bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐603: Evaluation of MLC‐Based Robotic Radiotherapy
Authors: Fahimian B , Soltys S , Xing L , Gibbs I , Chang S , Wang L
Published: July 2013

Purpose: A multi‐leaf collimator (MLC) system has been introduced for the CyberKnife M6 system, enabling conformal shaping of beam apertures in robotic radiotherapy. Through a multi‐disease site study, the potential for the use of MLC‐based robotic delivery is assessed for conventionally fractionated regimens. Methods: The InCise MLC, consisting of 41 leaf pairs, with leaf thickness of 2.5 mm at 800 mm SAD, and a maximum field‐of‐view field size of 120 mm × 100 mm was used in conjunction with the MultiPlan 5.0 platform for comparative planning study relative to the pseudo‐conical IRIS variable aperture collimator. Conformal avoidance technique with relaxed convergence was used for the optimization, and identical dose‐volume optimization parameters and normalization (95%) for the comparative studies. Disease sites, including the prostate, partial breast, and peri‐orbit carcinomas were evaluated, and the results were quantified with respect to total monitor units (MUs), treatment time, conformality, and dose‐volume coverage. Results: The MLC system results on average of 3– 4 modulated segments for a series of non‐coplanar nodes. Relative to plans generated by the IRIS variable aperture collimators, the MLC‐based plans resulted in a 38±10% reduction of both the MUs and treatment time. While similar dosimetry is achieved by both systems, for a dose rate of 1000 MU/min, it is shown that treatment times of less than 20 minutes are possible for most conventionally fractionated treatments with the MLC system. Conclusion: A limiting factor in the adaptation of the robotic delivery for conventional radiotherapy has been the prolonged treatment times. The introduction of compact MLC fixture enables reduction of MUs and treatment time, making conventionally fractionated treatments feasible to more efficiently leverage the higher delivering accuracy and intrafraction motion correction capabilities of robotic delivery.
SU‐E‐T‐607: Should We Care About Delivery Time in IMRT Planning?
Authors: Mittauer K , Lu B , Yan G , Kahler D , Liu C
Published: July 2013

Purpose: To model the delivery time for step and shoot IMRT through developing a method for the user to characterize their machine. To investigate the impact of IMRT parameters on delivery time and recommend planning strategies in light of delivery time and plan quality. Methods: A two‐step delivery time model was derived, and verified against 33 delivered IMRT plans using an Elekta LINAC. Eleven head and neck patients with preexisting IMRT plans were selected for this retrospective study. The Pinnacle TPS was used to compute new plans by varying modulation parameters. 41 plans per patient (451 plans total) were generated with the following variations: 12 minimum segment area parameter (MSAP) plans, 9 minimum MU parameter (MMUP) plans, and 20 minimum MU and segment area parameter (MMUSAP) plans. Plans were evaluated based on DVHs (plan quality) and delivery time. Results: The delivery time model accuracy was 1.8%, 10 s. Delivery efficiency improves above 5 MU for MMUP, but no improvement was found with MSAP. MMUP and MSAP had the greatest influence on the number of control points and the plan MU, respectively. MLC speed and gun delay were more costly than the plan MU. However, the plan MU could affect the delivery times for dose rate dependent plans. Threshold values for plan quality were 5 cm2 for MSAP and 5 MU for MMUP. Conclusion: The proposed formalism provides a valid method to assess delivery time and can be characterized for the users machine. For dose rate dependent cases or future deliveries with an enhanced MLC speed, treatment efficiency could be improved with MSAP and/or MMUP. But for most current clinical cases, only MMUP can improve delivery efficiency. We, however, do not recommend increasing these parameters for the sake of delivery efficiency at a cost to plan quality.
SU‐E‐T‐619: Dosimetric Comparison Between Static IMRT and VMAT for Cervical Cancer
Authors: Kang M , Dai J , Huang M , Xu Y , An J
Published: July 2013

Purpose: To evaluate the plan quality of static IMRT and VMAT for cervical cancer from comparing the dosimetric characteristic of IMRT and VMAT plans. Methods: For 16 patients with cervical cancer,7‐field step & shoot IMRT plan and 360° dual‐arc VMAT plan were optimized using Pinnacle 9.0 TPS(prescribed 95% PTV dose 50Gy).Plans were evaluated according to CI(conformity index),HI (homogeneity index),volume of the OARs and dose of the normal tissues from DVH. Results: The CI and HI of IMRT and VMAT plans were 0.82,0.86 and 1.09,1.09,respectively. Both of IMRT and VMAT could achieve the same homogeneity,while the VMAT had a better performance in conformity than IMRT. The V20,V30and V40 of rectum for VMAT were 1.4%, 6.9% and 4.5% less than those for IMRT, and the mean dose was lower by 1.3Gy. In VMAT, the V20, V30 and V40 of bladder were 4.3%, 6.5% and 3.5% less than those for IMRT plans, and mean dose was reduced by 1.6Gy. The V5 and V50 of rectum and bladder for IMRT and VMAT were comparable with less than 1% in difference. The V10 and V20 of intestine for VMAT were 11% and 4.5% less than those for IMRT, while the V10 of colon for VMAT was 6.6% higher than that for IMRT plans. For sigmoid the V30 and V40 of VMAT were 3.2% and 5.3% less than of IMRT, but the V50 of VMAT was slightly higher than that of IMRT by 1.3%. The V50 of pelvic for VMAT was 5.2% higher than that for IMRT, but the mean dose was reduced by 0.4Gy. For normal tissues, the V10 of VMAT was 2% higher than that of IMRT, while the V20 of VMAT was 5.4% less than that of IMRT. Conclusion: The dosimetric comparison indicated that VMAT can deliver prescribed dose more conformity onto the patient and spare rectum and bladder better than IMRT. Considering advantages of fewer MUs and faster treatment, the VMAT is a better choice for cervical cancer. National Natural Foundation of China
SU‐E‐T‐626: Three‐Beam Technique for Intensity Modulated Radiation Therapy in Oesophagus: Dosimetric Differences in Organs at Risk
Authors: Maneru F , Fuentemilla N , Otal A , Olasolo J , Martin M , Lozares S , Pellejero S , Miquelez S , Soto P , Arias F , Rubio A
Published: July 2013

