bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐408: Dosimetric Effect of Intrafraction Motion in Spine SRS: A Retrospective Study
Authors: Schulze D , Yan D , Grills I , Jawad MS , Wloch J , Martin S , Zhou J
Published: July 2013

Purpose: To investigate the dosimetric consequence of intrafraction motion in stereotactic radiosurgery (SRS) to the spine. Methods: Post‐treatment CBCT registration results from 103 spine SRS cases were used as surrogates to analyze the scale of intrafraction motion. For only those cases with motion vectors greater than the 2 mm planning margin (subgroup, n=20), dose was re‐calculated in the TPS assuming a worst case scenario where the entire treatment was delivered in the post‐treatment position. Dosimetric data was evaluated only for subgroup patients. DVH parameters, including PTV V100%, V90%, D99%, D80%, and maximum cord dose in equivalent dose of 2 Gy (EQD2_cord, α/β=2 Gy) were compared with those in the original plans. The correlations between DVH differences, treatment time, and motion distance were calculated. RESULTS: The intrafraction motions for all cases and the subgroup were 1.3±1.2 mm and 3.1±1.4 mm, respectively, with a max of 6.5 mm. In the subgroup, the re‐calculated PTV V100%, V90%, D99% and D80% values were significantly less than in the original plan: 78.6%, 90.6%, 60.2%, and 99.6% vs. 83.2%, 92.8%, 66.3%, and 102.2%, respectively (paired t‐tests, p<0.01). The corresponding differences were significantly correlated to motion distances, with V100% the best correlated parameter (R=0.834 and R2=0.695, p<0.01). The subgroup maximum EQD2_cord dose in the re‐calculated vs. original plans was 11.7±5.3 Gy vs. 10.4±4.4 Gy (p=0.14), with one case violating in‐house criteria. For all patients, the mean treatment time was 31.8±12.9 minutes, and no significant correlation was found between total treatment time and motion distance (R=−0.12, p=0.23). CONCLUSION: Intrafraction motion in spine SRS patients can cause significant deviations from planned tumor dose proportional to the motion magnitude. Since local failure is significantly correlated to PTV coverage, and intrafraction motion may exceed the 2mm PTV margin, intrafraction imaging and motion management could improve spine SRS local failure rates.
SU‐E‐T‐411: Monte Carlo Simulations for Quality Assurance of Varian TrueBeam 10XFFF VMAT SABR Treatments
Authors: Gete E , Bergman A , Duzenli C , Lee R , Viel F , Teke T
Published: July 2013

Purpose: To establish feasibility of performing quality assurance on 10X Flattening Filter Free (FFF) VMAT stereotactic ablative radiotherapy (SABR) treatments on the TrueBeam LINAC with Monte Carlo simulations using vendor‐supplied phase space data. Methods: Monte Carlo simulations were performed with BEAMnrc and DOSXYZnrc using the TrueBeam 10XFFF photon beam phase space data that were made available by the Varian Monte Carlo research team. To establish validity of the phase space, dose calculations in a water phantom for fields ranging from 2×2 cm2 to 40×40 cm2 were performed using DOSXYZnrc. Percent depth doses (PDDs), transverse profiles and output factors were calculated and compared with measurements for all the fields simulated. Monte Carlo simulations of 10XFFF SABR VMAT plans were performed on a homogeneous cylindrical phantom and on the Quasar™ phantom with a lung‐equivalent insert. Simulations were compared with both ion chamber measurement and Eclipse Treatment Planning System (TPS) dose calculations. 3D gamma analysis comparing Monte Carlo and TPS results was performed. Results: Monte Carlo simulations and measured values agreed within 1% and 2% for PDDs and profiles respectively. The agreement between measured and calculated output factors was within 1% including for highly asymmetric fields. These results indicate that the 10XFFF phase space data is sufficiently accurate for use in simulations for quality assurance purposes in radiation therapy. For the VMAT plans the point dose agreement between MC and both measured and TPS calculations was within 1.2%. The 3%, 3mm Gamma test pass rates were 95% and 92% for plans calculated on the homogeneous phantom and on the Quasar phantom respectively. Conclusion: We have demonstrated the feasibility of performing patient specific quality assurance on 10XFFF SABR treatment plans using Monte Carlo simulations of the TrueBeam LINAC. This is the first independent validation on the 10XFFF Varian phase space data presented to date. The work of Tony Teke, Cheryl Duzenli and Ermais Gete has been supported by Varian under a Master Research Agreement.
SU‐E‐T‐416: Targeting Accuracy of a TrueBeam System for Multi‐Lesion Cranial Radiosurgery with Single Isocenter
Authors: Li H , Kim J , Gordon J , Jin J , Huang Y , Chin K , Wen N , Chetty I , Ryu S
Published: July 2013

