bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐390: Impact of Collimator Angles During VMAT Planning and Delivery
Authors: Yang C , Mistry N , Chen Y , Doxsee K
Published: July 2013

Purpose: To evaluate the dosimetric impact from collimator angles during the VMAT planning and delivery. Methods: An early stage lung cancer treatment with Pinnacle SmartArc™ planning system was evaluated, for both planning and delivery with dosimetric differences on an Elekta Synergy™ platform. Conventional planning process was utilizing 450 collimator angle to maximize the necessary PTV margins. A single 3590 arc with 10 MV photons were adopted. We compared three various collimator angles (00, 450 and 900) with generated planning and delivery variations; SunNuclear 3DVH™ module was also implemented to review the dose delivery discrepancy associated with the VMAT techniques corresponding to various collimator angle settings. Results: VMAT delivery with various collimator setting introduces dosimetric differences. PTV D95% dose coverage for all angles is comparable (00, 450, 900 = 93.3%, 92.9%, 92.7%) while 450 collimator introduces more leakage doses through the superior/inferior directions. OARs of 00 and 900 collimators have different distributions such as 1% of cord volume doses of 47.9 cGy and 40.7 cGy per fraction, but all within clinical tolerances. Total lung doses are within limits with V20 values of 17.2%, 17.8%, 16.7% for 00, 450, 900 collimator, respectively. Treatment MUs for all collimators are within 2% variation due to the similar control point distributions. Conclusion: 450 collimator may not the best choice for VMAT delivery with tumor size less than the MLC limitation. The convention was defined to suit the LINAC limitation with compromise at initial implementation. To avoid extra MLC leakage, 00 or 900 collimator may be a proper choice. Conformity with target shape or avoidance with the OAR locations with BEV optimization in initial planning stage is also important to validate the collimator angles. Currently there is no optimum collimator choice built in the planning system, user experience is also an influential factor.
SU‐E‐T‐391: Quantitative Measurement and Modeling of the Variations in Dose Distributions Induced by Cyclic Motion
Authors: Taguenang J , Ahmad S , Ali I
Published: July 2013

Purpose: To assess by measurement the quantitative variations in dose distributions for different motion patterns. Mathematical modeling of dose variations induced by motion was developed.Materials and Methods: The dose distributions from various plans that included open and intensity‐modulated fields were measured using a multiple‐diode‐array detector (MapCHECK2). The MapCHECK2 phantom was mounted on a mobile platform that moves with adjustable calibrated motion patterns in one‐dimension (Y‐Axis). For each plan, the dose distributions were measured with MapCHECK2 using different ranges of motion (ROM) from 0–40 mm and a frequency of 15 cycles per minute. Mathematical modeling was developed to predict the variations in the dose distributions and their dependence on the motion parameters. Results: The central dose remains unchanged and agrees (< 3%) with that for the static phantom. At periphery of dose distributions along the motion direction, hot spots resulted in low dose regions while cold dose spots were induced close to penumbra due to phantom motion. The difference in dose outside the fields increased significantly as the ROM increased where maximal dose reached up to a factor of 5 at ROM = 25 mm. The modeling showed that maximal dose and spread‐out position at the edges of the field along motion direction increased linearly with ROM. The dose profile at the edge of field decreased linearly with ROM. The dose distributions from IMRT fields were smeared and optimization features were reduced due to motion. Conclusion: The dose distributions at the edges of the open or IMRT fields varied considerably with motion. Maximal and minimal dose variations, spatial position of maximal dose and dose drop rate in the dose distributions of the mobile phantom were modeled. This modeling provides quantitative characterization of dose variations induced by motion which might be employed in IMRT optimization to compensate of these dose artifacts.
SU‐E‐T‐392: Physical Characterization and Clinical Experience for An Integrated 160‐Leaf Multi‐Leaf Collimator with a New Concept Design
Authors: Nakaguchi Y , Araki F , Ono T , Inata H
Published: July 2013

Purpose: A new concept design of an Elekta radiation head (agilityTM) has an integrated 160‐leaf multi‐leaf collimator (MLC). The agilityTM consists of 160‐leaves with 90 mm height and 5 mm width at isocenter. The MLCs are located at a stair head in a linear accelerator head and works as X‐jaws. The purpose of this study is to conduct a measurement and treatment planning study on the dosimetric properties and delivery advantages of agilityTM. Methods: The dosimetric characterizations including dose leakage, leaf position accuracy, tongue‐and‐groove (T&G) effect, and field penumbra were evaluated using 4, 6 and 10 MV photon beams. Furthermore, clinical plans such as intensity modulated radiation therapy were tested using a Monaco (Elekta) treatment planning system (TPS). Results: The leakage was remarkably low with 0.44% (average) and 0.47% (maximum) for 10 MV due to a new design principle of tilted leaves. However, the T&G effect occurred due to the tilt and it was approximately 20.8% (average) and 22.3% (maximum) for 6 MV. The leaf position accuracy was within 0.5 mm for all gantry angles and each MLC. The penumbra width was greater with a wider field size and the maximum width of 8.5 mm for 4 MV. As for clinical plans, dose distributions for all plans with TPS were in good agreement with measurements. The absolute dose at isocenter agreed with TPS in less than 2%. The comparison of gamma analysis was more than 95% pass rate with criteria of 3 mm/3%. High position designed MLCs made wider penumbra but instead, it can gain a large head clearance. Conclusion: The experimental results in this study indicate that the dosimetric characteristics of agilityTM are capable of improving the quality of dose delivery. The agilityTM provides a large head clearance, the flexible and safe radiotherapy.
SU‐E‐T‐395: MCNPX Simulation of Dosimetry From Grid Tpye Multi‐Layer Pixel Collimator for Radiation Therapy Treatment
Authors: Yoon D , Suh T
Published: July 2013