Purpose: To compare planning results of intensity modulated radiotherapy (IMRT) with conformal external radiotherapy (3DCRT) for oesophagus cancer treatment. Methods: IMRT and 3DCRT options were planned for 6 patients of oesophagus cancer and dose‐volume histograms were evaluated for the main organs at risk: lungs, heart and spinal cord. The prescription dose was 54Gy in all cases and the treatment planning system used was Eclipse (10.0 version with Anisotropic Analytical Algorithm 10.0.28 version). A conventional field arrangement was applied for 3DCRT with antero‐posterior and lateral opposed fields and a 3 field technique (antero‐posterior and 2 oblique posterior entrances) for IMRT. Results: Similar PTV coverage was found and spinal cord maximal dose was under recommendations in both cases. Main difference was in lung and heart dose. A significant reduction on heart dose was obtained with IMRT: mean values of V30, V40, V45 and V50 (volume irradiated with 30, 40, 45 and 50Gy) were reduced by 13.2, 9.9, 2.7 and 2.3Gy respectively. For lungs, mean dose and V5 were quite similar between IMRT and 3DCRT (less than 1Gy of difference); a mean reduction of 2.8Gy and a mean increase of 5.6Gy were found for V10 and V20 respectively. Compared with other IMRT options reported in the literature, such as 5 or more field entrances, a reduction on lung volume irradiated at low dose (V5) was observed. Rest of parameters were close to shown values in this work. Conclusion: This study shows the dosimetric advantages of using a three‐field IMRT technique for heart and lung dose values, keeping the rest of parameters within tolerances. Special attention was put in low lung dose parameters.
SU‐E‐T‐628: Impact of Large SSD On the Plan Quality of Energy‐Intensity Modulated Electron Therapy
Authors: Jin L , Eldib A , Fan J , Li J , Wang L , Ma C
Published: July 2013

Purpose: In photon MLC (pMLC) delivered energy‐intensity modulated electron therapy, a short SSD was preferred for reducing beam penumbra caused by electron in‐air scatter. However, due to some restrictions (e.g. table height limit on some accelerators), a large SSD may be an only choice. This work presents our preliminary results of the impact of a large SSD on an ultimate MERT plan. Methods: A house‐grown Monte Carlo (MC)‐based optimization/dose calculation code was used to generate plans for the Artiste linac with a breast phantom, at 60 cm and 90 cm SSD, respectively. The plans employed four different electron energies (6, 9, 12, 15 MeV) and was normalized to ensure 85% of the CTV to receive 100% of the prescription dose. Their DVHs are then evaluated for target (breast), left lung and heart. Results: When a 90 cm SSD was used instead of a 60 cm SSD, the maximum dose of the CTV increased by 5% while the minimum dose decreased by 3.6%. The left lung showed a 10% increase in the maximum dose while D10% (dose to 10% of volume) and D30% of the lung increased by a factor of 1.39 and 2.23, respectively. The maximum dose to the heart increased by 20% and its D10% and D30% were about 1.5 times larger. Conclusion: With a larger SSD (e.g., 90 cm as compared to 60 cm), increased air‐scattered electrons may lead to substantial deterioration of the overall plan quality ‐ increased target dose heterogeneity and higher doses to critical structures. However, absolute doses received by these critical structures may be still low and further investigations are warranted to find out as to whether MERT with a large SSD is still a better treatment as compared with conventional treatments for some disease sites.
SU‐E‐T‐659: Inverse Treatment Planning for MERT Using Monte Carlo Calculations
Authors: Henzen D , Manser P , Frei D , Volken W , Neuenschwander H , Joosten A , Born EJ , Fix MK , Stampanoni M
Published: July 2013

Purpose: The use of electron beams to treat shallow tumors cou ld reduce the dose to the distal organs at risk. To employ modulated electron radiotherapy (MERT) an inverse treatment planning strategy which bases on a Monte Carlo (MC) Electron Beam Model (EBM) has been developed. Methods: The inverse planning process starts with the selection of the SSD, gantry angle and co llimator rotation for each electron field. These fields are then divided into a grid of beamlets. An MC EBM together with the macro MC (MMC) dose calculation algorithm is employed to pre‐calculate the dose distribution for each beamlet. Afterwards a direct aperture optimization (DAO) using simulated annealing minimizes a co st function which is the sum of the squared dose differences in all voxels of the PTV and the OARs between the actual value and a given upper or lower limit. For each step either a weight change or an aperture change is initiated. As the beamlet dose calculation neglects the MLC interaction a post processing weight optimization and MLC aperture adjustment has been carried out after the DAO has been finished. To test the algorithm an inverse treatment plan has been created for an academic situation and co mpared to the obtained results using a previously developed forward planning strategy. Results: The implementation of an inverse optimization inco rporating the home made EBM has been completed successfully. The time needed for the DAO of the academic situation is about 30 min. Compared to the forward planning the inverse optimization is able to reduce the dose to the OAR (mean dose from 41% to 38%) for the academic case. Conclusion: The developed inverse optimization employing the EBM and MMC can be used for treatment planning of MERT. This work was supported by Varian Medical Systems.

