bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐219: Verification of the Accuracy of a Relative Stopping Power (RSP) to Hounsfield Unit (HU) Calibration Curve Produced for Proton Treatment Planning Using EBT3‐Gafchromic Film Dosimetry
Authors: Schnell E , Ferreira C , Ahmad S , De La Fuente Herman T
Published: July 2016

Purpose:

Accuracy of a RSP‐HU calibration curve produced for proton treatment planning is tested by comparing the treatment planning system dose grid to physical doses delivered on film by a Mevion S250 double‐scattering proton unit.

Methods:

A single batch of EBT3 Gafchromic film was used for calibration and measurements. The film calibration curve was obtained using Mevion proton beam reference option 20 (15cm range, 10cm modulation). Paired films were positioned at the center of the spread out Bragg peak (SOBP) in solid water. The calibration doses were verified with an ion chamber, including background and doses from 20cGy to 350cGy. Films were scanned in a flatbed Epson‐Expression 10000‐XL scanner, and analyzed using the red channel. A Rando phantom was scanned with a GE LightSpeed CT Simulator. A single‐field proton plan (Eclipse, Varian) was calculated to deliver 171cGy to the pelvis section (heterogeneous region), using a standard 4×4cm aperture without compensator, 7.89cm beam range, and 5.36cm SOBP. Varied depths of the calculated distal 90% isodose‐line were recorded and compared. The dose distribution from film irradiated between Rando slices was compared with the calculated plans using RIT v.6.2.

Results:

Distal 90% isodose‐line depth variation between CT scans was 2mm on average, and 4mm at maximum. Fine calculation of this variation was restricted by the dose calculation grid, as well as the slice thickness. Dose differences between calibrated film measurements and calculated doses were on average 5.93cGy (3.5%), with the large majority of differences forming a normal distribution around 3.5cGy (2%). Calculated doses were almost entirely greater than those measured.

Conclusion:

RSP to HU calibration curve is shown to produce distal depth variation within the margin of tolerance (±4.3mm) across all potential scan energies and protocols. Dose distribution calculation is accurate to 2–4% within the SOBP, including areas of high tissue heterogeneity.
SU‐F‐T‐222: Dose of Fetus and Infant Following Accidental Intakes of I‐131 by the Mother
Authors: Wang Y , Hu P
Published: July 2016

Purpose:

To estimate the calculation of absorbed dose to the fetus and infants from intakes of I‐131 by the mother. Thus provide some advice to the radioprotection of radioactive accident.

Methods:

In this clinical case, a staff of nuclear medicine accidently intake I‐131 during (10–12 weeks) and after pregnancy. The infant was born at full term, but both lobes of the thyroid gland were found to be absent (bilobar thyroid agenesis). It was suspected that the fetal thyroid agenesis may be related with mother's contamination of I‐131 during pregnancy. Urine samples for 24h were collected at different times after administered and radioactivity were measured to calculate the dose of intake I‐131. Calculate the intake I‐131 by the results of personal TLD dosimeter. We adopted the mean of two calculated results as the I‐131 intake. According to the dose of intake I‐131 by the mother, effective dose and absorbed dose of thyroid for mother, fetus and infant were calculated.

Results:

The intake of I‐131 was estimated for 8.18 mCi. I‐131 intake was calculated for 7.9 mCi based on data of TLD dosimeter. We adopted the mean of two results as the I‐131 intake. The final result was 8.0 mCi. Effective dose and absorbed dose of thyroid for mother were 7.3Sv and 164 Gy, effective dose and absorbed dose of thyroid for fetus were 2.035 Sv and 40.7 Gy, effective dose and absorbed dose of thyroid for infant were 16.25 Sv and 355Gy.

Conclusion:

The intake during pregnancy was about 1mCi. The absorbed dose of thyroid of the mother was 19.5Gy, whereas the effective of infant was estimated for 40.7Gy. The function of the mother's thyroid was normal after diagnosis. But the infant was diagnosed as bilobar thyroid agenesis.
SU‐F‐T‐228: Analysis of Multi‐Leaf Collimator Leaf Position Errors in Volumetric Modulated Arc Therapy for Nasopharyngeal Carcinoma
Authors: Li C , Yin Y
Published: July 2016

Purpose:

The purpose of this study was evaluate the position error of multileaf collimator in volumetric modulated arc therapy of nasopharyngeal carcinoma via MLC logs from Varian machines and to provide a method for detecting the leaf position accuracy.

Methods:

Thirty one patients with nasopharyngeal carcinoma were randomly selected. Each patient was created with two 358° arcs. The MLC errors for all arcs, arc1 and arc2, left‐bank and right‐bank leafs of each arc were evaluated.

Results:

99.99% of the leaf position errors of all plans were within ± 2mm. The proportion of the leaf position errors within ± 1.5mm,± 1mm and ± 0.5mm were 99.90%, 98.98% and 94.17%,respectively. The leaf position errors range of ARC1 and ARC2 were −2.95 ∼ 2.99mm and −0.22 ∼ 0.23mm (t = 2.35, P = 0.00), The proportion of the leaf position errors within ± 1mm were 98.08% and 100% for ARC1 and ARC2. The leaf position errors range of Bank A and Bank B were −2.95 ∼ 2.68mm and −2.92 ∼ 2.99mm (t = 1.64, P = 0.31), The proportion of the leaf position errors within ± 1mm were 98.97% and 99.01%.

