bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐631: Preliminary Results for Analytical Investigation Into Effects of ArcCHECK Setup Errors
Authors: Kar S , Tien C
Published: June 2015

Purpose:

As three‐dimensional diode arrays increase in popularity for patient‐specific quality assurance for intensity‐modulated radiation therapy (IMRT), it is important to evaluate an array's susceptibility to setup errors. The ArcCHECK phantom is set up by manually aligning its outside marks with the linear accelerator's lasers and light‐field. If done correctly, this aligns the ArcCHECK cylinder's central axis (CAX) with the linear accelerator's axis of rotation. However, this process is prone to error. This project has developed an analytical expression including a perturbation factor to quantify the effect of shifts.

Methods:

The ArcCHECK is set up by aligning its machine marks with either the sagittal room lasers or the light‐field of the linear accelerator at gantry zero (IEC). ArcCHECK has sixty‐six evenly‐spaced SunPoint diodes aligned radially in a ring 14.4 cm from CAX. The detector response function (DRF) was measured and combined with inverse‐square correction to develop an analytical expression for output. The output was calculated using shifts of 0 (perfect alignment), +/−1, +/−2 and +/−5 mm. The effect on a series of simple inputs was determined: unity, 1‐D ramp, steps, and hat‐function to represent uniform field, wedge, evenly‐spaced modulation, and single sharp modulation, respectively.

Results:

Geometric expressions were developed with perturbation factor included to represent shifts. DRF was modeled using sixth‐degree polynomials with correlation coefficient 0.9997. The output was calculated using simple inputs such as unity, 1‐D ramp, steps, and hat‐function, with perturbation factors of: 0, +/−1, +/−2 and +/−5 mm. Discrepancies have been observed, but large fluctuations have been somewhat mitigated by aliasing arising from discrete diode placement.

Conclusion:

An analytical expression with perturbation factors was developed to estimate the impact of setup errors on an ArcCHECK phantom. Presently, this has been applied to simple functions, but is being developed to handle more realistic clinical cases.
SU‐E‐T‐632: Preliminary Study On Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculations
Authors: Jin L , Eldib A , Li J , Price R , Ma C
Published: June 2015

Purpose:

Uneven nose surfaces and air cavities underneath and the use of bolus present complexity and dose uncertainty when using a single electron energy beam to plan treatments of nose skin with a pencil beam‐based planning system. This work demonstrates more accurate dose calculation and more optimal planning using energy and intensity modulated electron radiotherapy (MERT) delivered with a pMLC.

Methods:

An in‐house developed Monte Carlo (MC)‐based dose calculation/optimization planning system was employed for treatment planning. Phase space data (6, 9, 12 and 15 MeV) were used as an input source for MC dose calculations for the linac. To reduce the scatter‐caused penumbra, a short SSD (61 cm) was used. Our previous work demonstrates good agreement in percentage depth dose and off‐axis dose between calculations and film measurement for various field sizes. A MERT plan was generated for treating the nose skin using a patient geometry and a dose volume histogram (DVH) was obtained. The work also shows the comparison of 2D dose distributions between a clinically used conventional single electron energy plan and the MERT plan.

Results:

The MERT plan resulted in improved target dose coverage as compared to the conventional plan, which demonstrated a target dose deficit at the field edge. The conventional plan showed higher dose normal tissue irradiation underneath the nose skin while the MERT plan resulted in improved conformity and thus reduces normal tissue dose.

Conclusion:

This preliminary work illustrates that MC‐based MERT planning is a promising technique in treating nose skin, not only providing more accurate dose calculation, but also offering an improved target dose coverage and conformity. In addition, this technique may eliminate the necessity of bolus, which often produces dose delivery uncertainty due to the air gaps that may exist between the bolus and skin.
SU‐E‐T‐633: Preparation and Planning of a VMAT Multi ‐ Arc Radiation Therapy Technique for Full Scalp Treatment
Authors: Araujo C , Bardock A , Berkelaar S , Gillund D , McGee K , Mohamed I , Lapointe C
Published: June 2015

Purpose:

The target volume for angiosarcoma of the scalp encompasses the entire scalp. Full scalp radiotherapy (FSRT) requires careful design of required bolus, immobilization and marking of the field before the patient CT is acquired. A VMAT multi‐arc technique was designed to deliver FSRT for a patient with angiosarcoma of the scalp to a dose of 6000cGy in 25 fractions.

Methods:

A custom bolus helmet was fabricated from a 0.5 cm thick sheet of aquaplast material, which was molded to the patient's head. With the bolus helmet in place the patient was then positioned supine on a H&N immobilization board. A custom vaclock bag positioned on a standard headrest and a thermoplastic mask were used to immobilize the patient. Additional bolus to cover the remaining treatment area was attached to the mask. We acquired two CT scans of the patient's head, one in treatment position and an additional scan without the immobilization mask with wires marking the treatment area that the oncologist had delineated on the patient's skin. The second scan was registered to the first and used to define the treatment CTV. A four‐arc VMAT treatment planned using Varian‐Eclipse was optimized to cover the skin with a PTV margin while sparing the brain and limiting the dose to the optic apparatus and lacrimal glands. Daily treatment setup was verified using anterior and lateral kV on‐board‐imaging. To verify the treated dose, TLDs were positioned on the patient's scalp during one fraction.

Results:

With full dose coverage to the PTV, the mean dose to the brain was less than 24 Gy. The dose measured by the TLDs (mean difference 1%, standard deviation 4%)showed excellent agreement with the treatment planning calculation.

