bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐138: Automated Chart Review Module Including Cross‐Vendor Data Transfer Verification Developed for IHE‐RO Initiative
Authors: Brewer M , Gordon C , Tien C
Published: June 2015

Purpose:

To follow the Integrating Healthcare Enterprise ‐ Radiation Oncology (IHE‐RO) initiative of proper cross‐vendor technology integration, an automated chart checker (ACC) was developed. ACC compares extracted data from an approved patient plan in the Eclipse treatment planning system (TPS) against data existing in the Mosaiq treatment management system (TMS). ACC automatically analyzes these parameters using built‐in quality checklists to provide further aid in chart review.

Methods:

Eclipse TPS data are obtained using Eclipse scripting API (ESAPI) while Mosaiq TMS data are obtained from a radiotherapy‐treatment‐planning (RTP) file. Using this information, ACC identifies TPS‐TMS discrepancies in 18 primary beam parameters including MU, energy, jaw positions, gantry angle, table angle, accessories, and bolus for up to 31 beams. Next, approximately 40 items from traditional quality checklists are evaluated such as prescription consistency, DRR graticule placement, plan approval status, global max dose, and dose tracking coefficients. Parameters were artificially modified to determine if ACC would detect an error in data transfer and to test each component of quality checklists.

Results:

Using ESAPI scripting and RTP file‐processing, ACC was able to properly aggregate data from TPS and TMS for up to 31 beams. Errors were artificially introduced into each plan parameter, and ACC was able to successfully detect all of them within seconds. Next, ACC was able to successfully detect mistakes in the chart by identifying deviations with its quality checklists, within seconds.

Conclusion:

ACC effectively addresses the potential issue of faulty cross‐vendor data transfer, as described by IHE‐RO. In addition, ACC was also able to detect deviations from its built‐in quality checklists. ACC is already an invaluable tool for efficient and standardized chart review and will continue to improve as its incorporated checklists become more comprehensive.
SU‐E‐T‐146: Beam Energy Spread Estimate Based On Bragg Peak Measurement
Authors: Anferov V , Derenchuk V , Moore R , Schreuder A
Published: June 2015

Purpose:

ProNova is installing and commissioning a two room proton therapy system in Knoxville, TN. Beam energy out of the 230MeV cyclotron was measured on Jan 24, 2015. Cyclotron beam was delivered into a Zebra multi layered IC detector calibrated in terms of penetration range in water. The analysis of the measured Bragg peak determines penetration range in water which can be subsequently converted into proton beam energy. We extended this analysis to obtain an estimate of the beam energy spread out of the cyclotron.

Methods:

Using Monte Carlo simulations we established the correlation between Bragg peak shape parameters (width at 50% and 80% dose levels, distal falloff) and penetration range for a monoenergetic proton beam. For large uniform field impinging on a small area detector, we observed linear dependence of each Bragg peak parameter on beam penetration range as shown in Figure A. Then we studied how this correlation changes when the shape of Bragg peak is distorted by the beam focusing conditions. As shown in Figure B, small field size or diverging beam cause Bragg peak deformation predominantly in the proximal region. The distal shape of the renormalized Bragg peaks stays nearly constant. This excludes usage of Bragg peak width parameters for energy spread estimates.

Results:

The measured Bragg peaks had an average distal falloff of 4.86mm, which corresponds to an effective range of 35.5cm for a monoenergetic beam. The 32.7cm measured penetration range is 2.8cm less. Passage of a 230MeV proton beam through a 2.8cm thick slab of water results in a ±0.56MeV energy spread. As a final check, we confirmed agreement between shapes of the measured Bragg peak and one generated by Monte‐Carlo code for proton beam with 0.56 MeV energy spread.

Conclusion:

Proton beam energy spread can be estimated using Bragg peak analysis.
SU‐E‐T‐147: Beam Specific Planning Target Volumes Incorporating 4DCT for Pencil Beam Scanning Proton Therapy of Thoracic Tumors
Authors: Lin L , Kang M , Huang S , Mayer R , Thomas A , McDonough J , Solberg T , Simone C
Published: June 2015

Purpose:

The purpose of this study is to determine whether organ sparing and target coverage can be simultaneously maintained for pencil beam scanning (PBS) proton therapy treatment of thoracic tumors in the presence of motion, stopping power uncertainties and patient setup variations.