This work was supported by Varian Medical Systems.
SU‐E‐T‐686: A New Plan Quality Index for Dose‐Painting Radiotherapy
Authors: Park Y , Kim S , Park S , Park J
Published: July 2013

Purpose: In dose‐painting by numbers, conventional plan quality indices such as homogeneity index (HI) and dose‐standard‐deviation (STD) have limitations in application. This study aims to introduce new indices for evaluating treatment plans of this radiotherapy technique. Methods: Deviation‐from‐prescription‐index (DFPI) was formulated as the volume‐weighted average of the deviation between prescription dose and planned dose. Two sub‐indices, index‐of‐hotness (IOH) and index‐of‐coldness (IOC) were also defined specifically for selected voxels of which planned dose was higher and lower than the prescribed dose, respectively. The new indices were first tested for 9 IMRT/VMAT plans having 3 different dose prescription levels. For comparison purpose, 4 conventional indices (three types of HI and STD) and difference between V98 and V110 [V110 + (100− V98)] were calculated in each prescription region, and then averaged. Using the Spearman rank correlation test, the relationship was investigated between the DFPI‐based ranks and the composite ranks based on all of 5 conventional indices. The new indices were also evaluated in 9 theoretically‐generated plans having a continuously varying function of dose prescription where the conventional indices are not applicable. Results: The plan quality ranks according to DFPI were found to be highly correlated with that from the composite of conventional indices (correlation coefficient = 0.95, where 1 means perfect correlation). It was also demonstrated that the new indices are applicable to dose painted plans in a continuously varying dose prescription. Conclusion: It was shown that the new plan quality indices formulated with voxel‐based prescription dose can be appropriately used for dose‐painting radiotherapy. The indices allow for a single‐value evaluation regardless of the number of prescribed dose levels, which cannot be achieved using the conventional indices.
SU‐E‐T‐690: Radiosurgery of Peripheral Brain Lesions by Spot Scanning Proton Therapy
Authors: Dirksen B , Wang D , Hyer D , Buatti J , Sheybani A , TenNapel M , Bayouth J , Flynn R
Published: July 2013

Purpose: To determine how small the lateral width in air of proton spots must be in order for proton spot scanning (SS) plan quality to be superior to x‐ray radiosurgery for peripheral brain lesions. Methods: Single‐beam proton SS plans with sigma (lateral spot intensity standard deviation) values ranging from 1 to 14 mm, x‐ray volumetric modulated arc therapy (VMAT) utilizing a 0.5 cm leaf thickness, and cone‐based x‐ray radiosurgery plans were generated for eleven patients with clinical target volumes ranging from 0.5 cm3 to 25 cm3. Plans were evaluated using brain necrosis normal tissue complication probability (NTCP), high dose conformity index, and integral dose metrics. Results: For proton SS plans, as sigma increased from 1 to 14 mm, integral dose relative to the cone plan increased from an average of 0.10 (range 0.05 to 0.17) to 0.63 (range 0.26 to 0.85) compared an average of 1.49 (range 0.90 to 3.00) for VMAT. As SS sigma increased from 1 mm to 14 mm, NTCP for healthy brain necrosis increased from an average of 0.02 (range 0.01 to 0.07) to 0.08 (range 0.01 to 0.18) compared to the averages of 0.06 (range 0.01 to 0.15) for cone and 0.05 (range 0.01 to 0.11) for VMAT plans. An in‐air sigma of less than 6 mm was required for the SS plans to have a statistically significant (p < 0.05) NTCP reduction relative to the x‐ray techniques. Conclusion: When treating peripheral brain lesions, which are ideal cases for SS since only a single proton beam direction is needed, SS only provides a superior NTCP to x‐ray radiosurgery techniques if the proton therapy system can produce an in‐air sigma of 6 mm or less.
SU‐E‐CAMPUS‐T‐02: Dose Variation and Migration Rule of Parotid Gland During Intensity Modulated Radiation Therapy for Nasopharyngeal Carcinoma
Authors: Wang W , Yang H , Hu W , Wang X , Ding W
Published: July 2013

Purpose: To quantify the position of parotid gland (PG) and expound rule of volume and dose changes during the Course of intensity modulated radiation therapy (IMRT) in nasopharyngeal carcinoma patients (NPC). Methods: A total of 141 CT images from 47 NPC patients (three images for each patient: acquired before treatment, at the 15th fraction and 25th fraction for each patient) who underwent radical IMRT were selected for this retrospective study. The distance between the lateral/medial aspects of PG and midline (DLM and DMM) at the level of odontoid process were measured. The parotid glands were divided into ipsilateral or contralateral base on with or without GTV contour. The variation between plan dose and actual dose were calculated. Results: The volume reduction of both PG was more in the second half of treatment(SHT) than in the first half of treatment(FHT) (4.68±3.23 cc Vs. 2.46 ±4.55cc for the right PG and 5.96±2.99cc Vs. 2.06 ±2.99cc for the left PG). But, the V30 of bilateral PG decreased more significantly in FHT than SHT( 5.10±16.04% Vs. 1.14 ±21.54% for the right PG and 6.87±15.58% Vs. 0.81 ±15.94cc for the left PG). And the volume of GTVnx and GTVnd decreased more significantly in FHT than SHT(8.23±13.61cc Vs.3.30±8.09cc and 10.27±13.27 Vs.4.88±8.41cc). The DLM and DMM of contralateral PG shifted all medially and laterally both FHT and SHT, respectively. The DLM of ipsilateral PG shifted more medially in the FHT(3.83±1.53mm) than SHT(1.65±2.04mm), and the DMM of ipsilateral PG shifted medially in the FHT(0.80±2.96mm), but laterally in the SHT(2.19±3.96mm). Conclusion: The reduction of GTV leads to the position change of the parotid gland, which appear more dramatic dose change of the parotid gland in the FHT than SHT. This study was supported by Enze Foundation 2013 and had no Disclosures and Conflict of Interest
SU‐E‐CAMPUS‐T‐03: Patient‐Based Study On Characteristic Prompt Gamma‐Ray Spectra Using a Prompt Gamma Imaging System During Proton Therapy
Authors: Lee E , Polf J , Mackin D , Dolney D , Beddar S , Avery S
Published: July 2013

