomas is well documented. On the other hand, the risk of side effects to the surrounding central nervous system normal tissue should not be underestimated. This retrospective study includes 58 patients with subtotally resected pituitary tumours. Photon from a 5,7 MV linear accelerator of a 60 cobalt unit with a source-isocenter distance of 80 cm were used throughout for treatment. The doses per fraction ranged from 45 Gy to 60 Gy. For a direct comparison of the different fractionation schedules, the biological effective total dose with 2 Gy per fraction was calculated for all the different application schemes with doses per fraction longer or smaller than 2 Gy. To do this, a fractionation sensitivity of the normal cerebral tissue by an square / square value of 2 Gy was assumed. Encephalopathy developed in 17 cases (28 percentage) after follow-up times of more than 5 years. Pathological CT- or MRI-findings were seen in 13 cases. Two factors were important for the genesis of radiogenic encephalopathy: 1. Multivariate analysis revealed that the risk of encephalopathy was associated with the radiation volume. 2. The location of the upper field border line was the strongest prognostic factor associated with the risk of encephalopathy (p<0.05).

308 poster Workable irradiation with a cobalt unit of head and neck cancer using conformal multisegmental fields for a better non involved tissue sparing

308 poster Workable irradiation with a cobalt unit of head and neck cancer using conformal multisegmental fields for a better non involved tissue sparing

Prise en charge du cancer du sein à Madagascar

Purpose. – Retrospective analysis of management and outcome of breast cancer in Madagascar. Patients and methods. – From January 1996 to December 1998, 259 women with breast cancer were seen in the only department of oncology of the island, located in Antananarivo. It is equipped with a cobalt unit (unavailable in 1996). There was no uniform policy on surgery. Chemotherapy and hormonotherapy were not available for all patients. Reduced equipment enabled a minimal pre-therapeutic workshop. Results. – Mean age was 48.5 years. One hundred and fifty-six women were premenopausal. The majority (69%) lived less than 50 km from the department. Tumours were at an advanced stage in 67% of the cases; the mean delay for diagnosis was 9.4 months. Treatments were done with curative intent in 118 cases and with palliative intent in 64 cases. Partial surgery (89) was adequate in 40.5% of the cases; total mastectomy concerned 94 women. Axillary lymph node dissection was done in 94 cases and was positive in 76 cases. The number of involved nodes was noticed in 47 cases. Curative radiotherapy concerned 106 patients, 41 after total mastectomy and 44 after lumpectomy, and was exclusive in 21 cases. Palliative irradiation was done locally with hypofractionation for 35 patients. Chemotherapy was performed in 86 women. The 4-year survival of the 136 assessable patients was 73%. Conclusion. Improvement in breast cancer treatment outcome in Madagascar is the result of earlier diagnosis of the disease. Information and education of the population together with caregivers are necessary, because updating and improving technical equipment is not currently possible due to the economic problems that the country has to face.

4. An analysis of the doses calculated and measured in-vivo during total body irradiation

Purpose The aim of this work was to estimate the error in dose calculations, to check the agreement between the measured and calculated doses and to analyse dose discrepancies in the group of thirty patients undergoing total body irradiation. Method A group of thirty consecutive patients, children aged from 5 to 12 years, was taken for dose comparison. A combination of lateral and anterior – posterior fields with electron boost was used in eight fractions and on four consecutive days. Cobalt unit was used as a source of radiation. Lung shields were used at two anterior-posterior fields. Compensators were attached at the neck, head and legs. Doses were preliminarily calculated and then measured in-vivo by thermoluminescent (TLD) and semiconductor (SEM) detectors attached to the body in ten representative transverse cross-sections. Calculations and measurements were carried out for the beam at the body entry and exit. The error in dose calculations was estimated for each dosimetrical point. A total dose of 12,6 Gy was prescribed in the body midline on the central beam axis (CAX). A dose of 8.2 Gy was delivered from six lateral fields and a dose of 4,4 Gy from two AP/PA fields. In the lungs dose was below 10 Gy. Lateral fields were set at a source to skin distance (SSD) of 305 cm with the dose rate to midline of 5,9 cGy/min and AP/PA fields were set at 210 cm with 11,5 cGy/min, respectively. A fractional dose specified on CAX and midline was 2.5 Gy during all anterior-posterior fields (from each side), 1.5 Gy (0.75 Gy from each side) during four lateral fields, and 1.1 Gy (0.55 Gy from each side) during two lateral fields. Results The error in the preliminary dose calculations was determined by a total differential method, taking into account of the accuracy of determining the following parameters: SSD, body thickness and contour, the thickness of compensators, lung shields, filter shape, lung dimensions and body density, where applicable. Calculations were done separately for each cross-section and for the beam entry and exit. The values of this error were rounded up to 3% for CAX, from 5% to 10% for head, neck, shoulders, abdomen, elbows, wrist, knee and feet and increased to 15% for lung at AP/PA fields. Per cent deviations for hole group of patients for lateral and AP/PA fields (on entry and exit) were below 10% (TLD and SEM detectors) with the exceptions for the neck at lateral and for the lungs at AP/PA fields where the errors exceeded 10%. Conclusions For the group of patients the per cent deviations exceeded 10% for the neck exit in lateral fields and for the lung exit in anterior – posterior fields. Standard deviations exceeded 10% at the neck and lung exits in lateral fields and at the lung exit in anterior – posterior fields.