Purpose: To investigate the targeting accuracy of a Varian TrueBeam System for delivering intracranial radiosurgery to multiple lesions using a single isocenter (ISO). Methods: The study was performed using hidden target (BB) tests along with a MV portal imager (EPID). Six BBs were inserted into a head phantom simulating the locations of multiple metastatic tumors. One BB acted as the common ISO. The distances from the ISO to the other BBs were 2.9 to 7.1 cm. Simulating the actual patient treatment in our clinic, the phantom was immobilized using a BrainLAB U‐shape frame and a head mask. CT image was acquired with 1 mm slice thickness. For a selected couch, gantry and collimator angle combination, a 3×3 cm MLC‐shaped field was created for each BB. The centers of BB and the field were aligned, and the distance from the plan was read out on the DRR. Before shooting the tests, CBCT was used to setup the phantom, and the translational/rotational mismatch was corrected iteratively until less than 1 mm and 0.1 degree respectively. The actual positions of the BBs relative to their corresponding field centers were measured on the portal images. The deviation between the measured and planned BB positions quantifies the geometric targeting error. The test was performed for various couch, gantry and collimator angle combinations (total 88 tests). Results: The mean±SD of the BB position deviations were 0.0±0.4 and 0.2±0.4 mm in the image transverse‐and longitudinal‐direction respectively; and 0.5±0.3 mm for the vector length. Six of 88 BB tests (6.8%) exceeded the vector length of 1 mm with a maximum of 1.2 mm Conclusion: The mechanical targeting accuracy of the TrueBeam System at our institution is acceptable for delivery of intracranial radiosurgery with a single isocenter for treatment of multiple targets. Application of this technique is being investigated.
SU‐E‐T‐417: Registration with and Without the Cranium When Using the ExacTrac System for Frameless Intracranial SRS
Authors: McCabe B , Li J , Yenice K
Published: July 2013

Purpose: To determine if the inclusion or exclusion of the cranium during image registration affects the delivery accuracy when using Brainlab Novalis ExacTrac (ExacTrac) for frameless intracranial SRS. Methods: Tests performed on a Varian TrueBeam™ STX linac with the 6D robotic couch ExacTrac system (0.6‐mm 3D mechanical isocenter accuracy established at acceptance). A head phantom with a 7‐mm dia. steel ball insert was the experimental subject. The hidden target was localized with the Brainlab H&N localizer. 1.5‐cm square fields were planned to treat the hidden target using the Brainlab planning system. The target was initially positioned at isocenter using the ExacTrac IR system. Then, stereoscopic kV images were acquired. The images were registered, using the bony anatomy, to the DRRs in two ways: with and without the cranium. Fifty‐one auto‐registration actions were performed to determine the residual registration uncertainty. Translational and rotational couch shifts were applied. Radiographic film captured the treatment field images at gantry angles of 0°, 90°, 180°, and 270°, and couch rotations of 0°, 45°, and 90°. The experiment was repeated with the cranium digitally removed from the registration using the ROI tool of the ExacTrac software. The treatment field hidden target images were analyzed using RIT113 software. Results: The residual uncertainties of translational and rotational shifts were ±0.13 mm and ±0.13°, respectively. The center of the hidden target was within 1.0 mm of radiation isocenter for all gantry angles and couch rotations (range 0.15 to 1.0 mm) whether the cranium was included or excluded from the registration. However, registration without the cranium produced small but significant improvements in accuracy of treatment delivery based on two‐tailed student t‐test analysis (p = 0.05). Conclusion: Removing the cranium with the ROI tool may help improve the treatment delivery accuracy when using the ExacTrac system for intracranial lesions.
SU‐E‐T‐422: Evaluation of PTV Dose Margins for Lung SBRT On Cyberknife Treatment
Authors: Fan J , Wang L , Jin L , Xu Q , Chen X , Li J , Price R , Ma C
Published: July 2013

Purpose: The purpose of this study is to retrospectively evaluate the PTV margins used on CyberKnife for lung SBRT treatment. Methods: The CyberKnife system uses an active tracking system that models the motion of the target based on information from orthogonal images and the skin markers. Deviations between the model predicted position and the real target position show up when patient breaths irregularly. This discrepancy can be up to 1 cm for some situations. Some previous research suggested that 5 mm or 6 mm PTV margins are needed to cover the target 96∼98% of the time. The CK lung SBRT treatment usually prescribed at 55–70% isodose line (Monte Carlo dose calculation), that means the region covered by the full prescription dose in real delivery will be larger than the planned PTV region when the tracking uncertainty is accounted. This indicates that the PTV margin could be less than 5∼6 mm when the real dose is considered. 20 previous treated lung SBRT patients were examined. The real target location relatives to the model position at that time were extracted and the dose was recalculated based on the real target position using an in‐house developed Monte Carlo program. Results: Analysis of all the CyberKnife 20 patients (94 treatments) showed that by using 2 mm physical PTV margin, the region received full prescription dose was 5.4 mm +/− 1.6mm from the GTV. The planning criteria are 100% GTV volume receives at least 100% prescription dose. By consider the tracking uncertainty, for 2 mm physical PTV margin, 99.5 +/− 0.4% GTV volume still receives at least 100% prescription dose. The maximum dose reduced by about 12% on average. Conclusion: Conclusions: Image tracking log from the CyberKnife indicate that a 5mm margin may be overkill when motion tracking is used.
SU‐E‐T‐423: Effect of X‐Ray Source Spot Size Modeling in AcurosXB Dose Calculation Algorithm On VMAT Based SBRT Treatments
Authors: Kathirvel M , Sai Subramanian VS , Thirumalai Swamy S , Arun G , Jagadheeskumar N , Arivarasan I , Subramani V
Published: July 2013

