bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐C‐213AB‐10: Computational Tumor Modeling for Dose Painting Candidate Stratification
Authors: Harmon S , Titz B , Jeraj R
Published: June 2012

Purpose: Dose painting plans are generally created by redistributing an arbitrarily chosen portion of the prescription dose (D Rx) according to a map of biological characteristics. This study investigated how different levels of redistributed dose affect patient‐specific therapeutic gain. Methods: Twelve canine patients with sinonasal tumors underwent pre‐therapy PET/CT imaging of proliferation using [1 8F]FLT. Following two fractions of uniform dose and two off‐treatment days, early proliferative response was assessed via follow‐up [1 8F]FLT PET/CT. Using an imaging‐based tumor simulation model, voxel‐based, ‘effective’ linear radio‐sensitivity values (a eff) were extracted from registered PET images. Based on these a eff maps, dose painting plans were generated featuring dose redistribution levels of 5%, 10%, 25%, 50%, and 100% D Rx. Individual end‐of‐treatment responses to each plan were simulated, analyzed, and compared to a reference uniform plan. Results: With increasing levels of dose redistribution, average cell kill increased in all but one patient, indicating therapeutic gain. As the redistributed dose increased from 5% to 100%, mean proliferative activity decreased by 3%–5% in three patients, while nine patients showed a more pronounced reduction by 8%–38%. For these nine benefiting patients, most substantial gains were observed when redistributing 10%, 25%, and 50% D Rx (up to 14%, 25%, and 33% increase in average cell kill, respectively). When redistributing 5% D Rx, the decrease in average cell survival was below 4% in ten patients, suggesting minimal therapeutic gain relative to the uniform plan. Similarly, increasing the redistributed dose from 50% to 100% D Rx resulted in only modest gains (less than 5% on average) in cell kill for all patients. Conclusions: Results indicate that the majority of patients would benefit from dose painting. Computational modeling based on imaged proliferative response to a uniform test dose could allow for candidate patient stratification. For suitable patients, the redistributed dose should be optimized to within 10–50% D Rx.
TH‐C‐BRCD‐01: Small Field Dosimetry: A Clinical Perspective
Authors: Das I
Published: June 2012

Small fields on the order of few millimeters are now being used in specialized radiation treatments such as intensity modulated radiation therapy (IMRT), stereotactic radiosurgery (SRS), cyber‐knife and gamma‐knife. Small‐field dosimetry is challenging due to finite source size, lack of electronic equilibrium, size of detectors, changes in energy spectrum with associated dosimetric parameters and stopping power ratio. Source size is dependent on the design of the accelerator and could be obstructed by the collimating system with decreasing field sizes. Electronic equilibrium is a phenomenon associated with the range of secondary particles and hence dependent on the beam energy, spectrum and the composition of the medium (homogeneous vs inhomogeneous). This talk will elaborate on current understanding of the small field dosimetry. It will provide insight of the new IAEA/AAPM non‐complainant dosimetry (1) IPEM report 103 (2) and AAPM task group report 155(3). Explanation of the difficulties and possible solutions to accurately measure dose in small fields with various techniques (ion chamber, diode, diamond, TLD, films (radiographic and Gafchromic), MOSFET, bang gel, and Monte Carlo) will be elaborated. Correction factors that have been published will be presented and the consequences in accuracy for patient care will be discussed.

Learning Objectives:

1. Description of absolute and relative dosimetry

2. Definition of small fields

3. Choice of detector

4. Correction factor

5. Understanding the implication of small fields in clinical practice1.

Alfonso P, Andreo P, Capote R, et al. A new formalism for refeence dosimetry of small and nonstandard fields. Med Phys 2008;35:5179‐5186.2.Aspradakis MM. Report No 103: Small Field MV dosimetry. York, England: IPEM; 2010.3. Das IJ, Francescon P, Ahnesjö A, et al. Task Group 155 report: Small fields and non‐equilibrium condition photon beam dosimetry. Med Phys (under review).
TH‐C‐BRB‐02: Dosimetric Analysis of Inverse‐Planned Modulated‐Arc Total‐Body Irradiation
Authors: Held M , Kirby N , Morin O , Pouliot J
Published: June 2012

Purpose: To determine the key dosimetric characteristics of a newly developed and clinically implemented inverse‐planned modulated‐arc total‐body irradiation (MATBI) technique, including optimal treatment beam parameters, a redefined beam model, and patient‐specific quality assurance (QA). Methods: During MATBI treatment, the patient is positioned prone and supine underneath the gantry at 2 m source‐to‐surface distance (SSD). The dose is delivered using open‐field beams at different gantry angles. Monitor units per beam are inverse‐planned through beam‐weight optimization based on the patient's anatomy from full‐body computed tomography (CT) images. Beam output characteristics were measured at extended SSD and a new beam model was commissioned. Delivery time and dose uniformity were studied vs. beam field size and geometry. Dose delivery accuracy was determined by comparing ion chamber measurements inside anthropomorphic water phantoms to planning system predictions. A phantom with Gaf‐Chromic film inserts was designed for clinical use to streamline patient‐specific QA. Results: MATBI was used on 17 patients so far. The best dose uniformity and shortest delivery time were achieved for a beam field size of 40×40 cm2 at isocenter with 5° step size between adjacent beams, using 16 to 28 beams per side depending on patient size. Compared to the original beam model, the new beam model improved the dose delivery accuracy by a fraction of a percent to 1.2%. The largest discrepancy between measurement and prediction was 3.2%. The patient‐specific QA procedure showed that QA with a 5% tolerance limit could be routinely performed. Conclusions: The new inverse‐planned MATBI technique permits dose optimization, dose‐volume histogram calculation and dosimetric analysis. MATBI beam setup parameters for optimal dose uniformity and treatment duration were determined. The developed phantom allows for a patient‐specific quality assurance procedure, which is now used routinely. These results are the basis for the safe and accurate clinical implementation of MATBI. Work supported by Siemens.
TH‐C‐BRB‐06: Tools and Methods for On‐Line Adaptive Radiation Therapy
Authors: Chang J , Heaton R , Cho Y , Jaffray D , Islam M
Published: June 2012

