bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐328: Dosimetric Impact of Cobalt‐Chrome Stabilization Hardware in Paraspinal Radiation Therapy
Authors: Tang G , LoSasso T , Saleh Z , Mechalakos J , Lim S , Laufer I , Bilsky M , Yamada J , Lovelock D 
Published: June 2015

Purpose:Due to saturation, high density materials Result in an apparent density of 3.2 g/cm3 in CT images. The true density of traditional titanium stabilization rods (∼4.4 g/cm3) is typically ignored in treatment planning. This may not be acceptable for new cobalt‐chrome rods with a density of 8.5 g/cm3. This study reports the dosimetric impact of cobalt‐chrome rods in paraspinal radiotherapy.Methods:For titanium and cobalt‐chrome rods, two planning studies were done for both IMRT and VMAT in Varian Eclipse using AAA. 1) The effect of planning without assigning the true rod density was assessed by comparing plans generated with the apparent density and recalculated with the true density for titanium and cobalt‐chrome. 2) To test if TPS can compensate for high density rods during optimization. Furthermore, TPS calculation accuracy was verified using MapCheck for a single 20 × 10 cm2 field. The MapCheck was incrementally shifted to achieve measurement resolution of 1 mm.Results:PTV coverage was ∼0.3% and ∼4.7% lower in plans that were recalculated with the true rod density of titanium and cobalt‐chrome, respectively. PTV coverage can be maintained if the correct density is used in optimization. Measurements showed that TPS overestimated the dose locally by up to 11% for cobalt‐chrome rods and up to 4% for titanium rods if the density is incorrect. With density corrected, maximum local differences of 6% and 3% were seen for cobalt‐chrome and titanium rods, respectively. At 2 cm beneath a rod, electrons scattered from the side of the rod increased the lateral dose and diminished as depth increases. TPS was not able to account for this effect properly even with the true rod density assigned.Conclusion:Neglecting the true density of cobalt‐chrome rods can cause under coverage to the PTV. Assigning the correct density during treatment planning can minimize unexpected decrease in PTV dose.
SU‐E‐T‐329: Dosimetric Impact of Implementing Metal Artifact Reduction Methods and Metal Energy Deposition Kernels for Photon Dose Calculations
Authors: Huang J , Followill D , Howell R , Liu X , Mirkovic D , Stingo F , Kry S 
Published: June 2015

Purpose:To investigate two strategies for reducing dose calculation errors near metal implants: use of CT metal artifact reduction methods and implementation of metal‐based energy deposition kernels in the convolution/superposition (C/S) method.Methods:Radiochromic film was used to measure the dose upstream and downstream of titanium and Cerrobend implants. To assess the dosimetric impact of metal artifact reduction methods, dose calculations were performed using baseline, uncorrected images and metal artifact reductionMethods:Philips O‐MAR, GE's monochromatic gemstone spectral imaging (GSI) using dual‐energy CT, and GSI imaging with metal artifact reduction software applied (MARs).To assess the impact of metal kernels, titanium and silver kernels were implemented into a commercial collapsed cone C/S algorithm.Results:The CT artifact reduction methods were more successful for titanium than Cerrobend. Interestingly, for beams traversing the metal implant, we found that errors in the dimensions of the metal in the CT images were more important for dose calculation accuracy than reduction of imaging artifacts. The MARs algorithm caused a distortion in the shape of the titanium implant that substantially worsened the calculation accuracy. In comparison to water kernel dose calculations, metal kernels resulted in better modeling of the increased backscatter dose at the upstream interface but decreased accuracy directly downstream of the metal. We also found that the success of metal kernels was dependent on dose grid size, with smaller calculation voxels giving better accuracy.Conclusion:Our study yielded mixed results, with neither the metal artifact reduction methods nor the metal kernels being globally effective at improving dose calculation accuracy. However, some successes were observed. The MARs algorithm decreased errors downstream of Cerrobend by a factor of two, and metal kernels resulted in more accurate backscatter dose upstream of metals. Thus, these two strategies do have the potential to improve accuracy for patients with metal implants in certain scenarios.This work was supported by Public Health Service grants CA 180803 and CA 10953 awarded by the National Cancer Institute, United States of Health and Human Services, and in part by Mobius Medical Systems.
SU‐E‐T‐330: Dosimetric Impact of Intrafraction Respiratory Motion On Lung SBRT Treatment Using Cyberknife 0‐View Tracking Mode
Authors: Rao M , Chen F , Cotrutz C , Ye J 
Published: June 2015

