bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐476: Improving KCl:Eu2+ Dosimeter Sensitivity: The Role of Oxygen
Authors: Xiao Z , Mazur T , Driewer J , Li H
Published: June 2015

Purpose:

Recent research has shown that KCl:Eu2+ has great potential for use in megavoltage radiation therapy dosimetry because this material exhibits excellent storage performance and is reusable due to strong radiation hardness. The purpose of this work is to determine if increased signal could be realized in KCl:Eu2+ by incorporating oxygen in the material fabrication process.

Methods:

The prototype KCl:Eu2+ dosimeters have a physical makeup similar to thermoluminescent dosimeter chips. The photostimulation light source consists of either a He‐Ne laser or a UV enhanced Xe arc lamp with wavelength selection provided by a motorized monochromator. X‐ray diffraction is used to determine the phase composition of the dosimeters. Photoluminescence (PL) and photostimulated luminescence (PSL) emission spectra are obtained using a Nanolog Spectrofluoremeter.

Results:

Europium activator is completely incorporated into the KCl parent‐matrix without the formation of a noticeable secondary phase. Regardless of synthesis atmosphere, air or pure nitrogen, PSL amplitude shows a maximum at 1.0 mol % Eu. Depending on europium concentration, dosimeters fabricated in air exhibit stronger PSL by a factor of 2 to 4 compared to those made in N2. There is no change in PSL stimulation spectrum while noticeable shifts in both PL and PSL emission spectra are observed for air versus nitrogen. Almost all charge‐storage centers are spatially correlated, suggesting oxygen's stabilization role in the PSL process. KCl:Eu2+ made in oxygen‐rich air is capable of measuring a dose‐to‐water as low as 0.01 cGy from a 6MV photon beam with a signal‐to‐noise ratio greater than 6.

Conclusions:

Synthesis in a reduction atmosphere, for example, nitrogen, was thought to be mandatory in order to retain europium activator's divalent status to be PSL active. Fortunately, divalent europium can be well preserved in an oxygen‐rich atmosphere. More importantly, oxygen can enhance PSL by a factor of 2 to 4.

HL is the founder of DoseImaging, LLC that is exclusively dedicated to commercializing this technology.
SU‐E‐T‐479: IMRT Plan Recalculation in Patient Based On Dynalog Data and the Effect of a Single Failing MLC Motor
Authors: Morcos M , Mitrou E
Published: June 2015

Purpose:

Using Linac dynamic logs (Dynalogs) we evaluate the impact of a single failing MLC motor on the deliverability of an IMRT plan by assessing the recalculated dose volume histograms (DVHs) taking the delivered MLC positions and beam hold‐offs into consideration.

Methods:

This is a retrospective study based on a deteriorating MLC motor (leaf 36B) which was observed to be failing via Dynalog analysis. To investigate further, Eclipse‐importable MLC files were generated from Dynalogs to recalculate the actual delivered dose and to assess the clinical impact through DVHs. All deliveries were performed on a Varian 21EX linear accelerator equipped with Millennium‐120 MLC. The analysis of Dynalog files and subsequent conversion to Eclipse‐importable MLC files were all performed by in‐house programming in Python. Effects on plan DVH are presented in the following section on a particular brain‐IMRT plan which was delivered with a failing MLC motor which was then replaced.

Results:

Global max dose increased by 13.5%, max dose to the brainstem PRV increased by 8.2%, max dose to the optic chiasm increased by 7.6%, max dose to optic nerve increased by 8.8% and the mean dose to the PTV increased by 7.9% when comparing the original plan to the fraction with the failing MLC motor. The reason the dose increased was due to the failure being on the B‐bank which is the lagging side on a sliding window delivery, therefore any failures on this side will cause an over‐irradiation as the B‐bank leaves struggles to keep the window from growing.

Conclusion:

Our findings suggest that a single failing MLC motor may jeopardize the entire delivery. This may be due to the bad MLC motor drawing too much current causing all MLCs on the same bank to underperform. This hypothesis will be investigated in a future study.
SU‐E‐T‐483: In Vivo Dosimetry of Conventional and Rotational Intensity Modulated Radiotherapy Using Integral Quality Monitor (IQM)
Authors: Lin L , Qian J , Gonzales R , Keck J , Armour E , Wong J
Published: June 2015

Purpose:

To investigate the accuracy, sensitivity and constancy of integral quality monitor (IQM), a new system for in vivo dosimetry of conventional intensity modulated radiation therapy (IMRT) or rotational volumetric modulated arc therapy (VMAT)

Methods:

A beta‐version IQM system was commissioned on an Elekta Infinity LINAC equipped with 160‐MLCs Agility head. The stationary and rotational dosimetric constancy of IQM was evaluated, using five‐field IMRT and single‐or double‐arc VMAT plans for prostate and head‐and‐neck (H&N) patients. The plans were delivered three times over three days to assess the constancy of IQM response. Picket fence (PF) fields were used to evaluate the sensitivity of detecting MLC leaf errors. A single leaf offset was intentionally introduced during delivery of various PF fields with segment apertures of 3×1, 5×1, 10×1, and 24×1cm2. Both 2mm and 5mm decrease in the field width were used.

Results:

Repeated IQM measurements of prostate and H&N IMRT deliveries showed 0.4 and 0.5% average standard deviation (SD) for segment‐by‐segment comparison and 0.1 and 0.2% for cumulative comparison. The corresponding SDs for VMAT deliveries were 6.5, 9.4% and 0.7, 1.3%, respectively. Statistical analysis indicates that the dosimetric differences detected by IQM were significant (p < 0.05) in all PF test deliveries. The largest average IQM signal response of a 2 mm leaf error was found to be 2.1% and 5.1% by a 5mm leaf error for 3×1 cm2 field size. The same error in 24×1 cm2 generates a 0.7% and 1.4% difference in the signal.