Design, construction, and performance of an asymmetrical collimator for a cobalt unit

Purpose: Besides four linear accelerators, our institute has a 100-cm SAD cobalt unit which has some specific and useful features for radiotherapy. The unit is equipped with a electronic portal imaging device (EPID) and an asymmetrical collimator to perform similar treatment techniques as on the linear accelerators, using the same shielding and half-beam techniques. The design, construction, and performance of the asymmetrical collimator are described. Methods and Materials: The new design includes the doubling of the drive and read-outs for both X and Y jaws. Spare parts of the standard collimator provided by the manufacturer were used as much as possible. Special trimmers were designed to allow asymmetry to the center of the field. The trimmers are removable, but the design allows the use of trimmers, wedges, and shadow tray simultaneously. Results: Transmission through the trimmers is less than 5% of the dose at d max. The use of the trimmers extends the source to diaphragm distance to 53 cm, resulting in a smaller penumbra as compared to the standard collimator. Without the trimmers, the maximum field size remains unchanged, i.e., 40 × 40 cm 2; with the trimmers, it is 38 × 36 cm 2. Percentage depth doses and output factors were similar to the standard collimator. Conclusion: The modified collimator is compact and allows use of the same shielding blocks as the linear accelerators, providing the same treatment techniques and capabilities. This simplifies an exchange of patients between our treatment machines.

A novel weakly diatropic dehydroannulene containing the cyclobutadiene(cyclopentadienyl)cobalt unit. An organometallic dehydroannulene that obeys Hückel's rule

This contribution describes the synthesis of novel dehydrobenzannulenes containing CpCo-stabilized cyclobutadiene complexes. These dehydrobenzannulenes were made in two different ways. The first access involves a shotgun approach in which 1,2-diethynyl-3,4-bistrimethylsilylcyclobutadiene(cyclopentadienyl)cobalt and 1,2-diiodobenzene are reacted under Heck-type conditions utilizing (PPh 3) 2PdCl 2 as catalyst. The formation of a dimeric dehydrobenzannulene containing two benzene rings, two cyclobutadiene units and four alkyne units — even though in low yield — was observed. The second approach to organometallic dehydroannulenes involves the construction of a precursor by coupling 1,2-diethynyl-3,4-bistrimethylsilylcyclobutadiene(cyclopentadienyl)cobalt to 1-bromo-2-trimethylsilylethynylbenzene under Pd catalysis, deprotection and Vögtle coupling of the formed precursor to furnish the corresponding monomeric cycle in high yield. This cycle has been characterized by X-ray single-crystal analysis.

