anders brahme - Profile on Academia.edu (original) (raw)
Papers by anders brahme
Optimal setting of multileaf collimators in stationary beam radiation therapy
PubMed, Jun 1, 1988
The new generation of high resolution double focused multileaf collimators is an important step t... more The new generation of high resolution double focused multileaf collimators is an important step towards true three-dimensional radiation treatment techniques. The principal advantages include increased flexibility in beam shaping and dose delivery using static radiation fields as well as the possibility to do conformation therapy employing dynamic computer controlled patient individual collimation in each CT slice and lateral dose plan. Beside the increased efficiency and flexibility and reduced set-up time, it is shown that multileaf collimation will often reduce the treated volume by as much as 20% or more in single fields and more than 30% when multiple fields are used instead of ordinary rectangular fields. When compared to conventional beam blocks the greater simplicity and flexibility will probably increase the use of individualized blockings by about the same percentages. The optimal rotation and setting of a multileaf collimator for static radiation fields is derived both for convex and for convex concave target volumes. Generally, the smallest cross-section or diameter of the target should be aligned with the direction of motion of the leaves.
The Narrow Proton Beam Therapy Unit at the Svedberg Laboratory in Uppsala
Acta Oncologica, 1991
The synchrocyclotron at the The Svedberg Laboratory (TSL) in Uppsala is now reconstructed and can... more The synchrocyclotron at the The Svedberg Laboratory (TSL) in Uppsala is now reconstructed and can presently operate with fixed frequency and proton energies up to 100 MeV. A first treatment room with a narrow proton beam unit for therapy of eye tumours is now in operation. Therapy of eye melanomas started in April, 1989 and during 1989 and 1990, 19 patients were treated with 72 MeV protons. The narrow beam unit provides a fixed horizontal beam and the patient is treated in a seated position. The present paper describes mainly the technical aspects of the unit which so far has been used only for eye melanomas. In the future, modifications of the unit will allow therapy of intracranial targets when higher proton energies are available. In its final form, the proton therapy facility at TSL will harbour a second treatment unit. Here a rotating gantry for 200 MeV protons will provide a broad beam, which will enable treatment of tumours located anywhere in the body.
Contamination of high-energy photon beams by scattered photons
PubMed, Mar 1, 1981
Absorbed dose and energy distribution of scattered photons that contaminate high-energy photon be... more Absorbed dose and energy distribution of scattered photons that contaminate high-energy photon beams have been calculated for 6-MV and 21-MV bremsstrahlung sources using the Monte Carlo method. The percentage of the absorbed dose at the central axis is less than 3%. The results show that the main sources of scattered photons are the primary collimator for 6-MV and the flattening filter for 21-MV bremsstrahlung sources respectively. The absorbed dose from the phantom scattered photons has been calculated by a semi-empirical method. These calculations show that the dominating contribution to the absorbed dose outside the primary beam is due to these phantom scattered photons. In the surface region of the phantom, however, electrons from the air and collimators may give rise to a high absorbed dose.
Recent Developments in Radiation Therapy Planning
ABSTRACT
Physics in Medicine and Biology, Apr 1, 1992
New radiobiological models are used to describe tumour and normal tissue reactions and to account... more New radiobiological models are used to describe tumour and normal tissue reactions and to account for their dependence on the irradiated volume and inhomogeneities o f the delivered dose distribution and cell sensitivity. The probability of accomplishing complication-free tumour control is maximized by an iterative algorithm. The algorithm is demonstrated by applying it to a one-dimensional (ID) tumour model but also to a more clinically relevant 2 0 case. The new algorithm is n-dimensional 50 it could simultaneously optimize the dose delivery in a 3 0 volume and io principle also select the ideal beam orientations, beam modalities (photons, electrons, neutrons, etc) and optimal spectral distributions of the corresponding modalities. To make calculation time reasonable, 2 0 -3 0 problems are most practical, and suitable beam orientations are preselected by the choice of irradiation kernel. The energy deposition kernel should therefore be selected in order to avoid irradiation through organs at risk. Clinically established dose response parameters for the tissues of interest are used to make the optimization as relevant as possible to the clinical problems at hand. The algorithm can be used even with a poorly selected kernel because it will always, as far as passible, avoid irradiating organs at risk. The generated dose distribution will be optimal with respect to the spatial distribution and assumed radiobiological properties of the tumour and normal tisues at risk for the kernel chosen. More specifically the probability of achieving tumour control without fatal complications in normal tissues is maximized. In the clinical examples a reduced tumour dose is seen at the border to sensitive organs at risk, but instead an increased dose just inside the tumour border is generated. The increased tumour dose has the effect that the dose fall-off is as steep as possible at the border to organs at risk.
