| 1. |
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| 2. |
- Blad, Börje, et al.
(författare)
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The influence of air humidity on an unsealed ionization chamber in a linear accelerator
- 1996
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 41:11, s. 2541-2548
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Tidskriftsartikel (refereegranskat)abstract
- The safe and accurate delivery of the prescribed absorbed dose is the central function of the dose monitoring and beam stabilization system in a medical linear accelerator. The absorbed dose delivered to the patient during radiotherapy is often monitored by a transmission ionization chamber. Therefore it is of utmost importance that the chamber behaves correctly. We have noticed that the sensitivity of an unsealed chamber in a Philips SL linear accelerator changes significantly, especially during and after the summer season. The reason for this is probably a corrosion effect of the conductive plates in the chamber due to the increased relative humidity during hot periods. We have found that the responses of the different ion chamber plates change with variations in air humidity and that they do not return to their original values when the air humidity is returned to ambient conditions.
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| 3. |
- Hansson, H, et al.
(författare)
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Verification of a pencil beam based treatment planning system: output factors for open photon beams shaped with MLC or blocks
- 1999
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Ingår i: Physics in Medicine and Biology. - 1361-6560. ; 44:9, s. 201-207
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Tidskriftsartikel (refereegranskat)abstract
- The accuracy of monitor unit calculations from a pencil beam based, three-dimensional treatment planning system (3D TPS) has been evaluated for open irregularly shaped photon fields. The dose per monitor unit was measured in water and in air for x-ray beam qualities from 6 to 15 MV. The fields were shaped either with a multileaf collimator (MLC) or with customized alloy blocks. Calculations from the 3D TPS were compared with measurements. The agreement between calculated and measured dose per monitor unit depended on field size and the amount of blocking and was within 3% for the MLC-shaped fields. The deviation could be traced to limitations in head scatter modelling for the MLC. For fields shaped with alloy blocks, the dose per monitor unit was calculated to be within 1.6% of measured values for all fields studied. The measured and calculated relative phantom scatter for fields with the same equivalent field size were identical for MLC and alloy shaped fields. These results indicate that the accuracy in the TPS calculations for open irregular fields, shaped with MLC or blocks, is satisfactory for clinical situations.
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| 4. |
- Hurkmans, Coen, et al.
(författare)
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Dosimetric verification of open asymmetric photon fields calculated with a treatment planning system based on dose-to-energy-fluence concepts
- 1996
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 41:8, s. 1277-1290
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Tidskriftsartikel (refereegranskat)abstract
- Output normalized dose profiles for asymmetric open photon fields has been calculated using a commercial treatment planning system (TPS) based on a dose-to-energy-fluence concept. The model does not require any additional measurements for off-axis fields. Calculations are compared with measurements for quadratic fields of 5 cm x 5 cm up to 20 cm x 20 cm, with their geometric field centre positioned 10 cm off-axis in the in-plane direction. The measurements include depth doses and profiles in-plane as well as cross-plane for nominal photon energies of 4, 6 and 18 MV x-rays. Both calculated and measured doses are normalized with respect to a 10 cm x 10 cm reference field, therefore making it possible to compare not only the relative distributions but also the absolute dose levels; that is, calculation of monitor units is included. The calculated depth-dose curves are generally in good agreement with measured data with an accuracy at the absolute dose level of 2% at depths beyond the dose maximum. The cross-plane profiles are calculated with an accuracy better than 3% within the field. The 'tilt' towards the collimator central axis of the in-plane profiles is predicted by the model, but is somewhat overestimated at large depths. The system provides the possibility to separate the primary and scattered parts of the dose and the cause of this tilting was studied by comparing calculated phantom-scattering and head-scattering dose profiles for a symmetric 40 cm x 20 cm field to dose profiles for an asymmetric 20 cm x 20 cm field. The tilting is shown to originate from a change both in phantom scattering and in head scattering compared to the case of symmetrical fields. The results indicate that the investigated TPS can calculate dose distributions in open asymmetric fields with a high degree of accuracy, typically better than 2-3%.