Conclusion:

During the VMAT treatment for NPC, it was found that the leaf positions were in control, the Dynalog files can be used as an effective way to analysis the leaf position errors.
SU‐F‐T‐229: A Novel Method for EPID‐Based In‐Vivo Exit Dose Verification for Intensity Modulated Radiotherapy
Authors: Wu Z , Wang J , Peng J , Wang J , Hu W
Published: July 2016

Purpose:

Electronic portal imaging device (EPID) can be used to acquire a two‐dimensional exit dose distribution during treatment delivery, thus allowing the in‐vivo verification of the dose delivery through a comparison of measured portal images to predicted portal dose images (PDI). The aim of this study was to present a novel method to easily and accurately predict PDI, and to establish an EPID‐based in‐vivo dose verification method during IMRT treatments.

Methods:

We developed a model to determine the predicted portal dose at the same plane of the EPID detector location. The Varian EPID (aS1000) positions at 150cm source‐to‐detector‐distance (SDD), and can be used to acquire in‐vivo exit dose using Portal Dosimetry (PD) function. Our model was generated to make an equivalent water thickness represent the buildup plate of EPID. The exit dose at extend SDD plane with patient CT data in the beam can be calculated as the predicted PDI in the treatment planning system (TPS). After that, the PDI was converted to the fluence at SDD of 150cm using the inverse square law coded in MATLAB. Five head‐and‐neck and prostate IMRT patient plans contain 32 fields were investigated to evaluate the feasibility of this new method. The measured EPID image was compared with PDI using the gamma analysis.

Results:

The average results for cumulative dose comparison were 81.9% and 91.6% for 3%, 3mm and 4%, 4mm gamma criteria, respectively. Results indicate that the patient transit dosimetry predicted algorithm compares well with EPID measured PD doses for test situations.

Conclusion:

Our new method can be used as an easy and feasible tool for online EPID‐based in‐vivo dose delivery verification for IMRT treatments. It can be implemented for fast detecting those obvious treatment delivery errors for individual field and patient quality assurance.
SU‐F‐T‐236: Comparison of Two IMRT/VMAT QA Systems Using Gamma Index Analysis
Authors: Dogan N , Denissova S
Published: July 2016

Purpose:

The goal of this study is to assess differences in the Gamma index pass rates when using two commercial QA systems and provide optimum Gamma index parameters for pre‐treatment patient specific QA.

Methods:

Twenty‐two VMAT cases that consisted of prostate, lung, head and neck, spine, brain and pancreas, were included in this study. The verification plans have been calculated using AcurosXB(V11) algorithm for different dose grids (1.5mm, 2.5mm, 3mm). The measurements were performed on TrueBeam(Varian) accelerator using both EPID(S1000) portal imager and ArcCheck(SunNuclearCorp) devices. Gamma index criteria variation of 3%/3mm, 2%/3mm, 2%/2mm and threshold (TH) doses of 5% to 50% were used in analysis.

Results:

The differences in Gamma pass rates between two devices are not statistically significant for 3%/3mm, yielding pass rate higher than 95%. Increase of lower dose TH showed reduced pass rates for both devices. ArcCheck's more pronounced effect can be attributed to higher contribution of lower dose region spread. As expected, tightening criteria to 2%/2mm (TH: 10%) decreased Gamma pass rates below 95%. Higher EPID (92%) pass rates compared to ArcCheck (86%) probably due to better spatial resolution. Portal Dosimetry results showed lower Gamma pass rates for composite plans compared to individual field pass rates. This may be due to the expansion in the analyzed region which includes pixels not included in the separate field analysis. Decreasing dose grid size from 2.5mm to 1.5mm did not show statistically significant (p<0.05) differences in Gamma pass rates for both QA devices.

Conclusion:

Overall, both system measurements agree well with calculated dose when using gamma index criteria of 3%/3mm for a variety of VMAT cases. Variability between two systems increases using different dose GRID, TH and tighter gamma criteria and must be carefully assessed prior to clinical use.
SU‐F‐T‐238: Analyzing the Performance of MapCHECK2 and Delta4 Quality Assurance Phantoms in IMRT and VMAT Plans
Authors: Lu SH , Tsai YC , Lan HT , Wen SY , Chen LH , Kuo SH , Wang CW
Published: July 2016

Purpose:

Intensity‐modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) have been widely investigated for use in radiotherapy and found to have a highly conformal dose distribution. Delta4 is a novel cylindrical phantom consisting of 1069 p‐type diodes with true treatments measured in the 3D target volume. The goal of this study was to compare the performance of a Delta4 diode array for IMRT and VMAT planning with ion chamber and MapCHECK2.

Methods:

Fifty‐four IMRT (n=9) and VMAT (n=45) plans were imported to Philips Pinnacle Planning System 9.2 for recalculation with a solid water phantom, MapCHECK2, and the Delta4 phantom. To evaluate the difference between the measured and calculated dose, we used MapCHECK2 and Delta4 for a dose‐map comparison and an ion chamber (PTW 31010 Semiflex 0.125 cc) for a point‐dose comparison.

Results:

All 54 plans met the criteria of <3% difference for the point dose (at least two points) by ion chamber. The mean difference was 0.784% with a standard deviation of 1.962%. With a criteria of 3 mm/3% in a gamma analysis, the average passing rates were 96.86%±2.19% and 98.42%±1.97% for MapCHECK2 and Delta4, respectively. The student t‐test of MapCHECK2/Delta4, ion chamber/Delta4, and ion chamber/MapCHECK2 were 0.0008, 0.2944, and 0.0002, respectively. There was no significant difference in passing rates between MapCHECK2 and Delta4 for the IMRT plan (p = 0.25). However, a higher pass rate was observed in Delta4 (98.36%) as compared to MapCHECK2 (96.64%, p < 0.0001) for the VMAT plan.

