anders brahme - Academia.edu (original) (raw)
Papers by anders brahme
Medical radiology, 1995
ABSTRACT
Physics in Medicine and Biology, Apr 29, 2004
The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of th... more The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of the transport of protons and heavier ions in tissue-like media is described. The code SHIELD-HIT, a spin-off of SHIELD (available as RSICC CCC-667), extends the transport of hadron cascades from standard targets to that of ions in arbitrary tissue-like materials, taking into account ionization energy-loss straggling and multiple Coulomb scattering effects. The consistency of the results obtained with SHIELD-HIT has been verified against experimental data and other existing Monte Carlo codes (PTRAN, PETRA), as well as with deterministic models for ion transport, comparing depth distributions of energy deposition by protons, 12C and 20Ne ions impinging on water. The SHIELD-HIT code yields distributions consistent with a proper treatment of nuclear inelastic collisions. Energy depositions up to and well beyond the Bragg peak due to nuclear fragmentations are well predicted. Satisfactory agreement is also found with experimental determinations of the number of fragments of a given type, as a function of depth in water, produced by 12C and 14N ions of 670 MeV u(-1), although less favourable agreement is observed for heavier projectiles such as 16O ions of the same energy. The calculated neutron spectra differential in energy and angle produced in a mimic of a Martian rock by irradiation with 12C ions of 290 MeV u(-1) also shows good agreement with experimental data. It is concluded that a careful analysis of stopping power data for different tissues is necessary for radiation therapy applications, since an incorrect estimation of the position of the Bragg peak might lead to a significant deviation from the prescribed dose in small target volumes. The results presented in this study indicate the usefulness of the SHIELD-HIT code for Monte Carlo simulations in the field of light ion radiation therapy.
IntechOpen eBooks, Jun 6, 2023
The lightest ions beyond protons, principally helium, lithium, and boron ions, make highly specif... more The lightest ions beyond protons, principally helium, lithium, and boron ions, make highly specific molecular Bragg peak radiation therapy of malignant tumors possible with minimal adverse normal tissue reactions. The Bragg peak ionization density is mainly elevated in a few mm wide spot at the end of these ions with substantially increased local apoptosis and senescence induction. Mainly placing Bragg peaks in the gross tumor volume with increased local therapeutic effect and only low ionization density and easily repairable damage in normal tissues. The possible geometrical accuracy of the dose delivery will be ≈1 mm with these ions. Interestingly, high-resolution molecular tumor imaging will then be possible, particularly with 8 Boron ions that are our lightest positron emitter allowing immediate accurate PET-CT imaging to delineate the target volume dose delivery. Compared to carbon ions the boron radiation damage to normal tissues in front of and behind the tumor is reduced at the same time as tumor apoptosis and senescence are increased. A mean tumor cure as high as 80% should be possible with Boron ion therapy using new clinical fractionation principles and even more when early tumor detection and malignancy estimation methods are brought into more regular clinical use.
This presentation briefly covers the ongoing development of a therapy center with multiple simult... more This presentation briefly covers the ongoing development of a therapy center with multiple simultaneous radiation modalities at Karolinska university hospital. The hearth of the facility will most likely be a superconducting cyclotron capable of delivering around 400 MeV/u carbon ions simultaneously to two separate excentric gantries who service four treatment rooms each. A number of different stable ions will be available ranging from hydrogen to oxygen but also PET emitting C11 ions and possibly B8 the lightest existing PET emitter. Several treatment rooms will also be equipped for narrow scanned high energy photon and electron beam treatments and a light ion research facility for physics and biology studies will be set up on two separate beamlines. The centre will include an advanced PET-CT and MRSI based diagnostic centre on the same floor and close to both the ion treatment facility and the high energy photon and electron facility. By docking the stereotactic treatment coach both to the treatment units and before and after the treatment to the diagnostic PET-CT units, iso dose delivery can be rapidly examined by imaging the radiation induced C11 and O15 activity produced during the treatment.