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| 5. |
- Hurkmans, Coen, et al.
(författare)
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Limitations of a pencil beam approach to photon dose calculations in the head and neck region
- 1996
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Ingår i: Medical Dosimetry. - : Elsevier BV. - 1873-4022 .- 0958-3947. ; 21:1, s. 38-38
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Tidskriftsartikel (refereegranskat)abstract
- The inherent limitations of a specific pencil beam model have been studied when applied to a cylindrical geometry simulating the neck region. A comparison is made between measured and calculated absorbed dose in a cylindrical phantom. The goal is to quantify the deviations in the absorbed dose level, i.e., the dose per monitor unit, when photons are used for the treatment of head and neck tumours. Square fields ranging from 5 x 5 up to 30 x 30 cm[super:2] are studied for photon beam energies of [super:60]Co, 4, 6 and 18 MV. Ionisation chamber measurements have been performed in the cylinder as well as in two other configurations in order to trace the origin of possible deviations. For 18 MV no significant deviations are found between measurement and calculation in the cylindrical configuration. For the lower energies, an over-estimation of the calculated dose in the cylindrical configuration up to about 6% for a 20 x 20-cm[super:2] [super:60]Co field has been found. These deviations have been traced to the basic approximation for the integration volume for phantom scatter calculations inherent in this pencil beam implementation.
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| 6. |
- Hurkmans, Coen, et al.
(författare)
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Limitations of a pencil beam approach to photon dose calculations in the head and neck region
- 1995
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Ingår i: Radiotherapy and Oncology. - 1879-0887. ; 37:1, s. 74-80
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Tidskriftsartikel (refereegranskat)abstract
- The inherent limitations of a specific pencil beam model have been studied when applied to a cylindrical geometry simulating the neck region. A comparison is made between measured and calculated absorbed dose in a cylindrical phantom. The goal is to quantify the deviations in the absorbed dose level, i.e., the dose per monitor unit, when photons are used for the treatment of head and neck tumours. Square fields ranging from 5 x 5 up to 30 x 30 cm2 are studied for photon beam energies of 60Co, 4, 6 and 18 MV. Ionisation chamber measurements have been performed in the cylinder as well as in two other configurations in order to trace the origin of possible deviations. For 18 MV no significant deviations are found between measurement and calculation in the cylindrical configuration. For the lower energies, an overestimation of the calculated dose in the cylindrical configuration up to about 6% for a 20 x 20-cm2 60Co field has been found. These deviations have been traced to the basic approximation for the integration volume for phantom scatter calculations inherent in this pencil beam implementation.
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| 7. |
- Johnsson, Stefan, et al.
(författare)
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Transmission measurements in air using the ESTRO mini-phantom
- 1999
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Ingår i: Physics in Medicine and Biology. - 1361-6560. ; 44:10, s. 2445-2450
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work is to study the possibility of using the ESTRO mini-phantom for transmission measurements of primary kerma in water at a point free in air. We discuss in-air measurements in general, with special attention given to in-air equivalent measurements using a water equivalent mini-phantom. The study includes four different photon energies (4, 6, 10 and 18 MV), where scoring of dose and primary kerma inside a mini-phantom in narrow beam geometry is performed with the Monte Carlo code EGS4. The results reveal that relative measurements (i.e. with and without a water absorber present) at 10 cm depth in a mini-phantom do not represent the variation of primary kerma in water at a point free in air (deviations as large as 7% at 4 MV are observed). Minimum deviations are obtained at depths somewhat larger than the depth of dose maximum. The observed deviations are due to a considerable beam hardening in the water absorber, which changes the amount of attenuation and scatter inside the mini-phantom.
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| 8. |
- Kjellén, Elisabeth, et al.
