| 1. |
- Weber, Lars, et al.
(författare)
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Verification of a dynamic wedge implementation in a pencil beam based dose planning system
- 1995
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 1879-0887 .- 0167-8140. ; 37:Suppl. 1, s. 26-26
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Tidskriftsartikel (refereegranskat)abstract
- The use of dynamic movements on linear accelerators during irradiation have found a revised interest lately due to the integration of computers to control the linear accelerator. An example of this is the generation of fields that resemble ordinary wedge fields. These fields are produced by moving one of the collimator blocks during irradiation, i. e. dynamic wedges.A pencil beam based system with the possibility of modelling dynamically modulated dose distributions from collimator movement specifications has extensively been investigated. Special interest has been focused on depth doses, profiles and output factors which have been generated by dynamic wedge fields. The data from the treatment planning system has been verified with measurements in water on a Varian 4 MV linear accelerator.The results indicate that calculations accurately predicts the outcome from dynamic wedges without any additional measurements than those used for characterisation of static open beams.
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| 2. |
- Adell, Gunnar, 1953-, et al.
(författare)
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p53 status : an indicator for the effect of preoperative radiotherapy of rectal cancer.
- 1999
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 51:2, s. 169-174
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Rectal carcinoma is a common malignancy, with a history of high local recurrence rates following surgery. In recent years. preoperative radiotherapy and refined surgical technique have improved local control rates.AIM: To investigate the relationship between expression of nuclear p53 protein and the outcome in rectal carcinoma, with and without short-term preoperative radiotherapy.MATERIAL: Specimens from 163 patients from the Southeast Swedish Health Care region included in the Swedish rectal cancer trial between 1987-1990.METHOD: New sections from the paraffin blocks of the preoperative biopsy and the surgical specimen were examined immunohistochemically using a p53 antibody (PAb 1801).RESULT: Expression of nuclear p53 protein was seen in 41% of the tumours. The p53 negative patients treated with preoperative radiotherapy had a significant reduction of local failure compared with the non-irradiated p53 negative patients (P = 0.0008). In contrast, p53 positive patients showed no benefit from preoperative radiotherapy. The interaction between p53 status and the benefit of radiotherapy was statistically significant (P = 0.018).CONCLUSION: Expression of nuclear p53 protein in rectal carcinoma seems to be a significant predictive factor for local treatment failure after preoperative radiotherapy. Further investigations are necessary to select patients for preoperative treatment based on analysis of the preoperative biopsies.
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| 3. |
- Blomquist, M, et al.
(författare)
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Test procedures for verification of an electron pencil beam algorithm implemented for treatment planning
- 1996
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 39:3, s. 271-286
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Tidskriftsartikel (refereegranskat)abstract
- The calculation of an electron dose distribution in a patient is a difficult problem because of the presence of tissue and surface inhomogeneities. Verification of the dose planning system is therefore essential. In this investigation, a novel method is used to evaluate a commercially available system (Helax-TMS), at electron energies between 10 and 50 MeV, both for a conventional treatment unit and an MLC-collimated scanned beam unit with a helium-filled treatment head. First, the experiments were designed to verify the local beam database and some fundamental characteristics of the electron beam calculations. Secondly, a number of generalised situations that would be encountered in the clinical treatment planning were evaluated: oblique incidence, field shaping with multi-leaf collimator, bolus edges, and air cavities. Dose distributions in two generalised anatomical phantoms simulating a neck and a nose were also analysed. The results have, when so possible, been presented as the dose ratio within the 'flattened area' for dose profiles and down to the 'treatment depth' (80% dose level) for depth doses. In the penumbra region and in the dose fall-off region, the comparison has been represented by the distance deviation between calculated and measured dose profiles or depth doses. A new tool, 'volume integration', was used to evaluate the deviations from a more clinical point of view. Most results were within +/-2% in dose for volumes larger than a sphere with a diameter of 15 mm, or +/-2 mm in position. Dose deviations were generally found for oblique incidences and below heterogeneities such as small air cavities and bolus edges in limited volumes.
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| 4. |
- Daşu, Alexandru, et al.
