bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐T‐529: Fully Automated Patient Specific Collision Check for Novalis Radiosurgery System
Authors: Deng H , Li S
Published: August 2010

Purpose: In Stereotactic treatment of cranial lesions multiple non‐coplanar beams or arcs are frequently used which can give rise to collision problem and consequently render a treatment plan undeliverable. In SBRT treatments for very large patients the same issue can also happen even if the treatment plan doesn't involve couch kick. We propose a easy‐to‐use, patient plan specific method to determine whether a certain plan will have collision problem and the parametric changes needed to avoid it. Method and Materials: Treatment couch dimension and relative position to immobilization device was measured, as well as the Novalis gantry head dimension and its clearance from the isocenter. A program was written to calculate, for a given gantry, couch, and collimator angle, the coordinates of the four corners of the front surface of the gantry head in the patient CT coordination system. Thus the collision can be checked by simply looking up the corresponding CT slice images with the treatment couch added. The projection of gantry head front surface on all slices are calculated and checked to assure that there's no collision with the couch or patient body. Results: We tested several cases of different disease sites and techniques and the method proposed here can detect the potential collision problem and also offer the advice regarding how much change needs to be made. Conclusion: The method proposed here can be easily implemented to provide institution customized, patient specific collision check for external beam radiation therapy plans, saving the trouble of manually checking for collision. Furthermore, it can be implemented with matlab or integrated with iPlan software to automatically check the collision and find correct setup way to avoid collision in SBRT cases.
SU‐GG‐T‐532: A Method for Dose Calculation and Collision Detection in Gamma Plan Pre‐Planning Mode
Authors: Bennett M. C. , Wiant D. , Gersh J. , Best R. , Bourland J. Daniel
Published: August 2010

Purpose: The latest version of the Gamma Plan treatment planning system allows for treatment “pre‐planning” using an image set with no headframe. However, in pre‐planning mode the user is not able to define the Gamma Knife coordinate system, so collision checks and dose time calculations cannot be performed. This restriction is particularly limiting when pre‐planning head and neck cases or cases for lesions located in the posterior fossa. We have developed a simple method to establish the Gamma Knife coordinate system and to therefore run collision checks and dose time calculations. Method and Materials: An image set of the Gamma Knife headframe and fiducial box is imported into Gamma Plan and opened in treatment mode. An MR or CT patient image set without a headframe is imported into the same treatment planning window. The two image sets are then co‐registered and fused. The resulting composite images may then be used to plan a treatment with the full Gamma Plan functionality, including collision monitoring and dose time calculations. Results: The headframe image set was successfully co‐registered and fused to patient image sets and used for treatment planning. The fused image set was then able to be checked for collisions and dose delivery times were able to be calculated. Conclusion: We have developed a simple method that allows for the Gamma Knife coordinate system to be established in Gamma Plan pre‐planning mode. This technique lets the user check for collisions and calculate dose times prior to headframe placement. It also may serve as an aid for determination of headframe placement on treatment day. The main limitation of this method is that it does not allow for gamma angles not equal to 90. Supported in part by NCI T‐32 CA113267.
SU‐GG‐T‐534: The Impact of Linac Static Jaw Setting on Dose Output from Small Field SRS/SRT Using an Add‐On Micro‐Multileaf Collimator
Authors: Han E , Zhang X , Velasco C , Yan Y , Moros E
Published: August 2010

Purpose: In small field SRS/SRT using an add‐on MMLC, the default jaw setting from the BrainLAB treatment planning is larger than the furthest end of MMLC‐defined segment. The purpose of this study is to evaluate how the dose output changes with varying static jaw setting. Methods and Material: The BrainLAB micro‐multileaf collimator (BrainLAB M3) was mounted on a Varian 2100EX linear Accelerator. Output factors were measured for six different MMLC and jaw field sizes (12×12mm2 ∼ 100×100mm2) and compared with different MMLC and fixed jaw setting (100×100mm2). A PTW 31016 PinPoint ionization chamber (0.016cc) was employed to measure the field sizes less than 42 × 42 mm and a PTW 30013 farmer chamber (0.6cc) was used to measure field sizes larger than 42 × 42mm. The measurement depth was 5 cm using solid water (Gammex). Source to surface distance was 100cm and 300 monitor units were used for each measurement. The measurements were repeated twice for each condition. Results: For 6 MV photon beams, compared to the output from the same static jaw settings as MMLC defined field size (12×12mm2 ∼ 100×100mm2), the dose percentage difference varies from 10.2% down to the 1.2 % for MMLC defined field size from 12×12mm2 to 80×80mm2 with the fixed static jaw setting(100×100mm2). For 18 MV photon beams, the dose percentage difference varies from 9.1% to 1.4% .Conclusion: The static jaw setting should be manually adjusted as close to the furthest end of MMLC segment to reduce summated leakages through the MMLC and reduce unintentional over‐irradiation to target and organs at risk. Future work: More retrospective studies will be conducted to include various tumor sites in order to quantitize dose deviations from beam limiting jaw settings.
SU‐GG‐T‐535: The Impact of Imaging Frequency on Intrafraction Setup Corrections in Frameless Image Guided Stereotactic Radiosurgery
Authors: Westerly D , Stuhr K , Altunbas C , Diot Q , Kavanagh B , Miften M
Published: August 2010