Purpose:To investigate the influence of respiratory motion on the delivered dose in lung stereotactic body radiotherapy (SBRT) using Cyberknife (CK) 0‐View tracking mode.Methods:CT scans at inspiration and expiration of an anthropomorphic motion phantom were fused base on the spine and an internal target volume (ITV) was created. A 5mm expansion around the ITV resulted in the planning target volume. Three CK plans were generated in Accuray MultiPlan using Lung Optimization Tracking 0‐View technique with the minimum MU per beam set to (a) 5MU, (b) 15MU and (c) 30MU, respectively. Doses were calculated on the expiration CT using Monte‐Carlo algorithm. Each plan was delivered 5 times with a range of different starting phases in the respiratory cycle to assess the dose variation due to interplay effect. The delivered dose was measured with EBT3 Gafchromic film which was inserted in the moving target of the phantom. The target motion range is 3 cm in superior‐inferior (SI) direction with the breathing period of 5 seconds.Results:The gamma analysis (5%/2mm) of the dose with the films in the transverse plane resulted in average passing rate of 95.5±4.1%, 96.7±2.6%, and 96.2±2.5% for plan (a), (b), and (c), respectively. For the sagittal films, the average passing rate was 91.1±4.9%, 92.1±3.6%, and 92.3±2.9% for the three plans, respectively. The disagreement between measurement and dose calculations were mostly on the target edges in SI direction. The mean measured versus calculated dose differences at the edge of target in SI direction were (a) 3.9±4.8%, (b) 2.4±3.3%, and (c) 2.2±3.2% for the three plans, respectively.Conclusions:The plans with low‐MU beams (below 10MU) tend to cause slightly larger dose variation. However in terms of target coverage, the overall clinical dosimetric impact of the intrafraction respiratory motion in lung SBRT is insignificant when averaged over 3∼5 fractions.
SU‐E‐T‐342: Dynamic Accuracy and Stability of Novel Multi‐Leaf Collimator (MLC) for Volumetric Modulated Arc Therapy (VMAT)
Authors: Nakaguchi Y 
Published: June 2015

Purpose:We have investigated the dynamic accuracy and long‐term stability of an Agility (Elekta, Stockholm, Sweden) multi‐leaf collimator (MLC) for volumetric modulated arc therapy (VMAT).Methods:The MLC leaf position accuracy during VMAT delivery was evaluated with the use of three different quality assurance tests for several months: (1) a leaf gap‐width test between opposing leaves by measurement of the isocenter dose during constant‐gap sliding‐window delivery with varied dose rates, MLC leaf speeds, and gantry angles; (2) a leaf position test by picket‐fence delivery with and without gantry rotation; and (3) the complicated VMAT test plans were evaluated by measurement using gamma analysis with criteria of 3 mm distance‐to‐agreement (DTA) and 3% percent dose difference (DD).Results:The leaf gap‐width deviation once a week for five months was within 0.15 mm under all the test fractions. There were not clear differences of the accuracy depending on the dose rates, the leaf speeds, and gantry angles. Agreement in the static vs. rotation picket fence test was better than 0.5 mm. This difference is near to the limit of the measurement and is not the difference between static and rotation. The pass rates of each complicated VAMT test plans once a day for a month were more than 90% in the gamma analysis. These pass rates are accuracy enough for VMAT because the test plans included strict test plans.Conclusion:MLC leaf position accuracy and long‐term stability were confirmed by the proposed procedures. The Agility MLC showed enough MLC leaf position accuracy and long‐term stability for VMAT.
SU‐E‐T‐346: Effect of Jaw Position On Dose to Critical Structures in 3‐D Conformal Radiotherapy Treatment of Pancreatic Cancer
Authors: Paudel N , Han E , Liang X , Morrill S , Zhang X , Hardee M , Penagaricano J , Ratanatharathorn V 
Published: June 2015

