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  1. Article: Imaging Advances in Stereotactic Radiosurgery.

    Tsien, Christina / Drzymala, Robert E / Rich, Keith

    Missouri medicine

    2015  Volume 112, Issue 5, Page(s) 373–378

    Abstract: Novel functional and metabolic MRI imaging provides the ability to analyze tumor tissue properties including tumor vasculature, vascular permeability, tumor cellularity, hypoxia, and tumor proliferation. Stereotactic radiosurgery involves the delivery of ...

    Abstract Novel functional and metabolic MRI imaging provides the ability to analyze tumor tissue properties including tumor vasculature, vascular permeability, tumor cellularity, hypoxia, and tumor proliferation. Stereotactic radiosurgery involves the delivery of a very precise, focal dose of radiation to a target. Recent advances in MR imaging have the potential to improve accuracy for target volume delineation and to potentially improve outcome. Novel MR imaging techniques may also be used in subsequent post-treatment follow-up to distinguish between tumor recurrences versus non-neoplastic treatment-related changes. In this paper, we address multiparametric MR imaging and cerebral angiography as tools to reduce toxicity.
    MeSH term(s) Brain Neoplasms/secondary ; Brain Neoplasms/surgery ; Humans ; Magnetic Resonance Imaging/methods ; Magnetic Resonance Imaging/trends ; Neoplasms/surgery ; Radiosurgery/methods ; Radiosurgery/trends ; Surgery, Computer-Assisted/methods ; Surgery, Computer-Assisted/trends
    Language English
    Publishing date 2015-11-24
    Publishing country United States
    Document type Journal Article
    ZDB-ID 427362-x
    ISSN 0026-6620
    ISSN 0026-6620
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  2. Article ; Online: Completion of Gamma Knife radiosurgery for AVM treatment after unplanned interruption-technical note.

    Raman, Hari S / Santanam, Lakshmi / Vellimana, Ananth K / Drzymala, Robert E / Tsien, Christina I / Zipfel, Gregory J

    Acta neurochirurgica

    2018  Volume 160, Issue 7, Page(s) 1343–1347

    Abstract: Background and importance: Gamma Knife radiosurgery is an established technique for non-urgent treatment of various intracranial pathologies. Intra-procedural dislodgement of the stereotactic frame is an uncommon occurrence that could lead to abortion ... ...

    Abstract Background and importance: Gamma Knife radiosurgery is an established technique for non-urgent treatment of various intracranial pathologies. Intra-procedural dislodgement of the stereotactic frame is an uncommon occurrence that could lead to abortion of ongoing treatment and necessitate more invasive treatment strategies.
    Clinical presentation: In this case report, we describe a novel method for resumption of Gamma Knife treatment after an unplanned intra-procedural interruption. The case example involves a radiosurgical treatment of a Spetzler-Martin grade I arteriovenous malformation.
    Conclusion: Our technique involves integration of scans and coordinate systems from two imaging sessions using the composite isodose line to resolve translational differences, thereby limiting delivery of remaining shots to the untreated region of the lesion. MRI follow-up at 13 months showed a reduction in the nidus size with no evidence of any radiation injury to the surrounding brain parenchyma. We believe this technique will allow care teams to effectively salvage interrupted Gamma Knife procedures and reduce progression to more invasive treatment options.
    MeSH term(s) Aged ; Equipment Failure ; Humans ; Intracranial Arteriovenous Malformations/surgery ; Male ; Postoperative Complications/etiology ; Postoperative Complications/therapy ; Radiosurgery/adverse effects ; Radiosurgery/instrumentation ; Radiosurgery/methods ; Salvage Therapy/methods
    Language English
    Publishing date 2018-02-17
    Publishing country Austria
    Document type Case Reports ; Journal Article
    ZDB-ID 80010-7
    ISSN 0942-0940 ; 0001-6268
    ISSN (online) 0942-0940
    ISSN 0001-6268
    DOI 10.1007/s00701-018-3493-0
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  3. Article ; Online: Recommendations on the practice of calibration, dosimetry, and quality assurance for gamma stereotactic radiosurgery: Report of AAPM Task Group 178.

