bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐351: Pre‐Treatment Simulation Tolerance and Dosimetry Effects On OARs for the Cylinder High Dose Rate (HDR) Brachytherapy Treatment of Vaginal Cuff Cancer
Authors: Shi C , Fang D , Iannuzzi C
Published: July 2013

Purpose: To statistically find out the achievable and practical simulation tolerance for HDR cylinder treatment using scout AP/LAT images and the corresponding organ at risks dosimetry effects. Methods: Five previously treated vaginal cuff cancer patients were randomly selected. All of the patients had prescription of 5 mm above the cylinder surface with 500 cGy per fraction for 5 fractions. The treatment plans were developed using the Oncentra treatment planning system with graphical local optimization method. Two scouts (AP/LAT) were taken during CT scan day and each fraction treatment day. The dummy source was placed in the cylinder and the tip of the dummy source to the top of the pubic bone vertical distance on the AP scout was recorded. The cylinder diameter was also measured. The LAT dummy source angle relative to the horizontal line was also recorded. The treatment for each fraction was then reconstructed using AP/LAT scout images. The source position was registered back to the planning CT. A dummy cumulative plan was then created with a prescription of 2500 cGy for 1 fraction. Results: The AP shifts were ranging from −5 mm to 10 mm and the LAT shifts were ranging from −13 deg to 9 deg. The percentage dose difference can be ranging up 0.3%–14% for the rectum and −17.8%–8.0% for the bladder. Based on the statistics results, we propose the pre‐treatment simulation tolerance: trying to maintain the cylinder in AP direction shift under 5 mm, a warning zone is 5 mm‐10 mm. For the lateral angle, the tolerance is trying to maintain the angle difference under 5 degree with 5–10 degree as warning zone. Conclusion: We have done pre‐treatment simulation quality assurance study using AP/LAT scout images. The tolerance for this pre‐treatment simulation was proposed. The relative dosimetry effects for the rectum and bladder were reported.
SU‐E‐T‐356: Brachytherapy Iodine‐125 Seeds: New Laboratory Developed in Brazil
Authors: de Souza C Daruich , Rostelato M Chuery Martins , Zeituini C , Moura J , de Mattos F Rodrigues , dos Santos Peleias F , de Moura E Santana , Feher A , da Costa O
Published: July 2013

Purpose: In Brazil, cancer has become a health issue. The prostate cancer is the first larger death cause among men. The country urges to develop new treatments such as Brachytherapy. The treatment is performed only in private hospitals due to its high cost. As a Result, brazilian public hospitals do not have brachytherapy as a treatment option. Energy and Nuclear Research Institute IPEN/CNEN established a program for the production of 125Iodine seeds in Brazil. The 125Iodine seeds demand in Brazil is around 8,000 seeds per year. Methods: The 125Iodine is fixated onto the silver substrate using a new procedure (methodology is under patent process). The process lasts only 5 hours and the efficiency is up to 90%. The seeds sealing is accomplished by laser welding process resulting in a homogeneous (with only one pulse) weld without inclusions, cracks or fissures. After sealing, the weld integrity was evaluated with the use of an optical microscopy and leakage test, better than those presented in ISO 9978 standard. All of these procedures are new developed by the Brazilian researchers. Results: After almost 10 years of research and implementation IPEN laboratory is ready. The 125iodine fixation process, the laser welding and the quality control is fully automated. This process took a long time mostly because the precision required due to the seed size. With the chemical process established, the waste management is under implementation. The dosimetry method is under implementation and the final parameters are being calculated. Conclusion: The group will start the production line in 2013. With the lower cost, we hope to make the treatment more feasible to more patients.
SU‐E‐T‐357: Dosimetric Verification of the Enhanced Dynamic Wedges Using a 2D Ion Chamber Array
Authors: Oh SA , Kim SK , Kang MK , Yea JW
Published: July 2013

Purpose: Wedge filters are commonly used to achieve dose uniformity in the target volume in radiotherapy and can be categorized as the physical wedge (PW) and the enhanced dynamic wedge (EDW. The EDW generates PW‐like dose profiles while moving the upper jaw in the Y directions with a varying dose rate in the treatment beams. Task Group 53 of the AAPM (American Association of Physicists in Medicine) recommended that the dynamic wedge should be verified before implementation in the radiation treatment planning (RTP) system in order to ensure the same capabilities between the PW and the dynamic wedge. The aim of this study was to verify the dose profiles of the EDWs manufactured by Varian with the ImRT MatriXX. Methods: The ImRT MatriXX was used to compare the dose distributions between PW and EDW with wedge angles of 15°, 30°, 45° and 60° in the axial plane. The passing criteria of DD and the DTA were selected as 1%/1mm, 2%/2mm and 3%/3mm. The gamma evaluations were performed with the calculated and measured dose distributions for the varied wedge angle in EDW. Results: The gamma index of the calculations and the measurements for the EDWs were 84.84% and 86.54% in 2%/2mm tolerance, and 99.47% and 99.64% in 3%/3mm tolerance for the wedge angles of 15°, 30°, 45° and 60°, respectively. The dose distributions differed between the treatment planning system (TPS) calculations and the measurements in the penumbra and the outer beam regions of the wedge fields. Conclusion: We confirmed that the dosimetric verifications of the EDW were acceptable with an acceptability criterion for external beam dose calculations of Task Group 53. This work has supported by the Yeungnam University Academic Research Fund (212A380146).
SU‐E‐T‐360: Development of a Detection System for Intra‐Fractional Motion in Intracranial Treatment Using Patient Surface Pressure
Authors: Inata H , Araki F , Nakaguchi Y , Nakayama S , Itoh Y , Uwatsu K , Nishizaki O
Published: July 2013