Conclusion:

IQM provides an effective means for real‐time dosimetric verification of IMRT/ VMAT treatment delivery. For VMAT delivery, the cumulative dosimetry of IQM needs to be used in clinical practice.
SU‐E‐T‐484: In Vivo Dosimetry Tolerances in External Beam Fast Neutron Therapy
Authors: Young L , Gopan O
Published: June 2015

Purpose:

Optical stimulated luminescence (OSL) dosimetry with Landauer Al2O3:C nanodots was developed at our institution as a passive in vivo dosimetry (IVD) system for patients treated with fast neutron therapy. The purpose of this study was to establish clinically relevant tolerance limits for detecting treatment errors requiring further investigation.

Methods:

Tolerance levels were estimated by conducting a series of IVD expected dose calculations for square field sizes ranging between 2.8 and 28.8 cm. For each field size evaluated, doses were calculated for open and internal wedged fields with angles of 30°, 45°, or 60°. Theoretical errors were computed for variations of incorrect beam configurations. Dose errors, defined as the percent difference from the expected dose calculation, were measured with groups of three nanodots placed in a 30 × 30 cm solid water phantom, at beam isocenter (150 cm SAD, 1.7 cm Dmax). The tolerances were applied to IVD patient measurements.

Results:

The overall accuracy of the nanodot measurements is 2–3% for open fields. Measurement errors agreed with calculated errors to within 3%. Theoretical estimates of dosimetric errors showed that IVD measurements with OSL nanodots will detect the absence of an internal wedge or a wrong wedge angle. Incorrect nanodot placement on a wedged field is more likely to be caught if the offset is in the direction of the “toe” of the wedge where the dose difference in percentage is about 12%. Errors caused by an incorrect flattening filter size produced a 2% measurement error that is not detectable by IVD measurement alone.

Conclusion:

IVD with nanodots will detect treatment errors associated with the incorrect implementation of the internal wedge. The results of this study will streamline the physicists’ investigations in determining the root cause of an IVD reading that is out of normally accepted tolerances.
SU‐E‐T‐486: In Vivo Skin Dosimetry Using the Exradin W1 Plastic Scintillation Detector for Passively Scattered Proton Beam Therapy
Authors: Alsanea F , Wootton L , Kudchadker R , Usama M , Beddar S
Published: June 2015

Purpose:

To evaluate the accuracy and usefulness of plastic scintillation detectors used for skin dosimetry of patients undergoing passive scatter proton therapy.

Methods:

Following an IRB approved protocol, six patients undergoing passively scattered proton beam therapy for prostate cancer were selected for in vivo skin dosimetry using the Exradin W1 plastic scintillator. The detector was calibrated on a Cobalt‐60 unit, and phantom measurements in the proton beam with the W1 and a calibrated parallel plate ion chamber were used to account for the under‐response due to high LET at energies used for treatment. Measurements made in a heated water tank were used to account for temperature dependence. For in vivo measurements, the W1 is fixed to the patient's skin with medical tape in the center of each of two laterally opposed treatment fields. Measurements will be performed once per week for each patient for the duration of treatment, for a total of thirty six measurements. The measured dose will be compared to the expected dose, extracted from the Eclipse treatment planning system. The average difference over all measurements and per‐patient will be computed, as well as standard deviations.

Results:

The calibrated detector exhibited a 7% under‐response in 225 and 250 MeV beams, and a 4% under‐response when used at 37 °C (relative to the response at the calibration temperature of 20 °C). Patient measurements are ongoing.

Conclusion:

The Exradin W1 plastic scintillator detector is a strong candidate for in vivo skin dosimetry in passively scattered proton beams as PSDs are water equivalent and very small (2mm in diameter), permitting accurate measurements that do not perturb the delivered dose.

This project was supported in part by award number CA182450 from the National Cancer Institute.
SU‐E‐T‐490: Independent Three‐Dimensional (3D) Dose Verification of VMAT/SBRT Using EPID and Cloud Computing
Authors: Ding A , Han B , Bush K , Wang L , Xing L
Published: June 2015

Purpose:

Dosimetric verification of VMAT/SBRT is currently performed on one or two planes in a phantom with either film or array detectors. A robust and easy‐to‐use 3D dosimetric tool has been sought since the advent of conformal radiation therapy. Here we present such a strategy for independent 3D VMAT/SBRT plan verification system by a combined use of EPID and cloud‐based Monte Carlo (MC) dose calculation.

Methods:

The 3D dosimetric verification proceeds in two steps. First, the plan was delivered with a high resolution portable EPID mounted on the gantry, and the EPID‐captured gantry‐angle‐resolved VMAT/SBRT field images were converted into fluence by using the EPID pixel response function derived from MC simulations. The fluence was resampled and used as the input for an in‐house developed Amazon cloud‐based MC software to reconstruct the 3D dose distribution. The accuracy of the developed 3D dosimetric tool was assessed using a Delta4 phantom with various field sizes (square, circular, rectangular, and irregular MLC fields) and different patient cases. The method was applied to validate VMAT/SBRT plans using WFF and FFF photon beams (Varian TrueBeam STX).