Purpose: The BrainLAB Novalis™ system allows for the delivery of image guided frameless stereotactic radiosurgery (SRS). At our institution, we use the Novalis Body ExacTrac™ to image the patient and make appropriate setup corrections prior to each treatment arc. Due to mechanical limitations, some arcs cannot be imaged — potentially decreasing treatment accuracy. The goal of this work is to assess the impact of our inability to image these arcs using setup correction data. Method and Materials: Thirty patients treated with intra‐cranial, frameless SRS at our institution were randomly selected for analysis. Patients' had 1–5 isocenters and were treated using 4–24 dynamic‐conformal arcs (DCAs). A total of 264 DCAs were delivered with 166 imaged. Setup correction data based on these images were acquired and differential corrections taken over intervals of either one or two DCAs (corresponding to time intervals of approximately 2.5 or 5 minutes) were obtained. Data were also separated based on treatment isocenter to gain a time series representation of the observed setup corrections. Results: Distributions of one and two arc interval corrections were compared using a two‐sample Kolmogorov‐Smirnov test and found to be similar (5% significance level) with mean values (± SD) for lateral, longitudinal, and vertical offsets of 0.2±1.1mm, −0.1±1.4mm, −0.1±1.2mm (one arc), and 0.1±0.9mm, 0.1±1.2mm, −0.2±1.2mm (two arc) respectively. The distribution of 3D vector displacements for all setup corrections indicated the mean 3D offset after a 2.5–5 minute interval to be 1.6±0.1mm (± SE). No clear trend in mean 3D vector displacements over the course of treatment was evident. Conclusion: Failure to image a DCA on the Novalis system is likely to have little impact on the overall setup accuracy when the time interval between corrections does not exceed 5 minutes. Our data suggests this fact is independent of the total treatment length.
SU‐GG‐T‐538: Preliminary Estimates of Adverse Event Probability for Selected Critical Anatomical Structures in SBRT
Authors: Grimm J , Xue J , Asbell S , Pahlajani N , Chew M , Karasick T , LaCouture T
Published: August 2010

Purpose: To make a preliminary estimate of the probability of adverse events for various critical anatomical structures for stereotactic body radiation therapy (SBRT). Method and Materials: An extensive literature search has uncovered a collection of more than 500 published dose tolerance limits for various anatomical critical structures for one to five fractions of SBRT. We have not found any TD5/5 or TD50/5 adverse event probabilities for SBRT yet, and an appreciable number of the authors do not even present minimum dosimetric information for the adverse events they report. We compiled a database from the available published data and performed statistical analysis to obtain a preliminary estimate of probability of adverse events. Results: Sixty five of the 500 dose tolerance limits correspond to a reported adverse event. For nineteen of these cases, the authors reported the number of patients exceeding the stated dose tolerance limit. For brain tumors, details of adverse events were reported in optic chiasm and optic nerve, and for lung tumors details of adverse events were reported in bronchi, lungs, and ribs. For these critical structures we can estimate the adverse event probability, although in some cases the number of data points is quite limited. Conclusion: It would be quite helpful for the future if more authors would present dosimetric data corresponding to the adverse events they report. At a minimum, it would be helpful to report the maximum dose received by the involved critical structure, the doses received by a few selected volumes, and the number of patients that received these dose levels. In the meantime, this work provides preliminary estimates of adverse event probability for selected anatomical critical structures from the sparse data available.
SU‐GG‐T‐539: Quantitative Analysis of Dosimetric Effects Due to Irregular Respiratory Motion in Stereotactic Body Radiotherapy of Lung Cancer
Authors: Mutaf Y , Michalski D , Yang Y , Li X , Li T , Bednarz G , Heron D , Huq M
Published: August 2010

Purpose: A dosimetric analysis of respiratory motion irregularities is presented for stereotactic body radiotherapy (SBRT) of lung cancer. The changes in target dosimetric coverage is quantified in terms of random and systematic variations in the respiratory motion and correlated with average tumor motion. Method and Materials: Treatment plans and respiratory motion data of 12 lung cancer patients treated under SBRT protocols are retrospectively analyzed. In addition to actual respiratory motion data, a set of simulated motion data is also generated demonstrating irregularities in form of random fluctuations as well as systematic variations. Delineated clinical target volumes (CTV) of patients are subjected to the motion pattern while the target voxels are individually tracked in three dimensions. These trajectories are finally used to map the dose accumulated in the voxels of CTV in its own frame‐of‐reference enabling dosimetric evaluation. Results: The reduction in target minimum dose (Dmin) due to irregular respiratory motion was −1.1% (s=0.7%) for mean target motion of 1.0 cm and −2.6% (s=1.4%) for 2.0 cm. Changes in tumor control probability (TCP) associated with these reductions were negligible. When investigated separately, random fluctuations in the respiratory motion accounted for no change in Dmin (s=0.2%) for 1.0 cm target motion and only −0.8% (s=0.4%) for 2.0 cm. However, systematic variations in the respiratory motion such as a change in the average target motion between the simulation and treatment sessions was observed to play a greater role, with −1.6% and −3.7% changes in Dmin for 1.0 and 2.0 cm target motions respectively. Conclusions: Dosimetric impact of irregular respiratory motion was observed to be minimal in the use of SBRT for lung cancer treatments. When individual types of uncertainties are evaluated, the systematic shifts in breathing pattern were observed to have larger effect than commonly observed random breathing fluctuations.
SU‐GG‐T‐541: Dosimetric Impact of Daily Setup Variations during Spine Radiosurgery
Authors: Kwak J , Park S
Published: August 2010

