bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐455: Is Contouring the Whole Breast Necessary for Two‐Field 3D Breast Planning?
Authors: Desai A , Ku Eric , Fang D , Lawrence C , Iannuzzi C , Shi C
Published: July 2016

Purpose:

To investigate the effect of contouring the whole breast on reducing the radiation dose to the heart and affected lung in tangential field‐in‐field 3D breast planning. We hypothesize that contouring the whole breast will simplify the plan normalization process, reduce dose to critical structures, while maintaining treatment plan quality and consistency.

Methods:

Twenty previously treated breast cancer patients using tangential field‐in‐field 3D planning technique were randomly selected. The affected breast was contoured following the RTOG breast atlas guideline. Breast PTV was created by shrinking 5 mm from the breast contour. The same plan has been pasted to the new contour and normalized to 95% of the Breast PTV receiving the prescribed isodose line. Lung V20 Gy% and Heart V25 Gy% were the primary study endpoints. Homogeneity Index (HI) and Conformity Index (CI) were calculated based on the following equations. HI= Dmax/ D95 and Nakamura's Conformity Index= PIV/TVPIV × TV/TVPIV.

Results:

The average CI for previous plans was 1.68 vs. 1.66 for the new hybrid plan: both plans were conformal to the breast with similar quality. The HI for both the previous and the new hybrid plan was 1.24. Lung V 20% slightly increased from 4.27% to 4.82%. Heart V 25% for LT breast patients slightly decreased from 0.38% to 0.29%. Heart V 25% for RT breast patients was close to zero in both cases.

Conclusion:

With similar conformal and homogeneity indices for the plan quality, by contouring the whole breast following RTOG breast atlas guideline will simplify the planning process. The study showed that contouring the whole breast for patients with left‐sided breast cancer reduced the heart V 25%, although not significantly, while maintaining the CI and HI. There was no measurable gain seen with whole breast contour for right‐sided breast cancer patients.
SU‐F‐T‐461: Dosimetric Evaluation of Indigenous Farmer Type Chamber FAR65‐ GB for Reference Dosimetry of FFF MV Photon Beam
Authors: Patwe P , Mhatre V , Dandekar P
Published: July 2016

Purpose:

Indigenous Farmer type chamber FAR 65 GB is a reference class 0.6 cc ion chamber. It can be used for dosimetric evaluation of photon and high energy electron beams. We studied dosimetric characteristics of the chamber for 6MV and 10MV Flattening filter free FFF photon beams available on trueBEAM STx Linac.

Methods:

The study was carried out on trueBEAM STx Linac having 6 and 10 MV FFF photon beam with maximum dose rate 1400 and 2400 MU per min respectively. The dosimetric device to be evaluated is Rosalina Instruments FAR 65‐GB Ion Chamber with active volume 0.65 cc, total active length 23.1cm, inner diameter of cylinder 6.2mm, wall thickness 0.4mm, inner electrode diameter 1mm. Inner and outer electrodes are made from Aluminium 2.7 gm per cc and graphite 1.82 gm per cc respectively. The ion chamber was placed along central axis of beam at 10cm depth and irradiated for 10cm × 10cm field size at SAD of 100 cm in plastic phantom. We studied Precision, Dose Linearity, Dose Rate dependence, directional dependence, Recombination effect. Recombination effect was determined using standard two‐voltage method.

Results:

1. Measurements were reproducible std deviation of 0.0105 and type A uncertainty 0.003265 under same set of reference conditions 2. Chamber exhibit dose linearity over a wider dose range. 3. Chamber shows dose rate independence for all available dose rate range. 4. Response of chamber with the angle of incidence of radiation is constant. 5. Recombination correction factors were 1.01848 and 1.02537 for dose rate 1400 and 2400 MU per min resp.

Conclusion:

Our study reveals that the chamber is prone to saturation effect at dose rate of 2400 MU per min. FAR 65‐GB can be used for reference dosimetry of FFF MV photon beam with proper calculation of recombination effect.
SU‐F‐T‐465: Two Years of Radiotherapy Treatments Analyzed Through MLC Log Files
Authors: Defoor D , Kabat C , Papanikolaou N , Stathakis S
Published: July 2016

Purpose:

To present treatment statistics of a Varian Novalis Tx using more than 90,000 Varian Dynalog files collected over the past 2 years.

Methods:

Varian Dynalog files are recorded for every patient treated on our Varian Novalis Tx. The files are collected and analyzed daily to check interfraction agreement of treatment deliveries. This is accomplished by creating fluence maps from the data contained in the Dynalog files. From the Dynalog files we have also compiled statistics for treatment delivery times, MLC errors, gantry errors and collimator errors.

Results:

The mean treatment time for VMAT patients was 153 ± 86 seconds while the mean treatment time for step & shoot was 256 ± 149 seconds. Patient's treatment times showed a variation of 0.4% over there treatment course for VMAT and 0.5% for step & shoot. The average field sizes were 40 cm2 and 26 cm2 for VMAT and step & shoot respectively. VMAT beams contained and average overall leaf travel of 34.17 meters and step & shoot beams averaged less than half of that at 15.93 meters. When comparing planned and delivered fluence maps generated using the Dynalog files VMAT plans showed an average gamma passing percentage of 99.85 ± 0.47. Step & shoot plans showed an average gamma passing percentage of 97.04 ± 0.04. 5.3% of beams contained an MLC error greater than 1 mm and 2.4% had an error greater than 2mm. The mean gantry speed for VMAT plans was 1.01 degrees/s with a maximum of 6.5 degrees/s.