Purpose: Aim of this study is to evaluate AcurosXB(AXB) dose calculation algorithm dosimetrically with different X‐ray source spot size modeling and its clinical effect on Volumetric Modulated Arc Therapy(VMAT) based Stereotactic Body Radiotherapy(SBRT). Methods: 10 SBRT cases were purposely selected to analyze the effect of source spot size for smaller field size. All the cases were planned in Varian Eclipse(V10.0) treatment planning system(TPS) which uses AXB algorithm for VMAT dose computation. For this study source spot sizes varied from 0.5mm, 1.0mm, 1.5mm and 2.0mm in X as well as Y‐direction in the beam data configuration. SBRT plans were optimized using Progressive Resolution Optimizer III(PRO‐III) and dose was calculated by AXB with different source spot sizes. Plan quality index such as conformity index(CI) and gradient measure for PTV and for normal tissues volume of 90% and 25% prescribed dose were used for analysis. VMAT plans were delivered with Varian Clinac‐iX and 2D‐planner dose was measured using iba iMatrixx 2D array in Multicube phantom. Gamma (3mm/3%) analyses were performed between measured and predicted doses for different spot sizes. Results: Conformity index value for PTV were found to be 1.16±0.21, 1.14±0.20, 1.13±0.2 & 1.08±0.17 and gradient measure were 1.45±0.26, 1.46±0.26, 1.47±0.25 & 1.52±0.27 for spot size of 0.5mm, 1.0mm, 1.5mm & 2.0mm respectively. Volume of normal tissue receiving 90% of prescribed dose for 2mm spot size was 2.7% more in compare to 0.5mm spot size. Gamma analysis(3mm/3%) were found to be 98.77±1.03%, 98.96±0.91%, 99.18±0.76% & 99.43±0.60% for spot size 0.5mm, 1.0mm, 1.5mm & 2.0mm respectively. Conclusion: The Result showed that spot size configuration of 1.5–2.0mm were matching very closely with our measurements. Based on the variation in the PTV coverage and dose to normal tissues it is highly recommended to fine tune spot size parameters for VMAT based SBRT.
SU‐E‐T‐426: Dynamic Conformal Sub‐Arc Vs VMAT Planning for SBRT Lung Treatment
Authors: Yount C , Sintay B , Wiant D , Pursley J , Terrell J , Maurer J , Baydush A
Published: July 2013

Purpose: Dynamic conformal arc (DCA) techniques offer many advantages for thoracic stereotactic body radiotherapy (SBRT) compared to VMAT, including the elimination of interplay effect between machine and target motion and increased treatment efficiency. Despite these advantages, DCA techniques are underutilized. One potential explanation for the limited DCA use is the perceived restricted user control on dose rate and conformality. We present a method for DCA planning that divides a full arc into sub‐arcs to provide better dose optimization. Methods: Thoracic SBRT patients were simulated free‐breathing and a 4DCT was acquired and binned into ten phase‐based scans to determine internal target volumes. Dynamic conformal sub‐arc (DCSA) and VMAT plans were created on the free‐breathing scan such that at least 95% of the planning target volume received the prescribed dose. For DCSA plans, IMRT‐like dose modulation was achieved by varying field weights and angle ranges for each arc to optimize dose rate and conformality. Plans for five patients were created with DCSA and VMAT. Dose metrics including ratios of prescription dose and 50% isodose to PTV volume, volume of dose outside the PTV receiving >105% of the prescription, maximum dose at 2cm from the PTV and volume of lung receiving 20Gy were measured and compared to assess DCSA and VMAT plan quality. Results: DCSA delivery offers reduced treatment time of up to a factor of 2. Although the conformity index was closer to the ideal value of 1 for all VMAT plans, conformity is also clinically acceptable with DCSA plans. Lung V20% is also comparable and in one case is lower for the DCSA technique. Conclusion: DCSA delivery techniques are an excellent alternative to VMAT for thoracic stereotactic radiotherapy.
SU‐E‐T‐429: Delivery Accuracy of Stereotactic Radiosurgery with Tomotherapy Using Treatment Planning System Version V4.0 and the Recent Upgrade V4.2
Authors: Thakur V , Ruo R , Seuntjens J , Parker W , Doucet R , Soisson E
Published: July 2013

Purpose: To compare the delivery accuracy of helical tomotherapy for stereotactic radiosurgery using two treatment planning system (TPS) versions, v4.0 and the recent upgrade that includes increased sampling in the dose calculation algorithm v4.2. Methods: Two spherical targets of diameter 6 mm and 10 mm were contoured on the CT scan of a Lucite phantom. Three sets of plans (targets positioned at the machine isocenter and 10 cm to both anterior and lateral to the machine isocenter) were generated, with both TPS v4.0 and v4.2 using Fine dose grid resolution of 2×2×1 mm3. Radiochromic film was used to measure the dose profiles and two ionization chambers (A1SL and MicroLion) were used to measure the point dose. Results: The agreement between delivered and calculated dose was inferior for v4.0 compared to v4.2. For both planning versions, the measured dose for the targets placed at the isocenter was higher than the planned dose whereas for off‐axis targets, v4.2 showed higher measured dose and v4.0 showed lower measured dose compared to the planned dose. For v4.0, the percentage dose difference varies 13%to 24%(depending upon the detector) when the targets were placed at 10 cm away from the machine isocenter instead of at the isocenter, whereas for v4.2 this range was 3% to 6%. Conclusion: The agreement between delivered and calculated dose depends upon the position of the target inside the treatment bore. The higher dose delivered at isocenter with both planning versions could be due to the relatively large size of smallest dose grid available at tomotherapy TPS. A further investigation to determine the cause of higher dose at isocenter is required and is ongoing.
SU‐E‐T‐433: Evaluation of the ArcCheck Device for Patient‐Specific Quality Assurance in Step‐And‐Shoot IMRT for Single‐Fraction Spinal SBRT
Authors: Daartz J , Winey B , Bussiere M , Gierga D , Crawford B , Sedlacek D , Cotter C
Published: July 2013