To examine the dosimetric stability against geometrical variations in the treatment plan of spine radiosurgery, the positioning data of CBCT image guidance for 28 patients were used to make a comparison between the treatment plans before and after image guidance. The dose distribution in treatment plans were recalculated with the same IMRT fluence map and the CT image shifted by the correction values. Some dosimetric parameters were employed to verify the tumor coverage and the spinal cord dose in the treatment plans. The Target volume which receive more than 95% of prescription dose(D95) for tumors and the equivalent uniform dose (EUD)for spinal cord were calculated to fish out the dosimetric variations. The relation between the tumor coverage and the geometric variations presents to be quadratic in all directions, while the EUD of spinal cord are linearly increased by geometrical variations in anterior‐posterior direction in which tumors are located in the view of spinal cord. Since there is no margin at the interface of tumor and spinal cord in most cases, the dosimetric effect of geometrical variation for spinal cord is significant. The tolerance dose of spinal cord in radiosurgery have to be considered very carefully with this dosimetric stability and the geometrical uncertainties.
SU‐GG‐T‐544: Delivery Time Minimization for Robotic Radiosurgery and IMRT Treatments
Authors: Dooley J R , Sims C , Orr G L , Kilby W , Lessard E , Maurer C R
Published: August 2010

Purpose: Robotic radiation delivery systems can accurately deliver conformal dose distributions for clinical applications throughout the body. Here we describe methods to reduce treatment times for step‐and‐shoot robotic radiation delivery while maintaining the dosimetric quality of the treatment plan. Method and Materials: Treatment delivery time, excluding patient setup, depends primarily on three parameters: beam‐on time, number of positions (called nodes) of the linear accelerator, and the number of beams delivered per node. New optimization techniques reduce treatment time by direct reduction of the number of nodes and beams. These techniques iteratively remove low‐utility nodes and beams from the solution space and optimize the beam weights of the remaining beams. Annealing schedules are developed based on a user‐specified treatment time and the number of nodes in the solution set. The algorithms were evaluated on plans for standard fractionated prostate robotic IMRT, hypo‐fractionated prostate radiosurgery, spine radiosurgery, and lung SBRT. Results: The algorithms reduced treatment delivery times (excluding patient setup time) per fraction by as much as 60% for prostate robotic IMRT, 35% for prostate radiosurgery, 25% for spine radiosurgery, and 50% for lung SBRT. The implementation of the new optimization features allows the user to explore trade‐offs in treatment plan quality and delivery time by generating a family of plans that correspond to varying treatment times. Substantial time reductions were obtained for most cases while maintaining plan quality and meeting established clinical criteria (e.g., RTOG‐0238 for prostate radiotherapy and RTOG‐0618 for lung radiosurgery). Although the number of nodes was reduced, the remaining nodes still encompassed a large non‐coplanar workspace. Conclusion: New optimization techniques are described that significantly reduce delivery times for robotic radiosurgery, SBRT, and IMRT treatments. Reduced treatment times increase patient throughput and improve patient comfort. Conflict of Interest: The authors are employed by Accuray Incorporated, Sunnyvale, CA.
SU‐GG‐T‐547: New Measures for Evaluating SBRT Dose Distribution Quality
Authors: Papiez L , Yaddanapudi S , Rangaraj D
Published: August 2010

Purpose. To define a measure that indicates how well the dose distribution in SBRT treatment satisfies standards of dose symmetry and compactness required by SBRT RTOG protocols. Method. Any SBRT dose has to provide the adequate coverage of the PTV and away from PTV it has to decrease fast enough to minimize the volume of tissue in the organ in which the tumor is contained (e.g. lung, liver) (see RTOG 0236). To measure the tightness of dose around PTV one may create a sequence of regions that increase their detachment from PTV quantifying the dose in subsequent regions away from the target. The convenient approach is to build histograms based on a sequence of shells that wrap the target one after the other. This can be achieved by creating sequence of shell structures in the TPS system (script in case of Pinnacle) for which values of minimal, maximal and average dose will be automatically assigned and displayed in the form of appropriate histogram. Results. The script has been written for Pinnacle 8.0m and examples of dose distributions for sequence of SBRT plans have been analyzed by means of computed for these plans histograms. Histograms provide natural means for verification of SBRT RTOG parameters denoted as R50 and D2cm. These histograms provide, however, also additional information on symmetry and steepness of dose gradient in SBRT dose distributions. Conclusion. As in SBRT the quality of treatment depends on the location relative to the target of volumes of tissue exposed to given dose levels measures that go beyond DVH and quantify spatial properties of dose distribution in tissue are needed for the assessment of SBRT treatment quality.
SU‐GG‐T‐557: Single‐Segment IMRT Treatment Planning for Stereotactic Body Radiotherapy
Authors: Bloch C , Baker K , Bradley J
Published: August 2010