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
6.1 General Each radiotherapy department must have absorbed dose distributions in water available... more 6.1 General Each radiotherapy department must have absorbed dose distributions in water available for each beam quality to be used. Standardized reference absorbeddose distrihntions for a given energy can generally not be used as extensively with electrons as with photon beams, because the shape of electron beam isodose curves can vary considerably between different treatment units. The dose distributions depend on several factors such as the quality of the initial electron beam when it meets the accelerator window and the scattering . and energy degradation in window, foils, transmission chambers, air, etc. These factors may also differ for accelerators of the same type and manufacturer and, therefore, a complete set of absorbed -dose distributions should be measured for each accelerator. All the data supplied by the manufacturer of the accelerator must be checked to confirm their applicability. This usually involves carrying out extensive measurements and must be done with great care. The number of absorbed-dose distributions needed for radiation treatments is often large because several combinations of nominal energies, field sizes, scattering foils, etc. may be used. Therefore, much emphasis must be given to rapid methods of absorbed-dose distribution determinations.
Medical radiology, 1995
ABSTRACT
Radiotherapy and Oncology, Aug 1, 2009
Physics in Medicine and Biology, Apr 29, 2004
The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of th... more The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of the transport of protons and heavier ions in tissue-like media is described. The code SHIELD-HIT, a spin-off of SHIELD (available as RSICC CCC-667), extends the transport of hadron cascades from standard targets to that of ions in arbitrary tissue-like materials, taking into account ionization energy-loss straggling and multiple Coulomb scattering effects. The consistency of the results obtained with SHIELD-HIT has been verified against experimental data and other existing Monte Carlo codes (PTRAN, PETRA), as well as with deterministic models for ion transport, comparing depth distributions of energy deposition by protons, 12C and 20Ne ions impinging on water. The SHIELD-HIT code yields distributions consistent with a proper treatment of nuclear inelastic collisions. Energy depositions up to and well beyond the Bragg peak due to nuclear fragmentations are well predicted. Satisfactory agreement is also found with experimental determinations of the number of fragments of a given type, as a function of depth in water, produced by 12C and 14N ions of 670 MeV u(-1), although less favourable agreement is observed for heavier projectiles such as 16O ions of the same energy. The calculated neutron spectra differential in energy and angle produced in a mimic of a Martian rock by irradiation with 12C ions of 290 MeV u(-1) also shows good agreement with experimental data. It is concluded that a careful analysis of stopping power data for different tissues is necessary for radiation therapy applications, since an incorrect estimation of the position of the Bragg peak might lead to a significant deviation from the prescribed dose in small target volumes. The results presented in this study indicate the usefulness of the SHIELD-HIT code for Monte Carlo simulations in the field of light ion radiation therapy.
Radiotherapy and Oncology, Oct 1, 1995
Electron beams with energies up to 25 MeV are routinely used to treat tumours at a shallow depth,... more Electron beams with energies up to 25 MeV are routinely used to treat tumours at a shallow depth, within the therapeutic range of the electrons. The range of the electrons has conventionally been modulated by the use of a bolus with varialbe thickness, and algorithms for designing the bolus have been developed. The purpose of this work was to investigate the possibility of combining fluence modulated electron beams of different energies to produce dose distributions that would be conformal to the target volumes, so that the dose to the target volume and organs at risk would also be radiobiologically optimized. A new generalized pencil beam algorithm for dose computation and an iterative constrained steepest descent algorithm for optimization were used to find radiobiologically optimized treatment plans by maximizing the propability of achieving tumour control without causing severe complications. Multiple fluence modulated electron beams with different energies but the same direction of incidence were used for superficial target volumes. The full optimization was made by using the energies from 5 MeV to 25 MeV at 5 MeV increments. We also evaluated, how much the dose distributions would differ if optimization were made with only two electron energies. In these cases the energies 10 and 20 MeV were used. It was shown that the optimization algorithm converges well with multiple electron fields of different energies but the same treatment portal, and that it is possible to use several equiportal fluence modulated electron fields to modify the range in a controlled manner. This could make it possible to use the technique as an alternative to the use of bolus in the future. The technique was tested both in simple test geometries, such as wedge and step shaped target volumes, and in clinically realistic sample cases such as oblique chest wall, parotis and spinal muscle irradiation. The local maxima in the dose distributions for the full energy range otimization were typically lower than with the conventional or advanced bolus techniques. We have also outlined the principles how the technique could be carried out in the future clinical practice using the fourth generation radiotherapy accelerators.