Conclusion:

FSRT delivered with a bolus helmet and a VMAT multi‐arc technique can be accurately delivered with high dose uniformity and conformality.
SU‐E‐T‐635: Process Mapping of Eye Plaque Brachytherapy
Authors: Huynh J , Kim Y
Published: June 2015

Purpose:

To apply a risk‐based assessment and analysis technique (AAPM TG 100) to eye plaque brachytherapy treatment of ocular melanoma.

Methods:

The role and responsibility of personnel involved in the eye plaque brachytherapy is defined for retinal specialist, radiation oncologist, nurse and medical physicist. The entire procedure was examined carefully. First, major processes were identified and then details for each major process were followed.

Results:

Seventy‐one total potential modes were identified. Eight major processes (corresponding detailed number of modes) are patient consultation (2 modes), pretreatment tumor localization (11), treatment planning (13), seed ordering and calibration (10), eye plaque assembly (10), implantation (11), removal (11), and deconstruction (3), respectively. Half of the total modes (36 modes) are related to physicist while physicist is not involved in processes such as during the actual procedure of suturing and removing the plaque.

Conclusion:

Not only can failure modes arise from physicist‐related procedures such as treatment planning and source activity calibration, but it can also exist in more clinical procedures by other medical staff. The improvement of the accurate communication for non‐physicist‐related clinical procedures could potentially be an approach to prevent human errors. More rigorous physics double check would reduce the error for physicist‐related procedures. Eventually, based on this detailed process map, failure mode and effect analysis (FMEA) will identify top tiers of modes by ranking all possible modes with risk priority number (RPN). For those high risk modes, fault tree analysis (FTA) will provide possible preventive action plans.
SU‐E‐T‐638: Proton Beam Delivery to a Moving Lung Tumor and Monte Carlo Simulation with TOPAS
Authors: Coruh M , Demez N , Ewell L
Published: June 2015

Purpose:

To estimate the dose delivered to a moving lung tumor by proton therapy beams of different modulation types, and compare with Monte Carlo predictions.

Methods:

A radiology support devices (RSD) phantom was irradiated with therapeutic proton radiation beams using two different types of modulation: uniform scanning (US) and double scattered (DS). The Eclipse© dose plan was designed to deliver 1.00Gy to the isocenter of a static ∼3×3×3cm (27cc) tumor in the phantom with 100% coverage. The peak to peak amplitude of tumor motion varied from 0.0 to 2.5cm. The radiation dose was measured with an ion‐chamber (CC‐13) located within the tumor. The time required to deliver the radiation dose varied from an average of 65s for the DS beams to an average of 95s for the US beams.

Results:

The amount of radiation dose varied from 100% (both US and DS) to the static tumor down to approximately 92% for the moving tumor. The ratio of US dose to DS dose ranged from approximately 1.01 for the static tumor, down to 0.99 for the 2.5cm moving tumor. A Monte Carlo simulation using TOPAS included a lung tumor with 4.0cm of peak to peak motion. In this simulation, the dose received by the tumor varied by ∼40% as the period of this motion varied from 1s to 4s.

Conclusion:

The radiation dose deposited to a moving tumor was less than for a static tumor, as expected. At large (2.5cm) amplitudes, the DS proton beams gave a dose closer to the desired dose than the US beams, but equal within experimental uncertainty. TOPAS Monte Carlo simulation can give insight into the moving tumor — dose relationship.

This work was supported in part by the Philips corporation.
SU‐E‐T‐639: Proton Dose Calculation for Irregular Motion Using a Sliding Interface
Authors: Phillips J , Gueorguiev G , Grassberger C , Paganetti H , Sharp G
Published: June 2015

Purpose:

While many techniques exist to evaluate dose to regularly moving lung targets, there are few available to calculate dose at tumor positions not present in the 4DCT. We have previously developed a method that extrapolates an existing dose to a new tumor location. In this abstract, we present a novel technique that accounts for relative anatomical shifts at the chest wall interface. We also utilize this procedure to simulate breathing motion functions on a cohort of eleven patients. Amplitudes exceeding the original range of motion were used to evaluate coverage using several aperture and smearing beam settings.

Methods:

The water‐equivalent depth (WED) technique requires an initial dose and CT image at the corresponding tumor position. Each dose volume was converted from its Cartesian geometry into a beam‐specific radiological depth space. The sliding chest wall interface was determined by converting the lung contour into this same space. Any dose proximal to the initial boundary of the warped lung contour was held fixed, while the remaining distal dose was moved in the direction of motion along the interface.

Results:

V95 coverage was computed for each patient using the updated algorithm. Incorporation of the sliding motion yielded large dose differences, with gamma pass rates as low as 69.7% (3mm, 3%) and V95 coverage differences up to 2.0%. Clinical coverage was maintained for most patients with 5 mm excess simulated breathing motion, and up to 10 mm of excess motion was tolerated for a subset of patients and beam settings.

Conclusion:

We have established a method to determine the maximum allowable excess breathing motion for a given plan on a patient‐by‐patient basis. By integrating a sliding chest wall interface into our dose calculation technique, we have analyzed the robustness of breathing patterns that differ during treatment from at the time of 4DCT acquisition.
SU‐E‐T‐642: PTV Is the Voxel‐Wise Worst‐Case of CTV in Prostate Photon Therapy
Authors: Harrington D , Schild S , Wong W , Vora S , Liu W
Published: June 2015

Purpose:

To examine the adequacy of the planning target volume (PTV) dose distribution as the worst‐case representation of clinical target volume (CTV) dose distribution in prostate volumetric‐modulated arc therapy (VMAT) plans.