External Beam Irradiation as an Adjunctive Treatment in Failing Dialysis Shunts

To evaluate the utility of low-dose irradiation as adjunctive treatment for failing dialysis shunts related to stenoses. Thirty-one patients with 41 lesions in their dialysis shunts were successfully enrolled for this study. After imaging of the shunt and calculation of venous stenoses, each patient was randomized into one of two segments of the protocol: (i) angioplasty and/or stent placement alone, and (ii) angioplasty and/or stent placement followed by external beam irradiation. All patients with significant venous stenoses (> or =50%) were treated with appropriately sized PTA (percutaneous transluminal angioplasty) and Wallstents. Patients randomized to the external irradiation segment underwent localized irradiation via a Theratron cobalt unit of 7 Gy 0-24 hours and 24-48 hours after intervention. Those patients randomized to the control group received no additional treatment. Clinical follow-up included resumption of successful dialysis with appropriate hemodynamic parameters. Two follow-up shunt images were obtained, follow-up 1 (fu-1) from 90 to 179 days and follow-up 2 (fu-2) from 180 to 365 days. Percentages of significant recurrent stenoses, defined as greater than 50%, were recorded and re-treated as needed. Sixteen of the 31 patients underwent external beam irradiation. There were 21 lesions in the test group that underwent irradiation after intervention, and 20 lesions were treated with intervention alone. There were seven native arteriovenous fistulas and 24 Gore-tex grafts. All stenoses were either venous outflow stenoses (68%) or central stenoses (32%). The authors utilized chi2 analysis to compare restenoses rates between the control and irradiated groups at fu-1 (P<.99) and fu-2 (P<.10). Although the results show that external beam irradiation has minimal effects on the restenoses of dialysis grafts when used in conjunction with PTA and stent placement, further studies with a larger, more homogenous population are needed to assess the trend of improving patency rates after external beam irradiation.

Total body irradiation before bone marrow transplantation. Technique and acute toxicity.

To evaluate the total body irradiation methods in the National Institute of Oncology between January 1984 and February 1998. One hundred and twenty-four patients underwent total body irradiation prior to bone marrow transplantation in the last 15 years. A special cobalt unit has been used, the dose rate was 6 to 8 cGy/min in the midline of the abdomen. The source-midline distance (SMD) was 340 cm and the field size was 80 x 200 cm. The dose calculation was done on the basis of a tissue-phantom ratio curve measured in total body irradiation conditions and effective tissue thickness (ETT). Between 1984 and 1992 the beam direction was horizontal, the patients laid in lateral position. In 11 cases the total dose to the abdominal midline was 10 Gy in 1 fraction. From 1986 the fractionation changed to 4 x 3 Gy in 4 days. Within individual lung shielding the average lung dose was 8.5 Gy. In 44/124 cases the order of conditioning treatment was chemo-radiotherapy. Since 1992 vertical beams were used, and the patients (80/124) laid in prone/supine position. The fractionation remained the same but radio-chemotherapy regime has been used. The irradiation in prone position proved to be safer than lateral because of smaller patient motion and it resulted in a more accurate positioning of lung shielding too. In all cases, the acute side effects (headache, nausea, vomiting) were moderate. Using radio-chemotherapy the acute side effects during the total body irradiation were uncommon and well tolerable. Our technique with the large source-midline distance, vertical beam direction and the supine/prone position is stable, convenient and safe to produce homogeneous dose distribution and ensures accurate and reproducible lung shielding.

In vivo radiosensitizing effect of the adenovirus E1A gene in murine and human malignant tumors.

The adenovirus E1A gene is a potent inducer of chemosensitivity and radiosensitivity through p53-dependent and independent mechanisms. We have studied the sensitivity of murine (MSC11A5, a sarcomatoid epidermoid carcinoma) and human (HeLa, human cervix carcinoma) E1A-expressing tumors, in vivo, after treatment with cisplatin or gamma-irradiation. In athymic mice, half-body irradiation was performed in an AECL Cobalt unit, at an SSD of 80 cm. Daily fractions of 300 cGy over 3 days, up to a total dose of 9 Gy. Cisplatin was injected intraperitoneally at a dose of 9 mg per kg of body weight. After gamma-irradiation or intraperitoneal injection of cisplatin, about 30% of the E1A-expressing tumors regressed completely or were associated with a marked decrease in tumorigenicity over the following weeks. We conclude that malignant tumors, when expressing adenovirus E1A, are very sensitive to treatment with DNA-damaging agents, in vivo, regardless of the p53 status of the tumors.

