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Mark J Rivard

Publications and source records attributed to Mark J Rivard.

At least 19 recordsLinked to original sources
PubMed2006

Interstitial brachytherapy dosimetry update.

In March 2004, the American Association of Physicists in Medicine (AAPM) published an update to the AAPM Task Group No. 43 Report (TG-43) which was initially published in 1995. This update was pursued primarily due to the marked increase in permanent implantation of low-energy photon-emitting brachytherapy sources in the United States over the past decade, and clinical rationale for the need of accurate dosimetry in the implementation of interstitial brachytherapy. Additionally, there were substantial improvements in the brachytherapy dosimetry formalism, accuracy of related parameters and methods for determining these parameters. With salient background, these improvements are discussed in the context of radiation dosimetry. As an example, the impact of this update on the administered dose is assessed for the model 200 (103)Pd brachytherapy source.

Brachytherapy↗
PubMed2006

Approaches to calculating AAPM TG-43 brachytherapy dosimetry parameters for 137Cs, 125I, 192Ir, 103Pd, and 169Yb sources.

Underlying characteristics in brachytherapy dosimetry parameters for medical radionuclides 137Cs, 125I, 192Ir, 103Pd, and 169Yb were examined using Monte Carlo methods. Sources were modeled as unencapsulated point or line sources in liquid water to negate variations due to materials and construction. Importance of phantom size, mode of radiation transport physics--i.e., photon transport only or coupled photon:electron transport, phantom material, volume averaging, and Monte Carlo tally type were studied. For noninfinite media, g(r) was found to degrade as r approached R, the phantom radius. MCNP5 results were in agreement with those published using GEANT4. Brachytherapy dosimetry parameters calculated using coupled photon:electron radiation transport simulations did not differ significantly from those using photon transport only. Dose distributions from low-energy photon-emitting radionuclides 125I and 103Pd were sensitive to phantom material by upto a factor of 1.4 and 2.0, respectively, between tissue-equivalent materials and water at r =9 cm. In comparison, high-energy photons from 137Cs, 192Ir, and 169Yb demonstrated +/- 5% differences in dose distributions between water and tissue substitutes at r=20 cm. Similarly, volume-averaging effects were found to be more significant for low-energy radionuclides. When modeling line sources with L < or = 0.5 cm, the two-dimensional anisotropy function was largely within +/- 0.5% of unity for 137Cs, 125I, and 192Ir. However, an energy and geometry effect was noted for 103Pd and 169Yb, with Pd-103F(0.5,0 degrees)=l.05 and yb-169F(0.5,0 degrees)=0.98 for L=0.5 cm. Simulations of monoenergetic photons for L=0.5 cm produced energy-dependent variations in F(r, theta) having a maximum value at 10 keV, minimum at 50 keV, and approximately 1.0 for higher-energy photons up to 750 keV. Both the F6 cell heating and *F4 track-length estimators were employed to determine brachytherapy dosimetry parameters. F6 was found to be necessary for g(r), while both tallies provided equivalent results for F(r, theta).

Brachytherapy↗
PubMed2006

Calculated and measured brachytherapy dosimetry parameters in water for the Xoft Axxent X-Ray Source: an electronic brachytherapy source.

A new x-ray source, the model S700 Axxent X-Ray Source (Source), has been developed by Xoft Inc. for electronic brachytherapy. Unlike brachytherapy sources containing radionuclides, this Source may be turned on and off at will and may be operated at variable currents and voltages to change the dose rate and penetration properties. The in-water dosimetry parameters for this electronic brachytherapy source have been determined from measurements and calculations at 40, 45, and 50 kV settings. Monte Carlo simulations of radiation transport utilized the MCNP5 code and the EPDL97-based mcplib04 cross-section library. Inter-tube consistency was assessed for 20 different Sources, measured with a PTW 34013 ionization chamber. As the Source is intended to be used for a maximum of ten treatment fractions, tube stability was also assessed. Photon spectra were measured using a high-purity germanium (HPGe) detector, and calculated using MCNP. Parameters used in the two-dimensional (2D) brachytherapy dosimetry formalism were determined. While the Source was characterized as a point due to the small anode size, < 1 mm, use of the one-dimensional (1D) brachytherapy dosimetry formalism is not recommended due to polar anisotropy. Consequently, 1D brachytherapy dosimetry parameters were not sought. Calculated point-source model radial dose functions at gP(5) were 0.20, 0.24, and 0.29 for the 40, 45, and 50 kV voltage settings, respectively. For 1<r<7 cm, measured point-source model radial dose functions were typically within 4% of calculated results. Calculated values for F(r, theta) for all operating voltages were within 15% of unity along the distal end (theta=0 degree), and ranged from F(1 cm, 160 degrees) = 0.2 to F(15 cm, 175 degrees) = 0.4 towards the catheter proximal end. For all three operating voltages using the PTW chamber, measured dependence of output as a function of azimuthal angle, psi, was typically on average +/-3% for 0 degree < or = psi < or = 360 degrees. Excluding an energy response function, measurements of normalized photon energy spectra were made for three operating voltages, and were typically within 2% agreement with the normalized Monte Carlo calculated spectra. In general, the model S700 Source exhibited depth dose behavior similar to low-energy photon-emitting low dose rate sources 125I and l03Pd, yet with capability for variable and much higher dose rates and subsequently adjustable penetration capabilities. This paper presents the calculated and measured in-water brachytherapy dosimetry parameters for the model S700 Source at the aforementioned three operating voltages.