Purpose: To develop grid type multi layer structure pixel collimator for radiation therapy treatment, feasibility of manufacture process and optimization of factors are essential using Monte Carlo simulation. Methods: The present work is focused on a MCNP simulation of grid type pixel collimator(N×N×N) for radiation therapy. To realize actual pixel collimator hardware model, precise radiation shielding data and construction standard of collimator frame have been demanded. the pixel collimator cover which has opening type to radiation protection is defined as square with 1mm scale thickness. Frame window to fix several pixel collimators as grid type is constructed in simulation. If these pixel collimators arrange in window frame, it composes one of collimator layer which can be combined as multi layer. For these process, it is need to satisfy at least MLC quality assurance(QA). Furthermore, it is need to prove more than one specific advantage comparison with MLC. Radiation attenuation about layers, leakage radiation among pixels, model bulk, absorbed dose in EPID were calculated by using MCNP. Results: About pixel type collimator, the main research respects are accurate degree of attenuation, leakage radiation among pixel cover and influence of collimator frames. In case of 2MeV photon beams, quantitative attenuation measurement data and leakage estimation were calculated a similar level of MLC QA, optimal collimator frame size and structure are being constructed. Conclusion: In this study we have developed a grid type pixel collimator for radiation therapy treatment using MCNP simulation based on multileaf collimator QA datas. This research has potential possibility of realization about actual new collimator as MCNP simulation data. Also in case of difficult pattern which has to consider intensity modulation like web, doughnut pattern, it was shown effective modulation
SU‐E‐T‐397: A Review of Rapid Arc Standard Deviations
Authors: Brandner E , Specht R , Bahri S , Poltinnikov I , Huq M
Published: July 2013

Purpose: he purpose of this study is to acquire baseline values for the standard deviations of MU and angle reported by a Varian 23ex linac following the delivery of a RapidArc field. Methods: During the delivery of RapidArc fields, the Varian linac records the gantry angle and cumulative MU every 50 ms. By comparing this data to the corresponding planned data, the system calculates the standard deviations of the MUs and the gantry angles for each field. These standard deviations are reported to the linac screen at the completion of each field and documented daily for each field along with the patient, plan, treatment site, and date. The data was then entered into Micorsoft Excel for analysis. This data was acquired for every RapidArc patient (88 total patients) over the course of the first year of RapidArc use. Results: The maximum MU standard deviation was 0.09 and the maximum gantry angle standard deviation was 0.30°. The averages are 0.05 MU and 0.19° respectively. No specific treatment site (prostate/prostate fossa, head and neck, brain, thorax, or other) differed significantly from these averages. Conclusion: If the MU standard deviation is greater than 0.1 or the gantry angle standard deviation is greater than 0.3°, the RapidArc QA tests of the linac and the plan should be promptly repeated to identify any possible problems. These baseline values may be specific to the linac in question but provide a point of reference for other linacs as well.
SU‐E‐T‐401: On the Use of Onboard Portal Dosimetry for Patient‐Specific QA of RapidArc Plans
Authors: Abbas H , Carlson D , Deng J , Nath R , Chen Z
Published: July 2013

Purpose: The goal of this project is to conduct a systematic investigation on the utility of an onboard portal dosimetry (PD) system for patient‐specific QA of RapidArc plans. This abstract reports the preliminary results of this ongoing investigation. Methods: The PD system of Varian Medical Systems has been used in many centers as a convenient and viable tool for patient‐specific QA of fixed‐beam IMRT plans. Because the onboard portal imager rotates with the x‐ray source, portal dose obtained at each pixel from a complete RapidArc delivery is a sum of portal doses delivered at different gantry angles of the arc. As a Result, the sensitivity of PD in detecting deviations of photon fluence delivered at different gantry angles is inherently low. We investigated the potential sensitivity loss and its implications for patient‐specific QA by 1) dividing the arc into multiple smaller arc‐segments, 2) analyzing the dose concordance as a function of arc‐segments, and 3) comparing the concordance of PD QA results with those obtained from 3D dose verification using the Delta4 system. Results: Preliminary studies were conducted using RapidArc plans for prostate and head & neck cases. For each case, three verification plans (using single arc (300°), five 60° arc‐segments and ten 30° arc‐segments) were examined. All PD QA plans passed the QA criteria based on the gamma index. Detailed comparison of portal‐°dose profiles indicated general concordance between the measured and predicted, with increased local variations for plans with smaller arc segments. The QA results using PD for all patients were concordant with that obtained by Delta4 based on 3D dose comparison. Conclusion: Although the preliminary results shown concordant QA results between PD and Delta4, this does not constitute a sufficient test of PD for RapidArc QA. Further investigation is ongoing and updated results will be reported in the meeting.
SU‐E‐T‐403: Intensity Modulated Proton Therapy Plans with Multiple Fields for Prostate Cancer
Authors: Dhanesar S , Sahoo N , Kerr M , Taylor M , Summers P , Alvarez P , Wu R , Poenisch F , Zhu X , Gillin M
Published: July 2013