Synthesis and Structural Characterization of Novel Organometallic Dehydroannulenes with Fused CpCo-Cyclobutadiene and Ferrocene Units Including a Cyclic Fullerenyne Segment

The synthesis of fused organometallic dehydroannulenes containing cyclobutadiene(cyclopentadienyl)cobalt or ferrocene units separated by butadiyne linkers is presented. Starting from the corresponding 1,2-diethynylated sandwich complexes, either Eglinton, Hay, or Vögtle-type coupling furnishes the desired dehydroannulenes. The choice of the coupling variant is critical for the success of this reaction. It was found that for diethynylferrocene a variant of the classic Eglinton system utilizing a Cu2Cl2/CuCl2 mixture in pyridine works successfully, while for the case of the cyclobutadiene(cyclopentadienyl)cobalt complexes the Vögtle coupling utilizing Cu(OAc)2 in acetonitrile gave the most impressive results, leading to a 87% yield of cyclized material. To obtain perethynylated organometallic dehydroannulenes, a novel synthesis of tetraethynylated cyclobutadiene complexes was developed. Flash vacuum pyrolysis of a bisbutadiynylated CpCo-ligated cyclobutadiene furnishes the desired tetraethynylated cyclobutadiene complex via a Bergman-type rearrangement. The two TMS and two TIPS substituents of the cyclobutadiene complex are oriented pairwise ortho with respect to each other. Removal of the TMS groups accesses a monomer, which under the conditions of the Vögtle coupling cyclizes to novel trimeric and tetrameric, perethynylated, cyclobutadieno fused, organometallic dehydroannulenes.

Feasibility of external beam radiation for prevention of restenosis following balloon angioplasty

Purpose: Brachytherapy has been shown to inhibit neointima formation after vascular balloon injury. This study was done to test the feasibility of low dose external radiation for prevention of restenosis in a non-stented balloon injury model. Materials and Methods: Twelve red Duroc swine underwent balloon overdilation injury of both iliac arteries. Twelve Gy was delivered to one side using a Theratron T-1000 Cobalt unit with the other side used as the control. Twelve weeks post injury arteriograms were performed. The animals were then sacrificed and iliac arteries explanted. Histomorphometric analysis of arterial cross sections was performed. Results: Neointima formation was observed in all arteries. Unilateral thrombosis was noted in two animals. The mean neointimal thickness in the radiated and control arteries was 0.63 ± 0.17 mm and 0.72 ± 0.31 mm, respectively. The differences in minimal luminal diameter and the neointimal thickness between the two groups were not statistically significant. Complications included superficial hair loss in the radiation port in 4 animals, and 2 deaths prior to the completion date (1 of hemorrhagic enteritis possibly related to the radiation, and 1 of iliac rupture). Conclusion: External radiation at this low dose is not effective in preventing vascular restenosis following balloon injury in this animal model.

Viability of an isocentric cobalt-60 teletherapy unit for stereotactic radiosurgery.

The potential for radiosurgery with an isocentric teletherapy cobalt unit was evaluated in three areas: (1) the physical properties of radiosurgical beams, (2) the quality of radiosurgical dose distributions obtained with four to ten noncoplanar converging arcs, and (3) the accuracy with which the radiosurgical dose can be delivered. In each of these areas the cobalt unit provides a viable alternative to an isocentric linear accelerator (linac) as a radiation source for radiosurgery. A 10 MV x-ray beam from a linac used for radiosurgery served as a standard for comparison. The difference between the 80%-20% penumbras of stationary radiosurgical fields in the nominal diameter range from 10 to 40 mm of the cobalt-60 and 10 MV photon beams is remarkably small, with the cobalt-60 beam penumbras, on average, only about 0.7 mm larger than those of the linac beam. Differences between the cobalt-60 and 10 MV radiosurgical treatment plans in terms of dose homogeneity within the target volume, conformity of the prescribed isodose volume to the target volume, and dose falloffs outside the target volume are also minimal, and therefore of essentially no clinical significance. Moreover, measured isodose distributions for a radiosurgical procedure on our Theratron T-780 cobalt unit agreed with calculated distributions to within the +/- 1 mm spatial and +/- 5% numerical dose tolerances, which are generally specified for radiosurgery. The viability of isocentric cobalt units for radiosurgery will be of particular interest to centers in developing countries where cobalt units, because of their relatively low costs, provide the only megavoltage source of radiation for radiotherapy, and could easily and inexpensively be modified for radiosurgery. Of course, the quality assurance protocols and mechanical condition of a particular teletherapy cobalt unit must meet stringent requirements before the use of the unit for radiosurgery can be advocated.