bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐155: Calibration of Variable Longitudinal Strength 103Pd Brachytherapy Sources
Authors: Reed J , Radtke J , Micka J , Culberson W , DeWerd L 
Published: June 2015

Purpose:Brachytherapy sources with variable longitudinal strength (VLS) allow for a customized intensity along the length of the source. These have applications in focal brachytherapy treatments of prostate cancer where dose boosting can be achieved through modulation of intra‐source strengths. This work focused on development of a calibration methodology for VLS sources based on measurements and Monte Carlo (MC) simulations of five 1 cm 1⁰ 3Pd sources each containing four regions of variable 1⁰3Pd strength.Methods:The air‐kerma strengths of the sources were measured with a variable‐aperture free‐air chamber (VAFAC). Source strengths were also measured using a well chamber. The in‐air azimuthal and polar anisotropy of the sources were measured by rotating them in front of a NaI scintillation detector and were calculated with MC simulations. Azimuthal anisotropy results were normalized to their mean intensity values. Polar anisotropy results were normalized to their average transverse axis intensity values. The relative longitudinal strengths of the sources were measured via on‐contact irradiations with radiochromic film, and were calculated with MC simulations.Results:The variable 1⁰3Pd loading of the sources was validated by VAFAC and well chamber measurements. Ratios of VAFAC air‐kerma strengths and well chamber responses were within ±1.3% for all sources. Azimuthal anisotropy results indicated that ≥95% of the normalized values for all sources were within ±1.7% of the mean values. Polar anisotropy results indicated variations within ±0.3% for a ±7.6° angular region with respect to the source transverse axis. Locations and intensities of the 1⁰3Pd regions were validated by radiochromic film measurements and MC simulations.Conclusion:The calibration methodology developed in this work confirms that the VLS sources investigated have a high level of polar uniformity, and that the strength and longitudinal intensity can be verified experimentally and through MC simulations.103Pd sources were provided by CivaTech Oncology, Inc.
SU‐E‐T‐158: Catching Errors with Trajectory Log Files
Authors: Wijesooriya K , Seitter K , Desai V , Dharia I , Read P , Larner J 
Published: June 2015

Purpose:To present our single institution experience on catching errors with trajectory log file analysis. The reported causes of failures, probability of occurrences (O), severity of effects (S), and the probability of the failures to be undetected (D) could be added to guidelines of FMEA analysis.Methods:From March 2013 to March 2014, 19569 patient treatment fields/arcs were analyzed. This work includes checking all 131 treatment delivery parameters for all patients, all treatment sites and all treatment delivery fractions. TrueBeam trajectory log files for all treatment field types as well as all imaging types were accessed, read in every 20ms, and every control point (total of 37 million parameters) compared to the physician approved plan in the planning system.Results:Couch angle outlier occurrence: N= 327, range = −1.7 −1.2 deg; gantry angle outlier occurrence: N =59, range = 0.09 – 5.61 deg, collimator angle outlier occurrence: N = 13, range = −0.2 – 0.2 deg. VMAT cases have slightly larger variations in mechanical parameters. MLC: 3D single control point fields have a maximum deviation of 0.04 mm, 39 step and shoot IMRT cases have MLC −0.3 – 0.5 mm deviations, all (1286) VMAT cases have −0.9 – 0.7 mm deviations. Two possible serious errors were found: 1) A 4 cm isocenter shift for the PA beam of an AP‐PA pair, under‐dosing a portion of PTV by 25%. 2) Delivery with MLC leaves abutted behind the jaws as opposed to the midline as planned, leading to a under‐dosing of a small volume of the PTV by 25%, by just the boost plan. Due to their error origin, neither of these errors could have been detected by pre‐treatment verification.Conclusion:Performing Trajectory Log file analysis could catch typically undetected errors to avoid potentially adverse incidents.
SU‐E‐T‐161: Characterization and Validation of CT Simulator Hounsfield Units to Relative Stopping Power Values for Proton Treatment Planning
Authors: Schnell E , Ahmad S , De La Fuente Herman T 
Published: June 2015

