bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐503: Trajectory Modulated Arc Therapy of Intracranial Lesions: Development of a Standardized Path‐Based Technique for Fully Dynamic Couch‐Gantry Modulated Treatments
Authors: Khan S , Chin E , Otto K , Xing L , Hristov D , Fahimian B 
Published: July 2016

Purpose:The integration of couch motion during arc delivery is necessitated to enable irradiation trajectories such as coronal arcs, and to enhance the geometrical sampling for dynamic deliveries to the highest extent. To enable such capability, a platform of Trajectory Modulated Arc Therapy (TMAT) is developed in conjunction with standardized noncollisional dynamic path‐set for irradiation of intracranial lesions.Methods:A generalized path‐set was constructed through the combination of sagittal arcs (45 degrees from the CAX), axial arcs, and coronal arcs produced through modulation of the dynamic rotation of couch. The standardized path was implemented in a contiguous manner enabling the formation of fully automated sub‐trajectories to provide maximal geometrical convergence with minimal number of arcs. Progressive sampling technique is used for direct aperture optimization of the MLCs and the selection of couch positions across the control points. Dosimetry of the resulting plans was assessed relative to clinically delivered plans. Using the TrueBeam Developer Mode, plan deliverability was tested.Results:Treatment planning of TMAT sub‐trajectories for central, anterior and posterior tumor sites with volumes ranging from 4.75cc to 107cc demonstrated radically reduced doses to the critical OARs when compared to the clinically treated VMAT. Specifically, percentage reduction in mean dose for critical organs such as brainstem, cochlea, and optic nerve are found to be as low as 74±15%, 50±26% and 74±30% respectively as compared to VMAT. Conformity Index, defined as the ratio of tumor volume (VPTV) and 100% dose volume (V(D100%)), was reduced up to 12% while the Gradient Index, defined as V(D100%)/V(D50%), was concurrently improved by up to 14%.Conclusion:An automated standardized trajectory with dynamically modulated couch‐gantry arcs has been developed for intracranial radiotherapy. Through the incorporation of coronal arcs, it is demonstrated that significantly reduced OAR doses can be achieved relative to clinically treated patient plans via VMAT.Research Grant Funding Support by Varian Medical Systems
SU‐F‐T‐505: A Novel Approach for Sparing Critical Organs at Risk for Cancer Patients Undergoing Radiation Oncology Treatments
Authors: Lavvafi H , Pourriahi M , Elahinia H , Elahinia M , Parsai E 
Published: July 2016

Purpose:A major goal of an effective radiation treatment plan is to deliver the maximum dose to the tumor while minimizing radiation exposure to the surrounding normal structures. For example, due to the radiation exposure to neighboring critical structures during prostate cancer treatment, a significant increase in cancer risk was observed for the bladder (77%) and the rectum (105%) over the following decade. Consequently, an effective treatment plan necessitates limiting the exposure to such organs which can best be achieved by physically displacing the organ at‐risk. The goal of this study is to present a prototype for an organ re‐positioner device designed and fabricated to physically move the rectum away from the path of radiation beam during external beam and brachytherapy treatments. This device affords patient comfort and provides a fully controlled motion to safely relocate the rectum during treatment.Methods:The NiTi shape memory alloy was designed and optimized for manufacturing a rectal re‐positioner device through cooling and heating the core alloy for its shaping. This has been achieved through a prototyped custom designed electronic circuit in order to induce the reversible austenitic transformation and was tested rigorously to ensure the integrity of the actuated motion in displacement of the target anatomy.Results:The desirable NiTi shape‐setting was configured for easy insertion and based on anatomical constraint. When the final prototype was evaluated, accuracy and precision of the maximum displacement and temperature changes revealed that the device could safely be used within the target anatomy.Conclusion:The organ re‐positioner device is a promising tool that can be implemented in clinical setting. It provides a controlled and safe displacement of the delicate organ(s) at risk. The location of the organ being treated could also be identified using conventional onboard imaging devices or MV imaging available on‐board most modern clinical accelerators.
SU‐F‐T‐509: Investigation into the Impact of the Linear Accelerator Treatment Table On Skin Dose to Prone Breast Patients
Authors: Pedersen K , Irwin J , Sansourekidou P , Kriminski S , Pavord D 
Published: July 2016