Purpose: To investigate the possible improvements in the dose conformity in intensity modulated proton therapy (IMPT) plans with multiple fields as compared to widely used single field optimized (SFO) plans with two lateral fields for spot scanned proton therapy (SSPT) and to verify the accuracy of the delivered dose using the Radiological Physics Center Proton Prostate Phantom (RPCPPP). Methods: The CT images of RPCPPP were used to design multiple IMPT plans using both SFO and multi field optimization (MFO) methods in the Varian Eclipse treatment planning system (TPS). The standard SFO clinical plan used two lateral fields going through the femoral heads. Non‐standard plans were generated using three or more oblique fields based on the SFO and MFO options of the TPS. The angles were carefully chosen to avoid bladder and rectum as much as possible. The RPC phantom containing films and TLDs was irradiated using the standard clinical SFO plan and the four field MFO plan to compare the planned and delivered dose. Results: Based on the DVHs, MFO plan with multiple oblique fields is found to have superior target conformity with reduced dose to organs at risk (OAR) and normal tissue, especially in the high dose regions, as compared to SFO plans. The point doses measured by TLDs and 2‐D dose distribution measured by GafChromic films in the RPCPPP irradiation passed the commonly used RPC acceptance criteria, namely +/− 7% agreement in point does and more than 85% of the voxels meeting the gamma index criteria of 7% dose or 4 mm distance agreement. Conclusion: The MFO SSPT plans for prostatic targets with multiple fields lead to better target conformity with lower doses to OARs as compared to SFO plans. The results of irradiations of the RPCPPP show that these plans can be delivered with acceptable accuracy
SU‐E‐T‐404: Quantification of Proton Dose Enhancement Resulting From Gold Nanoparticles
Authors: Schuemann J , Dowdell S , Barbone G , Paganetti H
Published: July 2013

Purpose: To quantify the proton dose enhancement from different sizes, shapes and distributions of gold nanoparticles (GNP). The high uptake of GNPs in tumors as compared to normal tissue provides the basis for GNP enhanced proton therapy. Method: Monte Carlo (MC) simulations were performed using TOPAS, which is based on Geant4. The Penelope physics package was instantiated for low energy electromagnetic physics. We calculated dose distributions of proton beams of energies ranging from 10–150 MeV incident upon a cube of liquid water containing a single GNP of a particular shape (spherical, cylindrical, cubic) and size (1–100nm). Dose enhancement distributions were analyzed in a scoring grid around the GNPs with a resolution of 10×10×10 nm3. The configuration yielding the highest dose enhancement was then used to study the overall dose enhancement for a variety of GNP concentrations (0–100 mg/ml) for homogeneous and clustered GNP distributions. Results: GNPs increase the dose delivered to a small volume (1×1×1 μm3) by up to 5%. Based on the diminishing return of dose enhancement with size for spherical GNPs we selected GNPs of 50 nm diameter as reference. GNP enhancement is proportional to the concentration in the concentrations investigated, a saturation is expected at very high concentrations. Conclusion: These results show that the use of GNPs is a promising approach to increase the ratio of tumor and normal tissue in proton therapy. Further investigation is required to determine the optimal specifications for GNPs to yield maximum benefit. The absorbed dose increases by 5% using GNPs of 50 nm diameter and is nearly independent of the proton energy. The upper limit of GNP concentration has to be established in future biological studies.
SU‐E‐T‐406: Dosimetric Impact of the Air‐Filled Rectal Balloon for Prostate Proton Treatment
Authors: Li J , Lin M , Luo W , Ma C
Published: July 2013

Purpose: To investigate the dosimetric impact of the air‐filled rectal balloon for prostate treatment with proton beams. Methods: Proton beam is used for prostate treatment because it can provide a conformal dose coverage to the target. Prostate localization accuracy is crucial to guarantee the treatment targeting. The use of rectal balloon has been shown to be effective in reducing the prostate motion during the treatment. Air‐filled rectal balloon has been used most commonly, but could create dose perturbation at the air‐tissue interface. In this work, intensity modulated proton treatment (IMPT) plans were generated for ten patients with air‐filled rectal balloon for prostate localization. Monte Carlo dose calculations were performed for each patient and the dose distribution were compared with those when the rectal balloons filling material is changed to water. The doses to the prostate and the rectal wall were compared for these two situations. The dosimetric impacts from the air‐filled balloon are then summarized. Results: It was found that the dosimetric impact to the prostate by the air‐filled balloon is minimum. The changes in the minimum dose, the maximum dose and the mean dose to the prostate caused by the air‐filled balloon are within 1%. The maximum dose to the rectal wall was reduced by 3.4% (from −0.4% to 5.3%) on average. However, the mean dose to rectal wall was increased by 13.3% (from 10.2% to 17%) on average. The DVH comparison show that the volume of the rectal wall receiving dose less than 50% of the prescription dose increased significantly. Conclusion: The air‐filled rectal balloon has no significant impact on the target dose coverage. It reduces the maximum dose of the rectum wall but increase its mean dose significantly. Overall, the air‐filled rectal balloon is feasible for prostate proton treatment.
SU‐E‐T‐410: Initial Results From Multiple Irradiations of An Anthropomorphic Liver Phantom
Authors: Molineu A , Alvarez P , Amador C , Craig T , Gillin M , Followill D
Published: July 2013