Purpose:To develop a calibration curve that includes and minimizes the variations of Hounsfield Unit (HU) from a CT scanner to Relative Stopping Power (RSP) of tissues along the proton beam path. The variations are due to scanner and proton energy, technique, phantom size and placement, and tissue arrangement.Methods:A CIRS 062 M phantom with 10 plugs of known relative electron density (RED) was scanned through a 16 slice GE Discovery CT Simulator scanner. Three setup combinations of plug distributions and techniques clinically implemented for five treatment regions were scanned with energies of 100, 120, and 140 kV. Volumetric HU values were measured for each plug and scan. The RSP values derived through the Bethe‐Bloch formula are currently being verified with parallel‐plate ionization chamber measurements in water using 80, 150, and 225 MeV proton beam. Typical treatment plans for treatment regions of brain, head‐&‐neck, chest, abdomen, and pelvis are being planned and dose delivered will be compared with film and Optically Stimulated Luminescence (OSL) measurements.Results:Percentage variations were determined for each variable. For tissues close to water, variations were <1% from any given parameter. Tissues far from water equivalence (lung and bone) showed the greatest sensitivity to change (7.4% maximum) with scanner energy and up to 5.3% with positioning of the phantom. No major variations were observed for proton energies within the treatment range.Conclusion:When deriving a calibration curve, attention should be placed to low and high HU values. A thorough verification process of calculated vs. water‐phantom measured RSP values at different proton energies, followed by dose validation of planned vs. measured doses in phantom with film and OSL detectors are currently being undertaken.
SU‐E‐T‐163: Characterization of a Novel High Resolution 1D Silicon Monolithic Array for Small Field Commissioning and Quality Assurance
Authors: Bisello F , McGlade J , Wang P , Kralik J , Kosterin P , Mooij R , Menichelli D , Celi J , Solberg T 
Published: June 2015

Purpose:To study the suitability of a novel 1D silicon monolithic array for dosimetry of small radiation fields and for QA of high dose gradient treatment modalities (IMRT and SBRT).Methods:A 1D array composed of 4 monolithic silicon modules of 64 mm length and 1 mm pixel pitch was developed by IBA Dosimetry. Measurements were carried out for 6MV and 15MV photons on two commercial different linacs (TrueBeam and Clinac iX, Varian Medical Systems, Palo Alto, CA) and for a CyberKnife G4 (Accuray Inc., Sunnyvale, CA). The 1D array was used to measure output factors (OF), profiles and off axis correction factors (OACF) for the Iris CyberKnife variable collimator (5–60 mm). In addition, dose profiles (at the isocenter plane) were measured for multiple IMRT and SBRT treatment plans and compared with those obtained using EDR2radiographic film (Carestream Health, Rochester NY), a commercial 2D diode array and with the dose distribution calculated using a commercial TPS (Eclipse, Varian Medical Systems, Palo Alto, CA).Results:Due to the small pixel pitch of the detector, IMRT and SBRT plan profiles deviate from film measurements by less than 2%. Similarly, the 1D array exhibits better performance than the 2D diode array due to the larger (7 mm) pitch of that device. Iris collimator OFs measured using the 1D silicon array are in good agreement with the commissioning values obtained using a commercial stereotactic diode as well as with published data. Maximum deviations are < 3% for the smallest field (5 and 7.5mm) and below 1% for all other dimensions.Conclusion:We have demonstrated good performances of the array for commissioning of small photon fields and in patient QA, compared with diodes and film typically used in these clinical applications. The technology compares favorably with existing commercial solutionsThe presenting author is founded by a Marie Curie Early Initial Training Network Fellowship of the European Communitys Seventh Framework Programme under contract number (PITN‐GA‐2011‐289198‐ARDENT).The research activity is hosted by IBA Dosimetry, Gmbh.
SU‐E‐T‐166: Characterization of Efficiency and Plan Quality for the FFF Beams On Various Anatomical Sites
Authors: Rassiah‐Szegedi P , Szegedi M , Sarkar V , Zhao H , Huang Y , Huang L , Salter B 
Published: June 2015