Conclusion:

The Pinnacle planning system can accurately calculate doses for VMAT and IMRT plans. The Delta4 shows a similar result when compared to ion chamber and MapCHECK2, and is an efficient tool for patient‐specific quality assurance, especially for rotation therapy.
SU‐F‐T‐250: What Does It Take to Correctly Assess the High Failure Modes of an Advanced Radiotherapy Procedure Such as Stereotactic Body Radiation Therapy?
Authors: Han D , Vile D , Rosu M , Palta J
Published: July 2016

Purpose:

Assess the correct implementation of risk‐based methodology of TG 100 to optimize quality management and patient safety procedures for Stereotactic Body Radiation Therapy.

Methods:

A detailed process map of SBRT treatment procedure was generated by a team of three physicists with varying clinical experience at our institution to assess the potential high‐risk failure modes. The probabilities of occurrence (O), severity (S) and detectability (D) for potential failure mode in each step of the process map were assigned by these individuals independently on the scale from1 to 10. The risk priority numbers (RPN) were computed and analyzed. The highest 30 potential modes from each physicist's analysis were then compared.

Results:

The RPN values assessed by the three physicists ranged from 30 to 300. The magnitudes of the RPN values from each physicist were different, and there was no concordance in the highest RPN values recorded by three physicists independently. The 10 highest RPN values belonged to sub steps of CT simulation, contouring and delivery in the SBRT process map. For these 10 highest RPN values, at least two physicists, irrespective of their length of experience had concordance but no general conclusions emerged.

Conclusion:

This study clearly shows that the risk‐based assessment of a clinical process map requires great deal of preparation, group discussions, and participation by all stakeholders. One group albeit physicists cannot effectively implement risk‐based methodology proposed by TG100. It should be a team effort in which the physicists can certainly play the leading role. This also corroborates TG100 recommendation that risk‐based assessment of clinical processes is a multidisciplinary team effort.
SU‐F‐T‐253: Volumetric Comparison Between 4D CT Amplitude and Phase Binning Mode
Authors: Yang G , Li X , Ma R , Yorke E , Mageras G , Tang X , Xiong W , Chan M , Reyngold M , Gewanter R , Wu A , Deasy J , Hunt M
Published: July 2016

Purpose:

Motion artifact in 4DCT images can affect radiation treatment quality. To identify the most robust and accurate binning method, we compare the volume difference between targets delineated on amplitude and phase binned 4DCT scans.

Methods:

Varian RPM system and CT scanner were used to acquire 4DCTs of a Quasar phantom with embedded cubic and spherical objects having superior‐inferior motion. Eight patients’ respiration waveforms were used to drive the phantom. The 4DCT scan was reconstructed into 10 phase and 10 amplitude bins (2 mm slices). A scan of the static phantom was also acquired. For each waveform, sphere and cube volumes were generated automatically on each phase using HU thresholding. Phase (amplitude) ITVs were the union of object volumes over all phase (amplitude) binned images. The sphere and cube volumes measured in the static phantom scan were Vsphere=4.19cc and Vcube=27.0cc. Volume difference (VD) and dice similarity coefficient (DSC) of the ITVs, and mean volume error (MVE) defined as the average target volume percentage difference between each phase image and the static image, were used to evaluate the performance of amplitude and phase binning.

Results:

Averaged over the eight breathing traces, the VD and DSC of the internal target volume (ITV) between amplitude and phase binning were 3.4%±3.2% (mean ± std) and 95.9%±2.1% for sphere; 2.1%±3.3% and 98.0% ±1.5% for cube, respectively.For all waveforms, the average sphere MVE of amplitude and phase binning was 6.5% ± 5.0% and 8.2%±6.3%, respectively; and the average cube MVE of amplitude and phase binning was 5.7%±3.5%and 12.9%±8.9%, respectively.

Conclusion:

ITV volume and spatial overlap as assessed by VD and DSC are similar between amplitude and phase binning. Compared to phase binning, amplitude binning results in lower MVE suggesting it is less susceptible to motion artifact.
SU‐F‐T‐270: A Technique for Modeling a Diode Array Into the TPS for Lung SBRT Patient Specific QA
Authors: Curley C , Ouhib Z , Leventouri T
Published: July 2016

Purpose:

To accurately match the treatment planning system (TPS) with the measurement environment, where quality assurance (QA) devices are used to collect data, for lung Stereotactic Body Radiation Therapy (SBRT) patient specific QA. Incorporation of heterogeneities is also studied.

Methods:

Dual energy computerized tomography (DECT) and single energy computerized tomography (SECT) were used to model phantoms incorporating a 2‐D diode array into the TPS. A water‐equivalent and a heterogeneous phantom (simulating the thoracic region of a patient) were studied. Monte Carlo and pencil beam planar dose distributions were compared to measured distributions. Composite and individual fields were analyzed for normally incident and planned gantry angle deliveries. γ‐ analysis was used with criteria 3% 3mm, 2% 2mm, and 1% 1mm.

Results:

The Monte Carlo calculations for the DECT resulted in improved agreements with the diode array for 46.4% of the fields at 3% 3mm, 85.7% at 2% 2mm, and 92.9% at 1% 1mm.For the SECT, the Monte Carlo calculations gave no agreement for the same γ‐analysis criteria. Pencil beam calculations resulted in lower agreements with the diode array in the TPS. The DECT showed improvements for 14.3% of the fields at 3% 3mm and 2% 2mm, and 28.6% at 1% 1mm.In SECT comparisons, 7.1% of the fields at 3% 3mm, 10.7% at 2% 2mm, and 17.9% at 1% 1mm showed improved agreements with the diode array.