Results:

It was found that the proposed method yielded results consistent with the Delta4 measurements. For points on the two detector planes, a good agreement within 1.5% were found for all the testing fields. Patient VMAT/SBRT plan studies revealed similar level of accuracy: an average γ‐index passing rate of 99.2± 0.6% (3mm/3%), 97.4± 2.4% (2mm/2%), and 72.6± 8.4 % ( 1mm/1%).

Conclusion:

A valuable 3D dosimetric verification strategy has been developed for VMAT/SBRT plan validation. The technique provides a viable solution for a number of intractable dosimetry problems, such as small fields and plans with high dose gradient.
SU‐E‐T‐491: Influence of Applicator Dimensions On Doses to Bladder, Rectum and Sigmoid in HDR Brachytherapy for Cervical Cancer
Authors: Dumane V , Rhome R , Yuan Y , Gupta V
Published: June 2015

Purpose:

To study the influence of dimensions of the tandem and ring applicator on bladder D2cc, rectum D2cc and sigmoid D2cc in HDR treatment planning for cervical cancer.

Methods:

53 plans from 13 patients treated at our institution with the tandem and ring applicator were retrospectively reviewed. Prescription doses were one of the following: 8 Gy × 3, 7 Gy × 4 and 5.5 Gy × 5. Doses to the D2ccs of the bladder, rectum and the sigmoid were recorded. These doses were normalized to their relative prescriptions doses. Correlations between the normalized bladder D2cc, rectum D2cc and sigmoid D2cc were investigated and linear regression models were developed to study the dependence of these doses on the ring diameter and the applicator angle.

Results:

Normalized doses to the D2cc of the bladder, rectum and sigmoid showed statistically significant correlation (P < 0.05) to the applicator angle. Significant correlation was also noted for the normalized D2cc of the rectum and the sigmoid with the ring diameter. The normalized bladder D2cc was found to decrease with applicator angle on an average by 22.65% ± 4.43% while the same for the rectum and sigmoid were found to increase on an average by 14.43% ± 1.65% and 14.01% ± 1.42% respectively. Both the rectum and sigmoid D2cc reduced with increasing ring diameter by 12.93% ± 1.95% and 11.27% ± 1.79%. No correlation was observed between the normalized bladder D2cc and the ring diameter.

Conclusion:

Preliminary regression models developed in this study can potentially aid in the choice of the appropriate applicator angle and ring diameter for tandem and ring implant so as to optimize doses to the bladder, rectum and sigmoid.
SU‐E‐T‐498: Initial Characterization of the New EBT XD Gafchromic Film
Authors: Grams M , Gustafson J , Long K , de los Santos L Fong
Published: June 2015

Purpose

To assess the dosimetric accuracy of the new EBT XD (eXtended Dose) Gafchromic film and to compare the lateral scan effect between EBT XD and EBT3 film.

Methods:

All films were exposed in solid water using a 6 MV beam and were analyzed with FilmQA Pro software and an Epson 10000 XL scanner. Calibration was performed using films exposed to 8 known doses from 0–3000 cGy. To assess dosimetric accuracy, a 15×18 cm2 60° EDW delivered a dose range of 200–2900 cGy to 4 separate EBT XD films. Comparison to treatment planning system (TPS) predictions was made using a gamma analysis with 2%/2mm passing criteria. To assess the lateral scan effect, 21 × 21 cm2 open fields delivered doses of 1000, 2000, and 3000 cGy isocentrically to both EBT3 and EBT XD films at 10 cm depth. Films were centered and scanned such that the widest parts of the exposed film extended lateral to the center of the scanner bed in order to maximize the lateral scan effect. Ratios of measured to TPS predicted doses for EBT3 and EBT XD film were calculated at 5 cm and 8 cm lateral from the center of the scanner bed to quantitatively assess the lateral scan effect.

Results

The average gamma passing rate for the EDW was 98.9% (range 98.7 – 99.1%). EBT XD film exhibited minimal lateral scan effect (<1%) up to 30 Gy. In contrast, EBT3 showed an under‐response of 13% and 25% at lateral positions of 5 cm and 8 cm respectively for the 30 Gy exposure.

Conclusion

EBT XD can accurately measure dose over a wide dynamic range. The non‐polarizing structure of its active ingredient essentially eliminates the lateral scan effect up to at least 30 Gy. EBT XD film is therefore well suited for SRS/SBRT verification measurements.
SU‐E‐T‐503: Intensity Modulated Proton Therapy (IMPT) Versus Intensity Modulated X‐Ray Therapy (IMRT) for Patient with Hepatocellular Carcinoma: A Dosimetric Comparison
Authors: Singh H , Zhao L , Prabhu K , Rana S , Zheng Y
Published: June 2015

Purpose

This study compares the dosimetric parameters in treatment of unresectable hepatocellular carcinoma between intensity modulated proton therapy (IMPT) and intensity modulated x‐ray radiation therapy (IMRT). Methods and Materials: We studied four patients treated at our institution. All patients were simulated supine with 4D‐CT using a GE light speed simulator with a maximum slice thickness of 3mm. The average CT and an internal target volume to account for respiration motion were used for planning. Both IMRT and IMPT plans were created using Elekta's CMSXiO treatment planning system (TPS). The prescription dose was 58.05 CGE in 15 fractions. The IMRT plans had five beams with combination of co‐planar and non‐co‐planar. The IMPT plans had 2 to 3 beams. Dose comparison was performed based on the averaged results of the four patients.