Purpose:To characterize efficiency and plan quality for the FFF beams for various sites.Methods:5 brain, Head and Neck, prostate, lung and liver cancer patients IMRT plans (25 total) were generated on either Prowess 4.6 or Eclipse 13.5 using the same dose constraints for each treatment site. Step and shoot with static gantry IMRT was used for treatment delivery. PTV coverage, critical structure doses, MUs, number of segments and beam on times were compared.Results:The average PTV size was 29.0, 34.9, 89.2, 257.6, 289.2 cm3 for liver, lung, prostate, head and neck and brain respectively.All plans were normalized such that 95% of the PTV volume would receive at least 95% of prescribed dose. All doses to the critical structures for both the FFF and flat beam met the targeted dose constraints.For plans with field sizes < 10 cm, the number of segments and MUs required to achieve the same plan quality were similar. For these small field sizes with large dose per fraction, an increase in efficiency up to 58.8% is seen.Plans with field sizes > 10 cm, required 10% – 20% more segments and MUs for the FFF beam to achieve the same plan quality as the flat beam. Despite this, for fraction sizes less than 2.5 Gy the FFF beam is still approximately 13.9% more efficient in terms of delivery time.Conclusion:For the various treatment sites studied here, plans generated with the FFF beam were dosimetrically similar to those generated with a flattened beam. Despite the greater number of MUs and segments required to achieve the same plan quality as the flat beam for some plans, the FFF beam is still more efficient compared to the flat beam.
SU‐E‐T‐171: Characterization of the New Xoft Axxent Electronic Brachytherapy Source Using PRESAGE Dosimeters
Authors: Steinmann A , Adamovics J , Followill D , Ibbott G 
Published: June 2015

Purpose:To characterize the Xoft Axxent electronic brachytherapy source using PRESAGE™ dosimeters to obtain independent confirmation of TG‐43U1 dosimetry values from previous studies and ascertain its reproducibility in HDR brachytherapy.Methods:PRESAGE™ dosimeters are solid, polyurethane‐based dosimeters doped with radiochromic leucodyes that produce a linear optical‐density response when exposed to radiation. Eight 1‐kg dosimeters were scanned prior to irradiation on an optical‐CT scanner to eliminate background signal and any optical imperfections from each dosimeter. To quantify potential imaging artifacts due to oversaturated responses in the immediate range of the source, half of the eight dosimeters were cast with a smaller channel diameter of 5.4 mm, and the other half were cast with a larger channel diameter of 15mm. During irradiation, the catheters were placed in the center of each channel. Catheters fit the 5.4mm diameters channels whereas polyurethane plugs were inserted into the larger channels to create a sturdy, immobile catheter which allowed uniform dose distributions. Two dosimeters of each 5.4mm and 15mm were irradiated at either 1517.3 cGy or 2017.5 cGy. Post‐irradiation scans were performed within 48 hours of irradiation. A 3D reconstruction based on subtraction of these two images and the relative dose measurements were made using in‐house software.Results:Comparing measured radial dose rates with previous results revealed smaller percent errors when PRESAGE™ irradiations were at lower maximum dose. The dosimeters showed small deviations in radial dose function, gp (r), from previous studies. Among the dosimeters irradiated at 1517.3 cGy, the gp(r) compared to previous studies fluctuated from 0.0043 to 0.3922. This suggests small fluctuations can drastically change radial dose calculations.Conclusion:The subtraction of pre‐irradiation and post‐irradiation scans of PRESAGE™ dosimeters using an optical‐CT scanner shows promising results in determining 3D dosimetry for Xoft Axxent devices; however, further research is recommended.NIH Grant#: 5‐U24‐CA081647‐13; ROI Grant#: 5R01CA100835
SU‐E‐T‐175: Clinical Evaluations of Monte Carlo‐Based Inverse Treatment Plan Optimization for Intensity Modulated Radiotherapy
Authors: Chi Y , Li Y , Tian Z , Gu X , Jiang S , Jia X 
Published: June 2015

