bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐290: Dosimetric Verification of Helical Tomotherapy against Experimental Measurements for Head and Neck Treatments
Authors: Lopez‐Vilanova N , Bueno M , Sevillano D , Minguez C , Ginjaume M , Sanchez‐Reyes A , Duch M
Published: June 2012

Purpose: To verify a Tomotherapy plan for a typical head and neck treatment against experimental measurements. Methods: The treatment plan for a head and neck case was generated by the Tomotherapy treatment planning system (TPS) to deliver ∼70 Gy in 33 sessions to the contoured PTV. The plan was calculated on a CIRS ATOM anthropomorphic phantom that provides a grid spacing of 3×3 cm2 holes to accommodate thermoluminescent detectors (TLD). The plan was verified against experimental measurements carried out by 7LiF:Mg,Ti (TLD‐700) TLD. Up to 20 locations were selected within the irradiated region and three detectors were used simultaneously at each point to decrease the statistical uncertainty. TLD locations were labeled in the planning system and dose comparisons between TPS prediction and experimental measurements were performed in terms of absolute dose to water for a single fraction. We examined the dose from (i) the corresponding 3.5MV Tomo‐scan alone and (ii) the complete treatment. TLD‐700 were found to fulfill the requirements of reproducibility, linearity and flat energy response in a previous study. In particular, TLD energy response was previously checked for 6 MV flattening filter free and conventional radiation beams under reference conditions. Results:
Doses derived from the TPS were in most cases in good agreement (4% on average) with TLD dose measurements within TLD statistical uncertainties (about 3%). Larger discrepancies up to 7% were found for points close to complex tissue inhomogeneities, such as bony structures. Dose from the scanning procedure alone is about 1 % of the dose per fraction. Conclusions: This work indicates that dose delivery plans created with Tomotherapy TPS are accurate for head and neck tumor localizations.
SU‐E‐T‐293: The Potential Application of High Energy Proton Beam‐Induced Positron for PET Imaging Technique
Authors: Barimah E Kumi , Shahnazi K , Keppel C
Published: June 2012

Purpose: An existing nuclear interaction cross‐section of a positron emitter was used to predict range accuracy of proton beams and cross section of the positron emitters detected by the PET scanner Methods: To achieve this goal, a MLIC phantom was irradiated to 2Gy dose using 124.61MeV, 143.08MeV and 155.25MeV proton beam corresponding to the depths of 6.88cm, 10cm and 16cm, respectively, in the phantom. The activity produced in each phantom was examined by PET scanner within a couple of minutes post‐irradiation. Hence, activity signal produced along the activated depth dose profile was recorded. In this project, the isotope production cross section for carbon from Landolt‐Bornstein (1973) has been utilized. Results: A good correlation (about 95%) between the positron emission and the isotope cross section of the carbon was observed. Consistency between the induced activity and the carbon isotope cross section occurred mainly at the distal aspect of the fall off zone of both relative cross‐sections (i.e. between 60 – 100%). These results were obtained using the high relative abundance of carbon (i.e. 70%) in the phantoms.Conclusions The ranges measured by the depth dose profiles and positron emission profiles were in good agreement at the distal‐fall off edge. Furthermore, it is confirmed that the interaction cross‐sections of individual elements in the tissues could be used to determine the range accuracy of the proton depth dose profiles. None Applicable
SU‐E‐T‐294: Maximizing the Availability of Positron Emitting Nuclei for Proton Therapy Verification Using Different Beam Irradiation Sequences
Authors: Yagi M , Oxley D , Dendooven P , Brandenburg S , Koizumi M , Teshima T
Published: June 2012

Purpose: To demonstrate that the amount of nuclei available for post‐ irradiation proton treatment verification using positron emission tomography (PET) can be enhanced by reversing the beam delivery sequence in proton scanning beam irradiations. Methods: A time‐dependent analytical model is used to calculate the distributions of positron emitting nuclei for three different irradiation sequences: a scattered beam and a scanning beam in both the conventional sequence, distal edge first, and reverse sequence, distal edge last. The simulated geometry emulates reference dosimetry measurements conducted at the Paul Scherrer Institute (PSI). The reference measurements irradiate a 10 ×10 cm2 field, delivering about 1 Gy to a 10 cm wide spread‐out Bragg peak (SOBP). Positron emitter availability with different beam sequence and imaging times and the impact of the different irradiation sequences on the statistical error on a range extrapolation were investigated. Results: The ratio of the amount of positron emitters from the distal last beam sequence to that from the distal first sequence was 2.22 in the last centimeter of the SOBP. The comparison between distal last and a scattered beam gave a ratio of about 1.7 in the same region. In the distal last irradiation, more isotopes decay within a 120 second window, than in a 240 second window using a distal first irradiation. The statistical fluctuation on a range extrapolation was also smallest in the distal last beam sequence. Conclusions: We demonstrated the effect of the irradiation beam sequence on the isotope production relevant for the verification of proton spot scanning therapy with PET. The largest amount of isotopes is available by irradiating the distal edge last. This new beam sequence reduces the PETmeasurement time while still offering higher counts and accuracy compared with both the conventional beam sequence and the scattering method. This project was supported by JSPS Core‐to‐Core Program.
SU‐E‐T‐295: Factors Affecting Accuracy in Proton Therapy
Authors: Cheng C , Zhao L , Zhao Q , Moskvin V , Buchsbaum J , Das I
Published: June 2012