Purpose: Current standard for patient specific spine SBRT IMRT QA in our institution is a combination of a point dose measurement in solid water under delivery of the beams at actual treatment angles, and 2D planar verification using an ion chamber (IC) array with all beams delivered at standard gantry angle of zero. The very small active area of ArcChecks diodes (∼0.6mm2) has the potential to improve measurement accuracy in high dose gradient regions present in spinal SBRT. Given high clinical workload we seek to improve ease of workflow and decrease time necessary for patient‐specific QA, by obtaining 2D verification and point dose measurement at actual treatment angles in one single measurement. Methods: The results of 10 patient specific QA measurements, as performed with single‐point and 2D IC array were compared to results obtained with ArcCheck. ArcCheck and 2D IC array pass rates are evaluated for 3%/3mm gamma criteria, single‐point measurement based on percent deviation from QA plan dose. The constancy of the device was assessed by re‐measuring the same treatment plan over the course of three weeks, and evaluating pass rate variationResults: The gamma pass rates are generally higher for ArcCheck (average 99.3%) than for Matrixx (average 93.1%). Average absolute deviation for the single‐point IC measurement was 3.4%. Maximum variation in pass rate between any two ArcCheck measurements within the three‐week evaluation period was 0.5%. Since ArcCheck allows for the use of an insert with an ion chamber in place, simultaneous redundant point measurement is possible with no time addedConclusion: Based on our results patient‐specific QA for spine SBRT treatments will be performed using ArcCheck with pass/fail criteria 98%. High sensitivity towards geometrical shifts necessitates careful initial alignment of the device.
SU‐E‐T‐436: Lung Material Phantom for Small Field Monte Carlo Dose Validation
Authors: McKay J , Das I , Cheng C , Xue J , Grimm J , Berg R
Published: July 2013

Purpose: Commissioning Monte Carlo beam data for clinical use within a treatment planning system (TPS) for Stereotactic Body Radiation Therapy (SBRT) should require validation both in homogeneous and in heterogeneous phantom materials. Compounding this task is the difficulty in accurately measuring small field sizes. This work outlines the use of a new lung phantom in conjunction with a new scintillation detector designed for small field measurement to verify the dose calculated in the TPS. Methods: The measurements were performed on a CyberKnife VSI. The Stereotactic Dose Verification Phantom (SDVP) from Standard Imaging (SI) was fitted with a newly designed 12cm lung material insert with a mass density of 0.28 g/cc. The scintillating detector was placed in a 1.5 cm diameter water‐equivalent insert, simulating the central dose measurement of a small tumor, which was then placed in the SDVP lung phantom and CT scanned. The new SI W1 pinpoint scintillator is nearly water equivalent but the 1mm diameter by 3mm long scintillating fiber was visible and was contoured in the MultiPlan TPS. After dose cross‐calibration with the SI A19 ion chamber in the basic SDVP water equivalent phantom, measurements were taken with the 5, 7.5, 10, 12.5, 15, 20, 30, and 60mm cones. For cross‐calibration to known larger field conditions, the SI A16 ion chamber was used to remeasure the 20, 30, and 60mm cones. Results: The measured dose matched the Monte Carlo dose within 2% for the three collimator sizes that were used with the A16. All measurements with the W1 matched Monte Carlo dose as well, with the exception of the 30mm cone, which was 3.18% deviant. Conclusion: The SDVP lung material inserts combined with the W1 scintillator Result in clinically acceptable correlation to the Monte Carlo dose calculated in the TPS for all CyberKnife fixed collimator sizes. Dr. Grimm received a consulting fee from Standard Imaging for guiding the research.
SU‐E‐T‐439: 3D Dosimetry for Volumetric Modulated Arc Stereotactic Delivery Using Compass
Authors: Vikraman S , Manigandan D , Mohanraj U , Karrthick K , karthikeyan N , Saranganathan B , Sambasivaselli R , Senniandavar V , Sathiyaraj P , Tejinder K
Published: July 2013

Purpose: To study the feasibility of 3D dosimetry for volumetric modulated arc stereotactic delivery using MatriXX with COMPASS verification software. Methods: Twenty patients CT images and RT structures were taken from Multiplan planning system for this study. All these patients underwent radical stereotactic treatment in Cyberknife. For each patient, linac based VMAT stereotactic plans were generated in Monaco TPS v3.1 using Elekta Beam modulator MLC. Dose prescription was in the range of 5–18Gy per fraction. Target prescription and critical organ constraints were tried to achieve the same dose as per the delivered treatment plans. Plan parameters like arc length, increment, grid size, beamlet width, calculation algorithm, minimum segment width, number of arcs and dose rate were kept common for all plans. Each patient data were exported to COMPASS verification software. Measurements were performed using MatriXX, mounted on gantry with gantry angle sensor. Results: Comparison of COMPASS reconstructed dose from measured fluence and COMPASS computed dose has shown a good agreement with TPS calculated dose. Each plan was evaluated based on dose volume parameters for target volumes such as dose at volume (95%) and average dose. For critical organs D20, D50 and maximum point doses were evaluated. Comparison was carried out using gamma analysis with passing criteria 3mm and 3%. Mean deviation of 1.9±1% was observed for D95 of target volumes, whereas very less difference was noticed for critical organs. However, significant dose difference was noticed in two cases due to the smaller tumor size. Conclusion: Analysis of this study revealed that the COMPASS 3D dosimetry is effective and ease to use as pretreatment patient specific QA for VMAT stereotactic delivery. 3D dosimetric QA with COMPASS provides additional degrees of freedom to check the high dose modulated stereotactic delivery with very high precision on patient CT images.
SU‐E‐T‐440: Analysis of Plan Quality with Different Penalties On Segment Width for Volumetric Modulated Arc Delivery of Stereotactic Body Radiotherapy
Authors: Karthikeyan N , Ganesh K , Vikraman S , Karrthick K , Mohanraj U , Saranganathan B , Senniandavar V , Sambasivaselli R , Sathiyaraj P , Tejinder K , Supe S
Published: July 2013