Conclusion:

This study demonstrates that modeling the diode array in the TPS is viable using DECT with Monte Carlo for patient specific lung SBRT QA. As recommended by task groups (e.g. TG 65, TG 101, TG 244) of the American Association of Physicists in Medicine (AAPM), pencil beam algorithms should be avoided in the presence of heterogeneous materials, including a diode array.
SU‐F‐T‐272: Patient Specific Quality Assurance of Prostate VMAT Plans with Portal Dosimetry
Authors: Darko J , Kiciak A , Badu S , Grigorov G , Fleck A , Osei E
Published: July 2016

Purpose:

To evaluate the effectiveness of using the Portal Dosimetry (PD) method for patient specific quality assurance of prostate VMAT plans.

Methods:

As per institutional protocol all VMAT plans were measured using the Varian Portal Dosimetry (PD) method. A gamma evaluation criterion of 3%‐3mm with a minimum area gamma pass rate (gamma <1) of 95% is used clinically for all plans. We retrospectively evaluated the portal dosimetry results for 170 prostate patients treated with VMAT technique. Three sets of criterions were adopted for re‐evaluating the measurements; 3%‐3mm, 2%‐2mm and 1%‐1mm. For all criterions two areas, Field+1cm and MLC‐CIAO were analysed.To ascertain the effectiveness of the portal dosimetry technique in determining the delivery accuracy of prostate VMAT plans, 10 patients previously measured with portal dosimetry, were randomly selected and their measurements repeated using the ArcCHECK method. The same criterion used in the analysis of PD was used for the ArcCHECK measurements.

Results:

All patient plans reviewed met the institutional criteria for Area Gamma pass rate. Overall, the gamma pass rate (gamma <1) decreases for 3%‐3mm, 2%‐2mm and 1%‐1mm criterion. For each criterion the pass rate was significantly reduced when the MLC‐CIAO was used instead of FIELD+1cm. There was noticeable change in sensitivity for MLC‐CIAO with 2%‐2mm criteria and much more significant reduction at 1%‐1mm. Comparable results were obtained for the ArcCHECK measurements. Although differences were observed between the clockwise verses the counter clockwise plans in both the PD and ArcCHECK measurements, this was not deemed to be statistically significant.

Conclusion:

This work demonstrates that Portal Dosimetry technique can be effectively used for quality assurance of VMAT plans. Results obtained show similar sensitivity compared to ArcCheck. To reveal certain delivery inaccuracies, the use of a combination of criterions may provide an effective way in improving the overall sensitivity of PD.

Funding provided in part by the Prostate Ride for Dad, Kitchener‐Waterloo, Canada.
SU‐F‐T‐273: Using a Diode Array to Explore the Weakness of TPS DoseCalculation Algorithm for VMAT and Sliding Window Techniques
Authors: Park J , Lu B , Yan G , Park J , Li F , Li J , Liu C
Published: July 2016

Purpose:

To identify the weakness of dose calculation algorithm in a treatment planning system for volumetric modulated arc therapy (VMAT) and sliding window (SW) techniques using a two‐dimensional diode array.

Methods:

The VMAT quality assurance(QA) was implemented with a diode array using multiple partial arcs that divided from a VMAT plan; each partial arc has the same segments and the original monitor units. Arc angles were less than ± 30°. Multiple arcs delivered through consecutive and repetitive gantry operating clockwise and counterclockwise. The source‐toaxis distance setup with the effective depths of 10 and 20 cm were used for a diode array. To figure out dose errors caused in delivery of VMAT fields, the numerous fields having the same segments with the VMAT field irradiated using different delivery techniques of static and step‐and‐shoot. The dose distributions of the SW technique were evaluated by creating split fields having fine moving steps of multi‐leaf collimator leaves. Calculated doses using the adaptive convolution algorithm were analyzed with measured ones with distance‐to‐agreement and dose difference of 3 mm and 3%..

Results:

While the beam delivery through static and step‐and‐shoot techniques showed the passing rate of 97 ± 2%, partial arc delivery of the VMAT fields brought out passing rate of 85%. However, when leaf motion was restricted less than 4.6 mm/°, passing rate was improved up to 95 ± 2%. Similar passing rate were obtained for both 10 and 20 cm effective depth setup. The calculated doses using the SW technique showed the dose difference over 7% at the final arrival point of moving leaves.

Conclusion:

Error components in dynamic delivery of modulated beams were distinguished by using the suggested QA method. This partial arc method can be used for routine VMAT QA. Improved SW calculation algorithm is required to provide accurate estimated doses.
SU‐F‐T‐276: Source Modeling and VMAT Quality Assurance Referring to the TrueBeam Representative Beam Data for Eclipse
Authors: Wu Q
Published: July 2016

Purpose:

To study quality assurance (QA) of volumetric modulated arc therapy (VMAT) after the 6MV and 10MV photon beam source modeling, referring to the Varian TrueBeam representative beam data for Eclipse.

Methods:

The source model needs specific measured beam data, such as PDDs and profiles, diagonal profile, output factors (OFs), and MLC transmission factor (TF) and dosimetric leaf gap (DLG), et al. We downloaded the representative data from myVarian website, which includes TrueBeam 4MV‐15MV photon beam data and 6MeV‐22MeV electron beam data in w2CAD file format for use with Eclipse and in Excel spreadsheet format for use in data comparison. The beam data in W2CAD format can be imported into the Eclipse system and calibrated for use, as appropriate. We used PTW MP3 water tank to measure the beam data in some typical field sizes, and compared the measured data with the representative data. We found that the PDDs, profiles and OFs are similar. However according to some papers and our measurements, we decided that our MLC TF and DLG are 1.58 and 1.33 (6MV), 1.79 and 1.57 (10MV), respectively. After we had configured the anisotropic analytical algorithm (AAA) with the representative data in Eclipse, we also have done dosimetric verification for 88 VMAT plans.