Purpose: To examine the various processes involved and to assess their effects on the accuracy in proton therapy. Methods: Proton therapy involved several processes: (1) Beam commissioning. (2) CT scan of patient. (3) Contouring. (4) Treatment planning. (5) Output factor measurements for each field. (6) Patient setup verification with image guidance. (7) Dose delivery. (8) Neutron dose and proton RBE at the distal edge. Within each step, there are several sub‐processes that each may contribute to the uncertainty in the treatment. By analyzing each of the subprocesseswithin each process, based on measurements or published data, we estimated a % uncertainty to each sub‐process and/or a distance uncertainty (in millimeter) on the proton range. A total uncertainty in proton therapy is estimated. Results: The uncertainties assessed for the various processes are : (1) ±1.5%; (4) ±3.0%, and 1–3mm; (5) ±2.0%; (6) ±2 mm; (7) ±2.0%, ±2mm. The uncertainties in (2) CT, (3) contouring and neutron dose in (8) strongly depend on the location and type of the tumor. On the other hand, the proton RBE at the distal edge in (9) is still debatable and may affect the dose uncertainty from 0–20% depending on which value we want to accept. Thus the overall uncertainty in proton therapy is at least ±4.5% and ±4 mm (by adding the various uncertainties in quadrature), without consideration of processes (2), (3) and (8), and the RBE effect. Conclusions: Due to the complexity in proton therapy and the various factors that may affect the accuracy in proton therapy, it is far more complicated to assess the accuracy in proton therapy. Our preliminary study showed that the accuracy in proton therapy is at least ± 4.5% in dose delivered to a tumor with an uncertainty of ±4mm to the distal edge of the SOBP.
SU‐E‐T‐304: Evaluation of Mammosite Multi‐Lumen Rotation and Its Dosimetric Consequences
Authors: Wiant D , Terrell J , Pursley J , Sintay B
Published: June 2012

Purpose: To evaluate the dosimetric impact of MammoSite Multi‐Lumen (MSML) rotation in phantom and patient studies. Methods and Materials: A MSML phantom with an asymmetric dose distribution was created. Target volume coverage and dose at a fixed point 1 cm from the MSML were evaluated as functions of rotation about three orthogonal axes (where the origin was set at the center of the MSML and axis one ran along the central catheter). Additionally, for three MSML patients that were set‐up by aligning the stem of the MSML to skin marks, CT scans were acquired before each fraction. Rotation about three axes and maximum point dose to skin and chestwall were evaluated. Results: In phantom, 10° rotations about the central, second, and third axes give average absolute point dose changes with respect to the maximum dose of 1.9%, 3.7%, and 4.2%, respectively; and changes in PTV coverage of 0.9%, 1.0%., and 0.8%, respectively. For patients 1–3 the average absolute rotation about the central axis was 13.60, 9.50, and 7.20, respectively; axis two was 7.00, 3.20, and 11.40, respectively; axis three was 2.90, 2.90, and 3.80, respectively. For cases 1–3 the average absolute change per fraction in maximum point dose to the skin was 0.29 Gy, 0.14 Gy, and 0.39 Gy, respectively; to the chestwall was 0.17 Gy, 0.20 Gy, and 0.21 Gy, respectively. Conclusion: Phantom studies showed change in point dose and PTV coverage for a 10° rotation about the central catheter yields < 2% variance. Patient data indicates skin mark alignment is capable of positioning the MSML with 10° accuracy about the central axis. Thus, central axis rotation can be adequately accounted for by skin mark alignment. However, review of the patient data shows that rotations about the other axes are equally important and should be considered and managed.
SU‐E‐T‐316: New Design of the Valencia Applicators to Reduce Radiation Leakage
Authors: Granero D , Vijande J , Perez‐Calatayud J , Richart J , Ballester F
Published: June 2012

Purpose: The Valencia applicators are designed to treat skin lesions with the microSelectron‐HDR afterloader. Although the radiation is highly directed to the treatment area, radiation might leak through the backside of the applicator. Recently, the manufacturer has introduced a new applicator design to reduce such radiation leakage. This new design consists mainly in the addition of about 4 mm of tungsten in the backside of the applicator making it thicker. The purpose of this study is to evaluate by means of the Monte Carlo method the radiation leakage of this new design and to evaluate whether this modification affects the dose rate distributions in the treatment area. Methods: The complete geometry of the new applicators has been introduced in the Monte Carlo code GEANT4. The applicators have been located on the surface of a cylindrical water phantom following a methodology similar to the used in the original study of the Valencia applicators by Granero et al [Med.Phys 2008;35:495–503]. Kerma in the water phantom and kerma in air outside the phantom have been evaluated to estimate the radiation leakage of the new designed Valencia applicators. Results: The Monte Carlo simulations of the new applicators show that the radiation leakage has been reduced significantly from the previous design. The largest radiation leakage of this design is now about 30% of the dose at the prescription point and about 10% at 1 cm from the backside of the applicators. The dose rate distributions in the area of treatment have not changed. Conclusions: In this study the radiation leakage of the new design of the Valencia applicators has been obtained. The radiation leakages have been largely reduced from the previous design without compromising dose rate distributions in the treatment area.
SU‐E‐T‐327: Tracking Palladium Seeds Implanted in Prostate Using Shape Analysis Approach
Authors: Zhai Y , Jiang Y , Papademetris X , Roberts K , Nath R , Chen Z
Published: June 2012