Purpose: To describe the Radiological Physics Center's new anthropomorphic liver phantom and to report the results from the initial irradiations. Methods: A new imaging and dosimetry insert was created for the RPC's pelvic phantom that includes non‐coplanar targets. The polystyrene insert represents the liver and includes two Solid WaterTM targets (PTV1 and PTV2) that mimic liver metastases. PTV1, located in the superior‐left‐posterior region of the insert, is an ovoid 2 cm in diameter and 2.5 cm long. PTV2, located in the inferior‐right‐anterior region of the insert is a 3 cm diameter sphere. The insert houses one TLD and 3 planes of radiochromic film in each PTV. The phantom, with a motion table to simulate respiratory motion, was sent to institutions planning to participate in an upcoming RTOG SBRT liver protocol. Institutions were instructed to design and deliver a stereotactic treatment plan that delivered 6 Gy to >=95% of each PTV. The maximum motion of the phantom on the motion table was 1 cm in the superior‐inferior direction. Results: Irradiations from 8 institutions have been analyzed. The acceptance criteria, based on the results of the 8 irradiations, were set at ±7% for the TLD and 85% of the pixels in a region surrounding each PTV passing a ±7%/4 mm global gamma analysis. Five of the 8 irradiations passed these criteria. The three irradiations that did not meet the criteria failed to meet only the film criteria. Breath hold, ITV, gating, and tracking techniques were used to account for motion. Pinnacle, Eclipse, and MultiPlan treatment planning systems were used for planning. Conclusion: The new liver insert along with a motion table tests the ability of the institution's ability to deliver dose to multiple moving targets and is a useful credentialing tool for clinical trials using SBRT. Supported by PHS grant CA10953 and CA081647 from the NCI, DHHS.
SU‐E‐T‐412: What Is the Benefit of Fiducial Marker Implantation for Pancreatic SBRT?
Authors: Jones B , Gan G , Schefter T , Miften M
Published: July 2013

Purpose: Localization of pancreatic tumors during Stereotactic Body Radiation Therapy (SBRT) is difficult due to the poor soft‐tissue contrast of abdominal cone‐beam CT (CBCT). The purpose of this study was to measure the increased accuracy of pancreas localization when radiopaque fiducial markers (RFM) are implanted into the tumor and peri‐pancreatic tissue to facilitate a reduction of margins and escalation of dose. Methods: 15 CBCT scans were acquired of patients implanted with RFM enrolled in a prospective study involving SBRT for pancreatic cancer, receiving 30 Gy in five fractions with PTV margins of 3–5 mm. In order to quantify the effect of RFM, matching sets of markerless CBCT images were created. An automated tracking algorithm was developed to identify the location of markers in each CBCT projection, and 2D Gaussian fitting was used to filter these markers from the images. The 3D dataset was re‐reconstructed using these filtered projections, yielding a CBCT image of the same patient geometry with no RFM. These markerless images were aligned to the reference CT images using the anterior vertebral surface/aorta and the pancreatic stent as a guide. Using the RFM images as a gold standard, the differences in position represent the error in localization due to the lack of RFM information. Results: The automated algorithm successfully yielded CBCT images without RFM, star artifacts due to markers, or artifacts due to the filtration process. When the vertebral bodies and aorta were used for localization, the average error (compared to RFM images) was 15.0±7.4 mm. When a pancreatic stent was used for localization, the average error was 3.9±2.1 mm. Conclusion: Implantation of RFM increases localization accuracy by 4–15 mm compared to conventional techniques. Marker implantation is necessary when using tight margins and/or increasing tumor dose, and can be used to increase the therapeutic ratio.
SU‐E‐T‐415: Dosimetric Measurements of An N‐Butyl Cyanoacrylate Embolization Material for Arteriovenous Malformations
Authors: Labby ZE , Roberts DA , Chaudhary N , Gemmete JJ , Pandey AS
Published: July 2013

Purpose: The therapeutic regimen for cranial arteriovenous malformations (AVMs) often involves both stereotactic radiosurgery and adjunct endovascular embolization. Embolization agents often contain radiopaque contrast to assist the neurointerventionalists, leading to concerns regarding the dosimetric effects of these contrast agents. This study investigated dosimetric properties of n‐butyl cyanoacrylate (n‐BCA) plus lipiodol (NPL) with and without tantalum powder. Methods: The NPL was provided cured from the manufacturer (Codman Trufill; Codman & Shurtleff, Inc., Raynham, MA) with and without tantalum. Attenuation measurements were made for the samples with and without tantalum powder and compared to the attenuation of a water substitute using a 6MV photon beam. Effective linear attenuation coefficients (ELAC) were derived from the attenuation measurements and measured sample thicknesses. Interface effects were investigated using a parallel plate ion chamber placed at set distances below fixed samples. Finally, Hounsfield units were measured using our department's standard stereotactic radiosurgery CT protocol. Results: For a 3cm square field, the ELAC was 0.0428 1/cm and 0.0474 1/cm for NPL without and with tantalum respectively, compared to 0.0461 1/cm for the water substitute. Non‐density corrected dose calculations would Result in errors of −0.33% and 0.13% per cm thickness of NPL without and with tantalum, respectively. Interface effects compared to water were less than 1.3% for both embolization materials. CT values at 120 kVp were 2082 HU and 2358 HU for NPL without and with tantalum, respectively. Conclusion: The dosimetric properties of NPL are very close to those of water for therapeutic energies. Therefore, treating the entire intracranial space as uniform in composition will Result in typically less than 1% dosimetric errors. However, due to the high attenuation of both embolization agents for diagnostic energies, artifacts may occur that necessitate MR imaging to accurately identify the spatial extent of the region to be treated.
SU‐E‐T‐424: Improved Dosimetric Accuracy for Cyberknife Patient Plans Using a Dual‐Detector Measurement Method for Relative Output Factors
Authors: Vandervoort E , La Russa D , Ploquin N , Szanto J , Henderson E , Francescon P
Published: July 2013