Results:

The end‐to‐end test procedures of VMAT were performed for 6MV and 10MV energy modes. The NE Farmer ion chamber mean measurements showed 1.2% (6MV, 38 cases) and 1.2% (10MV, 50 cases) between measurement and calculation; the Sun Nuclear ArcCheck mean measurements demonstrated gamma pass rates are as followings: 98.9%, 93.2%, 61.0% for 6MV, and 98.9%, 91.9%, 59.5% for 10MV, using 3%/3mm, 2%/2mm, 1%/1mm, 10% threshold criteria, respectively.

Conclusion:

The representative data is applicable to our TrueBeam for the VMAT plan, though our MLC factors are a little different, and its patientspecific QA is good.
SU‐F‐T‐278: Evaluation of Commercially Available System for Patient Specific QA Using Dose Volume Histograms
Authors: Alexandrian A , Kabat C , Roring J , Papanikolaou N , Stathakis S
Published: July 2016

Purpose:

To evaluate a commercial system for patient specific quality assurance using measurements and re‐calculated dose volume histograms.

Methods:

The PTW OCTAVIUS4D was used to physically measure the dose distribution from previously accepted IMRT patient plans for a variety of sites. PTW VeriSoft was used to for the IMRT QA evaluation. Patient plans, CT images, dose distribution and structures were imported in the VeriSoft. For each patient IMRT QA, the software can use the CT and structure information to calculate the dose to the patient from the measurement. The DVHs were then compared to the imported ones. The difference of the mean dose per organ was calculated for each plan and used in the comparison.

Results:

For treatment sites with no tissue inhomogeneities, such as pelvis, the DVHs produced by the TPS and VeriSoft showed good agreement; however, small structures such as eyes, optic nerves or brainstem did not adequately match up when comparing the DVH from the TPS to VeriSoft. For treatment sites with inhomogeneity, such as the lung, showed larger dose differences between the two methods, this is most likely due to dose calculation limitations of the PTW VeriSoft DVH algorithm.

Conclusion:

Overall, the DVHs produced by VeriSoft can give a physicist quick insight to the validity of the IMRT plan; however, there are limitations when plans of heterogeneous treatment sites are evaluated since the dose calculation algorithm in Verisoft cannot accurately account for it.
SU‐F‐T‐284: The Effect of Linear Accelerator Output Variation On the Quality of Patient Specific Rapid Arc Verification Plans
Authors: Sandhu G , Cao F , Szpala S , Kohli K
Published: July 2016

Purpose:

The aim of the current study is to investigate the effect of machine output variation on the delivery of the RapidArc verification plans.

Methods:

Three verification plans were generated using Eclipse™ treatment planning system (V11.031) with plan normalization value 100.0%. These plans were delivered on the linear accelerators using ArcCHECK− device, with machine output 1.000 cGy/MU at calibration point. These planned and delivered dose distributions were used as reference plans. Additional plans were created in Eclipse− with normalization values ranging 92.80%–102% to mimic the machine output ranging 1.072cGy/MU‐0.980cGy/MU, at the calibration point. These plans were compared against the reference plans using gamma indices (3%, 3mm) and (2%, 2mm). Calculated gammas were studied for its dependence on machine output. Plans were considered passed if 90% of the points satisfy the defined gamma criteria.

Results:

The gamma index (3%, 3mm) was insensitive to output fluctuation within the output tolerance level (2% of calibration), and showed failures, when the machine output exceeds ≥3%. Gamma (2%, 2mm) was found to be more sensitive to the output variation compared to the gamma (3%, 3mm), and showed failures, when output exceeds ≥1.7%. The variation of the gamma indices with output variability also showed dependence upon the plan parameters (e.g. MLC movement and gantry rotation). The variation of the percentage points passing gamma criteria with output variation followed a non‐linear decrease beyond the output tolerance level.

Conclusion:

Data from the limited plans and output conditions showed that gamma (2%, 2mm) is more sensitive to the output fluctuations compared to Gamma (3%,3mm). Work under progress, including detail data from a large number of plans and a wide range of output conditions, may be able to conclude the quantitative dependence of gammas on machine output, and hence the effect on the quality of delivered rapid arc plans.
SU‐F‐T‐285: Evaluation of a Patient DVH‐Based IMRT QA System
Authors: Zhen H , Redler G , Chu J , Turian J
Published: July 2016

Purpose:

To evaluate the clinical performance of a patient DVH‐based QA system for prostate VMAT QA.

Methods:

Mobius3D(M3D) is a QA software with an independent beam model and dose engine. The MobiusFX(MFX) add‐on predicts patient dose using treatment machine log files. We commissioned the Mobius beam model in two steps. First, the stock beam model was customized using machine commissioning data, then verified against the TPS with 12 simple phantom plans and 7 clinical 3D plans. Secondly, the Dosimetric Leaf Gap(DLG) in the Mobius model was fine‐tuned for VMAT treatment based on ion chamber measurements for 6 clinical VMAT plans. Upon successful commissioning, we retrospectively performed IMRT QA for 12 VMAT plans with the Mobius system as well as the ArcCHECK‐3DVH system. Selected patient DVH values (PTV D95, D50; Bladder D2cc, Dmean; Rectum D2cc) were compared between TPS, M3D, MFX, and 3DVH.

Results:

During the first commissioning step, TPS and M3D calculated target Dmean for 3D plans agree within 0.7%±0.7%, with 3D gamma passing rates of 98%±2%. In the second commissioning step, the Mobius DLG was adjusted by 1.2mm from the stock value, reducing the average difference between MFX calculation and ion chamber measurement from 3.2% to 0.1%. In retrospective prostate VMAT QA, 5 of 60 MFX calculated DVH values have a deviation greater than 5% compared to TPS. One large deviation at high dose level was identified as a potential QA failure. This echoes the 3DVH QA result, which identified 2 instances of large DVH deviation on the same structure. For all DVH's evaluated, M3D and MFX show high level of agreement (0.1%±0.2%), indicating that the observed deviation is likely from beam modelling differences rather than delivery errors.