Results

The mean dose and V95% to PTV were 58.24CGE, 98.57% for IMPT, versus 57.34CGE and 96.68% for IMRT, respectively. The V10, V20, V30 and mean dose of the normal liver for IMPT were 23.10%, 18.61%, 13.75% and 9.78 CGE; and 47.19%, 37.55%, 22.73% and 17.12CGE for IMRT. The spinal cord didn't receive any dose in IMPT technique, but received a maximum of 18.77CGE for IMRT. The IMPT gave lower maximum dose to the stomach as compared to IMRT (19.26 vs 26.35CGE). V14 for left and right kidney was 0% and 2.32% for IMPT and 3.89% and 29.54% for IMRT. The mean dose, V35, V40 and V45 for small bowl were similar in both techniques, 0.74CGE, 6.27cc, 4.85cc and 3.53 cc for IMPT, 3.47CGE, 9.73cc, 7.61cc 5.35cc for IMRT.

Conclusion

Based on this study, IMPT plans gave less dose to the critical structures such as normal liver, kidney, stomach and spinal cord as compared to IMRT plans, potentially leading to less toxicity and providing better quality of life for patients.
SU‐E‐T‐511: Inter‐Rater Variability in Classification of Incidents in a New Incident Reporting System
Authors: Pappas D , Reis S , Ali A , Kapur A
Published: June 2015

Purpose

To determine how consistent the results of different raters are when reviewing the same cases within the Radiation Oncology Incident Learning System (ROILS).

Methods

Three second‐year medical physics graduate students filled out incident reports in spreadsheets set up to mimic ROILS. All students studied the same 33 cases and independently entered their assessments, for a total of 99 reviewed cases. The narratives for these cases were obtained from a published International Commission on Radiological Protection (ICRP) report which included shorter narratives selected from the Radiation Oncology Safety Information System (ROSIS) database. Each category of questions was reviewed to see how consistent the results were by utilizing free‐marginal multirater kappa analysis. The percentage of cases where all raters shared full agreement or full disagreement was recorded to show which questions were answered consistently by multiple raters for a given case. The consistency among the raters was analyzed between ICRP and ROSIS cases to see if either group led to more reliable results.

Results

The categories where all raters agreed 100 percent in their choices were the event type (93.94 percent of cases 0.946 kappa) and the likelihood of the event being harmful to the patient (42.42 percent of cases 0.409 kappa). The categories where all raters disagreed 100 percent in their choices were the dosimetric severity scale (39.39 percent of cases 0.139 kappa) and the potential future toxicity (48.48 percent of cases 0.205 kappa). ROSIS had more cases where all raters disagreed than ICRP (23.06 percent of cases compared to 15.58 percent, respectively).

Conclusion

Despite reviewing the same cases, the results among the three raters was widespread. ROSIS narratives were shorter than ICRP, which suggests that longer narratives lead to more consistent results. This study shows that the incident reporting system can be optimized to yield more consistent results.
SU‐E‐T‐512: Intrinsic Characteristics of the Nine Detectors and Evaluation of Their Performance in Non‐Equilibrium Radiation Dosimetry
Authors: Markovic M , Stathakis S , Jurkovic I , Mavroidis P , Papanikolaou N
Published: June 2015

Purpose

The aim for the study was to compare intrinsic characteristics of the nine detectors and evaluate their performance in non‐equilibrium radiation dosimetry.

Methods

The intrinsic characteristics of the nine detectors that were evaluated are based on the composition and size of the active volume, operating voltage, initial recombination of the collected charge, temperature, the effective cross section of the detectors. The shortterm stability and collection efficiency has been investigated. The minimum radiation detection sensitivity and detectors leakage current has been measured. The sensitivity to changes in energy spectrum as well as change in incident beam angles were measured an analyzed.

Results

The short‐term stability of the measurements within every detector showed consistency in the measured values with the highest value of the standard deviation of the mean not exceeding 0.5%. Air ion chamber detectors showed minimum sensitivity to change in incident beam angles while diode detectors underestimated measurements up to 16%. Comparing the slope of the tangents for detector's sensitivity curve, diode detectors illustrate more sensitivity to change in photon spectrum than ion chamber detectors. The change in radiation detection sensitivity with increase in dose delivered has been observed for semiconductor detectors with maximum deviation 0.01% for doses between 1 Gy and 10 Gy. Leakage current has been mainly influenced by bias voltage (ion chamber detectors) and room light intensity (diode detectors). With dose per pulse varying from 1.47E−4 to 5.1E−4 Gy/pulse the maximum change in collection efficiency was 1.4% for the air ion chambers up to 8% for liquid filled ion chamber.

Conclusion

Broad range of measurements performed showed all the detectors susceptible to some limitations and while they are suitable for use in broad scope of applications, careful selection has to be made for particular range of measurements.
SU‐E‐T‐514: Investigating the Dose Distributions of Equiangular Spaced Noncoplanar Beams
Authors: Mitchell T , Maxim P , Hadsell M , Loo B
Published: June 2015

Purpose

It has been demonstrated that the use of noncoplanar beams in radiation therapy may Result in dose distributions that are comparable or better than standard coplanar beams [Pugachev, 2001]. A radiation therapy system designed with a noncoplanar beam geometry could allow for a full ring diagnostic quality imaging system to be placed around the patient. Additionally, if the noncoplanar beams were fixed in number and in their angle with respect to the patient's axial plane, then both treatment and imaging could be achieved concurrently without the need for moving parts, which could greatly reduce treatment times. For such a system to be designed, it is necessary to determine the appropriate number of beams and the beam angles to achieve optimal dose distributions. For simplicity, the beam angles are assumed to be equiangular in the patient's axial plane, and only the beam angle with respect to the axial plane are varied. This study aims to investigate the dose distributions produced by equiangular noncoplanar beams for multiple beam numbers and beam angles, and to compare these dose distributions with distributions achieved in coplanar volumetric arc therapy (VMAT).

