| 1. |
- Karlsson, Mikael, et al.
(författare)
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Matching of electron and photon beams with a multi-leaf collimator
- 1993
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 29:3, s. 317-326
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Tidskriftsartikel (refereegranskat)abstract
- Multi-leaf collimators (MLCs) are offered as an accessory to many accelerators for radiation therapy. However, beam edges generated with these collimators are not as smooth as can be achieved with individually made blocks. The clinical drawbacks and benefits of this ripple were evaluated both for single field treatments and for combined adjacent fields of different beam qualities. In this investigation the MLC-collimated beams of the MM50 racetrack microtron were studied. The distance between the field edge and the 90% isodose was measured at the reference depth for four beam qualities (20 MV photons and 10, 20 and 50 MeV electrons). This distance was found to vary from approximately 6 mm for straight beam edges (i.e., all collimator leaves aligned) to approximately 2 mm from the tip of the leaves for a saw-tooth shaped beam edge. The over- and under-dosage in the joint between combined adjacent fields was found to be typically +/- 10% in small volumes. Improved clinical techniques using adjacent photon and electron fields with the same isocentre and source position (without moving the gantry) have been developed. For treatments of the breast, including the mammary chain, a uniform dose distribution was created with special attention given to the irradiation of the heart and lung outside the target volume. A method for head and neck treatments was optimised to give uniform dose distribution in the joint between the photon and electron fields and a method of treating the mediastinum, including the chest wall in front of the left lung, was analysed with respect to dose uniformity in the tumour and shielding of the lung.
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| 2. |
- Olsson, L E, et al.
(författare)
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Three-dimensional dose mapping from gamma knife treatment using a dosimeter gel and MR-imaging
- 1992
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Ingår i: Radiotherapy and Oncology. - 0167-8140. ; 24:2, s. 6-82
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Tidskriftsartikel (refereegranskat)abstract
- A new method has been investigated for the mapping of dose distributions in three dimensions delivered by the Leksell gamma knife. The irradiation unit is used to selectively treat small volumes in the brain with single high doses of ionising radiation--a treatment procedure known as radiosurgery. The dosimetry method investigated utilises a dosimeter gel consisting of ferrous sulphate solution and agarose which is, prior to irradiation, loaded into a cavity in a spherical phantom. Chemical changes induced in the gel by the radiation are measured by means of an MR-scanner. This imaging method permits rapid evaluation of the dose distribution in an irradiated volume. It thus offers a potential verification of individual radiation intracranial target treatment regimes as well as quality assurance measurements, assuming that the precision and accuracy of the dose mapping are adequate. The dose and its distribution registered by the gel dosimeter, in this initial experiment, are in good agreement with corresponding computed data obtained with the KULA treatment planning system of the gamma knife. The gel has thus the potential of being an attractive alternative dose mapping method to those used at present in radiosurgery, i.e. radiographic film and small ionisation chambers. The precision of the dosimeter gel is, however, not yet sufficient high to be used as a basic dosimetry system for the gamma knife.
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| 3. |
- Bergquist, Jonas, et al.
(författare)
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Structure-activity relationships for unsaturated dialdehydes 8( *). Comparative effects of 10 sesquiterpenoids on the sea urchin gamete fertilization.
- 1993
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Ingår i: Toxicology in Vitro. - 0887-2333 .- 1879-3177. ; 7:3, s. 205-12
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Tidskriftsartikel (refereegranskat)abstract
- The effects of 10 sesquiterpenoids with unsaturated dialdehyde functionalities were studied on fertilization, first cleavage, and calcium permeability of egg membranes of sea urchin gametes. Fertilization was inhibited by nine compounds when sperm was exposed and by five compounds when eggs were exposed (50 mug/ml for 5 min). All compounds except one (9alpha-hydroxymerulidial) inhibited the first cleavage in a dose-response manner. Only one compound (velleral) increased the Ca(2+) permeability of egg membranes at 20 mug/ml. All compounds reduced to a varying extent the ATP-driven Ca(2+) sequestration by non-mitochondrial intracellular compartments. In general, when hydroxylated and non-hydroxylated derivatives of the compounds are compared, the hydroxylated ones present a lower toxicity when measuring fertilization and cleavage inhibition, and reduction of intracellular Ca(2+) sequestration.
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| 4. |
- Burnet, N G, et al.
(författare)
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The relationship between cellular radiation sensitivity and tissue response may provide the basis for individualising radiotherapy schedules.