Purpose: To investigate the plan quality and delivery efficiency with different penalty on minimum segment width in volumetric modulated arc delivery for SBRT cases. Methods: Total of eighteen cases with tumors in lung, liver and abdomen were taken for the study. For each case, three VMAT SBRT plans were generated with different penalties on minimum segment width of 0.5, 1.0 and 1.5cm using CMS Monaco v3.1 TPS. Dose prescriptions were in the range of 7 to 20Gy per fraction. Each plan with different penalty was developed in a way to achieve same dose distribution and evaluated with dose indices(DIs), Conformity Index, Conformity Number and Gradient Index. Plan efficiency was analyzed in terms of monitor units(MUs) and delivery accuracy. The plan with 0.5cm of minimum segment width was used as a reference plan. All these plans were delivered using Elekta Beam Modulator having 4mm leaf width. The delivery accuracy was verified by measured fluence and point dose using Matrixx 2D detector array. Results: The difference between the reference and compared plan DIs were achieved within 2%. When compared with reference plan the total MUs was increased on average of 15.04±8.0% and 22.14±10.7% for 1.0cm and 1.5cm of minimum segment width plans respectively. Analysis of measured dose with TPS calculated showed a deviation of 3.1±1.9%, 2.9±1.2% and 2.7±0.8% for point dose verification and 95.9±2.8%, 96.5±2.6% and 97.8±1.6% for planar dose measurements with pass criteria of 2%/2mm for 0.5, 1.0 and 1.5cm of minimum segment width plans respectively. Conclusion: VMAT SBRT plans with increased value of minimum segment width shows a clear merit of better plan quality and delivery efficiency. Reducing the MUs by controlling redundant modulation for VMAT SBRT plans with optimal values of minimum segment width will increase the comfort for the patients with motion management system.
SU‐E‐T‐441: First Results Using Thermoluminescent Chips to Estimate Neutron Doses Near Proton Dose Delivery Regions in Solid Water Phantoms
Authors: Allgower C , Reft C
Published: July 2013

Purpose: Demonstrate feasibility of using TLDs to estimate neutron doses near clinical proton dose delivery in solid water phantoms and compare relative readings for various conditions. The advantage of TLDs is their small size providing good spatial resolution. The issue of neutron levels adjuvant to proton therapy has been hotly debated for years. This effort aims at providing measured data of relevance to that question. Methods: TLD‐700 chips were irradiated in solid water stacks at locations a few cm distal and lateral to regions of proton dose delivered to 50 Gy. Readings were done at multiple beam energies (ranges in water) in a system that delivers beam via uniform scanning. A similar irradiation was done using a passive scattering system for further comparison. Absorbed doses were extracted from the two peak analysis of the TLD glow curves and cross calibration of the same chips in a proton beam and neutron therapy beams. Results: Neutron dose estimates were surprisingly low for the uniform scanning system, being of order 0.2% of the proton dose at isocenter. Readings distal and lateral to the dose region were about equal, which was also somewhat surprising. Readings for the passive scattering system are expected to be higher than for the uniform scanning system, and will also be presented. Conclusion: The feasibility of using TLDs to measure neturon levels near proton dose delivery regions is demonstrated, at least within the limitations of this method of data analysis. Additional work needs to be done, but initial results indicate that neutron levels appear to be lower than expected. Further study incorporating Monte Carlo simulations to estimate the neutron energy spectra at the locations of the chips will continue in the near future.
SU‐E‐T‐445: Prostate Motion Effect Evaluation in Proton Pencil Beam Scanning Delivery
Authors: Tang S , Deville C , McDonough J , Tochner Z , Wang K , Vapiwala N , Both S
Published: July 2013

Purpose: To quantitatively assess the impact of interplay effect associated with the intra‐and inter‐fraction prostate motion and the delivery of the scanning proton beam. Methods: A cohort of ten prostate patients with weekly verification CTs was treated by proton pencil beam scanning with bi‐lateral single field uniform dose modality. A typical field has 10–15 energy layers and 500–1000 spots. According to patient treatment logs, each layer delivery time was less than 1 second with average time to change layers of about 8 seconds. Real‐time intrafraction prostate motions were determined from a previously reported prospective study using the Calypso beacon transponder. The worst‐case‐scenario patient prostate motion was adopted in this study. The prostate motion and the beam delivering sequence were synchronized to demonstrate the interplay effect. Results: CTV coverage was altered due to intrafraction motion. In each individual fraction, the CTV D99% can vary more than 10% relative to the initial plan. However, over the entire course of treatment the total dose degradation of D99% had a mean of −1.5% and standard deviation of 1.2%. The large variation generally happens where one beam spot is significantly heavier weighted relative to the surrounding spots. The magnitude of deviation also depends on individual patient. The consideration of both intrafraction and interfraction motion further reduced the CTV coverage D99%, with mean of ‐ 1.7% and standard deviation of 1.3%. The mean dose to the anterior rectal wall varied about 10% due to either intrafraction or interfraction motion. Conclusion: The intrafraction and interfraction prostate motion have comparable dosimetric impact. The dose over the course of treatment can reduce ∼2% for CTV coverage and increase about 10% for anterior rectal wall.
SU‐E‐T‐447: Methods and Device for Dose Based Proton Radiography
Authors: Bentefour E , Samuel D , Testa M , Lu H
Published: July 2013