Methods

Dose distributions produced by noncoplanar beams were calculated using the Varian Eclipse treatment planning system by varying the gantry, collimator, and couch angles to simulate the noncoplanar delivery method. Noncoplanar intensity‐modulated (NC‐IMRT) beams using 8, 12, and 16 beams with angles varying from 45 degrees to 54 with respect to the patient's axial plane were studied.

Results

The NC‐IMRT beams produced dose distributions comparable to VMAT plans for a number of treatment sites, and were capable of meeting similar dose‐volume histogram constraints.

Conclusion

This study has demonstrated that a noncoplanar beam delivery method with fixed beam numbers and beam angles is capable of delivering dose distributions comparable to VMAT plans currently in use.
SU‐E‐T‐515: Investigating the Linear Energy Transfer Dependency of Different PRESAGE Formulations in a Proton Beam
Authors: Carroll M , Alqathami M , Blencowe A , Ibbott G
Published: June 2015

Purpose

Previous studies have reported an under‐response of PRESAGE in a proton beam as a Result of the extremely high LET in the distal end of the spread out Bragg peak (SOBP). This work is a preliminary investigation to quantify the effect of the formulation, specifically the concentration of halocarbon radical initiator relative to leuco dye, on radical recombination resulting in LET dependence.

Methods

The traditional PRESAGE formulation developed by Heuris Pharma was altered to constitute radical initiator concentrations of 5, 15, and 30% (low, medium, and high) by weight with all other components balanced to maintain proportionality. Chloroform was specifically examined in this study and all dosimeters were made in‐house. Cylindrical PRESAGE dosimeters (3.5cm diameter and 6cm length) were made for each formulation and irradiated by a 200‐MeV proton beam to 500 cGy across a 2cm SOBP. Dosimeters were read out using the DMOS optical‐CT scanner. The dose distributions were analyzed and dose profiles were used to compare the relative dose response to find the stability across the high‐LET region of the SOBP. LET dependence was measured by the variation to ion chamber measurements for the final 25% of the SOBP (∼0.5cm) prior to the distal‐90 of each profile.

Results

Relative to ion chamber data, all PRESAGE dosimeters showed an under‐response at the distal end of the SOBP. The medium concentration formulation matched most closely with an average 8.3% under‐response closely followed by the low concentration at 12.2% and then the high concentration at 22.8%. In all three cases, the highest points of discrepancy were in the distal most regions.

Conclusion

The radical initiator concentration in PRESAGE can be tailored to reduce the LET dependence in a proton beam. This warrants further study to quantify comprehensively the effect of concentration of different halocarbon radical initiators on LET dependency.

Grant number 5RO1CA100835
SU‐E‐T‐519: Investigation of the CyberKnife MultiPlan Monte Carlo Dose Calculation Using EBT3 Film Absolute Dosimetry for Delivery in a Heterogeneous Thorax Phantom
Authors: Lamberto M , Chen H , Huang K , Mourtada F
Published: June 2015

Purpose

To characterize the Cyberknife (CK) robotic system's dosimetric accuracy of the delivery of MultiPlan's Monte Carlo dose calculations using EBT3 radiochromic film inserted in a thorax phantom.

Methods

The CIRS XSight Lung Tracking (XLT) Phantom (model 10823) was used in this study with custom cut EBT3 film inserted in the horizontal (coronal) plane inside the lung tissue equivalent phantom. CK MultiPlan v3.5.3 with Monte Carlo dose calculation algorithm (1.5 mm grid size, 2% statistical uncertainty) was used to calculate a clinical plan for a 25‐mm lung tumor lesion, as contoured by the physician, and then imported onto the XLT phantom CT. Using the same film batch, the net OD to dose calibration curve was obtained using CK with the 60 mm fixed cone by delivering 0– 800 cGy. The test films (n=3) were irradiated using 325 cGy to the prescription point. Films were scanned 48 hours after irradiation using an Epson v700 scanner (48 bits color scan, extracted red channel only, 96 dpi). Percent absolute dose and relative isodose distribution difference relative to the planned dose were quantified using an in‐house QA software program. Multiplan Monte Carlo dose calculation was validated using RCF dosimetry (EBT3) and gamma index criteria of 3%/3mm and 2%/2mm for absolute dose and relative isodose distribution measurement comparisons.

Results

EBT3 film measurements of the patient plans calculated with Monte Carlo in MultiPlan resulted in an absolute dose passing rate of 99.6±0.4% for the Gamma Index of 3%/3mm, 10% dose threshold, and 95.6±4.4% for 2%/2mm, 10% threshold criteria. The measured central axis absolute dose was within 1.2% (329.0±2.5 cGy) of the Monte Carlo planned dose (325.0±6.5 cGy) for that same point.

Conclusion

MultiPlan's Monte Carlo dose calculation was validated using the EBT3 film absolute dosimetry for delivery in a heterogeneous thorax phantom.
SU‐E‐T‐523: Investigation of Various MR‐Compatible Shielding Materials for Direction Modulated Brachytherapy (DMBT) Tandem Applicator for Cervical Cancer Treatment
Authors: Safigholi H , Han D , Soliman A , Meigooni A Soleimani , Scanderbeg D , Song W
Published: June 2015

Purpose:

To evaluate various shielding materials such as Gold (Au), Osmium (Os), Tantalum (Ta), and Tungsten (W) based alloys for use with a novel intensity modulation capable direction modulated brachytherapy (DMBT) tandem applicator for image guided cervical cancer HDR brachytherapy.