Methods:

Ten consecutive patients that were previously treated with proton therapy to 66.6/1.8 Gy (RBE) using double scattering (DS) were replanned with PBS. Minimum and maximum intensity images from 4DCT were used to introduce flexible smearing in the determination of the beam specific PTV (BSPTV). Datasets from eight 4DCT phases, using ±3% uncertainty in stopping power, and ±3 mm uncertainty in patient setup in each direction were used to create 8*12*10=960 PBS plans for the evaluation of ten patients. Plans were normalized to provide identical coverage between DS and PBS.

Results:

The average lung V20, V5, and mean doses were reduced from 29.0%, 35.0%, and 16.4 Gy with DS to 24.6%, 30.6%, and 14.1 Gy with PBS, respectively. The average heart V30 and V45 were reduced from 10.4% and 7.5% in DS to 8.1% and 5.4% for PBS, respectively. Furthermore, the maximum spinal cord, esophagus and heart dose were decreased from 37.1 Gy, 71.7 Gy and 69.2 Gy with DS to 31.3 Gy, 67.9 Gy and 64.6 Gy with PBS. The conformity index (CI), homogeneity index (HI), and global maximal dose were improved from 3.2, 0.08, 77.4 Gy with DS to 2.8, 0.04 and 72.1 Gy with PBS. All differences are statistically significant, with p values <0.05, with the exception of the heart V45 (p= 0.146).

Conclusion:

PBS with BSPTV achieves better organ sparing and improves target coverage using a repainting method for the treatment of thoracic tumors. Incorporating motion‐related uncertainties is essential

This work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17‐W81XWH‐07‐2‐0121 and W81XWH‐09‐2‐0174.
SU‐E‐T‐152: Building An Ultrafast, Earthquake Proof Treatment Planning System
Authors: Bush K , Freeman J , Zavalkovskiy B
Published: June 2015

Purpose:

Situated 20 miles from 5 major fault lines in California's Bay Area, Stanford Universityhas a critical need for IT infrastructure planning to handle the high probability devastating earthquakes. Recently, a multi‐million dollar project has been underway to overhaul Stanford's radiation oncology information systems, maximizing planning system performance and providing true disaster recovery abilities. An overview of the project will be given with particular focus on lessons learned throughout the build.

Methods:

In this implementation, two isolated external datacenters provide geographical redundancy to Stanford's main campus datacenter. Real‐time mirroring is made of all data stored to our serial attached network (SAN) storage. In each datacenter, hardware/software virtualization was heavily implemented to maximize server efficiency and provide a robust mechanism to seamlessly migrate users in the event of an earthquake. System performance is routinely assessed through the use of virtualized data robots, able to log in to the system at scheduled times, perform routine planning tasks and report timing results to a performance dashboard. A substantial dose calculation framework (608 CPU cores) has been constructed as part of the implementation.

Results:

Migration to a virtualized server environment with a high performance SAN has resulted in up to a 45% speed up of common treatment planning tasks. Switching to a 608 core DCF has resulted in a 280% speed increase in dose calculations. Server tuning was found to further improved read/write performance by 20%. Disaster recovery tests are carried out quarterly and, although successful, remain time consuming to perform and verify functionality.

Conclusion:

Achieving true disaster recovery capabilities is possible through server virtualization, support from skilled IT staff and leadership. Substantial performance improvements are also achievable through careful tuning of server resources and disk read/write operations. Developing a streamlined method to comprehensively test failover is a key requirement to the system's success.
SU‐E‐T‐153: Burst‐Mode Modulated Arc Therapy with Flattening‐Filter‐Free Beams Versus Flattening‐Filtered Beams
Authors: Kainz K , Lawton C , Li X
Published: June 2015

Purpose:

To compare the dosimetry and delivery of burst‐mode modulated arc radiotherapy using flattening‐filter‐free (FFF) and flattening‐filtered (FF) beams.