Purpose:To investigate the impact of the treatment table on skin dose for prone breast patients for which the breast contacts the table and to develop a method to decrease skin dose.Methods:We used 12cm stack of 15cmx15cm solid water slabs to imitate breast. Calibrated EBT3 radiochromic film was affixed to the bottom of the phantom. Treatments for 32 patients were analyzed to determine typical prone breast beam parameters. Based on the analysis, a field size and a range of gantry angles were chosen for the test beams. Three experimental setups were used. The first represented the patient setup currently used in our clinics with the phantom directly on the table. The second was the skin sparing setup, with a 1.5cm Styrofoam slab between the phantom and the table. The third used a 7.5cm Styrofoam slab to examine the extent of skin sparing potential. The calibration curve was applied to each film to determine dose. Percent difference in dose between the current and skin sparing setups was calculated for each gantry angle and gantry angle pair.Results:Data showed that beams entering through the table showed a skin dose decrease ranging from 13%–30% with the addition of 7.5cm Styrofoam, while beams exiting through the table showed no significant difference. The addition of 1.5cm Styrofoam resulted in differences ranging from 0.5%–13% with the skin sparing setup.Conclusion:The results demonstrate that skin in contact with the table receives increased dose from beams entering through the table. By creating separation between the breast and the table with Styrofoam the skin dose can be lowered, but 1.5 cm did not fully mitigate the effect. Further investigation will be performed to identify a clinically practical thickness that maximizes this mitigation.
SU‐F‐T‐510: Single Isocenter Radiosurgery for the Simultaneous Treatment of Multiple Brain Metastases: Volumetric Modulated Arc Therapy Or Dynamic Conformal Arc?
Authors: Maurer J , Sintay B , Manning M , Wiant D , Liu H 
Published: July 2016

Purpose:This study evaluates a novel algorithm that can be used with any treatment planning system for simple and rapid generation of stereotactic radiosurgery (SRS) plans for treating multiple brain metastases using a single isocenter dynamic conformal arc (DCA) approach. This technique is compared with a single isocenter volumetric modulated arc therapy (VMAT) technique in terms of delivery time, conformity, low dose spread and delivery accuracy.Methods:Five patients, with a total of 37 (5 – 11) targets were planned using a previously published method for generating optimal VMAT plans and using the proposed DCA algorithm. All planning target volumes (PTVs) were planned to 20 Gy, meeting a minimum 99% coverage and maximum 135 % hot spot for both techniques. Quality assurance was performed using radiochromic film, with films placed in the high dose regions of each PTV. Normal tissue volumes receiving 12 Gy and 6 Gy (V12 and V6) were computed for each plan. Conformity index (CI) and gamma evaluations (95% of points passing 4%/0.5mm) were computed for each PTV.Results:Delivery times, including beam on and table rotation times, were comparable: 17 – 22 minutes for all deliveries. V12s for DCA plans were (18.5±15.2 cc) vs. VMAT (19.7±14.4 cc). V6s were significantly lower for DCA (69.0±52.0 cc) compared with VMAT (154.0±91.0 cc) (p <<0.05). CIs for VMAT targets were (1.38±0.50) vs. DCA (1.61±0.41). 36 of 37 DCA planned targets passed gamma tests, while 29 of 37 VMAT planned targets passed.Conclusion:Single isocenter DCA plans were easily achieved. The evaluation suggests that DCA may represent a favorable technique compared with VMAT for multiple target SRS by reducing dose to normal tissue and more accurately depicting deliverable dose.
SU‐F‐T‐514: Evaluation of the Accuracy of Free‐Breathing and Deep Inspiration Breath‐Hold Gated Beam Delivery Using An Elekta Linac
Authors: Jermoumi M , Xie R , Cao D , Housley D , Shepard D 
Published: July 2016