Purpose: To develop a dedicated real‐time monitoring system to detect intra‐fractional motion in intracranial radiotherapy using patient surface pressure. Methods: The motion for two volunteers was analyzed by a new type of immobilization system that detect load given to a patient head. The immobilization system consists of sensors with a thickness of 0.55 mm and a radius of 9.1 mm, a thermoplastic mask, a vacuum bag, and an acrylic baseplate. The four pieces of sensors were positioned at left‐right sides, superior‐inferior sides on the vacuum bag, respectively. The other four pieces of sensors were positioned at up‐down sides, left‐right sides of chin just under the thermoplastic mask, respectively. The load given to the volunteer was detected by the immobilization system that the eight sensors were attached. The pressures for sensors were calculated using a measuring resistor in a voltage divider configuration. The three pieces of light‐emitting diodes (LEDs) were located on the thermoplastic mask at the chin and the pair of cheeks to detect the volunteer motion. The three‐dimensional positions of LEDs were continuously detected using the Cyberknife Synchrony system. The sensor's pressures were compared with the root mean square (RMS) of LEDs displacement during the 30 min interval. Results: The RMS values of LEDs displacement within 1 mm or less were almost related to the pressures of sensors at left and superior sides on the vacuum bag. The pressures of other sensors were not detected or no relationship with the RMS values of LEDs displacement in two volunteers. Conclusion: The dedicated real‐time monitoring system using patient surface pressure can detect intra‐fractional motion in intracranial treatment with high precision of 1 mm or less.
SU‐E‐T‐361: Use of a MEMS Accelerometer to Detect Motion in Patients During Delivery of Radiotherapy
Authors: Markovic A
Published: July 2013

Purpose: Patient movement during radiotherapy treatments can Result in delivery of dose to unintended areas resulting in a poor prognosis. It is desirable to minimize intra‐fraction (during treatment) motion since treatment times typically range from 5 to 30 minutes. A small MEMS (micro electromechanical systems) accelerometer can be placed on the patient's skin and be used to instantaneously detect slight motions exhibited by the patient. Information about patient motion can be displayed on the therapist's console and be used to interrupt the treatment or to coach the patient when a significant deflection occurs. Methods: A 12‐bit ST Microelectronics accelerometer (LIS3DH) of dimensions 3×3×1 mm on a 5×6 cm breadboard (Fig. 1) was used to measure deflections under simulated treatment conditions. The accelerometer can transfer data at rates ranging from 100 to 1600 Hz via either a USB cable or Bluetooth that relays acceleration data to a computer running a MATLAB program. This highspeed data rate allows for averaging which reduces random noise. The accelerometer provides a resolution of 9.8×10−3 m/sec2. We are currently investigating the use of a new low‐noise 16‐bit accelerometer which will improve signal to noise response. Results: Figs. 3 and 4 display data acquired at a rate of 100Hz while the accelerometer was attached to a subject's forehead. The data in Fig. 3 show the subject intentionally making two short, small movements. The data in Fig 4. show movement from the same subject intentionally turning their head slowly over a deflection of approximately 8 degrees. Conclusion: A MEMS accelerometer was used in this pilot study to detect subject motion in real time involving quick as well as slow deflections of the head. Data rates of 100Hz allowed point averaging which resulted in smooth traces. Thresholds can be configured in the monitoring software to alert when a significant deflection occurs.
SU‐E‐T‐363: Combination of Dental Putty Based Bite Block and Immobilization Mask Improves the Setup Accuracy of Stereotactic Radiosurgery of Brain Metastasis
Authors: Liu Z , Tazi A , Barrett J , Sha S
Published: July 2013

Purpose: To evaluate if the addition of dental putty based bite block improves the setup accuracy over the immobilization mask alone in the treatment of brain metastasis using linear accelerator based stereotactic radiosurery. Methods: Localization shift data from on‐board kV CBCT images relative to reference CT images of 16 patients receiving brain stereotactic radiosurgery were retrieved and analyzed for this study. Out of the 16 patients, 8 were treated with immobilization mask alone and the remaining were treated with a combination of dental putty based bite block and immobilization mask. Due to the unavailability of 6D couch in our clinic, we used only the translational registration between CBCT images and reference CT images for couch shifts in patient treatment. The clinical localization shifts were used for data analysis. To compare the two immobilization methods comprehensively, the CBCT images were retrospectively co‐registered with the reference images with six degree of freedom (3 translations and 3 rotations). A paired t‐test was used to evaluate the statistical significance of the two immobilization methods. Results: For the clinical patient treatment, localization shifts from immobilization mask only were 1.5±1.8 mm, 0.1±2.6 mm, and −1.0±2.2 mm, in the vertical, longitudinal, and lateral directions respectively. The addition of dental putty based bite block improves the localization shifts to 0.2±0.2 mm, 0.7±0.6 mm, and 0.9±1.2 mm in the vertical, longitudinal, and lateral directions respectively. Furthermore, the addition of dental putty based bite block reduces significantly the rotational variations of patient head in the immobilization mask. Conclusion: The combination of dental putty based bite block and immobilization mask improves the setup accuracy of linear accelerator based intracranial stereotactic radiosurgery. The formation of a reliable dental putty impression to the upper jaw of each patient is essential for a successful implementation of the procedure.
SU‐E‐T‐365: Respiratory Motion‐Induced Dose Uncertainty in Step‐And‐Shoot IMRT
Authors: Li H , Park P , Liu W , Matney J , Liao Z , Zhang X , Zhu X
Published: July 2013