Purpose: To develop and test a shape‐based image registration algorithm to register and analyze serial CT image datasets of a given patient, and then to track the motions of the implanted seeds for a quantitative characterization of prostate deformation and edema. Methods: Sequential 3D CT image datasets for a prostate cancer patient, acquired before palladium source implantation and after implantation, were used to perform deformable image registrations with shape‐based algorithm to track the sources motions. The seed centers were detected in a group‐wise fashion after extracting the seed surfaces, i.e. using consistency across the sequence of images acquired from the same subject as an extra constraint, to maximize the reliability of seed detections. Results: The shape analysis approach was applied to the series of CT scans at day 0, 1, and 30 for one prostate cancer patient. The motion of seeds was visualized in plots, from which the non‐rigid deformation of prostate was interpolated. It was observed that the prostate volume was shrinking from Day 0 to Day 30, while it expanded from Day 0 to Day 1. Our data also showed that the prostate deformation caused by the resolution of prostate edema was anisotropic. Conclusions: A shape analysis approach was developed for quantitative characterization of post‐implant seed tracking and the prostate deformation. The advantage over other methods is that the constraints of consistency among different images made our method more reliable than other seed localization methods that estimate the seed centers for each image individually. The precise localization of implanted seeds as function of time would enable a more accurate calculation and proper summation of radiation dose delivered to each tumor sub‐volume in post‐implant dosimetry. This research project is currently funded by the NIH grant R01CA134627‐01 â€œProstate Edema in Permanent Interstitial Brachytherapyâ€.
SU‐E‐T‐330: Evaluation of Prostate Edema and Seed Migration via Seed Position Change from Consequent Post‐Implant CT Scan in Prostate Brachytherapy
Authors: Peng Y
Published: June 2012

Purpose: To evaluate prostate edema and seed migration based on seed position change determined from post‐implant CT scans. Methods: Early stage prostate cancer patients with permanent seed implant brachytherapy were acquired post‐implant CT scans on Day‐0 and Day‐30, respectively. Seeds coordinates(x,y,z) were determined directly from those CTs and were sorted to different slices according to their z coordinates. The prostate center (xc,yc,zc) was the mathematic average of the coordinates for all seeds for one CT scan. Distance from each seed to the prostate center and weighted distance, defined as fraction of seeds in a certain distance to the prostate center, were calculated and compared between at day‐0 and at day‐30. Slice center was the average coordinates of all seeds in that slice. We assume the boundary of the edema is determined by the largest convex polygon constructed by those seeds having largest distance to the slice center at each direction. The area (A) of the convex polygon was summation of (xiyi+1−xi+1yi), where xi and yi were the ith seed coordinate on the apex. We further assume the edema is the summation of volume [Vi=(Ai+Ai+1+(Ai*Ai+1)̂0.5)*hi/3] between each slice, where hi was distance between adjacent slices. Results: Distance from prostate center to each seed, volumes between adjacent slices and the total volumes show the shrinkage of the prostate from day‐0 to day‐30. Population weighted distance was 2.1 and 1.9 cm on subsequent CTs. The volume ratio of the edema ranged from 1.3 to 1.7 from day‐0 and day‐30 CTs. Conclusion: Post‐implant edema increased the prostate volume by factors ranging from 1.3 to 1.7. The results showed that the distance index method was consistent with that of volume calculation in the evaluation of the edema change. The method proposed in this study can be used to evaluate seed migration and edema change.
SU‐E‐T‐333: Immobilization for Proton Therapy ‐ How Is It Different to Photon Therapy?
Authors: Wroe A , Schulte R , Slater JD , Slater JM
Published: June 2012

Purpose: To describe considerations in proton therapy immobilization and the effects which design elements have on the proton dose distribution. Methods: Proton therapy has dose distribution advantages over photons through the Bragg peak. This high dose region and sharp distal fall off that produces no primary particle exit dose can be placed at any point within the patient leading to the use of fewer beams and lower integral doses. Proton patient immobilization needs to reduce patient motion to the largest extent feasible, as is the case with other radiation therapy modalities, but also needs to consider the effect of the immobilization device on the proton range and whether this is accurately reflected in the dose calculation. Results: Our proton treatment center has treated patients with protons for over 20 years, and the development of effective immobilization methods has been an integral part of this experience. For the various anatomic sites, specific devices have been developed that position and immobilize the patient reproducibly and effectively. Attention was paid to minimal proton water equivalent thickness (WET) to minimize the effect on proton beam penumbra. The WET of each immobilization material has been well characterized and incorporated in the (CT‐based) proton range calculation to minimize systematic errors in the proton range uncertainty. In our experience, proton immobilization devices should have beveled edges when possible to avoid edge effects that can drastically affect the depth of proton penetration. Effective use of internal immobilization, such a rectal balloons or breath holding, is also important to minimize ITV margins and suppress motion‐related beam range uncertainties that are unique to proton therapy. Conclusions: In proton therapy patient immobilization, additional considerations are needed to ensure that the immobilization device does not negatively impact the proton dose distribution and its uncertainty.
SU‐E‐T‐334: Clinical Implementation of Gating and Dose Verification with Scanned Ion Beams at HIT
Authors: Chaudhri N , Richter D , Haertig M , Ecker S , Ackermann B , Naumann J , Haberer T , Bert C , Habermehl D , Herfarth K , Ellerbrock M , Jaekel O
Published: June 2012