Purpose: To demonstrate the advantages of a new planning technique, “single‐segment IMRT” (SS‐IMRT): field optimization via inverse planning for static fields. Field optimization extends beyond beam weighting to field shaping via MLC leaves. This can present a non‐uniform beam fluence to the PTV for single fields while the total plan still provides excellent dose coverage. Unlike typical IMRT, the fields are entirely static, presenting no problem for moving targets nor significantly more monitor units. This can be particularly beneficial in the case of SBRT for lung. Method and Materials: Multiple treatment plans were generated for 10 patients with lung tumors adjacent to the chest wall. All patients were planned for SBRT, typically 54Gy in 3 fractions. Conventional plans had MLCs conforming to the PTV, with minor manual adjustments made to achieve conformity and protect normal structures. SS‐IMRT plans used the treatment planning system's IMRT optimization to achieve those same goals while limiting each beam to a single segment. Plans were compared in terms of dose conformity and uniformity in the PTV, sparing of the normal structures, and planning time. Results: In all 10 cases SS‐IMRT achieved superior treatment plans with little increase in planning time. Improvements in dose conformity and uniformity depended primarily on the quality of the conventional forward plan. Significant reductions in the maximum chest‐wall dose were always achieved, although sometimes the volume of chest wall receiving low to intermediate dose was increased. Overall, SS‐IMRT plans were more consistent in their quality, and planning time was not significantly longer. Conclusion: Inverse planning algorithms developed for IMRT can be very useful for optimizing static field shapes when dynamic treatments are not ideal (e.g. lung SBRT). The inverse planning optimization algorithm was consistently able to improve PTV coverage, reduce hotspots overall, and shift high‐dose regions away from the chest wall.
SU‐GG‐T‐564: Secondary Cancer Risk Characterization of Pediatric Craniospinal Irradiation (CSI) Using Helical Tomotherapy and Conventional 3‐Field Technique
Authors: Gutiérrez A , Dick D , Stathakis S , Papanikolaou N
Published: August 2010

Purpose: To assess the excess relative risk of developing secondary malignancies in pediatric patients treated with craniospinal irradiation (CSI) using helical tomotherapy and conventional 3‐field treatment technique. Method and Materials: Five previously irradiated patients were replanned using the tomotherapy treatment planning system (TPS) and Pinnacle3 TPS. For each patient, two plans were generated with thirteen organs at risk (OAR) contoured. Planning target volumes (PTV) were created by expanding the CT‐based anatomy with a 0.3 and 1.0cm margin, respectively. All plans were prescribed and normalized so that 95% of the PTV received at least 23.4Gy in 13 fractions. Conventional plans were created using lateral brain fields and single/dual extended SSD spine fields. Dose calculations were performed using 4mm dose voxels. Excess relative risks to each organ and total body were computed by volumetrically weighting the risk. Plans were also compared on the basis of normal tissue sparing, PTV homogeneity, and overall risk. Results: When using tomotherapy, Dmax to all the critical structures had a mean reduction of 42.8%. Dmean to six critical structures showed a mean reduction of 39%. With conventional techniques, four structures showed a mean dose reduction of 39%. The risk of a secondary malignancy for 50% of the critical structures had a mean reduction of 41.8% with tomotherapy. When using conventional techniques, the other 50% experienced a mean reduction of 44.6%. PTV homogeneity improved by a factor of 3 when using tomotherapy. Conclusion: Helical tomotherapy, on average, reduces the maximum (∼42%) dose to the OARs as well as improves the homogeneity to the PTV by 3x. Though the incidence of secondary malignancy risk is lower in 50% of the OARs when using tomotherapy, a mean reduction of 0.86%/Sv (43.3%) was observed whereas with the other 50%, there is a mean reduction of 0.16%/Sv (35.3%) when using conventional techniques.
SU‐GG‐T‐565: Radiotherapy of Patients with Bilateral Hip Replacement Using Volumetric Modulated Arc Therapy (RapidArc)
Authors: Aydogan B , Yeginer M
Published: August 2010

Purpose: To investigate a volumetric modulated arc therapy (RapidArc)‐based scheme to improve dose homogeneity, target coverage and organ at risk sparing in prostate cancer patients with hip replacement. Method and Materials: RapidArc (RA) treatment plans for previously treated 7 prostate patients with hip replacement are generated and compared with the IMRT plans used in their treatments. The total prescription dose of 50.4 Gy is delivered in 28 fractions of 1.8 Gy/fraction. Organs at risk (OARs) include bladder, rectum, small bowel and femoral heads. Magnetic Resonance images are co‐registered with computed tomography images to correctly delineate prostate volume. Inhomogeneity correction is turned off for both IMRT and RA plans. Single (sRA) and double (dRA) RapidArc plans are generated and compared with the seven‐field IMRT plans. Two 60‐degree lateral sectors between 60–120 degrees and 240–300 degrees were skipped to avoid irradiation through the high Z materials in the hip. All plans are optimized and normalized to provide a minimum of 94% target coverage with the prescription dose. Results: The maximum PTV doses are 54.5Gy (IMRT), 57.1Gy (sRA) and 52.8Gy (dRA). Overall, dRA performed better in PTV coverage, dose homogeneity and the OAR sparing than did sRA and IMRT. For instance, V100 for rectum is 13%, 30% and 50% with dRA, IMRT and sRA. Homogeneity index (HI) is 103.5%, 106.7% and 109% for dRA, IMRT and sRA, respectively. The total monitor unit is 968 MU (IMRT), 429 MU (sRA) and 518 MU (dRA). Conclusion: RapidArc with one and two arcs is investigated in prostate cancer patients with hip replacement. Only RapidArc with two arcs (dRA) showed some improvements in OAR and healthy tissue sparing, target coverage and dose homogeneity with respect to IMRT. The treatment delivery is more efficient with single arc RapidArc.