生物学的に最適化された放射線療法の開発 : アポトーシスによる細胞死の最大化 (特集 第4回放医研 国際オープンラボラトリーワークショップ「細胞および分子に及ぼす軽イオンの影響」)
放射線科学, Jul 1, 2009
軽イオン線治療の更なる進化 : 究極の原体照射法 (特集/第1回放医研国際オープンラボ開設記念ワークショップ「放射線治療における技術革新」)
放射線科学, Feb 1, 2009
Iron ii sulfate dosimetry for electrons a reevaluation
8. Electron Beam Monitors
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
In the present context, a monitor is an instrument which gives an indication proportional to cert... more In the present context, a monitor is an instrument which gives an indication proportional to certain parameters of the radiation beam such as electron fluence rate or absorbed dose rate in air at a position in the beam, or absorbed dose rate at some point in the irradiated object. However, many other parameters can be monitored, such as beam uniformity or electron energy. The response of the monitor should, as far as possible, be directly proportional to the parameter of interest in a particular irradiation and the constant of proportionality should be independent of other parameters of the beam. A monitor will not, however, give an absolute value of any parameter of the beam unless the relationship of its response to this parameter has been experimentally established. A further essential property of a monitor is that the necessary information can be ohtained from the heam without causing appreciable perturbation of the beam. A number of different instruments and methods have been used for monitoring electron beams: transmission ionization chambers, secondary electron emission detectors, electromagnetic induction detectors, and sampling, either by ionization chambers, or collection of electrons. Except in the case of sampling, the instruments are placed where the electron beam emerges from the accelerator. This has the advantage of leaving the radiation field free for the disposition of experimental apparatus, samples to be irradiated, or patients. The sampling method involves placing one of these monitors close to the position where the material being irradiated is located. This has the advantage of monitoring at a position close to that part of the beam which is actually being used, instead of the total beam as it emerges from the accelerator. In some circumstances, the response of a monitor used in this way is the best indication of the reproducibility of irradiation conditions at the point of measurement. However, the sampling method must be used together with another method; it gives an indication of only a part of the beam. and important changes occurring in another part of the beam may not be noticed. Only transmission ionization chambers, which are , used in most of the modern high-energy electron generators, will be described here. For the description of other types of electron beam monitors, the reader is referred to the literature, e.g., secondary emiss~on monitors (Tautfest and Fechter, 1955; Taimuty and Deaver, 1961; Vanhuyse et al., 1962; Isabelle and Roy, 1963; Frerejacque and Benaksas, 1964; Karzmark, 1964), induction monitors (Bess and Hanson, 1948; Bess et al., 1959; Grishaev et al., 1960; Bergere et al., 1962;
5. Absorbed Dose Measurement Techniques
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
This section describes systems that are used to carry out both kinds of measurements. The first t... more This section describes systems that are used to carry out both kinds of measurements. The first three systems described, calorimeters, chemical dosimeters and ionization chambers, are those that can be used for the absolute determination of the absorbed dose at a given location, while the last three, liquid ionization chambers. solid-state dosimeters and film dosimetry. are generally used for relative absorbed dose measurements.