Purpose: Essential tools required for daily field modifications for compensating small target variations have been investigated. A deformable registration method was used to generate deformation vector field (DVF), which is subsequently used to modify treatment fields. An on‐line beam monitor was evaluated for validating the adapted fields. Methods: An adaptive treatment process consists of the following steps: (1) Determine the DVF using the irradiated volumes (IV) of the reference and daily image sets. The IV is constructed by back‐projections of respective complete irradiation area outlines of all beams. (2) The deformed contours (CD) were calculated using DVF and the reference contours. (3) Determine MLC leaf adjustments using CD and DVF to form the adapted fields. This approach was investigated using two CT image sets, one acquired during the treatment course, and corresponding IMRT plan data for patients undergoing prostate treatment. A planning study was performed to compare the dose distributions between optimized IMRT and the adapted plans. The adapted field delivery was validated by an online beam monitoring system, termed IQM; which consists of a spatially sensitive area ion chamber mounted below the MLC to provide a fluence‐area‐product signal and a calculation module to predict the signal. Results: Approximately 10 minutes were required to generate the DVF between the reference IV and a daily IV using readily available computer hardware. The dose distribution using adapted fields compare well with the optimized plans in terms of DVH and conformity indices. The average agreement between the IQM predicted signals of the adapted fields with those of measured were within 2%. Conclusions: The method of generating the DVF was promising, in terms of speed and effectiveness for small variations of target. The IQM system was able to validate the delivery of appropriate adapted fields, fulfilling the requirement for pre‐treatment quality control. Ontario Consortium for Adaptive Interventions in Radiation Oncology (OCAIRO)
TH‐C‐BRB‐07: Feasibility of Online Range Adaptive Spot Scanning Proton Therapy
Authors: Cheung J , Park P , Zhu X , Frank S , Court L , Kudchadker R , Dong L
Published: June 2012

Purpose: To assess the feasibility of an online adaptive proton therapy technique for discrete spot scanning proton therapy (SSPT) to correct for interfractional anatomic changes. Methods: An adaptive algorithm was developed to compensate for range changes without full reoptimization. The individual spot energies from the original treatment plan were adjusted to match the new anatomy based on the water equivalent pathlength to the distal edge of the target on a ray‐by‐ray basis. Remaining spots outside of (proximal‐ and lateral‐to) the target were then removed or spots were added if necessary. The newly adapted plan was imported back to the treatment planning system for dose computation using the new spot arrangement. Three lung patients were selected with targets of variable sizes in the right upper lobe and a single beam (Right Lateral) SSPT plan was tested using this approach. These patients were selected based on large anatomical changes over the course of treatment, with an average GTV and CTV shrinkage of 38% and 19%, respectively, by the end of treatment. A total of 19 weekly CT images were analyzed. Results: The dose to normal tissue, especially distal to the target, was reduced after applying the proposed adaptive technique. The maximum improvement in mean and V20Gy contralateral lung dose between the adapted and non‐adapted plans were 13.4Gy and 18.6Gy, respectively. The maximum improvement in spinal cord Dmax and D1cc were 31.2Gy and 38.9Gy, respectively. Target coverage decreased for both the adapted and non‐adapted plans, but the D95% target dose for the adapted plan remained =80% while the D95% target dose for the non‐adapted plans dropped to as low as 43.1%. Conclusions: The adaptive procedure shows promise to reduce normal tissue doses and improve target coverage without a full reoptimization. Improvement in spot adjustment strategy may be needed to further improve target coverage. Funding support provided by: The University of Texas Gradate School of Biomedical Sciences at Houston and the University of Texas MD Anderson Cancer Center, Houston, TX. Supported in part by NCI P01CA021239‐29A1.
TH‐C‐BRB‐08: Four‐Dimensional Monte Carlo Simulations of Lung Cancer Patients Treated with Proton Beam Scanning to Assess Interplay Effects
Authors: Grassberger C , Shackleford J , Sharp G , Paganetti H
Published: June 2012