Methods:

Ten intact prostate cancer cases treated by VMAT at our institution were randomly selected. Isocenter was shifted in the three cardinal directions by a displacement equal to the PTV expansion on the CTV (±3 mm) for a total of six shifted plans per original plan. Rotationally‐perturbed plans were generated with a couch rotation of ±1° to simulate patient yaw. The eight perturbed dose distributions were recalculated in the treatment planning system using the same, fixed fluence map as the original plan. The voxel‐wise worst‐case CTV dose distribution was constructed from the minimum value per voxel from the eight perturbed doses. The resulting dose volume histograms (DVH) were evaluated for statistical correlation between the worst‐case CTV and nominal PTV dose distributions based on D95% by Wilcoxon signed‐rank test with significance level p ≤ 0.05.

Results:

Inspection demonstrates the PTV DVH in the nominal dose distribution is bounded by the CTV DVH in the worst‐case dose distribution. Comparison of D95% for the two dose distributions by Wilcoxon signed‐rank test gives p = 0.131. Therefore the null hypothesis cannot be rejected since the difference in median values is not statistically significant.

Conclusion:

The assumption that the nominal dose distribution for PTV represents the worst‐case dose distribution for CTV appears valid for the ten plans under examination. Although the worst‐case dose distribution is unphysical since the dose per voxel is chosen independently, it serves as a lower bound for the possible CTV coverage. Furthermore, this is consistent with the unphysical nature of the PTV. Minor discrepancies between the two dose distributions are expected since the dose cloud is not strictly static.

Funding Support: NIH/NCI K25CA168984, Eagles Cancer Research Career Development, The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, Mayo ASU Seed Grant, and The Kemper Marley Foundation
SU‐E‐T‐643: Pure Alanine Dosimeter for Verification Dosimetry in IMRT
Authors: Al‐Karmi Anan M. , Zraiqat Fadi
Published: June 2015

Purpose:

The objective of this study was evaluation of accuracy of pure alanine dosimeters measuring intensity‐modulated radiation therapy (IMRT) dose distributions in a thorax phantom.

Methods:

Alanine dosimeters were prepared in the form of 110 mg pure L‐α‐alanine powder filled into clear tissue‐equivalent polymethylmethacrylate (PMMA) plastic tubes with the dimensions 25 mm length, 3 mm inner diameter, and 1 mm wall thickness. A dose‐response calibration curve was established for the alanine by placing the dosimeters at 1.5 cm depth in a 30×30×30 cm3 solid water phantom and then irradiating on a linac with 6 MV photon beam at 10×10 cm2 field size to doses ranging from 1 to 5 Gy. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the absorbed dose in alanine. An IMRT treatment plan was designed for a commercial heterogeneous CIRS thorax phantom and the dose values were calculated at three different points located in tissue, lung, and bone equivalent materials. A set of dose measurements was carried out to compare measured and calculated dose values by placing the alanine dosimeters at those selected locations inside the thorax phantom and delivering the IMRT to the phantom.

Results:

The alanine dose measurements and the IMRT plan dose calculations were found to be in agreement within ±2%. Specifically, the deviations were −0.5%, 1.3%, and −1.7% for tissue, lung, and bone; respectively. The slightly large deviations observed for lung and bone may be attributed to tissue inhomogeneity, steep dose gradients in these regions, and uncontrollable changes in spectrometer conditions.

Conclusion:

The results described herein confirmed that pure alanine dosimeter was suitable for in‐phantom dosimetry of IMRT beams because of its high sensitivity and acceptable accuracy. This makes the dosimeter a promising option for quality control of the therapeutic beams, complementing the commonly used ionization chambers, TLDs, and films.
SU‐E‐T‐649: Quality Assurances for Proton Therapy Delivery Equipment
Authors: Arjomandy B , Klein E , Taylor P , Ainsley C , Safai S , Sahoo N , Pankuch M , Park S , Farr J , Kase Y , Flanz J , Yorke E , Followill D
Published: June 2015

Purpose:

The number of proton therapy centers has increased dramatically over the past decade. Currently, there is no comprehensive set of guidelines that addresses quality assurance (QA) procedures for the different technologies used for proton therapy. The AAPM has charged task group 224 (TG‐224) to provide recommendations for QA required for accurate and safe dose delivery, using existing and next generation proton therapy delivery equipment.

Methods:

A database comprised of QA procedures and tolerance limits was generated from many existing proton therapy centers in and outside of the US. These consist of proton therapy centers that possessed double scattering, uniform scanning, and pencil beams delivery systems. The diversity in beam delivery systems as well as the existing devices to perform QA checks for different beam parameters is the main subject of TG‐224. Based on current practice at the clinically active proton centers participating in this task group, consensus QA recommendations were developed. The methodologies and requirements of the parameters that must be verified for consistency of the performance of the proton beam delivery systems are discussed.

Results:

TG‐224 provides procedures and QA checks for mechanical, imaging, safety and dosimetry requirements for different proton equipment. These procedures are categorized based on their importance and their required frequencies in order to deliver a safe and consistent dose. The task group provides daily, weekly, monthly, and annual QA check procedures with their tolerance limits.