Purpose: Medical physics aspects of gated irradiation to moving tumors using scanned ion beams. Methods: At our institute, more than 700 patients have been treated with proton and carbon ion beams since its start. The first patient has now been treated with the application of gating. For this purpose, the Anzai respiratory motion detection and gating system was interfaced with the treatment control system such as to control spill pausing. The patient presented with a liver tumor moving with peak‐to‐peak amplitude of ∼1cm due to breathing. Treatment planning was performed using the Siemens Syngo RT‐Planning system on a 3DCT dataset. The gating window was determined from 4DCT. Plan verification was performed in a motion phantom, consisting of a PMMA block equipped with a 3D set of 24 pinpoint chambers mounted on the Quasar moving platform. The breathing motion perpendicular to the beam was simulated based on the trajectory obtained from the Anzai system during 4DCT acquisition. Dose was measured at three conditions: static phantom, moving phantom with continuous beam delivery, and moving phantom with gated irradiation. The statically delivered dose distribution was used as a reference. Further, a 4D dose calculation was performed on the 4DCT dataset using a research treatment planning system. Results: The relative rms deviations in the homogenous dose region were ∼18% without gating, and ∼6% with gating. The 4D dose calculation showed a decrease in target coverage by ∼20% and ∼6%, respectively, for the 95% isodose line. Conclusions: Gating of a scanned carbon ion beam was applied for treatment of a moving liver tumor and a workflow was developed to verify the dose to be actually delivered. With respect to continuous dose delivery, the target dose improvement achieved due to gating is considered to be significant for this patient.
SU‐E‐T‐337: Dynamic Tomotherapy Delivery with Running‐Start‐Stop: Comparing to Conventional Tomotherapy and VMAT Deliveries
Authors: Rong Y , Chen Y , Chen Q , Lu W
Published: June 2012

Purpose: Despite of superior target dose uniformity, previous studies of helical tomotherapy (HT) show inferior longitudinal conformity and longer deliver time compared to volumetric‐modulated arc therapy (VMAT) plans, due to fixed jaw size with conventional HT. Dynamic delivery techniques were introduced to overcome these problems. This study is to compare the dosimetric performance of dynamic tomotherapy delivery (5.0cm jaw running‐start‐stop (RSS)) with fixed jaw HT and VMAT deliveries. Methods: Sixteen patient cases, including brain, head&neck (HN), lung and prostate, were selected and de‐identified prior to treatment planning. VMAT plans were generated using Varian RapidArc™ (RA) (one or two arcs) and HT plans using TomoTherapy® (fixed 2.5cm jaw). The tomotherapy RSS plans were generated using tomotherapy's research engine and optimized based on 5.0cm dynamic jaw, which allows larger jaw opening for lower dose gradient and smaller jaw opening at the target border when sharp penumbra is required. All 16 cases were planned based on identical contours, prescriptions, and planning objectives. Dose indices for targets and critical organs were compared based on dose‐volume histograms, delivery time, and monitor units. Results: The average delivery time was reduced from 4.8min (HT) to 2.92min (RSS). RSS showed comparable target dose homogeneity to HT. Three delivery techniques showed comparable normal tissue sparing for lung cases, with improved sparing of cord with RSS. For prostate cases, RSS showed improved bladder and rectum doses compared to HT due to better longitudinal sparing. Superior normal tissue sparing was observed in RSS plans for optical nerves in brain cases and larynx or parotids for HN cases. Conclusions: Tomotherapy RSS with 5.0cm dynamic jaw is overall comparable, if not better, to 2.5cm fixed jaw HT, with faster treatment delivery. It also showed improved longitudinal dose conformity to critical structures adjacent to the target, which is comparable to RA technique. Yu Chen is employee of Accuray‐Tomotherapy, Inc.
SU‐E‐T‐340: Estimation of the Delivered Fractional and Accumulative Patient Dose in IMRT and VMAT
Authors: Graves Y , Zhen X , Kim G , Gautier Q , Tian Z , Cervino L , Lambrecht M , Jia X , Jiang S
Published: June 2012

Purpose: To estimate the delivered dose after each fraction of treatment as well as the delivered accumulative dose distribution. The goal of this project is to develop an automatic verification system using daily images and machine log files. Methods: First, we perform deformable registration from CT to CBCT and correct CBCT artifacts and CT numbers. Due to the limitation of the current scanning protocol, CBCT may not cover the whole treatment region needed for dose reconstruction. In that case, we use deformed CT for dose calculation which has correct CT number as well as daily patient geometry within whole treatment region. With machine log files, we generate actually delivered fluence maps at all delivery angles for that fraction. Then a GPU‐based Monte Carlo dose calculation package, gDPM, is employed to get delivered fractional dose on deformed CT or corrected CBCT. To compare the planned dose with the delivered dose, the delivered dose on new daily image is transferred back to the original CT geometry using the deformation vector fields obtained in the first step. This procedure is employed for each fraction to get the accumulative dose on original CT. Results: We demonstrate this treatment verification system on VMAT patients. We plot the DVHs for delivered and planned dose distributions and summarize the absolute errors in dose matrix report. Conclusions: We have proposed a procedure to estimate the delivered fractional and accumulative patient doses in IMRT and VMAT. If big errors are observed in the dose matrix report, then a warning should be sent out to responsible personnel, so the error can be indentified and corrected promptly.
SU‐E‐T‐341: Characterization of a New Commercially Available System for Patient Specific IMRT/VMAT QA
Authors: Stathakis S , Myers P , Esquivel C , Gutierrez A , Mavroidis P , Papanikolaou N
Published: June 2012