Brachytherapy↗
PubMed2005

A technical evaluation of the Nucletron FIRST system: conformance of a remote afterloading brachytherapy seed implantation system to manufacturer specifications and AAPM Task Group report recommendations.

The Fully Integrated Real-time Seed Treatment (FIRST) system by Nucletron has been available in Europe since November 2001 and is being used more and more in Canada and the United States. Like the conventional transrectal ultrasound implant procedure, the FIRST system utilizes an ultrasound probe, needles, and brachytherapy seeds. However, this system is unique in that it (1) utilizes a low-dose-rate brachytherapy seed remote afterloader (the seedSelectron), (2) utilizes 3D image reconstruction acquired from electromechanically controlled, nonstepping rotation of the ultrasound probe, (3) integrates the control of a remote afterloader with electromechanical control of the ultrasound probe for integrating the clinical procedure into a single system, and (4) automates the transfer of planning information and seed delivery to improve quality assurance and radiation safety. This automated delivery system is specifically intended to address reproducibility and accuracy of seed positioning during implantation. The FIRST computer system includes two software environments: SPOT PRO and seedSelectron; both are used to facilitate treatment planning and brachytherapy seed implantation from beginning to completion of the entire procedure. In addition to these features, the system is reported to meet certain product specifications for seed delivery positioning accuracy and reproducibility, seed calibration accuracy and reliability, and brachytherapy dosimetry calculations. Consequently, a technical evaluation of the FIRST system was performed to determine adherence to manufacturer specifications and to the American Association of Physicists in Medicine (AAPM) Task Group Reports 43, 53, 56, 59, and 64 and recommendations of the American Brachytherapy Society (ABS). The United States Nuclear Regulatory Commission (NRC) has recently added Licensing Guidance for the seedSelectron system under 10 CFR 35.1000. Adherence to licensing guidance is made by referencing applicable AAPM Task Group recommendations. In general, results of this evaluation indicated that the system met its claimed specifications as well as the applicable recommendations outlined in the AAPM and ABS reports.

Brachytherapy↗
PubMed2005

The US national isotope program: current status and strategy for future success.

Since their introduction in the 1940s, peaceful use of stable isotopes and radioisotopes in the United States has expanded continuously. Today, new isotopes for diagnostic and therapeutic uses are not being developed, critical isotopes for national security are in short supply, and demand for isotopes critical to homeland security exceeds supply. While commercial suppliers, both domestic and foreign, can only meet specific needs, the nation needs a consistent, reliable supply of radioactive and stable isotopes for research, medical, security, and space power applications. The national isotope infrastructure, defined as both facilities and trained staff at national laboratories and universities, is in danger of being lost due to chronic underfunding. With the specific recommendations given herein, the US Department of Energy may realign and refocus its Isotope Program to provide a framework for a successful National Isotope Program.

Government Agencies↗
PubMed2005

Recommendations of the American Association of Physicists in Medicine regarding the impact of implementing the 2004 task group 43 report on dose specification for 103Pd and 125I interstitial brachytherapy.