Purpose: The measurement of output factors (OFs) for small fields can lead to large dosimetric errors if detector effects are not accounted for. With its high spatial resolution and tissue equivalence, GAFCHROMIC film provides a correction free measure of OFs. We recently changed the OFs used in our Cyberknife planning system from uncorrected diode values to a dual detector method employing a diode with Monte‐Carlo corrections for the smallest collimators and a micro ion chamber for collimators >10 mm in diameter. Methods: We measured OFs for the CyberKnife G4 fixed collimators (5 to 60 mm) using an A16 microchamber and an Edge diode detector. The diode measured OFs for collimator sizes <10 mm were corrected using Monte‐Carlo correction factors. OFs were also measured using GAFCHROMIC film. We evaluated how this change in OFs influenced the dosimetric accuracy of patient specific QA measurements for 13 patient plans (9 before and 4 after the OF change) using film and the A16 chamber. Results: The OFs measured using the dual‐detector method agree with film to within two standard deviations for the full range of collimator sizes. When the dual detector method OFs are used, we achieve better dosimetric agreement (<2 sigma for pixels within the 80% isodose) than with uncorrected diode OFs for all patient specific QA plans measured using film. For patient specific QA using the microchamber, we get good agreement (<3%) for collimator sizes >5 mm, with differences observed for the 5 mm collimator consistent with volume averaging and a 1 mm setup uncertainty. Conclusions: OFs can be determined consistently using the dual‐detector method and verified using film. For patient specific QA, we achieve good agreement with microchambers for collimators >5 mm in diameter but film is the most appropriate detector for patient specific QA using the 5 mm collimator.
SU‐E‐T‐425: Implementation of the TG‐147 Protocol in Conjunction with the Calypso GPS Tracking System for Higher Confidence of Prostate Patients Being Treated On RTOG Study 0938
Authors: Morris A , Hasson B , Sullivan P , Hand C , Philbrook S
Published: July 2013

Purpose: There are multiple factors that have lead to the need for an increased precision and accuracy in Radiation Therapy. The increased use of IMRT and SBRT with hypofractionated doses requires optimal precision and accuracy in aligning the treatment delivery with the target. Recent advances in imaging and motion management of patients during the treatment process have provided a higher level of confidence for these types of treatments. The GPS based Calypso system is a non‐radiographic localization and tracking systems. In order to ensure these systems are localizing and tracking with the high accuracy needed, a set of robust quality assurance procedures are required. Task Group Report (TG‐147) of the AAPM describes QA for non‐radiographic localization systems. The purpose of this work was to implement TG‐147 with the Calypso 4D. Methods: The Calypso 4D system is composed of a console and a tracking station. The Calypso 4D is delivered with several quality assurance tools for initial and ongoing QA tests of the system. There are 3 distinct QA tools, which were adapted to the TG‐147 protocol tests for the purpose of this study. TG‐147 was analyzed for the application of QA procedures to Calypso. Calypso was then used to track prostate movement during standard IMRT and SBRT treatments. Results: Based on the review of TG‐147 recommendations for daily, monthly, and annual tests new departmental QA procedures were implemented. The addition of an end‐end localization plan, static and dynamic localization tests, and stability tests were incorporated into the existing QA program. Using Calypso, prostate movement during treatment was analyzed. Movement ranged from 0–3mm in the posterior and inferior directions.ConclusionThe TG‐147 recommendations provided a robust set of QA procedures that confirmed the Calypsos accuracy within 1mm. The new QA procedures have increased the confidence for tracking prostate movement during treatments.
SU‐E‐T‐431: Validation of Dose Escalation in Hypofractionated Hemi‐Larynx Irradiation of Early‐Stage True Vocal Cord Cancer Based On Anthropomorphic Phantom Measurements
Authors: Ding C , Chun S , Hrycushko B , Solberg T , Timmerman R
Published: July 2013

Purpose: To evaluate the use of the CyberKnife delivery platform and Multiplan treatment planning system (TPS) to achieve acceptable target coverage and normal tissue sparing for dose escalation when treating the involved hemi‐larynx and at risk paraglottic space for early‐stage laryngeal cancer. Methods: Specialized anthropomorphic phantoms containing a hollow larynx were constructed based upon patient CT images with earlystage glottic cancer. Contours of the hemi‐larynx clinical target volume (CTV) as well as the thyroid gland, arytenoids, contralateral vocal cord, and anterior commissure were created in the Multiplan TPS. Treatment plans were created using the ray‐tracing algorithm and were re‐calculated using the Monte Carlo algorithm. Radiochromic EBT2 film was sandwiched in the phantom at the level of the vocal cords to determine the dose delivered to the target and critical structures. Phantoms were irradiated with multiple fractionation schemes including 50 Gy in 15 fractions, 45 Gy in 10 fractions, and 42.5 Gy in 5 fractions using 6 MV photons. Film dose distributions were compared with that predicted by the TPS. Results: For plans generated using the Monte Carlo algorithm, greater than 95% PTV coverage by the prescription dose was achieved with conformality indices ranging from 1.4 to 1.5. Mean dose to the contralateral vocal cord and arytenoids was less than 40% and 25% of the prescription dose, respectively. A gamma passing rate of 90% was seen using a 3%/3mm criteria when comparing the Monte Carlo algorithm with film, while a 79% passing rate was seen when comparing the ray‐tracing algorithm with film. Conclusion: Adequate dose delivery with significant sparing of uninvolved normal tissue is feasible and practical with CyberKnife radiotherapy when using the Monte Carlo dose calculation algorithm. This technique has the potential to allow hypofractionation for the purpose of improving local control, voice quality outcome, and patient convenience.
SU‐E‐T‐438: Dosimetric Effect of Patient Arm Position in Spinal CyberKnife Robotic Radiosurgery
Authors: Mihaylov IB , Tien CJ , Hepel JT
Published: July 2013