Purpose:Pencil‐beam or superposition‐convolution type dose calculation algorithms are routinely used in inverse plan optimization for intensity modulated radiation therapy (IMRT). However, due to their limited accuracy in some challenging cases, e.g. lung, the resulting dose may lose its optimality after being recomputed using an accurate algorithm, e.g. Monte Carlo (MC). It is the objective of this study to evaluate the feasibility and advantages of a new method to include MC in the treatment planning process.Methods:We developed a scheme to iteratively perform MC‐based beamlet dose calculations and plan optimization. In the MC stage, a GPU‐based dose engine was used and the particle number sampled from a beamlet was proportional to its optimized fluence from the previous step. We tested this scheme in four lung cancer IMRT cases. For each case, the original plan dose, plan dose re‐computed by MC, and dose optimized by our scheme were obtained. Clinically relevant dosimetric quantities in these three plans were compared.Results:Although the original plan achieved a satisfactory PDV dose coverage, after re‐computing doses using MC method, it was found that the PTV D95% were reduced by 4.60%–6.67%. After re‐optimizing these cases with our scheme, the PTV coverage was improved to the same level as in the original plan, while the critical OAR coverages were maintained to clinically acceptable levels. Regarding the computation time, it took on average 144 sec per case using only one GPU card, including both MC‐based beamlet dose calculation and treatment plan optimization.Conclusion:The achieved dosimetric gains and high computational efficiency indicate the feasibility and advantages of the proposed MC‐based IMRT optimization method. Comprehensive validations in more patient cases are in progress.
SU‐E‐T‐176: Clinical Experience of Brass Mesh Bolus: Patient‐Specific Parameters as Predictors of Measured Dosimetric Effect
Authors: Yock A , Manger R , Einck J , Yashar C , Sanghvi P , Hattangadi‐Gluth J , Cervino L 
Published: June 2015

Purpose:Increasingly, brass mesh bolus is used to insure dosimetric coverage of the skin for patients treated post‐mastectomy for breast cancer. Contribution of photoelectrons from interactions between the bolus and the primary beam increases dose superficially without affecting dose at greater depths. We present our experience using brass mesh bolus – including patients for whom the bolus was dosimetrically inadequate – along with analysis of relevant patient‐specific parameters.Methods:Optically‐stimulated luminescent dosimeters (OSLDs) were used to determine the effect of the bolus for 15 patients. They were positioned beneath the bolus within the tangent fields at three positions: 1.5–3cm inside the medial and lateral field edges, and midway between the two. All OSLDs were midfield in the cranial‐caudal direction. The measurements were compared with patient‐specific parameters including separation, chest wall/breast tissue thickness, beam angle incidence, and planned surface dose.Results:The average OSLD measurement at the medial field edge, midfield, and lateral field edge position was 86.8%, 101.8%, and 92.8% of the prescription dose, respectively. A measurement for one patient was low enough (77.0%) to warrant a switch to an alternative type of bolus. Anatomic parameters were analyzed to investigate the low dose in this case, not observed in the planning system. The patient was observed to have a thin chest wall and very oblique beam angles. A second patient was also switched to an alternative type of bolus due to her being high risk and treated with an electron patch that extended onto the breast.Conclusion:Brass mesh bolus increases dose superficially while leaving dose at greater depths unaffected. However, our results suggest that this effect may be insufficient in patients with a thin chest wall or very oblique beam angles. More data and analysis is necessary to proactively identify patients for whom brass mesh bolus is effective.
SU‐E‐T‐178: Clinical Feasibility of Multi‐Leaf Collimator Based Dynamic Wedge
Authors: Jeong C , Kwak J , Ahn S , Kim J , Park J , Yoon S , Cho B 
Published: June 2015