Purpose: The objective of this study was to quantify respiratory motion induced dose uncertainty at the planning stage for step and shoot intensity modulated radiation therapy (IMRT) using a novel analytical technique. Methods: Ten patients with stage II/III lung cancer who had undergone a planning 4DCT scan and step and shoot IMRT planning were selected with a mix of motion and tumor size for this study. The maximum and minimum doses with respiratory motion were calculated for each plan, and the mean deviation from the 4D dose was calculated, taking delivery time, fractionation, and patient breathing cycle into consideration. Results: For all patients evaluated in this study, the mean difference between the total delivered dose and the 4D dose in the planning target volume (PTV) was <2.5%, with a standard deviation <1.2%, and maximum point dose variation from the 4D dose was <6.2% in the PTV with delivery dose rate (DR) of 200 MU/min and patient breathing cycle of 8 seconds. The motion induced dose uncertainty is a function of fractionation, MU (plan modulation), dose rate, and patient breathing cycle. Conclusion: Respiratory motion induced dose uncertainty varies from patient to patient. Patient specific respiratory motion induced dose uncertainty quantification could be useful for plan evaluation and treatment strategy determination.
SU‐E‐T‐372: Quality Assurance Plan Veto (QAPV): Reincarnation of Record and Verify System and Its Potential Value
Authors: Gutti V , Noel C , Yang D , Bosch W , Mutic S , Ford E , Terezakis S , Santanam L
Published: July 2013

Purpose: To quantify the potential impact of implementation of IHE‐RO Quality Assurance Plan Veto (QAPV) profile on patient safety of external beam radiation therapy operations. Methods: An institutional database of events (errors and near misses) was used to evaluate the ability of QAPV to prevent the clinically observed events.. We analyzed those reported events which were related to inconsistencies between DICOM RT plan parameters between the intended treatment (treatment planning system) and the delivered treatment (treatment machine). Critical DICOM RT plan parameters were identified. Each event was scored for importance using the Failure Mode & Effects Analysis (FMEA) methodology. Potential error occurrence (frequency) was derived based on the collected event data, along with the potential event severity, and probability of detection with and without the theoretical implementation of QAPV plan comparison check. FMEA Risk Priority Numbers (RPNs) with and without QAPV were compared to quantify the potential benefit of clinical implementation of QAPV. This analysis considered the highest risk parameters with RPN>200. Results: The clinical implementation of the IHE‐RO QAPV reduced RPN scores to below 200 for 7 (out of 8) high‐risk parameters. For example, RPN values reduced from 324 to 108 for ‘beam MU' s’ inconsistencies, 288 to 96 for ‘treatment machine’ inconsistencies, 200 to 40 for ‘beam limiting device type’ inconsistencies, and 252 to 72 for ‘wedge’ inconsistencies. Conclusion: This analysis quantifies the value of the IHE‐RO QAPV implementation in clinical workflow. We demonstrate that although QAPV does not provide a comprehensive solution for error prevention in radiation therapy, it can have a significant impact on a subset of the most severe clinically observed events.
SU‐E‐T‐378: IMRT Severity Scoring for TG‐100: Do You Really Know?
Authors: Tonigan J , Kry S , Balter P , Faught A , Followill D
Published: July 2013

Purpose: Failure modes and effects analysis (FMEA) as defined in TG‐100 has become a popular concept throughout the radiotherapy community. This risk mitigation technique involves detailed process mapping, analysis, and ranking of potential errors by means of a subjective, ordinal scoring system. This study aims to reduce the subjectivity of FMEA severity scoring for IMRT delivery by providing quantitative values. Methods: First we created an IMRT delivery process map for physics‐applicable processes and identified 11 physical failure modes (FMs). To determine the magnitude of dose delivery errors for several of the physical FMs (i.e., the severity of the FM), FMs were induced and dosimetry measurements were performed on a Varian Clinac accelerator going out of clinical service. Treatment planning studies to simulate remaining FMs are to follow. The quantitative severity scores will be compared to recommended FMEA subjective scores. Results: We identified the following physical FMs to investigate: photon beam energy, symmetry, MLC position, MLC transmission and leakage, MLC rounded‐end and leaf offset, MLC tongue‐and‐groove, CT look‐up table, gantry angle, collimator angle, couch angle and displacement, and MU linearity. Within the PTV of a H&N IMRT phantom, the maximum dose delivery error of 3% absolute dose was seen for 2 mm systematic MLC offsets, 4% for 1.1% increased energy, and 4% for 3.5% symmetry error. Measurements will be compared to computational study results and then used for quantitative severity scoring determination. Conclusion: Current FMEA practice for radiotherapy requires quantitative data in order to make accurate assessments associated with clinical QA programs. This study has shown examples of error magnitudes induced by IMRT physical FMs that can be used to quantitate and rank FMEA severity scoring. Work supported by grants CA10953 and CA81647 (NCI, DHHS).
SU‐E‐T‐383: 3D Dose Reconstruction From Tomotherapy Detector Response of the Pre‐Treatment QA
Authors: Suh S , Liu A , Wong J , Schultheiss T
Published: July 2013