Development of High Quality Beams for Uniform and Intensity-Modulated Radiation Therapy
Evaluation of fractionation regimens in stereotactic radiotherapy using a mathematical model of repopulation and reoxygenation
PubMed, Aug 10, 1999
Purpose: Various forms of stereotactic fractionation regimens have been used in the clinic. The p... more Purpose: Various forms of stereotactic fractionation regimens have been used in the clinic. The purpose of this article is to evaluate the influence of the number of fractions on tumor control in stereotactic radiotherapy. Methods: The 50% curative dose (D50) is calculated using a mathematical model of reoxygenation and repopulation. A review of the literature of stereotactic fractionation regimens is also presented. Results: The number of fractions required to achieve the best therapeutic ratio is strongly influenced by the pattern of reoxygenation and the potential doubling time of the tumor. In the case of rapid repopulation, well-oxygenated clonogenic cells present a greater danger than hypoxic cells in a prolonged fractionated treatment schedule. In a slowly growing tumor, repopulation is relatively unimportant and the response is dominated by the pattern of reoxygenation. For a small number of large dose fractions, the potential doubling time and the time interval between fractions have a negligible effect on the D50 values. Conclusion: If a small number of large dose fractions is used in stereotactic radiotherapy and if reoxygenation occurs more efficiently with the passage of time, the therapeutic ratio can be enlarged by a sufficient time interval between fractions.
BioArt: Biologically Optimized 3D In Vivo Predictive Assay-Based Radiation Therapy
WORLD SCIENTIFIC eBooks, Mar 20, 2014
Quantification of the steepness of the dose response relation
PubMed, Aug 1, 1999
Elsevier eBooks, 2014
Both, Bethe, Fermi, Eyges, Yang, Brahme Kempe-Brahme Asadzedeh-Gebäck Angular scattering Bipartit... more Both, Bethe, Fermi, Eyges, Yang, Brahme Kempe-Brahme Asadzedeh-Gebäck Angular scattering Bipartition method Slowing-down equation Spatially and angularly integrated transport equation Figure 1 Overview of different approaches to solving transport theoretical problems. þ . . .
Geometric parameters of clinical electron beams
PubMed, 1983
The influence of different components in the treatment head of a therapy accelerator on the geome... more The influence of different components in the treatment head of a therapy accelerator on the geometric properties of the delivered electron beams have been analysed based on the theory of small angle multiple scattering. The analyses show that it is possible to define and compute the properties of an effective electron source which, when placed in vacuum at some distance from the patient, produces exactly the same electron fluence at the patient as the real beam. The effective source is fully described by three parameters: its angular spread, its radial width and the distance from the patient. A numerical example indicates that the half width of the effective source could be considerable, often as large as 10 cm or more at low energies.
Recent developments in radiation therapy planning and treatment optimization
PubMed, Jun 1, 1996
Radiation therapy of cancer is today going through a very dynamic development with the introducti... more Radiation therapy of cancer is today going through a very dynamic development with the introduction of a large number of new treatment principles, new types of treatment units and new radiobiologically based optimization algorithms for treatment planning. All of these make use of the recent developments in three dimensional tumor diagnostics, molecular biology of cancer, the fractionation sensitivity of different tissues and most recently predictive assays of radiation sensitivity. The most efficient but also least developed area of treatment optimization is to use a few (approximately 3) non uniform radiation beams directed towards the tumor. Today patient individual collimation with beam blocks or multileaf collimators protect organs at risk laterally outside the tumor volume. Non uniform dose delivery also allows protection of normal tissues anterior, posterior and even inside the target volume by shaping the isodoses tightly around the tumor tissues and thereby also allowing longitudinal protection of normal tissues. Some of the most advanced new algorithms are even treating therapy optimization as an inverse problem where the optimal incident beam shapes are determined directly from the location of gross disease, presumed microscopic tumor spread and organs at risk. The optimization is then performed such that the probability, P+, to eradicate all clonogenic tumor cells without severely damaging healthy normal tissues is as high as possible. Already with a few non uniform beams the treatment outcome is within a few percent of what can be achieved with infinitely many co-planar beams in a dynamic mood. With such optimized non uniform treatments it should be possible to improve the treatment outcome by as much as 20% and more, particularly in patients with a local complex spread of the disease or several organs at risk.