Conflict of Interest: Sponsored by Varian Medical Systems, Inc.
SU‐GG‐T‐566: VMAT Optimization on MVCT Dose and the Affects on Prostate IMRT Acceptance Criteria
Authors: Price R , Tafo A Guemnie , Horwitz E , Ma C
Published: August 2010

Purpose: Daily image guidance techniques may contribute significant dose to the patient, particularly in the case of megavoltage conebeam CT. Methods to account for this dose include (1) not altering the prescription, (2) subtracting the MVCT dose from the prescription, and (3) including the daily MVCT dose in the optimization process. This work evaluates the aforementioned methods with respect to the plan acceptance criteria for prostate IMRT at Fox Chase Cancer Center. Method and Materials: MVCT dose was measured in phantom for a Siemens' Artiste linear accelerator. The 15MU mode utilized was for a 27.4 × 27.4cm2 field size, 6MV full rotation beam. The dose measured was scaled using TMR ratios to mimic irradiation in an elliptical phantom with major and minor axis lengths of 40cm and 20cm, respectively and was found to be approximately 9.71cGy. The MVCT beam was simulated on patient geometry within the Nucletron Oncentra MasterPlan system. Dual arc VMAT plans were generated to meet our acceptance criteria with respect to the methods above. Results: Method 1 above results in dose increases in high and low dose rectal cut‐points of 5.7% and 11.7%, respectively. Method 2 results in 1.4% and 7.3% increases while method 3 results in 5.1% and 3.9% increases without changing the input parameters from those used for the dual arc plan. Conclusions: Dose from MVCT on a daily basis can adversely affect plan acceptance criteria. Lower MU protocols can be used but may result in decreased image quality. All plans in this study met our clinical acceptance criteria although those optimized on the MVCT dose demonstrated the lowest increase in lower dose regions. As the significance of adverse effects may be amplified for serial vs. parallel critical structures it may be prudent to optimize on the MVCT dose when generating IMRT plans.
SU‐GG‐T‐567: Comparison of Two Different Implementations for Volumetric Modulated Arc Therapy
Authors: Papanikolaou N , Stathakis S , Holmes R , Gutiérrez A , Esquivel C , Shi C , Mavroidis P , Mihailidis D
Published: August 2010

Purpose Volumetric Modulated Arc Therapy (VMAT) is an efficient and effective way to plan and deliver IMRT treatment. There are different implementations of this technique depending primarily on the equipment capabilities. In this investigation, we explore the differences and the equivalence of two such implementations, namely the Rapidarc and the Smartarc from Varian and Philips respectively. Material and Methods In this study we report on the treatment planning differences between two VMAT implementations for several patients that were planned with two different RTP systems. The plans included several different anatomical sites and were developed for a Novalis TX machine with the high definition MLC as well as a Varian 2100C/D with the millennium 120MLC. Pinnacle version 9.0 with smartarc and Eclipse version 8.6 were used for this planning study. Results Twelve patients were planned with both planning systems for either the Novalis or the 2100C/D linac, depending on the anatomy treated and the size of the target volume. The plans were evaluated based on a comparison of region of interest dose statistics, including the min, max and mean dose as well as dose volume histograms and adherence to prescribed dose volume objectives. In most cases, the plans produced from each RTP system were equivalent both in dosimetry as well as in total treatment planning time and time to deliver the plans. Conclusions Two popular implementations of VMAT were compared in this planning study. Based on our findings, there is no significant difference between the quality of plans produced by either planning system in terms of ease of planning, time required to develop a plan and dosimetric equivalence of the plans we developed.
SU‐GG‐T‐569: A Real‐Time Graphical User Interface‐Driven Radiotherapy Treatment Planning Simulator
Authors: Barbiere J , Napoli J , Hanley J
Published: August 2010

