Siemens Artiste Linear Accelerator Research Articles

Clinical Commissioning and Dosimetric Verification of the Raystation Treatment Planning System

Background: The software used by treatment planning systems (TPS) plays an important role for treatments using radiation. The accuracy of the calculated dose in radiation treatments depends on the assumptions made by the TPS. In this study, we summarize our methods and results regarding clinical commissioning of the basic functions needed for photon therapy. Materials and Method: Measurements were obtained for the 6 and 15 MV photon energies obtained from the Siemens Artiste linear accelerator device. Important data such as percent deep dose, profile and output measurements were taken in the water phantom and transferred to the RayStation Treatment Planning System. Results: When the absolute dose values calculated by the RayStation TPS are compared with the water phantom data, the differences obtained are less than 3%. When the 2-dimensional quality control of asymmetrical areas and patients with IMRT plan was controlled by gamma analysis method, the gamma rate was more than 95%. Conclusion: One of the most important quality control tests is TPS acceptance tests, which must be performed before clinical use. In this study, in which we checked the basic dose measurement and patient planning, it was seen that the RayStation TPS can be used in patient treatment for clinical use. The doses calculated by the RayStation TPS were found to be reliable and within the expected accuracy range. These results are sufficient for the application of 3-dimensional conformal radiotherapy (3D-CRT) and IMRT technique.

Corrections of photon beam profiles of small fields measured with ionization chambers using a three-layer neural network.

The purpose of this work is to study the feasibility of photon beam profile deconvolution using a feedforward neural network (NN) in very small fields (down to 0.56 × 0.56 cm2). The method's independence of the delivery and scanning system is also investigated. Lateral beam profiles of photon fields between 0.56 × 0.56 cm2 and 4.03 × 4.03 cm2 were collected on a Siemens Artiste linear accelerator. Three scanning ionization chambers (SNC 125c, PTW 31021, and PTW 31022) of sensitive volumes ranging from 0.016 cm3 to 0.108 cm3 were used with a PTW MP3 water phantom. A reference dataset was also collected with a PTW 60019 microDiamond detector to train and test individual NNs for each ionization chamber. Further testing of the trained NNs was performed with additional test data collected on an Elekta Synergy linear accelerator using a Sun Nuclear 3D Scanner. The results were evaluated with a 1D gamma analysis (0.5 mm/0.5%). After the deconvolution, the gamma passing rates increased from 54.79% to 99.58% for the SNC 125c, from 57.09% to 99.83% for the PTW 31021, and from 91.03% to 96.36% for the PTW 31022. The delivery system, the scanning system, the scanning mode (continuous vs. step‐by‐step), and the electrometer had no significant influence on the results. This study successfully demonstrated the feasibility of using NN to correct the beam profiles of very small photon fields collected with ionization chambers of various sizes. Its independence of the delivery and scanning system was also shown.

The Improving Therapeutic Effects of SIRT6 in Lung Adenocarcinoma Cells after Irradiation

Although certain clinical efficacy has been significantly improved in non-small cell lung cancer patients, recurrence and metastasis are still main causes of poor prognosis. SIRT6 plays an important role in tumor invasion and migration, inflammatory response and radiotherapy resistance; however, its function in lung cancer is limited. It is crucial to delineate the molecular mechanism of tumor development for better treatments. Our previous result showed that SIRT6 expression was lower in lung cancer tissues than that in adjacent normal tissues. The aim of this study is to further investigate the influences of SIRT6 on radiosensitivity and metastasis of lung adenocarcinoma cells. Adenocarcinoma cells were infected by packaged lentivirus or knocked out by CRISPR/Cas9 gene editing technology, so stable SIRT6 over-expression and knockout cell lines were constructed and selected successfully. The metastasis and invasion of these 2 cell lines were investigated by using cell wound healing experiment and transwell invasion assay. Phenotype changes of epithelial-mesenchymal transition (EMT), including E-cadherin, N-cadherin, and vimentin, were detected by qRT-PCR assay and Western blot assay. These 2 assays were also used to indicate the activation of ERK1/2 and HIF-1α signaling pathways. The CCK-8 assay and colony formation assay were used to measure cell viability and survival capacity. Adenocarcinoma cells were irradiated with 6 MV-X rays generated by a Siemens ARTISTE linear accelerator at a dose rate of 600 MU per minute in vitro. The morphology of adenocarcinoma cells changed clearly from polygonal or oval to elongate when SIRT6 was knockout. Meanwhile, E-cadherin expression was down-regulated, and the expressions of N-cadherin and vimentin were obviously up-regulated, which were often correlated with strong invasive potential. Cell migration ability was determined by the cell number that migrated across scratch parts between cells, and the wound closure ratio of the SIRT6 knockout group was significantly increased compared to the control. Further results showed that SIRT6 inhibited the activation of ERK1/2 signaling pathway, which were closely relevant to cell proliferation and differentiation. Moreover, the cell viability and survival capacity of SIRT6 knockout adenocarcinoma cells distinctly increased after irradiation, where the over-expressions of HIF-1α protein and mRNA were also observed, and HIF-1α plays important role in the formation of tumor hypoxia. Our study found out that SIRT6 could improve the therapeutic effects of irradiation through inhibiting cell proliferation and migration in lung adenocarcinoma cells by repressing ERK1/2 and HIF-1α signaling pathways. SIRT6 might be a potential treatment target for lung adenocarcinoma resulting in increasing radiosensitivity and improving prognosis.