Conclusions:

The procedures outlined in this protocol provide sufficient information to qualified medical physicists to perform QA checks for any proton delivery system. Execution of these procedures should provide confidence that proton therapy equipment is functioning as commissioned for patient treatment and delivers dose safely and accurately within the established tolerance limits. The report will be published in late 2015.
SU‐E‐T‐656: Quantitative Analysis of Proton Boron Fusion Therapy (PBFT) in Various Conditions
Authors: Yoon D , Jung J , Shin H , Kim M , Jang H , Suh T
Published: June 2015

Purpose:

Three alpha particles are concomitant of proton boron interaction, which can be used in radiotherapy applications. We performed simulation studies to determine the effectiveness of proton boron fusion therapy (PBFT) under various conditions.

Methods:

Boron uptake regions (BURs) of various widths and densities were implemented in Monte Carlo n‐particle extended (MCNPX) simulation code. The effect of proton beam energy was considered for different BURs. Four simulation scenarios were designed to verify the effectiveness of integrated boost that was observed in the proton boron reaction. In these simulations, the effect of proton beam energy was determined for different physical conditions, such as size, location, and boron concentration.

Results:

Proton dose amplification was confirmed for all proton beam energies considered (< 96.62%). Based on the simulation results for different physical conditions, the threshold for the range in which proton dose amplification occurred was estimated as 0.3 cm. Effective proton boron reaction requires the boron concentration to be equal to or greater than 14.4 mg/g.

Conclusion:

We established the effects of the PBFT with various conditions by using Monte Carlo simulation. The results of our research can be used for providing a PBFT dose database.
SU‐E‐T‐658: Quantitative Comparison of VMAT Arc Geometry for Locally Advanced Lung Cancer with Large PTVs
Authors: Zhu T , Wilkinson J , Burger P , Matuszak M
Published: June 2015

Purpose:

Overall low dose to lung for patients with locally advanced lung cancer with large PTVs is a concern, prompting investigation into the preferred arc geometry for lung VMAT.

Methods:

8 subjects (6 males, 64±7 years, stage III/IV=5/3) were enrolled with a mean PTV size of 595±303cc. A standard dose scheme of 60Gy in 30 fractions was used for all subjects. For each subject, four VMAT plans with different combinations of the number of arcs (1 arc vs. two arcs) and the arc range (full vs. partial arc) were generated in Eclipse. Dosimetric characteristics for each plan were evaluated by PTV coverage and OAR sparing. PTV coverage was quantified by mean, max dose, homogeneity index HI5/95 defined as (D5%–D95%)/Mean_dose and conformity index (CI). OAR sparing was measured by mean, V10 and V20 for lung minus GTV, mean, max, V30 and V40 for heart and max dose for cord. For each metric abovementioned, a two‐way repeated ANOVA analysis was performed to evaluate whether the number of arcs and the arc range will significantly affect dose distribution of VMAT plans.

Results:

In general partial arc geometry provided better PTV coverage with significantly smaller HI5/95 (p<0.05) and higher mean dose (p=0.15) when keeping the total MU similar. For OAR sparing, partial arc geometry resulted in more dose sparing to the contralateral lung with significantly reduced mean lung dose (p=0.006). On the other hand, full arc geometry significantly reduced mean dose to the ipsilateral lung (p=0.02) as well as dose to the heart and the cord (p<0.05) especially with a two‐full arc geometry.

Conclusion:

Results of this study suggest that choice of an optimal VMAT geometry depends on clinical goals. For example, partial arc geometry should be preferred over full arc when considering overall low lung dose for patients with poor lung functions.
SU‐E‐T‐659: Quantitative Evaluation of Patient Setup Accuracy of Stereotactic Radiotherapy with the Frameless 6D‐ExacTrac System Using Statistical Modeling
Authors: Keeling V , Jin H , Hossain S , Algan O , Ahmad S , Ali I
Published: June 2015

Purpose:

To evaluate patient setup accuracy and quantify individual and cumulative positioning uncertainties associated with different hardware and software components of the stereotactic radiotherapy (SRS/SRT) with the frameless‐6D‐ExacTrac system.

Methods:

A statistical model was used to evaluate positioning uncertainties of the different components of SRS/SRT treatment with the BrainLAB 6D‐ExacTrac system using the positioning shifts of 35 patients having cranial lesions (49 total lesions treated in 1, 3, 5 fractions). All these patients were immobilized with rigid head‐and‐neck masks, simulated with BrainLAB‐localizer and planned with iPlan treatment planning system. Infrared imaging (IR) was used initially to setup patients. Then, stereoscopic x‐ray images (XC) were acquired and registered to corresponding digitally‐reconstructed‐radiographs using bony‐anatomy matching to calculate 6D‐translational and rotational shifts. When the shifts were within tolerance (0.7mm and 1°), treatment was initiated. Otherwise corrections were applied and additional x‐rays were acquired (XV) to verify that patient position was within tolerance.

