bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐558: ArcCheck for Patient Specific QA in Stereotactic AblativeRadiotherapy
Authors: Ramachandran P , Tajaldeen A , Taylor D , Wanigaratne D , Roozen K , Esen N , Geso M , Kron T 
Published: July 2016

Purpose:Stereotactic Ablative Radiotherapy (SABR) is one of the most preferred treatment techniques for early stage lung cancer. This technique has been extended to other treatment sites like Spine, Liver, Scapula, Sternum etc., This has resulted in increased physics QA time on machine. In this study, we've tested the feasibility of using ArcCheck as an alternative method to replace film dosimetry.Methods:Twelve patients with varied diagnosis of Lung, Liver, scapula, sternum and Spine undergoing SABR were selected for this study. Pre‐treatment QA was performed for all the patients which include ionization chamber and film dosimetry. The required gamma criteria for each SABR plan to pass QA and proceed to treatment is 95% (3%,1mm). In addition to this routine process, the treatment plans were exported on to an ArcCheck phantom. The planned and measured dose from the ArcCheck device were compared using four different gamma criteria: 2%,2 mm, 3%,2 mm, 3%,1 mm and 3%, 3 mm. In addition to this, we've also introduced errors to gantry, collimator and couch angle to assess sensitivity of the ArcCheck with potential delivery errors.Results:The ArcCheck mean passing rates for all twelve cases were 76.1%±9.7% for gamma criteria 3%,1 mm, 89.5%±5.3% for 2%,2 mm, 92.6%±4.2% for 3%,2 mm, and 97.6%±2.4% for 3%,3 mm gamma criteria. When SABR spine cases are excluded, we observe ArcCheck passing rates higher than 95% for all the studied cases with 3%, 3mm, and ArcCheck results in acceptable agreement with the film gamma results.Conclusion:Our ArcCheck results at 3%, 3 mm were found to correlate well with our non‐SABR spine routine patient specific QA results (3%,1 mm). We observed significant reduction in QA time on using ArcCheck for SABR QA. This study shows that ArcCheck could replace film dosimetry for all sites except SABR spine.
SU‐F‐T‐560: Measurement of Dose Blurring Effect Due to Respiratory Motion for Lung Stereotactic Body Radiation Therapy (SBRT) Using Monte Carlo Based Calculation Algorithm
Authors: Badkul R , Pokhrel D , Ramanjappa T , Jiang H , Lominska C , Wang F 
Published: July 2016

Purpose:Intra‐fractional tumor motion due to respiration may potentially compromise dose delivery for SBRT of lung tumors. Even sufficient margins are used to ensure there is no geometric miss of target volume, there is potential dose blurring effect may present due to motion and could impact the tumor coverage if motions are larger. In this study we investigated dose blurring effect of open fields as well as Lung SBRT patients planned using 2 non‐coplanar dynamic conformal arcs(NCDCA) and few conformal beams(CB) calculated with Monte Carlo (MC) based algorithm utilizing phantom with 2D‐diode array(MapCheck) and ion‐chamber.Methods:SBRT lung patients were planned on Brainlab‐iPlan system using 4D‐CT scan and ITV were contoured on MIP image set and verified on all breathing phase image sets to account for breathing motion and then 5mm margin was applied to generate PTV. Plans were created using two NCDCA and 4‐5 CB 6MV photon calculated using XVMC MC‐algorithm. 3 SBRT patients plans were transferred to phantom with MapCheck and 0.125cc ion‐chamber inserted in the middle of phantom to calculate dose. Also open field 3×3, 5×5 and 10×10 were calculated on this phantom. Phantom was placed on motion platform with varying motion from 5, 10, 20 and 30 mm with duty cycle of 4 second. Measurements were carried out for open fields as well 3 patients plans at static and various degree of motions. MapCheck planar dose and ion‐chamber reading were collected and compared with static measurements and computed values to evaluate the dosimetric effect on tumor coverage due to motion.Results:To eliminate complexity of patients plan 3 simple open fields were also measured to see the dose blurring effect with the introduction of motion. All motion measured ionchamber values were normalized to corresponding static value. For open fields 5×5 and 10×10 normalized central axis ion‐chamber values were 1.00 for all motions but for 3×3 they were 1 up to 10mm motion and 0.97 and 0.87 for 20 and 30mm motion respectively. For SBRT plans central axis dose values were within 1% upto 10mm motions but decreased to average of 5% for 20mm and 8% for 30mm motion. Mapcheck comparison with static showed penumbra enlargement due to motion blurring at the edges of the field for 3×3,5×5,10×10 pass rates were 88% to 12%, 100% to 43% and 100% to 63% respectively as motion increased from 5 to 30mm. For SBRT plans MapCheck mean pass rate were decreased from 73.8% to 39.5% as motion increased from 5mm to 30mm.Conclusion:Dose blurring effect has been seen in open fields as well as SBRT lung plans using NCDCA with CB which worsens with increasing respiratory motion and decreasing field size(tumor size). To reduce this effect larger margins and appropriate motion reduction techniques should be utilized.
SU‐F‐T‐561: Energy Dependence of a Scintillation Detector
Authors: Volotskova O , Xu A , Jozsef G 
Published: July 2016