Purpose: To study the effects of breathing motion on lung cancer patients treated with active scanning proton therapy using four‐dimensional Monte Carlo simulations. Beam data and machine parameters from two proton therapy centers are used to study the effect of varying spot‐sizes and time to switch between energy layers. Methods: For Monte Carlo simulations we employ TOPAS (TOol for PArticle Simulation), a toolkit based on Geant4. We developed methods to convert the output of our scanning treatment planning system into input suitable for Monte Carlo simulations. Furthermore we take into account the exact timeline of delivery, from the momentum‐dependent spot movement to the time to switch between energy layers, enabling our Monte Carlo code to deliver the right spots to each of the 10 breathing phases of the patient's 4DCT dataset. Deformable image registration is employed to translate the dose delivered to each phase back to a reference phase for analysis. Results: Patients show signs of interplay effect already at peak‐to‐peak movement amplitudes of 7.5mm. The spot size seems to have a significant impact on the dose homogeneity in the target: in one patient case the D95 of the CTV drops by only 2.7% for the large spot‐size, while it is reduced by 8.9% for the smaller one. In this patient the mean dose in the CTV is reduced as well for small spots (−4.7%), while remaining stable for the broader peaks. The time to switch energy layers has also a significant impact, though the changes seem to be more related to the absolute length of the treatment compared to the breathing cycle. Conclusions: This is the first time Monte Carlo is employed to study the interplay effect in proton beam scanning. The results show a clear variation of the effect for varying machine parameters in different patient cases. This research has been supported by NIH/NCI grant R01 CA111590.
TH‐C‐BRB‐09: Commissioning of Intensity Modulated Neutron Radiotherapy (IMNRT)
Authors: Burmeister J , Spink R , Liang L , Bossenberger T , Halford R , Brandon J , Delauter J , Snyder M
Published: June 2012

Purpose: A system for planning and delivery of Intensity Modulated Neutron Radiotherapy (IMNRT) was developed using in‐house treatment planning and delivery systems. Results of commissioning tests are presented including validation measurements using representative patient plans and the TG‐119 test suite, and evaluation of total body dose. Methods: Tissue Equivalent (TE) ionization chambers flowed with TE gas and an ionization chamber array filled with TE gas were used for point dose and planar dose distribution comparisons with calculated values. Validation plans were delivered to water and solid water phantoms using TG‐119 measurement points and evaluation techniques. Planar dose measurements were performed in solid water and gamma pass rates calculated using 3%/3mm and 5% threshold criteria. Gamma and neutron doses were evaluated at 50cm off axis for IMNRT and conventional neutron therapy plans to evaluate effects on out‐of‐field dose. Results: Measured and calculated doses for eleven representative plans (6 prostate/5 H&N) agree to within ‐0.8±1.4% and 5.0±6.0% within and outside the target, respectively. All twelve TG‐119 point measurements delivered in solid water were within respective confidence intervals derived by TG‐119. Ten of twelve measurements in water were within respective confidence intervals. Mean differences for all measurements were 0.5% (max=7.0%) and 1.4% (max=4.1 %) in water and solid water, respectively. The mean gamma pass rate for all cases was 92.7% (min=88.6%). Out‐of‐field dose equivalent from IMNRT is ∼10 times higher than from photon IMRT but not significantly higher than from conventional fast neutron therapy. Conclusions: Ion chamber validation results for IMNRT commissioning are comparable to those from photon IMRT. Gamma pass rates for planar dose distributions are lower than typical for photon IMRT but may be improved with improved planar dosimetry techniques. Significantly higher out‐of‐field doses require careful clinical consideration to assure that benefits of IMNRT outweigh potential risks of second malignancy.
TH‐C‐BRB‐10: Clinical Implication of the New Dosimetry Formalism in IMRT Quality Assurance
Authors: Chung E , Conneely E , Ruo R , Foley M , Seuntjens J
Published: June 2012

Purpose: To apply the new dosimetry formalism [Med. Phys. 35, 5179 (2008)] to clinical IMRT quality assurance (QA). Methods: 20 different linear accelerator (Varian Clinac 21 EX)‐based clinical IMRT fields were transferred to the CT images of a 30×30×17 cm3 Solid Water phantom to create IMRT QA fields. The phantom position was adjusted for each QA field to place the detector or chamber at the lowest dose gradient region in a virtual PTV. The reference doses in the IMRT QA and 10×10 cm2 fields were measured using a PTW micro liquid ion chamber (microLion). Based on the new dosimetry formalism, the clinical correction factor of each IMRT QA field was measured for a calibrated Exradin A12 Farmer‐type chamber in a fully‐rotated delivery and a delivery at a single gantry angle, a collapsed delivery. For each QA field, the measured dose with the correction factor was compared with a calculated dose using Analytical Anisotropic Algorithm (AAA) or Monte Carlo (MC) methods. Results: The clinical correction factor deviated from unity by up to 2.4% and 3.7% in the fully‐rotated and collapsed deliveries, respectively, depending on the dose homogeneity at the Exradin A12 collecting volume. In the fully‐rotated delivery, the measured dose with the correction factor is different from the calculated dose to within 5% and 3% for the AAA and MC, respectively. In the collapsed delivery, the discrepancy between the measured and AAA‐calculated doses was to within 8%, while it was improved to within 3.5% compared with the MC‐calculated dose. When applying the clinical correction factor, the decrease of the measured and calculated dose discrepancy is more significant for an IMRT QA field having higher dose heterogeneity. Conclusions: This work proves that the suggested dosimetry technique is effective to improve the dosimetric consistency of clinical IMRT QA.
TH‐C‐BRB‐12: The Magnitude of H&N IMRT Dose Delivery Errors from Three Possible Failure Modes: Beam Quality, Symmetry, and MLC Position
Authors: Tonigan J , Kry S , Summers P , Balter P , Diel T , Followill D
Published: June 2012