Purpose: To evaluate the reconstructed 3D dose from the Tomotherapy detector response as a pre‐treatment patient‐specific dose verification tool by comparing the reconstructed dose with the 3D dose from the Tomotherapy treatment planning system (TPS). Methods: A simple dry‐run of a patient plan was performed to capture the fluence sinogram with the detectors. Then, DosimetryCheck™ (DC) was used to calculate the 3D dose using the detector sinogram, CT images, and treatment delivery parameters. The couch attenuation was corrected mathematically. The reconstructed dose was compared with the Tomotherapy TPS 3D dose in the patient anatomy. Results: TPS dose and DC reconstructed dose were compared for 5 prostate plans, 1 head and neck plan, and 1 SRS plan. For the prostate plans, the average dose differences of the bladder, rectum, femur, and prostate were 3.0+−1.8%, 4.2+−1.1%, 3.0+−2.0%, and 0.1+−1.1% (+−S.D.). For the head and neck plan, the average differences of the spinal cord, parotid, mandible, and PTV were 6.9%, 8.6%, 1.2%, and 0.2%. For the SRS plan, the average differences of the brain stem, optical chiasm, left eye, and the PTV were −0.5%, 0.6%, 1.5%, and −3.4%. The overall gamma factor (3%, 3mm) passing rate was >90% for all the cases. Conclusion: It is feasible to perform patient specific QA without Tomotherapy phantom DQA. The QA is more meaningful beca use the dose difference is visualized over patient anatomy instead of over a phantom. The statistics with prostate plans show a consistent match between the measured and planning dose. The head and neck plan suggests that DC Pencil Beam algorithm may need improvement in accuracy for areas with dramatic electron density changes. The SRS plan indicates DC accuracy is independent of jaw width and pitch. All the differences between the Tomotherapy TPS and the reconstructed doses were within clinical tolerance.
SU‐E‐T‐385: Comparison of Breast Radiotherapy Induced Secondary Cancer Risk for 3D‐Conformal Therapy, IMRT and VMAT
Authors: Lee B , Sung J , Yoon M
Published: July 2013

Purpose: The objective of this study was to evaluate the secondary cancer risk of various organs due to the radiation treatment of breast cancer. Methods: The organ doses were measured with photoluminescent dosimeter (PLD) in anthropomorphic phantom for the treatment of breast cancer with 3D conformal radiation therapy (3D), intensity‐modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT). The cancer risk based on measured dose was calculated using the BEIR (Biological Effects of Ionizing Radiation) VII models which yield lifetime attributable risks (LAR) for radiotherapy techniques. Results: The secondary dose per treatment dose (50.4 Gy) from 3D‐CRT in various organs ranged from 0.02 to 0.36 Gy. The secondary doses per treatment dose from IMRT and RapidArc, however, ranged between 0.07 and 8.48 Gy, indicating that IMRT and RapidArc are associated with higher doses of secondary radiation than 3D‐CRT. The organ specific LARs of the thyroid, contralateral breast and ipsilateral lung were 0.02, 19.76, 0.74 per 100,000 population in 3D‐CRT which is much lower compared with IMRT (0.11, 463.6, 10.2) or RapidArc (0.11, 290.37, 11.71). Conclusion: The overall estimation of LAR indicated that the radiation‐induced cancer risk due to the beast radiation therapy was lower with 3D‐CRT than with IMRT or RapidArc.
SU‐E‐T‐388: The Feasibility Study for the New IMRT Technique of Expansion Radiation Field Using the Vero4DRT Gimbal Mechanism
Authors: Kabuki S , Yoshida M , Yamakawa T , Kunieda E
Published: July 2013

Purpose: We have developed and evaluate a field size‐expansion IMRT using the gimbal mechanism for the vero4DRT, which have been developed by Mitsubishi Heavy Industries LTD/Brainlab is one of the linacs for the next generation. Methods: A beam head of vero4DRT can move along the pan and tilt direction independently using the gimbal mechanism. In this study, we individually investigated the new technique of the gimbal usage for expanding a field size by an intensity modulated radiation therapy (IMRT), which was first reported by Kyoto University. Our basic method is to expand the effective field size created by two main fields with two irradiation directions using gimbal mechanism. A dose distribution for the case with multi gantry and two gimbal angles were calculated by a Monte Carlo simulation (Geant4 9.4pathch03) for the conventional IMRT and the field size‐expansion IMRT. These results were compered each other.. The conditions were as follows; using the cylindrical shaped phantom with two targets and the beams from 7 directions. Results: We have developed a program for the simulation and calculated the dose distribution of IMRT. The program succeeded to expand the field size 15 cm ×15 cm to 15 cm × 23 cm with IMRT calculation. We were able to demonstrate the potential of expanding IMRT radiation field using the optimization program. It allows us to evaluate the possibility of the improved dose distribution using the gimbal mechanism for IMRT. Conclusion: We have proposed a new method of irradiation using a gimbal mechanism of vero4DRT. By using this method, the possibility of a new radiotherapy can be realized. Moreover, not only due to the gimbal mechanism, vero4DRT has a possibility of realizing a new and unparalleled treatment all independent mechanical freedom, depending on the development of the controlling software and the treatment planning algorithm. This work was supported by Mitsubishi Heavy Industries, LTD.
SU‐E‐T‐394: Evaluation of Volumetric Modulated Arc Therapy (VMAT) Efficiency Using the Elekta Agility
Authors: Moore J , Smith K , Duhon M , Qian J , Gonzales R , McNutt T , Wong J
Published: July 2013