Results:

The uncertainties from the mask, localizer, IR‐frame, x‐ray imaging, MV and kV isocentricity were quantified individually. Mask uncertainty (Translational: Lateral, Longitudinal, Vertical; Rotational: Pitch, Roll, Yaw) was the largest and varied with patients in the range (−1.05−1.50mm, −5.06–3.57mm, −5.51−3.49mm; −1.40−2.40°, −1.24−1.74°, and −2.43−1.90°) obtained from mean of XC shifts for each patient. Setup uncertainty in IR positioning (0.88,2.12,1.40mm, and 0.64,0.83,0.96°) was extracted from standard‐deviation of XC. Systematic uncertainties of the localizer (−0.03,−0.01,0.03mm, and −0.03,0.00,−0.01°) and frame (0.18,0.25,−1.27mm,−0.32,0.18, and 0.47°) were extracted from means of all XV setups and mean of all XC distributions, respectively. Uncertainties in isocentricity of the MV radiotherapy machine were (0.27,0.24,0.34mm) and kV‐imager (0.15,−0.4,0.21mm).

Conclusion:

A statistical model was developed to evaluate the individual and cumulative systematic and random uncertainties induced by the different hardware and software components of the 6D‐ExacTrac‐system. The immobilization mask was associated with the largest positioning uncertainty.
SU‐E‐T‐660: Quantitative Fault Testing for Commissioning of Proton Therapy Machines
Authors: Reilly M , Rankine L , Grantham K , Klein E
Published: June 2015

Purpose:

To ensure proper fault testing for the first single room proton therapy machine by establishing a common set of acceptance testing and commissioning parameters with the manufacturer. The following work details the parameters tested and associated results.

Methods:

Dose rates in service mode were varied to ensure that when the threshold for maximum or minimum MU/min was met, the beam promptly shut off. The flatness parameter was tested by purposely assigning an incorrect secondary scatter, to ensure the beam shut off when detecting a heterogeneous profile. The beam symmetry parameter was tested by altering the steering coil up to 3.0A, thereby forcing the beam to be asymmetric and shut off. Lastly, the quench system was tested by ramping down the magnet to 5% capacity, whereby the quench button was engaged to bring down the magnet current to a safe level.

Results:

A dose rate increase or decrease in excess of 10% shut the beam off within 5 seconds as observed by the current on a Matrixx ionization chamber array (IBA Dosimetry, Bartlett, TN) A 3.0A change in the beam steering coil introduced a 2% change in the flatness and symmetry profiles with respect to baseline measurements resulting in the beam shutting off within 5 seconds. An incorrect 2nd scatterer introduced a flatness of 4.1% and symmetry of 6.4% which immediately triggered a beam shut off. Finally, the quench system worked as expected during the ramp down procedure.

Conclusion:

A fault testing plan to check dosimetric faults and the quench system was performed for the first single room proton therapy system. All dosimetric parameters and machine conditions were met to our satisfaction. We propose that the same type of fault testing should be applied to any proton system during commissioning, including scanning beam systems.
SU‐E‐T‐662: Quick and Efficient Daily QA for Compact PBS Proton Therapy Machine
Authors: Patel B , Syh J , Ding X , Syh J , Song X , Freund D , Wu H
Published: June 2015

Purpose:

As proton therapy machines become widespread the need for a quick simple routine daily QA like that for linear accelerators becomes more important. Willis‐Knighton has developed an accurate and efficient daily QA that can be performed in 15 minutes.

Methods:

A holder for a 2D ionization chamber array (MatriXX PT) was created that is indexed to the couch to allow for quick setup, lasers accuracy with respect to beam isocenter, and couch reproducibility. Image position/reposition was performed to check Isocentricity accuracy by placing BBs on the MatriXX. The couch coordinates are compared to that of commissioning. Laser positions were confirmed with the MatriXX isocenter. After IGRT, three beams were separately delivered according to setup. For the first beam, range shifter was inserted and dose at R90, field size, flatness and symmetry in X and Y direction was measured. R90 was used so any minor changes in the range shifter can be detected. For the open beam, dose at center of SOBP, flatness and symmetry in X and Y direction was measured. Field size was measured in ±X and ±Y direction at FWHM. This is measured so any variation in spot size will be detected. For the third beam additional solid water was added and dose at R50 was measured so that any variation in beam energy will be detected. Basic mechanical and safety checks were also performed.

Results:

Medical physicists were able to complete the daily QA and reduce the time by half to two‐third from initial daily QA procedure. All the values measured were within tolerance of that of the baseline which was established from water tank and initial MatriXX measurements.

Conclusion:

The change in daily QA procedure resulted in quick and easy setup and was able to measure all the basic functionality of the proton therapy PBS.
SU‐E‐T‐663: Radiation Properties of a Water‐Equivalent Material Formulated Using the Stoichiometric Analysis Method in Heavy Charged Particle Therapy
Authors: Yohannes I , Hild S , Vasiliniuc S , Langner O , Graeff C , Bert C
Published: June 2015

Purpose:

A material has been designed to be employed as water‐equivalent in particle therapy using a previously established stoichiometric analysis method (SAM). After manufacturing, experimental verification of the material's water‐equivalent path length (WEPL) and analysis of its total inelastic nuclear interaction cross sections for proton beams were performed.

Methods:

Using the SAM, we optimized the material composed of three base materials, i.e., polyurethane, calcium carbonate and microspheres. From the elemental composition of the compound, electron density, linear attenuation coefficients, particle stopping powers and inelastic nuclear cross sections for protons using data from ICRU 63 were calculated. The calculations were then compared to Hounsfield units (HUs) measured with 350 mAs at 80, 100, 120 and 140 kV and the WEPLs measured with three different ions: proton (106.8 MeV/u), helium (107.93 MeV/u) and carbon (200.3 MeV/u).