Methods:

Burst‐mode modulated arc therapy (mARC, Siemens) plans were generated for six prostate cases with FFF and FF beam models, using the Elekta Monaco v. 5.00 planning system. One 360‐degree arc was used for five cases, and for one case two 360‐degree coplanar arcs were used. The maximum number of optimization points (OPs) per arc was set to 91, and OPs with less than 4 MU were disregarded. All plans were delivered on the Siemens Artiste linear accelerator with 6MV FF (300 MU/min) and comparable‐energy FFF (2000 MU/min, labeled as 7UF) beams.

Results:

For all cases studied, the plans with FFF beams exhibited DVHs for the PTV, rectum, and bladder that were nearly identical to those for the plans with FF beams. The FFF plan yielded reduced dose to the right femoral head for 5 cases, and lower mean dose to the left femoral head for 4 cases. For all but the two‐arc case, the FFF and FF plans resulted in an identical number of segments. The total number of MUs was slightly lower for the FF plans for five cases. The total delivery time per fraction was substantially lower for the FFF plans, ranging from 25 to 50 percent among all cases, as compared to the FF plans.

Conclusion:

For mARC plans, FFF and FF beams provided comparable PTV coverage and rectum and bladder sparing. For the femoral heads, the mean dose was slightly lower in most cases when using the FFF beam. Although the flat beam plans typically required slightly fewer MUs, FFF beams required substantially less time to deliver a plan of similar quality.

This work was supported by Siemens Medical Solutions and the MCW Cancer Center Fotsch Foundation.
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 solutions

The 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.
SU‐E‐T‐189: Commission Range Shifter On a Spot Scanning Proton System Using Raystation Treatment Planning System
Authors: Ding X , Rosen L , Wu H
Published: June 2015

Purpose:

To treat superficial target e.g. chest wall, head&neck or cranial cases, we commissioned two range shifter(RS) in Raystation4.0 with 7.37cm(RS1) and 4.1cm(RS2) Water Equivalent Thickness(WET) respectively. However, current beam model has limitations due to the secondary scattered proton. This study provides a detailed and critical commission data and provides suggestions for using RS in clinic.

Methods:

RS’ WET was verified by Multi‐Layer Ionization Chamber from 120MeV to 226.7MeV before TPS modeling. Spot characteristics were measured using 2D scintillate detector at ISO with different air gap. A 8×8×10cm3 cube is created in 8cm depth of water to verify the absolute dose accuracy. Plans were created with different air gap using both RS. Absolute dose verification was measured along the central axis from distal end to surface using PPC05. 10 clinical RS2 plans were measured using MatriXXPT in 3 planes (proximal, distal and midSOBP).

Results:

RS material's proton stopping power is energy dependent(from 70MeV to 226.7MeV) ranging from 7.42 to 7.31cm and from 4.10 to 4.03cm respectively. We chose 7.37cm (RS1) and 4.10cm (RS2) to favor the low and median proton energy. With different air gap(3cm to 32cm), spot size expands from 3.2mm to 5.5mm(RS1) and from 3.1mm to 4.1mm(RS2) respectively(226.7MeV in air, 1‐sigma). For the absolute dose verification, the larger air gap and shallower depth causes larger discrepancy between TPS and measurements. All 10 clinical plans with 5–10cm air gap passed gamma index 95% with 3%/3mm criteria and outputs differences were within 3%.

Conclusion:

We strongly recommend each institution to verify the WET independently and choose the value to fit the clinical needs. To minimize the output difference in Raystation4.0 while avoid potential collision to the patient, we recommend to use 5–10cm air gap to minimize the output difference within 2% and preferably use RS with smaller WET if possible.
SU‐E‐T‐191: Commissioning and Dosimetric Characteristics of Elekta Agility for Total Skin Electron Beam (TSEB) Therapy
Authors: Sayler E , Charpentier P , Micaily B , Miyamoto C , Li S
Published: June 2015

Purpose

The purpose of this work is to publish beam data from Elekta Synergy(R) linear accelerators with Agility(TM) MLC for total skin electron beam (TSEB) therapy using the HDRE1 (High Dose Rate Electron 6MeV) energy.