Purpose: To evaluate the efficiency of VMAT delivery using the Elekta Agility head with 160 5mm leaves. The Agility head is promoted as having significantly faster leaf motion and therefore delivery time. Improvement of efficiency allows for more patients to be treated in a day and reduces the time that each patient must be on the treatment table. Methods: Six plans initially treated on an 80‐leaf Elekta Infinity were selected. The sites represented were Pancreas, two Head and Neck plans, Pelvis, Retroperitoneal Mass, and Rectal. For each plan, a film measurement in a 30×30×30 cm phantom is conducted. The beam‐on time of each plan delivery is recorded. To compare plans with the 160‐leaf Agility, the plans optimized for the 80‐leaf Infinity are converted to 160‐leaf plans by pairing adjacent MLC leaves. This produces a plan in which the aperture shapes on both machines are matched. Additionally, another plan is optimized using the 160‐leaf Agility to show the improved capabilities of the higher resolution device. Results: The plans delivered on the 80‐leaf Infinity took on average 273 seconds to deliver. On the 160‐leaf Agility, paired plans took on average 112 seconds to deliver. The re‐optimized Agility plans took on average 204 seconds to deliver. All of the paired plans took significantly less time (less than half) to deliver (p<0.01). Plans re‐optimized for the Agility took significantly less time on average (p×0.02), however one plan did Result in an increase in delivery time from 267 seconds to 298 seconds. Conclusion: The Agility head is shown to greatly improve the efficiency of VMAT delivery when compared to the Infinity. Additional research is needed to refine the planning objectives to reduce treatment time when optimized using the Agility MLC.
SU‐E‐T‐398: Case Study of Performance Testing Method for An Intensity Modulated Radiation Therapy Treatment Planning System Named RayStation
Authors: Wu Q , Zhang X , Yang X , Yan W , Li G
Published: July 2013

Purpose: Referring to the Standard of the Pharmaceutical Industry of the People's Republic of China “Performance and test methods for intensity modulated radiation therapy(IMRT) treatment planning system”, we will do a series of tests to an IMRT planning system named RayStation, before its registration and certification. Methods: The Standard is put forward by the state food and drug administration(SFDA) of China, and adapted from AAPM TG119 report. Referring to the Standard, the tests include: dose goals used for planning, point dose calculation accuracy and dose distribution calculation accuracy. And test phantoms include: AAPM TG119 report's test cases and solid water phantom for verification, and IMRT test cases include: multitarget, mock prostate, mock head/neck and CShape(easier version and harder version) and so on. Referring to the Standard, we optimize and calculate doses of interest in RayStation, and use the common measurement equipments and tools, such as an ionization chamber, films, a detector array, and etc, to measure the doses on the accelerator, then calculate and analyze the errors between them. Results: The results of dose goals for five different mock plans meet well with the requirements of the Standard. And the point dose ionization chamber measurements are in line with the requirements of the Standard, and the total error of the mock plans is (0.83 ± 1.65)%. The gamma criteria pass rates of per‐field measurements using detector array are all greater than 99.0%, and the pass rates of composite film measurements are all greater than 92.5%. Conclusion: This study has done a set of tests to IMRT performance of RayStation, and the results of three trials are in full compliance with the requirements of the Standard. The test method can also be reference for the user commissioning of IMRT treatment planning system and IMRT clinical dosimetric verification.
SU‐E‐T‐400: Impact of Inhomogeneous Tissue On IMRT QA for MatriXX
Authors: Yin Y , Chen J
Published: July 2013

Purpose: By applying self‐made inhomogeneous phantom to MatriXX, a group of IMRT plans were delivered, to observe the impact on test results on different measuring condition. Methods: two foam planks were made to simulate the low density tissue, e.g lung tissue, in the size of (40×40×3)cm, identical to virtual water. Three measurement condition using MatriXX were arranged: A. virtual water only (8cm top and 5cm bottom); B. one foam plank was used plus 5cm virtual water on its top, and 5cm virtual water on MatriXX bottom; C. two planks were used on the top and at the bottom of MatriXX, with 5cm and 2cm virtual water planks wrapped. The sizes in B and C condition were same to A. CT scanning images for three conditions were obtained and transmitted to TPS. QA plans were generated to the scanning images respectively. The original plans were 10 esophageal cancer IMRT plans. The QA plans were calculated in CMS xio‐release 4.62, using superposition algorithm, and then delivered to Elekta Synergy. Each plan was measured in different condition, and the gamma passing rate was obtained. Results: there was no significant difference (P<0.05) among the three measuring condition. The results, i.e gamma passing rate, in B (98.78±1.34)% and C (98.71±1.16)% were as good as in A (98.49±1.10)%. Conclusion: the results showed that there is no difference in MatriXX measurement, no matter what phantom is used. However, more measurements should be needed to make it confirmed.
SU‐E‐T‐405: Basic Performance Comparison Between Two Types of Proton Beam Modulated Scanning Systems
Authors: Farr J , Dessy F , DeWilde O , Bietzer O , Schoenenberg D , Stuschke M
Published: July 2013