Purpose:To investigate the response and dose rate dependence of a scintillation detector over a wide energy range.Methods:The energy dependence of W1 scintillation detector was tested with: 1) 50–225 keV beams generated by an animal irradiator, 2) a Leksell Gamma Knife Perfexion Co‐60 source, 3) 6MV, 6FFF, 10FFF and 15MV photon beams, and 4) 6–20MeV electron beams from a linac. Calibrated linac beams were used to deliver 100 cGy to the detector at dmax in water under reference conditions. The gamma‐knife measurement was performed in solid water (100 cGy with 16mm collimator). The low energy beams were calibrated with an ion chamber in air (TG‐61), and the scintillation detector was placed at the same location as the ionization chamber during calibration. For the linac photon and electron beams, dose rate dependence was tested for 100–2400 and 100–800 MU/min.Results:The scintillation detector demonstrated strong energy dependence in the range of 50–225keV. The measured values were lower than the delivered dose and increased as the energy increased. Therapeutic photon beams showed energy independence with variations less than 1%. Therapeutic electron beams displayed the same sensitivity of ∼2–3% at their corresponding dmax depths. The change in dose‐rate of photon and electron beams within the therapeutic energy range did not affect detector output (<0.5%). Measurements acquired with the gamma knife showed that the output data agreed with the delivered dose up to 3%.Conclusion:W1 scintillation detector output has a strong energy dependence in the diagnostic and orthovoltage energy range. Therapeutic photon beams exhibited energy independence with no observable dose‐rate dependence. This study may aid in the implementation of a scintillation detector in QA programs by providing energy calibration factors.
SU‐F‐T‐623: Dosimetric and Radiobiological Comparison of Conventional and Monte Carlo Treatment Plans of Lung Tumors Using SBRT
Authors: Stathakis S , Mavroidis P , Tuazon B , Defoor D , Kirby N , Papanikolaou N 
Published: July 2016

Purpose:This study aims at estimating the dosimetric differences of Pinnacle and Monte Carlo (MC) calculation algorithms in computing the dose distributions in lung cancer SBRT cases. Furthermore, to interpret the dosimetric findings into expected tissue response rates in order to estimate their clinical impact.Methods:17 patients were studied and for each one, two treatment plans (one from Pinnacle and one MC) were created. The structures that were used for the optimization were: PTV, ipsilateral and contralateral lungs, spinal cord, heart, esophagus and stomach. The same dosimetric constraints were used for both pairs of plans. These dosimetric indices were used for the comparison of the two calculation modalities. Additionally, the TCP and NTCP values of the different targets and organs at risk (OAR) were calculated and compared together with the complicationfree tumor control probability.Results:The proposed plan evaluation shows that the plans by Pinnacle deliver higher doses to the OAR than MC. The same is observed for the PTV (minimum dose and BEUD: 58.3 vs. 55.1Gy, respectively). However, these dosimetric differences are translated to negligible differences in TCP and NTCP.Conclusion:The results of this work indicate that for the fractionation scheme of 18Gy in 3 fractions, the treatment plans in Pinnacle and Monte Carlo show minor differences in the doses to the organs at risk (in all the cases the doses by MC were lower than those calculated by Pinnacle). Those doses are predicted to cause 0.0% of side effects. On the other hand, the findings of the analysis indicate that Pinnacle calculation is shown to deliver higher dose to the PTV than MC. However, the dosimetric differences do not appear to have a measurable impact in the expected TCP rates of the targets.
SU‐F‐T‐624: Dose Sparing to Normal Brain Tissue for Stereotactic Radiosurgery Utilizing Negative Margins
Authors: Baker J , Gibb J , Ailawadi S , Hsia A , Han J , Kim J , Xu Z , Ryu S 
Published: July 2016