Purpose: To present a stand‐alone Radiotherapy Treatment Planning simulator (RTPsim) that physicists can use for interactive classroom instruction and provide to students for independent study. Method and Materials: A PC with MATLAB programming language and the imaging toolbox is required. The RTPsim components are (1) a set of grayscale images for dose computation with regions of interest for dose area histogram analysis; (2) a double Gaussian pencil beam algorithm to create treatment fields; (3) dose distribution calculation routines for individual open or wedged beams and for a composite of weighted beams; and (4) a Graphical User Interface (GUI) to run the system with such user friendly features as command buttons to run algorithms, text or cursor variable input, list boxes for patient selection, and radio buttons for beam modifiers such as wedges. Results: The percent depth dose (%DD) for a typical 10×10 cm 6MV beam created by pencil beams closely approximates the actual clinical data. By computing and storing a correction factor table, the %DD values match exactly. The incorporation of divergence and a low dose region beyond the geometrical field edge result in excellent agreement in calculated versus clinical data for open beam profiles. Wedged field profiles show reasonable agreement with our clinical system. Several test cases from texts were reproduced accurately for interactive teaching purposes. As an example, an RTPsim wedged tangent field breast plan comparable to a clinical plan was produced. Variations in wedge, weighting, and normalization point can be demonstrated in real time. Use of a MATLAB GUI is suitable for planning demonstration; physicists and dosimetrists found the GUI convenient and easy to use. Conclusion: The user‐friendly Radiotherapy Treatment Planning simulator can simulate a clinical treatment planning computer with sufficient accuracy and speed for interactive educational purposes and independent learning.
SU‐HH‐BRB‐01: A Water Equivalent and Angular Independent Two‐Dimensional Plastic Scintillation Detector Array for Quality Assurance of IMRT Treatments
Authors: Guillot M , Gingras L , Archambault L , Beddar S , Beaulieu L
Published: August 2010

Purpose: The goals of this study are: 1) to present a novel two Dimensional Plastic Scintillation Detector array (2D‐PSD) for dose measurements of IMRT treatments, 2) to demonstrate that the dose distribution in the irradiated volume is not perturbed by the presence of the 781 detectors and 3) to demonstrate that the 2D‐PSD can be used for high accuracy dose measurements for variable beam incidences. Methods and Materials: The 2D‐PSD consists of 781 PSDs inserted vertically in a plastic water slab covering a 26×26 cm2 region. The prototype is built entirely from nearly water equivalent plastic materials. To characterize the angular dependence of the 2D‐PSD, the detector array was irradiated with a square field size 10×10 cm2 using variable beam incidences from 0° to 120°. Furthermore, a clinical head and neck IMRT plan composed of six beam incidences was delivered on the 2D‐PSD in two configurations: 1) the gantry angle of the linear accelerator is keep fixed at 0°, 2) using planned gantry angle values. The dose distributions measured with the 2D‐PSD were compared to those calculated with a treatment planning system (Pinnacle3, Philips Medical Systems) on a CT scan of the detector array. Results: The results of the angular dependence study indicate an excellent agreement between the measured and calculated dose distributions. For the IMRT plan delivered at a fixed gantry angle, the gamma evaluation was successful for 98.5% of the detectors for a dose tolerance of 3% and a distance to agreement of 3 mm. For the IMRT plan delivered with planned gantry angles, the gamma evaluation was successful for 99% of the detectors (tolerances of 4% and 4 mm). Conclusion: The results presented in this work suggest that the developed 2D‐PSD could be used as a quality assurance tool for IMRT and arc therapy patient plan verification.
SU‐HH‐BRB‐02: A Study on the Focusing Power of Dynamic Photon Painting
Authors: Chen Z , Luan S , Riofrio D , Ma L
Published: August 2010

Purpose: Cross‐firing technique is widely used in photon‐based radiosurgery to create sharp dose falloff near the target. In this technique, a large number of beams are focused to the isocenter in order to minimize contribution from individual beams. In this study, we investigated a technique called dynamic photon painting (DPP), where a radiation beam changed dynamically in direction to irradiate a target, to significantly enhance dose falloff rate. The dynamic motion of the beam source is equivalent to focusing tens of thousands of beams, creating a sharp dose gradient that potentially rival proton Bragg peaks. Materials and Methods: To study DPP, we took a Cybeknife cone beam and rotate it in a hemispherical trajectory to create DPP dose kernels. The parameters determining a kernel include: (1) range of latitude angles from 0 to 90 degrees, (2) range of longitude angles from 0 to 360 degrees, and (3) source to axis distance (SAD). Using these dose kernels, a complex 3D dose distribution can be created via traversing or “painting” a kernel inside a 3D target volume. Results: We found: (1) The dose gradient of DPP kernels rivals that of proton Bragg peaks. (2) As the latitude angular range increases, the dose gradient of DPP kernel increases in the plane defined by the circle of latitude and decreases in the plane defined by the circle of longitude. (3) As the starting latitude angle increases, the dose distribution of low dose regions becomes less regular in the plane of the circle of longitude. (4) When DPP kernels are used in treatment planning via dose painting, we get better plans than Gamma Knife radiosurgery. Conclusions: We have demonstrated that Dynamic Photon Painting has the potential to rival proton therapy and outperform Gamma Knife radiosurgery for our studied cases.
SU‐HH‐BRB‐04: Dosimetry of Low‐Energy Characteristic X‐Rays
Authors: Tucker M , Starin R , McCray M , Rakowski J
Published: August 2010