Conclusion:

Varian Dynalog files are useful for monitoring machine performance treatment parameters. The Dynalog files have shown that the performance of the Novalis Tx is consistent over the course of a patients treatment with only slight variations in patient treatment times and a low rate of MLC errors.
SU‐F‐T‐466: An Enhanced Daily Quality Assurance Process for a Six Degrees of Freedom Robotic Table
Authors: Kremmel E , Doyle L , Yu Y , Harrison A
Published: July 2016

Purpose:

A Varian PerfectPitch six degrees of freedom robotic table necessitates daily quality assurance (QA). Therapists were credentialed for this QA procedure which was easily incorporated into the existing daily warmup process. This procedure adds depth to TG‐142 requirements without additional morning time costs.

Methods:

This PerfectPitch table QA introduces a consistent rotation of the QUASAR™ Penta‐Guide phantom and requires automatic table corrections through image fusions. Rotational offsets are generated by inserting a platform tool under a specified corner of the phantom; then a conebeamCT is performed. This conebeamCT image is fused with a planned reference CT image set and the table is auto‐adjusted to correct for induced translational and rotational offsets. After executing table shifts, a second conebeamCT verifies the table movement and the phantom's return to isocenter.

Results:

Pre‐shift and post‐shift table corrections were recorded daily. It was discovered that due to slight variations in the setup, it took three performances of the QA for each therapist to have consistent induced rotations. Four therapists performed this QA and after the initial training period, the inter‐user variability was minimal. Consistency of the induced rotation was evaluated by the variation of the pre‐shift table corrections. Excluding the first three attempts of each therapist, the pre‐shift table correction standard deviations were ≤ 0.67mm for the translational axes and ≤ 0.49° for the rotational axes. Accuracy of the automatic table movement was confirmed by the post‐shift table corrections. The average post‐shift table corrections for the translational axes were ≤ 0.15mm and for the rotational axes were ≤ 0.42°. Using our clinic's existing table corrections tolerance of <1mm and <0.5°, these results were deemed acceptable.

Conclusion:

Therapists successfully and rapidly adopted daily QA procedures using the PerfectPitch table; automated rotational robotic table motions were confirmed through image fusions. This procedure enhances existing TG‐142 recommendations.
SU‐F‐T‐467: A Cross‐Checking Approach for Dosimetric Verification of Beam‐ Matched Elekta Linear Accelerators
Authors: Zheng Y , Yuan J , Geis P , Colussi V , Machtay M , Ellis R , Wessels B
Published: July 2016

Purpose:

To verify the similarity of the dosimetric characteristics between two Elekta linear accelerators (linacs) in order to treat patients interchangeably on these two machines without re‐planning.

Methods:

To investigate the viability of matching the 6 MV flattened beam on an existing linac (Elekta Synergy with Agility head) with a recently installed new linca (Elekta Versa HD), percent depth doses (PDD), flatness and symmetry output factors were compared for both machines. To validate the beam matching among machines, we carried out two approaches to cross‐check the dosimetrical equivalence: 1) the prior treatment plans were re‐computed based on the newly built Versa HD treatment planning system (TPS) model without changing the beam control points; 2) The same plans were delivered on both machines and the radiation dose measurements on a MapCheck2 were compared with TPS calculations. Three VMAT plans (Head and neck, lung, and prostate) were used in the study.

Results:

The difference between the PDDs for 10×10 cm2 field at all depths was less than 0.8%. The difference of flatness and symmetry for 30×30 cm2 field was less than 0.8%, and the measured output factors varies by less than 1% for each field size ranging from 2×2 cm2 to 40×40 cm2. For the same plans, the maximum difference of the two calculated dose distributions is 2% of prescription. For the QA measurements, the gamma index passing rates were above 99% for 3%/3mm criteria with 10% threshold for all three clinical plans.

Conclusion:

A beam modality matching between two Elekta linacs is demonstrated with a cross‐checking approach.
SU‐F‐T‐468: Efficient Scanning Data Analysis for TomoTherapy
Authors: Sintay B , Pearman K , Maurer J , Liu H , Hayes T , Wiant D
Published: July 2016

Purpose:

The standard TomoTherapy 2D scanning system requires manual analysis using spreadsheets or similar software. Manual analysis is time consuming and does not allow efficient use of the medical physicist or timely results that may indicate issues during the acquisition of data. The purpose of this study is to determine if an in‐house solution can provide timely analysis of TomoTherapy scan data.

Methods:

A custom MATLAB program utilizing a streamlined graphical interface was developed to interpret the native scanning data acquired by the TomoTherapy Electrometer Measurement System (TEMS). The gold beam data provided by the manufacturer was used as a baseline for the acquired data. Two separate sets of scan data were used including longitudinal, transverse, and percent depth dose (PDD). The scan data were compared visually in an overlay and analytically for each beam width using the full width half max (FWHM) for longitudinal profiles and difference inside the field core for the transverse profiles as recommended by TG‐148. A plot of the PDD percent error at each point along the curve was generated to show agreement. The time to analysis was measured on a laptop running an Intel i5 processor with 8GB of RAM.

Results:

The software program required on average less than 5 seconds to load and analyze the results. No conversion or reformatting of the data was required. This allowed real‐time visualization of the comparison to the gold beam data as well as the parameters recommended by TG‐148. The average percent difference was 0.3% for the longitudinal profiles and 0.1% for the transverse profiles. All PDD data was less than 1% different beyond dmax.