Purpose: For treatment of spine lesions with robotic CyberKnife (Accuray, Sunnvale, CA) radiosurgery, patients are simulated in the supine position with arms along the torso. Treatments often include lateral beams passing through the arms. Variation in arm position between simulation and delivery could affect delivered doses. The purpose of this work is to evaluate the potential dosimetric effect of patient extremity motion on spinal CyberKnife treatments. Methods: Thirteen patients were selected with spinal lesions between T10 and L4. Prescription doses ranged between 1800 and 4000 cGy, delivered in 1 to 5 fractions. In addition to the treatment plan used as reference standard, a comparison plan was created with the arms contoured and contour density set to zero for each patient. This represented the extreme scenario of the patient moving their arm completely out of the field. Results: Results: The mean difference for the minimum dose to the PTV, the maximum dose to the spinal cord, and dose to 250 cc of spinal cord are 2.4%, 4.8% and 4.5%. PTV coverage in compared plans was changed by 1.4% on average, with the coverage improved, due to less attenuation from the patient arms. As the mean arm dose relative to the prescription dose increased, the impact of removing the arms also increased. Conclusion: The most extreme scenario of extremity motion in CyberKnife spinal radisurgery was investigated. It was found that the dosimetric impact of the arms is small. The difference in PTV coverage was 1.4%, with a difference % in minimum dose to the PTV was 2.4%. Dose differences to critical organs were within 5%. Therefore, any reasonable motion due to set‐up variations and deviation from patient simulation position will be negligible.
SU‐E‐T‐451: Patient and Site‐Specific Assessment of the Value of Routine Monte Carlo Dose Calculation in Proton Therapy
Authors: Schuemann J , Testa M , Bueno M , Min C , Moteabbed M , Giantsoudi D , Paganetti H
Published: July 2013

Purpose: To assess the clinical impact of Monte Carlo (MC) dose calculations in proton therapy by analyzing uncertainties of analytical algorithms when predicting dose to target and critical structures and beam ranges in patient geometries. Methods: We used TOPAS to simulate double scattering proton treatments, which were compared to analytical treatment planning dose calculations (TPC). We investigated: 1)beam ranges, dose distributions, does‐rate profiles and output factors using various dedicated experiments.range differences caused by the patient heterogeneity considering 48 fields and 4 treatment sites. We calculated distal 2)dose surfaces composed of beam ranges and assessed average range difference (dR) and root‐mean‐square deviation (RMSD).3)dose delivery accuracy using a DVH based analysis considering patient treatment plans from 3 sites. 4)the accuracy of dose delivery for small fields (diameter below 7cm) based on patient heterogeneity for 38 head fields. We assess differences in D50. Results: 1)MC and measurements agree within statistical uncertainties.2)For 3 of 4 patient sites the RMSD between TPC and TOPAS was <2mm. Head treatments indicate significant RMSD of up to 6mm. 3)TPC DVHs showed underdosage for head cases by 2% compared to TOPAS, discrepancies in critical volumes can reach up to 50%, prostate patients show significant penumbra differences, liver patients show good agreement between TOPAS and TPC. The site‐specific findings can be explained by beam range and geometrical complexities.4)For small proton fields, discrepancies of up to 5.4% were found in D50 for single fields. A clear correlation between the accuracy and patient heterogeneity was established. Conclusion: This study highlights treatment sites and scenarios where MC simulations are recommended for proton therapy, i.e. small fields (due to scattering disequilibrium) and head treatments with bone/air/tissue interfaces affecting the ability of analytical algorithms to predict the correct beam range. Absolute dose differences where typically within 2% for large fields.
SU‐E‐T‐461: Cervical HDR Optimization Using Oncentra Masterplan's IPSA Algorithm
Authors: Knill C , Halford R , Dominello M , Miller S
Published: July 2013