(författare)
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New insights into factors influencing the clinically relevant oxygen enhancement ratio
- 1998
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 46:3, s. 269-277
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND PURPOSE: This paper deals with the variations in the oxygen enhancement ratios that could be observed (OER') when comparing oxic and hypoxic cells in different types of fractionated experiments as a consequence of the non-linearity of the underlying cell survival curves. Calculations have been made of the OER' that would be obtained for fractionated irradiations with a series of small doses to allow the comparison of isoeffective doses in oxic and hypoxic conditions. Two styles of fractionated experiment were modelled. In one, the dose per fraction was kept constant in the oxic and hypoxic arms of the experiment, necessitating more fractions in hypoxia to achieve the same level of cell kill. In the other the number of fractions was kept constant and the fraction size was varied to obtain equal levels of damage. The first is the relevant design for the clinic, whereas the second is the design most commonly used in animal studies. MATERIALS AND METHODS: Three models of the survival curve were used to simulate the response of cells to radiation injury, all based on the linear quadratic model, but with various added assumptions. A simple classical LQ model is compared with two models in which the concept of inducible repair is added. In one of these the induction dose for 'switching on' the more resistant response is assumed to be increased in hypoxia and in the other it is assumed to be independent of the oxygen tension. RESULTS: These calculations show a clear and previously unsuspected dependence of the measured OER' on the design of the fractionated experiment. The values obtained in the clinical and animal types of study differ considerably with all three models. The direction and magnitude of that difference depends critically on the assumptions about the fine structure of the survival curve shape. The authors suggest that the inducible repair version with an oxygen-dependent induction dose is probably the most relevant model. Using this, the measured OER' is reduced at doses around 2 Gy for the clinically relevant design of constant sized fractions to the oxic and hypoxic cells. It may even, in certain model assumptions, fall below unity resulting in an increased sensitivity, not resistance, from the hypoxia. CONCLUSIONS: These calculations indicate the urgent need for more knowledge about the fine structure of the low dose region of the survival curves for human tumour cells and especially for comparisons in the presence and absence of oxygen. The extent of the hypersensitivity at very low doses, the trigger dose needed to induce the repair and its oxygen modification may be dominant factors in determining the response of tumour cells to clinically relevant fractionation schedules.
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| 5. |
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| 6. |
- Karlsson, Mikael, et al.
(författare)
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Exploration of new treatment modalities offered by high energy (up to 50 MeV) electrons and photons
- 1997
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 43:3, s. 303-309
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: A number of deep seated tumours are difficult to treat conformally with photon beams mainly dub to the almost exponential dose decrease with depth. Materials and methods: In order to improve the conformity of these treatments a number of useful characteristics of high energy (above 20 MeV) electron beams of the MM50 Racetrack Microtron have been systematically investigated and clinically applied. Results: A typical characteristic of electron beams with energies up to 20 MeV is the sharp dose fall-off with depth. At higher energies this effect is less pronounced but may be improved by adding a small fraction of photons with a matching dose gradient (wedge). With this technique, high energy electrons can be used close to sensitive organs down to 17 cm depth. Another physical characteristic of high energy electrons is the sharp penumbra at depths down to 4-5 cm and the possibility to use opposed electron beams in order to enhance the dose centrally or near the centre of a body. Skin sparing by delivering a part of the absorbed dose with photons through the same beam portal as the electrons has also been systematically studied. These characteristics of the high-energy electron beams have been utilised in the optimisation of some clinical treatments. Conclusions: Electron beams in this high energy region give increased possibilities to achieve dose conformity. Enhanced conformity can be obtained especially if electrons and photons are combined to augment some specific characteristics of the electron beams.
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| 7. |
- Karlsson, Magnus G, et al.
(författare)
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Semi-conductor detectors in output factor measurements
- 1997
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 42:3, s. 293-296
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: Output factors are generally measured with cylindrical ionization chambers. It was investigated if Si-diodes of p-type instead could be used. The advantage would be the small detector size and the robust construction of the detector. Materials and methods: Two types of diodes were studied, one with a shielding layer of tungsten specially made to reduce the excess response for scattered photons and one standard diode without any extra shielding. The measurements were performed at accelerating potentials between 4 and 50 MV and beam sizes between 4 cm x 4 cm and 40 cm x 40 cm. Results: The results showed that both types of diodes are suitable for measurements of head scatter factors in mini-phantoms. However, the diodes were found inappropriate for measurement of output factors for large fields in extended water phantoms. For small fields (<10 cm x 10 cm) a small detector is advantageous and no errors due to the scatter contribution were seen. Conclusions: An cylindrical ionization chamber is the best choice for output factor measurements in extended water phantoms for large field sizes while diodes are an alternative in small fields. There were negligible differences between the detectors in head scatter measurements in mini phantoms.
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| 8. |
- Rojas, Ana Maria, et al.
