The purpose of this paper is to describe mathematically the observed dependence of the number of ... more The purpose of this paper is to describe mathematically the observed dependence of the number of DNA single-strand breaks (SSBs) per unit dose on radiation quality (e.g., LET) by invoking the concept of matrix saturation (i.e., the fact that a nucleotide can be the site of one SSB only and therefore further local energy deposition is wasted), and to show that, based on this, one obtains a characteristic variation of the yield of DNA double-strand breaks with variation of LET, in qualitative agreement with certain experimental determinations. The formalism developed here makes use of methodology from the field of integral geometry, introduced by Kellerer [Radiat. Prot. Dosim. 31, 9-16, 1990] in microdosimetry.
Our purpose was to describe the process and outcome of performing postimplantation dosimetric ass... more Our purpose was to describe the process and outcome of performing postimplantation dosimetric assessment and intraoperative dose correction during prostate brachytherapy using a novel image fusion-based treatment-planning program. Twenty-six consecutive patients underwent intraoperative real-time corrections of their dose distributions at the end of their permanent seed interstitial procedures. After intraoperatively planned seeds were implanted and while the patient remained in the lithotomy position, a cone beam computed tomography scan was obtained to assess adequacy of the prescription dose coverage. The implanted seed positions were automatically segmented from the cone-beam images, fused onto a new set of acquired ultrasound images, reimported into the planning system, and recontoured. Dose distributions were recalculated based upon actual implanted seed coordinates and recontoured ultrasound images and were reviewed. If any dose deficiencies within the prostate target were id...
Inaccuracy in seed placement during permanent prostate implants may lead to significant dosimetri... more Inaccuracy in seed placement during permanent prostate implants may lead to significant dosimetric deviations from the intended plan. In two recent publications (Todor et al 2002 Phys. Med. Biol. 47 2031 48, Todor et al 2003 Phys. Med. Biol. 48 1153 71), methodology was described for identifying intraoperatively the positions of seeds already implanted, thus allowing re-optimization of the treatment
Skin surface dosimetric discrepancies between measured and treatment planning system predicted va... more Skin surface dosimetric discrepancies between measured and treatment planning system predicted values were traced to source position sag inside the applicator and to source transit time. We quantified their dosimetric impact and propose corrections for clinical use. We measured the dose profiles from the Varian Leipzig-style high-dose-rate (HDR) skin applicator, using EBT3 film, photon diode, and optically stimulated luminescence dosimeter for three different GammaMedplus HDR afterloaders. The measured dose profiles at several depths were compared with BrachyVision Acuros calculated profiles. To assess the impact of the source sag, two different applicator orientations were considered. The dose contribution during source transit was assessed by comparing diode measurements using an HDR timer and an electrometer timer. Depth doses measured using the three dosimeters were in good agreement, but were consistently higher than the Acuros dose calculations. Measurements with the applicato...
A review of 15 cases suggests that posterior-lip sclerectomy can be performed safely with extraca... more A review of 15 cases suggests that posterior-lip sclerectomy can be performed safely with extracapsular cataract extraction (ECCE) and posterior chamber lens implantation. The anterior chamber was filled with viscoelastic at the end of each procedure; no case required reoperation for shallow chamber or hypotony. The mean intraocular pressure after 1 year was 12.1 mm Hg. The astigmatism induced by the triple procedure did not differ significantly from that caused by ECCE alone during the initial 2 postoperative years. A new mathematical model that describes the change over time of postoperative astigmatism associated with these procedures is described.
In the past decade, a large amount of effort has gone into the development of hit size effectiven... more In the past decade, a large amount of effort has gone into the development of hit size effectiveness functions (HSEFs), with the ultimate aim of replacing the present absorbed dose-RBE-Q system. However, the absorbed dose determined at the tissue level is incapable of providing information on single hits on (doses to) the single cell. As a result, it is necessary to resort to microdosimetry, which is capable of providing not only the number of hits on cells, but the distribution of hit sizes as well. From this information, an HSEF can be derived. However, to date there have been no sets of data available on animals exposed to radiations of several qualities, and for which microdosimetric data were available. The objective of the present set of experiments was to remedy this situation. Large numbers of mice were exposed to radiations of several different qualities, and were observed throughout their entire lifespan for the appearance of myeloid leukemia. The HSEF developed for this neoplasm is presented and discussed.
Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2000
Treatment of retinoblastoma dates back to the first reported (and unsuccessful) enucleation in 17... more Treatment of retinoblastoma dates back to the first reported (and unsuccessful) enucleation in 1767. Over 200 years later, enucleation is a far more humane and common procedure, yet brachytherapy is often the treatment of choice for small to medium-size tumors offering both function-preservation and good survival-rates (usually employing Co60, Ir192 and I125). Use of Ru106/Rh106(T½=1 y; a˜Emax=3.54 MeV) for ocular
The purpose of this paper is to describe mathematically the observed dependence of the number of ... more The purpose of this paper is to describe mathematically the observed dependence of the number of DNA single-strand breaks (SSBs) per unit dose on radiation quality (e.g., LET) by invoking the concept of matrix saturation (i.e., the fact that a nucleotide can be the site of one SSB only and therefore further local energy deposition is wasted), and to show that, based on this, one obtains a characteristic variation of the yield of DNA double-strand breaks with variation of LET, in qualitative agreement with certain experimental determinations. The formalism developed here makes use of methodology from the field of integral geometry, introduced by Kellerer [Radiat. Prot. Dosim. 31, 9-16, 1990] in microdosimetry.
Our purpose was to describe the process and outcome of performing postimplantation dosimetric ass... more Our purpose was to describe the process and outcome of performing postimplantation dosimetric assessment and intraoperative dose correction during prostate brachytherapy using a novel image fusion-based treatment-planning program. Twenty-six consecutive patients underwent intraoperative real-time corrections of their dose distributions at the end of their permanent seed interstitial procedures. After intraoperatively planned seeds were implanted and while the patient remained in the lithotomy position, a cone beam computed tomography scan was obtained to assess adequacy of the prescription dose coverage. The implanted seed positions were automatically segmented from the cone-beam images, fused onto a new set of acquired ultrasound images, reimported into the planning system, and recontoured. Dose distributions were recalculated based upon actual implanted seed coordinates and recontoured ultrasound images and were reviewed. If any dose deficiencies within the prostate target were id...
Inaccuracy in seed placement during permanent prostate implants may lead to significant dosimetri... more Inaccuracy in seed placement during permanent prostate implants may lead to significant dosimetric deviations from the intended plan. In two recent publications (Todor et al 2002 Phys. Med. Biol. 47 2031 48, Todor et al 2003 Phys. Med. Biol. 48 1153 71), methodology was described for identifying intraoperatively the positions of seeds already implanted, thus allowing re-optimization of the treatment
Skin surface dosimetric discrepancies between measured and treatment planning system predicted va... more Skin surface dosimetric discrepancies between measured and treatment planning system predicted values were traced to source position sag inside the applicator and to source transit time. We quantified their dosimetric impact and propose corrections for clinical use. We measured the dose profiles from the Varian Leipzig-style high-dose-rate (HDR) skin applicator, using EBT3 film, photon diode, and optically stimulated luminescence dosimeter for three different GammaMedplus HDR afterloaders. The measured dose profiles at several depths were compared with BrachyVision Acuros calculated profiles. To assess the impact of the source sag, two different applicator orientations were considered. The dose contribution during source transit was assessed by comparing diode measurements using an HDR timer and an electrometer timer. Depth doses measured using the three dosimeters were in good agreement, but were consistently higher than the Acuros dose calculations. Measurements with the applicato...
A review of 15 cases suggests that posterior-lip sclerectomy can be performed safely with extraca... more A review of 15 cases suggests that posterior-lip sclerectomy can be performed safely with extracapsular cataract extraction (ECCE) and posterior chamber lens implantation. The anterior chamber was filled with viscoelastic at the end of each procedure; no case required reoperation for shallow chamber or hypotony. The mean intraocular pressure after 1 year was 12.1 mm Hg. The astigmatism induced by the triple procedure did not differ significantly from that caused by ECCE alone during the initial 2 postoperative years. A new mathematical model that describes the change over time of postoperative astigmatism associated with these procedures is described.
In the past decade, a large amount of effort has gone into the development of hit size effectiven... more In the past decade, a large amount of effort has gone into the development of hit size effectiveness functions (HSEFs), with the ultimate aim of replacing the present absorbed dose-RBE-Q system. However, the absorbed dose determined at the tissue level is incapable of providing information on single hits on (doses to) the single cell. As a result, it is necessary to resort to microdosimetry, which is capable of providing not only the number of hits on cells, but the distribution of hit sizes as well. From this information, an HSEF can be derived. However, to date there have been no sets of data available on animals exposed to radiations of several qualities, and for which microdosimetric data were available. The objective of the present set of experiments was to remedy this situation. Large numbers of mice were exposed to radiations of several different qualities, and were observed throughout their entire lifespan for the appearance of myeloid leukemia. The HSEF developed for this neoplasm is presented and discussed.
Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2000
Treatment of retinoblastoma dates back to the first reported (and unsuccessful) enucleation in 17... more Treatment of retinoblastoma dates back to the first reported (and unsuccessful) enucleation in 1767. Over 200 years later, enucleation is a far more humane and common procedure, yet brachytherapy is often the treatment of choice for small to medium-size tumors offering both function-preservation and good survival-rates (usually employing Co60, Ir192 and I125). Use of Ru106/Rh106(T½=1 y; a˜Emax=3.54 MeV) for ocular
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Papers by Marco Zaider