Methods:

The novel MRI‐compatible DMBT tandem, made from nonmagnetic tungsten‐alloy rod with diameter of 5.4 mm, has 6 symmetric peripheral holes of 1.3 mm diameter with 2.05 mm distance from the center for a high degree intensity modulation capacity. The 0.3 mm thickness of bio‐compatible plastic tubing wraps the tandem. MCNPX was used for Monte Carlo simulations of the shields and the mHDR Ir‐192 V2 source. MC‐generated 3D dose matrices of different shielding materials of Au, Os, Ta, and W with 1 mm3 resolution were imported into an in‐house‐coded inverse optimization planning system to evaluate 19 clinical patient plans. Prescription dose was 15Gy. All plans were normalized to receive the same HRCTV D90.

Results:

In general, the plan qualities for various shielding materials were similar. The OAR D2cc for bladder was very similar for Au, Os, and Ta with 11.64±2.30Gy. For W, it was very close 11.65±2.30Gy. The sigmoid D2cc was 9.82±2.46Gy for Au and Os while it was 9.84±2.48Gy for Ta and W. The rectum D2cc was 7.44±3.06Gy for Au, 7.43±3.07Gy for Os, 7.48±3.05Gy for Ta, and 7.47±3.05Gy for W. The HRCTV D98 and V100 were very close with 16.37±1.87 Gy and 97.37±1.93 Gy, on average, respectively.

Conclusion:

Various MRI‐compatible shielding alloys were investigated for the DMBT tandem applicator. The clinical plan qualities were not significantly different among these various alloys, however. Therefore, the candidate metals (or in combination) can be used to select best alloys for MRI image guided cervical cancer brachytherapy using the novel DMBT applicator that is capable of unprecedented level of intensity modulation.
SU‐E‐T‐525: Ionization Chamber Perturbation in Flattening Filter Free Beams
Authors: Czarnecki D , Voigts‐Rhetz P von , Zink K
Published: June 2015

Purpose:

Changing the characteristic of a photon beam by mechanically removing the flattening filter may impact the dose response of ionization chambers. Thus, perturbation factors of cylindrical ionization chambers in conventional and flattening filter free photon beams were calculated by Monte Carlo simulations.

Methods:

The EGSnrc/BEAMnrc code system was used for all Monte Carlo calculations. BEAMnrc models of nine different linear accelerators with and without flattening filter were used to create realistic photon sources. Monte Carlo based calculations to determine the fluence perturbations due to the presens of the chambers components, the different material of the sensitive volume (air instead of water) as well as the volume effect were performed by the user code egs_chamber.

Results:

Stem, central electrode, wall, density and volume perturbation factors for linear accelerators with and without flattening filter were calculated as a function of the beam quality specifier TPR20/10. A bias between the perturbation factors as a function of TPR20/10 for flattening filter free beams and conventional linear accelerators could not be observed for the perturbations caused by the components of the ionization chamber and the sensitive volume.

Conclusion:

The results indicate that the well‐known small bias between the beam quality correction factor as a function of TPR20/10 for the flattening filter free and conventional linear accelerators is not caused by the geometry of the detector but rather by the material of the sensitive volume. This suggest that the bias for flattening filter free photon fields is only caused by the different material of the sensitive volume (air instead of water).
SU‐E‐T‐528: Is It Essential to QA HDR Applicators Annually in Clinic?
Authors: Xu H , Yang X , Yi B
Published: June 2015

Purpose:

There is no rigid prescription recommended for the periodic QA of HDR applicators in terms of what must be done and in what frequency. This study investigates the necessity of an annual QA program for HDR applicators, which was performed at an HDR clinic.

Methods:

In this clinic, all HDR applicators and dummy sources used for HDR treatment are tested on an annual basis. 10 different types of gyn applicators were involved including CT‐compatible and non‐CT compatible tandem & ovoid set, interstitial tandem &ring set, cylinder set Miami set, vaginal applicator set, ring set, Fletcher Williamson set. The annually QA tests for these applicators included (1) visual inspection, (2) mechanical integrity, (3) source positioning accuracy tests using kV imaging, or a combination of (1)– (3). The source positioning accuracy tolerance was 2mm. Over 100 tests were performed on 48 and 61 pieces of applicator components in 2013 and 2014, respectively.

Results:

Due to the annual QA, the degraded of applicators or dummy source were ascertained. The degradation either affected the feasibility of source delivery or introduced significant source position errors. The failure rate of the HDR applicator annual QA was 1.6% in 2013 and 2.4% in 2014. Each year, different problems on difference components were detected. The unacceptable applicator components were discarded and replaced by the new orders before affecting any patient treatment. This annual QA takes physicist half to one day to finish depending on his or her experience and expertise.

Conclusion:

The annual QA tests are determined as essential in clinic and should include visual inspection, mechanical integrity and source positioning accuracy tests. It is strongly suggested to perform annual HDR applicator QA in clinic to increase the confidence to deliver a safe, accurate and appropriate HDR treatment.
SU‐E‐T‐529: Is MFO‐IMPT Robust Enough for the Treatment of Head and Neck Tumors? A 2‐Year Outcome Analysis Following Proton Therapy On the First 50 Oropharynx Patients at the MD Anderson Cancer Center
Authors: Frank S , Garden A , Anderson M , Rosenthal D , Morrison W , Gunn B , Fuller C , Phan J , Zhang X , Poenisch F , Wu R , Li H , Gautam A , Sahoo N , Gillin M , Zhu X
Published: June 2015

Purpose:

Multi‐field optimization intensity modulated proton therapy (MFO‐IMPT) for oropharyngeal tumors has been established using robust planning, robust analysis, and robust optimization techniques. While there are inherent uncertainties in proton therapy treatment planning and delivery, outcome reporting are important to validate the proton treatment process. The purpose of this study is to report the first 50 oropharyngeal tumor patients treated de‐novo at a single institution with MFO‐IMPT.