Assessment of radiation leakage from treatment applicator of Siemens Primus Plus and Siemens Artiste linear accelerators.

The purpose of this study is to measure radiation leakage of Siemens Primus Plus and Siemens Artiste linear accelerators in electron mode and to compare the leakage level with that recommended by the International Electrotechnical Commission (IEC) standard. In this assessment, Siemens Primus Plus linear accelerator with 10 cm × 10 cm, 15 cm × 15 cm, and 25 cm × 25 cm applicators was used. The radiation leakage in lateral and vertical directions was measured for Siemens Primus Plus and Siemens Artiste linear accelerators. Data derived from radiation leakage measurement for Siemens Primus Plus and Siemens Artiste linear accelerators in lateral direction from the field edge and in vertical direction from the applicator were reported. The radiation leakage data were then compared with the IEC standard to evaluate in-air field leakage. Comparing the radiation leakage level from fields with the IEC standard for two applicators, the maximum that was occurred for 12 MeV electron beam and applicator size of 10 cm × 10 cm in Siemens Artiste linear accelerator was 2.3%, which is less than the IEC's recommended limit of 10%. It is concluded that the leakage amount is much less than the specified limit and that both of the linear accelerators have high level of safety. Considering the measurement stage, it also needs to be noted that the beam angle affected the radiation leakage level from field edge, and in 25° angle, it is higher than in 0° angle. Comparing radiation leakage from the right side of the field for the two linear accelerators, the amount of leakage for Siemens Primus Plus linear accelerator is more than Siemens Artiste linear accelerator.

Evaluation of Three-dimensional Treatment Planning System (TPS) performance in dose calculation of virtual wedged fields using film dosimetry

Introduction: Nowadays radiotherapy plays an important role in cancer treatment. Different radiotherapy techniques improvement emphasizes on using of the precise ، appropriate and useful algorithms. one of these techniques are wedged which is used in radiotherapy to compensate missing tissues and create a uniform dose distribution in tissues. The Siemens Artiste linear accelerator supports a virtual wedge ، that this wedge creates a dose distribution similar to a physical wedge without the use of any extra accessory and wedged profiles are produced moving collimator jaw during irradiation with a constant speed but varying the dose rate. In this study ، TPS performance is evaluated in virtual wedged fields by comparing the calculated and measured results. Materials and Methods: The calculations were performed by the collapsed cone superposition algorithm based TPS for two tangent fields in anthropomorphic slab phantom using 15، 30، 45، 60 virtual wedges for field size of 20 × 20 cm2 for 6 and 15 MV photon beams. Measurements were produced by Gafchromic EBT films and reading exposed films with scanner. Results: Good agreement between the measured dose with film dosimetry and calculated dose with collapsed cone superposition algorithm based TPS with using virtual wedge in heterogeneous environment and different energies were found ، with the maximum difference not exceed 3 -5%. The increase in wedge angle due to increase in the difference between calculated and measured data. Conclusion: : The results from this study showed that the accuracy of collapsed cone superposition algorithm based TPS used with the virtual wedges for two tangent fields is enough for the clinical usage under the studied experimental conditions.