Purpose: We report on the development of high spatial resolution, large active area proton radiography device that uses the dose measurement method for WEPL determination for both passive scattering (DS) and Pencil Beam Scanning (PBS). Methods: We used on the shelf appropriately CMOS sensor with an active area of 27mm × 22mm and active pixel size of 21.7 μm2. The read out electronics can record images at 2000 fps over 1024 × 1024 pixels. This technology is combined with an on the shelf QA device that uses 900cm2 gadolinium based scintillator and geometric optical system that focus the image on a 45 degree mirror on the above CMOS sensor. When placed behind the patient, the assembled device measures the 2D exit dose distribution. For DS fields, the method utilizes the periodic time dependence of the dose. By measuring the time‐dependence of dose at each pixel and comparing it against a library of time‐dependence patterns for all depths in water, the radiological path length to the point of measurement can be determined with millimeter accuracy. For PBS fields, the method uses test beam that contains a few scanning layers in depth with properly spaced ranges. Each layer has a known dose profile in water phantom. The ratio between the measured doses from each layer provides the WEPL information through the patient. Results: The assembled device achieved high performances as proton radiography device. The WEPL of large objects, up to 900cm2, are imaged, using both passive and active beams, with 0.6mm2 spatial resolutions and mm accuracy. The dose needed to achieve such performance is less than 1cGy for both DS and PBS. Conclusion: The assembled device proves to be a versatile proton imager. It has the potential for use as in‐room tool for pre‐treatment QA for patient WEPL verification.
SU‐E‐T‐448: Effectiveness of An In‐Gate Beam Tracking Method in Spot‐Scanning Proton Therapy
Authors: Matsuura T , Fujii Y , Fujimoto R , Umezawa M , Miyamoto N , Sutherland K , Takao S , Nihongi H , Toramatsu C , Shimizu S , Megaki KU , Shirato H
Published: July 2013

Purpose: To mitigate the impact of tumor motion in spot‐scanning proton beam therapy, the gating technique has been considered as a powerful tool. Although residual tumor motion of a few millimeters of gate volume can still cause a dose error, the error can be minimized by repainting. However, a larger number of paintings also results in the prolongation of treatment time. We propose a method which improves the dose uniformity while minimally increasing the number of paintings. Methods: Lateral beam tracking was applied in conjunction with gating. A simulation study was performed using the VQA treatment planning system (Hitachi Ltd., Japan) to assess the effectiveness of this method. A gated proton beam provided by a synchrotron was irradiated to spherical clinical target volumes (CTVs) with a diameter of 5 cm located at 10 cm and 15 cm depth in a heterogeneous phantom. The system delay time was 66 ms. Gate width was set to 2 mm. Rigid motion was assumed for CTVs which were shifted in synchronization with 20 patients' tumor trajectory data. A dose of 2 Gy was prescribed with the minimum repainting scheme. The cases that fulfilled the ICRU 50 criteria (CTVmax<107% and CTVmin>95%) were accepted. Results: When only gating was used, 12 and 16 out of 20 cases were accepted for targets at 10 cm and 15 cm depth, respectively. On the other hand, when beam tracking was also applied, all cases were accepted for both target depths. Conclusion: The results suggest that the application of lateral beam tracking in gate volume can improve the dose uniformity without (or minimally) increasing the number of paintings. A simulation including non‐rigid patient motion will be considered in the future.
SU‐E‐T‐449: In‐Vivo Dosimetry and Range Verification for Proton Therapy
Authors: Zheng Y
Published: July 2013

Purpose: Accurate calculation of proton dose and penetration range is critical in proton therapy. However, in‐vivo studies on dose and range verification are very limited, and there is no consensus on the appropriate amount of range uncertainty. The purpose of this study is to verify the proton dose and range and evaluate the range uncertainty using in‐vivo measurement of patients under proton therapy. Methods: Gafchromic EBT2 films were used in the study. The film was calibrated using proton beams, and its energy dependence was measured for various proton energy beams. Water phantom and animal tissues were first used to test the application of EBT2 on dose and range verification before the in‐vivo dosimetry study. Several patients, such as lung and brain cases, were carefully selected for in‐vivo film measurement. For example, we measured a lung case with tumor located posterior, and the EBT2 film was placed immediately under the patient to measure the dose in the distal falloff region from an anterior‐posterior beam. The measured plane dose was compared to the calculated dose from the treatment plan, which was created using the XiO treatment planning system (TPS). The dose difference at the distal falloff region was used to evaluate the range difference between measurement and planning. Results: The EBT2 film showed a minimal energy dependence and was able to measure proton range accurately, within 1 mm in a phantom setting. Preliminary data for a lung treatment indicate a less than 3 mm range difference between EBT2‐measured range and the TPS‐calculated one. More studies for various disease sites are in progress. Conclusions: Our animal tissue and in‐vivo study shows that the measured and calculated proton ranges are within 2% plus 2 mm for most cases. Further in‐vivo studies are needed to confirm our findings and evaluate range uncertainties at different facilities.
SU‐E‐T‐452: Episcleral Eye Plaque Dosimetry Comparison for the Eye Physics EP917 Using Plaque Simulator and Monte Carlo Simulation
Authors: Zimmermann L , Amoush A , Wilkinson D
Published: July 2013