IntechOpen eBooks, Jun 6, 2023
The lightest ions beyond protons, principally helium, lithium, and boron ions, make highly specif... more The lightest ions beyond protons, principally helium, lithium, and boron ions, make highly specific molecular Bragg peak radiation therapy of malignant tumors possible with minimal adverse normal tissue reactions. The Bragg peak ionization density is mainly elevated in a few mm wide spot at the end of these ions with substantially increased local apoptosis and senescence induction. Mainly placing Bragg peaks in the gross tumor volume with increased local therapeutic effect and only low ionization density and easily repairable damage in normal tissues. The possible geometrical accuracy of the dose delivery will be ≈1 mm with these ions. Interestingly, high-resolution molecular tumor imaging will then be possible, particularly with 8 Boron ions that are our lightest positron emitter allowing immediate accurate PET-CT imaging to delineate the target volume dose delivery. Compared to carbon ions the boron radiation damage to normal tissues in front of and behind the tumor is reduced at the same time as tumor apoptosis and senescence are increased. A mean tumor cure as high as 80% should be possible with Boron ion therapy using new clinical fractionation principles and even more when early tumor detection and malignancy estimation methods are brought into more regular clinical use.
Radiotherapy and Oncology, Mar 1, 2012
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
6.1 General Each radiotherapy department must have absorbed dose distributions in water available... more 6.1 General Each radiotherapy department must have absorbed dose distributions in water available for each beam quality to be used. Standardized reference absorbeddose distrihntions for a given energy can generally not be used as extensively with electrons as with photon beams, because the shape of electron beam isodose curves can vary considerably between different treatment units. The dose distributions depend on several factors such as the quality of the initial electron beam when it meets the accelerator window and the scattering . and energy degradation in window, foils, transmission chambers, air, etc. These factors may also differ for accelerators of the same type and manufacturer and, therefore, a complete set of absorbed -dose distributions should be measured for each accelerator. All the data supplied by the manufacturer of the accelerator must be checked to confirm their applicability. This usually involves carrying out extensive measurements and must be done with great care. The number of absorbed-dose distributions needed for radiation treatments is often large because several combinations of nominal energies, field sizes, scattering foils, etc. may be used. Therefore, much emphasis must be given to rapid methods of absorbed-dose distribution determinations.
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
Standard central-axis depth VB. absorbed dose and isodose distributions discussed in Section 6 re... more Standard central-axis depth VB. absorbed dose and isodose distributions discussed in Section 6 refer to a cuboid water phantom. However, the dose distribution in a patient may differ appreciably from the standard dose distributions when the elemental composition, density, and shape of the irradiated tissues differ from that of the water phantom. Furthermore, the irradiated tissue may change in these respects during the course of the treatment.