Purpose:The volume of normal brain tissue exposed to doses above 12 Gy (V12) strongly predicts the risk of radionecrosis. A negative margin MLC aperture results in fields smaller than the PTV. The aim of this study is to investigate the relationship between V12 and the negative margin MLC while keeping adequate PTV coverage with proper dose normalization.Methods:Spherical PTVs were contoured with a center of mass in the frontal and left temporal lobe ranging in size from 1 cm to 4 cm in diameter. A field arrangement was determined for each PTV location using five dynamic conformal arcs for the frontal PTV and three dynamic conformal arcs for the left temporal PTV. Treatment plans for each PTV were generated using a MLC aperture with a positive margin of 1 mm and dose normalized so that the prescribed 18 Gy covers 95% of the PTV. New plans were generated with MLC aperture margins reduced in 1 mm increments, until the max point dose reached is greater than 200%. The volume of dose outside the PTV to 12, 9 and 5 Gy was analyzed.Results:Depending on the PTV size, the greatest negative margin planned was between −4 mm and −2 mm. Negative margins of −1 mm yielded the lowest significant volumes to all doses. Reductions in V12 in relation to the PTV volumes were between 15% and 31% for PTV sizes of 4 and 1 cm, when compared to the 1 mm positive margin plan.Conclusion:Doses to normal tissue were reduced most with margins of −1 and −2 mm for all PTV sizes. In general the −2 mm margin was minimally superior, so a −1 mm margin can be followed in most circumstances to limit maximum PTV dose.
SU‐F‐T‐626: Intracranial SRS Re‐Treatment Without Acquisition of New CT Images
Authors: Wiant D , Manning M , Liu H , Maurer J , Hayes T , Sintay B 
Published: July 2016

Purpose:Linear accelerator based stereotactic radiosurgery (SRS) for multiple intracranial lesions with frequent surveillance is becoming a popular treatment option. This strategy leads to retreatment with SRS as new lesions arise. Currently, each course of treatment uses magnetic resonance (MR) and computed tomography (CT) images for treatment planning. We propose that new MR images, with course 1 CT images, may be used for future treatment plans with negligible loss of dosimetric accuracy.Methods:Ten patients that received multiple courses of SRS were retrospectively reviewed. The treatment plans and contours from non‐initial courses were copied to the initial CTs and recalculated. Doses metrics for the plans calculated on the initial CTs and later CTs were compared. All CT scans were acquired on a Philips CT scanner with a 600 mm field of view and 1 mm slice thickness (Philips Healthcare, Andover, MA). All targets were planned to 20 Gy and calculated in Eclipse V. 13.6 (Varian, Palo Alto, CA) using analytic anisotropic algorithm with 1 mm calculation grid.Results:Sixteen lesions were evaluated. The mean time between courses was 250 +/− 215 days (range 103–979). The mean target volume was 2.0 +/− 2.9 cc (range 0.1–10.1). The average difference in mean target dose between the two calculations was 0.2 +/− 0.3 Gy (range 0.0 – 1.0). The mean conformity index (CI) was 1.28 +/− 0.14 (range 1.07 – 1.82). The average difference in CI was 0.03 +/− 0.16 (range 0.00 – 0.44). Targets volumes < 0.5 cc showed the largest changes in both metrics.Conclusion:Continued treatment based on initial CT images is feasible. Dose calculation on the initial CT for future treatments provides reasonable dosimetric accuracy. Changes in dose metrics are largest for small volumes, and are likely dominated by partial volume effects in target definition.
SU‐F‐T‐631: Linear Accelerator‐Based Frameless Extracranial Radiosurgery for Treatment of Occipital Neuralgia for Non‐Surgical Candidates
Authors: Denton T , Howe J , Spalding A 
Published: July 2016