In March 2004, the recommendations of the American Association of Physicists in Medicine (AAPM) on the interstitial brachytherapy dosimetry using 125I and 103Pd were reported in Medical Physics [TG-43 Update: Rivard et al., 31, 633-674 (2004)]. These recommendations include some minor changes in the dose-calculation formalism and a major update of the dosimetry parameters for eight widely used interstitial brachytherapy sources. A full implementation of these recommendations could result in unintended changes in delivered dose without corresponding revisions in the prescribed dose. Because most published clinical experience with permanent brachytherapy is based upon two widely used source models, the 125I Model 6711 and 103Pd Model 200 sources, in this report we present an analysis of the dosimetric impact of the 2004 TG-43 dosimetry parameters on the history of dose delivery for these two source models. Our analysis indicates that the currently recommended prescribed dose of 125 Gy for Model 200 103Pd implants planned using previously recommended dosimetry parameters [AAPM 103Pd dose prescription: Williamson et al., Med. Phys. 27, 634-642 (2000)] results in a delivered dose of 120 Gy according to dose calculations based on the 2004 TG-43 update. Further, delivered doses prior to October 1997 varied from 113 to 119 Gy for a prescribed dose of 115 Gy compared to 124 Gy estimated by the AAPM 2000 report. For 125I implants using Model 6711 seeds, there are no significant changes (less than 2%). Practicing physicians should take these results into account when selecting the clinically appropriate prescribed dose for 103Pd interstitial implant patients following implementation of the 2004 TG-43 update dose-calculation recommendations. The AAPM recommends that the radiation oncology community review this report and consider whether the currently recommended dose level (125 Gy) needs to be revised.

Anisotropy↗
PubMed2005

A radiobiological model for the relative biological effectiveness of high-dose-rate 252Cf brachytherapy.

While there is significant clinical experience using both low- and high-dose-rate 252Cf brachytherapy, there are minimal data regarding values for the neutron relative biological effectiveness (RBE) with both modalities. The aim of this research was to derive a radiobiological model for 252Cf neutron RBE and to compare these results with neutron RBE values used clinically in Russia. The linear-quadratic (LQ) model was used as the basis to characterize cell survival after irradiation, with identical cell killing rates (S(N) = S(gamma)) between 252Cf neutrons and photons used for derivation of RBE. Using this equality, a relationship among neutron dose and LQ radiobiological parameter (i.e., alpha(N), beta(N), alpha(gamma), beta(gamma)) was obtained without the need to specify the photon dose. These results were used to derive the 252Cf neutron RBE, which was then compared with Russian neutron RBE values. The 252Cf neutron RBE was determined after incorporating the LQ radiobiological parameters obtained from cell survival studies with fast neutrons and teletherapy photons. For single-fraction high-dose-rate neutron doses of 0.5, 1.0, 1.5 and 2.0 Gy, the total biologically equivalent doses were 1.8, 3.4, 4.7 and 6.0 RBE Gy with 252Cf neutron RBE values of 3.2, 2.9, 2.7 and 2.5, respectively. Using clinical data for late-responding reactions from 252Cf, Russian investigators created an empirical model that predicted high-dose-rate 252Cf neutron RBE values ranging from 3.6 to 2.9 for similar doses and fractionation schemes and observed that 252Cf neutron RBE increases with the number of treatment fractions. Using these relationships, our results were in general concordance with high-dose-rate 252Cf RBE values obtained from Russian clinical experience.

Animals↗
PubMed2004

MammoSite and interstitial brachytherapy for accelerated partial breast irradiation: factors that affect toxicity and cosmesis.

BACKGROUND: In interstitial brachytherapy (IB), cosmesis and toxicity correlate with volume of tissue irradiated, dose homogeneity index (DHI), and adjuvant doxorubicin/cyclophosphamide based chemotherapy (ACCT). MammoSite brachytherapy (MSB) irradiates smaller volumes than IB, and lower dose homogeneity does not appear to affect toxicity. However, clinical experience suggests that other factors may also play an important role in cosmesis and toxicity with MSB. We reviewed our prospectively maintained data base of women who underwent accelerated partial breast irradiation (APBI) to assess this issue. METHODS: Beginning in September 1995, 115 women were enrolled in a trial evaluating APBI as monotherapy after lumpectomy. The first 75 eligible patients received IB, and the most recent 28 eligible patients received MSB. All patients received 34 gray (Gy) in 10 twice-daily fractions through high-dose rate iridium-192 brachytherapy; 19% of patients in the IB group and 0% of patients in the MSB group received ACCT. RESULTS: At 1 year after treatment, MSB caused significantly less Grade 2-4 subcutaneous fibrosis (as graded by a radiation oncologist according to the Radiation Therapy Oncology Group/Eastern Cooperative Oncology Group system) compared with IB (10.7% vs. 32%; P = 0.04). However, when only ACCT-naïve patients in the IB group were compared with patients in the MSB group, this finding became nonsignificant. Among the patients who received MSB, significantly smaller volumes were irradiated, and the DHI was lower. CONCLUSIONS: Current studies suggest an improved toxicity profile with MSB compared with IB that is attributed to lower irradiated volumes with MSB. When only chemotherapy-naïve patients were compared, however, toxicity and cosmesis were found to be similar between MSB and IB, suggesting a more complex interplay between irradiated volumes, DHI, and chemotherapy. The relation of ACCT to toxicity in this scenario is intriguing and warrants further investigation.