Purpose: Investigate the error in IMRT dose delivery from changes in beam quality, symmetry, and MLC positional errors. Methods: A complex (3533 MU, 216 segments, 0.181 modulation complexity score) H&N IMRT plan was delivered to the RPC's IMRT H&N phantom on a Varian Clinac 2100CD. The plan was delivered as a baseline and then again after adjusting the in‐plane and cross‐plane symmetry by 5% and 3%, respectively. The beam was adjusted back to baseline performance and the beam quality was hardened by nearly 2% (%dd) by altering the bending magnet current. The beam was then readjusted to baseline and the plan was delivered with MLC offsets of +1 mm and +3 mm. Radiochromic film and TLD within the phantom were used to analyze the 2D dose distributions and absolute doses. Results: Relative to the baseline delivery, differences in absolute dose delivery of up to 0.6% and 3.2% were observed with changes in in‐plane and cross‐plane symmetry, respectively. The beam symmetry changes gamma analyses (±7%/4mm) resulted in a 0.4–11% change in the percent of pixels passing. The small change in beam quality resulted in a 6% average absolute dose and 24% pixel pass rate difference. MLC offsets of 1 mm and 3mm resulted in average absolute dose differences of 12% and 32%, respectively, and a gamma analyses 21% and 33% change in pixel pass rate for each offset, respectively. Conclusions: Accurate IMRT dose delivery is a long, complicated chain of events, each of which might contribute to dose delivery errors. Performing a risk‐based FMEA analysis (presented by TG‐100) to establish a QA program for IMRT requires knowledge of the error magnitude in dose delivery from key failure modes. Beam quality and MLC offsets resulted in the largest dose delivery errors. Additional failure modes are being investigated. Work supported by grants CA10953 and CA81647 (NCI, DHHS).
TH‐C‐BRA‐08: Prescription Isodose Line Definitions and Not Set Up Uncertainty Limit the Normal Tissue Irradiation in SBRT of Lung Patients
Authors: Narayanasamy G , Feddock J , Gleason J , McGarry R , Molloy J
Published: June 2012

Purpose: To verify the adequacy of dose delivery in stereotactic body radiotherapy (SBRT) of lung tumor and demonstrate the feasibility of reducing toxicity by revision of treatment margins and prescription isodose lines. Methods: Gross tumor volume (GTV) and others organs were manually segmented by the physician and planning target volume (PTV) was automatically generated in planning computed tomography (pCT) and cone‐beam CT (CBCT) images. These contours were transferred from CBCT to the pCT image, after rigid‐registration. Planned and delivered doses to GTV, PTV and other organs were compared. To study reduction in normal tissue dose (NTD), multiple PTVs were generated using smaller margins around the GTV and a dose‐volume constraint of 95% of prescription dose (Rx) irradiating at least 95% of PTV volume was targeted. An alternate strategy of revising the prescription isodose line was also employed. NTD was measured using volumes of the various isodose lines. Results: In this retrospective study on ten primary lung cancer SBRT patients, the mean dose to the GTV and PTV were lower than planned dose by 1% and 2%, respectively. The mean dose delivered to GTV exceeded the Rx by 19%, proving adequate dosimetric coverage. While reducing treatment margins, the block margins had to be opened up such that the field aperture was almost a constant, in order to meet target dosimetric coverage. Prescribing to lower isodose lines (as % of maximum dose) allowed for reduction in NTD, especially in small tumors and small margins. Conclusions: The feasibility of independent verification of radiation dose delivered by utilizing CBCT imaging system has been demonstrated. NTD could not be changed with tumor margin reduction, but by lowering the prescription isodose line in a stereotactic‐like prescription technique.
TH‐C‐BRA‐11: First Experiments of a Prototype Device for Simultaneous Imaging and Dose Verification in Radiotherapy
Authors: Vial P , Deshpande S , Blake S , McNamara A , Holloway L , Greer P , Kuncic Z
Published: June 2012

Purpose: Current model electronic portal imaging devices (EPIDs) used in radiotherapy are optimised for imaging but problematic for accurate dosimetry. The aim of this project is to develop a new EPID capable of simultaneous imaging and water equivalent dosimetry. This work reports our first experimental results. Methods: A prototype device based on a segmented plastic scintillator (SegmentedPS) was developed. The prototype device was tested in comparison with three other detector configurations, all utilising the same a‐Si photodiode array used in conventional EPIDs. The configurations tested were; i) standard indirect configuration with phosphor/copper (STANDARD), ii) direct configuration with 1.5 cm solid water build‐up (DIRECT), iii) 2 cm thick sheet of plastic scintillator (PSsheet), and iv) 1.5 cm thick prototype SegmentedPS. The sensitivity, dose response and image quality was assessed in each configuration. The dose response was assessed in terms of field size response and off‐axis response relative to reference dose in water measurements at the equivalent depth. The image quality was assessed using an image quality phantom. Results: The sensitivity of each device relative to the STANDARD configuration was 0.03(DIRECT), 0.63(PSsheet), and 0.35(SegmentedPS). The agreement in field size response relative to dose in water data for square field sizes 4 cm to 15 cm was within 4.8%(STANDARD), 0.9%(DIRECT), 22%(PSsheet), and 1.3%(SegmentedPS). The agreement in off‐axis ratios at 15 cm off‐axis, relative to dose in water data, was within 23%(STANARD), 4%(DIRECT), 5%(PSsheet), and 4%(SegmentedPS). Image quality parameters (f50/CNR) for each configuration were 0.41/993(STANDARD), 0.30/167(DIRECT), 0.22/125(PSsheet) and 0.23/214(SegmentedPS). Conclusions: First experiments with the prototype SegmentedPS EPID demonstrated the potential for simultaneous imaging and water equivalent dosimetry. Further design optimisation is required to approach the imaging performance of STANDARD a‐Si EPIDs, while maintaining water equivalent dose response. Cancer Council NSW Research Project Grant (RG 11‐06) Cancer Institute NSW Research Equipment Grant (10/REG/1‐20)
TH‐C‐BRA‐12: Tomographic Measurement of X‐Ray Beam Spot Profiles Using a Rotating Edge
Authors: Star‐Lack J , Etmektzoglou T , Davidi R , Abel E , Sun M , Virshup G , Kielar K , Fahrig R
Published: June 2012