YAG:Ce-Phosphor Scintillators for Optical Fiber Radiation Sensors With High Temporal Resolution

A miniature optical fiber real-time X-ray radiation sensor based on plastic optical fiber coupled with a fast decay time trivalent cerium-activated yttrium aluminum garnet Y3Al5O12 (YAG:Ce) scintillator material is reported. The YAG material was tested in powder and ceramic form. Three separate sensors were irradiated three times on a Siemens Artiste linear accelerator (linac). The measured light output of the YAG:Ce ceramic to the detector at the distal end of the fiber is 4.52 times greater than the YAG:Ce powder, and its output intensity detected by photon counter is further increased 2.52 times using a two-layer highly reflective Teflon tape. The sensor made with YAG:Ce powder shows excellent repeatability, being a maximum of 0.36 %, but the value using YAG:Ce ceramic exhibits orientation sensitivity when located in orthogonal positions relative to the X-ray beam. To the best of our knowledge, the work described in this letter is the first instance of the direct high temporal resolution detection of the individual (circa 3.9 ms) output of X-ray light pulses of clinical linacs. The experimental results of pulsewidths are in good agreement with the manufacturer’s stated value of $3.45~\pm ~0.21~\mu \text{s}$ .

Assessment of Imprecise Small Photon Beam Modeling by Two Treatment Planning System Algorithms

Dosimetric accuracy in intensity-modulated radiation therapy (IMRT) is the main part of quality assurance program. Improper beam modeling of small fields by treatment planning system (TPS) can lead to inaccuracy in treatment delivery. This study aimed to evaluate of the dose delivery accuracy at small segments of IMRT technique using two-dimensional (2D) array as well as evaluate the capability of two TPSs algorithm in modeling of small fields. Irradiation were performed using 6 MV photon beam of Siemens Artiste linear accelerator. Dosimetric behaviors of two dose calculation algorithms, namely, collapsed cone convolution/superposition (CCCS) and full scatter convolution (FSC) in small segments of IMRT plans were analyzed using a 2D diode array and gamma evaluation. Comparisons of measurements against TPSs calculations showed that percentage difference of output factors of small fields were 2% and 15% for CCCS and FSC algorithm, respectively. Gamma analysis of calculated dose distributions by TPSs against those measured by 2D array showed that in passing criteria of 3 mm/3%, the mean pass rate for all segment sizes is higher than 95% except for segment sizes below 3 cm × 3 cm optimized by TiGRT TPS. High pass rate of gamma index (95%) achieved in planned small segments by Prowess relative to results obtained with TiGRT. This study showed that the accuracy of small field modeling differs between two dose calculation algorithms.

Comparison of surface dose delivered by 7MV-unflattened and 6MV-flattened photon beams.

The purpose of this study is to determine the central-axis dose in the buildup region and the surface dose delivered by a 6MV flattened photon beam (6MV-FB) and a higher energy unflattened (7MV-FFF) therapeutic photon beam for different-sized square fields with open fields and modifying filters. The beams are produced by a Siemens Artiste linear accelerator with a NACP-02 ionization chamber and the dose is measured by using GafChromic film and two different, commonly used, dosimeters: a p-type photon semiconductor dosimeter (PFD) and a cylindrical ionization chamber (CC13). The results indicate that the surface dose increases linearly with FS for both open and wedged fields for the 6MV-FB and 7MV-FFF beams. The surface dose delivered by the 7MV-UFB beam is consistent with that delivered by the 6MV-FB beam for field sizes up to 10cm×10cm, after which the surface dose decreases. The buildup dose for the 7MV-UFB beam is slightly less than that for the 6MV-FB beam for field sizes ranging from 5cm×5cm to 15cm×15cm. For both the 6MV-FB and 7MV-FFF beams, the measured surface dose clearly increases with increasing field size, regardless of the detector used in the measurement. The surface dose measured with the PFD dosimeter and the NACP-02 and CC13 chambers differ significantly from the results obtained when using GafChromic film. The 7MV-FFF beam results in a slightly smaller surface dose in the buildup region compared with the 6MV-FB beam. The surface dose delivered by the higher energy 7MV-FFF beam is less than that delivered by the energy-unmatched FFF beam in previously published works.