Purpose: To evaluate and characterize the 3D dose reconstruction algorithm of a new commercially available system for patient specific IMRT QA. Methods: champalimaud The new Octavius 4D system and its accompanying software (Verisoft) by PTW were evaluated for the dose reconstruction accuracy. OCTAVIUS 4D measures the dose in the isocenter. The phantom rotates synchronously with the gantry by means of an inclinometer and a motor. The collected measurements are then reconstructed to a 3D dose volume for comparison with the calculated dose in the phantom. In this study, we evaluated the 3D dose reconstruction algorithm of the system using a series of tests. Dose distributions for various field sizes, orientations, shapes and combination of fields were calculated using the Pinnacle TPS on the phantom and the respective DICOMRT dose exported to the Verisoft. Example of these fields included 3×3cm2 to 25×25cm2, wedged fields, AP/PA arrangements, as well as lateral fields and IMRT fields. The respective measurements were performed and comparisons were made based on gamma index, profiles and isodose distributions. Results: The 3D gamma index ranged from 88.3 to 99.9%. Individual dose planes (axial, sagittal, and coronal) were also evaluated and their gamma was within the 3D gamma range. The new system independent of angular dependence as it rotates with gantry and the measuring array is at constant SAD and perpendicular to the beams axis. Conclusions: The new phantom for patient specific IMRT QA in this study can effectively be used for clinical use. The ability of the software to compute 3D dose distribution from all measurements taken is powerful tool that aids the physicist to evaluate the verification plan by providing 3D information not available from other commercial systems. This work has been partially funded by an education grant from PTW.
SU‐E‐T‐344: Practicality of Pyroelectric X‐Ray Sources for Grenz and Conventional Radiotherapy
Authors: Klopfer M , Satchouk V , Alivov Y , Molloi S
Published: June 2012

Purpose: Pyroelectric crystals can be used as a compact and low cost source for electrons and high energy photons. Only periodic heating cycles are required for energy input. In this study we examine the performance of a simulated pyroelectric x‐ray source in delivering a single 2Gy dose fraction for soft x‐ray (Grenz) and dermatological conventional x‐ray radiotherapy. Grenz radiotherapy applications include the treatment of persistent dermatitis and psoriasis. Methods: Dose delivery was calculated as the energy deposited per photon in soft tissue for a monoenergetic x‐ray source with a beam area of 1.0cm2. Monoenergetic x‐ray photon energies between 1 and 30keV were plotted for delivered tissue dose between 1 and 3 mm tissue depth in 100 micron volume recording elements. From prior experimentation 5×10̂13 electrons emitted are assumed to be converted to 5.84×10̂10 photons per pyroelectric crystal heating cycle. Absorbed photons are assumed to deliver full energy dose upon absorption. Delivered volume element dose, average dose, heating cycles per fractional dose, and energy absorption efficiency are used as metrics for application performance. Results: Delivered photons between 8−15KeV produced the lowest number of cycles for delivered doses to 2 and 3mm tissue depth. At 10keV a 2Gy fractional dose can be delivered at 2mm depth in 11 heating cycles. At energies below 6keV, nearly 100% energy deposition occurs within 1 mm, and the dose is delivered to shallow to cover treatment volume depth. Above 15keV, dose delivery efficiency decreases, requiring 106 cycles at 80keV to deliver 2Gy at 3mm. Conclusions: Further study in device design will seek to maximize pyroelectric output x‐ray flux, decrease cycle time, and increase treatment coverage area using tiled sources. With decreased cycle times and increased flux, pyroelectric sources can be practical for photon radiotherapy applications.
SU‐E‐T‐346: Clinical Results of 3D in Vivo Dose Verification of VMAT
Authors: Mijnheer B , Olaciregui‐Ruiz I , Rozendaal R , Sonke J , Stroom J , Tielenburg R , van Herk M , Vijlbrief R , Mans A
Published: June 2012