    Petti, Paula L / Rivard, Mark J / Alvarez, Paola E / Bednarz, Greg / Daniel Bourland, J / DeWerd, Larry A / Drzymala, Robert E / Johansson, Jonas / Kunugi, Keith / Ma, Lijun / Meltsner, Sheridan G / Neyman, Gennady / Seuntjens, Jan P / Shiu, Almon S / Goetsch, Steven J

    Medical physics

    2021  Volume 48, Issue 7, Page(s) e733–e770

    Abstract: The American Association of Physicists in Medicine (AAPM) formed Task Group 178 (TG-178) to perform the following tasks: review in-phantom and in-air calibration protocols for gamma stereotactic radiosurgery (GSR), suggest a dose rate calibration ... ...

    Abstract The American Association of Physicists in Medicine (AAPM) formed Task Group 178 (TG-178) to perform the following tasks: review in-phantom and in-air calibration protocols for gamma stereotactic radiosurgery (GSR), suggest a dose rate calibration protocol that can be successfully utilized with all gamma stereotactic radiosurgery (GSR) devices, and update quality assurance (QA) protocols in TG-42 (AAPM Report 54, 1995) for static GSR devices. The TG-178 report recommends a GSR dose rate calibration formalism and provides tabulated data to implement it for ionization chambers commonly used in GSR dosimetry. The report also describes routine mechanical, dosimetric, and safety checks for GSR devices, and provides treatment process quality assurance recommendations. Sample worksheets, checklists, and practical suggestions regarding some QA procedures are given in appendices. The overall goal of the report is to make recommendations that help standardize GSR physics practices and promote the safe implementation of GSR technologies.
    MeSH term(s) Calibration ; Gamma Rays ; Phantoms, Imaging ; Radiometry ; Radiosurgery ; United States
    Language English
    Publishing date 2021-02-19
    Publishing country United States
    Document type Journal Article
    ZDB-ID 188780-4
    ISSN 2473-4209 ; 0094-2405
    ISSN (online) 2473-4209
    ISSN 0094-2405
    DOI 10.1002/mp.14831
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  4. Article ; Online: Patient-specific independent 3D GammaPlan quality assurance for Gamma Knife Perfexion radiosurgery.

    Mamalui-Hunter, Maria / Yaddanapudi, Sridhar / Zhao, Tianyu / Mutic, Sasa / Low, Daniel A / Drzymala, Robert E

    Journal of applied clinical medical physics

    2013  Volume 14, Issue 1, Page(s) 3949

    Abstract: One of the most important aspects of quality assurance (QA) in radiation therapy is redundancy of patient treatment dose calculation. This work is focused on the patient-specific time and 3D dose treatment plan verification for stereotactic radiosurgery ... ...