Purpose: X‐ray beam spot size and shape are critical performance determinants of an imaging or treatment system. However, quantitative assessment of such spot profiles can prove difficult, particularly at MV energies. We have developed a novel and convenient tomographic spot measurement technique that uses a rotating edge phantom. The method can be applied to x‐ray systems equipped with flat panel imagers. Methods: Data were acquired at 10MV and 6MV on a Varian TrueBeam system. A 0.5 mm thick tantalum sheet (attenuation ∼5%) was placed on the system's rotatable treatment head with an edge abutting the axis of rotation. A total of 144 projections, each 10MU, were acquired at 2.5 degree steps. For each projection, a line‐spread function (LSF) is generated by differentiating the measured edge spread function. For sufficiently high source magnifications, the LSF, taken at a given rotation angle, is a tomographic projection of the x‐ray beam spot at that angle. The LSF's were then assembled into a sinogram and the corresponding spot profile was reconstructed using a parallel‐beam CT algorithm. The reconstructed profiles were compared to those measured using a film‐based ‘spot camera’ made from a 15 cm thick tungsten cylinder pierced with an array of small holes. Monte Carlo simulations of the edge and the spot camera experiments were also performed. Results: The edge technique produced profiles similar to those from the spot camera yet with higher resolution (0.17mm vs. 0.25mm). These results were confirmed by Monte Carlo simulations. The measured FWHM of the 10 MV spot was 1.6 mm. The 6 MV spot was slightly asymmetric with an average FWHM of 1.5 mm. Conclusions: A thin rotating edge with low attenuation can be used to accurately and conveniently measure x‐ray beam spot profiles. NIH NIH 1R01CA138426 Employees of Varian Medical Systems
TH‐C‐217BCD‐06: Acoustic Radiation Force Based Imaging: An Overview
Authors: Nightingale K , Wang M , Rosenzweig S , Rotemberg V , Rouze N , Palmeri M
Published: June 2012

Acoustic radiation force impulse (ARFI) based elasticity imaging methods have been under investigation in research laboratories for over 15 years. In ARFI imaging methods, temporally impulsive (i.e. < 1 msec) focused acoustic radiation force is used to mechanically excite tissue, and the dynamic displacement response is monitored using the same transducer and ultrasonic correlation based techniques. High resolution qualitative images can be generated that portray relative differences in tissue stiffness, maintaining structural integrity in heterogeneous media. These images are generated by monitoring the tissue response along the central axis of the excitation, and sequentially interrogating a 2D (or 3D) field of view (i.e. on‐axis, or ARFI imaging). Shear waves are generated by each of the ARFI excitations, and their propagation speed is related to the underlying tissue stiffness. Time‐of‐flight based algorithms have been developed to estimate shear wave propagation speed, and, under certain simplifying assumptions, the tissue stiffness can be quantified based upon these speeds. In the past 3 years, both Siemens Medical Systems and Supersonic Imagine (SSI) have released commercial ARFI based elasticity imaging products. This talk will provide an overview of the underlying physics of radiation force based elasticity imaging techniques, and a review of the initial clinical reports using these methods.

Learning Objectives:

1. To understand the differences between acoustic images, qualitative elasticity images, and shear wave images

2. To understand the tradeoffs between resolution and accuracy in shear wave imaging3) to understand the limitations of the assumptions made by time‐of‐flight based algorithms

Disclosures: Some authors hold patents related to radiation force based techniques, and our lab has a research agreement with Siemens Medical Solutions. Funding: NIH R01 EB002132; R01 CA142824
TH‐C‐218‐02: Cranial SRS and SRT on a Siemens Artist Using the Brainlab IPlan Treatment Planning System
Authors: Gayou O
Published: June 2012

Linear accelerator‐based stereotactic radiosurgery (SRS) or radiotherapy (SRT) is a well accepted technique for the treatment of cranial primary and metastatic lesions and acoustic neuromas. The requirements in terms of accuracy and reliability of the linac are more stringent for these modalities than they are for more highly fractionated treatments. However these requirements have been identified and standardized in the TG142 report on external beam quality assurance (QA). It is usually not difficult for a newly purchased modern linac to meet these requirements, giving users a wider variety of choice when considering starting an SRS/SRT program. The compatibility of these linacs with SRS/SRT‐specific equipment and software, such as cones, frames or treatment planning systems, must be established. I will report on the use at our institution of a Siemens Artiste™ linac for cranial SRS/SRT, in conjunction with the Brainlab iPlan® treatment planning system. I will discuss the various combinations of using the Brainlab SRS cones or the Siemens 160‐leaf multileaf collimator (160‐MLC) for beam shaping; the Brainlab frame or frameless system for immobilization; the Brainlab target positioning system or the Siemens MVision™ MV‐CBCT system for localization. I will describe the commissioning steps of the system, including data acquisition for beam modeling in iPlan® and end‐to‐end testing. Various issues that arose throughout the use of this Siemens/Brainlab hybrid system over the last 3 years will be discussed.