Results:

The material's measured HUs (0.7±3.0 to 2.6±6.2 HU) as well as its calculated relative electron density (1.0001) are in close agreement with water as reference. The WEPLs measured on a 20.00 mm thick target were 20.16±0.12, 20.29±0.12 and 20.38±0.12 mmH2O for proton, helium and carbon ions, respectively. Within measurement uncertainties, these values verified the calculated WEPLs of 20.28 mmH2O (proton), 20.28 mmH2O (helium) and 20.26 mmH2O (carbon). Moreover, the calculated proton inelastic cross sections of the material differed only by 0.89% (100 MeV/u) and 0.01% (200 MeV/u) when compared to water.

Conclusion:

The SAM is capable of optimizing material with defined properties, e.g., HU, electron density, WEPL and inelastic nuclear interaction cross section for particle therapy. Such material will have a wide range of applications amongst others absolute dosimetry.

This work was supported by grant ZIM KF2137107AK4 from the German Federal Ministry for Economic Affairs and Energy.
SU‐E‐T‐666: Radionuclides and Activity of the Patient Apertures Used in a Proton Beam of Wobbling System
Authors: Wang B.Y. , Chen H.H. , Tsai H.Y. , Sheu R.J.
Published: June 2015

Purpose:

To identify the radionuclides and quantify the activity of the patient apertures used in a 190‐MeV proton beam of wobbling system.

Methods:

A proton beam of wobbling system in the first proton center in Taiwan, Chang Gung Memorial Hospital at Linkou, was used to bombard the patient apertures. The patient aperture was composed of 60.5 % copper, 39.4 % Zinc, 0.05 % iron, 0.05 % lead. A protable high‐purity germanium (HPGe) coaxial detector was used to measure the spectra of the induced nuclides of patient apertures. The analysis of the spectra and the identification of the radionuclides were preliminarily operated by the Nuclide Navigator III Master Library. On the basis of the results by Nuclide Navigator III Master Library, we manually selected the reliable nuclides by the gamma‐ray energies, branching ratio, and half life. In the spectra, we can quantify the activity of radionuclides by the Monte Carlo efficiency transfer method.

Results:

In this study, the radioisotopes activated in patient apertures by the 190‐MeV proton beam were divided into two categories. The first category is long half‐life radionuclides, such as Co‐56 (half life, 77.3 days). Other radionuclides of Cu‐60, Cu‐61, Cu‐62, Cu‐66, and Zn‐62 have shorter half life. The radionuclide of Cu‐60 had the highest activity. From calculation with the efficiency transfer method, the deviations between the computed results and the measured efficiencies were mostly within 10%.

Conclusion:

To identify the radionuclides and quantify the activity helps us to estimate proper time intervals for cooling the patient apertures.

This study was supported by the grants from the Chang Gung Memorial Hospital (CMRPD1C0682).
SU‐E‐T‐668: Radiosensitizing Effect of Bosutinib On Prostate and Colon Cancers: A Pilot in Vitro Study
Authors: Wang B , Cvetkovic D , Wang C , Chen L , Ma C
Published: June 2015

Purpose:

Recently it has been reported that Bosutinib, a clinical kinase inhibitor, can enhance the tumor cell chemosensitivity by overriding DNA damage checkpoints. However, to the best of our knowledge, there is no report on its effect on cell radiosensitivity in the literature. The objective of the present study is to determine whether Bosutinib has the potential to be used as a radiosensitizer for various cancer cell lines.

Methods:

In this study, we tested 4 cell lines derived from human prostate (LNCaP, PC‐3, DU‐145) and colon (HT‐29) cancers. The cells were seeded into 12‐well plates 24 hours prior to the radiation treatments. For each cell line, we designed 4 study groups, namely, the control, Bosutinib, radiotherapy, and radiotherapy+Bosutinib groups. We used 6 MV photon beams from a Siemens Artiste accelerator to deliver 2 Gy dose in one fraction to the cells in the radiotherapy and radiotherapy+Bosutinib groups. Immediately after irradiation, the cells in the radiotherapy+Bosutinib group were treated with Bosutinib (1µM) for 3 hours. The cell survival was evaluated through clonogenic assays.

Results:

The cell survival rates of the LNCaP, PC‐3, DU‐145, and HT‐29 cells were found to be 21%, 92%, 76%, and 93% for the radiotherapy group; 21%, 69%, 67%, and 81% for the radiotherapy+Bosutinib group; and 103%, 107%, 86%, and 102% for the Bosutinib group, respectively. Although synergetic cell killing was not seen for the LNCaP and DU‐145 cell lines in this study, the cell survival data from the clonogenic assay indicated that Bosutinib could enhance the sensitivity of PC‐3 and HT‐29 cells to radiation treatment.

Conclusion:

Our preliminary results demonstrated the possibility of Bosutinib as a radiosensitizer for certain prostate and colon cancers, which are resistant to radiotherapy. Further studies are warranted to quantify the radiosensitizing effect of Bosutinib.
SU‐E‐T‐669: Radiosurgery Failure for Trigeminal Neuralgia: A Study of Radiographic Spatial Fidelity
Authors: Howe J , Spalding A
Published: June 2015

Purpose:

Management of Trigeminal Neuralgia with radiosurgery is well established, but often met with limited success. Recent advancements in imaging afford improvements in target localization for radiosurgery.