Methods:

The data from the first 50 patients with squamous cell carcinoma of the oropharynx treated at MD Anderson Cancer Center from January 2011 to December 2014 on a prospective IRB approved protocol were analyzed. Outcomes were analyzed to include local, regional, and distant treatment failures. Acute and late toxicities were analyzed by CTCAE v4.0.

Results:

All patients were treated with definitive intent. The median follow‐up time of the 50 patients was 25 months. Patients by gender were male (84%) and female (16%). The average age was 61 years. 50% of patients were never smokers and 4% were current smokers. Presentation by stage; I–1, II–0, III– 9, IVA–37 (74%), IVB–3. 88% of patients were HPV/p16+. Patients were treated to 66–70 CGE. One local failure was reported at 13 months following treatment. One neck failure was reported at 12 months. 94% of patients were alive with no evidence of disease. One patient died without evidence of disease. There were no Grade 4 or Grade 5 toxicities.

Conclusion:

MFO‐IMPT for oropharyngeal tumors is robust and provides excellent outcomes 2 years after treatment. A randomized trial is underway to determine if proton therapy will reduce chronic late toxicities of IMRT.
SU‐E‐T‐542: Measurement of Internal Neutrons for Uniform Scanning Proton Beams
Authors: Islam M , Zheng Y , Collums T , Monsoon J , Rana S , Ahmad S , Benton E
Published: June 2015

Purpose:

In proton radiotherapy, the production of neutrons is a wellknown problem since neutron exposure can lead to increased risk of secondary cancers later in the patient's lifetime. The assessment of neutron exposure is, therefore, important for the overall quality of proton radiotherapy. This study investigates the secondary neutrons created inside the patient from uniform scanning proton beams.

Methods:

Dose equivalent due to secondary neutrons was measured outside the primary field as a function of distance from beam isocenter at three different angles, 45, 90 and 135 degree, relative to beam axis. Plastic track nuclear detector (CR‐39 PNTD) was used for the measurement of neutron dose. Two experimental configurations, in‐air and cylindrical‐phantom, were designed. In a cylindrical‐phantom configuration, a cylindrical phantom of 5.5 cm diameter and 35 cm long was placed along the beam direction and in an in‐air configuration, no phantom was used. All the detectors were placed at nearly identical locations in both configurations. Three proton beams of range 5 cm, 18 cm, and 32 cm with 4 cm modulation width and a 5 cm diameter aperture were used. The contribution from internal neutrons was estimated from the differences in measured dose equivalent between in‐air and cylindrical‐phantom configurations at respective locations.

Results:

The measured ratio of neutron dose equivalent to the primary proton dose (H/D) dropped off with distance and ranged from 27 to 0.3 mSv/Gy. The contribution of internal neutrons near the treatment field edge was found to be up to 64 % of the total neutron exposure. As the distance from the field edge became larger, the external neutrons from the nozzle appear to dominate and the internal neutrons became less prominent.

Conclusion:

This study suggests that the contribution of internal neutrons could be significant to the total neutron dose equivalent.
SU‐E‐T‐556: Monte Carlo Generated Dose Distributions for Orbital Irradiation Using a Single Anterior‐Posterior Electron Beam and a Hanging Lens Shield
Authors: Duwel D , Lamba M , Elson H , Kumar N
Published: June 2015

Purpose:

Various cancers of the eye are successfully treated with radiotherapy utilizing one anterior‐posterior (A/P) beam that encompasses the entire content of the orbit. In such cases, a hanging lens shield can be used to spare dose to the radiosensitive lens of the eye to prevent cataracts.

Methods:

This research focused on Monte Carlo characterization of dose distributions resulting from a single A‐P field to the orbit with a hanging shield in place. Monte Carlo codes were developed which calculated dose distributions for various electron radiation energies, hanging lens shield radii, shield heights above the eye, and beam spoiler configurations. Film dosimetry was used to benchmark the coding to ensure it was calculating relative dose accurately.

Results:

The Monte Carlo dose calculations indicated that lateral and depth dose profiles are insensitive to changes in shield height and electron beam energy. Dose deposition was sensitive to shield radius and beam spoiler composition and height above the eye.

Conclusion:

The use of a single A/P electron beam to treat cancers of the eye while maintaining adequate lens sparing is feasible. Shield radius should be customized to have the same radius as the patient's lens. A beam spoiler should be used if it is desired to substantially dose the eye tissues lying posterior to the lens in the shadow of the lens shield. The compromise between lens sparing and dose to diseased tissues surrounding the lens can be modulated by varying the beam spoiler thickness, spoiler material composition, and spoiler height above the eye. The sparing ratio is a metric that can be used to evaluate the compromise between lens sparing and dose to surrounding tissues. The higher the ratio, the more dose received by the tissues immediately posterior to the lens relative to the dose received by the lens.
SU‐E‐T‐557: Monte Carlo Modeling of Philips RT‐250 Orthovoltage Unit for Beam Spectrum Modulation
Authors: Reynoso F , Cho S
Published: June 2015

Purpose:

To develop and validate a Monte Carlo (MC) model of a Phillips RT‐250 orthovoltage unit to test various beam spectrum modulation strategies for in vitro/vivo studies. A model of this type would enable the production of unconventional beams from a typical orthovoltage unit for novel therapeutic applications such as gold nanoparticle‐aided radiotherapy.