Aged↗
PubMed2004

Analysis of dose conformity and normal-tissue sparing using two different IMRT prescription methodologies for irregularly shaped CNS lesions irradiated with the Beak and 1-cm MIMiC collimators.

PURPOSE: To determine whether intensity modulated sequential tomotherapy using the NOMOS Beak provides superior dose conformity and organ sparing to the MIMiC "1-cm" mode, and if so, to identify a subset of patients most likely to benefit from Beak intensity modulated sequential tomotherapy. METHODS AND MATERIALS: Twelve patients with irregularly shaped central nervous system tumors were selected for intensity modulated radiation therapy planning. Two treatment plans, one using the Beak collimator and the other using the 1-cm MIMiC collimator, were generated for each patient with identical anatomic contouring, prescriptions, and optimization algorithms. The Beak attaches to the MIMiC collimator and truncates the 1-cm MIMiC mode beamlet size from 1.00 x 0.85 cm(2) to 1.00 x 0.39 cm(2) at isocenter. Conformity indexes were calculated for each lesion using two different prescription methodologies, and mean doses to critical structures were recorded. RESULTS: For the first prescription methodology using uniform prescribed isodose, mean conformity index was 2.19 (range, 1.33-3.90) for the Beak compared to 2.67 (range, 1.64-4.75) for the 1-cm mode (p = 0.0003). Mean doses to the brainstem, right orbit, and left optic nerve were significantly lower with the Beak than with the 1-cm mode (p = 0.0150, 0.0068, and 0.0284, respectively). For the second prescription methodology using uniform target volume coverage prescription, mean conformity index was 2.04 (range, 1.56-2.70) for the Beak compared to 2.73 (range, 1.70-8.58) for the 1-cm mode (p = 0.07). Mean doses to the brain, brainstem, optic chiasm, right optic nerve, left optic nerve, and left orbit were significantly lower with the Beak than with the 1-cm mode (p = <0.0001, <0.0026, <0.0016, <0.0076, <0.0007, and <0.046, respectively). CONCLUSION: Beak intensity modulated sequential tomotherapy is superior to the 1-cm MIMiC mode for irregularly shaped central nervous system tumors, because it provides better conformity and critical organ sparing. These differences may allow for safer dose escalation and retreatment, so the method presents an alternative to gamma knife stereotactic radiosurgery.

Algorithms↗
PubMed2004

A comparison of the expected costs of high dose rate brachytherapy using 252Cf versus 192Ir.

A cost analysis to compare high dose rate (HDR) brachytherapy using either californium-252 (252Cf) or 192Ir was performed to determine the prospects of widespread clinical implementation of HDR 252Cf. Interest in the neutron-emitting 252Cf radioisotope as a radiotherapy nuclide has undergone a resurgence given recent efforts to fabricate HDR remotely afterloaded sources, and other efforts to create a miniature source for improved accessibility to a variety of anatomic sites. Therefore, HDR 252Cf brachytherapy may prove to be a potential rival to the use of HDR 192Ir remotely afterloaded brachytherapy--the current standard-of-care treatment modality using HDR brachytherapy. Considering the possible improvements in clinical efficacy using HDR 252Cf brachytherapy and the enormous costs of other high-LET radiation sources, the cost differences between 252Cf and 192Ir may be well-justified.

Brachytherapy↗
PubMed2004

Moderated 252Cf neutron energy spectra in brain tissue and calculated boron neutron capture dose.

While there is significant clinical experience using both low- and high-dose (252)Cf brachytherapy, combination therapy using (10)B for neutron capture therapy-enhanced (252)Cf brachytherapy has not been performed. Monte Carlo calculations were performed in a brain phantom (ICRU 44 brain tissue) to evaluate the dose enhancement predicted for a range of (10)B concentrations over a range of distances from a clinical (252)Cf source. These results were compared to experimental measurements and calculations published in the literature. For (10)B concentrations </=50 microg/g, the (10)B neutron capture dose enhancement was small in comparison to the (252)Cf fast neutron dose.