Purpose: Traditionally, cervical HDR planning was done using standard loading techniques, and prescription points defined in 2D. Currently, widespread availability of 3D imaging allows for structure contouring, inverse plan optimization, and structure based dose prescriptions. However, many institutions still use traditional techniques for some portion of HDR planning. The goal of this research is to compare inverse‐optimized plans with structure based dose prescriptions, to forward‐optimized plans with point A based prescriptions. Methods: 41 clinical cervical HDR plans (12 patients), originally optimized using forward‐planning techniques, were retrospectively optimized using Oncentra MasterPlans (Nucletron, Veenendal, the Netherlands) inverse planning simulated annealing (IPSA) algorithm. Dose objectives for the high risk CTV (HRCTV) and Organs at risk (OARs) were used in the inverse optimization. The inverse optimization plans were normalized to match the HRCTV D90 dose with their forward‐planned counterparts. For each plan, the following values were recorded: the dose to Point A, D90 for intermediate risk CTV (IRCTV); D2cc, D0. 1cc for OARs (rectum, bladder, sigmoid colon, small bowel) and total treatment time. Results: Inverse optimization changed the dose to point A and IRCTV D90 by −12.77+/−32.86% and −17.17+/−31.52%, respectively. Changes in the OARs [D2cc, D0.1cc] were: [−15.89+/−27.10%,−12.87 +/− 31.40%] for rectum, [−14.88+/−23.70%, −11.50+/−27.69%] for bladder, [− 18.32+/−38.81%, −17.52+/−41.35%] for sigmoid colon, and [−24.10+/− 36.61%,−22.47+/−39.64%] for small bowel. The treatment time changed by — 25.49 +/−24.44%. Conclusion: On average, the IPSA optimized plans decreased the dose to the IRCTV, point A, and OARs. However, the large standard deviations in the dosimetric changes indicate that the performance of the IPSA optimization is highly case dependent. Further IPSA studies are needed to determine whether dose can be increased to IRCTV and point A, while maintaining OAR sparing.
SU‐E‐T‐462: Energy Modulated Photon Radiotherapy: A Monte Carlo Investigation
Authors: Zhang Y , Feng Y , Ming X , Nath R , Deng J
Published: July 2013

Purpose: To investigate the feasibility of energy modulated photon radiation therapy (EMXRT) using Monte Carlo simulations of photon beams of various energies. Methods: An EMXRT plan was generated for a prostate cancer patient treated with 10‐MV 5‐field intensity modulated radiotherapy (IMRT) optimized using Eclipse treatment planning system. Based on beam characterization of a Varian Clinac with EGS4/BEAM Monte Carlo code, multiple source models were first generated to represent the photon beams with energy of 1, 2, 3, 4, 5, 6, 10 and 15 MV, respectively. Optimal beam energy was then selected based on the effective path‐length in the patient via ray‐tracing for each beam angle. An inverse planning system based on gradient search algorithm was used to optimize photon beam intensity of various beam energies with pre‐simulated Monte Carlo pencil beam dose distributions in patient anatomy. Finally, both EMXRT and IMRT plans were simulated with EGS4/MCSIM for 3D dose distributions in patient and compared. Results: Based on different path‐lengths, 5, 6 and 10 MV photons were chosen in our EMXRT plan with lower energy photons used for shorter path‐lengths. DVH analysis indicated that the target coverage in EMXRT plan was less uniform with Dmax and Dmin at 111.6% and 92.6% of prescription dose, respectively, as compared to 106.2% and 97.8% in regular IMRT plan. On the other hand, critical structures were much more spared in EMXRT plan than in IMRT plan, with 32% dose reduction in rectum and 40% reduction in bladder, respectively. The integral dose to the surrounding normal tissues was significantly reduced by 56% in EMXRT plan. Conclusion: This work demonstrates the potential of this Monte Carlo based tool for investigating the feasibility and desirability of EMXRT. Further investigation on more complex tumor sites such as head and neck cancer are now in progress.
SU‐E‐T‐467: A New Conversion Method of Pixel Values to Hounsfield Units for Cone Beam CT Images
Authors: Tateoka K , Abe T , Nakazawa T , Saito Y , Nakata A , Yano M , Sakata K
Published: July 2013

Purpose: The purpose of this study is to develop a new correction method for converting pixel values to Hounsfield units (HUs) using the histograms of pixel values for the cone beam computed tomography (CBCT) to calculate the dose distributions on the CBCT images. Methods: The simulation computed tomography (sim‐CT) and CBCT images of an electron density phantom and 5 prostate cancer patients were acquired. The histograms of pixel values for each slice of the sim‐CT and CBCT images of the electron density phantom and of the prostatic cancer patients were obtained with an in‐house program. To perform correction of the pixel values for each slice of the CBCT images, the shapes of the histograms for each slice of the CBCT images were closed to the shapes of the histograms of the sim‐CT images using linear scaling method with a minimum sum of squared differences for the regions of soft tissue and bone. To evaluate clinical significance, the dose distribution on the mCBCT images was compared with the original plan on the sim‐CT images by using gamma analysis with a 3% / 2 mm criterion. Results: The linear scaling of pixel values in the CBCT images was successfully applied to the histograms. After the linear scaling, the histograms of mCBCT resembled the histograms of sim‐CT. Thus, it is possible to judge pixel values for CBCT images in HUs. However, because the artifacts peculiar to CBCT remained, differences between both HUs were observed The pass rate of gamma analysis (3% / 2 mm) were more than 95%. Conclusion: The proposed novel method using histograms is a feasible method for converting pixel values in CBCT images to HUs; this may facilitate calculation of accurate doses using CBCT images.
SU‐E‐T‐468: Daily KV Cone‐Beam CT and Deformable Image Registration as a Method for Studying Dosimetric Consequences of Anatomic Changes in Adaptive CRT of Lung Cancer
Authors: Ma C
Published: July 2013