Method & Materials

The optimal gantry angles for TSEB were determined using ion chamber measurements along a vertical profile at 450cm SSD. After gantry angles were chosen, field uniformity was measured over the entire treatment area. Uniformity was measured with and without the patient support device, allowing the dosimetric effect of the support device to be determined. Beam output and PDD were measured at the calibration point (450cm SSD) for a dual beam using a parallel plate chamber in solid water. These measurements were repeated with the chamber and phantom rotated about the patient isocenter at various angles, in order to measure the contribution from oblique beams. This technique provides a precise measurement of the treatment skin dose (TSD). Lastly, ion chamber measurements were verified by film and diodes.

Results

The optimal gantry angle for 450 cm SSD was determined to be 90±16°. This achieved uniformity better than 96% on the vertical axis, and 92% along the horizontal axis. HDRE1 was calibrated to deliver 10 cGy/MU at standard geometry (100 cm SSD, 1.2 cm depth). Thus at TSEB geometry (450 cm SSD, 0.1 cm depth) the output of the AP dual field was measured to be 0.35 cGy/MU. The TSD of a 20 cm radius cylinder for six (equally, 60° spaced) dual fields was measured to be 1.19 cGy/MU. Percent Depth Dose data for the AP dual field and TSD are shown in Figure 2.

Conclusion

This paper provides a modern procedure for commissioning TSEB therapy on a linear accelerator, and clinical beam data for the Elekta Synergy(R) with Agility(TM) MLC.
SU‐E‐T‐197: Comparing Quality Assurance Strategies for Single Isocenter Treatments of Multiple Brain Metastases
Authors: Maurer J , Liu H , Wiant D , Koch K , Manning M , Sintay B
Published: June 2015

Purpose:

To demonstrate a new quality assurance (QA) technique for single isocenter volumetric modulated arc therapy (VMAT) plans for stereotactic radiosurgery of multiple brain metastases and to compare quantitative QA results using this method with results using a cylindrical diode array and full field coronal films.

Methods:

This study employs a phantom built of 28 thin slabs to accommodate radiochromic film insertions near all planning target volume (PTV) locations, providing target specific data for individual PTVs. Single isocenter VMAT plans were designed for two patients with 5 and 11 intra‐cranial metastases. Both plans were modified three times to create plans that overdosed a target by 10%, and underdosed a target by 10 % and 20%. Gamma analyses were performed for full field coronal films, the diode array measurements and for individual PTVs with the proposed film stack method using square ROIs centered on the PTVs, measuring twice the length of the PTV's equivalent sphere diameter. Passing gamma criteria was 95% of points passing at 5%/1mm and a threshold of 10% of the prescription dose.

Results:

Of the 6 introduced errors, 1 was detected by the diode array gamma test (93.1% pass rate). Pass rates for the other 5 ranged from 95.4–98.8%. None of the errors were detected using the full field film gamma test (pass rates: 98.7–99.9%). Using the proposed film stack method, 5 of 6 errors were detected by failed gamma tests (pass rates: 51, 53, 71, 87.3, 93.9 and 97.8%). The two high pass rates were due to attempts to underdose a PTV that measured too high in the original plan.

Conclusion:

The results suggest that current methods may be lacking quantitative value and rely heavily on challenging qualitative evaluation, while the proposed method offers a much needed practical method for meaningful quantitative results.
SU‐E‐T‐199: Comparison Between Acuros XB and AAA in Homogeneous Phantoms for Volumetric Modulated Arc Therapy Plans
Authors: Lu J‐Y , Huang B‐T , Zhang J‐Y
Published: June 2015

Purpose:

To investigate the differences among Acuros XB (AXB) with dose‐to‐water report mode (AXBw), AXB with dose‐to‐medium report mode (AXBm) and Anisotropic Analytical Algorithm (AAA), in homogeneous phantoms and for volumetric modulated arc therapy (VMAT) plans.