    Abstract One of the most important aspects of quality assurance (QA) in radiation therapy is redundancy of patient treatment dose calculation. This work is focused on the patient-specific time and 3D dose treatment plan verification for stereotactic radiosurgery using Leksell Gamma Knife Perfexion (LGK PFX). The virtual model of LGK PFX was developed in MATLAB, based on the physical dimensions provided by the manufacturer. The ring-specific linear attenuation coefficients (LAC) and output factors (OFs) reported by the manufacturer were replaced by the measurement-based collimator size-specific OFs and a single LAC = 0.0065 mm-1. Calculation depths for each LGK PFX shot were obtained by ray-tracing technique, and the dose calculation formalism was similar to the one used by GammaPlan treatment planning software versions 8 and 9. The architecture of the QA process was based on the in-house online database search of the LGK PFX database search for plan-specific information. A series of QA phantom plans was examined to verify geometric and dosimetric accuracy of the software. The accuracy of the QA process was further evaluated through evaluation of a series of patient plans. The shot time/focus point dose verification for each shot took less than 1 sec/shot with full 3D isodose verification taking about 30 sec/shot on a desktop PC. GammaPlan database access time took less than 0.05 sec. The geometric accuracy (location of the point of maximum dose) of the phantom and patient plan was dependent on the resolution of the original dose matrix and was of the order of 1 dose element. Dosimetric accuracy of the independently calculated phantom and patient point (focus) doses was within 3.5% from the GammaPlan, with the mean = 2.3% and SD= 1.1%. The process for independent pretreatment patient-specific Gamma Knife Perfexion time and dose verification was created and validated.
    MeSH term(s) Equipment Design ; Equipment Failure Analysis ; Humans ; Patient-Centered Care/standards ; Quality Assurance, Health Care/methods ; Radiosurgery/instrumentation ; Radiosurgery/methods ; Radiosurgery/standards ; Radiotherapy Dosage ; Radiotherapy Planning, Computer-Assisted/methods ; Radiotherapy Planning, Computer-Assisted/standards ; United States
    Language English
    Publishing date 2013-01-07
    Publishing country United States
    Document type Journal Article
    ZDB-ID 2010347-5
    ISSN 1526-9914 ; 1526-9914
    ISSN (online) 1526-9914
    ISSN 1526-9914
    DOI 10.1120/jacmp.v14i1.3949
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  5. Article ; Online: Effect of liquid embolic agents on Gamma Knife surgery dosimetry for arteriovenous malformations. Clinical article.

    Mamalui-Hunter, Maria / Jiang, Thomas / Rich, Keith M / Derdeyn, Colin P / Drzymala, Robert E

    Journal of neurosurgery

    2011  Volume 115, Issue 2, Page(s) 364–370

    Abstract: Object: The effectiveness of Gamma Knife stereotactic surgery to obliterate brain arteriovenous malformations (AVMs) may be diminished by the preoperative adjunctive use of endovascular liquid embolic agents. The purpose of the present investigation was ...

    Abstract Object: The effectiveness of Gamma Knife stereotactic surgery to obliterate brain arteriovenous malformations (AVMs) may be diminished by the preoperative adjunctive use of endovascular liquid embolic agents. The purpose of the present investigation was to determine if commercially available liquid embolic agents reduce the radiation dose to the target because of attenuation of the (60)Co beam.
    Methods: The apparent linear attenuation coefficients for 120- to 140-keV radiographs in embolized regions were retrieved from CT scans for several patients with AVMs who had undergone embolization procedures with liquid embolic agents to reduce nidal volumes. Based on these coefficients and a virtual model of Gamma Knife surgery (GKS) with basic ray tracing, the authors obtained the path lengths and densities of the embolized regions. The attenuation of (60)Co beams was then calculated for various sizes and positions of embolized AVM regions and for the number of beams used for treatment. Published experiments for several high-atomic-number materials were used to estimate the effective (60)Co beam attenuation coefficients for the N-butyl cyanoacrylate (NBCA, suspended in ethiodized oil) and ethylene vinyl alcohol copolymer (EVOH, with suspended micronized tantalum powder, Onyx) used in the AVM embolizations. Dose reductions during GKS were calculated for a theoretical model based on the CT-documented apparent linear attenuation coefficients and for the (60)Co energy attenuation coefficient. Dose measurements were obtained in a phantom study with EVOH for comparison with the estimates generated from the two attenuation coefficients.
    Results: Based on CT (keV) apparent attenuation coefficients, the authors' theoretical model predicted that the cumulative effect of either of the embolic agents decreased the number of kilovoltage photons in an embolized nidus by -8% to -15% because of the increased atomic number and density of NBCA and Onyx. However, in using the effective attenuation coefficient for the (60)Co energies as is used in GKS, the authors' theoretical model yielded only a 0.2% dose reduction per beam and a < 0.01%-0.2% dose reduction in total. These theoretical results were validated by measurements in a head phantom containing Onyx.
    Conclusions: Dose reduction due to attenuation of the (60)Co beam by the AVM embolization material was negligible for both NBCA and EVOH because of the high-energy (60)Co beam.
    MeSH term(s) Dimethyl Sulfoxide/therapeutic use ; Embolization, Therapeutic/methods ; Enbucrilate/therapeutic use ; Humans ; Intracranial Arteriovenous Malformations/diagnostic imaging ; Intracranial Arteriovenous Malformations/drug therapy ; Intracranial Arteriovenous Malformations/surgery ; Polyvinyls/therapeutic use ; Radiography ; Radiosurgery/instrumentation ; Radiotherapy Dosage
    Chemical Substances Onyx copolymer ; Polyvinyls ; Enbucrilate (F8CEP82QNP) ; Dimethyl Sulfoxide (YOW8V9698H)
    Language English
    Publishing date 2011-08
    Publishing country United States
    Document type Journal Article
    ZDB-ID 3089-2
    ISSN 1933-0693 ; 0022-3085
    ISSN (online) 1933-0693
    ISSN 0022-3085
    DOI 10.3171/2011.3.JNS10717
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  6. Article: Acute Hemorrhage Following Gamma Knife Radiosurgery to a Clival Meningioma.