(författare)
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Radiosensitisation in normal tissues with oxygen, carbogen and nicotinamide: therapeutic gain comparisons for fractionated X-ray schedules
- 1996
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 39:1, s. 53-64
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Tidskriftsartikel (refereegranskat)abstract
- METHODS: Radiosensitisation with oxygen, carbogen or nicotinamide alone and oxygen or carbogen combined with nicotinamide was compared in early and late responding normal tissues in rodents. X-ray treatments were delivered as single doses or fractionated schedules of 2 fractions in 1 day, 2, 12 and 36 fractions in an overall time of 12 days and 10 fractions in 5 or 12 days. Acute skin reactions, survival of intestinal crypts, breathing rate, reduction in the packed red-cell volume and clearance of 51Cr-EDTA were used as assays of epidermal, gut, lung and renal damage. RESULTS: Relative to air-breathing mice, carbogen or oxygen produced a small, and not always significant, increase in sensitivity (enhancement ratios < or = 1.15) in gut, lung and kidneys; however, in skin a dose enhancement of 1.2-1.3 was observed. The effect of nicotinamide in air, carbogen or oxygen was studied only in lung and gut. The drug produced variable but generally significant increases in radiosensitisation ( < or = 1.26) in all three gases. Relative to treatments in air, enhancement ratios for nicotinamide alone were usually slightly higher than those observed when either carbogen or oxygen were administered without the drug. With all three modifiers (i.e. oxygen, carbogen, nicotinamide alone or for the drug-gas combinations) there was no significant change in the enhancement ratios observed as the number of radiation dose fractions was varied. CONCLUSIONS: Comparisons with fractionated X-ray studies done previously in rodent tumours indicate that a therapeutic benefit, relative to lung, gut and renal damage, would be observed with oxygen or carbogen alone but not with nicotinamide alone. The greatest gain would be achieved with the combination of carbogen and nicotinamide, with which a benefit was observed even relative to epidermal damage. These results indicate that some decrease in normal tissue tolerance could be observed when using these modifiers in clinical radiotherapy and, although small, the appropriate dose reductions should be considered; caution should be exercised especially when carbogen and nicotinamide are used in conjunction with the more radical accelerated schedules.
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| 9. |
- Sjögren, Rickard, et al.
(författare)
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Depth for dose calibration in high energy photon beams
- 1997
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 43:3, s. 311-313
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: The normalisation depth for determination of output factors in photon fields has frequently been the depth of dose maximum. At high energies the contribution from contaminating electrons is significant at dose maximum and is critically dependent on the beam geometry parameters, which is why a larger depth should be preferred. Materials and methods: The effect of electron contamination was studied using a purging magnet to remove charged particles from the treatment head and a helium bag to minimise production between the head and the phantom. Results: A depth of 10 cm was found to be beyond the range of the contaminating electrons for photon energies up to 20 MV (TPR1020 = 0.772). However, at 50 MV (TPR1020 = 0.810) contaminating electrons contribute 2-3% to the absorbed dose at 10 cm depth. Conclusions: 10 cm is recommended as both reference and normalisation depth for all megavoltage photon beam qualities, i.e. Co-60 and X-rays from accelerators up to 50 MV. (C) 1997 Elsevier Science Ireland Ltd.
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| 10. |
- Tilly, Nina, et al.
(författare)
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In vitro determination of toxicity, binding, retention, subcellular distribution and biological efficacy of the boron neutron capture agentDAC-1
- 1996
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 38:1, s. 41-50
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Tidskriftsartikel (refereegranskat)abstract
- In boron neutron capture therapy (BNCT), 10B is delivered selectively to the tumour cells and the nuclide then forms high-LET radiation (4He2+ and 7Li3+) upon neutron capture. Today much research is focused on development of a variety of boron compounds aimed for BNCT. The compounds must be thoroughly analysed in preclinical tests regarding basic characteristics such as binding and subcellular distribution to enable accurate estimations of dose-modifying factors. DAC-1,2-[2-(3-amino-propyl)-1,2-dicarba-closo-dodecaboran (12)-1-yl-methoxy]- 1,3-propanediol was synthesized at our laboratories and the human colon carcinoma cells LS-174T were used as an in vitro model. The boron compound showed a remarkable intracellular accumulation, 20-100 times higher than the boron content in the culture medium, in cultured cells and was not removed by extensive washes. Approximately half of the boron taken up also remained within the cells for at least 4 days. The DAC-1 compound alone was not toxic at boron concentrations below 2.5 micrograms B/g. The intracellular distribution of the boron compound was investigated by subcellular fractionation experiments and low pH treatments. It is possible that DAC-1 binds to some intracellular molecules or to membranes connected with organelles in the cytoplasm or even to the inside of the outer cell membrane. Another possibility is that the compound, due to the somewhat lipophilic properties, is embedded in the membranes. Thermal neutron irradiations were carried out at the Brookhaven Medical Research Reactor (BMRR). At a survival level of 0.1, DAC-1 + thermal neutrons were about 10.5 times more effective in cell inactivation than the thermal neutrons alone. Monte Carlo calculations gave a mean value of the 10B-dependent specific energy, the dose, of 0.22 Gy. The total physical dose during irradiation of DAC-1-containing cells with a neutron fluence of 0.18 x 10(12) n/cm2 was 0.39 Gy. The dose-modifying factor, at survival level 0.1, when comparing irradiation with thermal neutrons with and without DAC-1 was 3.4, while the dose-modifying factor when comparing neutron irradiations of cells with DAC-1 and irradiation of the cells with 60Co-gamma was 7.3. The results are encouraging and in vivo tests of tissue distributions and tumour uptake should now be carried out.
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