Conclusion:

Mobius system provides a viable solution for DVH based VMAT QA, with the capability of separating TPS and delivery errors.
SU‐F‐T‐286: Calculation‐Based Patient Specific IMRT QA Detects Potential Errors That Measurement‐Based QA Does Not
Authors: Mossahebi S , Langen K , Guerrero M , Yi B , Lu W , Kalavagunta C , Prado K , Chen S
Published: July 2016

Purpose:

Calculation‐based patient‐specific IMRT/VMAT QA, as a DICOM‐RT‐based plan verification system, has been commissioned and is currently being used at our institution. We report our investigation of IMRT/VMAT plan verification failures/warnings out of more than 1,000 plans verified over an 18‐month period.

Methods:

Seven patients with QA failures/warnings from our calculation‐based IMRT/VMAT QA were selected. Dose to 95% of PTV volume (D95%) and mean PTV dose with a difference of greater than 3%, a global gamma passing rate of less than 95%, and a mean dose difference to organ at risk (OAR) larger than 5% were set as the failure/warning criteria. The treatment sites of the selected patients included pelvis, leg, head and neck, brain, and breast. Measurement‐based IMRT/VMAT QA was done on each patient using MapCHECK2. Root cause analysis (RCA) was performed on all patients to investigate the IMRT/VMAT failures/warnings.

Results:

All seven patients’ plans passed measurement‐based IMRT/VMAT QA with a gamma passing rate of more than 95%. Our RCA of patients showed the IMRT/VMAT QA failures detected by the calculation‐based method were mainly due to inclusion of the skin in PTV, and tissue heterogeneity effects particularly at tissue‐air and tissue‐bone interfaces.

Conclusion:

Calculation‐based IMRT/VMAT QA can detect potential failures which cannot be detected by standard measurement‐based QA.
SU‐F‐T‐290: Modeling MLC Penumbra Within the Eclipse TPS ‐ A Major Mode of IMRT QA Failure
Authors: Grams M , Antolak J , Deisher A , Fong de los Santos L
Published: July 2016

Purpose:

To illustrate how inaccurate modeling of the MLC penumbra within the Eclipse TPS can lead to dosimetric differences and decreased IMRT QA passing rates.

Methods:

Gafchromic film was used to compare 6 MV measured profiles from 2×2 cm2 MLC‐defined fields to profiles calculated by the Eclipse TPS (v13.6) under two different scenarios. The first scenario involved calculations using the original MLC opening (original Eclipse). In the second, we selectively broadened the penumbra by summing two appropriately weighted fields: One with 95% of MUs delivered using the original MLC opening, and a second with the remaining MUs delivered with all MLCs opened an additional 5 mm (modified Eclipse). MATLAB code was written to generate MLC patterns and MU weighting in this manner and used to calculate modified Eclipse doses for 25 different clinical IMRT and VMAT plans. Patient specific QA measurements were made with film and compared to both original and modified Eclipse calculations.

Results:

For the 2×2 cm2 fields, agreement was observed between measured and original Eclipse profiles everywhere except in the penumbral region 5–10 mm from the end of the MLC where doses 10–30% higher than expected were measured. Near perfect agreement throughout the entire profile was observed when comparing measurement to the modified Eclipse calculation with the broadened penumbra. For the 25 clinical treatment plans, the average 2%/0 mm gamma passing rate using the original Eclipse calculations was 82.3%, while for the modified Eclipse calculations it improved to 90.1%.

Conclusion:

The approximation used by the Eclipse TPS to model the rounded end of the MLC is a failure mode that could lead to poor quality and/or failing QA for IMRT and VMAT plans. Improved modeling of the penumbra in the region 5–10 mm from the end of the MLC is required to completely correct this discrepancy.
SU‐F‐T‐248: FMEA Risk Analysis Implementation (AAPM TG‐100) in Total Skin Electron Irradiation Technique
Authors: Ibanez‐Rosello B , Bautista‐Ballesteros J , Bonaque J , Perez‐Calatayud J , Gonzalez‐Sanchis A , Lopez‐Torrecilla J , Brualla‐Gonzalez L , Garcia‐Hernandez T , Vicedo‐Gonzalez A , Granero D , Serrano A , Borderia B , Solera C , Rosello J
Published: July 2016

Purpose:

Total Skin Electron Irradiation (TSEI) is a radiotherapy treatment which involves irradiating the entire body surface as homogeneously as possible. It is composed of an extensive multi‐step technique in which quality management requires high consumption of resources and a fluid communication between the involved staff, necessary to improve the safety of treatment. The TG‐100 proposes a new perspective of quality management in radiotherapy, presenting a systematic method of risk analysis throughout the global flow of the stages through the patient. The purpose of this work has been to apply TG‐100 approach to the TSEI procedure in our institution.

Methods:

A multidisciplinary team specifically targeting TSEI procedure was formed, that met regularly and jointly developed the process map (PM), following TG‐100 guidelines of the AAPM. This PM is a visual representation of the temporal flow of steps through the patient since start until the end of his stay in the radiotherapy service.

Results:

This is the first stage of the full risk analysis, which is being carried out in the center. The PM provides an overview of the process and facilitates the understanding of the team members who will participate in the subsequent analysis. Currently, the team is implementing the analysis of failure modes and effects (FMEA). The failure modes of each of the steps have been identified and assessors are assigning a value of severity (S), frequency of occurrence (O) and lack of detection (D) individually. To our knowledge, this is the first PM made for the TSEI. The developed PM can be useful for those centers that intend to implement the TSEI technique.