Purpose: To elucidate our approach of 3D in vivo dose verification of VMAT and to present the clinical results since its introduction in 2009. Methods: An EPID‐based method using a back‐projection algorithm is clinically applied for 3D in vivo dose verification of the delivery of VMAT plans, created using the SmartArc module of Pinnacle. Single‐arc treatment is applied for VMAT of prostate cancer, while two arcs are used for most other VMAT treatments (head‐and‐neck, lung‐SBRT, and brain‐SRS). EPID ‘movies' are acquired during VMAT delivery on Elekta linacs using in‐house developed software. Our routine clinical procedure is to perform 3D in vivo dose verification of the first three fractions. The comparison of the EPID‐reconstructed and planned dose distributions is done by a 3D γ‐evaluation method, based on 3%/3mm γ‐criteria. Since August 2011 dose‐reconstruction and γ‐evaluation software runs automatically. Results: The analysis of the results of about 4000 VMAT arcs (February 2012) showed that γ‐evaluation data are comparable to the values found previously for 2D IMRT verification. The average difference between measured and predicted isocenter dose was (−0.2±3.7)%. More than 90% of the in vivo VMAT analyses were directly approved (no interaction of any kind needed); the remaining required further inspection by a clinical physicist. The limitations of the model and anatomical changes of the patient, confirmed by cone‐ beam CT scans, were the main reasons for the observed deviations. Examples will be given of differences between (in vivo) measured and planned dose distributions that were not observed during phantom measurements. Using the automatical software, a dosimetry report is available for inspection within minutes after treatment delivery without any manual intervention. Conclusions: EPID dosimetry is a simple and accurate tool for 3D in vivo dose verification of VMAT delivery. It is faster than pre‐ treatment verification and provides clinically more relevant information.
SU‐E‐T‐350: Three Year Analysis Using Ionization Chamber Array for Patient Specific IMRT QA
Authors: Regan M , Stathakis S , Nayebi N , McKinsey R , Myers P , Knaup C , Quino L Vazquez , Gutierrez A , Esquivel C , Mavroidis P , Papanikolaou N
Published: June 2012

Purpose: To analyze the patient specific IMRT QA results at our institution over the past 3 years and evaluate the procedures and methods of our IMRT QA program. Methods: 1466 patient specific IMRT QAs were performed at our institution from March 2009 to December 2011. The passing criteria for each IMRT QA are that 90% of all evaluated points must have a gamma =1.0. The gamma is calculated using the TPS calculated planar dose as reference and the reference value is 90% of the maximum dose in the plane. A dose threshold of 10% is used in order to remove very low dose points from the calculation. The planar dose and the measurements are computed and obtained using the actual beam angles. The measurements were performed on Varian linacs equipped with Millennium 80, Millennium 120 and High‐Definition 120 MLC. Results: The IMRT QA results were analyzed with respect to the linac, treatment site, number of beams, IMRT vs. TOMO vs. VMAT, and number of control points. The overall average gamma index value was 96.85% (±1.5%). Head and Neck had the lowest gamma index (95.97%) while brain had the highest (97.85%). Conclusions: After evaluation of 700 patients, it can be determined that there are significant variations in the average measured gamma value based on treatment site, number of beams, machine type, and number of control points. This work provides a foundation for future analysis of possible underlying issues in the gamma value deviations for each comparison.
SU‐E‐T‐351: Investigation of Clinically Relevant Dose of Small Field Brain IMRT Using Planned Dose Perturbation
Authors: Jin H , Ali I , Keeling V , Ahmad S
Published: June 2012

Purpose: Clinically relevant dose errors of small field brain IMRT were evaluated using planar per‐beam dosimetry and planned dose perturbation (PDP; used in the Sun Nuclear 3DVH+MapCHEKC2) algorithm. Methods: Ten BrainLAB IMRT plans were retrospectively selected. PTVs ranged from 0.5 to 29.0 cc and most of the field sizes were smaller than 4×4 cm2 (beamlets were much smaller). The Varian TrueBEAM STx with high‐definition MLC (2.5 mm width at isocenter) was employed to deliver treatment plans. The conventional per‐beam IMRT QA was performed using the 2D diode array (diode detector size of 0.7×0.7 mm2). Two shifted QA measurements were merged for each plan to achieve a grid spacing of 5 mm. The 3DVH reconstructed a ‘true’ DVH of plans using the measured errors back‐projected on to 3D patient dose calculation. Dose coverage in PTVs and critical structures was compared between treatment planning and actual delivery. 2D (conventional planar QA) and 3D (PDP‐reconstructed dose) gamma analyses were also performed. Results: In DVH‐based analysis using 3DVH, the percent differences of maximum dose between planning and delivery for PTV were −0.4 to 20.2% (p‐value: 0.02) and for normal tissue −5.67 to 1.32% (brainstem), −2.50 to 2.51% (eye), and −4.9 to 4.9% (optic nerve). The D95 percent differences for PTV were −3.2 to −0.56% (p‐value: 0.0001). Average pass rates (1 standard deviation) of the gamma test with 3%‐3 mm criteria were 95.7 (4.9)% (2D) and 97.6 (3.4)% (3D), respectively. The correlation coefficients between 2D/3D gamma tests and the change in PTV coverage were 0.76/0.68 (Dmax of PTV) and −0.86/−0.96 (D95 of PTV), respectively. Conclusions: There was a strong correlation between the gamma analysis and the predicted PTV coverage in small field dosimetry. Using 3D reconstructed dose maps, statistically significant dose difference between planning and delivery was observed in PTVs for the small field IMRT.
SU‐E‐T‐357: Error Detection with a 3D Patient Specific QA System
Authors: Rivest R , Aviles J Alpuche , Nakonechny K , Beck J , McCurdy B
Published: June 2012