Purpose:Occipital neuralgia is a condition wherein pain is transmitted by the occipital nerves. Non‐invasive therapies generally alleviate symptoms; however, persistent or recurring pain may require invasive procedures. Repeated invasive procedures upon failure are considered higher risk and are often contraindicated due to compounding inherent risk. SRS has not been explored as a treatment option largely due to the extracranial nature of the target (as opposed to the similar, more established trigeminal neuralgia), but advances in linear‐accelerator frameless‐based SRS now present an opportunity to evaluate the novel potential of this modality for this application.Methods:Patient presented with severe occipital pain following decompression and fusion of the cervical vertebrae with prior intervention attempted via radiofrequency ablation yielding temporary pain cessation. A 0.6 mm slice spacing CT was obtained for treatment planning, and a cervical spine oriented 1.0 mm slice spacing CT myelogram was obtained for the purpose of defining the targeted C2 occipital dorsal root ganglion (to receive 80 Gy to the isocenter) and spinal cord.Results:The spinal cord was most proximally 12.0 mm from the isocenter receiving a maximum dose of 3.36 Gy, and doses to 0.35 and 1.2 cc of 1.84 Gy and 0.79 Gy, respectively. The brain maximum dose was 2.29 Gy. The treatment was successfully performed with a NovalisTX (Varian) equipped with ExacTrac stereoscopic x‐ray image guidance (BrainLAB). Treatment time was 59 minutes for 18,323 MUs. Imaging was performed prior to each arc delivery resulting in twenty‐one imaging sessions (twelve requiring positional corrections with the remaining verified within tolerance). The average deviation magnitude requiring a positional or rotational correction was 0.96±0.25 mm, 0.8±0.41° while the average deviation magnitude deemed within tolerance was 0.41±0.12 mm, 0.57±0.28°.Conclusion:Linear accelerator‐based frameless radiosurgery provides an accurate, non‐invasive alternative for treating occipital neuralgia where an invasive procedure is contraindicated.
SU‐F‐T‐633: Cyberknife Boost Versus Conventional Tandem and Ovoid Treatment for Cervical Cancer
Authors: Santoro J , Witten M , Haas J 
Published: July 2016

Purpose:Brachytherapy has been the standard of care for cervical cancer for 100 years. The treatment can be administered using an HDR (high dose rate) remote afterloader with a 192Ir source in an outpatient setting, a PDR afterloader with a 192Ir source, or with LDR manually loaded or a remote afterloader utilizing 192Ir or 137Cs sources in an inpatient setting. The procedure involves the placement of a tandem and ovoid, tandem and ring, or tandem and cylinder applicator in an operating room setting with the patient under general anesthesia. Inaccuracies introduced into the process occurring between placement of the applicator and actual delivery can introduce uncertainty into the actual dose delivered to the tumor and critical organs. In this study we seek to investigate the dosimetric difference between an SBRT‐based radiotherapy boost and conventional Brachytherapy in treating cervical cancer.Methods:Five HDR tandem and ovoid patients were planned using the Brachyvision treatment planning system and treated in four fractions using the Varian Varisource afterloader (Varian Medical Systems). For the same cohort, the patient planning CTs were imported into Multiplan (Accuray Inc) and a dose/fractionation‐equivalent CyberKnife SBRT plan was retrospectively generated. Dosimetric quantities such as target/CTV D90, V90, D2cc for rectum, bladder, and bowel were measured and compared between the two modalities.Results:The CTV D90 for the tandem and ovoid was 2540cGy (90.7%) and 3009cGy (107.5%) for the CyberKnife plan. The D2cc for the rectum, bladder, and bowel were 1576cGy, 1641cGy, and 996cGy for the tandem and ovoid and 1374cGy, 1564cGy, and 1547cGy for CyberKnife.Conclusion:The D2cc doses to critical structures are comparable in both modalities. The CTV coverage is far superior for the CyberKnife plan. The dose distribution for CyberKnife has the advantage of increased conformality and lower maximum CTV dose.
SU‐F‐T‐636: Comprehensive Approach to Motion Assessment for Liver and Pancreas SBRT Patients
Authors: Halvorsen P , Iftimia I , Hunter K 
Published: July 2016

Purpose:Our past practice for liver and pancreas SBRT consisted of free breathing (FB) with gated treatment delivery using a 30‐70% phase window. We have recently adopted an assessment method leading to individualized motion management to minimize target motion. We present our results from 47 patients treated with this new approach.Methods:We perform an initial patient coaching and assessment session in our conventional simulator suite to observe the motion of the implanted fiducials with FB anterior and lateral 20‐second cine acquisitions. The physician decides whether to attempt inhale or exhale breath‐hold (BH). The patient is coached while observing with cine to ascertain their ability to achieve the desired BH mode for long periods as needed for treatment delivery. If the patient cannot comply, a FB approach is adopted using gating or simple ITV method (for patients without fiducials). After achieving a patient‐specific motion management mode, we perform CT‐simulation using the Varian RPM system to reproduce the chosen mode and record a reference session for treatment delivery. For pre‐treatment imaging, the fiducials are observed under fluoro while coaching the patient.Results:Of 47 SBRT cases analyzed, 32 were liver and 15 were pancreas. The chosen techniques were: 32 exhale BH (12 with abdominal compression), 7 FB gated, 4 inhale BH, and 4 FB ITV. Maximum fiducial motion amplitude was 5 mm for the FB gated patients, and less than 5 mm for all BH patients with most able to achieve a maximum amplitude of 3 mm.Conclusion:This study showed that an individualized motion management approach can reduce the target volume and, therefore, the volume of irradiated healthy tissue from liver or pancreas SBRT. Effective coaching is essential in achieving consistent BH with 3 mm amplitude. The fluoro/cine session is helpful in establishing the right coaching approach for each patient.
SU‐F‐T‐642: Sub Millimeter Accurate Setup of More Than Three Vertebrae in Spinal SBRT with 6D Couch
Authors: Wang X , Zhao Z , Yang J , Yang J , McAleer M , Brown P , Li J , Ghia A 
Published: July 2016