Conclusion:

The PM of TSEI technique has been established, as the first stage of full risk analysis, performed in a reference center in this treatment.
SU‐F‐T‐249: Application of Human Factors Methods: Usability Testing in the Radiation Oncology Environment
Authors: Warkentin H , Bubric K , Giovannetti H , Graham G , Clay C
Published: July 2016

Purpose:

As a quality improvement measure, we undertook this work to incorporate usability testing into the implementation procedures for new electronic documents and forms used by four affiliated radiation therapy centers.

Methods:

A human factors specialist provided training in usability testing for a team of medical physicists, radiation therapists, and radiation oncologists from four radiotherapy centers. A usability testing plan was then developed that included controlled scenarios and standardized forms for qualitative and quantitative feedback from participants, including patients. Usability tests were performed by end users using the same hardware and viewing conditions that are found in the clinical environment. A pilot test of a form used during radiotherapy CT simulation was performed in a single department; feedback informed adaptive improvements to the electronic form, hardware requirements, resource accessibility and the usability testing plan. Following refinements to the testing plan, usability testing was performed at three affiliated cancer centers with different vault layouts and hardware.

Results:

Feedback from the testing resulted in the detection of 6 critical errors (omissions and inability to complete task without assistance), 6 non‐critical errors (recoverable), and multiple suggestions for improvement. Usability problems with room layout were detected at one center and problems with hardware were detected at one center. Upon amalgamation and summary of the results, three key recommendations were presented to the document's authors for incorporation into the electronic form. Documented inefficiencies and patient safety concerns related to the room layout and hardware were presented to administration along with a request for funding to purchase upgraded hardware and accessories to allow a more efficient workflow within the simulator vault.

Conclusion:

By including usability testing as part of the process when introducing any new document or procedure into clinical use, associated risks can be identified and mitigated before patient care and clinical workflow are impacted.
SU‐F‐T‐254: Dose Volume Histogram (DVH) Analysis of Breath Hold Vs Free Breathing Techniques for Esophageal Tumors
Authors: Badkul R , Doke K , Pokhrel D , Aguilera N , Lominska C
Published: July 2016

Purpose:

Lung and heart doses and associated toxicity are of concern in radiotherapy for esophageal cancer. This study evaluates the dosimetry of deep‐inspiration‐breath‐hold (DIBH) technique as compared to freebreathing(FB) using 3D‐conformal treatment(3D‐CRT) of esophageal cancer.

Methods:

Eight patients were planned with FB and DIBH CT scans. DIBH scans were acquired using Varian RPM system. FB and DIBH CTs were contoured per RTOG‐1010 to create the planning target volume(PTV) as well as organs at risk volumes(OAR). Two sets of gross target volumes(GTV) with 5cm length were contoured for each patient: proximal at the level of the carina and distal at the level of gastroesophageal junction and were enlarged with appropriate margin to generate Clinical Target Volume and PTV. 3D‐CRT plans were created on Eclipse planning system for 45Gy to cover 95% of PTV in 25 fractions for both proximal and distal tumors on FB and DIBH scans. For distal tumors celiac nodes were covered electively. DVH parameters for lung and heart OARs were generated and analyzed.

Results:

All DIBH DVH parameters were normalized to FB plan values. Average of heart‐mean and heart‐V40 was 0.70 and 0.66 for proximal lesions. For distal lesions ratios were 1.21 and 2.22 respectively. For DIBH total lung volume increased by 2.43 times versus FB scan. Average of lung‐mean, V30, V20, V10, V5 are 0.82, 0.92, 0.76, 0.77 and 0.79 for proximal lesions and 1.17,0.66,0.87,0.93 and 1.03 for distal lesions. Heart doses were lower for breath‐hold proximal lesions but higher for distal lesions as compared to free‐breathing plans. Lung doses were lower for both proximal and distal breath‐hold lesions except mean lung dose and V5 for distal lesions.

Conclusion:

This study showed improvement of OAR doses for esophageal lesions at mid‐thoracic level utilizing DIBH vs FB technique but did not show consistent OAR sparing with DIBH for distal lesions.
SU‐F‐T‐264: VMAT QA with 2D Radiation Measuring Equipment Attached to Gantry
Authors: Fung A
Published: July 2016

Purpose:

To introduce a method of VMAT QA by 2D measuring device. The 2D device is attached to the gantry throughout measurement duration. This eliminates error caused by the angular dependence of the radiation detectors.

Methods:

A 2D radiation measuring device was attached to the gantry of linear accelerator. The center of the detector plane was at the isocenter. For each patient plan, two verification plans were created for QA purpose. One was like an ordinary VMAT plan, to be used for radiation delivery. The other is a plan with gantry angle fixed at zero, so the dose distribution as seen by the rotating 2D device. Points above 10% dose threshold were analyzed. Data is in tolerance if it fits within the 3 mm or 3% dose gamma criteria. For each patient, the plan was passed when 95% of all the points in the 2D matrix fit the gamma criteria. The following statistics were calculated: number of patient plans passed, percentage of all points passed, average percentage difference of all points.

Results:

VMAT QA was performed for patients during one year in our department, and the results were analyzed. All irradiation was with 6 MV photon beam. Each plan has calculated and measured doses compared. After collecting one year's result, with 81 patient plans analyzed, all (100%) of the plans passed the gamma criteria. Of the points analyzed from all plans, 98.8% of all points passed.