Photon scatter kernels for intensity modulating radiation therapy filters
Physics in Medicine and Biology, Nov 14, 2001
The most important beam property while optimizing photon therapy is the ability to modulate the i... more The most important beam property while optimizing photon therapy is the ability to modulate the intensity of the beam. The use of photon absorbers for intensity modulation of beam profiles requires special attention to be paid to the alteration of beam properties due to scatter and spectral changes, in addition to the desired intensity modulation. In this study the influence of photon scatter in high-density filters irradiated with very narrow photon pencil beams was investigated. A simple analytical relation is developed to quantify the contribution by scattered photons. A scatter kernel was derived by convolving the first Compton scatter distribution with an approximate expression for the second-order scattered photons. The calculations were validated experimentally with film dosimetry and also by using Monte Carlo simulations. Results show that the difference in photon scatter estimation by different methods is relatively small when higher order scattering is accounted for. At 6 MV x-rays the agreement is slightly better than that for 18 MV x-rays results. The simple relation presented in this paper can be used to account for the scattered photon contribution in filter optimization codes to deliver biologically or physically optimized intensity modulated treatments.
Fluence and absorbed dose in high energy electron beams
PubMed, 1983
The depth dependence of fluence, vectorial and planar fluence, energy fluence, vectorial and plan... more The depth dependence of fluence, vectorial and planar fluence, energy fluence, vectorial and planar energy fluence and absorbed dose has been calculated in 5 and 20 MeV electron beams in water. The shape of these distributions has been compared with analytic expressions for fluence and absorbed dose and the general mechanisms governing the shape of the depth dose curve have been explained. In particular it is demonstrated that the depth dependence of planar energy fluence and mean energy is very similar, and so is the case for fluence and absorbed dose and primary fluence and absorbed dose from primaries with inclusion of fast secondaries. The results are useful for dosimetry and dose planning in high energy electron beams.
Optimal setting of multileaf collimators in stationary beam radiation therapy
PubMed, Jun 1, 1988
The new generation of high resolution double focused multileaf collimators is an important step t... more The new generation of high resolution double focused multileaf collimators is an important step towards true three-dimensional radiation treatment techniques. The principal advantages include increased flexibility in beam shaping and dose delivery using static radiation fields as well as the possibility to do conformation therapy employing dynamic computer controlled patient individual collimation in each CT slice and lateral dose plan. Beside the increased efficiency and flexibility and reduced set-up time, it is shown that multileaf collimation will often reduce the treated volume by as much as 20% or more in single fields and more than 30% when multiple fields are used instead of ordinary rectangular fields. When compared to conventional beam blocks the greater simplicity and flexibility will probably increase the use of individualized blockings by about the same percentages. The optimal rotation and setting of a multileaf collimator for static radiation fields is derived both for convex and for convex concave target volumes. Generally, the smallest cross-section or diameter of the target should be aligned with the direction of motion of the leaves.
The Narrow Proton Beam Therapy Unit at the Svedberg Laboratory in Uppsala
Acta Oncologica, 1991
The synchrocyclotron at the The Svedberg Laboratory (TSL) in Uppsala is now reconstructed and can... more The synchrocyclotron at the The Svedberg Laboratory (TSL) in Uppsala is now reconstructed and can presently operate with fixed frequency and proton energies up to 100 MeV. A first treatment room with a narrow proton beam unit for therapy of eye tumours is now in operation. Therapy of eye melanomas started in April, 1989 and during 1989 and 1990, 19 patients were treated with 72 MeV protons. The narrow beam unit provides a fixed horizontal beam and the patient is treated in a seated position. The present paper describes mainly the technical aspects of the unit which so far has been used only for eye melanomas. In the future, modifications of the unit will allow therapy of intracranial targets when higher proton energies are available. In its final form, the proton therapy facility at TSL will harbour a second treatment unit. Here a rotating gantry for 200 MeV protons will provide a broad beam, which will enable treatment of tumours located anywhere in the body.