    Reynolds, Matthew R / Hawasli, Ammar H / Murphy, Rory K J / Ray, Wilson Z / Simpson, Joseph R / Drzymala, Robert E / Rich, Keith M

    Journal of spine & neurosurgery

    2014  Volume 2, Issue 2, Page(s) 108

    Abstract: Background: Gamma Knife radiosurgery (GKS) is a primary treatment modality for small, surgically-challenging meningiomas of the skull base in carefully selected patients. Despite the overall low incidence of complications from this procedure, rare ... ...

    Abstract Background: Gamma Knife radiosurgery (GKS) is a primary treatment modality for small, surgically-challenging meningiomas of the skull base in carefully selected patients. Despite the overall low incidence of complications from this procedure, rare instances of hemorrhagic events following GKS have been reported. In fact, only a single, probable case of acute hemorrhage after GKS for a meningioma exists in the literature.
    Case description: The authors present the case of a 59-year-old female treated with GKS to a clival meningioma who suffered an acute intra- and peritumoral hemorrhage within three hours after the procedure. The patient also had an ST-elevation myocardial infarction associated with the hemorrhage. At the time of her GKS she was taking aspirin and clopidogrel for treatment of coronary artery disease with multiple cardiac stents. Cerebral catheter angiography failed to reveal a source for the hemorrhage.
    Conclusion: Acute hemorrhage following GKS to a meningioma is a rare, but potentially serious, complication and consideration should be given to counseling patients of this risk prior to treatment. We hypothesize that acute change to the structural integrity of the vascular endothelium after GKS may have precipitated cerebrovascular dysfunction resulting in hemorrhage. While the administration of anti-platelet therapy may have been a contributing factor to his event, it appears that the low incidence of acute tumoral bleeding after GKS does not justify routinely discontinuing anti-platelet and/or anti-coagulation in patients with severe associated medical co-morbidities.
    Language English
    Publishing date 2014-03-17
    Publishing country United States
    Document type Journal Article
    ISSN 2325-9701
    ISSN 2325-9701
    DOI 10.4172/2325-9701.1000108
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  7. Article ; Online: Dosimetric predictors of chest wall pain after lung stereotactic body radiotherapy.

    Creach, Kimberly M / El Naqa, Issam / Bradley, Jeffrey D / Olsen, Jeffrey R / Parikh, Parag J / Drzymala, Robert E / Bloch, Charles / Robinson, Clifford G

    Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology

    2012  Volume 104, Issue 1, Page(s) 23–27

    Abstract: Purpose: To identify risk factors for the development of chest wall (CW) pain after thoracic stereotactic body radiotherapy (SBRT).: Methods and materials: A registry of patients with lung lesions treated with lung SBRT was explored to identify ... ...