Purpose:In this study, we evaluated the performance of an Elekta linac in the delivery of gated radiotherapy. We examined whether the use of either a short gating window or a long beam hold impacts the accuracy of the deliveryMethods:The performance of an Elekta linac in the delivery of gated radiotherapy was assessed using a 20cmX 20cm open field with the radiation delivered using a range of beam‐on and beam‐off time periods. Two SBRT plans were used to examine the accuracy of gated beam delivery for clinical treatment plans. For the SBRT cases, tests were performed for both free‐breathing based gating and for gated delivery with a simulated breath‐hold. A MatriXX 2D ion chamber array was used for data collection, and the gating accuracy was evaluated using gamma score.Results:For the 20cmX20cm open field, the gated beam delivery agreed closely with the non‐gated delivery results. Discrepancies in the agreement, however, began to appear with a 5‐to‐1 ratio of the beam‐off to beam‐on. For these tight gating windows, each beam‐on segment delivered a small number of monitor units. This finding was confirmed with dose distribution analysis from the delivery of the two VMAT plans where the gamma score(±1%,2%/1mm) showed passing rates in the range of 95% to 100% for gating windows of 25%, 38%, 50%, 63%, 75%, and 83%. Using a simulated sinusoidal breathing signal with a 4 second period, the gamma score of freebreathing gating and breath‐hold gating deliveries were measured in the range of 95.7% to 100%.Conclusion:The results demonstrate that Elekta linacs can be used to accurately deliver respiratory gated treatments for both free‐breathing and breath‐hold patients. The accuracy of beams delivered in a gated delivery mode at low small MU proved higher than similar deliveries performed in a non‐gated (manually interrupted) fashion.
SU‐F‐T‐516: Effects of Inter‐Fraction Organ Displacement/deformation On the Delivered Doses to the Heart, Esophagus, and Lungs in Patients Receiving Thoracic Radiotherapy
Authors: Hammers J , Matney J , Kaidar‐Person O , Zagar T , Marks L , Das S , Mavroidis P 
Published: July 2016

Purpose:To quantitatively assess the effects of inter‐fraction changes in organ shape and location on the delivered dose distribution to the organs at risk (OAR) in lung cancer patients.Methods:This study analyzes treatment data of 10 patients, who were treated to 60Gy in 30 fractions. In each fraction a cone beam CT (CBCT) was acquired. Each CBCT was registered with the planning CT using deformable registration tools within MIM Software. The daily setup shifts were used to translate the planned dose distribution on the deformed planning CT. The structures of lungs, esophagus and heart were re‐delineated by a physician on each CBCT. The doses delivered to each OAR, reflecting changes in the position and shape variations, were recomputed. Resultant daily dose volume histograms (DVHs) for OARs were computed and compared to those from the planning CT.Results:Based on the findings of two patients and 24 CBCTs analyzed so far, higher doses are delivered to the lungs and esophagus compared to the treatment plan. The dose differences per fraction between the delivered doses and those in the treatment plan are: for patient 1, lung mean dose = 5.3±1.3cGy and esophagus mean dose = 3.4±3.5cGy. For patient 2, lung mean dose = 12.0±3.9cGy and esophagus mean dose = 34.2±7.5cGy. Regarding the maximum dose to heart, the results varied (−18.9±22.0cGy for patient1 and 53.0±62.2cGy for patient2).Conclusion:The dosimetric effects of inter‐fractional anatomical variations could be estimated using deformable image registration and manual organ segmentation for each CBCT. A considerable dose distribution variation between fractions was observed for the OARs. These changes are currently not taken into account while treating the patients and these may explain cases with severe side effects even when the treatment plan looks satisfactory. These results suggest the need for automated daily dose tracking and accumulation.
SU‐F‐T‐517: Determining the Tissue Equivalence of a Brass Mesh Bolus in a Reconstructed Chest Wall Irradiation
Authors: Shekel E , Epstein D , Levin D 
Published: July 2016

Purpose:To determine the tissue equivalence of a brass mesh bolus (RPD) in the setting of a reconstructed chest wall irradiationMethods:We measured breast skin dose delivered by a tangential field plan on an anthropomorphic phantom using Mosfet and nanoDot (Landauer) dosimeters in five different locations on the breast. We also measured skin dose using no bolus, 5mm and 10 mm superflab bolus. In the Eclipse treatment planning system (Varian, Palo Alto, CA) we calculated skin dose for different bolus thicknesses, ranging from 0 to 10 mm, in order to evaluate which calculation best matches the brass mesh measurements, as the brass mesh cannot be simulated due to artefacts.Finally, we measured depth dose behavior with the brass mesh bolus to verify that the bolus does not affect the dose to the breast itself beyond the build‐up region.Results:Mosfet and nanoDot measurements were consistent with each other.As expected, skin dose measurements with no bolus had the least agreement with Eclipse calculation, while measurements for 5 and 10 mm agreed well with the calculation despite the difficulty in conforming superflab bolus to the breast contour. For the brass mesh the best agreement was for 3 mm bolus Eclipse calculation. For Mosfets, the average measurement was 90.8% of the expected dose, and for nanoDots 88.33% compared to 83.34%, 88.64% and 93.94% (2,3 and 5 mm bolus calculation respectively).The brass mesh bolus increased skin dose by approximately 25% but there was no dose increase beyond the build‐up region.Conclusion:Brass mesh bolus is most equivalent to a 3 mm bolus, and does not affect the dose beyond the build‐up region. The brass mesh cannot be directly calculated in Eclipse, hence a 3mm bolus calculation is a good reflection of the dose response to the brass mesh bolus.
SU‐F‐T‐530: Characterization of a 60‐Leaf Motorized MLC Designed for Cobalt‐60 Units
Authors: Xu L , Smith L , Ciresianu A 
Published: July 2016