Conclusion:

We have developed a tool to analyze TomoTherapy scan data in real‐time. This allows an efficient method to perform beam commissioning, annual QA, and adjust the beam parameters if necessary.
SU‐F‐T‐470: Implementation of a Daily Quality Assurance Phantom for Six Degrees‐Of‐Freedom Couch Testing
Authors: Gaballa H , O'Brien M , Riegel A , Jamshidi A , Klein E
Published: July 2016

Purpose:

To develop a daily quality assurance (QA) device that can test the 6DoF (degrees of freedom) couch repositioning accuracy, prior to SBRT treatment deliveries, with an accuracy of ±0.3 degrees and ±0.3 mm.

Methods:

A daily QA phantom is designed with a focus on the derived center of projections of its markers, rather than tracking its individual markers one at a time. This approach can be the most favorable to address the intended machining accuracy of the QA phantom and the CBCT spatial resolution limitations, primarily 1 mm min slice thickness, simultaneously. With the current design, ±0.1 mm congruence of the resultant center of gravity of the markers with reference CT (0.6 mm minimum slice thickness) vs CBCT (1.0 mm minimum slice thickness) can be achieved. If successful, the QA device should be qualified to test 6DoF couch performance with a gauged accuracy of ±0.3 degrees/±0.3 mm. Testing is performed for the Varian True Beam 2.0 6DoF system.

Results:

Once the QA phantom is constructed and tested, agreement of the center of gravity of the reference CT scan and the CBCT scan of ±0.1 mm is achieved. This has translated into a consistent 3D‐3D match on the treatment machine, CT vs CBCT, with a repetitive ±0.1 mm variation, thus exceeding our expectations. We have deployed the phantom for daily QA on one of our accelerators, and found that the QA time has increased by only 10 minutes.

Conclusion:

A 6DoF phantom has been designed (patent pending) and built with a realistic work flow in mind where the daily couch accuracy QA checks taking less than 10 minutes. Current developments include integration with the Varian's Machine Performance Check consistency module.
SU‐F‐T‐473: Evaluation of Off‐Axis And Peripheral Dose Using Different Detectors
Authors: Ganesan B , Prakasarao A , Palraj T , Rai R , Singaravelu G
Published: July 2016

Purpose:

In radiation therapy, measurement of off‐axis and peripheral dose is a tedious task. The dose distribution along the beam central axis give only part of the information required for an accurate dose description inside the patient. Dose distributions in 2‐D and 3‐D are determined with central axis data in conjunction with off‐axis dose profiles. Combining a central axis dose distribution with off‐axis data results in volume dose matrix that provides 2‐D and 3‐D information on dose distribution. By considering the importance of these two parameters this study investigates and compares the off axis and peripheral dose measurement using Ionization chamber, MOSFET, Radiochromic film and EDR2 film.

Methods:

In the measurement of off‐axis and peripheral doses 0.6cc farmer type chamber, EDR‐2 film, MD‐55 radiochromic film and MOSFET detectors were used for both 6MV and 15MV beams. The off‐axis and peripheral dose was measured at every 1 cm interval by changing the position of the couch without disturbing the other experimental setup in particular, the phantom with detector position.

Results:

Readings were obtained for both 6MV and 15MV photon beams at SSD technique for various field size using MOSFET, Ionization chamber and Radiochromic film. The results shows the percentage difference between various detectors for various field sizes. For Peripheral dose measurement were taken from the edge of the field size and for off axis it is measured form central axis dose.

Conclusion:

In conclusion, our study shows that no detector is ideal and only a comparison between different detectors highlights the weaknesses of each detector. MOSFET provides adequate dose assessment in off‐axis and peripheral regions in 6MV and 15MV photon beams. Film dosimetry in general a convenient method to generate one‐ and two‐dimensional dose distributions. The result of this indicates that MOSFET is flexible tool for relative dosimetry as films.
SU‐F‐T‐474: Evaluation of Dose Perturbation, Temperature and Sensitivity Variation With Accumulated Dose of MOSFET Detector
Authors: Ganesan B , Prakasarao A , Palraj T , Rai R , Singaravelu G
Published: July 2016

Purpose:

The use of mega voltage gamma and x‐ray sources with their skin sparring qualities in radiation therapy has been a boon in relieving patient discomfort and allowing high tumor doses to be given with fewer restrictions due to radiation effects in the skin. However, high doses given to deep tumors may require careful consideration of dose distribution in the buildup region in order to avoid irreparable damage to the skin.

Methods:

To measure the perturbation of MOSFET detector in Co60,6MV and 15MV the detector was placed on the surface of the phantom covered with the brass build up cap. To measure the effect of temperature the MOSFET detector was kept on the surface of hot water polythene container and the radiation was delivere. In order to measure the sensitivity variation with accumulated dose Measurements were taken by delivering the dose of 200 cGy to MOSFET until the MOSFET absorbed dose comes to 20,000 cGy

Results:

the Measurement was performed by positioning the bare MOSFET and MOSFET with brass build up cap on the top surface of the solid water phantom for various field sizes in order to find whether there is any attenuation caused in the dose distribution. The response of MOSFET was monitored for temperature ranging from 42 degree C to 22 degree C. The integrated dose dependence of MOSFET dosimeter sensitivity over different energy is not well characterized. This work investigates the dual‐bias MOSFET dosimeter sensitivity response to 6 MV and 15 MV beams.