Purpose: To demonstrate the adaptation of prompt gamma (PG) imaging for the spot scanning in a patient phantom as an independent tool for non‐invasive proton beam range verification. Methods: A cylindrical high‐purity germanium (HPGe) detector was modeled using GEANT4 Monte Carlo toolkit and implemented into a modulated proton beam scanning model. Simulations were run to calculate the spectrum of energy deposited by gamma ray interactions in the modeled HPGe detector from a water phantom and a patient CT phantom during irradiations with proton beam. Images for individual spots (spot patterns were determined from a real patient treatment plan) will be reconstructed using all detected gammas as well as the gamma characteristic of specific nuclear excitations. Results: Dose depth profiles along arbitrary lines in the beam direction showed the dependence of PG 50% falloff on the location of the dose falloff within the water phantom and the patient CT phantom. The PG energy spectra at the emission point (inside phantoms) and the detector outside phantoms were illustrated. Reconstructed gamma emission profile will be compared with dose depth profile. Prompt gamma images will be reconstructed for spot and/or treatment field. Conclusion: This work indicated the first study of clinical implementation of the PG imaging for proton range verification using the incorporated detector response to the patient CT phantom irradiated with proton beam. The results showed feasible correlation between the spot scanning does distribution and prompt gamma ray production. This study will be used in future investigation of detector design optimization following measurements that will be carried out using custom‐build prototype detector system using Compton reconstruction.
SU‐E‐CAMPUS‐T‐06: Dose Perturbations by Electromagnetic Transponders in the Proton Environment
Authors: Dolney D , McDonough J , Vapiwala N , Metz J
Published: July 2013

Purpose: Surgically implanted electromagnetic transponders have been used in external beamradiotherapy for target localization and position monitoring in real time. The effect of transponderson proton therapy dose distributions has not been reported. This study determines the level of thedose deficit that results from the presence of Calypso Beacon™ transponders in the path of thetreatment beam. Methods: A Monte Carlo implementation of the transponder geometry is validated against measurements using Gafchromic EBT2 film in a proton field and subsequently used to generate dosedistributions for transponders at different positions and orientations in the proton spread‐out Braggpeak. The maximum dose deficit is extracted in each case. Results: Dose shadows of up to 60% occur for transponders positioned very near the end ofrange of the Bragg peak. However, if transponders are positioned further than 5 mm from the endof range, and are not oriented parallel to the beam direction, then the dose deficit can be keptbelow 10%. Conclusion: Beacon electromagnetic transponders could be used for patient setup and motionmanagement for proton therapy provided some guidelines regarding their placement and orien‐tation with respect to the beam can be met. In cases of difficult transponder positions, optionsto minimise the shadow include careful plan design with multiple beam angles to distribute theshadow over a larger volume, or possibly increasing the dose in the expected shadow region tooffset the deficit.
SU‐F‐500‐02: Early Prediction of Brain Metastases Response to Radiation Therapy by Combination of Changes in Tumor Vascular and Cellularity Properties
Authors: Farjam R , Tsien C , Feng F , Gomez‐Hassan D , Hayman J , Lawrence T , Cao Y
Published: July 2013

Purpose: To investigate the impact of combining image‐based measurements related to alterations of vascular and cellularity properties of brain metastases for early prediction of tumor response to radiation therapy (RT). Methods: 24 patients undergoing treatment for metastases had perfusion (DCE) and diffusion MRI scans. Tumor subvolumes with high regional cerebral blood volume (rCBV) and high Gd‐DTAP transfer constant (Ktrans) were extracted. The apparent diffusion coefficient (ADC) histograms of the tumor volume were categorized into low, normal and high ADC subvolumes. Changes in different tumor subvolumes and their combination from pre‐RT to week 2 after start of radiation were evaluated in differentiation of responsive, stable and progressive tumors for patients treated by either whole brain radiation therapy (WBRT, 28 lesions) alone or combined with Bortezomib as a radiation sensitizer (39 lesions). Receiver Operating Characteristic (ROC) analysis compared a combined perfusion/diffusion prediction model with changes in gross tumor volume (GTV) within the same time interval. Results: For lesions treated with WBRT alone, a decrease in both high cellularity and edema subvolumes were associated with response. A decrease in the tumor subvolumes with high cellularity and vascularity was associated with response in lesions treated with RT combined with Bortezomib. In ROC analysis, areas under curve (AUCs) of 0.96 (WBRT alone) and 0.96 (WBRT + Bortezomib) were seen in prediction of non‐responsive lesions when changes in different subvolumes were combined. Also, GTV changes could predict the non‐responsive lesions treated with WBRT alone (AUC = 0.91) but failed to predict the response in lesions treated with WBRT combined with Bortezomib (AUC = 0.57). Conclusion: Combining the changes in tumor cellularity and vascularity could be used for early prediction of brain metastases response to RT and perform better than the GTV changes, suggesting that physiological changes could occur earlier than the morphological changes. (Support: NIH RO1NS064973) NIH grant ROl NS064973
SU‐F‐500‐05: MRI‐Linac Systems: Can a Standard MLC Be Incorporated Into Such a Device?
Authors: Kolling S , Oborn B , Keall P
Published: July 2013