Purpose: The purpose of this investigation was to compare and contrast the fundamental properties of two new types of modulated proton scanning systems. A secondary purpose was to develop and apply new characterization approaches where necessary to do so. Methods: The following performances of the proton scanning systems were investigated: beamlet alignment, static in‐air beamlet size and shape, scanned in‐air penumbra, scanned fluence map accuracy, geometric alignment of scanning system to iso‐center, maximum field size, lateral and longitudinal field uniformity of a one liter cubic uniform field, output stability over time, gantry angle invariance, monitoring system linearity and reproducibility. A range of detectors was used: film, ionization chambers, multi‐ionization chamber lateral and longitudinal detectors, and a scintillation screen combined with a digital video camera. Characterization of the scanned fluence maps was performed with a software analysis tool. Results: The resulting measurements and analysis indicated that the two types of delivery systems performed within specification for those aspects investigated. The significant differences observed between the two type of scanning systems where: One type exhibits a smaller spot size and associated penumbra than the other. The differential is minimum at maximum energy and increases inversely with decreasing energy. Additionally, the large spot system showed an increase in dose precision to a static target with layer re‐scanning whereas the small spot system did not. Conclusion: The measured results from the two types of modulated scanning types of systems were consistent with their designs. The most significant difference between the types of systems was their proton spot size and associated resolution, factors of magnetic optics and vacuum length. The need and benefit of muti‐element detectors and high‐resolution sensors was also shown. The use of a fluence map analytical software tool was particularly effective in characterizing the dynamic proton energy‐layer scans.
SU‐E‐T‐407: Dosimetric Influence of Setup Errors On RapidArc‐Based SRS for Simultaneous Irradiation of Multiple Intracranial Targets
Authors: Yang Y , Zhang Y , Li T , Li X , Heron D , Huq M
Published: July 2013

Purpose: To evaluate the dosimetric influence of setup errors on RapidArc‐based SRS for simultaneous irradiation of multiple intracranial targets. Methods: Eight patients previously treated with RapidArc™ technique for multiple intracranial lesions were included in this study. A RapidArc plan was designed to irradiate multiple targets simultaneously with one isocenter and 4 non‐coplanar arcs. 1 mm margin was added to generate PTVs from GTVs. BrainLAB Novalis system was used to position the targets with 6D corrections and monitor patient position during treatment. CBCT was acquired for verification before irradiation. Velocity AI was used for image registration and dose mapping for CBCT, planning CT, contours and dose matrix. The DVHs of targets and critical structures and dose distributions were compared with the planned results and dosimetric influence from setup errors was analyzed. Results: We found that the translational errors were less than 1 mm in the three directions and rotational errors were less than 0.6 degree for all the patients. The overall PTV coverage decreases of ∼10 percent on average while the overall GTV coverage slightly influenced. Although prescribed dosed still covered most of GTVs, there were still some targets with a GTV coverage drop greater than 5 percent even with a 1 mm margin. Most of influenced targets were small targets and relatively far from isocenter. Our study also showed that the dosimetric influence on critical structures was negligible. Conclusions: Although RapidArc technique can generate good plans for effectively treating multiple intracranial lesions simultaneously using stereotactic radiosurgery, this technique is more susceptible to the setup errors, especially rotational errors. 0.5 degree rotational error may Result in non‐ignorable drop in target coverage. Our study show that a 1 mm margin for PTV and 6D positioning are necessary for a successful treatment with this technique.
SU‐E‐T‐409: A Probability Density Function Based Dose Calculation for Gated Volumetric Modulated Arc Therapy in Lung Stereotactic Body Radiotherapy
Authors: Zhang Y , Yang Y , Li X , Li T , Heron D , Huq M
Published: July 2013

Purpose: To evaluate the accuracy of probability density function based dose calculation for phase gated volumetric modulated arc therapy (VMAT) in lung stereotactic body radiotherapy, and to quantify the dose uncertainty induced by tumor motion. Methods: During VMAT gating delivery the tumor position, gantry, MLC leaves and dose rate change independently and continuously. To compute the accumulated dose, we convert the target motion into MLC motion for each control point by convolution of MLC leaf positions with target motion probability density function. The new VMAT plan file was imported back to treatment planning system (Eclipse) to reconstruct the dose distribution. The planar dose distribution was compared to a mobile phantom (QUASAR) measurement with the gating technique with an amplitude gating window of 5 mm. This method mentioned above was used to compute the gated VMAT dose distribution and evaluate the motion effect to the PTV and GTV coverage and normal tissues. Results: The probability density function based VMAT gated dose calculation can greatly simplify the dose calculation procedure since only the reference/planning image is used for the accumulated dose calculation. Our results show good agreement between the modified plan and measured dose distribution. Calculated results show that motion can greatly reduce the PTV coverage but its effect on GTV coverage is insignificant for the gated VMAT for the treatment of lung cancer. The gated dose distribution is comparable to the static plan for spinal cord and lung dose. Conclusion: The dose distribution comparison shows good agreement between the modified plan and the measured dose distribution. The VMAT gated dose distribution can be calculated using the probability density function so that the accumulated dose calculation procedure can be greatly simplified.
SU‐E‐T‐414: 4D Vs 3D Dose Calculations for Non‐Small‐Lung‐Cancer: A Comparison Using Tumor Control Probability (TCP)
Authors: Valdes G , Lamb J , Low D , Lee P , Iwamoto K
Published: July 2013