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
At the time of the introduction of high-energy electrons into radiotherapy, there were controvers... more At the time of the introduction of high-energy electrons into radiotherapy, there were controversies amongst radio biologists and radiotherapists about the following problems: (1) The RBE of high-energy electron beams with respect to conventional or high-energy x-ray beams (2) the existence of a possible "therapeutic differential effect" (i.e., that the ratio of tumor response to normal tissue response may be different for electron and photon beams) (3) the practical consequences of the above in radiotherapy, concerning, in particular, when one should use electron beam therapy in preference to photons, and the choice of the type !:lull uf ihe energy uf the electron beam accelerators. It is now generally accepted that these controversies were due. at least partly. to dosimet.ric difficult.ies which were not fully understood at that time, as indicated by Sinclair and Kohn (1964). The situation has been progressively clarified although it will always remain difficult, when asses~ing clinical effects, to distinguish what is to be related to the purely "physical" dose distribution and what could be related, specifically, to the radiobiulogkw prupertie:s of the electron beams. The problem of the time-dose distribution (pulsed irradiation, see Section 3.4) in electron therapy has also been raised. At the present time, it can be assumed that biological effects are not significantly modified by the pulsed characteristics of high-energy electron beams for the conditions currently encountered in radiotherapy (Hall, 1978). However, modifications in the biological effects have been observed when large doses were delivered in very short pulses (Hornsey and Alper, 1966; Epp et al., 1968; Hornsey, 1970; Nias et al., 1973; Mill 1979). '
Radiation Research, Jul 14, 2022
Radiation Research, Sep 23, 2019
In this work, we compared the genomic distribution of common radiation-induced chromosomal breaks... more In this work, we compared the genomic distribution of common radiation-induced chromosomal breaks to eight different data sets covering the whole human genome. Sites with a high probability of chromatid breakage after exposure to low and high ionization density radiations were often located inside common and rare fragile sites, indicating that they may be a new and more local type of DNA repair-related fragility. Breaks in specific chromosome bands after acute exposure to oil and benzene also showed strong correlation with these sites and fragile sites. In addition, close correlation was found with cytologically detected chiasma and MLH1 immunofluorescence sites and with the HapMap recombination density distributions. Also, of interest, copy number changes occurred predominantly at radiation-induced breaks and fragile sites, at least for breast cancers with poor prognosis, and they decreased weakly but significantly in regions with increasing recombination and CpG density. An increased CpG density is linked to regions of high gene density to secure high-fidelity reproduction and survival. To minimize cancer induction, cancer-related genes are often located in regions of decreased recombination density and/or higher-than-average CpG density. It is compelling that all these data sets were influenced by the cells' handling of double-strand breaks and, more generally, DNA damage on its genome. In fact, the DNA repair genes systematically avoid regions with a high recombination density, as they need to be intact to accurately handle repairable DNA lesions.
Medical radiology, 1995
ABSTRACT
Physics in Medicine and Biology, Apr 29, 2004
The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of th... more The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of the transport of protons and heavier ions in tissue-like media is described. The code SHIELD-HIT, a spin-off of SHIELD (available as RSICC CCC-667), extends the transport of hadron cascades from standard targets to that of ions in arbitrary tissue-like materials, taking into account ionization energy-loss straggling and multiple Coulomb scattering effects. The consistency of the results obtained with SHIELD-HIT has been verified against experimental data and other existing Monte Carlo codes (PTRAN, PETRA), as well as with deterministic models for ion transport, comparing depth distributions of energy deposition by protons, 12C and 20Ne ions impinging on water. The SHIELD-HIT code yields distributions consistent with a proper treatment of nuclear inelastic collisions. Energy depositions up to and well beyond the Bragg peak due to nuclear fragmentations are well predicted. Satisfactory agreement is also found with experimental determinations of the number of fragments of a given type, as a function of depth in water, produced by 12C and 14N ions of 670 MeV u(-1), although less favourable agreement is observed for heavier projectiles such as 16O ions of the same energy. The calculated neutron spectra differential in energy and angle produced in a mimic of a Martian rock by irradiation with 12C ions of 290 MeV u(-1) also shows good agreement with experimental data. It is concluded that a careful analysis of stopping power data for different tissues is necessary for radiation therapy applications, since an incorrect estimation of the position of the Bragg peak might lead to a significant deviation from the prescribed dose in small target volumes. The results presented in this study indicate the usefulness of the SHIELD-HIT code for Monte Carlo simulations in the field of light ion radiation therapy.