SU‐F‐T‐674: In Vitro Study of 5‐Aminolevulinic Acid‐Mediated Photo Dynamic Therapy in Human Cancer Cell Lines

Purpose:Photodynamic therapy (PTD) is a promising cancer treatment modality. 5‐sminolevulinic acid (ALA) is a clinically approved photosensitizer. Here we studied the effect of 5‐ALA administration with irradiation on several cell lines in vitro.Methods:Human head and neck (FaDu), lung (A549) and prostate (LNCaP) cancer cells (104/well) were seeded overnight in 96‐well plates (Figure 1). 5‐ALA at a range from 0.1 to 30.0mg/ml was added to confluent cells 3h before irradiation in 100ul of culture medium. 15MV photon beams from a Siemens Artiste linear accelerator were used to deliver 2 Gy dose in one fraction to the cells. Cell viability was evaluated by WST1 assay. The development of orange color was measured 3h after the addition of WST‐1 reagent at 450nm on an Envision Multilabel Reader (Figure 2) and directly correlated to cell number. Control, untreated cells were incubated without 5‐ALA. The experiment was performed twice for each cell line.Results:The cell viability rates for the head and neck cancer line are shown in Figure 3. FaDu cell viability was reduced significantly to 36.5% (5‐ALA) and 18.1% (5‐ALA + RT) only at the highest concentration of 5‐ALA, 30mg/ml. This effect was observed in neither A549, nor LNCaP cell line. No toxicity was detected at lower 5‐ALA concentrations.Conclusion:Application of 5‐ALA and subsequent PDT was found to be cytotoxic at the highest dose of the photosensitizer used in the FaDu head and neck cell line, and their effect was synergistic. Further efforts are necessary to study the potential therapeutic effects of 5‐ALA PTD in vitro and in vivo. Our results suggest 5‐ALA may improve the efficacy of radiotherapy by acting as a radiomediator in head and neck cancer.

Analysis of Small Field Dosimetry for 15 MV Photon Beams

Accepted: 04.09.2015 The aim of this study is to obtain the optimum measurement method to overcome the dosimetric problems in small field dosimetry which is very important in Intensity Modulated Radio Therapy. In this study, the relative dose factors obtained by Farmer, Semiflex, PinPoint, Marcus PP ionisation chambers and thermoluminescence dosimetry of the square fields between 1x1 15x15 cm generated by multi leaf collimator of Siemens Artiste linear accelerator (6-15 MV) were researched. For each field in d=10 cm, the measurements are performed thrice using 100 MU and averages are obtained. Same fields are created in computer treatment planning system and reference point doses are recorded. The measurement results obtained from different devices are compared. Then, relative dose factors are compared with data obtained by computer treatment planning system. In 15 MV, the data obtained by PinPoint ion chamber and thermoluminescence dosimetry were similar, but this data was higher dose response to other devices. However, all ion chambers have similar dose response in fields larger than 4x4 cm. Farmer ion chamber presents rapid dose decrease in fields smaller than 4x4 cm. As a result, usage of high resolution ion chambers and thermoluminescence dosimetry in dose efficiency measurement are shown appropriate. Furthermore, large sensitive measurement volume ion chambers such as 0.6 cm3 aren’t suitable for using absorbed dose measurement in small fields. PinPoint ion chamber is a good choice for absorbed dose measurement in small fields.

SU‐E‐T‐153: Burst‐Mode Modulated Arc Therapy with Flattening‐Filter‐Free Beams Versus Flattening‐Filtered Beams

Purpose:To compare the dosimetry and delivery of burst‐mode modulated arc radiotherapy using flattening‐filter‐free (FFF) and flattening‐filtered (FF) beams.Methods:Burst‐mode modulated arc therapy (mARC, Siemens) plans were generated for six prostate cases with FFF and FF beam models, using the Elekta Monaco v. 5.00 planning system. One 360‐degree arc was used for five cases, and for one case two 360‐degree coplanar arcs were used. The maximum number of optimization points (OPs) per arc was set to 91, and OPs with less than 4 MU were disregarded. All plans were delivered on the Siemens Artiste linear accelerator with 6MV FF (300 MU/min) and comparable‐energy FFF (2000 MU/min, labeled as 7UF) beams.Results:For all cases studied, the plans with FFF beams exhibited DVHs for the PTV, rectum, and bladder that were nearly identical to those for the plans with FF beams. The FFF plan yielded reduced dose to the right femoral head for 5 cases, and lower mean dose to the left femoral head for 4 cases. For all but the two‐arc case, the FFF and FF plans resulted in an identical number of segments. The total number of MUs was slightly lower for the FF plans for five cases. The total delivery time per fraction was substantially lower for the FFF plans, ranging from 25 to 50 percent among all cases, as compared to the FF plans.Conclusion:For mARC plans, FFF and FF beams provided comparable PTV coverage and rectum and bladder sparing. For the femoral heads, the mean dose was slightly lower in most cases when using the FFF beam. Although the flat beam plans typically required slightly fewer MUs, FFF beams required substantially less time to deliver a plan of similar quality.This work was supported by Siemens Medical Solutions and the MCW Cancer Center Fotsch Foundation.