Purpose:Three‐dimensional conformal therapy remains a valid and widely used modality for pancreatic radiotherapy treatment. It usually meets dose constraints on critical structures. However, careful positioning of collimation jaws can reduce dose to the critical structures. Here we investigate the dosimetric effect of jaw position in MLC‐based 3‐D conformal treatment planning on critical structures.Methods:We retrospectively selected seven pancreatic cancer patients treated with 3‐D conformal radiotherapy. We started with treatment plans (Varian Truebeam LINAC, Eclipse TPS, AAA, 18MV) having both × and y jaws aligned with the farthest extent of the block outline (8mm around PTV). Then we subsequently moved either both x‐jaws or all × and y jaws outwards upto 3 cm in 1 cm increments and investigated their effect on average and maximum dose to neighboring critical structures keeping the same coverage to treatment volume.Results:Lateral displacement of both x‐jaws by 1cm each increased kidney and spleen mean dose by as much as 1.7% and 1.3% respectively and superior inferior displacement increased liver, right kidney, stomach and spleen dose by as much as 2.1%, 2%, 5.2% and 1.6% respectively. Displacement of all × and y‐jaws away by 1cm increased the mean dose to liver, right kidney, left kidney, bowels, cord, stomach and spleen by as much as 4.9%, 5.9%, 2.1%, 2.8%, 7.4%, 10.4% and 4.2% respectively. Percentage increase in mean dose due to 2 and 3cm jaw displacement increased almost linearly with the displaced distance. Changes in maximum dose were much smaller (mostly negligible) than the changes in mean dose.Conclusion:Collimation jaw position affects dose mostly to critical structures adjacent to it. Though treatment plans with MLCs conforming the block margin usually meet dose constraints to critical structures, keeping jaws all the way in, to the edge of the block reduces dose to the critical structures during radiation treatment.
SU‐E‐T‐357: Electronic Compensation Technique to Deliver Total Body Dose
Authors: Lakeman T , Wang I , Podgorsak M 
Published: June 2015

Purpose:Total body irradiation (TBI) uses large parallel‐opposed radiation fields to suppress the patient's immune system and eradicate the residual cancer cells in preparation of recipient for bone marrow transplant. The manual placement of lead compensators has conventionally been used to compensate for the varying thickness through the entire body in large‐field TBI. The goal of this study is to pursue utilizing the modern electronic compensation technique to more accurately and efficiently deliver dose to patients in need of TBI.Methods:Treatment plans utilizing electronic compensation to deliver a total body dose were created retrospectively for patients for whom CT data had been previously acquired. Each treatment plan includes two, specifically weighted, pair of opposed fields. One pair of open, large fields (collimator=45°), to encompass the patient's entire anatomy, and one pair of smaller fields (collimator=0°) focused only on the thicker midsection of the patient. The optimal fluence for each one of the smaller fields was calculated at a patient specific penetration depth. Irregular surface compensators provide a more uniform dose distribution within the smaller opposed fields.Results:Dose‐volume histograms (DVH) were calculated for the evaluating the electronic compensation technique. In one case, the maximum body doses calculated from the DVH were reduced from the non‐compensated 195.8% to 165.3% in the electronically compensated plans, indicating a more uniform dose with the region of electronic compensation. The mean body doses calculated from the DVH were also reduced from the non‐compensated 120.6% to 112.7% in the electronically compensated plans, indicating a more accurate delivery of the prescription dose. All calculated monitor units were well within clinically acceptable limits.Conclusion:Electronic compensation technique for TBI will not substantially increase the beam on time while it can significantly reduce the compensator setup time and the potential risk of errors in manually placing lead compensators.
SU‐E‐T‐364: Estimating the Minimum Number of Patients Required to Estimate the Required Planning Target Volume Margins for Prostate Glands
Authors: Bakhtiari M , Schmitt J , Sarfaraz M , Osik C 
Published: June 2015

Purpose:To establish a minimum number of patients required to obtain statistically accurate Planning Target Volume (PTV) margins for prostate Intensity Modulated Radiation Therapy (IMRT).Methods:A total of 320 prostate patients, consisting of a total number of 9311 daily setups, were analyzed. These patients had gone under IMRT treatments. Daily localization was done using the skin marks and the proper shifts were determined by the CBCT to match the prostate gland. The Van Herk formalism is used to obtain the margins using the systematic and random setup variations. The total patient population was divided into different grouping sizes varying from 1 group of 320 patients to 64 groups of 5 patients. Each grouping was used to determine the average PTV margin and its associated standard deviation.Results:Analyzing all 320 patients lead to an average Superior‐Inferior margin of 1.15 cm. The grouping with 10 patients per group (32 groups) resulted to an average PTV margin between 0.6–1.7 cm with the mean value of 1.09 cm and a standard deviation (STD) of 0.30 cm. As the number of patients in groups increases the mean value of average margin between groups tends to converge to the true average PTV of 1.15 cm and STD decreases. For groups of 20, 64, and 160 patients a Superior‐Inferior margin of 1.12, 1.14, and 1.16 cm with STD of 0.22, 0.11, and 0.01 cm were found, respectively. Similar tendency was observed for Left‐Right and Anterior‐Posterior margins.Conclusion:The estimation of the required margin for PTV strongly depends on the number of patients studied. According to this study at least ∼60 patients are needed to calculate a statistically acceptable PTV margin for a criterion of STD < 0.1 cm. Numbers greater than ∼60 patients do little to increase the accuracy of the PTV margin estimation.
SU‐E‐T‐365: Estimation of Neutron Ambient Dose Equivalents for Radioprotection Exposed Workers in Radiotherapy Facilities Based On Characterization Patient Risk Estimation
Authors: Irazola L , Domingo C , Romero‐Exposito M , Garcia‐Fuste M , Terron J , Sanchez‐Nieto B , Bedogni R , Sanchez‐Doblado F 
Published: June 2015