Methods:

A Trigeminal Neuralgia radiosurgery specific protocol was established for MR enhancement of the trigeminal nerve using a CISS scan with slice spacing of 0.7mm. Computed Tomography simulation was performed using axial slices on a 40 slice CT with slice spacing of 0.6mm. These datasets were registered using a mutual information algorithm and localized in a stereotactic coordinate system. Image registration between the MR and CT was evaluated for each patient by a Medical Physicist to ensure accuracy. The dorsal root entry zone target was defined on the CISS MR by a Neurosurgeon and dose calculations performed on the localized CT. Treatment plans were reviewed and approved by a Radiation Oncologist and Neurosurgeon. Image guided radiosurgery was delivered using positioning tolerance of 0.5mm and 1°. Eight patients with Trigeminal Neuralgia were treated with this protocol.

Results:

Seven patients reported a favorable response to treatment with average Barrow Neurological Index pain score of four before treatment and one following treatment. Only one patient had a BNI>1 following treatment and review of the treatment plan revealed that the CISS MR was registered to the CT via a low resolution (5mm slice spacing) T2 MR. All other patients had CISS MR registered directly with the localized CT. This patient was retreated 6 months later using direct registration between CISS MR and localized CT and subsequently responded to treatment with a BNI of one.

Conclusion:

Frameless radiosurgery offers an effective solution to Trigeminal Neuralgia management provided appropriate technology and imaging protocols (utilizing submillimeter imaging) are established and maintained.
SU‐E‐T‐670: Radiotherapy Vault Shielding Evaluation Method for a Flattening Filter‐Free (FFF) Linac‐Practical Considerations and Recommendations
Authors: Mihailidis D
Published: June 2015

Purpose:

To date, there isn't formal approach for flattening filter‐free (FFF) linac vault shielding evaluation, thus, we propose an extension to NCRP#151 to accommodate the recent large number of FFF linac installations.Methods and Materials: We extended the approach in NCRP#151 to design two Truebeam vaults in our new cancer center for hypofractionated treatments. Monte Carlo calculations have characterized primary, scattered, leakage and neutron radiations from FFF‐modes. These calculations have shown that: a) FFF primary beam is softer on the central‐axis compared to flattening filtered (FF), b) the lateral dose profile is peaked on the central axis and less integral target current is required to generate the same tumor dose with the FF beam. Thus, the TVLs for FFF mode are smaller than those of the FF mode and the scatter functions of the FF mode (NCRP#151) may not be appropriate for FFF‐mode, c) the neutron source strength and fluence for 18X‐FFF is smaller than 18X‐FF, but it is not of a concern here, no 18X‐FFF‐mode is available on the linac under investigation.

Results:

These barrier thickness are smaller (12% reduction on the average) than those computed for conventional FF mode with same realistic primary workload since, the primary TVLs used here are smaller and the WL is smaller than the conventional (almost half reduced), keeping the TADR in tolerance.

Conclusions:

A comprehensive method for shielding barrier calculations based on dedicated data for FFF‐mode linacs is highly desired. Meanwhile, we provide an extension to NCRP#151 to accommodate the shielding design of such installations. It is also shown that if a vault is already designed for IMRT/VMAT and SABR hypofractionated treatments with FFF‐mode linac, the vault can also be used for a FFF mode linac replacement, leaving some leeway for slightly higher workload on the FFF linac.
SU‐E‐T‐671: Range‐Modulation Effects of Carbon Ion Beams in Lung Tissue
Authors: Witt M , Weber U , Simeonov Y , Zink K
Published: June 2015

Purpose:

When particles traversing inhomogeneous materials like lung they show a characteristic range modulation which cannot be observed in homogeneous materials. It is possible to describe the range modulation by a convolution of an unperturbed Bragg‐Curve and a normal distribution. The sigma of the normal distribution is a parameter for the strength of the modulation effect. A new material parameter (modulation power, P_mod) is introduced which is independent of the material thickness. It is defined as the square of sigma divided by the mean water equivalent thickness of the target (µ).

Methods:

The modulation power of lung tissue was determined by actual Bragg‐peak measurements after traversing an ex‐vivo porcine lung and by Monte‐Carlo simulations with micro‐CT data of human lung tissue. The determined modulation powers were used to show the effect of range modulation effects in a simplified treatment situation. A four centimeter spread‐out Bragg‐peak after traversing eight centimeter of lung tissue was simulated in FLUKA. The SOBP with and without consideration of range modulation effects were compared.

Results:

As well in the measurements as in the MC simulations range modulation effects of lung tissue were observed. The determined modulation powers showed a great range from 0.05 mm, in the micro‐CT data, to 0.7 mm in the lung measurements. The SOBP comparison showed that range modulation effects Result in over‐ and underdosages at the distal and proximal edge of the SOBP. In the investigated case, the last 0.5 cm of the SOBP showed an underdosage of up to 50% at the distal edge, while 0.5 cm distal to the SOBP an overdosage of up to 50% was observed.

Conclusion:

Range modulation effects occur in inhomogeneous materials like lung. These modulation effects may Result in clinically relevant over‐ and underdosages but are currently not considered in commercially available treatment planning systems.
SU‐E‐T‐672: Real‐Time In Vivo Dosimeters Using LiPCDA and Optical Fibers
Authors: Rink A , Croteau A , Caron S , Mermut O , Jaffray DA
Published: June 2015

Purpose:

To investigate dosimeter prototypes made with lithium pentacosa‐10,12‐diynoate (LiPCDA, the material used in GafChromic EBT films) and optical fibers for their suitability in real‐time in vivo measurements.