Purpose: To investigate the utility of four dimensional (4D) dose calculations for design and optimization of stereotactic lung radiotherapy treatment plans. Methods: Radiotherapy plans for stage I–II lung cancer were created for 8 patients. Clinically acceptable treatment plans were created with dose calculated on the end‐exhale 4D‐CT phase, using a Monte Carlo algorithm. Dose was then projected onto the remaining 9 phases of 4D‐CT using the Monte Carlo algorithm and accumulated onto the end‐exhale phase using commercially available deformable registration software. The resulting DVHs of the gross tumor volume (GTV), planning tumor volume (PTV), and PTVsetup were compared according to target coverage and dose. The PTVsetup was defined as a volume including the GTV and a margin for setup uncertainties but not for respiratory motion. Tumor control probabilities (TCP) resulting from these DVHs were estimated using a wide range of alphas, betas, and tumor cell densities. Results: Differences of up to 5 Gy were observed in dosimetric indices related to the tumor between 3D and 4D calculations. When the TCP was calculated using the resulting DVHs for fractionation schedules typically used in stereotactic body radiation therapy (SBRT), the TCP differed at most by 5% between 4D and 3D cases, and in most cases differed less than 1%. Conclusion: In some cases moderate dosimetric differences may be obtained between 3D and 4D dose calculations. Even when dosimetric differences exist between 3D and 4D calculations, the resulting TCPs do not differ greatly for commonly‐used SBRT dose prescriptions.
SU‐E‐T‐418: Dynamic Arc Technique Improves Delivery Accuracy of Stereotactic Body Radiation Therapy (SBRT) for Spine
Authors: Huang L , Djemil T , Chao S , Suh J , Xia P
Published: July 2013

Purpose: To investigate whether delivery accuracy can be improved with volumetric intensity modulated arc (VMAT), a hybrid dynamic arc therapy (HA) with fixed beam IMRT when compared to fixed beam IMRT alone for spine SBRT. Methods: Ten spine patients who underwent SBRT treatment using fixed beam IMRT were randomly chosen from an IRB approved registry. All cases were replanned with VMAT and HA techniques. The VMAT plans were created using the Pinnacle 9.0 with four 120 degree coplanar arcs and 120 segments. HA plans and clinical IMRT plans were created from Brainlab iplan. All HA plans used one 360 dynamic arc and 5–7 IMRT fixed beams, consisting 150–180 segments. All clinically IMRT plans used 7–9 fixed IMRT beams with 200–250 segments. All VMAT and HA plans were similar or better than clinical IMRT plans, meeting clinical objectives. All thirty plans were delivered with the same linear accelerator and measured with a 2D ion chamber array. The gamma index (GI) (3mm/3% and 2mm/2%) was used to test the delivery accuracy for each plan. Results: For the three delivery techniques, VMAT, HA, and IMRT, the average GI of 3mm/3% were 98.9±0.6%, 96.5±2.7%, and 92.6±1.1%, respectively. The average GI of 2mm/2% were 92.3±2.4%, 90.4±2.1%, and 82.0±2.2%, respectively. There is no significant difference on delivery accuracy between the VMAT plans and HA plans(P =0.09 for GI (3mm/3%) and P=0.229 for GI(2mm/2%)). There is a significant difference (P<0.05) on delivery accuracy between VMAT (or HA) and IMRT plans based on GI of 3mm/3% and 2mm/2% criteria. Conclusions Dynamic arc techniques improve delivery accuracy of stereotactic body radiation therapy for the spinal lesions. VMAT or HA is a better choice than fixed beam IMRT with improved delivery accuracy.
SU‐E‐T‐420: Optimizing Accuracy of the Brain Lab SRS Mask System On a Varian TrueBeam Linac
Authors: Rasmussen B , Chu K
Published: July 2013

Purpose: Compare the geometric accuracy of the BrainLab cone SRS system with paper target overlays against the Varian TrueBeam CBCT image guidance system as well as to optimize CT protocols for planning. Methods: A head phantom with rigid geometric inserts (mounted in the BrainLab headring) was used to test the localization accuracy of the BrainLab system and the TrueBeam CBCT system. A 2 mm diameter BB (to act as a target) was placed on one of the surfaces inside the phantom. Planning CT scans were acquired with both helical and sequential techniques with a range of slice thicknesses. Localization was performed using the BrainLab CT/X‐ray localizer box and subsequent planning was performed in iPlan. Printed target position overlays were then used to set up the phantom on the TrueBeam. A CBCT was acquired, 3D/3D matching was performed, and the differences in position between the paper printouts and 3D/3D match were recorded. Position of laser intersection on BB target was used as the standard for accuracy assessment. Results: The BrainLab localization system was found to align the phantom to within approximately 1.0 mm in any one direction of the target BB center. CBCT image guidance with 3D/3D matching was able to improve alignment to within approximately 0.5 mm in any one direction. The observed difference is partially attributed to a 0.1° mechanical misalignment of the couch mount and thus in the BrainLab localizer box. Conclusion: CBCT guidance was found to be more accurate than BrainLab localizer alone. Oversampled, helical scanning for planning is recommended because of the smooth table motion, quicker scan time, and no loss of localization accuracy compared to sequential scanning. Quality assurance testing of the CBCT system accuracy should be performed after verifying the lasers with the standard Winston‐Lutz test and just prior to each treatment.
SU‐E‐T‐421: Commissioning of Brainlab Cones for 6×FFF and 10×FFF Beams On a Varian TrueBeam STx
Authors: Wiant D , Sintay B
Published: July 2013