Purpose: Integrated MRI‐linac systems for real‐time image guidance are currently under development to master intrafraction tumor motion. As the multileaf collimator (MLC) is a crucial component of such systems, this study is aimed to answer if a standard MLC can be incorporated based on (a) its impact on the MRI field homogeneity and (b) the electromagnetic force acting on the MLC in the MRI field. Methods: A 1.0 T split‐bore magnet and the key ferromagnetic components of a Varian Millennium 120 MLC, namely the leaves and motors, were modelled using the finite element method (FEM). In this work both the parallel and perpendicular configuration for such a system were investigated, i.e. the linac treatment beam was orientated parallel and perpendicular to the MRI field direction. Simulations were performed for isocentre distances in the range from 100 to 200 cm. From the resultant magnetic field distributions, the introduced field distortion over the MRI imaging volume, a 30 cm diameter sphere volume (DSV) around the isocentre, and the net electromagnetic force acting on the MLC were evaluated. Results: For all distances of 140 cm or larger, the field distortion was below 300 ppm which is commonly referred to as maximum pre‐shim inhomogeneity of MRI devices. The total force pulling the MLC towards the MRI magnet was found to be maximum at a 120 cm isocentre distance with 1706 N and 3499 N in parallel and perpendicular configuration, respectively, and to decrease for larger distances. Conclusion: The theoretical results suggest that the distortion introduced by a standard MLC can be corrected for by shimming for isocentre distances of 140 cm or larger. Appropriate mounting of the MLC to withstand the electromagnetic forces is considered mechanically challenging and may require an isocentre distance larger than 140 cm. NHMRC Australia Fellowship, Australian Endeavour Research Fellowship
SU‐F‐500‐07: A Single Device for Mechanical and Radiation Quality Assurance (QA) Measurements of Medical Accelerators
Authors: Velarde E , Iordachita I , Mirota D , Moore J , Wong J
Published: July 2013

Purpose: To develop a single unifying device that will record, document and track mechanical, optical and dosimetric measurements to reduce the number of devices used and time spent to perform the monthly Quality Assurance (QA) tasks recommended in AAPM Task Group 142 Report. Methods: This device includes a novel multi‐mirror system with rotating capabilities which directs the optical and radiation sources to a stationary camera to acquire images of all planes centered on the isocenter of the medical accelerator. A single phosphor screen is used as the receptor for optical light imaging. A plastic buildup sheet is added for radiation measurements. A computer interface allows efficient pass/fail analysis for laser alignment, light/radiation field coincidence, flatness and symmetry tests and MLC QA. Results: The system has been used to successfully acquire images that have never been recorded before, such as a combination of the light field, optical distance indicator and lasers as well as radiation field. QA of mechanical motions such as table rotation is readily captured. Radiation QA measurements accommodate both x‐ray and electron beams. QA of gantry motion can be performed by rotating the device. The time spent in Monthly QA according to TG‐142 for these tasks will be reduced in half. Conclusion: A single device has been successfully developed to unify all mechanical, optical and radiation components for required and recommended monthly QA tasks, reducing monthly machine maintenance time. In particular, the device records and documents optical measurements that are now only evaluated visually which will strengthen the confidence for safe patient treatment. Dr. John W. Wong is a founder of JPLC Associates LLC which has licensed the technology from Johns Hopkins University. Dr. Daniel J. Mirota's participation in this publication was as a paid consultant for JPLC Associates LLC. All opinions expressed and implied by Dr. Daniel J. Mirota in this publication are solely those of Dr. Daniel J. Mirota and do not represent or reflect the views of Johns Hopkins University. The work is supported in part by a grant from Technology Development Corporation (TEDCO) of Maryland.
SU‐F‐500‐08: Correlation of Model and Human Observer Performance On a Lesion Shape Discrimination Task Using Realistic and Repeated CT Scans
Authors: Zhang Y , Leng S , Yu L , McCollough C
Published: July 2013

Purpose: To investigate how well a channelized Hotelling observer (CHO) can predict the human observer performance in a lesion shape discrimination task using realistic and repeated CT scans for both filtered backprojection (FBP) and iterative reconstruction (IR). Methods: Eight lesion mimicking rods (2 contrasts, 2 sizes, 2 shapes) were inserted into a 35 by 26 cm water phantom and scanned 100 times on a 128‐slice CT scanner (Definition Flash, Siemens Healthcare) with 120 kV at 120, 180, 240, 360 and 480 quality reference mass (careDose4D). CT images were reconstructed using a FBP and an IR method. A region of interest centered in the rod was extracted to construct the 2‐alternative forced choice (2AFC) study with hexagon and circle rod images put side‐by‐side in randomized order. Total 4000 2AFC trials were read by three medical physicists and the CHO with Gabor filter (5 passbands, 5 orientations, 2 phases). An edge‐emphasis binary mask was applied at the CHO input end. Percent correct was calculated and non‐parametric statistical analysis was performed to compare the performance between human and model observers, and between FBP and IR. Results: The Spearman rank correlation coefficient was 0.879 for FBP and 0.916 for IR (P<0.01). Bland‐Altman plots showed excellent agreement between human and model observers for all lesions sizes and contrasts with a mean difference of 0.5%±3.6% for FBP and 0.2%±3.1% for IR. IR significantly increased the human and model observers performances compared to FBP (Wilcoxon signed rank test, P<0.01). Conclusion: This study demonstrates a high correlation between human and model observers in a discrimination task using realistic CT images. Masking the image input to the CHO by an edge emphasis mask mimics the higher weighting applied towards the edge when humans performed the shape discrimination task. IR significantly increased both human and model performance compared to FBP. This work was supported in part by NIH grant R01 EB071095 from the National Institute of Biomedical Imaging and Bioengineering.
MO‐A‐105‐01: Volumetric Modulated Arc Therapy
Authors: Shepard D , Popple R
Published: July 2013