Purpose: To measure dose rates in water and obtain percent depth dose (PDD) curves in phosphate‐buffered saline (PBS) solution for low‐energy (< 20 keV) characteristic x‐rays emitted from various metals. Dose‐rate data obtained here will be used to support measurements of RBE in human glioma and other cells. Method and Materials: Characteristic x‐rays were produced by irradiation of metal targets with a 55 kVp x‐ray spectrum from an Ag anode at constant mA. Dosimetry was performed using an extrapolation chamber. The chamber was oriented with its window parallel to the target surface at a distance of 65 mm from the target such that the charge produced in the chamber was due to the characteristic x‐ray emissions from the metal target. Dose rate to water at the position of the chamber window was determined using Burlin cavity theory, by varying the chamber electrode spacing and window thickness, while measuring the resulting change in the charge collected. Dose rates were used to create a calibration curve relating the optical density of Gafchromic EBT film to the dose to water. Percent depth dose was measured by sequentially irradiating pieces of film submerged in a PBS‐filled cell culture dish at a range of distances from the bottom of the dish. Results: Dose rates to water for this experimental arrangement were found to be approximately 4.17 cGy/min for Mo, 10.75 cGy/min for Ti, and 12.55 cGy/min for Zn. As expected, the slopes of the PDD curves were dependent on the characteristic x‐ray energies of each metal. Conclusion: The PDD curves may prove useful in assessing the trade‐off between RBE and depth of penetration in, for example, electronic brachytherapy devices that could make use of characteristic x‐rays produced by an apparatus similar to that in the present experiment.
SU‐HH‐BRB‐06: Emission Guided Radiation Therapy: A Simulation Study of Treatment without Margin
Authors: Fan Q , Zhu L
Published: August 2010

Purpose: Accurate tumor tracking remains as a major challenge in radiation therapy. Margins are added to the clinical target volume (CTV) to ensure the treatment of tumor in the presence of patient setup uncertainty. Fiducial seeds and calypso markers are commonly implanted into the disease sites to further reduce the dose delivery error due to tumor motion. For more accurate dose delivery and improved patient comfort, the use of radioactive tracers in positron emission tomography (PET) as non‐invasive tumor markers has been proposed ‐ a concept called emission‐guided radiation therapy (EGRT). Method and Materials: Instead of using images obtained from a stand‐alone PET scanner for treatment guidance, we mount a positron imaging system on a radiation therapy machine. Such an EGRT system is able to track the tumor in real time based on the lines of response (LOR) of the tumor positron events, and perform radiation therapy simultaneously. One main algorithmic difficulty of EGRT implementation is how to deliver the dose based on an existing treatment plan and the acquired real‐time tumor location information. In this work, we illustrate the EGRT concept using computer simulations and propose an adaptive algorithm for dose delivery. Results: EGRT's advantage on increased dose delivery accuracy is demonstrated using a prostate treatment case without the setup margin. The emission process is simulated by Geant4 Application for Tomographic Emission package and Linac dose delivery is simulated using a voxel‐based Monte Carlo algorithm. A treatment setup error of 1cm is simulated on the prostate. The dose distributions show that the proposed EGRT can accurately deliver the prescribed dose to the CTV without using margins to compensate for the setup error. Conclusion: Although still in a preliminary research stage, EGRT has the potential to substantially reduce tumor location uncertainties and to greatly increase the performance of current radiation therapy.
MO‐A‐201C‐01: Modern US Equipment and US Physics
Authors: Fowlkes B
Published: August 2010

Diagnostic ultrasound imaging has advance substantially over the past 25 years and this has been accelerated by the progressive move toward digital systems. Modern ultrasound systems rely heavily on multi‐element array transducers, image reconstruction, and signal processing to produce the clinical images seen today. In addition, there has been a significant effort to make ultrasound more portable and less expensive while trying to maintain image quality and performance. Those involved in the operation and evaluation of ultrasound systems need to understand the technology and approaches being used in ultrasound imaging today.

This lecture will provide the background understanding of ultrasound physics and its application in imaging systems and the evolution of imaging toward the modern digital devices being used today.

Learning Objectives:

1. Understand fundamental physics and operation of b‐mode and Doppler.

2. Understand recent advances in signal processing including harmonic imaging, coded excitation, automated optimization methods, compound imaging and speckle reduction.

3. Understand the methods for image improvements by the processing methods used in ultrasound imaging.
MO‐A‐202‐01: Patient Dose and the Modern Angiographic System
Authors: Schueler B
Published: August 2010

Recently, the FDA announced a new initiative to promote the safe use of fluoroscopy and CT devices which includes enhancement of radiation dose measurement, display and recording. This initiative has resulted from increased scrutiny of patient radiation exposure from medical procedures and notable incidents of deterministic effects resulting from high exposure levels. In the present environment, it is critical that medical physicists have a clear understanding of radiation dose quantities and measurement methods. This course will focus on radiation dose in fluoroscopic equipment.

Quality control testing of fluoroscopy systems should include measurement of patient dose to ensure dose rates are appropriate and meet regulatory requirements and verify that displayed dose values are accurate. The medical physicist should also understand the variation in dose rate and image quality with respect to spectral filtration, kVp, pulse rate and patient thickness. This understanding is necessary to ensure appropriate dose settings are available to the operator. Education of fluoroscopy operators in how to optimize image quality and minimize patient dose is another important role for the medical physicist.

Learning Objectives:

1. Review fluoroscopic dose quantities.

2. Understand the operation of kerma‐area‐product meters.

3. Learn how to verify the accuracy of displayed dose values, including recommended quality control testing frequencies and control limits.

4. Understand how to measure fluoroscopy and fluorography phantom entrance air kerma for comparison to expected reference standards and regulatory maximum limits.