Purpose: To the best of our knowledge no data has been published on the use cones at 10×FFF and very little for 6×FFF. We report our experience commissioning and validating beam models for 4, 6, 7.5, 10, 12.5, and 15 mm cones on a Varian TrueBeam STx (Varian Medical Systems, Palo Alto, CA)). Methods: Scatter factors, radial profiles, and percent depth dose curves were measured per Brainlab protocol using a Sun Nuclear Edge Detector diode (Sun Nuclear Corp., Melboune, FL). The resulting Brainlab iPlan (Brainlab AG, Germany) beam models were validated with measurements of absolute dose and profiles at depths of 5, 10, and 15 cm in a polystyrene phantom using EBT3 radiochromic film (Ashland Inc., Covington, KY). Absolute doses were evaluated by comparing the average of pixels in the planned dose that had values > 80% of the maximum dose to the average of the corresponding pixels in the film. Results: The 6×FFF commissioning data was reviewed by Brainlab and found to be in good agreement with other user submitted data. Brainlab did not have a 10×FFF reference set at this time. The measured absolute dose agreed with planned dose to within 4.7% for all 6×FFF measurements (average difference of 2.1%) and within 4.9% for all 10×FFF measurements (average difference of 3.6%). Vertical and horizontal profiles through film planes gave full‐width‐at‐half‐maximum values that agreed with planned values to 0.4 mm for 6×FFF and to 0.2 mm for 10×FFF. Conclusion: The calculated dose distributions showed acceptable geometric agreement with measured values. The measured absolute dose for both energies was consistently lower than planned dose, with the difference more noticeable for the 10×FFF energy. This effect may be explained by reported over responses of diodes at small fields and under responses of EBT film at small fields.
SU‐E‐T‐427: Beam‐Attenuation in the Aktin a Memorial Body Cradle: An SBRT Frame
Authors: Hipp E , Becker S , Osterman K
Published: July 2013

Purpose: Stereotactic Body Radiotherapy (SBRT) frames are used to immobilize the patient during hypo‐fractionated treatments. Ideally, a frame would provide 100% transmission of treatment beams. However, attenuation must be accounted for during treatment planning. This study measures the attenuation of the Aktina Memorial Body Cradle and compares the results to treatment planning calculations. Methods: Attenuation was measured by making two sets of ion chamber readings in an homogeneous solid water phantom (CNMC Best Medical) with a ion chamber (Exradin A16)‐one with the phantom in the frame and one with the phantom directly on the couch. Five coplanar 6 MV beams, 5 × 5 cm field size, (180, 230, 250, 270, 285) designed to intersect with specific cradle components were evaluated. To determine calculated transmission, a CT scan of the phantom in the cradle was acquired and two plans were then generated; one with the cradle included in the body contour and one with the cradle excluded (GE Lightspeed; Eclipse). Each plan was calculated with the pencil beam convolution algorithm (PBC) and with the anisotropic analytical algorithm (AAA). Results: The cross‐bars resulted in a measured attenuation of the beam of 4.8%, while the attenuation through the side paddles was small, at 1.4%. The beam passing through the intersection of the base frame and the crossbar fixation hardware (250°) resulted in the largest measured attenuation of 19.7%. The corresponding calculated attenuation was 21.9% and 22.5% for PBC and AAA, respectively. Inclusion of the frame in the body contour during calculation resulted in close agreement between calculations and measurements. Conclusion: The positioning of movable SBRT frame components should be carefully considered during simulation as attenuation can vary from 1.4% for paddles to 20% for fixation hardware. Inclusion of the frame in treatment planning calculations allows flexibility in choice of treatment angles.
SU‐E‐T‐428: A Comparative Study of Conventional Radiotherapy, Hypofractionation, and SBRT in Prostate Cancer Using Biological Effective Dose
Authors: Sigler M , Snyder M
Published: July 2013

Purpose: Patient setup in SBRT treatments typically involves specialized immobilization devices to mitigate the greater risk of target under‐dosing due to inter‐fraction positional differences. However there is little evidence of their necessity for prostate treatments. Here we evaluate for prostate SBRT treatments the potential consequences of inter‐fraction motion on biologically effective doses to prostate and normal tissue. Methods: The original planning scan and daily CBCT scans for a patient treated with conventional prostate radiotherapy were used as simulated phantoms for this study. On the patient's original planning scan, a 2 Gy/fx VMAT plan was created in accordance with RTOG 0938. The plan was then transferred to each daily CBCT and recalculated to represent a daily “delivered” dose. BEDs for rectum, bladder and prostate were calculated for each day and summed to a full‐course BED. The plan was then renormalized into hypofractionated (4.3Gy) and SBRT (7.25Gy) plans and recalculated on each CBCT. For the hypothetical SBRT and hypofractionation courses, each CBCT was viewed as a possible setup scan during the course of treatment. As such, all possible full‐course BEDs for each tissue were found by selecting all possible combinations of 12 treatment days from 44 for the hypofractionated plan, and all possible combinations of 5 treatment days for the SBRT plan. Results: Conventional treatment delivered a prostate dose of 159.3Gy over 44 fractions, versus an average of 175.1Gy and 182.2Gy over all possible hypofractionated and SBRT courses respectively. Conventional rectal doses were 80.8Gy, versus an average of 68.1Gy for hypofractionation and 61.8Gy for SBRT. Conclusion: For every possible combination of fractions, SBRT rectal and bladder doses proved lower than their conventional counterparts, while prostate doses increased and remained consistent for all combinations. Intra‐fraction motion notwithstanding, it appears that conventional immobilization techniques are sufficient for high dose per fraction treatments.