Contamination of high-energy photon beams by scattered photons
PubMed, Mar 1, 1981
Absorbed dose and energy distribution of scattered photons that contaminate high-energy photon be... more Absorbed dose and energy distribution of scattered photons that contaminate high-energy photon beams have been calculated for 6-MV and 21-MV bremsstrahlung sources using the Monte Carlo method. The percentage of the absorbed dose at the central axis is less than 3%. The results show that the main sources of scattered photons are the primary collimator for 6-MV and the flattening filter for 21-MV bremsstrahlung sources respectively. The absorbed dose from the phantom scattered photons has been calculated by a semi-empirical method. These calculations show that the dominating contribution to the absorbed dose outside the primary beam is due to these phantom scattered photons. In the surface region of the phantom, however, electrons from the air and collimators may give rise to a high absorbed dose.
Recent Developments in Radiation Therapy Planning
ABSTRACT
Physics in Medicine and Biology, Apr 1, 1992
New radiobiological models are used to describe tumour and normal tissue reactions and to account... more New radiobiological models are used to describe tumour and normal tissue reactions and to account for their dependence on the irradiated volume and inhomogeneities o f the delivered dose distribution and cell sensitivity. The probability of accomplishing complication-free tumour control is maximized by an iterative algorithm. The algorithm is demonstrated by applying it to a one-dimensional (ID) tumour model but also to a more clinically relevant 2 0 case. The new algorithm is n-dimensional 50 it could simultaneously optimize the dose delivery in a 3 0 volume and io principle also select the ideal beam orientations, beam modalities (photons, electrons, neutrons, etc) and optimal spectral distributions of the corresponding modalities. To make calculation time reasonable, 2 0 -3 0 problems are most practical, and suitable beam orientations are preselected by the choice of irradiation kernel. The energy deposition kernel should therefore be selected in order to avoid irradiation through organs at risk. Clinically established dose response parameters for the tissues of interest are used to make the optimization as relevant as possible to the clinical problems at hand. The algorithm can be used even with a poorly selected kernel because it will always, as far as passible, avoid irradiating organs at risk. The generated dose distribution will be optimal with respect to the spatial distribution and assumed radiobiological properties of the tumour and normal tisues at risk for the kernel chosen. More specifically the probability of achieving tumour control without fatal complications in normal tissues is maximized. In the clinical examples a reduced tumour dose is seen at the border to sensitive organs at risk, but instead an increased dose just inside the tumour border is generated. The increased tumour dose has the effect that the dose fall-off is as steep as possible at the border to organs at risk.
生物学的に最適化された放射線療法の開発 : アポトーシスによる細胞死の最大化 (特集 第4回放医研 国際オープンラボラトリーワークショップ「細胞および分子に及ぼす軽イオンの影響」)
放射線科学, Jul 1, 2009
軽イオン線治療の更なる進化 : 究極の原体照射法 (特集/第1回放医研国際オープンラボ開設記念ワークショップ「放射線治療における技術革新」)
放射線科学, Feb 1, 2009
Iron ii sulfate dosimetry for electrons a reevaluation
8. Electron Beam Monitors
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
In the present context, a monitor is an instrument which gives an indication proportional to cert... more In the present context, a monitor is an instrument which gives an indication proportional to certain parameters of the radiation beam such as electron fluence rate or absorbed dose rate in air at a position in the beam, or absorbed dose rate at some point in the irradiated object. However, many other parameters can be monitored, such as beam uniformity or electron energy. The response of the monitor should, as far as possible, be directly proportional to the parameter of interest in a particular irradiation and the constant of proportionality should be independent of other parameters of the beam. A monitor will not, however, give an absolute value of any parameter of the beam unless the relationship of its response to this parameter has been experimentally established. A further essential property of a monitor is that the necessary information can be ohtained from the heam without causing appreciable perturbation of the beam. A number of different instruments and methods have