Volumetric Modulated Arc Therapy (VMAT) is a rotational approach to the delivery of intensity modulated radiation therapy (IMRT) that can be delivered on a conventional linear accelerator. VMAT has become a widely adopted clinical tool due to the conformal nature of the dose distributions and the efficiency of VMAT delivery. In this session, we will provide an overview of the VMAT delivery technique and will describe recommended steps for starting a VMAT program including VMAT commissioning, machine quality assurance, and patient‐specific quality assurance. We will describe commercial treatment planning systems and discuss tips and tricks for the use of VMAT for key clinical sites such as head‐and‐neck and prostate. Additionally, we will detail the role of VMAT for stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT). More advanced VMAT topics will also be discussed such as flattening filter free VMAT, gated VMAT, and the use of couch rotations during VMAT delivery.

Learning Objectives:

1. Describe volumetric modulated arc therapy (VMAT).

2. Describe commissioning of a VMAT delivery system.

3. Summarize the key elements of starting a VMAT program.

4. Review patient‐and machine‐specific VMAT quality assurance.

5. Survey VMAT treatment planning systems and planning techniques.

6. Describe advanced VMAT techniques such as gated VMAT and flattening filter free VMAT.

Conflict of Interest: Richard Popple has a sponsored research agreement with Varian. David Shepard has a sponsored research agreement with Elekta.

Richard Popple has a sponsored research agreement with Varian. David Shepard has a sponsored research agreement with Elekta.
MO‐A‐137‐03: Effective Heuristic Cuts for Beam Angle Optimization in Radiation Therapy
Authors: Yarmand H , Craft D
Published: July 2013

Purpose: To improve the solution efficiency (i.e., reducing computation time while obtaining high‐quality treatment plans) for the beam angle optimization problem (BAO) in radiation therapy treatment planning. Methods: We formulate BAO as a mixed integer programming problem (MIP) whose solution gives the optimal beam orientation as well as optimal beam intensity map. We then incorporate a family of heuristic cuts into the resultant MIP based on the observation that the number of candidate beams is usually much larger than the number of beams used in the treatment plan, and therefore, it is less likely that adjacent beams are simultaneously used in the optimal treatment plan. The proposed cuts, referred to as ((neighbor cuts)), force the optimization system to choose one or a few beams from any set of adjacent beams. As a Result, the search space and the computation time are reduced considerably. The neighbor cuts can be added to any MIP formulation for BAO including the cases of coplanar/noncoplanar beams for intensity modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT). For the numerical experiments a liver case (both IMRT and SBRT) with 34 and a head and neck case (only IMRT) with 36 coplanar beams were considered. Each beam was divided into 109‐144 beamlets of size 1*1 cm2. Results: We first solved the corresponding MIP without the neighbor cuts and recorded the optimal solution and the computation time. Then we incorporated the neighbor cuts into the MIP and resolved it. Our results show that incorporating the neighbor cuts into the MIP reduces the computation time considerably and results in solutions with negligible optimality gaps. Conclusion: This research incorporates the observation that optimal beam configurations are typically a sparse set of well‐spaced beams to improve the efficiency of the solution technique drastically. The project was supported by the Federal Share of program income earned by Massachusetts General Hospital on C06 CA059267, Proton Therapy Research and Treatment Center and also partially by RaySearch laboratories.
MO‐A‐137‐07: Assessment of Metrics to Identify Which Left‐Sided Breast Cancer Patients Will Benefit From a Moderate Deep Inspiration Breath‐Hold Technique
Authors: Yu J , Brinkmann D , Mutter R , Yan E , Petersen I , Herman M , Park S
Published: July 2013

Purpose: To derive and examine the robustness of metrics for prediction of dosimetric benefits for left‐sided breast cancer patients from a moderate deep inspiration breath‐hold (mDIBH) technique. Methods: Radiotherapy treatment plans using a field‐in‐field tangent approach were retrospectively generated on both free‐breathing (FB) and mDIBH CT scans acquired for fourteen consecutive left‐sided breast cancer patients. Breast PTV‐eval, heart and left anterior descending coronary artery (LAD) were defined as per RTOG and the heart atlas (Feng et al. IJROBP 79:10‐18, 2011). The same PTV coverage was maintained in both FB and mDIBH plans. Volumetric metrics, irradiated heart and lung volume, and distance metrics from representative images were defined. Correlations with dosimetric parameters and robustness were examined. Results for single planner retrospective plans were compared with results from treated plans prepared by a group of dosimetrists for both the cohort of 14 mDIBH patients as well as a cohort of 19 previously treated FB left‐sided breast cancer patients. Results: FB cardiac dosimetric parameters for our cohort appeared to follow exponential distributions, with a significant reduction of sigma shown for mDIBH. The extent of dosimetric benefit is patient specific. Linear correlations were found between cardiac and pulmonary dosimetric parameters and volumetric metrics using irradiated volumes, as well as for distance metrics if volumetric corrections were applied. Linear correlations were preserved (R > 0.9) regardless of whether determined from a single planner or a group of dosimetrists. Fitted parameters were slightly higher for data derived from the group of planners, however, the difference was not found to be significant via signed rank test. Conclusion: Linear correlations between cardiac and pulmonary dosimetric parameters and several metrics were identified and determined to be robust for left‐sided breast cancer patients planned at our institution, which facilitates reliable selection of patients who will benefit from a mDIBH technique.
MO‐A‐137‐08: Direct Leaf Trajectory Optimization for Volumetric Modulated Arc Therapy with Sliding Window Delivery
Authors: Papp D , Unkelbach J
Published: July 2013