Purpose:Previous measurements with Bonner spheres1 showed that normalized neutron spectra are equal for the majority of the existing linacs2. This information, in addition to thermal neutron fluences obtained in the characterization procedure33, would allow to estimate neutron doses accidentally received by exposed workers, without the need of an extra experimental measurement.Methods:Monte Carlo (MC) simulations demonstrated that the thermal neutron fluence distribution inside the bunker is quite uniform, as a consequence of multiple scatter in the walls⁴. Although inverse square law is approximately valid for the fast component, a more precise calculation could be obtained with a generic fast fluence distribution map around the linac, from MC simulations⁴. Thus, measurements of thermal neutron fluences performed during the characterization procedure3, together with a generic unitary spectra2, would allow to estimate the total neutron fluences and H*(10) at any point⁵. As an example, we compared estimations with Bonner sphere measurements1, for two points in five facilities: 3 Siemens (15–23 MV), Elekta (15 MV) and Varian (15 MV).Results:Thermal neutron fluences obtained from characterization, are within (0.2–1.6×10⁶) cm−2•Gy−1 for the five studied facilities. This implies ambient equivalent doses ranging from (0.27–2.01) mSv/Gy 50 cm far from the isocenter and (0.03–0.26) mSv/Gy at detector location with an average deviation of ±12.1% respect to Bonner measurements.Conclusion:The good results obtained demonstrate that neutron fluence and H*(10) can be estimated based on: (a) characterization procedure established for patient risk estimation in each facility, (b) generic unitary neutron spectrum and (c) generic MC map distribution of the fast component.[1] Radiat. Meas (2010) 45: 1391 – 1397; [2] Phys. Med. Biol (2012) 5 7:6167–6191; [3] Med. Phys (2015) 42:276 ‐ 281. [4] IFMBE (2012) 39: 1245–1248. [5] ICRU Report 57 (1998)
SU‐E‐T‐368: Evaluating Dosimetric Outcome of Modulated Photon Radiotherapy (XMRT) Optimization for Head and Neck Patients
Authors: McGeachy P , Villarreal‐Barajas JE , Zinchenko Y , Khan R 
Published: June 2015

Purpose:The dosimetric outcome of optimized treatment plans obtained by modulating the photon beamlet energy and fluence on a small cohort of four Head and Neck (H and N) patients was investigated. This novel optimization technique is denoted XMRT for modulated photon radiotherapy. The dosimetric plans from XMRT for H and N treatment were compared to conventional, 6 MV intensity modulated radiotherapy (IMRT) optimization plans.Methods:An arrangement of two non‐coplanar and five coplanar beams was used for all four H and N patients. Both XMRT and IMRT were subject to the same optimization algorithm, with XMRT optimization allowing both 6 and 18 MV beamlets while IMRT was restricted to 6 MV only. The optimization algorithm was based on a linear programming approach with partial‐volume constraints implemented via the conditional value‐at‐risk method. H and N constraints were based off of those mentioned in the Radiation Therapy Oncology Group 1016 protocol. XMRT and IMRT solutions were assessed using metrics suggested by International Commission on Radiation Units and Measurements report 83. The Gurobi solver was used in conjunction with the CVX package to solve each optimization problem. Dose calculations and analysis were done in CERR using Monte Carlo dose calculation with VMC₊₊.Results:Both XMRT and IMRT solutions met all clinical criteria. Trade‐offs were observed between improved dose uniformity to the primary target volume (PTV1) and increased dose to some of the surrounding healthy organs for XMRT compared to IMRT. On average, IMRT improved dose to the contralateral parotid gland and spinal cord while XMRT improved dose to the brainstem and mandible.Conclusion:Bi‐energy XMRT optimization for H and N patients provides benefits in terms of improved dose uniformity to the primary target and reduced dose to some healthy structures, at the expense of increased dose to other healthy structures when compared with IMRT.
SU‐E‐T‐370: Evaluating Plan Quality and Dose Delivery Accuracy of Tomotherapy SBRT Treatments for Lung Cancer
Authors: Blake S , Hansen C , Deshpande S , Phan P , Franji I , Holloway L , Thwaites D 
Published: June 2015