Conclusion:

This method of attaching a 2D measuring device on the linac gantry proves to be an accurate way for VMAT QA. It is simple to use and low cost, and it eliminates the problem of directional dependence.
SU‐F‐T‐296: Modulated Therapy Down Under: A Survey of IMRT & VMAT Physics Practice in Australia and New Zealand
Authors: Barber J , Vial P
Published: July 2016

Purpose:

A comprehensive survey of Australasian radiation oncology physics departments was undertaken to capture a snapshot of current usage, commissioning and QA practices for intensity‐modulated therapies.

Methods:

An online survey was developed and advertised to Australian and New Zealand radiation oncology physicists through the local college (ACPSEM) in April 2015. The survey consisted of 147 questions in total, covering IMRT, VMAT and Tomotherapy, and details specific to different treatment planning systems. Questions captured detailed information on equipment, policies and procedures for the commissioning and QA of each treatment technique.

Results:

41 partial or complete responses were collected, representing 59 departments out of the 78 departments operational. 137 and 84 linacs from these departments were using IMRT and VMAT respectively, from a total 150 linacs. 100% and 78% of respondents were treating with IMRT and VMAT respectively. There are at least 8 different treatment planning systems being used for IMRT or VMAT, and large variations in all aspects of QA policies and procedures. 29 responses indicated 72 methods routinely used for pre‐treatment QA, when breaking down by device and analysis type. Similar numbers of departments use field‐by‐field analysis compared to composite analysis (56% to 44%) while a majority use true gantry angle delivery compared to fixed gantry at 0° (72% to 28%). 19 different implementations of gamma index analysis parameters were reported from 33 responses. A follow‐up one‐day workshop to highlight the results, discuss the role of QA and share equipment‐specific knowledge across users was conducted in November 2015.

Conclusion:

While IMRT and VMAT are almost universally available in Australasia, large variations in practice indicate a need for national or consensus guidelines.
SU‐F‐T‐301: Planar Dose Pass Rate Inflation Due to the MapCHECK Measurement Uncertainty Function
Authors: Bailey D , Spaans J , Kumaraswamy L , Podgorsak M
Published: July 2016

Purpose:

To quantify the effect of the Measurement Uncertainty function on planar dosimetry pass rates, as analyzed with Sun Nuclear Corporation analytic software (“MapCHECK” or “SNC Patient”). This optional function is toggled on by default upon software installation, and automatically increases the user‐defined dose percent difference (%Diff) tolerance for each planar dose comparison.

Methods:

Dose planes from 109 IMRT fields and 40 VMAT arcs were measured with the MapCHECK 2 diode array, and compared to calculated planes from a commercial treatment planning system. Pass rates were calculated within the SNC analytic software using varying calculation parameters, including Measurement Uncertainty on and off. By varying the %Diff criterion for each dose comparison performed with Measurement Uncertainty turned off, an effective %Diff criterion was defined for each field/arc corresponding to the pass rate achieved with MapCHECK Uncertainty turned on.

Results:

For 3%/3mm analysis, the Measurement Uncertainty function increases the user‐defined %Diff by 0.8–1.1% average, depending on plan type and calculation technique, for an average pass rate increase of 1.0–3.5% (maximum +8.7%). For 2%, 2 mm analysis, the Measurement Uncertainty function increases the user‐defined %Diff by 0.7–1.2% average, for an average pass rate increase of 3.5–8.1% (maximum +14.2%). The largest increases in pass rate are generally seen with poorly‐matched planar dose comparisons; the MapCHECK Uncertainty effect is markedly smaller as pass rates approach 100%.

Conclusion:

The Measurement Uncertainty function may substantially inflate planar dose comparison pass rates for typical IMRT and VMAT planes. The types of uncertainties incorporated into the function (and their associated quantitative estimates) as described in the software user's manual may not accurately estimate realistic measurement uncertainty for the user's measurement conditions. Pass rates listed in published reports or otherwise compared to the results of other users or vendors should clearly indicate whether the Measurement Uncertainty function is used.
SU‐F‐T‐305: Clinical Effects of Dosimetric Leaf Gap (DLG) Values Between Matched Varian Truebeam (TB) Linacs
Authors: Mihailidis D , Mallah J , Zhu D
Published: July 2016

Purpose:

The dosimetric leaf gap (DLG) is an important parameter to be measured for dynamic beam delivery of modern linacs, like the Varian Truebeam (TB). The clinical effects of DLG‐values on IMRT and/or VMAT commissioning of two “matched” TB linacs will be presented.Methods and Materials: The DLG values on two TB linacs were measured for all energy modalities (filtered and FFF‐modes) as part of the dynamic delivery mode commissioning (IMRT and/or VMAT. After the standard beam data was modeled in eclipse treatment planning system (TPS) and validated, IMRT validation was performed based on TG1191 benchmark, IROC Head‐Neck (H&N) phantom and sample of clinical cases, all measured on both linacs. Although there was a single‐set of data entered in the TPS, a noticeable difference was observed for the DLG‐values between the linacs. The TG119, IROC phantom and selected patient plans were furnished with DLG‐values of TB1 for both linacs and the delivery was performed on both TB linacs for comparison.

Results:

The DLG values of TB1 was first used for both linacs to perform the testing comparisons. The QA comparison of TG119 plans revealed a great dependence of the results to the DLG‐values used for the linac for all energy modalities studied, especially when moving from 3%/3mm to 2%/2mm γ‐analysis.

Conclusion:

The DLG‐values have a definite influence on the dynamic dose, delivery that increases with the plan complexity. We recommend that the measured DLG‐values are assigned to each of the “matched” linacs, even if a single set of beam data describes multiple linacs. The user should perform a detail test of the dynamic delivery of each linac based on end‐to‐end benchmark suites like TG119 and IROC phantoms.1Ezzel G., et al., “IMRT commissioning: Multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119.” Med. Phys. 36:5359–5373 (2009).

partly supported by CAMC Cancer Center and Alliance Oncology