Purpose: We present a new single‐step algorithm for volumetric modulated arc therapy (VMAT) planning. The algorithm is inspired by the observation that IMRT plans with a large number of beams (e.g., N=20) yield near‐optimal treatment plans. However, an arc sequencing step to convert an IMRT plan into a deliverable VMAT plan compromises quality or delivery efficiency. To avoid this caveat, we devise a single‐step method to directly optimize the MLC leaf trajectories. Methods: In our approach, a full 360‐degree arc is divided into N arc segments in which the leaves move unidirectionally, i.e. an intensity‐modulated field is delivered over each arc segment using a sliding window technique. We formulate the VMAT optimization problem in terms of the leaf trajectories over each arc segment, including all machine and time constraints. Assuming constant dose‐influence matrices in each arc segment and constant gantry speed, this optimization problem is convex. Thus, we can reliably determine the optimal VMAT plan under these restrictions. An extension of this basic model is devised that accounts for a varying dose influence matrix within each arc segment. Results: The algorithm allows us to find highly conformal treatment plans, deliverable in a short time. Allowing for enough delivery time, the algorithm is guaranteed to match the ideal IMRT plan. For prostate cases, the plans are observed to closely approximate the ideal plan with 3–4 minutes delivery time. Head‐and‐neck results are similarly promising. Conclusion: The results indicate that high quality single‐arc treatments can be delivered with 20 arc segments if sufficient time is allowed for modulation in each segment. Our current implementation is customized towards finding optimal VMAT plans for constant gantry speed and dose rate, which is desirable in practice. In the future, the model can be extended to allow variable dose rate and more general leaf trajectories. Research supported by Philips Radiation Oncology Systems.
MO‐A‐137‐11: How Successful Are We in Meeting SBRT Planning Goals? A Multi‐Institutional Study
Authors: Surucu M , Harkenrider MM , Fan J , Aydogan B , Laureckas R , Vali F , Roeske JC
Published: July 2013

Purpose: To assess the variability in treatment planning of stereotactic body radiotherapy (SBRT) of lung lesions, a multi‐institutional planning comparison study was performed. Methods: A total of 150 patients receiving lung SBRT treatments in five different institutions were reviewed. Treatment plans were generated using Varian/Eclipse™ (82), CMS/Xio™ (53) and Cyberknife/Multiplan™ (15) systems. Most tumors were located peripherally (126/150) and in right lung (82/150). Various dose fractionations were used: 3x18Gy (5 cases), 3x20Gy (13), 4x12Gy (18), 4x12.5Gy (9), 5x10Gy (65), 5x12Gy (38), and 5x8or9Gy (2). The following planning criteria derived from RTOG trials and literature were used to evaluate the 4 or 5 fraction SBRT plans (133 cases): PTV‐V100>=95°/o, PTVV95>=99%, conformality index (CI‐100%) <1.2, CI‐50% isodose <4 for PTV>50cc or <5 for PTV<50cc, total lung‐ITV: V20Gy<10%, V12.5Gy<15%, V5Gy<37%, contralateral lung V5Gy<26%, cord: maximum<25 Gy, D0.25cc<22.5Gy, esophagus: max<30Gy, D5cc<27.5Gy, trachea/bronchus maximum<40Gy, heart & great vessels maximum<45Gy. The mean, standard deviation (±) and dosimetric criteria pass rates (PR) were reported. Results: The median PTV volume was 27.0cc (range:3.8/188.9cc). The mean PTV‐V100 was 96.0% (±3.6, PR:87.1%). The mean PTV‐V95 was 99.4% (±2.1, PR:90.2%) and the mean CI‐100% was 1.16 (±0.18, PR:74.0%). The mean CI‐50% was 4.14 (±0.67, PR:46.4%) for PTV>50cc (28 cases) and 7.36 (±3.36, PR:29.4%) for PTV<50cc (102 cases). The planning criteria were met for all the critical structure such as lung, heart, cord, esophagus, and trachea for at least 90% of the patients. The mean of all OAR criteria PR was 97.7% for peripheral and 88.6% for central lesions. Conclusion: Five fraction regimens were the most common lung SBRT fractionation (70%). Among the various parameters that were used to evaluate the SBRT plans, the CI‐100% and CI‐50% were the most challenging criteria to meet. Although the OAR PRs were higher among all cases, their proximity to the PTV was a significant factor.
MO‐A‐116‐01: TG151: Radiographic System Quality Control
Authors: Hulme K , Arbique G
Published: July 2013