IntechOpen eBooks, Jun 6, 2023
The lightest ions beyond protons, principally helium, lithium, and boron ions, make highly specif... more The lightest ions beyond protons, principally helium, lithium, and boron ions, make highly specific molecular Bragg peak radiation therapy of malignant tumors possible with minimal adverse normal tissue reactions. The Bragg peak ionization density is mainly elevated in a few mm wide spot at the end of these ions with substantially increased local apoptosis and senescence induction. Mainly placing Bragg peaks in the gross tumor volume with increased local therapeutic effect and only low ionization density and easily repairable damage in normal tissues. The possible geometrical accuracy of the dose delivery will be ≈1 mm with these ions. Interestingly, high-resolution molecular tumor imaging will then be possible, particularly with 8 Boron ions that are our lightest positron emitter allowing immediate accurate PET-CT imaging to delineate the target volume dose delivery. Compared to carbon ions the boron radiation damage to normal tissues in front of and behind the tumor is reduced at the same time as tumor apoptosis and senescence are increased. A mean tumor cure as high as 80% should be possible with Boron ion therapy using new clinical fractionation principles and even more when early tumor detection and malignancy estimation methods are brought into more regular clinical use.
This presentation briefly covers the ongoing development of a therapy center with multiple simult... more This presentation briefly covers the ongoing development of a therapy center with multiple simultaneous radiation modalities at Karolinska university hospital. The hearth of the facility will most likely be a superconducting cyclotron capable of delivering around 400 MeV/u carbon ions simultaneously to two separate excentric gantries who service four treatment rooms each. A number of different stable ions will be available ranging from hydrogen to oxygen but also PET emitting C11 ions and possibly B8 the lightest existing PET emitter. Several treatment rooms will also be equipped for narrow scanned high energy photon and electron beam treatments and a light ion research facility for physics and biology studies will be set up on two separate beamlines. The centre will include an advanced PET-CT and MRSI based diagnostic centre on the same floor and close to both the ion treatment facility and the high energy photon and electron facility. By docking the stereotactic treatment coach both to the treatment units and before and after the treatment to the diagnostic PET-CT units, iso dose delivery can be rapidly examined by imaging the radiation induced C11 and O15 activity produced during the treatment.
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
6.1 General Each radiotherapy department must have absorbed dose distributions in water available... more 6.1 General Each radiotherapy department must have absorbed dose distributions in water available for each beam quality to be used. Standardized reference absorbeddose distrihntions for a given energy can generally not be used as extensively with electrons as with photon beams, because the shape of electron beam isodose curves can vary considerably between different treatment units. The dose distributions depend on several factors such as the quality of the initial electron beam when it meets the accelerator window and the scattering . and energy degradation in window, foils, transmission chambers, air, etc. These factors may also differ for accelerators of the same type and manufacturer and, therefore, a complete set of absorbed -dose distributions should be measured for each accelerator. All the data supplied by the manufacturer of the accelerator must be checked to confirm their applicability. This usually involves carrying out extensive measurements and must be done with great care. The number of absorbed-dose distributions needed for radiation treatments is often large because several combinations of nominal energies, field sizes, scattering foils, etc. may be used. Therefore, much emphasis must be given to rapid methods of absorbed-dose distribution determinations.
Medical radiology, 1995
ABSTRACT
Radiotherapy and Oncology, Aug 1, 2009
Physics in Medicine and Biology, Apr 29, 2004
The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of th... more The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of the transport of protons and heavier ions in tissue-like media is described. The code SHIELD-HIT, a spin-off of SHIELD (available as RSICC CCC-667), extends the transport of hadron cascades from standard targets to that of ions in arbitrary tissue-like materials, taking into account ionization energy-loss straggling and multiple Coulomb scattering effects. The consistency of the results obtained with SHIELD-HIT has been verified against experimental data and other existing Monte Carlo codes (PTRAN, PETRA), as well as with deterministic models for ion transport, comparing depth distributions of energy deposition by protons, 12C and 20Ne ions impinging on water. The SHIELD-HIT code yields distributions consistent with a proper treatment of nuclear inelastic collisions. Energy depositions up to and well beyond the Bragg peak due to nuclear fragmentations are well predicted. Satisfactory agreement is also found with experimental determinations of the number of fragments of a given type, as a function of depth in water, produced by 12C and 14N ions of 670 MeV u(-1), although less favourable agreement is observed for heavier projectiles such as 16O ions of the same energy. The calculated neutron spectra differential in energy and angle produced in a mimic of a Martian rock by irradiation with 12C ions of 290 MeV u(-1) also shows good agreement with experimental data. It is concluded that a careful analysis of stopping power data for different tissues is necessary for radiation therapy applications, since an incorrect estimation of the position of the Bragg peak might lead to a significant deviation from the prescribed dose in small target volumes. The results presented in this study indicate the usefulness of the SHIELD-HIT code for Monte Carlo simulations in the field of light ion radiation therapy.