Learning Objectives:

1. To assess the safety and usefulness of a multivendor solution for cranial SRS/SRT.

2. To understand the commissioning and quality assurance steps of a Siemens Artiste™ / Brainlab iPlan® hybrid system for cranial SRS/SRT

3. To understand the limitations of the hybrid system.
TH‐D‐BRCD‐01: TG‐51 Addendum: New KQ Values
Authors: Rogers D
Published: June 2012

The addendum to TG‐51, which is currently under review, will provide an expanded new set of beam quality conversion factors, kQ. The calculated values of kQ in the TG‐51 protocol are based on analytic calculations which make use of various tabulated values of measured and calculated factors uch as the water to air stopping‐power ratio, Pwall, Prepl and Pcel (for details see Ch 9 of the 2009 AAPM Summer School book, Med. Phys. Publishing, Madison, WI). However, with the development of the EGSnrc Monte Carlo system (Kawrakow, Med Phys 27(2000) 499) it is possible to accurately calculate the response of ion chambers. Also computers have became faster per unit cost and clever variance reduction techniques have been implemented for doing ion chamber calculations in complex geometries (Wulff et al, Med Phys 35(2008)1328). Hence ab initio Monte Carlo calculations of kQ have become both accurate and feasible using large clusters of computers. Values of kQ have been calculated this way for a total of 33 commonly used cylindrical ion chambers (Muir and Rogers, Med Phys 37(2010)5939) and these kQ values are accurately fit as a quadratic function of the beam quality specifier, %dd(10)x. Detailed estimates of the systematic uncertainty in these calculations have been made and range between 0.6% and 1.0%, depending on the assumptions made. The largest component is the uncertainty (previously 0.5%) in the assumed constancy with beam quality of (W/e)air, which relates the energy deposited in the cavity to the charge released in the air. In a detailed comparison of the calculated kQ values to the extensive high‐quality measurements by McEwen (Med Phys 37(2010)2179), Muir et al (Med Phys 38 (2011) 4600) found the mean percentage differences between the calculations and the experiments are 0.08(0.17), 0.07(0.32) and 0.23(0.31) in 6, 10 and 25 MV beams respectively (bracketed values are rms deviations). These discrepancies are well within the stated uncertainties of the measurements (about 0.3% to 0.4%) and the calculations (about 0.3% to 0.4% ignoring W/e uncertainties and assuming correlated uncertainties in photon cross section). These and similar comparisons for plane‐parallel chambers (Muir et al, Med Phys 39(2012) 1618) can be used to set an upper limit of 0.36% on the variation of (W/e)air with beam quality between 60Co and 25 MV beams (95% confidence). More importantly, the close agreement with experiment gives confidence in the accuracy of the Monte Carlo calculated values of kQ with a 68% confidence uncertainty of between 0.4% and 0.5%.The addendum to TG‐51 recommends use of these calculated values of kQ for the 21 ion chambers which meet the requirements for a reference class ion chamber.

Learning Objectives

1. To become aware of the new addendum to TG‐51 regarding reference dosimetry in photon beams.

2. Understand how ab initio calculations of the TG‐51's beam quality conversion factor, kQ, are done

3. Understand the uncertainties involved in ab initio calculations of kQ.
TH‐E‐213AB‐01: Review of Radiobiological Principles of Radiotherapy and Radiation Protection
Authors: Orton C , Borras C
Published: June 2012

Mechanisms by which radiation kills cells and ways cell damage can be repaired will be reviewed. The effect of radiobiological parameters which we can control for radiotherapy will be discussed including dose/fraction, number of fractions, time between fractions, overall treatment time, and the LET of the radiation. Reasons why we fractionate the way we do will be discussed, along with how sparing of normal tissues using conformal techniques might affect optimal fractionation. The linear‐quadratic model for cell survival for high and low dose rate treatments and the effect of repopulation will be presented and discussed. Radiation protection and the dose response of normal tissues will be reviewed, including effects on the developing embryo/fetus. The concepts of equivalent dose and effective dose in medical radiation protection, the Sv unit, and radiation and tissue‐weighting factors will be presented. The latest information on human data on radiation‐induced cancer, genetic effects and harmful tissue effects, especially cerebrovascular and cardiovascular diseases as well as cataract formation, published by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the Biological Effects of Ionizing Radiation (BEIR) Committee and the International Commission on Radiological Protection (ICRP) will be examined. Estimates of risk per unit exposure will be presented. Their use in the development of radiation protection guidelines and standards will be discussed.