been used for monitoring electron beams: transmission ionization chambers, secondary electron emission detectors, electromagnetic induction detectors, and sampling, either by ionization chambers, or collection of electrons. Except in the case of sampling, the instruments are placed where the electron beam emerges from the accelerator. This has the advantage of leaving the radiation field free for the disposition of experimental apparatus, samples to be irradiated, or patients. The sampling method involves placing one of these monitors close to the position where the material being irradiated is located. This has the advantage of monitoring at a position close to that part of the beam which is actually being used, instead of the total beam as it emerges from the accelerator. In some circumstances, the response of a monitor used in this way is the best indication of the reproducibility of irradiation conditions at the point of measurement. However, the sampling method must be used together with another method; it gives an indication of only a part of the beam. and important changes occurring in another part of the beam may not be noticed. Only transmission ionization chambers, which are , used in most of the modern high-energy electron generators, will be described here. For the description of other types of electron beam monitors, the reader is referred to the literature, e.g., secondary emiss~on monitors (Tautfest and Fechter, 1955; Taimuty and Deaver, 1961; Vanhuyse et al., 1962; Isabelle and Roy, 1963; Frerejacque and Benaksas, 1964; Karzmark, 1964), induction monitors (Bess and Hanson, 1948; Bess et al., 1959; Grishaev et al., 1960; Bergere et al., 1962;
5. Absorbed Dose Measurement Techniques
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
This section describes systems that are used to carry out both kinds of measurements. The first t... more This section describes systems that are used to carry out both kinds of measurements. The first three systems described, calorimeters, chemical dosimeters and ionization chambers, are those that can be used for the absolute determination of the absorbed dose at a given location, while the last three, liquid ionization chambers. solid-state dosimeters and film dosimetry. are generally used for relative absorbed dose measurements.
Development of High Quality Beams for Uniform and Intensity-Modulated Radiation Therapy
Evaluation of fractionation regimens in stereotactic radiotherapy using a mathematical model of repopulation and reoxygenation
PubMed, Aug 10, 1999
Purpose: Various forms of stereotactic fractionation regimens have been used in the clinic. The p... more Purpose: Various forms of stereotactic fractionation regimens have been used in the clinic. The purpose of this article is to evaluate the influence of the number of fractions on tumor control in stereotactic radiotherapy. Methods: The 50% curative dose (D50) is calculated using a mathematical model of reoxygenation and repopulation. A review of the literature of stereotactic fractionation regimens is also presented. Results: The number of fractions required to achieve the best therapeutic ratio is strongly influenced by the pattern of reoxygenation and the potential doubling time of the tumor. In the case of rapid repopulation, well-oxygenated clonogenic cells present a greater danger than hypoxic cells in a prolonged fractionated treatment schedule. In a slowly growing tumor, repopulation is relatively unimportant and the response is dominated by the pattern of reoxygenation. For a small number of large dose fractions, the potential doubling time and the time interval between fractions have a negligible effect on the D50 values. Conclusion: If a small number of large dose fractions is used in stereotactic radiotherapy and if reoxygenation occurs more efficiently with the passage of time, the therapeutic ratio can be enlarged by a sufficient time interval between fractions.
BioArt: Biologically Optimized 3D In Vivo Predictive Assay-Based Radiation Therapy
WORLD SCIENTIFIC eBooks, Mar 20, 2014
Quantification of the steepness of the dose response relation
PubMed, Aug 1, 1999
Elsevier eBooks, 2014
Both, Bethe, Fermi, Eyges, Yang, Brahme Kempe-Brahme Asadzedeh-Gebäck Angular scattering Bipartit... more Both, Bethe, Fermi, Eyges, Yang, Brahme Kempe-Brahme Asadzedeh-Gebäck Angular scattering Bipartition method Slowing-down equation Spatially and angularly integrated transport equation Figure 1 Overview of different approaches to solving transport theoretical problems. þ . . .