Purpose: To compare the dosimetry calculated by the treatment planning software, Plaque Simulator™, to the dosimetry calculated using Monte Carlo methods. Methods: MCNPX 2.6.0 Monte Carlo Simulation (MC) code was used to model the Eye Physics model EP917 eye plaque. The IsoAid Advantage, IA1‐125A, 125I seed was also modeled using MCNPX and compared to published data by Meigooni et al. Energy deposition tally in unit of MeV/g was used to calculate the dose averaged over a cell.Bebig Plaque Simulator (PS) v574 treatment‐planning software was used to calculate the dose based on AAPM TG‐43U1 dose formalism; single factors are used to account for source collimation and backscattering from the gold alloy plaque.Relative doses, normalized to a prescription point of 6 mm (5 mm from the inner sclera surface), from MCNPX and PS, along the eye central axis from 1 mm to 12 mm from the scleral surface, were compared for a single seed in the plaque. Results: The IsoAid Advantage, IA1‐125A, 125I seed dose rate constant and radial dose function were calculated and agreed within 5% and 4% respectively with Meigooni et al. published data. For the central seed position, the dose differences between the MC simulation along the central axis of the eye at 1 mm and 2 mm from the scleral surface and the predicted doses by the Plaque Simulator were 32.4% and 15.2%, respectively. For distances from 3 mm to 12 mm from the scleral surface, MCNPX agreed with PS within 5%. Conclusion: For the first source position, Plaque Simulator underestimated the dose at 1 mm and 2 mm from the scleral surface by 32.4% and 12.5%. Beyond 3 mm, PS agrees within uncertainties with MCNPX results. Further investigation is needed to better identify the sources of these differences.
SU‐E‐T‐453: PET Image‐Guided Dose Escalation Study for Cervical Cancer Patients Receiving HDR Brachytherapy
Authors: Anderson J , Kiel K , Yao R , Liao Y , Bernard D , Biswal N , Turian J , Chu J
Published: July 2013

Purpose: To study the feasibility and benefit of boosting dose to active regions of cervical cancer identified by positron emission tomography (PET) imaging during brachytherapy. Methods: 5 patients imaged with MRI and PET/CT were retrospectively studied. An experienced physician contoured the GTV and HR‐CTV using the MRI scan alone, and then contoured the region of PET‐hot activity using a PET/CT image. The MRI and PET/CT images where then fused, and a PET‐HR‐CTV volume was constructed from the union of the HR‐CTV and PET‐GTV.Each patient had been treated using a Syed applicator with 4–20 needles. Two new plans were optimized using Oncentra's IPSA package with the following objectives: 1) a “PET‐blindA plan in which the HR‐CTV‐D90 received the prescription dose (Rx), and 2) a plan where the PET‐HR‐CTV D90 received Rx and the PET‐GTV D90 was boosted to 1.5 times Rx. In both cases the EQD2 D2cc dose to the bladder and rectum were kept below the GEC‐ESTRO guidelines of 90 and 75 Gy, including the contribution from external beam therapy. Dose‐volume parameters and TCP biological predictors were calculated for the PET‐target volumes in both plans. Results: Significant differences were seen between the non‐PET and PET‐GTV (average size difference 21.8cc, average overlap 50%). In the unboosted plans, the average percent D90 to the PET‐GTV was 171%, whereas in the boosted plans it increased to 223%. Average TCP, calculated using risk‐scaled parameters for IR‐, HR‐CTV and GTV, increased from 76% to 84% with the boost to the PET positive region. Conclusion: PET imaging modality has the potential to identify residual cervical cancer otherwise not visible on MRI and CT studies. This work has found that MRI target contouring regularly does not include regions of PET activity, and PET‐based planning can lead to improved outcome predictions over plans using MRI alone. Funding support partly provided by a Varian research grant.
SU‐E‐T‐454: Comparative Dosimetry of the Xoft Cervical Applicator and HDR Ir‐192 Henschke Applicator
Authors: Holt R , Kelley L , Rusch T , Hausen H
Published: July 2013

Purpose: To evaluate HDR dosimetry for the Xoft Axxent ™cervical tandem and ovoid (T&O) applicator using the 50‐kV electronic brachytherapy (eBx) source. The titanium wall of this Henschke‐style applicator filters lower energies which flattens the radial dose function. Dose distributions around the T&O for 50‐kV‐Ti were investigated with comparison to Ir‐192. Methods: TG‐43u parameters were derived from film measurements of the 50‐kV‐Ti. To account for varying filtration effects on anisotropy from tip to barrel in the tandem, a mixed source model using the anisotropy at two dwell positions was implemented. Stylized geometry of cervical PTV, rectum and bladder were created on a CT scan of a gelatin phantom with the 15‐degree T&O. Plans for each source were optimized on BrachyVision™ using identical constraints and normalization. The GMP‐192 source was used for the Ir‐192 plans. Results: Both plans were normalized at 6‐Gy (D95) and have classic pear‐shaped doses. Doses at Points A‐H are within 5% for each plan, but are 20% lower for 50‐kV‐Ti at Point B. Along the tandem length peak Ir‐192 doses are 50% higher. The Ir‐192 dose dip at the tandem tip is absent for 50‐kV‐Ti. PTV DVHs are similar except for the effect of the peak tandem surface doses. PTV coverage (D95) for both is 6 Gy (+/− 1%) and the median dose for both was 950 cGy (+/− 2%). The peak dose region (D5) is 14% lower for 50‐kV‐Ti (18.1 Gy vs 20.7 Gy). D5 of rectum and bladder are 13% and 20% respectively for 50‐kV‐Ti and Ir‐192. Median doses to critical structures are 18–20% lower for 50‐kV‐Ti. Conclusion: PTV doses for Ir‐192 HDR and 50‐kV‐Ti eBx have similar target coverage, except at the tandem surface where doses were lower for eBx. Critical organs dose outside the PTV will be lower for eBx. Funding for this study was providing by Xoft, Inc — an iCad subsidiary
SU‐E‐T‐456: Prospective Investigation of Feasibility of Three‐Dimensional Treatment Planning of Intracavitary Brachytherapy for Cervical Cancer Based On Computed Tomography Images
Authors: Yoshifumi O , Hidetaka A , Yoshiyuki H , Yasumasa S , Masahiko T , Mutsumi I , Noboru F , Masayuki N , Hideki H
Published: July 2013