Conclusion:

From this study it is observed that unlike diode, bare MOSFET does not perturb the radiation field.. It is observed that the build‐up influences the temperature dependency of MOSFET and causes some uncertainty in the readings. In the case of sensitivity variation with accumulated dose MOSFET showed higher sensitivity with dose accumulation for both the energies.
SU‐F‐T‐484: Initial Evaluation of a Novel 6D QA Phantom (HexaCheck) for Daily 6D Couch Correction Assessment
Authors: Roring JE , Stanley D , Papanikolaou N , Gutierrez AN
Published: July 2016

Purpose:

Treatment couches with 6D correction capabilities have become a regular part of IGRT. While 6D couches have been shown to function mechanically well, phantoms for daily angular QA accuracy assessment have yet to be commercially available. Standard Imaging™ has developed a phantom designed for daily verification of pitch, roll, and yaw corrections. In this study, the mechanical integrity, reproducibility, and daily 6D correction stability of the phantom using both volumetric (Elekta− XVI kV‐CBCT) and orthogonal kV (Brainlab ExacTrac) imaging was evaluated.

Methods:

The HexaCheck is a rotating base that works in conjunction with the MIMI imaging phantom. The MIMI is placed inside the HexaCheck and secured to prevent motion. The HexaCheck has screws in each rotational direction (pitch, roll, and yaw) along with a spring‐loaded peg to lock each direction firmly. When a peg is released, the HexaCheck rotates 2.5° solely in that direction. Mechanical integrity was assessed using a level with 0.05° precision. For daily 6D corrections, a high resolution reference CT (0.59 × 0.59 × 1.25 mm3) of the HexaCheck was acquired. Ten (n=10) independent, daily acquisitions using both the ExacTrac with the 6D Brainlab™ couch and the Elekta XVI kV‐CBCT with the HexaPOD™ couch were acquired to test detection and positioning accuracy.

Results:

Physical measurements show that the HexaCheck rotations for pitch, roll, and yaw were 2.43±0.05 deg, 2.50±0.05 deg, and 2.62±0.05 deg, respectively. Maximum mean values for the imaging registration accuracy were 0.2° and 0.3° for ExacTrac and XVI, respectively. Maximum mean values for the couch positioning accuracy were 0.1° and 0.2° for the Brainlab couch and HexaPOD, respectively.

Conclusion:

The HexaCheck performance yields consistent results for daily testing in all three rotational directions using both 2D and 3D imaging modalities and also appears to be a simple method for daily 3D rotational testing.
SU‐F‐T‐486: A Simple Approach to Performing Light Versus Radiation Field Coincidence Quality Assurance Using An Electronic Portal Imaging Device (EPID)
Authors: Herchko S , Ding G
Published: July 2016

Purpose:

To develop an accurate, straightforward, and user‐independent method for performing light versus radiation field coincidence quality assurance utilizing EPID images, a simple phantom made of readily‐accessible materials, and a free software program.

Methods:

A simple phantom consisting of a blocking tray, graph paper, and high‐density wire was constructed. The phantom was used to accurately set the size of a desired light field and imaged on the electronic portal imaging device (EPID). A macro written for use in ImageJ, a free image processing software, was then use to determine the radiation field size utilizing the high density wires on the phantom for a pixel to distance calibration. The macro also performs an analysis on the measured radiation field utilizing the tolerances recommended in the AAPM Task Group #142. To verify the accuracy of this method, radiochromic film was used to qualitatively demonstrate agreement between the film and EPID results, and an additional ImageJ macro was used to quantitatively compare the radiation field sizes measured both with the EPID and film images.

Results:

The results of this technique were benchmarked against film measurements, which have been the gold standard for testing light versus radiation field coincidence. The agreement between this method and film measurements were within 0.5 mm.

Conclusion:

Due to the operator dependency associated with tracing light fields and measuring radiation fields by hand when using film, this method allows for a more accurate comparison between the light and radiation fields with minimal operator dependency. Removing the need for radiographic or radiochromic film also eliminates a reoccurring cost and increases procedural efficiency.
SU‐F‐T‐488: Comparison of the TG‐51 and TG‐51 Addendum Calibration Protocols
Authors: McCaw T , Hwang M , Jang S , Huq M
Published: July 2016

Purpose:

To quantify differences between the TG51 and TG51 addendum calibration protocols.

Methods:

Beam energies of 6X, 6XSRS, 10X, 15X, 23X, 6XFFF, and 10XFFF were calibrated following both the TG51 and TG51 addendum protocols using both a Farmer and a scanning ionization chamber with traceable absorbed dose‐to‐water calibrations. For the TG51 addendum procedure, the collimating jaws were positioned to define a 10×10cm2 radiation field, a lead foil was only used for kQ measurements of FFF energies, and a volume‐averaging correction was applied based on crossline and inline dose profiles. For the TG51 procedure, the collimating jaws were set to 10×10cm2 according to the digital readout, and a lead foil was used for kQ measurements of energies greater than 10MV.