    Abstract Purpose: To identify risk factors for the development of chest wall (CW) pain after thoracic stereotactic body radiotherapy (SBRT).
    Methods and materials: A registry of patients with lung lesions treated with lung SBRT was explored to identify patients treated with 54 Gy in three fractions or 50 Gy in five fractions. One hundred and forty-six lesions in 140 patients were identified; complete electronic treatment plans were available on 86 CWs. The CW was contoured as a 3 cm outward expansion from the involved lung. Univariate and multivariate analyses were used to correlate patient, tumor, and dosimetric factors to the development of CW toxicity.
    Results: CW pain occurred in 22 patients (15.7%). The Kaplan-Meier estimated risk of CW pain at 2 years was 20.1% (95% C.I., 13.2-28.8%). On univariate analysis of patient factors, elevated BMI (p=0.026) and connective tissue disease (p=0.036) correlated with CW pain. The percent of CW receiving 30, 35, or 40 Gy was most predictive of CW pain on multivariate analysis using logistic regression, while V40 alone was predictive using Cox regression. A V30 threshold of 0.7% and V40 threshold of 0.19% was correlated with a 15% risk of CW pain.
    Conclusions: We have described patient and dosimetric parameters that correlate with CW pain after lung SBRT. The risk of CW pain may be mitigated by attempting to reduce the relative proportion of CW receiving 30-40 Gy during treatment planning.
    MeSH term(s) Adult ; Aged ; Aged, 80 and over ; Female ; Humans ; Logistic Models ; Lung Neoplasms/surgery ; Male ; Middle Aged ; Pain/etiology ; Radiosurgery/adverse effects ; Radiotherapy Dosage ; Thoracic Wall/radiation effects
    Language English
    Publishing date 2012-07
    Publishing country Ireland
    Document type Journal Article
    ZDB-ID 605646-5
    ISSN 1879-0887 ; 0167-8140
    ISSN (online) 1879-0887
    ISSN 0167-8140
    DOI 10.1016/j.radonc.2012.01.014
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  8. Article ; Online: Errors in radiation oncology: a study in pathways and dosimetric impact.

    Klein, Eric E / Drzymala, Robert E / Purdy, James A / Michalski, Jeff

    Journal of applied clinical medical physics

    2005  Volume 6, Issue 3, Page(s) 81–94

    Abstract: As complexity for treating patients increases, so does the risk of error. Some publications have suggested that record and verify (R&V) systems may contribute in propagating errors. Direct data transfer has the potential to eliminate most, but not all, ... ...