Purpose: To determine if our in‐house patient specific QA process, which utilizes the COMPASS (v2.1, IBA‐Dosimetry) system, can detect delivery errors introduced in clinical IMRT plans. Methods: The COMPASS system consists of a 2D chamber array mounted in the gantry, an independent gantry angle sensor and associated software. Patient specific QA at our clinic involves the creation of two QA structures, one consisting of all clinical PTVs, the other generated from the 20% isodose line. The gamma agreement index (GAI) within the two QA structures is used to compare 3D COMPASS reconstructed dose with planned dose distributions. Ten clinical DMLC‐IMRT plans (5 prostate, 5 head & neck) were included in this study. Plans were modified by systematically shifting leaf pair positions so that that all nonzero leaf gaps were increased by 2.0 mm and 1.0 mm for the two sites, respectively. Verification plans were created for both the original and modified plans in order to quantify the dosimetric effect of the introduced errors via in‐phantom ion chamber measurements. Finally, plans were delivered to COMPASS and 3D dose distributions were reconstructed on both the phantom and patient CT datasets. Reconstructed doses on the patient CT were analyzed as per our QA procedure. Results: On average, measured ion chamber values for the modified plans deviated from the original planning doses by 3.1 ± 1.2% (Range: 1.0%–5.3%). For each of the six modified plans in which this metric exceeded 3%, GAI values for at least one of the QA structures were below 95%, which would be flagged by our QA process. Only one of the other modified and none of the original plans had GAI values <95%. Conclusions: Gamma analysis of patient specific QA with COMPASS can effectively detect dosimetrically significant delivery errors introduced by systematically increasing leaf gaps in clinical IMRT plans. CancerCare Manitoba has a research agreement with IBA‐Dosimetry.
SU‐E‐T‐362: A Novel Technique to Evaluate 3D Dose Delivery to a Moving Tumor
Authors: Wijesooriya K , Aliotta E , Geesey C , Benedict S , Read P , Larner J
Published: June 2012

Purpose: Delivering highly modulated radiation beams accurately to a moving tumor is a difficult task; it is crucial to have tools to evaluate the efficacy of treatment delivery in such cases. We are reporting a novel technique to evaluate 3D dose delivery to moving tumors. We are also presenting an evaluation of RapidArc treatment delivery using this method. 3D position dependant dose is crucial because the peripheral regions of the tumor may not get adequate dose due to moving out of the MLC aperture. In our procedure we accomplish the position dependant dose evaluation by creating the effects of tumor motion as follows: instead of moving the tumor, we simulate to move the active MLC's in the direction opposite to the tumor motion by the corresponding motion amplitude calculated at the time of delivery. Methods: Ten RapidArc plans were created, delivered at a Varian Trilogy unit and corresponding log files were recorded. A simulation, written in MATLAB, reads in the dynalog files, and calculates average time per each control point delivery with respect to beam initiation. A sinusoidal respiratory motion signal with a given maximum amplitude and period was implemented to obtain the motion amplitude at the time of delivery of each control point. A modified DICOM file was created where the active MLC's were moved to simulate the effects of tumor motion. This DICOM plan was reimported to Eclipse treatment planning system, and 3D dose was recalculated. To verify the accuracy of our simulation, a sample plan with 2.5cm motion amplitude was compared with delivery. Results: Simulation agrees well with the dose measurement (3%3mm gamma acceptance of 98%). GTV under‐dosing is observed for large motion amplitudes, and small tumor volumes. Conclusions: A novel technique is developed to obtain delivered 3D dose distributions for moving tumors using machine log files.
SU‐E‐T‐366: Patient Specific IMRT Pre‐Treatment Verification Using a Commercial Portal Dosimetry Software
Authors: Varatharaj C , Moretti E , Manickam R , Padovani R
Published: June 2012

Purpose: To implement the newly developed portal dosimetry software using independent dose prediction algorithm EPIDoseTM and evaluate this new tool for the pretreatment IMRT plan QA of whole pelvis with simultaneous integrated boost (WP‐SIB‐IMRT) of prostate cases by comparing with routine 2D array detector system (MapCHECKTM). Methods: All measurements were performed using 6 MV X‐ray beam at CLINAC 600C linear accelerator (Varian Associates, Palo Alto CA, USA) equipped with Millennium120 multileaf collimator (MLC). We have compared the measured doses between the two detectors (EPIDose and MapCHECK) and TPS calculated ones for every split field. In the current investigation gamma value distribution for 104 split fields were analyzed using gamma distributions. In particular, for each split field the following gamma distribution parameters were determined: mean gamma value, gamma delta value, defined as the previous mean gamma value + 1.5 SD and Percentage of points with gamma <1, gamma <1.5 and gamma >2. Results: We have investigated 104 split fields using gamma distributions in terms of pre‐defined gamma frequency parameters. The mean gamma values are found to be 0.42 (SD:0.06) and 0.44 (SD: 0.06) for the EPIDose and MapCHECK, respectively. The average gamma delta for EPIDose and MapCHECK are found as 0.51 (SD:0.06) and 0.53 (SD: 0.07), respectively. Furthermore, the percentage of points with gamma<1, gamma<1.5 and gamma >2 are 97.4%, 99.3% and 0.56%, respectively for EPIDose and 96.4%, 99.0% and 0.62% for MapCHECK. Conclusions: Based on our results obtained with EPIDose and strong agreement with MapCHECK, we may conclude that the EPIDose portal dosimetry system has been successfully implemented and validated with our routine 2D array detector. Project was supported by, INTERNATIONAL CENTRE for THEORETICAL PHYSICS
SU‐E‐T‐369: Evaluation of Dose Control System Performance on a TomoTherapy Hi‐Art System
Authors: Staton R , Biddle J , Langen K , Meeks S
Published: June 2012