Purpose: Our aim of this study was to prospectively investigate the feasibility of three‐dimensional (3D) treatment planning of intracavitary brachytherapy for cervical cancer based on computed tomography (CT) images. Two‐dimensional (2D) treatment planning based on Manchester method and the 3D treatment planning based on Groupe Europeen de Curietherapie‐European Society for Therapeutic Radiology and Oncology recommendations were compared using 2D and 3D‐based dose evaluation indices. Methods: The 2D and 3D treatment plans were made on Oncentra for six patients with stage IB‐IIB cervical cancer, who had undergone intracavitary brachytherapy (five fractions at 6Gy/fraction). Planning CT images were acquired on a 20‐slice CT scanner at the lithotomy position after inserting the applicator. Point A‐based and D90 dose prescriptions were employed for 2D and 3D treatment planning, respectively. The GTV plus 1‐cm margin was defined as a CTV in 3D treatment planning. The two kinds of treatment plans were evaluated by a conformity index (CI), homogeneity index (HI), and tumor control probability (TCP) for CTV, and doses at bladder and rectum evaluation points, D2cc, and normal tissue complication probability (NTCP) for organs at risk (OAR). Results: The CIs for 2D and 3D plans were 2.59 ± 0.59 and 1.12 ± 0.18 (p < 0.05), respectively, and the HIs were 2.18 ± 0.28 (2D) and 1.34 ± 0.27 (3D) (p < 0.05). The bladder D2cc for 2D and 3D plans were 378 ± 58.2 cGy and 504 ±47.2 cGy (p < 0.05), respectively, and the rectum D2cc were 316 ± 58.3 cGy (2D) and 455 ± 36.1 cGy (3D) (p < 0.05). There were no statistical significant differences for the TCP and NTCP. Conclusion: The 3D treatment planning could provide better dose conformity and uniformity in CTVs. The results suggested that the doses for OAR with 2D treatment planning may be underestimated.
SU‐E‐T‐457: Evaluation of Image‐Guided LDR Syed Implant and Differential Loading in the Treatment of Uterine Cervix
Authors: Bhandare N
Published: July 2013

Purpose: To evaluate the efficacy of image guided LDR Syed implant with differential loading for the treatment of cervical cancer. Methods: CT image sets of 20 patients with Syed applicator were used to generate 2 sets of treatment plans(40 Plans). Target volume (PTV) were delineated using CT/MR fusion. In 1st set of plans, uniform needle length and uniform loading was used as conventional method. In the 2nd set, the locations, lengths of the needles as well as the number, location and source activity were optimized using iterative variation of these parameters in context of anatomical information to obtain a coverage of PTV with a reference dose rate of 50 cGy/hr of 85% while limiting the dose to bladder, urethra and rectum. For both sets of the plans Conformity index (COIN), Homogenity index (HI), Overdose volume index (OVI) and doses to 2 cc of bladder, urethra and rectum, sigmoid were estimated. Results: For 1st set of plans COIN, varied between 0.47 to 0.60, for the 2nd, it varied between 0.60 to 0.72. For 1st set of plans HI varied between 0.4 to 0.52, for the 2nd, it varied between 0.3 to 0.0.4.For 1st set of plans OVI varied between 0.33 to 0.45, for the 2nd, it varied between 0.20 to 0.30.A 15–45 % reduction of dose to 2 cc of bladder and urethra, 20–40% reduction in dose to 2 cc of rectum and sigmoid were obtained in 2nd set of plans. Conclusion: Image guided brachytherapy with optimization of needle location, length and activity of Ir‐192 ribbons yields higher conformity of prescribed dose to target volume while reducing the doses to OARs.
SU‐E‐T‐458: Adjoint Sensitivity Based Greedy Heuristic Treatment Planning Algorithm: Application To Multicatheter Interstitial High Dose Rate Brachytherapy For Accelerated Partial Breast Irradiation
Authors: Chaswal V , Thomadsen B
Published: July 2013

Purpose: Development of an automated, 3‐D greedy heuristic optimization algorithm utilizing the adjoint sensitivity fields for treatment planning in multi‐catheter interstitial high dose rate breast implants is presented. The optimization is based on maximizing the dose homogeneity in a breast implant. Methods: Patient CT‐scans were taken from the UW‐hospitals and clinics and the ROI volumes were redrawn and catheters marked. CTV was defined as 1.5cm margin around the seroma. The CTV contour is limited 5mm inside the skin surface and near the pectoralis muscle. For ROI‐adjiont maps skin and muscle are contoured. The contoured volumes were — Seroma: 5.7cc, CTV: 75.0cc, Skin: 79.5cc, Muscle: 55.9, Body: 1736.6cc. Prescribed dose was 3.4Gy to the CTV. Isodoses, dose volume histograms and a list of evaluation parameters were quantified to assess the quality of treatment plan generated. Results: On all CT slices, the 150% isodoses were well separated from each other, the 100% isodose always stayed inside the skin surface with separation from the skin between 7mm−3mm, the 80% isodose covered the PTV entirely and stayed inside the outer skin surface. The V100, V150 and V200 for the PTV were 96%, 17.6% and 7.2%, respectively with DHI of 0.82 and CN of 0.68. The V100 and D100 for the seroma were 100% and 3.58Gy, respectively. The V100, V85 and D90 for the contoured skin were 0.85%, 4.46% and 0.15Gy, respectively. The V100 and D90 for the contoured muscle were 15.8% and 0.92Gy. Conclusions: Our work demostrates development and use of new treatment planning engine based on adjoint sensitivity data, for breast brachytherapy. The treatment planning tool maximizes dose homogeneity in a breast implant and offers the capability of dose quantification and modulation in any number of contoured structures like the PTV, skin and pectoralis muscle doses.