Methods:

Nineteen clinically applied VMAT plans were transplanted to a Delta4 phantom and an I'mRT phantom to generate phantom plans, respectively. Each plan was calculated using AXBw, AXBm and AAA, respectively, utilizing the distributed calculation framework (DCF), and the calculation times were recorded. Each plan was delivered by the TrueBeam linear accelerator and measured using the Delta4 phantom and ionization chamber, respectively. The 3D gamma pass rates and point dose deviations were compared among AXBw, AXBm and AAA.

Results:

In terms of the gamma pass rates with both the criteria of 3 mm/3% (3 mm distance‐to‐agreement, 3% dose difference) and 2 mm/2%, AXBm demonstrated the significantly worst results, and no significant difference was found between AXBw and AAA. In terms of the point dose, AXBw was slightly closer to the measured dose compared with AAA, and AXBm demonstrated the maximum dose deviation from the measured dose. Moreover, AXB calculation consumed comparable time when the DCF was not busy, and consumed significantly less time when the DCF was busy.

Conclusion:

In the homogeneous phantoms and for the VMAT plans, AXBw has the best dose accuracy, and AAA is comparable to or slightly worse than AXBw, wheras AXBm has the worst dose accuracy. Furthermore, AXB has higher calculation efficiency than AAA.
SU‐E‐T‐200: Comparison Between HybridARC and Sliding Windows IMRT for Spine SBRT Tumors
Authors: Venencia C , Vacca N , Garrigo E , Caussa L
Published: June 2015

Purpose:

Spine SBRT treatments require high dose to PTV, located close to OAR. Treatment time should be short due to patient condition. The objective of this work is to compare HybridARC (HA) with sliding windows IMRT treatment modality

Methods:

A 6MV photon beam with 1000MU/min (SRS beam) produced by a NovalisTX (Varian/BrainLAB) equipped with HDMLC was used. The TPS was iPlan v4.5.3 (BrainLAB). Treatment plans comparison was done for 5 patients. Dose prescription was 27Gy in 3 fractions. HA used 1 arc plus 3 (HA), 5 (HA5) and 8 (HA8) IMRT fields. HA plans used OAR high. Between 60–40% of the prescribed dose was given by the arc. IMRT plans used 15 beams. Treatment times, MU, CI, V50% and V20% was used for plans comparisons.

Results:

Assuming IMRT plan as reference, the treatment time was reduced by −14.6% with HA8, −8.6% with HA5 and −23% with HA3. Increasing arc dose proportion in HA (arc MU > 2000) requires 2 or more arcs which increments treatment time. HA3 and HA5 exhibits beam hold off for fixed IMRT fields which in some cases need to be split in 2 segments. MU varied +4% with HA8, +3.7% with HA5 and −5% with HA3. CI increased +5% with HA8, +23% with HA5 and +37% with H3. V50% increased +5% with HA8, +43% with HA5 and +62% with HA3. V20% increased +13.2% with HA8, +7.6% with HA5 and +1% with HA3. OARs doses were keep within tolerances in all plans.

Conclusion:

HybridARC for spine SBRT with 8 fix IMRT gantry angle shows a treatment time reduction, comparable MU and similar dose conformation to dMLC IMRT. HybridARC with 5 or 3 fix IMRT fields produce undesirable beam hold off, worse dose conformation and increments the total volume with 50% of the prescribed dose.
SU‐E‐T‐202: Comparison of 4D‐Measurement‐Guided Dose Reconstructions (MGDR) with COMPASS and OCTAVIUS 4D System
Authors: Leung R , Wong M , Blanck O , Lee V , Law G , Lee K , Tung S , Chan M
Published: June 2015

Purpose:

To cross‐validate the MGDR of COMPASS (IBA dosimetry, GmbH, Germany) and OCTAVIUS 4D system (PTW, Freiburg, Germany).