Results:

For beam energies with a flattening filter, absorbed dose‐to‐water determined by the two protocols differed by 0.1%–0.3%. For FFF beam energies, differences between the protocols were up to 0.2% and 0.8% for the scanning and Farmer ionization chambers, respectively. Differences between the protocols were due to kQ determination, volume‐averaging correction, and measurement of raw ionization. Differences in kQ values between the two protocols were up to 0.4% and 0.2% for the scanning and Farmer ionization chambers, respectively. Volume‐averaging corrections were less than 0.1% for the scanning ionization chamber, and up to 0.4% and 0.6% for the Farmer ionization chamber in beams with a flattening filter and FFF beams, respectively. Raw ionization measurements differed up to 0.3%±0.07% due to differences in jaw settings.

Conclusion:

The TG51 and TG51 addendum calibration protocols differed less than 0.3% for the scanning ionization chamber. For the Farmer chamber in FFF energies, volume‐averaging corrections of up to 0.6% contributed to calibration differences of up to 0.8%. Failure to verify the radiation field size can produce calibration differences of up to 0.3%.
SU‐F‐T‐490: Separating Effects Influencing Detector Response in Small MV Photon Fields
Authors: Wegener S , Sauer O
Published: July 2016

Purpose:

Different detector properties influence their responses especially in field sizes below the lateral electron range. Due to the finite active volume, the detector density and electron perturbation at other structural parts, the response factor is in general field size dependent. We aimed to visualize and separate the main effects contributing to detector behavior for a variety of detector types. This was achieved in an experimental setup, shielding the field center. Thus, effects caused by scattered radiation could be examined separately.

Methods:

Signal ratios for field sizes down to 8 mm (SSD 90 cm, water depth 10 cm) of a 6MV beam from a Siemens Primus LINAC were recorded with several detectors: PTW microDiamond and PinPoint ionization chamber, shielded diodes (PTW P‐60008, IBA PFD and SNC Edge) and unshielded diodes (PTW E‐60012 and IBA SFD). Measurements were carried out in open fields and with an aluminum pole of 4 mm diameter as a central block. The geometric volume effect was calculated from profiles obtained with Gafchromic EBT3 film, evaluated using FilmQA Pro software (Ashland, USA).

Results:

Volume corrections were 1.7% at maximum. After correction, in small open fields, unshielded diodes showed a lower response than the diamond, i.e. diamond detector over‐response seems to be higher than that for unshielded diodes. Beneath the block, this behavior was amplified by a factor of 2. For the shielded diodes, the overresponse for small open fields could be confirmed. However their lateral response behavior was strongly type dependent, e.g. the signal ratio dropped from 1.02 to 0.98 for the P‐60008 diode.

Conclusion:

The lateral detector response was experimentally examined. Detector volume and density alone do not fully account for the field size dependence of detector response. Detector construction details play a major role, especially for shielded diodes.
SU‐F‐T‐491: Photon Beam Matching Analysis at Multiple Sites Up to Twelve Years Post Installation
Authors: Able C , Zakikhani R , Yan K , Sha D , Chopra A
Published: July 2016

Purpose:

To determine if the photon beams associated with several models of accelerators are matched with ‘Golden Beam’ data (VGBD) to assess treatment planning modeling and delivery.

Methods:

Six accelerators’ photon beams were evaluated to determine if they matched the manufacturer's (Varian Medical Systems, Inc.) VGBD. Additional direct comparisons of the 6X and 18X beams using the manufacturer's specification of Basic and Fine beam matching were also performed. The Cseries accelerator models were 21 EX (3), IX (2), and a IX Trilogy, ranging from three to twelve years post installation. Computerized beam scanning was performed (IBA Blue Phantom 2) with 2 CC13 ion chambers in water at 100 cm SSD. Dmax (10 cm2 field size), percentage depth dose (6 cm2, 10 cm2, 20 cm2, and 30 cm2 field sizes) and beam uniformity (10 cm2, 30 cm2 and 40 cm2 field sizes) were evaluated.

Results:

When comparing the beams with VGBD using the ‘Basic’ matching criteria, all beams were within the specifications (1.5mm at dmax, 1% PDD, and 2% Profiles). When considering the “Fine” matching criteria (1.5mm at dmax, 0.5% PDD, and 2% Profiles), only three of six 6MV beams and two of six high energy (five 18MV & one 15MV) beams passed. Direct comparisons between accelerators using the Clinac IX (installed 2012) as the reference beam datasets resulted in all 6 MV and 18MV beams meeting both the “Basic” and “Fine” criterion with the exception of two accelerators.

Conclusion:

Linear accelerators installed up to nine years apart are capable of meeting the manufacturers beam matching criteria for “Basic” matching. Without any adjustments most beams, when evaluated, may meet the “Fine” match criteria. The use of a single dataset (VGBD or designated accelerator reference data) for treatment planning commissioning is acceptable and can provide quality treatment delivery.
SU‐F‐T‐493: An Investigation Into the Feasibility of Using PipsPro Software with Film for Linac QA
Authors: Underwood R
Published: July 2016

Purpose:

To determine the feasibility of using radiochromic and radiographic film with Pipspro software for quality assurance of linear accelerators with no on‐board imaging.

Methods:

The linear accelerator being used is a Varian Clinac 21EX. All IGRT is performed using the BrainLab ExacTrac system. Because of the lack of on board imaging, certain monthly and annual TG‐142 quality assurance tests are more difficult to perform and analyze to a high degree of accuracy. Pipspro was not designed to be used with hard film, and to our knowledge its use with film had not been investigated. The film used will be GafChromic EBT3 film and Kodak EDR2 film, scanned with an Epson V700 scanner. The following routine tests will be attempted: MLC picket fence, light vs. radiation field coincidence, starshots, and MLC transmission.