Radiotherapy and Oncology, Oct 1, 1995
Electron beams with energies up to 25 MeV are routinely used to treat tumours at a shallow depth,... more Electron beams with energies up to 25 MeV are routinely used to treat tumours at a shallow depth, within the therapeutic range of the electrons. The range of the electrons has conventionally been modulated by the use of a bolus with varialbe thickness, and algorithms for designing the bolus have been developed. The purpose of this work was to investigate the possibility of combining fluence modulated electron beams of different energies to produce dose distributions that would be conformal to the target volumes, so that the dose to the target volume and organs at risk would also be radiobiologically optimized. A new generalized pencil beam algorithm for dose computation and an iterative constrained steepest descent algorithm for optimization were used to find radiobiologically optimized treatment plans by maximizing the propability of achieving tumour control without causing severe complications. Multiple fluence modulated electron beams with different energies but the same direction of incidence were used for superficial target volumes. The full optimization was made by using the energies from 5 MeV to 25 MeV at 5 MeV increments. We also evaluated, how much the dose distributions would differ if optimization were made with only two electron energies. In these cases the energies 10 and 20 MeV were used. It was shown that the optimization algorithm converges well with multiple electron fields of different energies but the same treatment portal, and that it is possible to use several equiportal fluence modulated electron fields to modify the range in a controlled manner. This could make it possible to use the technique as an alternative to the use of bolus in the future. The technique was tested both in simple test geometries, such as wedge and step shaped target volumes, and in clinically realistic sample cases such as oblique chest wall, parotis and spinal muscle irradiation. The local maxima in the dose distributions for the full energy range otimization were typically lower than with the conventional or advanced bolus techniques. We have also outlined the principles how the technique could be carried out in the future clinical practice using the fourth generation radiotherapy accelerators.
IntechOpen eBooks, Jun 6, 2023
The lightest ions beyond protons, principally helium, lithium, and boron ions, make highly specif... more The lightest ions beyond protons, principally helium, lithium, and boron ions, make highly specific molecular Bragg peak radiation therapy of malignant tumors possible with minimal adverse normal tissue reactions. The Bragg peak ionization density is mainly elevated in a few mm wide spot at the end of these ions with substantially increased local apoptosis and senescence induction. Mainly placing Bragg peaks in the gross tumor volume with increased local therapeutic effect and only low ionization density and easily repairable damage in normal tissues. The possible geometrical accuracy of the dose delivery will be ≈1 mm with these ions. Interestingly, high-resolution molecular tumor imaging will then be possible, particularly with 8 Boron ions that are our lightest positron emitter allowing immediate accurate PET-CT imaging to delineate the target volume dose delivery. Compared to carbon ions the boron radiation damage to normal tissues in front of and behind the tumor is reduced at the same time as tumor apoptosis and senescence are increased. A mean tumor cure as high as 80% should be possible with Boron ion therapy using new clinical fractionation principles and even more when early tumor detection and malignancy estimation methods are brought into more regular clinical use.