Methods:

The MCNP5 code system was used to create a MC model of the head of RT‐250 and a 30 × 30 × 30 cm3 water phantom. For the x‐ray machine head, the current model includes the vacuum region, beryllium window, collimators, inherent filters and exterior steel housing. For increased computational efficiency, the primary x‐ray spectrum from the target was calculated from a well‐validated analytical software package. Calculated percentage‐depth‐dose (PDD) values and photon spectra were validated against experimental data from film and Compton‐scatter spectrum measurements.

Results:

The model was validated for three common settings of the machine namely, 250 kVp (0.25 mm Cu), 125 kVp (2 mm Al), and 75 kVp (2 mm Al). The MC results for the PDD curves were compared with film measurements and showed good agreement for all depths with a maximum difference of 4 % around dmax and under 2.5 % for all other depths. The primary photon spectra were also measured and compared with the MC results showing reasonable agreement between the two, validating the input spectra and the final spectra as predicted by the current MC model.

Conclusion:

The current MC model accurately predicted the dosimetric and spectral characteristics of each beam from the RT‐250 orthovoltage unit, demonstrating its applicability and reliability for beam spectrum modulation tasks. It accomplished this without the need to model the bremsstrahlung xray production from the target, while significantly improved on computational efficiency by at least two orders of magnitude.

Supported by DOD/PCRP grant W81XWH‐12‐1‐0198
SU‐E‐T‐559: Monte Carlo Simulation of Cobalt‐60 Teletherapy Unit Modeling In‐Field and Out‐Of‐Field Doses for Applications in Computational Radiation Dosimetry
Authors: Petroccia H , Li Z , Mendenhall N , Bolch W
Published: June 2015

Purpose:

Mean organ doses from structures located in field and outside of field boundaries during radiotherapy treatment must be considered when looking at secondary effects. Treatment planning in patients with 40 years of follow‐up does not include 3‐D treatment planning images and did not estimate dose to structures out of the direct field. Therefore, it is of interest to correlate actual clinical events with doses received.

Methods:

Accurate models of radiotherapy machines combined with whole body computational phantoms using Monte Carlo methods allow for dose reconstructions intended for studies on late radiation effects. The Theratron‐780 radiotherapy unit and anatomically realistic hybrid computational phantoms are modeled in the Monte Carlo radiation transport code MCNPX. The major components of the machine including the source capsule, lead in the unit‐head, collimators (fixed/adjustable), and trimmer bars are simulated. The MCNPX transport code is used to compare calculated values in a water phantom with published data from BJR suppl. 25 for in‐field doses and experimental data from AAPM Task Group No. 36 for out‐of‐field doses. Next, the validated cobalt‐60 teletherapy model is combined with the UF/NCI Family of Reference Hybrid Computational Phantoms as a methodology for estimating organ doses.

Results:

The model of Theratron‐780 has shown to be agree with percentage depth dose data within approximately 1% and for out of field doses the machine is shown to agree within 8.8%. Organ doses are reported for reference hybrid phantoms.

Conclusion:

Combining the UF/NCI Family of Reference Hybrid Computational Phantoms along with a validated model of the Theratron‐780 allows for organ dose estimates of both in‐field and out‐of‐field organs. By changing field size, position, and adding patient‐specific blocking more complicated treatment set‐ups can be recreated for patients treated historically, particularly those who lack both 2D/3D image sets.
SU‐E‐T‐566: Neutron Dose Cloud Map for Compact ProteusONE Proton Therapy
Authors: Syh J , Patel B , Syh J , Rosen L , Wu H
Published: June 2015

Purpose:

To establish the base line of neutron cloud during patient treatment in our new compact Proteus One proton pencil beam scanning (PBS) system with various beam delivery gantry angles, with or without range shifter (RS) at different body sites. Pencil beam scanning is an emerging treatment technique, for the concerns of neutron exposure, this study is to evaluate the neutron dose equivalent per given delivered dose under various treatment conditions at our proton therapy center.

Methods:

A wide energy neutron dose equivalent detector (SWENDI‐II, Thermo Scientific, MA) was used for neutron dose measurements. It was conducted in the proton therapy vault during beam was on. The measurement location was specifically marked in order to obtain the equivalent dose of neutron activities (H). The distances of 100, 150 and 200 cm at various locations are from the patient isocenter. The neutron dose was measured of proton energy layers, # of spots, maximal energy range, modulation width, field radius, gantry angle, snout position and delivered dose in CGE. The neutron dose cloud is reproducible and is useful for the future reference.

Results:

When distance increased the neutron equivalent dose (H) reading did not decrease rapidly with changes of proton energy range, modulation width or spot layers. For cranial cases, the average mSv/CGE was about 0.02 versus 0.032 for pelvis cases. RS will induce higher H to be 0.10 mSv/CGE in average.

Conclusion:

From this study, neutron per dose ratio (mSv/CGE) slightly depends upon various treatment parameters for pencil beams. For similar treatment conditions, our measurement demonstrates this value for pencil beam scanning beam has lowest than uniform scanning or passive scattering beam with a factor of 5. This factor will be monitored continuously for other upcoming treatment parameters in our facility.