MARC vs. IMRT radiotherapy of the prostate with flat and flattening-filter-free beam energies.

BackgroundThere as yet exists no systematic planning study investigating the novel mARC rotational radiotherapy technique, which is conceptually different from VMAT. We therefore present a planning study for prostate cancer, comparing mARC with IMRT treatment at the same linear accelerator equipped with flat and flattening-filter-free (FFF) photon energies.MethodsWe retrospectively re-contoured and re-planned treatment plans for 10 consecutive prostate cancer patients. Plans were created for a Siemens Artiste linear accelerator with flat 6 MV and FFF 7 MV photons, using the Prowess Panther treatment planning system. mARC and IMRT plans were compared with each other considering indices for plan quality and dose to organs at risk. All plans were exported to the machine and irradiated while measuring scattered dose by thermoluminescent dosimeters placed on an anthropomorphic phantom. Treatment times were also measured and compared.ResultsAll plans were found acceptable for treatment. There was no marked preference for either technique or energy from the point of view of target coverage and dose to organs at risk. Scattered dose was significantly decreased by the use of FFF energies. While mARC and IMRT plans were of very similar overall quality, treatment time could be markedly decreased both by the use of mARC and FFF energy.ConclusionsHighly conformal treatment plans could be created both by the use of flat 6 MV and FFF 7 MV energy, using IMRT or mARC. For all practical purposes, the FFF 7 MV energy and mARC plans are acceptable for treatment, a combination of both allowing a drastic reduction in treatment time from over 5 minutes to about half this value.

SU-E-T-88: Comprehensive Automated Daily QA for Hypo- Fractionated Treatments

Purpose: The trend towards more SBRT treatments with fewer high dose fractions places increased importance on daily QA. Patient plan specific QA with 3%/3mm gamma analysis and daily output constancy checks may not be enough to guarantee the level of accuracy required for SBRT treatments. But increasing the already extensive amount of QA procedures that are required is a daunting proposition. We performed a feasibility study for more comprehensive automated daily QA that could improve the diagnostic capabilities of QA without increasing workload. Methods: We performed the study on a Siemens Artiste linear accelerator using the integrated flat panel EPID. We included square fields, a picket fence, overlap and representative IMRT fields to measure output, flatness, symmetry, beam center, and percent difference from the standard. We also imposed a set of machine errors: MLC leaf position, machine output, and beam steering to compare with the standard. Results: Daily output was consistent within +/− 1%. Change in steering current by 1.4% and 2.4% resulted in a 3.2% and 6.3% change in flatness. 1 and 2mm MLC leaf offset errors were visibly obvious in difference plots, but passed a 3%/3mm gamma analysis. A simple test of transmission in a picket fence canmore » catch a leaf offset error of a single leaf by 1mm. The entire morning QA sequence is performed in less than 30 minutes and images are automatically analyzed. Conclusion: Automated QA procedures could be used to provide more comprehensive information about the machine with less time and human involvement. We have also shown that other simple tests are better able to catch MLC leaf position errors than a 3%/3mm gamma analysis commonly used for IMRT and modulated arc treatments. Finally, this information could be used to watch trends of the machine and predict problems before they lead to costly machine downtime.« less