Radiotherapy and Oncology, Mar 1, 2012
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
6.1 General Each radiotherapy department must have absorbed dose distributions in water available... more 6.1 General Each radiotherapy department must have absorbed dose distributions in water available for each beam quality to be used. Standardized reference absorbeddose distrihntions for a given energy can generally not be used as extensively with electrons as with photon beams, because the shape of electron beam isodose curves can vary considerably between different treatment units. The dose distributions depend on several factors such as the quality of the initial electron beam when it meets the accelerator window and the scattering . and energy degradation in window, foils, transmission chambers, air, etc. These factors may also differ for accelerators of the same type and manufacturer and, therefore, a complete set of absorbed -dose distributions should be measured for each accelerator. All the data supplied by the manufacturer of the accelerator must be checked to confirm their applicability. This usually involves carrying out extensive measurements and must be done with great care. The number of absorbed-dose distributions needed for radiation treatments is often large because several combinations of nominal energies, field sizes, scattering foils, etc. may be used. Therefore, much emphasis must be given to rapid methods of absorbed-dose distribution determinations.
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
Standard central-axis depth VB. absorbed dose and isodose distributions discussed in Section 6 re... more Standard central-axis depth VB. absorbed dose and isodose distributions discussed in Section 6 refer to a cuboid water phantom. However, the dose distribution in a patient may differ appreciably from the standard dose distributions when the elemental composition, density, and shape of the irradiated tissues differ from that of the water phantom. Furthermore, the irradiated tissue may change in these respects during the course of the treatment.
Journal of the International Commission on Radiation Units and Measurements, Sep 15, 1984
At the time of the introduction of high-energy electrons into radiotherapy, there were controvers... more At the time of the introduction of high-energy electrons into radiotherapy, there were controversies amongst radio biologists and radiotherapists about the following problems: (1) The RBE of high-energy electron beams with respect to conventional or high-energy x-ray beams (2) the existence of a possible "therapeutic differential effect" (i.e., that the ratio of tumor response to normal tissue response may be different for electron and photon beams) (3) the practical consequences of the above in radiotherapy, concerning, in particular, when one should use electron beam therapy in preference to photons, and the choice of the type !:lull uf ihe energy uf the electron beam accelerators. It is now generally accepted that these controversies were due. at least partly. to dosimet.ric difficult.ies which were not fully understood at that time, as indicated by Sinclair and Kohn (1964). The situation has been progressively clarified although it will always remain difficult, when asses~ing clinical effects, to distinguish what is to be related to the purely "physical" dose distribution and what could be related, specifically, to the radiobiulogkw prupertie:s of the electron beams. The problem of the time-dose distribution (pulsed irradiation, see Section 3.4) in electron therapy has also been raised. At the present time, it can be assumed that biological effects are not significantly modified by the pulsed characteristics of high-energy electron beams for the conditions currently encountered in radiotherapy (Hall, 1978). However, modifications in the biological effects have been observed when large doses were delivered in very short pulses (Hornsey and Alper, 1966; Epp et al., 1968; Hornsey, 1970; Nias et al., 1973; Mill 1979). '
Radiation Research, Jul 14, 2022
Radiation Research, Sep 23, 2019
In this work, we compared the genomic distribution of common radiation-induced chromosomal breaks... more In this work, we compared the genomic distribution of common radiation-induced chromosomal breaks to eight different data sets covering the whole human genome. Sites with a high probability of chromatid breakage after exposure to low and high ionization density radiations were often located inside common and rare fragile sites, indicating that they may be a new and more local type of DNA repair-related fragility. Breaks in specific chromosome bands after acute exposure to oil and benzene also showed strong correlation with these sites and fragile sites. In addition, close correlation was found with cytologically detected chiasma and MLH1 immunofluorescence sites and with the HapMap recombination density distributions. Also, of interest, copy number changes occurred predominantly at radiation-induced breaks and fragile sites, at least for breast cancers with poor prognosis, and they decreased weakly but significantly in regions with increasing recombination and CpG density. An increased CpG density is linked to regions of high gene density to secure high-fidelity reproduction and survival. To minimize cancer induction, cancer-related genes are often located in regions of decreased recombination density and/or higher-than-average CpG density. It is compelling that all these data sets were influenced by the cells' handling of double-strand breaks and, more generally, DNA damage on its genome. In fact, the DNA repair genes systematically avoid regions with a high recombination density, as they need to be intact to accurately handle repairable DNA lesions.