Learning Objectives

1. To understand the radiobiological basis of radiation protection standards.

2. To define the radiation protection magnitudes and units, their values and their practical measurement.

3. To distinguish between stochastic and deterministic effects.
TH‐E‐213AB‐02: Review of the Radiobiological Principles of Radiation Protection
Authors: Borras C
Published: June 2012

The radiobiological principles underlying radiation protection guidelines will be reviewed, analyzing the published results of the effects of ionizing radiation at the cellular level, in animal experiments and, especially, in epidemiological studies. To ensure a consistent terminology, the radiation dosimetry terms used in radiation biology and in radiation protection will be presented. The concepts of equivalent dose vs dose equivalent as well as the term effective dose, the Gray and Sv units, and the radiation and tissue weighting factors will be explained and illustrated. Human data on radiation induced cancer, including increases in the risk of second cancers following radiation therapy, as well as data on radiation induced tissue reactions, published by the International Commission on Radiological Protection (ICRP), the National Council on Radiation Protection and Measurements (NCRP) and the Biological Effects of Ionizing Radiation (BEIR) Committee, with their latest estimates of risk per unit dose, will be introduced. The dose response of normal tissues will be discussed, including effects on children and the developing embryo and fetus. Recent findings in NCRP and ICRP publications, which include follow up times for some tissues much longer than those common in radiotherapy (up to 20 to 40 versus 5 to 10 years), will be assessed. In particular, current information on acute and chronic radiation syndromes, as well as the newly proposed threshold dose of 0.5 Gy for cataract induction and cardiovascular effects, will be examined. The impact of the new findings and recommendations on the development of radiation protection guidelines and standards, especially in the International Basic Safety Standards on Protection against Ionizing Radiation and for the Safety of Radiation Sources (BSS), soon to be adopted world‐wide, will be evaluated.

Learning Objectives:

1. To define the radiation protection magnitudes and units, their values and their practical measurement

2. To understand the radiobiological basis of radiation protection standards

3. To distinguish between stochastic effects and tissue reactions
TH‐E‐BRCD‐01: Automatic Treatment Planning ‐ an MCO Perspective
Authors: Craft D
Published: June 2012

We review three multi‐criteria optimization (MCO) approaches for automatic IMRT treatment planning: goal programming, prioritized optimization, and Pareto surface based MCO. After comparing and contrasting these approaches, we describe a hybrid approach where in step one — using any of those alternatives — a “first pass” plan is constructed. When this plan is presented to the treatment planner (or physician), the planner is allowed to navigate on a Pareto surface centered around that plan, allowing for a tuning of the plan. For this tuning step to be most useful, we require directly deliverable MCO (DMCO), by which we mean navigating on the Pareto surface in such a way that the plan you are currently viewing is ready‐to‐go from a delivery perspective (i.e. it does not need to be leaf sequenced first, the multi‐leaf collimator segmentation has already been done). We discuss current approaches to solving this DMCO problem, and finish with a discussion of how the above ideas apply to automatic volumetric modulated arc therapy (VMAT) planning.

Learning objectives:

1. Understand three types of multi‐criteria optimization: goal programming, prioritized optimization, and Pareto surface based MCO

2. Understand the idea of Pareto surface navigation refinement of an automatically generated plan.

3. Understand directly deliverable navigation. Research sponsored in part by RaySearch Laboratories.
TH‐E‐BRCD‐02: Automated Treatment Planning Using a Database of Prior Patient Treatment Plans
Authors: McNutt T , Wu B , Moore J , Petit S. , Kazhdan M. , Taylor R
Published: June 2012

Intensity modulated RT (IMRT) is used to deliver highly conformal radiation treatments. Its broad adoption has introduced considerable inter‐patient and inter‐institutional variability in plan quality. As part of our Oncospace program, we have built a system that uses patient geometric information and a database of previously treated patients for IMRT treatment plan quality assessment and automated planning. The system uses the relationship between organs at risk (OARs) and target volumes to predict the achievable dose distributions for a given patient from a database of prior patients. It then uses this achievable dose distribution to guide the planning process for the new patient. This system also employs a feedback model to insure the database improves over time through continual improvement in plan quality. The basic premise is the overlap volume histogram (OVH), a shape descriptor we introduced to describe the complex spatial relationship between an OAR and the target volume. The OVH describes the volume of overlap between the OAR and an expanded/contracted target as a function of the expansion/contraction distance. It is determined by expanding/contracting the target volume and calculating the volume of overlap for each distance. The OVH tells us what percentage of the OAR is within a given distance of the target and thus contains information about how hard it is to dosimetrically spare the OAR using IMRT. The OVH allows us to characterize patients based on their OAR‐target relationships, and thus allows us to search into the database of prior patients. We can query for patients with similar OVH characteristics, or we can find a group of patients whose OVHs suggest they are harder to plan .We have used our OVH query for both quality management and automatic treatment planning of head and neck and pancreatic cancers. For quality assessment, we take a new patient's OVHs and dosimetry data; look in to the database to find the best dose distribution achieved from the set of all patients whose OVH indicates they are harder to plan; then compare that queried dose distribution to the new patient's dose to indicate if the current treatment plan can be improved upon. For the automatic planning case, we use the queried doses to initialize the dosimetric objective function used in the inverse planning process of IMRT. The presentation will include an in‐depth discussion of the database and infrastructure design; the research and clinical results of the OVH based auto‐planning, and the software developed for clinical deployment with the dosimetrists.
TH‐A‐213CD‐01: Compton Scatter in X‐Ray Fluorescence CT Imaging
Authors: Bazalova M , Kuang Y , Pratx G , Xing L
Published: June 2012