Purpose: TomoTherapy Hi'¢Art systems may exhibit rotational dose fluctuation and dose drift during treatment delivery. A dose servo system has been developed by Accuray, Inc. to monitor and control the dose output on TomoTherapy Hi'‐Art systems. The Dose Control System (DCS) provides continuous control of the linear accelerator output through a closed loop control system to maintain a constant dose output. The purpose of this study is to evaluate the clinical performance of the DCS and to quantify the stability of the dose output after the installation of DCS on our Hi'¢Art unit. Methods: Daily ion chamber measurements in a solid water phantom for static and IMRT deliveries were compared for a time period of two months before and after the DCS installation. Weekly beam measurements using onboard MVCT detector and ion chamber data acquired by field service engineers were also analyzed. Dose stability and intra‐procedure dose drift were assessed from data before and after the DCS installation. Results: Both the range and standard deviations of daily static and IMRT ion chambermeasurements improved with the DCS. The standard deviation of the daily IMRT measurements improved from 0.96% to 0.5%. The dose drift also improved significantly with the DCS. The intra‐dose dose drift during a 200 second rotating procedure decreased from an average of 1.02% to 0.02% based on on‐board ion chamber data. The data show that the dose output is much more stable overall and more consistent from day to day. Conclusions: Based on dosimetric QA endpoints, the DCS has shown a marked improvement in machine dose stability and intra‐procedure dose drift when compared to data from before DCS was installed. MD Anderson Cancer Center Orlando holds a research grant from Accuray, Inc.
SU‐E‐T‐374: An Improved Leaf Sequencing Algorithm Based on MLC Shape Regulation
Authors: Jing J , Lin H , Li G , Chow J
Published: June 2012

Purpose: Intensity modulated radiotherapy (IMRT) requires the determination of the appropriate multileaf collimator (MLC) settings to deliver segmental fluence maps. In this study, we purposed a leaf sequencing algorithm to regulate the MLC aperture between adjacent apertures in the delivery.Method and Materials: Based on the algorithm of Xia and Verhey, our proposed algorithm improved the shape of each MLC segment so that the basic frame can be preserved. The MLC aperture can be subjected to the distances of adjacent leaf rows based on the segmentation Result of the algorithm of Xia and Verhey. As the row distances decreased, the distance value became smaller. The distance value between adjacent rows can be controlled by user to omit the low‐weight monitor unit segments and tiny MLC segments. Conjugate Gradient algorithm was used to optimize segmental weight, and readjust segment and shape which can minimize the error in the anterior‐posterior leaf sequencing. Results: By comparisons and analyses of the total number of monitor unit and number of segment with benchmark results, our proposed algorithm performed well. The segmental aperture constraint produces segments with more compact shapes when delivering the planned fluence maps, which may help to reduce the MLC specific effects. As an improved leaf sequencing algorithm, Shape regulation was validated with a series of fluence maps using treatment planning system performed previously by the benchmark algorithm of Xia and Verhey. Conclusions: Our improved algorithm performed a good agreement among the NS and TNMU value of the benchmark results and finished this segmentation in fraction of a second, faster than the DAO method. Moreover, it can keep the MLC aperture compact shapes. We concluded that our algorithm is acceptable as a module in IMRT treatment planning. The work is supported by the National Natural Science Foundation of China (60872112 and 10805012), the Natural Science Foundation of Anhui Province (11040606M132) and the Fundamental Research Funds for the Central Universities and the Science Research and Development Fund of Hefei University of Technology (2012HGXJ0062).
SU‐E‐T‐380: Evaluation of Patient Specific Machine Delivery Performance Based on Analysis of Trajectory Log Files
Authors: Stakhursky V , Stanley T , Yi W
Published: June 2012

Purpose: Comparison of delivered and treatment planning dose to a phantom is routinely done before first patient treatment for IMRT and VMAT treatment courses, and is an important part of QA program. It is assumed that the delivery parameters are reproducible for each treatment in the course, and additional tests to validate the assumption are rarely performed. We use the analysis of Trajectory log files to verify the interfractional constancy of treatment delivery. Methods: Trajectory Log files present a record of machine coordinate snapshots every 10ms of beam on state. We designed an automated data mining engine capable of extracting machine parameters recorded for the treated fractions for a selected patient, and generating easy to review statistical report quantifying machine delivery performance. The application was tested on 3 head and neck and 4 pelvis test courses in our clinic. Results: The worst observed instant error in Gantry angle position during the delivery of VMAT treatments was 0.22deg, while the time‐averaged gantry error during the delivery was less than 0.002deg. The maximum observed discrepancy between planned and actual treatment position for MLC leaves was 0.11 mm. When machine parameter interfractional variance was analyzed, the worst difference in gantry position between any fraction delivered for a patient was 0.013deg. The worst instantaneous discrepancy between any fraction of treatment for MLC leaves was only 0.028mm. Conclusions: The analysis of Varian TrueBeam accelerator Trajectory Log files generated during the course of treatment of 3 head and neck and 4 pelvis patients showed high reproducibility in dynamics of machine position parameter during the delivery of treatments. Continuous monitoring of treatment logs enables verification of treatment delivery constancy, and should be integrated in clinical QA programs.