Purpose:A multi‐leaf collimator (MLC) based dynamic wedge (MDW), which provide similar dose profile of physical wedge (PW) along x‐jaw direction while significant monitor unit (MU) reduction, was developed and investigated for clinical use.Methods:A novel technique was used to create the wedge profile using MLC. A modification was applied to the DICOM‐RT format file of the plan made with the PW to replace PW with MDW. The Varian enhanced dynamic wedge profile was used to produce MLC sequence, while the MU of the wedged field was recalculated using PW factor and fluence map. The profiles for all possible MDWs to substitute PWs were verified in 6/15 MV x‐ray irradiations. New plans with MDWs were compared with the original plans in 5 rectal, 5 RT breast and 5 liver cases.Results:The wedge profile of the MDW fields were well matched with those of PWs inside the fields while less scatter than PW out of the fields. For plan comparisons of the clinical cases no significant dose discrepancy was observed between MDW plan and PW's with the dose volume histograms. The maximum and mean doses in PTVs are agreed within 1.0%. The Result of OARs of MDW plans are slightly improved in the maximum doses (3.22 ∼ 150.4 cGy) and the mean doses (17.18 ∼ 85.52 cGy) on average for all cases while the prescribed doses are 45 Gy for rectal cases, 40 or 45 Gy for liver cases and 50 Gy for breast cases. The MUs of the fields which replace PW with MDW are reduced to 68% of those of PW.Conclusion:We developed a novel dynamic wedge technique with MLC that shows clinical advantage compared to PW.
SU‐E‐T‐181: Clinical Implementation of Task Group 176
Authors: Burgdorf B , Yeager C , Zhou F , Hand C 
Published: June 2015

Purpose:The implementation of TG‐176 with regards to immobilization devices and couch tops as they effect dosimetric treatment planning.Methods:The external devices used clinically were scanned to measure their HU values. Plans were created in the Eclipse treatment planning system (TPS) using these devices, one that accounted for the correct HU value of the each device and another that did not include the device as a structure. A dose subtraction was performed between the two plans to evaluate the dosimetric differences. The metrics used for evaluation included attenuation and surface dose. Plan parameters were varied to evaluate the impact of the devices in different clinical scenarios.Results:While the exact HU values of our results are clinic‐dependent, the protocol being implemented is widely applicable. We recommend a four step process for implementing this task group. First, physics should scan each treatment device to determine accurate HU values. Second, CT therapists should include in the setup note which table top was used during patient CT simulation and are asked to make immobilization devices as uniform in thickness as possible. Therapists should also index the devices whenever possible so beam will traverse the same area of the device. Third, the dosimetrist should manually correct the HU value for any external device, including the couch. For H&N cases, the rails must be removed from the couch structure. When rails are used during treatments, it is important to make note of their exact position in the setup notes. Finally, physicians should be made aware that there could be changes in surface doses depending on whether or not immobilization devices or couch tops are in the beam path.Conclusion:The protocol outlined above was implemented to reduce the errors that arise from ignoring effects of external devices, thus ensuring safer, more accurate patient treatments.
SU‐E‐T‐184: Clinical VMAT QA Practice Using LINAC Delivery Log Files
Authors: Johnston H , Jacobson T , Gu X , Jiang S , Stojadinovic S 
Published: June 2015

Purpose:To evaluate the accuracy of volumetric modulated arc therapy (VMAT) treatment delivery dose clouds by comparing linac log data to doses measured using an ionization chamber and film.Methods:A commercial IMRT quality assurance (QA) process utilizing a DICOM‐RT framework was tested for clinical practice using 30 prostate and 30 head and neck VMAT plans. Delivered 3D VMAT dose distributions were independently checked using a PinPoint ionization chamber and radiographic film in a solid water phantom. DICOM RT coordinates were used to extract the corresponding point and planar doses from 3D log file dose distributions. Point doses were evaluated by computing the percent error between log file and chamber measured values. A planar dose evaluation was performed for each plan using a 2D gamma analysis with 3% global dose difference and 3 mm isodose point distance criteria. The same analysis was performed to compare treatment planning system (TPS) doses to measured values to establish a baseline assessment of agreement.Results:The mean percent error between log file and ionization chamber dose was 1.0%±2.1% for prostate VMAT plans and −0.2%±1.4% for head and neck plans. The corresponding TPS calculated and measured ionization chamber values agree within 1.7%±1.6%. The average 2D gamma passing rates for the log file comparison to film are 98.8%±1.0% and 96.2%±4.2% for the prostate and head and neck plans, respectively. The corresponding passing rates for the TPS comparison to film are 99.4%±0.5% and 93.9%±5.1%. Overall, the point dose and film data indicate that log file determined doses are in excellent agreement with measured values.Conclusion:Clinical VMAT QA practice using LINAC treatment log files is a fast and reliable method for patient‐specific plan evaluation.