Purpose:In a continuing effort to improve conformal radiation therapy with Cobalt‐60 units, a 60‐leaf MLC was designed, manufactured, and released to market. This work describes the physics measurements taken to characterize the clinical performance of this MLC.Methods:A 60 leaf MLC was custom designed with tungsten leaves of 4.5 cm height, single focused, achieving field size of 30×30 cm^2 when mounted on a 100cm SAD Cobalt‐60 unit. Leakage and output factor measurements were performed using a single ion chamber in a solid water phantom. Penumbra and surface dose were measured using scanning chambers and diodes in a water phantom. Radiation‐light coincidence measurements were performed using radiographic films.Results:With MLC mounted, measured penumbras at all depths are smaller than with jaws only. Surface doses were not significantly affected by the presence of MLC, and remained below values recommended by regulatory bodies. Light‐radiation coincidences were found to be better than 3 mm for all field sizes. Leakage through the MLC was found to be strongly dependent on field size, increasing from 1.0 % for a 10×10 cm field to 2.0% for a 30×30 cm field. Such results meet the requirements of IEC 60601‐2‐11. The MLC was found to have significant influence on the output factor, when field size defined by MLC is significantly smaller than field size defined by jaws. Such effect is also observed on linear accelerators, but it is more pronounced on Cobalt‐60 units. A 10×10 “diamond” MLC shape inside a 14×14 cm jaw showed output factor that is 5.7% higher than 10×10 cm field defined by matching MLC and jaws.Conclusion:The MLC offers clinically acceptable performance in penumbra, surface dose, and light‐radiation coincidence. Several units of this MLC have recently been installed and used clinically. Validation of Cobalt‐60 based IMRT with this MLC is ongoing.The authors are employees of Best Theratrnics Ltd.
SU‐F‐T‐533: Study of Dosimetric Properties of Cadmium Free Alloy Used in Compensator Based IMRT
Authors: Tyagi A , Kaushik S , Punia R , Singh M 
Published: July 2016

Purpose:To study the dosimetric properties of cadmium free alloy which is used in compensator based IMRT.Methods:A mixture of 30% of lead,52% of bismuth and 18% of tin was used to prepare alloy. We prepared slabs of different thicknesses ranging from 0.71 cm to 6.14 cm. Density of alloy was measured by Archimedes’ principle using SI‐234 Denver instrument and water as buoyant liquid. Transmission, linear attenuation coefficient (µ), tissue phantom ration (TPR), beam hardening, surface dose (Ds), percentage depth dose (PDD) and effect of scatter were measured and analyze for different field size and different thickness of compensator for 6 MV photon beam. Measurements were carried out at 100 cm SSD and 160 cm SSD.Results:Density of alloy was found to be 9.5456 gm/cm3. Melting point of alloy is 90–95 °C. For a field size of 10×10 cm2 µ was 0.4253 cm‐1 at 100 cm SSD. Calculated TPR was found to be within 3 % of measured TPR. Ds was found to be decreasing with increasing thickness of compensator. 1cm, 1.98 cm and 4.16 cm thick compensator slab decreased surface dose by 4.2%, 6.1% and 9.5% respectively for a field size of 10×10cm2 at 100 cm SSD. As field size increases Ds increases for a given compensator thickness. This is due to increase in amount of scattered dose from wider collimator opening. For smaller field size, PDDs are increased from 3.0% to 5.5% of open beam PDDs as compensator thickness increases from 1 cm to 6.14 cm at a depth of 10 cm in water. For larger field size variation in PDDs is not significant.Conclusion:High degree of modulation can be achieved from this compensator material, which is essential in compensator based IMRT. Dosimetric properties analyzed in this study establish this alloy as a reliable, cost effective, reusable compensator material.
SU‐F‐T‐534: Using Daily Images to Verify Dosimetric Advantage of Dual‐Isocentric Technique for High‐Risk Prostate Cancer Treated with Pelvic Lymph Node
Authors: Cui T , Shang Q , Li W , Vassil A , Xia P 
Published: July 2016