    Abstract As complexity for treating patients increases, so does the risk of error. Some publications have suggested that record and verify (R&V) systems may contribute in propagating errors. Direct data transfer has the potential to eliminate most, but not all, errors. And although the dosimetric consequences may be obvious in some cases, a detailed study does not exist. In this effort, we examined potential errors in terms of scenarios, pathways of occurrence, and dosimetry. Our goal was to prioritize error prevention according to likelihood of event and dosimetric impact. For conventional photon treatments, we investigated errors of incorrect source-to-surface distance (SSD), energy, omitted wedge (physical, dynamic, or universal) or compensating filter, incorrect wedge or compensating filter orientation, improper rotational rate for arc therapy, and geometrical misses due to incorrect gantry, collimator or table angle, reversed field settings, and setup errors. For electron beam therapy, errors investigated included incorrect energy, incorrect SSD, along with geometric misses. For special procedures we examined errors for total body irradiation (TBI, incorrect field size, dose rate, treatment distance) and LINAC radiosurgery (incorrect collimation setting, incorrect rotational parameters). Likelihood of error was determined and subsequently rated according to our history of detecting such errors. Dosimetric evaluation was conducted by using dosimetric data, treatment plans, or measurements. We found geometric misses to have the highest error probability. They most often occurred due to improper setup via coordinate shift errors or incorrect field shaping. The dosimetric impact is unique for each case and depends on the proportion of fields in error and volume mistreated. These errors were short-lived due to rapid detection via port films. The most significant dosimetric error was related to a reversed wedge direction. This may occur due to incorrect collimator angle or wedge orientation. For parallel-opposed 60 degrees wedge fields, this error could be as high as 80% to a point off-axis. Other examples of dosimetric impact included the following: SSD, approximately 2%/cm for photons or electrons; photon energy (6 MV vs. 18 MV), on average 16% depending on depth, electron energy, approximately 0.5 cm of depth coverage per MeV (mega-electron volt). Of these examples, incorrect distances were most likely but rapidly detected by in vivo dosimetry. Errors were categorized by occurrence rate, methods and timing of detection, longevity, and dosimetric impact. Solutions were devised according to these criteria. To date, no one has studied the dosimetric impact of global errors in radiation oncology. Although there is heightened awareness that with increased use of ancillary devices and automation, there must be a parallel increase in quality check systems and processes, errors do and will continue to occur. This study has helped us identify and prioritize potential errors in our clinic according to frequency and dosimetric impact. For example, to reduce the use of an incorrect wedge direction, our clinic employs off-axis in vivo dosimetry. To avoid a treatment distance setup error, we use both vertical table settings and optical distance indicator (ODI) values to properly set up fields. As R&V systems become more automated, more accurate and efficient data transfer will occur. This will require further analysis. Finally, we have begun examining potential intensity-modulated radiation therapy (IMRT) errors according to the same criteria.
    MeSH term(s) Medical Errors/prevention & control ; Medical Errors/statistics & numerical data ; Missouri/epidemiology ; Particle Accelerators/statistics & numerical data ; Radiation Oncology/statistics & numerical data ; Radiometry/statistics & numerical data ; Radiotherapy Dosage ; Radiotherapy Planning, Computer-Assisted/statistics & numerical data ; Risk Assessment/methods ; Risk Factors
    Language English
    Publishing date 2005-08-12
    Publishing country United States
    Document type Journal Article
    ZDB-ID 2010347-5
    ISSN 1526-9914 ; 1526-9914
    ISSN (online) 1526-9914
    ISSN 1526-9914
    DOI 10.1120/jacmp.v6i3.2105
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  9. Article ; Online: A Gamma-Knife-Enabled Mouse Model of Cerebral Single-Hemisphere Delayed Radiation Necrosis.

    Jiang, Xiaoyu / Yuan, Liya / Engelbach, John A / Cates, Jeremy / Perez-Torres, Carlos J / Gao, Feng / Thotala, Dinesh / Drzymala, Robert E / Schmidt, Robert E / Rich, Keith M / Hallahan, Dennis E / Ackerman, Joseph J H / Garbow, Joel R

    PloS one

    2015  Volume 10, Issue 10, Page(s) e0139596

    Abstract: Purpose: To develop a Gamma Knife-based mouse model of late time-to-onset, cerebral radiation necrosis (RN) with serial evaluation by magnetic resonance imaging (MRI) and histology.: Methods and materials: Mice were irradiated with the Leksell Gamma ... ...

    Abstract Purpose: To develop a Gamma Knife-based mouse model of late time-to-onset, cerebral radiation necrosis (RN) with serial evaluation by magnetic resonance imaging (MRI) and histology.
    Methods and materials: Mice were irradiated with the Leksell Gamma Knife® (GK) PerfexionTM (Elekta AB; Stockholm, Sweden) with total single-hemispheric radiation doses (TRD) of 45- to 60-Gy, delivered in one to three fractions. RN was measured using T2-weighted MR images, while confirmation of tissue damage was assessed histologically by hematoxylin & eosin, trichrome, and PTAH staining.
    Results: MRI measurements demonstrate that TRD is a more important determinant of both time-to-onset and progression of RN than fractionation. The development of RN is significantly slower in mice irradiated with 45-Gy than 50- or 60-Gy, where RN development is similar. Irradiated mouse brains demonstrate all of the pathologic features observed clinically in patients with confirmed RN. A semi-quantitative (0 to 3) histologic grading system, capturing both the extent and severity of injury, is described and illustrated. Tissue damage, as assessed by a histologic score, correlates well with total necrotic volume measured by MRI (correlation coefficient = 0.948, with p<0.0001), and with post-irradiation time (correlation coefficient = 0.508, with p<0.0001).
    Conclusions: Following GK irradiation, mice develop late time-to-onset cerebral RN histology mirroring clinical observations. MR imaging provides reliable quantification of the necrotic volume that correlates well with histologic score. This mouse model of RN will provide a platform for mechanism of action studies, the identification of imaging biomarkers of RN, and the development of clinical studies for improved mitigation and neuroprotection.
    MeSH term(s) Animals ; Brain/pathology ; Brain/radiation effects ; Dose Fractionation, Radiation ; Female ; Magnetic Resonance Imaging ; Mice ; Mice, Inbred BALB C ; Necrosis/pathology ; Radiation Injuries, Experimental/pathology ; Radiosurgery
    Language English
    Publishing date 2015-10-06
    Publishing country United States
    Document type Journal Article ; Research Support, N.I.H., Extramural
    ISSN 1932-6203
    ISSN (online) 1932-6203
    DOI 10.1371/journal.pone.0139596
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  10. Article: Validation of calculations for electrons modulated with conventional photon multileaf collimators.