Purpose: To design an x‐ray fluorescence CT (XFCT) imaging system for high‐sensitivity molecular imaging of gold and platinum probes by means of minimizing Compton scatter contamination using Monte Carlo (MC) simulations. Methods: XFCT and conventional CT images of 5‐cm diameter phantoms containing solutions of gold and platinum were simulated in a modified version of the EGSnrc/DOSXYZnrc MC code. In our MC model, fluorescence x‐rays excited by heavily filtered 110 kVp x‐ray pencil beam were detected by photon‐counting detectors arranged in a number of geometries with the aim to vary the contribution of Compton scatter. XFCT images were reconstructed based on sinograms generated using the net number of fluorescence x‐rays with simple back‐projection. The extraction of the net number of fluorescence x‐rays and XFCT image quality as a function of MC‐estimated Compton scatter for a range of scattering angles was investigated. A number of detector arrangements (angular distributions and thicknesses) as well as their energy resolution were studied. Results: We found that the imaging sensitivity significantly increases when forward Compton scattered photons are excluded from data acquisition. For 2‐cm wide detectors with 1 % energy resolution and a dose of ∼5 cGy, the imaging sensitivity for a full detector ring was 0.086% and 0.060% for gold and platinum, respectively, and it increased to 0.057% and 0.037% when x‐rays scattered by less than 90° and 45° degrees were excluded from data acquisition. Moreover, we observed a decrease in sensitivity with decreasing the detector width and its energy resolution. Conclusions: XFCT data acquisition geometry should be carefully chosen for each combination of excitation x‐ray spectrum, detector energy resolution, and imaging probe to minimize the contribution of Compton scatter in order to maximize XFCT imaging sensitivity. Based on our MC simulations, the design of an x‐ray fluorescence CT scanner will be proposed.
A Programmable Dual-RNA–Guided DNA Endonuclease in Adaptive Bacterial Immunity
Authors: Jinek Martin , Chylinski Krzysztof , Fonfara Ines , Hauer Michael , Doudna Jennifer A. , Charpentier Emmanuelle
Published: June 2012

Ditching Invading DNA

Bacteria and archaea protect themselves from invasive foreign nucleic acids through an RNA-mediated adaptive immune system called CRISPR (clustered regularly interspaced short palindromic repeats)/CRISPR-associated (Cas).

Jinek
et al.

(p.
816
, published online 28 June; see the Perspective by

Brouns

) found that for the type II CRISPR/Cas system, the CRISPR RNA (crRNA) as well as the trans-activating crRNA—which is known to be involved in the pre-crRNA processing—were both required to direct the Cas9 endonuclease to cleave the invading target DNA. Furthermore, engineered RNA molecules were able to program the Cas9 endonuclease to cleave specific DNA sequences to generate double-stranded DNA breaks.
Screening Education And Recognition in Community pHarmacies of Atrial Fibrillation to prevent stroke in an ambulant population aged ≥65 years (SEARCH-AF stroke prevention study): a cross-sectional study protocol
Authors: Lowres Nicole , Freedman Saul Benedict , Redfern Julie , McLachlan Andrew , Krass Ines , Bennett Alexandra , Briffa Thomas , Bauman Adrian , Neubeck Lis
Published: June 2012

Background

Atrial fibrillation (AF) is associated with a high risk of stroke and may often be asymptomatic. AF is commonly undiagnosed until patients present with sequelae, such as heart failure and stroke. Stroke secondary to AF is highly preventable with the use of appropriate thromboprophylaxis. Therefore, early identification and appropriate evidence-based management of AF could lead to subsequent stroke prevention. This study aims to determine the feasibility and impact of a community pharmacy-based screening programme focused on identifying undiagnosed AF in people aged 65 years and older.

Methods and analysis

This cross-sectional study of community-based screening to identify undiagnosed AF will evaluate the feasibility of screening for AF using a pulse palpation and handheld single-lead electrocardiograph (ECG) device. 10 community pharmacies will be recruited and trained to implement the screening protocol, targeting a total of 1000 participants. The primary outcome is the proportion of people newly identified with AF at the completion of the screening programme. Secondary outcomes include level of agreement between the pharmacist's and the cardiologist's interpretation of the single-lead ECG; level of agreement between irregular rhythm identified with pulse palpation and with the single-lead ECG. Process outcomes related to sustainability of the screening programme beyond the trial setting, pharmacist knowledge of AF and rate of uptake of referral to full ECG evaluation and cardiology review will also be collected.

Ethics and dissemination

Primary ethics approval was received on 26 March 2012 from Sydney Local Health District Human Research Ethics Committee—Concord Repatriation General Hospital zone. Results will be disseminated via forums including, but not limited to, peer-reviewed publication and presentation at national and international conferences.

Clinical trials registration number

ACTRN12612000406808.
Reversible heart failure: toxins, tachycardiomyopathy and mitochondrial abnormalities
Authors: Morris Paul D , Robinson Tim , Channer Kevin S
Published: June 2012

Heart failure is usually a relentless condition associated with a poor prognosis. Triggered by a physiological insult, maladaptive neurohumoral processes result in an ever-spiralling deterioration of cardiovascular function. However, there are certain underlying conditions which are associated with a temporary reduction in contractile function leading to reversible heart failure. These conditions affect a relatively small number of patients when compared with heart failure secondary to inherited cardiomyopathies and ischaemic heart disease. There are two broad mechanisms responsible for reversible myocyte dysfunction: acute inflammatory activation in which cytokines depress myocyte function, and toxic effects in which there is impairment of intra-cellular energetics. In this review, we discuss reversible heart failure caused by toxic effects. These effects can be caused by drugs (prescribed and illicit) and by tachycardic arrhythmia (tachycardiomyopathy), and are caused by abnormalities of mitochondrial function and myocytic calcium processing. The underlying pathological mechanisms, clinical features and management options are discussed, illustrated by clinical case studies.