Purpose:To evaluate a dual‐isocentric technique to compensate for the daily independent movements of prostate and pelvic lymph nodes (PLN) of high‐risk prostate cancer patients.Methods:Three patients, who received 78 Gy to the prostate, 66 Gy to the seminal vesicle (SV), and 50.4 Gy to the PLN in 39 fractions under CT‐on‐rail (CTOR) imaging guidance, were retrospectively selected. Each patient was planned with volumetric modulated arc therapy (VMAT) techniques using (1) single isocenter with a 6 mm margin except 4 mm posteriorly (6/4 mm), to the prostate‐CTV and a uniform 5 mm margin to the PLN‐CTV, and (2) two isocenters, located at the centroids of the prostate or the PLN, with a 5/3 mm margin to the prostate‐CTV and a 5 mm uniform margin to the PLN‐CTV. Both plans met the established clinical guidelines, and were subsequently applied to the daily CTOR images, where prostate, SV, rectum and bladder were contoured by the same physician. On each of 117 CTOR images, two plans were created by registering only the bony anatomy for the single‐isocentric one, or by registering both the bony anatomy and the prostate for the dual‐isocentric one. These plans were then compared based on V78Gy of prostate‐CTV, V66Gy of SV‐CTV, and V50.4Gy of PLN‐CTV. The paired Student's t‐test was performed to test for significance.Results:The V78Gy of prostate‐CTV in the dual‐isocentric plans from 117 CTOR images was 99.32±0.89%, significantly (p<0.01) better than that in the single‐isocentric ones (98.29±2.11%). Both V66Gy of SV‐CTV and V50.4Gy of PLN‐CTV were increased from 99.15±3.28% and 99.38±0.74% in the dual‐isocentric plans to 99.31±2.02% and 99.48±0.90% in the single‐isocentric ones, respectively, but neither were statistically significant (p=0.47 and 0.34).Conclusion:By targeting prostate and PLN accordingly in the daily verification images, the dosimetric advantage of dual‐isocentric technique is verified even with a reduced margin.
SU‐F‐T‐537: Prone Breast Accelerated Partial Breast Irradiation Using Non‐Coplanar Volumetric Arc Therapy
Authors: Beninati G , Barbiere J , Godfrey L , Ndlovu A 
Published: July 2016

Purpose:To demonstrate that Volumetric Modulated Arc Therapy (VMAT) can be an alternative technique to Brachytherapy Accelerated Partial Breast Irradiation (APBI) for treating large breasted women. The non‐coplanar VMAT technique uses a commercially available couch and a small number of angles. This technique with the patient in the prone position can reduce high skin and critical structure doses in large breasted women, which are usually associated with Brachytherapy APBI.Methods:Philips Pinnacle treatment planning system with Smart Arc was used to plan a left sided laterally located excision cavity on a standard prone breast patient setup. Three thirty‐degree arcs entered from the lateral side at respective couch angles of 345, 0, and 15 degrees. A fourth thirty degree arc beam entered from the medial side at a couch angle of 0 degrees. The arcs were selected to avoid critical structures as much as possible. A test run was then performed to verify that the beams did not collide with the patient nor support structures. NSABP B‐39/RTOG 0413 protocol guidelines were used for dose prescription, normal tissue, and target definition.Results:Dose Volume Histogram analysis indicated that all parameters were equal or better than RTOG recommendations. Of particular note regarding the plan quality:1.(a) For a prescribed dose of 3850cGy the PTV‐EVAL target volume receiving 100 percent of the dose(V100) was 93; protocol recommendation is V90 > 90 percent. (b) Maximum dose was 110 percent versus the allowed 120 percent .2. Uninvolved percentage of normal breast V100 and V50 were 17 and 47 versus allowed 35 and 60 percent respectively.3. For the skin, V100 was 5.7cc and the max dose to 0.1 cc was 4190cGy.Conclusion:Prone Breast non‐coplanar VMAT APBI can achieve better skin cosmesis and lower critical structure doses than Brachytherapy APBI.