Quality control (QC) in medical imaging is often viewed as a series of infrequent, detailed evaluations of a piece of medical imaging equipment by a qualified medical physicist (QMP). The day‐to‐day operational process is largely neglected absent regulatory or accreditation requirements. However, QC should be viewed as an ongoing process that occurs on an image‐by‐image basis. Ongoing QC was inherent in the screen‐film imaging workflow, where rejected image rates were calculated by counting rejected films and improperly exposed films resulted in images that were too dark or light and were repeated out of necessity, and the rejected films counted. During the early years of the shift to digital imaging in radiography, ongoing QC was largely abandoned, owing to both a perceived lack of need and difficulty in performing ongoing QC with early digital imaging systems, which lacked standardized exposure indicators and tools for counting rejected images.The QC process involves key personnel in the imaging department, including the radiologist, radiologic technologist, and QMP. The radiologist administers and oversees the QC program, which is carried out by the radiologic technologist. The radiologic technologists collects and analyzes data, and results that are outside the acceptance levels for the QC program are investigated, and corrective action taken to bring these results back to an acceptable level. The QMP consults with the radiologist in the design and implementation of the QC program, works with the technologist to triage problems, and carefully evaluates the imaging equipment on a regular basis for proper calibration, function, and compliance with applicable regulations. The continued need for ongoing QC in digital radiography has been highlighted in the scientific literature, and Task Group 151 was charged with recommending consistency tests designed to be performed by a QMP, or a radiologic technologist under the direction of a QMP, to identify problems with an imaging system that need further evaluation by a QMP, including a fault tree to define actions that need to be taken when certain fault conditions are identified. The focus of the final report of TG 151 was the ongoing QC process, including rejected image analysis, ongoing exposure analysis, and artifact identification. These three QC tasks are vital for the optimal operation of a department performing digital radiography.

Learning Objectives:

1. Learn methods for performing rejected image analysis in digital radiography, including learning trends and patterns that are common

2. Learn methods for performing ongoing exposure analysis in digital radiography, including learning trends and patterns that are common

3. Understand how to incorporate ongoing QC into your radiography department
MO‐D‐105‐06: Dose‐Area Product as a Method for Small Field Geometric QA
Authors: Nikolic M , Masterson‐McGary M , Toner S , Kilby W , Thomson L , Colliander S , Noll M , Goggin L
Published: July 2013

Purpose: To investigate the use of dose‐area product (DAP) as a highresolution tool for QA of small field sizes as an alternative to more complex alternatives such as film or water tank scanning. Method: An 81 mm diameter PTW Bragg Peak parallel plate chamber was used in combination with an Iris variable circular aperture collimator fitted to a CyberKnife System and a vendor‐supplied alignment jig. The Iris collimator is designed to deliver field diameters between 5 mm and 60 mm, with a tolerance of ±0.2 mm. First the sensitivity of the chamber reading to influence parameters (SSD, angle misalignment, lateral displacement, output variation) was investigated. Next the dependency of DAP on field diameter was investigated. Finally the sensitivity of the method to detect small field size changes consistent with the device specification was evaluated. Comparisons were made with film and diode water scans using four CyberKnife systems and three chambers. Results: Expected variations in chamber position/orientation within the jig resulted in measurement changes <0.2%. Measurement variations due to LINAC output changes can be removed by normalising measurements to a fixed collimator reading obtained at the same time. The variation in chamber reading with field size followed a quadratic dependency over the 5mm ‐ 60mm range. The change in chamber reading associated with a 0.2 mm field diameter change ranged from 10% at 5 mm nominal to 0.5% at 60 mm, and was reasonably consistent across tests performed on four units. Measurements were more consistent than routine film tests, and were stable over two years. Conclusion: DAP provides a practical, efficient, robust, and sensitive method for routine QA of field aperture changes as small as ±0.2mm across the field size range 5 mm – 60 mm. The method may also have applications for QA of small fields formed by MLC.
MO‐D‐105‐07: Results of Applying FMEA and Fault Tree Analysis to the Online Incident Reporting Database
Authors: Nurushev T , Miller B , Dickinson M , Esposito A , Movsas B , Siddiqui M , Chetty I
Published: July 2013

Purpose: As part of the continuous quality of care improvement, an internal online database for processing reported incidents was established. In 3 years, 710 incidents were reported by 5 clinics. We have ranked the fault trees of the reported incidents using the AAPM report TG‐100 Failure Mode and Effects Analysis (FMEA) tools Methods: Risk Probability Number (RPN) generated as a Result of applying FMEA is based on the severity, probability of occurrence and probability of going undetected. The reports were sorted in two categories. Potentially affecting dose delivery, e.g. incorrect setup instructions; and deviations from an established workflow defined by policies and procedures (P&P), e.g., incorrect naming of the fields. In addition to FMEA, the impact of new, as well as periodic reviews of P&P by staff members is assessed Results: Of 710 reports 676 were analyzed, 374 were variation in the workflow not directly affecting quality of care, 302 were potentially affecting dose delivery. 19 of 302 had dosimetric impact; however, due to low occurrence only 4 instances, related to bolus placement, reached the RPN above 200. Review of current P&P reduced the RPN from 270 to 9. Periodic review, introduction of the new or revising the existing P&P had a dual effect: drop in dose‐affecting incidents and increased reporting of process deviations Conclusion: Analysis of reported incidents and review by the departmental QA committee is an essential part of any QA program. By defining the fault trees and applying FMEA to the reported incidents, we were able to reduce the RPN from an average of 150 for dose related incidents to 9, and for process variations from 295 to 28 on average. Event‐triggered revising of P&Ps and periodic review with staff of the existing P&P is an effective tool in incident reduction