Methods:

Volumetric‐modulated arc plans (5 head‐and‐neck and 3 prostate) collapsed to 40° gantry on the OCTAVIUS 4D phantom in QA mode on Monaco v5.0 (Elekta, CMS, Maryland Heights, MO) were delivered on a Elekta Agility linac. This study was divided into two parts: (1) error‐free measurements by gantry‐mounted EvolutionXX 2D array were reconstructed in COMPASS (IBA dosimetry, GmbH, Germany), and by OCTAVIUS 1500 array in Versoft v6.1 (PTW, Freiburg, Germany) to obtain the 3D doses (COM4D and OCTA4D). COM4D and OCTA4D were compared to the raw measurement (OCTA3D) at the same detector plane for which OCTAVIUS 1500 was perpendicular to 0° gantry axis while the plans were delivered at gantry 40°; (2) beam steering errors of energy (Hump=‐2%) and symmetry (2T=+2%) were introduced during the delivery of 5 plans to compare the MGDR doses COM4D_Hump (COM4D_2T), OCTA4D_Hump (OCTA4D_2T), with raw doses OCTA3D_Hump (OCTA3D_2T) and with OCTA3D to assess the error reconstruction and detection ability of MGDR tools. All comparisons used Υ‐criteria of 2%(local dose)/2mm and 3%/3mm.

Results:

Averaged Υ passing rates were 85% and 96% for COM4D,and 94% and 99% for OCTA4D at 2%/2mm and 3%/3mm criteria respectively. For error reconstruction, COM4D_Hump (COM4D_2T) showed 81% (93%) at 2%/2mm and 94% (98%) at 3%/3mm, while OCTA4D_Hump (OCTA4D_2T) showed 96% (96%) at 2%/2mm and 99% (99%) at 3%/3mm. For error detection, OCTA3D doses were compared to COM4D_Hump (COM4D_2T) showing Υ passing rates of 93% (93%) at 2%/2mm and 98% (98%), and to OCTA4D_Hump (OCTA4D _2T) showing 94% (99%) at 2%/2mm and 81% (96%) at 3%/3mm, respectively.

Conclusion:

OCTAVIUS MGDR showed better agreement to raw measurements in both error‐ and error‐free comparisons. COMPASS MGDR deviated from the raw measurements possibly owing to beam modeling uncertainty.
SU‐E‐T‐206: Comparison of EBT and EBT3 RadioChromic Films in Radiation Field of Parotid Cancer Radiotherapy
Authors: Toosi T Bahreyni , Mianaei F Khorshidi , Ghorbani M , Khabbaz Kazemi N Mohammadian , Mohammadi M , Meigooni A Soleimani
Published: June 2015

Purpose:

The aim of the current study is to compare EBT and EBT3 RadioChromic films in dosimetry of radiotherapy fields for treatment of parotid cancer.

Methods:

The calibrations of EBT and EBT3 films were performed with the same setups for doses ranging from 0.2 Gy to 5 Gy using 6 MV photon beam of a Siemens Primus linac. These films were scanned in color mode (RGB) by a Microtek (1000XL) scanner and the red color channel data was extracted. Treatment planning for parotid cancer radiation therapy was performed on a RANDO phantom. Skin dose was measured at different points in the right anterior oblique (RAO) and right posterior oblique (RPO) fields by EBT and EBT3 films.

Results:

Dosimetry was performed with the same conditions for the two film types for calibration and in‐phantom in parotid cancer radiotherapy. The measured net optical density (NOD) in EBT film was in some extent higher than that from EBT3 film. The minimum difference between these two films under calibration conditions was about 2.9% (for 0.2 Gy). However, the maximum difference was 35.5% (for 0.5 Gy). In the therapeutic fields of parotid cancer radiotherapy at different points, the measured dose from EBT film was higher than the EBT3 film. In these fields the minimum and maximum measured dose differences were 16.0% and 25.5%, respectively.

Conclusion:

With the same irradiation and reading conditions, EBT film demonstrates higher NOD than the EBT3 film. This effect may be related to the higher sensitivity of EBT film over EBT3 film. However, the obtained dose differences between these two films in low dose range can be due to the differences in fitting functions applied following the calibration process.