Boron Neutron Capture Therapy↗
PubMed2004

Intravascular brachytherapy using 90Sr for saphenous vein grafts having diameters ranging from 2.0-5.0 mm.

PURPOSE: Symptomatic coronary artery disease is routinely treated with angioplasty and stenting. Unfortunately, treatment failure in the form of in-stent restenosis (ISR) occurs relatively frequently. Intravascular brachytherapy (IVBT) is a safe and effective method proven to markedly reduce the rate of ISR in native coronary arteries. The commercially available devices for IVBT are not FDA-approved for treatment of saphenous vein grafts (SVG). This article presents calculated dosimetry for treatment of a wide range of SVG, in addition to further evaluating the dose homogeneity for native coronary arteries. METHODS AND MATERIALS: AAPM Task Group 43 and 60 formalisms permitted dose calculations for a wide range of vessel internal diameters (phi) in both native coronary arteries and SVG. Doses were analytically calculated for the Novoste Beta-Cath 5.0 French (F) treatment devices (30, 40, and 60 mm sourcetrains) when employed for the treatment of native vessels with 2.7 <or= phi <or= 4.0 mm and for SVG with 2.0 <or= phi <or= 5.0 mm. This latter range of phi was segmented into 7 bins to facilitate rapid clinical implementation with minimal errors. Calculations of dose and dose rate for the 3.5 F devices were also performed. Dose inhomogeneity in the form of dose maxima and minima were calculated for the 3.5 and 5.0 F catheters, with the 30, 40, and 60 mm sourcetrains, and for 2.0 <or= phi <or= 5.0 mm. RESULTS: The calculated doses rates for the 30 mm device were in agreement (typically +/- 0.3%) with measured dose rates. Reference dose calculations performed for SVG with 2.0 <or= phi <or= 5.0 mm were in alignment with those used for the more narrow range of native coronary arteries currently approved for IVBT. Errors associated with using a phi binning technique for simplifying clinical implementation did not exceed 15%, and were typically under 9%. The degree of dose inhomogeneity at a depth of 0.5 mm increased as phi increased, catheter size decreased, and sourcetrain length decreased, and was -42% and +101% relative to the prescribed dose for the 40 mm 5.0 F system with phi = 4.0 mm. CONCLUSIONS: Use of 7 phi bins facilitates rapid clinical implementation of IVBT in the typical cardiac catheterization laboratory. While calculation of reference dose for treatment of large vessels is possible with established formalisms, the degree of dose inhomogeneity in light of current clinical results suggests further research is needed.

Brachytherapy↗
PubMed2004

Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations.

Since publication of the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report in 1995 (TG-43), both the utilization of permanent source implantation and the number of low-energy interstitial brachytherapy source models commercially available have dramatically increased. In addition, the National Institute of Standards and Technology has introduced a new primary standard of air-kerma strength, and the brachytherapy dosimetry literature has grown substantially, documenting both improved dosimetry methodologies and dosimetric characterization of particular source models. In response to these advances, the AAPM Low-energy Interstitial Brachytherapy Dosimetry subcommittee (LIBD) herein presents an update of the TG-43 protocol for calculation of dose-rate distributions around photon-emitting brachytherapy sources. The updated protocol (TG-43U1) includes (a) a revised definition of air-kerma strength; (b) elimination of apparent activity for specification of source strength; (c) elimination of the anisotropy constant in favor of the distance-dependent one-dimensional anisotropy function; (d) guidance on extrapolating tabulated TG-43 parameters to longer and shorter distances; and (e) correction for minor inconsistencies and omissions in the original protocol and its implementation. Among the corrections are consistent guidelines for use of point- and line-source geometry functions. In addition, this report recommends a unified approach to comparing reference dose distributions derived from different investigators to develop a single critically evaluated consensus dataset as well as guidelines for performing and describing future theoretical and experimental single-source dosimetry studies. Finally, the report includes consensus datasets, in the form of dose-rate constants, radial dose functions, and one-dimensional (1D) and two-dimensional (2D) anisotropy functions, for all low-energy brachytherapy source models that met the AAPM dosimetric prerequisites [Med. Phys. 25, 2269 (1998)] as of July 15, 2001. These include the following 125I sources: Amersham Health models 6702 and 6711, Best Medical model 2301, North American Scientific Inc. (NASI) model MED3631-A/M, Bebig/Theragenics model I25.S06, and the Imagyn Medical Technologies Inc. isostar model IS-12501. The 103Pd sources included are the Theragenics Corporation model 200 and NASI model MED3633. The AAPM recommends that the revised dose-calculation protocol and revised source-specific dose-rate distributions be adopted by all end users for clinical treatment planning of low energy brachytherapy interstitial sources. Depending upon the dose-calculation protocol and parameters currently used by individual physicists, adoption of this protocol may result in changes to patient dose calculations. These changes should be carefully evaluated and reviewed with the radiation oncologist preceding implementation of the current protocol.