Purpose:To assess the initial setup accuracy in treating more than 3 vertebral body levels in spinal SBRT using a 6D couch.Methods:We retrospectively analyzed last 20 spinal SBRT patients (4 cervical, 9 thoracic, 7 lumbar/sacrum) treated in our clinic. These patients in customized immobilization device were treated in 1 or 3 fractions. Initial setup used ExacTrac and Brainlab 6D couch to align target within 1 mm and 1 degree, following by a cone beam CT (CBCT) for verification. Our current standard practice allows treating a maximum of three continuous vertebrae. Here we assess the possibility to achieve sub millimeter setup accuracy for more than three vertebrae by examining the residual error in every slice of CBCT. The CBCT had a range of 17.5 cm, which covered 5 to 9 continuous vertebrae depending on the patient and target location. In the study, CBCT from the 1st fraction treatment was rigidly registered with the planning CT in Pinnacle. The residual setup error of a vertebra was determined by expanding the vertebra contour on the planning CT to be large enough to enclose the corresponding vertebra on CBCT. The margin of the expansion was considered as setup error.Results:Out of the 20 patients analyzed, initial setup accuracy can be achieved within 1 mm for a span of 5 or more vertebrae starting from T2 vertebra to inferior vertebra levels. 2 cervical and 2 upper thoracic patients showed the cervical spine was difficult to achieve sub millimeter accuracy for multi levels without a customized immobilization headrest.Conclusion:If the curvature of spinal columns can be reproduced in customized immobilization device during treatment as simulation, multiple continuous vertebrae can be setup within 1 mm with the use of a 6D couch.
SU‐F‐T‐644: Reproducibility of Target Position Using Moderate Voluntary Breath‐ Hold During Liver Stereotactic Ablative Radiotherapy
Authors: Cui G , Trakul N , Chang E , Shiu A 
Published: July 2016

Purpose:To evaluate the reproducibility of target position using moderate voluntary breath‐hold during liver stereotactic ablative radiotherapy (SABR).Methods:Two patients who underwent liver SABR on a Varian TrueBeam STx linac were used for this study. Fiducial markers were placed in and around the target in the liver as surrogates for the target position and motion. GTVs were contoured by assessing tumor extent on contrast enhanced CT. The PTV was created from the GTV by adding 2 mm margins to account for the residual motion during breath‐holds. A portable biofeedback system was used to facilitate the breath‐hold to a reproducible position. The Varian RPM system was used for gating the linac. Proceeding each treatment, orthogonal kV pairs were taken, and alignment to nearby bony anatomy was performed. Then the breath‐hold CBCT was acquired to align the fiducial markers. On‐line fluoroscopy was used to fine‐tune the breath‐hold gating thresholds to correlate with the positions of the fiducial markers. The inter‐fraction reproducibility of the target was evaluated by the offsets of the daily breath‐hold CBCTs from the paired kV matches as a direct measure of the target position relative to the bony anatomy. The intra‐fraction reproducibility of the target position was assessed by the gated window of the RPM marker block for each fraction.Results:The absolute mean offsets between the CBCT and paired kV matches in the vertical, longitudinal, and lateral directions were 0.06 cm, 0.10 cm, and 0.06 cm for patient 1, and 0.37 cm, 0.62 cm, and 0.09 cm for patient 2. The gated window of the RPM marker block for the breath‐hold for each fraction was within 0.63 ± 0.16 cm and 0.59 ± 0.12 cm for patients 1 and 2, respectively.Conclusion:Moderate voluntary breath‐hold showed good inter‐ and intra‐fraction reproducibility of target position during liver SABR.