Results:

The only tests that gave accurate and reliable results were the couch, gantry, and collimator starshots. Typical MV and kV images are acquired with a much higher level of contrast between the irradiated and non‐irradiated areas when compared to film. Pipspro relies on this level of contrast to be able to automatically detect the fiducial points from its phantom devices, leaf edges for picket fence and transmission tests, and jaw edges for light vs. radiation field tests. Because of this, certain tests gave erroneous results and others were not able to be performed in the software at all, with either type of film. The number of monitor units delivered to the film, the experimental setup, and the scan settings was not able to rectify the problem.

Conclusion:

For linear accelerators with no on‐board imaging, it is not recommended to use hard film with PipsPro to perform TG‐142 quality assurance tests. Other software or methods should instead be investigated.
SU‐F‐T‐494: A Multi‐Institutional Study of Independent Dose Verification Using Golden Beam Data
Authors: Itano M , Tachibana R , Yamashita M , Shimizu H , Sugawara Y , Kotabe K , Kamima T , Takahashi R , Ishibashi S , Uchida Y , Yamazaki T , Tachibana H
Published: July 2016

Purpose:

In general, beam data of individual linac is measured for independent dose verification software program and the verification is performed as a secondary check. In this study, independent dose verification using golden beam data was compared to that using individual linac's beam data.

Methods:

Six institutions were participated and three different beam data were prepared. The one was individual measured data (Original Beam Data, OBD) .The others were generated by all measurements from same linac model (Model‐GBD) and all linac models (All‐GBD). The three different beam data were registered to the independent verification software program for each institute. Subsequently, patient's plans in eight sites (brain, head and neck, lung, esophagus, breast, abdomen, pelvis and bone) were analyzed using the verification program to compare doses calculated using the three different beam data.

Results:

1116 plans were collected from six institutes. Compared to using the OBD, the results shows the variation using the Model‐GBD based calculation and the All‐GBD was 0.0 ± 0.3% and 0.0 ± 0.6%, respectively. The maximum variations were 1.2% and 2.3%, respectively. The plans with the variation over 1% shows the reference points were located away from the central axis with/without physical wedge.

Conclusion:

The confidence limit (2SD) using the Model‐GBD and the All‐GBD was within 0.6% and 1.2%, respectively. Thus, the use of golden beam data may be feasible for independent verification. In addition to it, the verification using golden beam data provide quality assurance of planning from the view of audit.

This research is partially supported by Japan Agency for Medical Research and Development(AMED)
SU‐F‐T‐496: An Investigation of Two Novel Devices for Testing Linac Clearance During CT Simulation
Authors: Morrow A , Massingill B
Published: July 2016

Purpose:

This work's objective is to determine the efficacy of two newly patented devices termed the Mor‐O rings, Mark1 and Mark2, developed to predict collisions between the patient and a linac at the time of CT simulation.

Methods:

Mark1: A ring with an inner radius equal to the distance between the isocenter and the nearest portion of a linac head(diso) was made. This is mounted to a stand that allows vertical repositioning. The ring is placed around the patient on the CT table and aligned with isocenter. The patient is moved through the ring. If the ring touches the patient, a collision is predicted. To test this device, predicted collisions were marked on a phantom. The phantom was then repositioned on the linac table where the collisions were verified. Mark2: An arc with the radius diso was created with a re‐locatable half‐linac head wire‐frame. The Mark2 is positioned in the same way as the Mark1 but can additionally mimic couch and gantry angulations. The Mark2 was tested with a volunteer using multiple couch, gantry and isocenter positions. The volunteer was then repositioned on the linac table to verify the angles of collisions.

Results:

Mark1: One isocenter out of ten showed negative clearance (0.9mm) on the linac table. All other collisions were predicted with 1 to 36mm of additional clearance. Mark2: All collisions were prevented with an additional 1.3 to 14.8 degrees of clearance.

Conclusion:

The Mark1 prototype is able to predict all collisions when no couch angulation is used. This device takes less than a minute to setup and is simple to use. The Mark2, when testing beam geometries used for noncoplanar SBRT, was able to prevent all collisions with 1.3 to 14.8 degrees additional clearance. Improvements in construction for both devices could increase accuracy and usability.

Andrew Morrow owns Morrow Physics, LLC and Brian Massingill owns Spur Physics, LLC. We are both listed on the patent for the devices investigated in this work (patent 9220922). Our current employer, Baylor Scott and White, is also on the patent.
SU‐F‐T‐497: Spatiotemporally Optimal, Personalized Prescription Scheme for Glioblastoma Patients Using the Proliferation and Invasion Glioma Model
Authors: Kim M , Rockhill J , Phillips M
Published: July 2016

Purpose:

To investigate a spatiotemporally optimal radiotherapy prescription scheme and its potential benefit for glioblastoma (GBM) patients using the proliferation and invasion (PI) glioma model.

Methods:

Standard prescription for GBM was assumed to deliver 46Gy in 23 fractions to GTV1+2cm margin and additional 14Gy in 7 fractions to GTV2+2cm margin. We simulated the tumor proliferation and invasion in 2D according to the PI glioma model with a moving velocity of 0.029(slow‐move), 0.079(average‐move), and 0.13(fast‐move) mm/day for GTV2 with a radius of 1 and 2cm. For each tumor, the margin around GTV1 and GTV2 was varied to 0–6 cm and 1–3 cm respectively. Total dose to GTV1 was constrained such that the equivalent uniform dose (EUD) to normal brain equals EUD with the standard prescription. A non‐stationary dose policy, where the fractional dose varies, was investigated to estimate the temporal effect of the radiation dose. The efficacy of an optimal prescription scheme was evaluated by tumor cell‐surviving fraction (SF), EUD, and the expected survival time.