Geometric parameters of clinical electron beams
PubMed, 1983
The influence of different components in the treatment head of a therapy accelerator on the geome... more The influence of different components in the treatment head of a therapy accelerator on the geometric properties of the delivered electron beams have been analysed based on the theory of small angle multiple scattering. The analyses show that it is possible to define and compute the properties of an effective electron source which, when placed in vacuum at some distance from the patient, produces exactly the same electron fluence at the patient as the real beam. The effective source is fully described by three parameters: its angular spread, its radial width and the distance from the patient. A numerical example indicates that the half width of the effective source could be considerable, often as large as 10 cm or more at low energies.
Recent developments in radiation therapy planning and treatment optimization
PubMed, Jun 1, 1996
Radiation therapy of cancer is today going through a very dynamic development with the introducti... more Radiation therapy of cancer is today going through a very dynamic development with the introduction of a large number of new treatment principles, new types of treatment units and new radiobiologically based optimization algorithms for treatment planning. All of these make use of the recent developments in three dimensional tumor diagnostics, molecular biology of cancer, the fractionation sensitivity of different tissues and most recently predictive assays of radiation sensitivity. The most efficient but also least developed area of treatment optimization is to use a few (approximately 3) non uniform radiation beams directed towards the tumor. Today patient individual collimation with beam blocks or multileaf collimators protect organs at risk laterally outside the tumor volume. Non uniform dose delivery also allows protection of normal tissues anterior, posterior and even inside the target volume by shaping the isodoses tightly around the tumor tissues and thereby also allowing longitudinal protection of normal tissues. Some of the most advanced new algorithms are even treating therapy optimization as an inverse problem where the optimal incident beam shapes are determined directly from the location of gross disease, presumed microscopic tumor spread and organs at risk. The optimization is then performed such that the probability, P+, to eradicate all clonogenic tumor cells without severely damaging healthy normal tissues is as high as possible. Already with a few non uniform beams the treatment outcome is within a few percent of what can be achieved with infinitely many co-planar beams in a dynamic mood. With such optimized non uniform treatments it should be possible to improve the treatment outcome by as much as 20% and more, particularly in patients with a local complex spread of the disease or several organs at risk.
Photon scatter kernels for intensity modulating radiation therapy filters
Physics in Medicine and Biology, Nov 14, 2001
The most important beam property while optimizing photon therapy is the ability to modulate the i... more The most important beam property while optimizing photon therapy is the ability to modulate the intensity of the beam. The use of photon absorbers for intensity modulation of beam profiles requires special attention to be paid to the alteration of beam properties due to scatter and spectral changes, in addition to the desired intensity modulation. In this study the influence of photon scatter in high-density filters irradiated with very narrow photon pencil beams was investigated. A simple analytical relation is developed to quantify the contribution by scattered photons. A scatter kernel was derived by convolving the first Compton scatter distribution with an approximate expression for the second-order scattered photons. The calculations were validated experimentally with film dosimetry and also by using Monte Carlo simulations. Results show that the difference in photon scatter estimation by different methods is relatively small when higher order scattering is accounted for. At 6 MV x-rays the agreement is slightly better than that for 18 MV x-rays results. The simple relation presented in this paper can be used to account for the scattered photon contribution in filter optimization codes to deliver biologically or physically optimized intensity modulated treatments.
Fluence and absorbed dose in high energy electron beams
PubMed, 1983
The depth dependence of fluence, vectorial and planar fluence, energy fluence, vectorial and plan... more The depth dependence of fluence, vectorial and planar fluence, energy fluence, vectorial and planar energy fluence and absorbed dose has been calculated in 5 and 20 MeV electron beams in water. The shape of these distributions has been compared with analytic expressions for fluence and absorbed dose and the general mechanisms governing the shape of the depth dose curve have been explained. In particular it is demonstrated that the depth dependence of planar energy fluence and mean energy is very similar, and so is the case for fluence and absorbed dose and primary fluence and absorbed dose from primaries with inclusion of fast secondaries. The results are useful for dosimetry and dose planning in high energy electron beams.