(författare)
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A Phase I/II Evaluation of Metoclopramide as a Radiosensitiser in Patients with Inoperable Squamous Cell Carcinoma of the Lung
- 1995
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Ingår i: European Journal of Cancer. - : Elsevier BV. - 1879-0852 .- 0959-8049. ; 31:13-14, s. 2196-2202
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Tidskriftsartikel (refereegranskat)abstract
- The feasibility of administering metoclopramide (MCA) as a radiosensitizer has been evaluated in 23 patients with a pathological or cytological diagnosis of a squamous cell carcinoma of the lung, clinically evaluated as inoperable. All patients received 40-60 Gy radiotherapy fractionated into 1.8 Gy fractions 5 times per week (Monday-Friday). Two MCA treatment regimens were used: (i) MCA at 2 mg/kg administered by intravenous infusion 1-2 h prior to radiotherapy 3 times per week (Monday, Wednesday, Friday); and (ii) MCA at 1 mg/kg administered by intravenous infusion 1-2 h prior to radiotherapy 5 times per week (Monday-Friday). 11 of the 23 patients treated with radiotherapy and MCA had none to mild pneumonitis or fibrosis and another 8 of the 23 had moderate levels. No patient had their therapy interrupted due to radiation-related side-effects. The MCA-related side-effects were as expected, i.e. 78% of the patients experienced sedation/tiredness and 48% expressed restlessness/anxiety symptoms. Both the total dose and serum levels of MCA were significantly associated to the MCA side-effect profile. Tumour response, duration of tumour response and survival were significantly positively correlated to the total and weekly doses of MCA administered to the patients during their radiotherapy treatment. These favourable phase II data have justified the initiation of a phase II/III randomised multicentred trial being carried out in Europe to evaluate MCA as a radiosensitiser.
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| 9. |
- Knöös, Tommy, et al.
(författare)
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Limitations of a pencil beam approach to photon dose calculations in lung tissue
- 1995
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 40:9, s. 1411-1420
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Tidskriftsartikel (refereegranskat)abstract
- A common limitation in treatment planning systems for photon dose calculation is to ignore the impact on electron transport and photon scatter from patient heterogeneities. The heterogeneity correlation is often based on scaling operations along beam rays as for the method according to Batho or the more novel approach of 1D convolutions along beam paths applied in pencil-beam-based systems. The effects of the limitation have been studied in a mediastinum geometry for a wide range of beam qualities by comparing the results from a pencil-beam-based treatment planning system with the results from Monte Carlo calculations. As expected, the deviations within unit-density volumes are small while deviations in low-density volumes increase with increasing beam energy from approximately 3% for 4 MV to 14% for 18 MV x-rays as a result of increased electron disequilibrium.
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| 10. |
- Knöös, Tommy, et al.
(författare)
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Volumetric and dosimetric evaluation of radiation treatment plans: radiation conformity index
- 1998
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Ingår i: International Journal of Radiation Oncology, Biology, Physics. - 0360-3016. ; 42:5, s. 1169-1176
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The use of conformal radiation therapy has grown substantially during the last years since three-dimensional (3D) treatment planning systems with beams-eye-view planning has become commercially available. We studied the degree of conformity reached in clinical routines for some common diagnoses treated at our department by calculating a radiation conformity index (RCI). METHODS AND MATERIALS: The radiation conformity index, determined as the ratio between the target volume (PTV) and the irradiated volume, has been evaluated for 57 patients treated with 3D treatment plans. RESULTS AND CONCLUSION: The RCI was found to vary from 0.3 to 0.6 (average 0.4), a surprisingly low figure. The higher RCI is typical for pelvic treatments (e.g., prostate) and stereotactic treatments. The lower RCI is found for extended tumors, such as mammary carcinomas where the adjacent nodes are included. The latter is also valid for most lung cancer patients studied. The RCI gives a consistent method for quantifying the degree of conformity based on isodose surfaces and volumes. Care during interpretation of RCI must always be taken, since small changes in the minimum dose can dramatically change the treated volume.
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