Results:

Optimal prescription for the slow‐move tumors was to use 3.0(small)‐3.5(large) cm margins to GTV1, and 1.5cm margin to GTV2. For the average‐ and fast‐move tumors, it was optimal to use 6.0cm margin for GTV1 suggesting that whole brain therapy is optimal, and then 1.5cm (average‐move) and 1.5–3.0cm (fast‐move, small‐large) margins for GTV2. It was optimal to deliver the boost sequentially using a linearly decreasing fractional dose for all tumors. Optimal prescription led to 0.001–0.465% of the tumor SF resulted from using the standard prescription, and increased tumor EUD by 25.3–49.3% and the estimated survival time by 7.6–22.2 months.

Conclusion:

It is feasible to optimize a prescription scheme depending on the individual tumor characteristics. A personalized prescription scheme could potentially increase tumor EUD and the expected survival time significantly without increasing EUD to normal brain.
SU‐F‐T‐498: A Comparative Evaluation of 6MV Flatten Beam and Flattening Filter Free Photon Beam in Carcinoma Breast
Authors: Tamilarasu Suresh , Saminathan Madeswaran
Published: July 2016

Purpose:

Aim of the current study is to look plan quality, treatment beam ON time for IMRT using 6MV FB (Flatten Beam) and FFFB (Flattening Filter Free Beam) in left breast cancer cases.

Methods:

Ten left breast cancer patients treated with breast conserving surgical (BCS) procedure approach and adjuvant radiotherapy were selected from the department database. Simultaneous Integrated boost (SIB) technique was used to irradiate the total left breast (PTV) to a dose of 50.40Gy with concomitant enhance to the lumpectomy cavity known as gross tumour volume (GTV) to a dose of 59.40Gy in 28 fractions. Plans 6MV FB IMRT and 6MV FFFB IMRT had been generated to achieve dose to 95% target volume (TV) and spare Organ at risks (OAR's). Homogeneity index (HI), conformity index (CI), treatment monitor unit (MU),normal tissues integral dose (NTID) and low dose volume of normal tissue were compared.

Results:

There was no statistically huge difference among the plans with respect to target volume coverage, CI HI, Ipsilateral Lung and Breast. But statistically significant difference (p< 0.05) as observed in Heart, V5Gy of Contralateral Lung, MU's NTID and low dose volume of normal tissue.

Conclusion:

6MV FB and FFF beam produce almost equivalent plans in IMRT modality with admire to target volume coverage, HI, CI. Beam on time and NTID was determined to be much less in 6MV FFFB IMRT. FFF beam leads to a time saving treatment delivery and fewer NTID in cancer of left breast cases
SU‐F‐T‐499: Anatomic Features for Selection of Electronic Tissue Compensation Radiotherapy in Early‐Stage Breast Cancer Patients After Breast‐Conserving Surgery
Authors: Song Y , Zhang M , Yue N , Gan L , Chen X , Zhang T , Ren G
Published: July 2016

Purpose:

To explore the correlations between anatomic features and dose‐volumetric parameters in 3DCRT and eComp whole breast irradiation and identify the feasibility of anatomic parameters to predict the planning method selection.

Methods:

We compared the effectiveness between conventional three‐dimensional conformal radiotherapy (3DCRT) and electronic tissue compensation (eComp) for whole breast irradiation. 3DCRT and eComp planning techniques were used to generate treatment plans for 60 whole breast patients, respectively. The planning goal was to cover 95% of the planning target volume (PTV) with 95% of the prescription dose while minimizing dose to lung, heart, and skin. Statistical analyses were performed between critical organ doses and patient anatomic features, i.e., central lung distance (CLD), maximal heart distance (MHD), maximal heart length (MHL) and breast separation (BS).

Results:

Comparing to 3DCRT plans, on the average, eComp treatment planning process was about 7 minutes longer, but resulted in lower lung V20Gy, lower mean skin dose, with similar heart dose. The benefits were more pronounced for larger breast patients. To keep the lung V20Gy lower than 20% and mean skin dose lower than 85% of the prescription dose, eComp was the preferred method for patients with more than 2.3 cm CLD or larger than 22.5 cm BS.

Conclusion:

The study results may be useful in providing a handy criterion in clinical practice allowing us to easily choose between different planning techniques to satisfy the planning goal with minimal increase in complexity and cost.

This study was supported by National Natural Science Foundation of China (NO. 31420103915) and Chongqing Health and Family Planning Commission Project (2015MSXM012).
SU‐F‐T‐501: Dosimetric Comparison of Single Arc‐Per‐Beam and Two Arc‐Per‐Beam VMAT Optimization in the Monaco Treatment Planning System
Authors: Kalet A , Richardson H , Cao N , Meyer J , Dempsey C
Published: July 2016

Purpose:

The purpose of this study was to evaluate the dosimetric and practical effects of the Monaco treatment planning system “max arcs‐per‐beam” optimization parameter in pelvic radiotherapy treatments.