5. Review equipment factors and operator factors that affect patient fluoroscopy dose and image quality optimization.
MO‐B‐202‐01: Status/Impact of Lowering the Annual Limit from 5‐2 Rem
Authors: Cool D
Published: August 2010

Options to Revise the Nuclear Regulatory Commission's Radiation Protection Regulations

The Nuclear Regulatory Commission (NRC) is in the process of engaging stakeholders on issues associated with possible changes to the radiation protection regulations contained in 10 CFR Part 20, and other parts of the NRC regulations, to increase alignment with recent recommendations of the International Commission on Radiological Protection. The Commission is particularly seeking to explore implications, as appropriate and where scientifically justified, of greater alignment with ICRP Publication 103. Other information from national and international sources are also being considered. Given that the NRC regulations provide adequate protection, the discussion has been focusing on discerning the benefits and burdens associated with revising the radiation protection regulatory framework. The NRC staff is to provide recommendations to the Commission in late 2011.

The staff has identified a number of key issues for ongoing discussion, as a result of its initial analysis, and as a result of consultations with stakeholders during 2009 and early 2010. These key issues include: 1) the use of effective dose and implications of incorporating the latest recommendations for tissue and radiation weighting factors; 2) the occupational dose limits; 3) the dose limits for special populations, such as the dose limit for the embryo/fetus of a declared pregnant woman; and 4) the use of constraints as a formal part of licensee radiation protection programs and the process of keeping exposures As Low As Reasonably Achievable.

Learning Objectives:

1. Understand the issues and background for possible changes to NRC's radiation protection regulations.

2. Understand implications of possible changes, and provide user feedback to be incorporated into the ongoing technical basis development.
MO‐D‐BRA‐01: Nano ‐ Cancer and Radiation Therapy
Authors: Khan M , Lanza G , Miften M
Published: August 2010

The field of nanotechnology in cancer includes the use of materials precisely constructed at the molecular level to develop devices and novel imaging and therapy techniques to improve the therapeutic ratio of cancer treatments. Recent advances in the application of nanotechnology to cancer hold a great promise to improve the detection, treatment, and prevention of cancer. In this scientific symposium, we will present a primer on the science of nanotechnology and discuss how it can be used to improve the imaging and treatment of cancer, including radiation therapy. We will describe the latest research and development in this exciting and rapidly advancing field. We will review newly developed cancer diagnostics and therapies, including the combination of imaging combined with drug delivery, based on nanotechnology and identify future directions.

The specific objectives of the symposium are to:

1. Provide a primer on nanotechnology in cancer and the science behind it.

2. Describe the potential use of nanotechnology to improve the imaging of cancer and imaging combined with drug delivery.

3. Describe the potential use of nanotechnology to improve the treatment of cancer, including radiation treatment.

4. Describe the potential use of nanotechnology to deliver the treatment directly to the tumor while sparing healthy tissue, including radiation treatment.

5. Describe promising newly developed cancer diagnostics and therapies based on nanotechnology, future directions, and the role medical physicists can play to advance the field.

6. Describe the challenges of translating nanotechnology from the academic bench to the clinic.
MO‐D‐204B‐03: Correlation of PET Images of Metabolism, Proliferation and Hypoxia to Characterize Tumor Phenotype in Patients with HNSCC
Authors: Nyflot M , Harari P , Perlman S , Jeraj R
Published: August 2010

Purpose: As positron emission tomography gains increasing prominence in tumor staging, radiotherapy target definition, and treatment assessment, better descriptions of tumor physiology are desired. In order to establish interrelation between tumor phenotypes, we have correlated PET images of metabolism, proliferation, and hypoxia in patients with head and neck squamous cell carcinoma (HNSCC). Method and Materials: PET/CT images of patients with HNSCC were acquired using [18F]FDG (a surrogate of metabolism), [18F]FLT (proliferation), and [61Cu]CuATSM (hypoxia). Patients were immobilized with thermoplastic head masks. Images were coregistered via bony anatomy and normalized to SUV. For each patient, ROIs were drawn on PET images over primary tumors (n=8) and nodal volumes (n=7). Correlation coefficients between FDG, FLT, and CuATSM distributions were calculated 1) at the voxel level, by comparing image values and 2) at the ROI level, by comparing mean SUV. Results: When comparing primary tumors at the voxel level, highest correlation coefficients were observed between FLT and FDG uptake. FDG:FLT on average had R=0.77 [range 0.52–0.89] compared to R=0.54 for FDG:CuATSM [range 0.09–0.79] and R=0.49 for FLT:CuATSM [range −0.02–0.76]. Nodal volumes showed similar trends. When comparing tumors at the ROI level, correlations were low (R<0.35) for all primary volumes and all nodal volumes except for FDG:CuATSM (R=0.72). Conclusion: FDG:FLT had the highest degree of correlation at the voxel level, while FLT:CuATSM and FDG:CuATSM exhibited high variability between patients. Voxel‐based regression of imaging surrogates may represent a superior technique to ROI‐based regression, which lacks spatial information, and is a valuable first step in the implementation of spatial correlation for tumor staging, radiotherapy target definition, or treatment assessment.

Conflict of Interest: Research sponsored in part by Genentech.