- 1994
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Ingår i: Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. - 0167-8140. ; 33:3, s. 228-38
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Tidskriftsartikel (refereegranskat)abstract
- There is a wide variation in normal tissue reactions to radiotherapy and in many situations the severity of these reactions limits radiotherapy dose. Clinical fractionation studies carried out in Gothenburg have demonstrated that a large part of the spectrum of normal tissue reactions is due to differences in individual normal tissue sensitivity. If this variation in normal tissue reactions is due to differences in intrinsic cellular radiosensitivity, it should be possible to predict tissue response based on measurement of cellular sensitivity. Here we report the initial results of a study aimed at establishing whether a direct relationship exists between cellular radiosensitivity and tissue response. Ten fibroblasts strains, including four duplicates, were established from a group of patients in the Gothenburg fractionation trials who had received radiotherapy following mastectomy. Skin doses were measured and both acute and late skin changes were observed following radiotherapy. Right and left parasternal areas were treated with different dose fractionation schedules. Clonogenic assays were used to assess intrinsic cellular radiosensitivity, and all experiments were carried out without prior knowledge of the clinical response, or which strains were duplicates. Irradiation was carried out using 60Co gamma-rays at high dose-rate (HDR) of 1-2 Gy/min and low dose-rate (LDR) of 1 cGy/min. A spectrum of sensitivity was seen, with SF2 values of 0.17-0.28 at HDR and 0.25-0.34 at LDR, and values of D0.01 of 5.07-6.38 Gy at HDR and 6.43-8.12 Gy at LDR. Comparison of the in vitro results with the clinical normal tissue effects shows a correlation between cellular sensitivity and late tissue reactions, which is highly significant with p = 0.02. A correlation between cellular sensitivity and acute effects was noted in the left-sided parasternal fields, but not the right. This is thought to be coincidental, and without biological significance. Our results suggest that cellular sensitivity might form the basis for the development of an assay system capable of predicting late normal tissue effects to curative radiotherapy, which might allow dose escalation in some patients. Increased local control and cure, with unchanged or improved normal tissue complications, could result from such individualised radiotherapy prescriptions.
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| 5. |
- Ceberg, Crister, et al.
(författare)
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Neutron capture imaging of 10B in tissue specimens
- 1993
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Ingår i: Radiotherapy and Oncology. - 1879-0887. ; 26:2, s. 139-146
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Tidskriftsartikel (refereegranskat)abstract
- Boron Neutron Capture Therapy (BNCT) is an attractive concept for radiation treatment of malignant tumours. The patients receive a 10B-carrying compound with selective uptake in tumour cells, after which they are irradiated with epithermal neutrons. Theoretically, the tumour cells are killed by the high-LET particles produces in 10B(n, alpha)7Li reactions inside or close to the cell nucleus, while healthy brain cells with no boron uptake will be spared. In practice, a successful BNCT depends on the actual boron-distribution in the tissue, and consequently a new boron-compound aimed for BNCT must undergo detailed bio-distribution studies before clinical trials. In experimental work there is accordingly a great need for methods for quantitative bio-distribution measurements in tissue samples. In this paper we present an improved technique for neutron activated autoradiography providing quantitative boron images of freeze-sectioned tissue specimens from highly malignant rat brain gliomas. Particular attention has been paid to the correlation with the morphology of the specimens and to the altered self-absorption properties due to freeze-drying. A self-absorption correction factor for tumour tissue has been experimentally determined.
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| 6. |
- Nyman, Jan, 1956, et al.
(författare)
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Basal cell density in human skin for various fractionation schedules in radiotherapy.
- 1994
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Ingår i: Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. - 0167-8140. ; 33:2, s. 117-24
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the epidermal basal cell density (BCD) in human skin were determined during and immediately after fractionate radiotherapy. The basal cells are one of the target cell types responsible for acute skin reactions and measuring the BCD is a histological method for studying the time course and degree of reaction. Thirty-two patients with breast cancer participated in this study. They received postmastectomy radiotherapy to the thoracic wall. A 3-mm punch biopsy was taken from the irradiation field once a week for 6-10 weeks and the linear basal cell density was determined. Standard fractionation at two different dose levels (40 and 50 Gy) as well as hypofractionation and accelerated treatment have been investigated. For the first 3 weeks we found a constant decline in the BCD (about 0.8%/day), independent of dose and fractionation schedule. Using the nadir value as endpoint we found a dose-response relationship between 40 and 50 Gy, and for total effect (TE)-values in the range 430-1015. Compared to standard fractionation, hypofractionation showed somewhat less effect and accelerated fractionation showed significantly less effect. The reduced effect of accelerated fractionation is interpreted as a result of lack of cell cycle redistribution of cells between the two daily fractions in this type of tissue. The removal rate of dead or doomed cells could also affect the results for schedules with different overall time. The results of BCD were also compared to erythema.(ABSTRACT TRUNCATED AT 250 WORDS)
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