Methods:

The prototypes, made with 500 µm plastic optical fibers and 8.5 µm thickness of LiPCDA at fiber tip, were irradiated with a 6 MV beam. To investigate the efficacy of pre‐irradiation calibration, the probes were irradiated to 2 Gy twice, with 5 minutes in between. Net optical density values (netOD) around the main absorbance peak were compared, and effect of correcting second measurement by the first was assessed. Ageing was assessed by irradiating two prototypes to 2 Gy and comparing the netOD to that obtained for 15 prototypes from the same batch 12–14 months earlier. To measure angular dependence, the probes were pre‐irradiated with beam perpendicular to fiber axis and then, 5 minutes later either perpendicular or parallel to fiber axes. The thickness‐corrected netOD measurements were compared.

Results:

Standard deviation of netOD for probes of the same batch was measured to be 5–6%. When netOD was corrected for material thickness by using results from the first irradiation, the standard deviation decreased to 1.3%. This was comparable to the uncertainty in measurements observed with a single probe and is attributed to variations in light output, spectrometer noise and splitter‐to‐probe connection variations. Comparison of netOD values obtained a year apart failed to illustrate statistically significant decrease in sensitivity due to ageing (0.38 ± 0.03 and 0.3656 ± 0.0003). NetOD measured with MV beam parallel to fiber was within error of netOD measured with MV beam perpendicular to fiber.

Conclusion:

Current prototype construction allows for shelf life of at least one year. With material thickness corrected for, the prototypes can measure dose with an uncertainty below 2% at a given energy and dose rate.

This work has been funded by the Ontario Centres of Excellence Market Readiness grant. The authors have no conflict of interest to declare.
SU‐E‐T‐674: Relationship Between Conformity Indices and Treatment Characteristics in Cone Based Linac Stereotactic Radiosurgery
Authors: Li K
Published: June 2015

Purpose:

To investigate the correlation between conformity indices and dose prescription methodologies for LINAC based stereotactic surgery (SRS) cone plans.

Methods:

A vestibular schwannoma Linac based SRS cone plan was selected for this study. The target volume was 0.49cc and its equivalent sphere diameter is 1.0cm. Single 360 degree ARC Plans with different sizes of cones were done in Eclipse Cone planning System from Varian Medical. The plans were prescribed to satisfy to be normalized to 50% isodose line, 80% isodose line, 100% isodose line covering 95% of the target volume, at target mean dose and target minimum dose. The cones were select to be 10mm, 12mm, 14mm, 16mm, 18mm, 20mm, and 22mm in diameter. The indices for this study were conformity index(CI), which is defined to be the ratio between prescription isodose volume (PIV) and target volume (TV), and integrated conformity index (ICI), which is defined to be (TVpiv)2/(PIVxTV), where TVpiv is the intersection between PIV and TV.

Results:

When the plans were normalized to 50% of maximum dose, 80% of maximum dose, 100% isodose line covering 95% of the target volume, at target mean dose and target minimum dose, the corresponding values of ICI ranged from 0.45 to 0.04, 0.68 to 0.08, 0.58 to 0.54, 0.65 to 0.58, and 0.37 to 0.26; and the corresponding values of CI ranged from 2.2 to 22.8, 0.9 to 11.4, 1.5 to 1.7, 0.7 to 0.5, and 2.7 to 3.9.

Conclusion:

The values of indices used to describe SRS plans vary with different prescription conditions for single 360 degree ARC cone plans. For plans satisfied 100 % isodose covering 95% of target volume, the values of CI were between 1 and 2. A dynamic sensitive analysis system should be developed to correlate the plan evaluation index such as CI and ICI with clinical parameters.
SU‐E‐T‐679: Retrospective Analysis of the Sensitivity of Planar Dose Measurements To Gamma Analysis Criteria
Authors: Elguindi S , Ezzell G , Gagneur J
Published: June 2015

Purpose:

IMRT QA using planar dose measurements is still a widely used method for checking the accuracy of treatment plans. A pass/fail judgment is made using gamma analysis based on a single endpoint. Using more stringent criteria is a way to increase the sensitivity to planning and delivery errors. Before such implementation, it is necessary to understand how the sensitivity to different gamma criteria settings affects gamma passing rates (GPR).

Methods:

752 IMRT QA measurements were re‐analyzed with varying distance to agreement (DTA) and dose difference (DD) percentages using a Matlab program. Other quantifying information such as the mean dose difference in the treatment target (defined as points that are greater than 80% of maximal dose) were stored in a relational database for retrospective analysis.

Results:

The average and standard deviation of GPR (%) fell from 99.84 ± (0.43) to 89.61 ± (6.08) when restricting DD from 5 − 1% respectively, as compared to a drop from 99.15 ± (1.19) to 95.00 ± (4.43), when restricting the DTA from 5 − 1 mm respectively. The mean dose difference (%) in the treatment target between measured and calculated dose was −1.96 ± (0. 83), −0.09 ± (0.98), and 1.44 ± (0. 86) for each of our institution's three matched linear accelerators (LINAC 1, 2, and 3 respectively). For plans that are approximately 2.7 sigma below the mean GPR, an average of 78.4% of those plans were measured on LINAC 1 or 3, while only 48% of the total plans were run on those machines.

Conclusion:

The data demonstrates that when restricting gamma criterion, such as the DD, the greatest indicator of reduced GPR in our institution is which matched LINAC the plan was measured on. While small, these differences manifest themselves to levels comparable to other treatment related differences and possibly confound the gamma analysis.