Methods:

A total of 17 previously treated patients were selected for this study with a range of pelvic disease site including prostate(9), bladder(1), uterus(3), rectum(3), and cervix(1). For each patient, two plans were generated, one using a arc‐per‐beam setting of ‘1’ and another with setting of ‘2’. The setting allows the optimizer to add a gantry direction change, creating multiple arc passes per beam sequence. Volumes and constraints established from the initial clinical treatments were used for planning. All constraints and dose coverage objects were kept the same between plans, and all plans were normalized to 99.7% to ensure 100% of the PTV received 95% of the prescription dose. We evaluated the PTV conformity index, homogeneity index, total monitor units, number of control points, and various dose volume histogram (DVH) points for statistical comparison (alpha=0.05).

Results:

We found for the 10 complex shaped target volumes (small central volumes with extending bilateral ‘arms’ to cover nodal regions) that the use of 2 arcs‐per‐beam achieved significantly lower average DVH values for the bladder V20 (p=0.036) and rectum V30 (p=0.001) while still meeting the high dose target constraints. DVH values for the simpler, more spherical PTVs were not found significantly different. Additionally, we found a beam delivery time reduction of approximately 25%.

Conclusion:

In summary, the dosimetric benefit, while moderate, was improved over a 1 arc‐per‐beam setting for complex PTVs, and equivalent in other cases. The overall reduced delivery time suggests that the use of multiple arcs‐per‐beam could lead to reduced patient on table time, increased clinical throughput, and reduced medical physics quality assurance effort.
SU‐F‐T‐503: Trajectory Modulated Arc Therapy of Intracranial Lesions: Development of a Standardized Path‐Based Technique for Fully Dynamic Couch‐Gantry Modulated Treatments
Authors: Khan S , Chin E , Otto K , Xing L , Hristov D , Fahimian B
Published: July 2016

Purpose:

The integration of couch motion during arc delivery is necessitated to enable irradiation trajectories such as coronal arcs, and to enhance the geometrical sampling for dynamic deliveries to the highest extent. To enable such capability, a platform of Trajectory Modulated Arc Therapy (TMAT) is developed in conjunction with standardized noncollisional dynamic path‐set for irradiation of intracranial lesions.

Methods:

A generalized path‐set was constructed through the combination of sagittal arcs (45 degrees from the CAX), axial arcs, and coronal arcs produced through modulation of the dynamic rotation of couch. The standardized path was implemented in a contiguous manner enabling the formation of fully automated sub‐trajectories to provide maximal geometrical convergence with minimal number of arcs. Progressive sampling technique is used for direct aperture optimization of the MLCs and the selection of couch positions across the control points. Dosimetry of the resulting plans was assessed relative to clinically delivered plans. Using the TrueBeam Developer Mode, plan deliverability was tested.

Results:

Treatment planning of TMAT sub‐trajectories for central, anterior and posterior tumor sites with volumes ranging from 4.75cc to 107cc demonstrated radically reduced doses to the critical OARs when compared to the clinically treated VMAT. Specifically, percentage reduction in mean dose for critical organs such as brainstem, cochlea, and optic nerve are found to be as low as 74±15%, 50±26% and 74±30% respectively as compared to VMAT. Conformity Index, defined as the ratio of tumor volume (VPTV) and 100% dose volume (V(D100%)), was reduced up to 12% while the Gradient Index, defined as V(D100%)/V(D50%), was concurrently improved by up to 14%.

Conclusion:

An automated standardized trajectory with dynamically modulated couch‐gantry arcs has been developed for intracranial radiotherapy. Through the incorporation of coronal arcs, it is demonstrated that significantly reduced OAR doses can be achieved relative to clinically treated patient plans via VMAT.

Research Grant Funding Support by Varian Medical Systems
SU‐F‐T‐505: A Novel Approach for Sparing Critical Organs at Risk for Cancer Patients Undergoing Radiation Oncology Treatments
Authors: Lavvafi H , Pourriahi M , Elahinia H , Elahinia M , Parsai E
Published: July 2016

Purpose:

A major goal of an effective radiation treatment plan is to deliver the maximum dose to the tumor while minimizing radiation exposure to the surrounding normal structures. For example, due to the radiation exposure to neighboring critical structures during prostate cancer treatment, a significant increase in cancer risk was observed for the bladder (77%) and the rectum (105%) over the following decade. Consequently, an effective treatment plan necessitates limiting the exposure to such organs which can best be achieved by physically displacing the organ at‐risk. The goal of this study is to present a prototype for an organ re‐positioner device designed and fabricated to physically move the rectum away from the path of radiation beam during external beam and brachytherapy treatments. This device affords patient comfort and provides a fully controlled motion to safely relocate the rectum during treatment.

Methods:

The NiTi shape memory alloy was designed and optimized for manufacturing a rectal re‐positioner device through cooling and heating the core alloy for its shaping. This has been achieved through a prototyped custom designed electronic circuit in order to induce the reversible austenitic transformation and was tested rigorously to ensure the integrity of the actuated motion in displacement of the target anatomy.

Results:

The desirable NiTi shape‐setting was configured for easy insertion and based on anatomical constraint. When the final prototype was evaluated, accuracy and precision of the maximum displacement and temperature changes revealed that the device could safely be used within the target anatomy.

Conclusion:

The organ re‐positioner device is a promising tool that can be implemented in clinical setting. It provides a controlled and safe displacement of the delicate organ(s) at risk. The location of the organ being treated could also be identified using conventional onboard imaging devices or MV imaging available on‐board most modern clinical accelerators.