    Klein, Eric E / Vicic, Milos / Ma, Chang-Ming / Low, Daniel A / Drzymala, Robert E

    Physics in medicine and biology

    2008  Volume 53, Issue 5, Page(s) 1183–1208

    Abstract: Treating shallow tumors with a homogeneous dose while simultaneously minimizing the dose to distal critical organs remains a challenge in radiotherapy. One promising approach is modulated electron radiotherapy (MERT). Due to the scattering properties of ... ...

    Abstract Treating shallow tumors with a homogeneous dose while simultaneously minimizing the dose to distal critical organs remains a challenge in radiotherapy. One promising approach is modulated electron radiotherapy (MERT). Due to the scattering properties of electron beams, the commercially provided secondary and tertiary photon collimation systems are not conducive for electron beam delivery when standard source-to-surface distances are used. Also, commercial treatment planning systems may not accurately model electron-beam dose distributions when collimated without the standard applicators. However, by using the photon multileaf collimators (MLCs) to create segments to modulate electron beams, the quality of superficial tumor dose distributions may improve substantially. The purpose of this study is to develop and evaluate calculations for the narrow segments needed to modulate megavoltage electron beams using photon beam multileaf collimators. Modulated electron radiotherapy (MERT) will be performed with a conventional linear accelerator equipped with a 120 leaf MLC for 6-20 MeV electron beam energies. To provide a sharp penumbra, segments were delivered with short SSDs (70-85 cm). Segment widths (SW) ranging from 1 to 10 cm were configured for delivery and planning, using BEAMnrc Monte Carlo (MC) code, and the DOSXYZnrc MC dose calculations. Calculations were performed with voxel size of 0.2 x 0.2 x 0.1 cm3. Dosimetry validation was performed using radiographic film and micro- or parallel-plate chambers. Calculated and measured data were compared using technical computing software. Beam sharpness (penumbra) degraded with decreasing incident beam energy and field size (FS), and increasing SSD. A 70 cm SSD was found to be optimal. The PDD decreased significantly with decreasing FS. The comparisons demonstrated excellent agreement for calculations and measurements within 3%, 1 mm. This study shows that accurate calculations for MERT as delivered with existing photon MLC are feasible and allows the opportunity to take advantage of the dynamic leaf motion capabilities and control systems, to provide conformal dose distributions.
    MeSH term(s) Electrons ; Monte Carlo Method ; Photons/therapeutic use ; Radiotherapy Dosage ; Radiotherapy, Conformal/methods
    Language English
    Publishing date 2008-03-07
    Publishing country England
    Document type Journal Article ; Validation Studies
    ZDB-ID 208857-5
    ISSN 1361-6560 ; 0031-9155
    ISSN (online) 1361-6560
    ISSN 0031-9155
    DOI 10.1088/0031-9155/53/5/003
    Database MEDical Literature Analysis and Retrieval System OnLINE

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