Purpose:This study evaluated the plan quality and dose delivery accuracy of stereotactic body radiotherapy (SBRT) helical Tomotherapy (HT) treatments for lung cancer. Results were compared with those previously reported by our group for flattening filter (FF) and flattening filter free (FFF) VMAT treatments. This work forms part of an ongoing multicentre and multisystem planning and dosimetry audit on FFF beams for lung SBRT.Methods:CT datasets and DICOM RT structures delineating the target volume and organs at risk for 6 lung cancer patients were selected. Treatment plans were generated using the HT treatment planning system. Tumour locations were classified as near rib, near bronchial tree or in free lung with prescribed doses of 48Gy/4fr, 50Gy/5fr and 54Gy/3fr respectively. Dose constraints were specified by a modified RTOG0915 protocol used for an Australian SBRT phase II trial. Plan quality was evaluated using mean PTV dose, PTV volume receiving 100% of the prescribed dose (V100%), target conformity (CI=VD100%/VPTV) and low dose spillage (LDS=VD50%/VPTV). Planned dose distributions were compared to those measured using an ArcCheck phantom. Delivery accuracy was evaluated using a gamma‐index pass rate of 95% with 3% (of max dose) and 3mm criteria.Results:Treatment plans for all patients were clinically acceptable in terms of quality and accuracy of dose delivery. The following DVH metrics are reported as averages (SD) of all plans investigated: mean PTV dose was 115.3(2.4)% of prescription, V100% was 98.8(0.9)%, CI was 1.14(0.03) and LDS was 5.02(0.37). The plans had an average gamma‐index passing rate of 99.3(1.3)%.Conclusion:The results reported in this study for HT agree within 1 SD to those previously published by our group for VMAT FF and FFF lung SBRT treatments. This suggests that HT delivers lung SBRT treatments of comparable quality and delivery accuracy as VMAT using both FF and FFF beams.
SU‐E‐T‐374: Evaluation and Verification of Dose Calculation Accuracy with Different Dose Grid Sizes for Intracranial Stereotactic Radiosurgery
Authors: Han C , Schultheiss T 
Published: June 2015

Purpose:In this study, we aim to evaluate the effect of dose grid size on the accuracy of calculated dose for small lesions in intracranial stereotactic radiosurgery (SRS), and to verify dose calculation accuracy with radiochromic film dosimetry.Methods:15 intracranial lesions from previous SRS patients were retrospectively selected for this study. The planning target volume (PTV) ranged from 0.17 to 2.3 cm3. A commercial treatment planning system was used to generate SRS plans using the volumetric modulated arc therapy (VMAT) technique using two arc fields. Two convolution‐superposition‐based dose calculation algorithms (Anisotropic Analytical Algorithm and Acuros XB algorithm) were used to calculate volume dose distribution with dose grid size ranging from 1 mm to 3 mm with 0.5 mm step size. First, while the plan monitor units (MU) were kept constant, PTV dose variations were analyzed. Second, with 95% of the PTV covered by the prescription dose, variations of the plan MUs as a function of dose grid size were analyzed. Radiochomic films were used to compare the delivered dose and profile with the calculated dose distribution with different dose grid sizes.Results:The dose to the PTV, in terms of the mean dose, maximum, and minimum dose, showed steady decrease with increasing dose grid size using both algorithms. With 95% of the PTV covered by the prescription dose, the total MU increased with increasing dose grid size in most of the plans. Radiochromic film measurements showed better agreement with dose distributions calculated with 1‐mm dose grid size.Conclusion:Dose grid size has significant impact on calculated dose distribution in intracranial SRS treatment planning with small target volumes. Using the default dose grid size could lead to under‐estimation of delivered dose. A small dose grid size should be used to ensure calculation accuracy and agreement with QA measurements.