Purpose: To evaluate anatomic lung tumor changes assessment and actually delivered doses utilizing the deformable kV CBCT Image Registration and compare to 3D CRT for lung cancer. Methods: Five patients diagnosed with lung tumors were treated with 3D CRT and daily KV CBCT images were acquired. Each of the kV CBCT and plan CT images were imported into the Deformable Image Registration (DIR) system. The generated CT image was deformed by the DIR system and new contours were obtained by using the adaptive re‐contouring function of the DIR. These contours of 30 sets were individually marked CBCT contours and imported into Varian Eclipce system. The plan for each pair of the new contours and the original contours of the CT image was individually designed with 3D CRT with the same filed angle. These CBCT plans were added by applying a dose accumulation plan (DA plan)and were compared to CT plans. Results: The maximum, minimum, and mean doses to the PTV in the DA plans were avarage separately 1.2%, 29.7%, and 17% less than the CT plans. V5, V10, V20, V30and V50 of the left, the right lung and total lung in DA plans were less than those of the CT plans. The maximum dose of the spinal cord in the DA plans were avarage 27. 9% less than the CT plans. The mean dose of the left, right lung and total lung in the DA plans were reduced by 13.8%, 23.7%, and 15.3% respectively. Conclusion: The adaptive 3D CRT of DA plans based on the deformable registration provides dose escalation on lung cancer, which is helpful in improving the local control and excluding the surrounding normal tissues. It provides a method for further adaptive radiotherapy exploration.
SU‐E‐T‐470: Monte Carlo Simulation of Fast Neutron Treatments for Head and Neck Cancers
Authors: Moffitt G , Stewart R , Sandison G , Emery R , Jevremovic T
Published: July 2013

Purpose: To quantify the physical characteristics of a therapeutic fast neutron beam at the University of Washington (UW) using a Monte Carlo model validated against measured percentage depth‐dose (PDD) and lateral profiles. Methods: MCNPX modeling and simulation of the UW neutron therapy system's treatment head is divided into three stages. In Stage I, 50.5 MeV protons are directed at a Be target. Neutrons produced in the target pass through the primary collimator and flattening filter; photons and neutrons produced in Stage I are saved to a 100×100 cm2 phase space file located just below the flattening filter. In Stage II, neutrons and photons are transported through the MLC and saved to a second phase space file. Automatic adjustment of the 40 individual MLC to create regular or irregular field shapes with or without a wedge is controlled by an in‐house developed python script. In Stage III, neutral particles are transported from the phase space file at the bottom of the MLC into a 40×40×40 cm3 water phantom (150 cm source to surface distance). PDD curves and lateral dose profiles are computed from dose tallies in rectangular (0.1 cm3) volumes. Results: PDD simulation for an open 10.4×10.3 cm2 field agrees with measurement to within 4% up to 17 cm and within 8% up to 30 cm. A lateral dose profile at a depth of 1.7 cm matches well the overall shape of the profile. A representative simulation (1011 source particles) requires about 150 hours of CPU time on a dual, 2.4 GHz 8‐core Intel Xeon server. Conclusion: The developed MCNPX model is capable of reproducing measured data with sufficient accuracy for clinical applications. Efforts to improve agreement in the penumbra of lateral profiles are underway as well as tests of the model for various sizes of open and wedged fields.
SU‐E‐T‐474: Adaptive Stereotactic Body Radiation Therapy (SBRT) Planning for Lung Cancer: Can We Predict Who Will Benefit?
Authors: Qin Y , Kelsey C , Yoo D , Yin F , Cai J
Published: July 2013

Purpose: We have previously shown that adaptive lung SBRT planning can mitigate dose to adjacent organs at risk (OARs). The aim of this study is to investigate factors that affect dosimetric effectiveness of adaptive lung SBRT, so that we may predict which patients benefit most from an adaptive strategy. Methods: 20 patients who underwent SBRT for lung cancer at our institution were included. Cone‐beam CT(CBCT) images acquired before each fraction were retrospectively analyzed to determine tumor volume changes throughout the course of treatment. Adaptive plans were created for each CBCT dataset using the same planning parameters as the original CT‐based plan. Two accumulative dose plans, non‐adaptive(PNON) and adaptive(PADP), were generated for each patient using deformable image registration to sum dose from each fraction. Dosimetric comparisons between PNON and PADP were performed for cord, lung, chest wall, and esophagus. Statistical significances were tested using paired t‐test(significance level=0.05). Correlations were evaluated between dosimetric changes from adaptive planning(Delta_D) and potential impacting factors, including tumor‐to‐OAR distances(dT‐OAR), initial ITV(ITV1), ITV change(Delta_ITV), and effective ITV diameter change(Delta_dITV). Results: Compared to PNON, PADP significantly reduced dosimetric metrics of all OARs (p=0∼0.03). Dealta_D was found to positively correlate with Delta_dITV/dT‐OAR for dose‐to‐5cc (D5cc) of esophagus (r=0.77), Dmax of esophagus (r=0.76), and D30cc of chest wall (r=0.72). Stronger correlations between Delta_dITV/dT‐OAR and Delta_D30cc of chest wall were discovered for peripheral (r=0.82) and central tumors (r=0.94), respectively. No correlation was found between Delta_dITV/dT‐OAR and Delta_D1.2cc or Delta_D0.35cc of spinal cord, largely due to two IMRT patients planned with tight cord constraints. After removing these two cases, good correlations were recovered between Delta_dITV/dT‐OAR and Delta_D1.2cc, Delta_D0.35cc of spinal cord (r=0.75 and 0.71, respectively). Conclusion: Adaptive SBRT planning for selected patients resulted in significant dose reduction in adjacent OARs. Tumor diameter change and tumor‐to‐OAR distance are potential indicators for dosimetric effectiveness of adaptive lung SBRT.