Air↗
PubMed2004

Brachytherapy dosimetry parameters calculated for a new 103Pd source.

A new brachytherapy source having 103Pd adsorbed onto silver beads has been designed. The dose distributions of this source have been characterized using version 5 of the MCNP Monte Carlo radiation transport code available from Oak Ridge National Laboratory. These results are presented in terms of the updated AAPM Task Group No. 43 (TG-43U1) formalism, dosimetry parameters, and recommended calculation methodology.

Body Burden↗
PubMed2004

Treatment of in-stent restenosis for saphenous vein grafts using intravascular brachytherapy: regulatory challenges and clinical application.

Treatment of in-stent restenosis using intravascular brachytherapy (IVBT) has been demonstrated to be successful and has become the standard of care for native coronary artery disease. Based on the current Food and Drug Administration (FDA) indications for use and the clinical demand to increase the scope of this form of therapy to include saphenous vein grafts for the Beta-Cath System (Novoste Corporation, Norcross, Georgia), we set out to obtain institutional approval for off-label use. Identification of institutional regulatory bodies and related procedures for obtaining off-label device use was performed. Additionally, the IVBT written directive proscription and patient informed consent forms were revised to accurately administer radiation dose and to disclose the regulatory status of using IVBT for this anatomic site. While the specifics are outlined in this report, this process and the resources needed to obtain institutional approval for off-label use are indicative of that to be expected at similar institutions.

Blood Vessel Prosthesis Implantation↗
PubMed2003

Limited resection for non-small cell lung cancer: observed local control with implantation of I-125 brachytherapy seeds.

BACKGROUND: Limited resection for lung cancer has been associated with a relatively high incidence of local recurrence. This retrospective study evaluates the impact of implanting radioactive iodine-125 (125I) seeds along the resection margin in these patients. METHODS: Thirty-three patients with lung cancer who were not candidates for lobectomy or pneumonectomy underwent a limited resection of 35 primary non-small cell lung cancers. 125I brachytherapy seeds were implanted along the resection margin to reduce the risk of local recurrence. Survival using the Kaplan-Meier method and sites of recurrence were documented. Follow-up ranged from 20 to 98 months (median, 51 months). RESULTS: The 5-year survival was 47% for all patients. For patients with T1N0 tumors, it was 67%, and for patients with T2N0 tumors, it was 39%. However, the cancer-specific survivals were 77% and 53% for patients with T1N0 and T2N0 tumors, respectfully. Ten patients experienced recurrence, with two local (at the resection margin) and six regional recurrences (five mediastinum, one chest wall). Both local recurrences and one regional recurrence occurred in the 19 patients with T1N0 tumors. CONCLUSIONS: 125I seed implantation along the resected margin for compromised patients undergoing limited resection of lung cancer results in a relatively low incidence of local recurrence and may prolong survival.

Aged↗
PubMed2003

Determination of the 4 mm Gamma Knife helmet relative output factor using a variety of detectors.

Though the 4 mm Gamma Knife helmet is used routinely, there is disagreement in the Gamma Knife users community on the value of the 4 mm helmet relative output factor. A range of relative output factors is used, and this variation may impair observations of dose response and optimization of prescribed dose. To study this variation, measurements were performed using the following radiation detectors: silicon diode, diamond detector, radiographic film, radiochromic film, and TLD cubes. To facilitate positioning of the silicon diode and diamond detector, a three-dimensional translation micrometer was used to iteratively determine the position of maximum detector response. Positioning of the films and TLDs was accomplished by manufacturing custom holders for each technique. Results from all five measurement techniques indicate that the 4 mm helmet relative output factor is 0.868 +/- 0.014. Within the experimental uncertainties, this value is in good agreement with results obtained by other investigators using diverse techniques.

Radiometry↗