The impact of flattening-filter-free beam technology on 3D conformal RT

BackgroundThe removal of the flattening filter (FF) leads to non-uniform fluence distribution with a considerable increase in dose rate. It is possible to adapt FFF beams (flattening-filter-free) in 3D conformal radiation therapy (3D CRT) by using field in field techniques (FiF). The aim of this retrospective study is to clarify whether the quality of 3D CRT plans is influenced by the use of FFF beams.MethodThis study includes a total of 52 CT studies of RT locations that occur frequently in clinical practice. Dose volume targets were provided for the PTV of breast (n=13), neurocranium (n=11), lung (n=7), bone metastasis (n=10) and prostate (n=11) in line with ICRU report 50/62. 3D CRT planning was carried out using FiF methods. Two clinically utilized photon energies are used for a Siemens ARTISTE linear accelerator in FFF mode at 7MVFFF and 11MVFFF as well as in FF mode at 6MVFF and 10MVFF. The plan quality in relation to the PTV coverage, OAR (organs at risk) and low dose burden as well as the 2D dosimetric verification is compared with FF plans.ResultsNo significant differences were found between FFF and FF plans in the mean dose for the PTV of breast, lung, spine metastasis and prostate. The low dose parameters V5Gy and V10Gy display significant differences for FFF and FF plans in some subgroups. The DVH analysis of the OAR revealed some significant differences. Significantly more fields (1.9 – 4.5) were necessary in the use of FFF beams for each location (p<0.0001) in order to achieve PTV coverage. All the tested groups displayed significant increases (1.3 – 2.2 times) in the average number of necessary MU with the use of FFF beams (p<0.001).ConclusionsThis study has shown that the exclusive use of a linear accelerator in FFF mode is feasible in 3D CRT. It was possible to realize RT plans in comparable quality in typical cases of clinical radiotherapy. The 2D dosimetric validation of the modulated fields verified the dose calculation and thus the correct reproduction of the characteristic FFF parameters in the planning system that was used.

Position detection accuracy of a novel linac-mounted intrafractional x-ray imaging system

The authors have developed a system that monitors intrafractional target motion perpendicular to the treatment beam with the aid of radioopaque markers by means of separating kV image and megavoltage (MV) treatment field on a single flat-panel detector. They equipped a research Siemens Artiste linear accelerator (linac) with a 41 × 41 cm(2) a-Si flat-panel detector underneath the treatment head. The in-line geometry allows kV (imaging) and MV (treatment) beams to share closely aligned beam axes. The kV source, usually mounted directly across from the flat-panel imager, was retracted toward the gantry by 13 cm to intentionally misalign kV and MV beams, resulting in a geometric separation of MV treatment field and kV image on the detector. Two consecutive images acquired within 140 ms (the first with MV-only and the second with kV and MV signal) were subtracted to generate a kV-only image. The images were then analyzed "online" with an automated threshold-based marker detection algorithm. They employed a 3D and a 4D phantom equipped with either a single radioopaque marker or three Calypso beacons to mimic respiratory motion. Measured room positions were either cross-referenced with a phantom voltage signal (single marker) or the Calypso system. The accuracy of the back-projection (from detected marker positions into room coordinates) was verified by a simulation study. A phantom study has demonstrated that the imaging framework is capable of automatically detecting marker positions and sending this information to the tracking tool at an update rate of 7.14 Hz. The system latency is 86.9 ± 1.0 ms for single marker detection in the absence of MV radiation. In the presence of a circular MV field of 5 cm diameter, the latency is 87.1 ± 0.9 ms. The total RMS position detection accuracy is 0.20 mm (without MV radiation) and 0.23 mm (with MV). Based on the evaluated motion patterns and MV field size, the positional accuracy and system latency indicate that this system is suitable for real-time adaptive applications.

SU‐E‐T‐660: Does CMS XiO Electron Monte Carlo Model of a Siemens Artiste Linac Produce Accurate Dose Distribution for a Highly Irregular Electron Field?

Purpose: To evaluate the ability of CMS XiO Electron Monte Carlo algorithm (eMC) to accurately simulate irregularly shaped electron fields from a Siemens Artiste linear accelerator. Methods: Irregular electron fields where defined using a 1.5 cm thick Cerrobend cutout. For accuracy, the pattern was cut using a milling machine. eMC calculated planar dose distributions for 6, 9, 12, 15 and 18 MeV electron beams produced by Siemens Artiste linear accelerator were compared with measurements done with EBT Gafchromic films. All measurements and dose calculations were performed at the depth of maximum dose of the particular beam, at a standard SSD of 100 cm. The EBT films were scanned with Epson Perfection V7000 scanner. The red channel data of the 48 bit TIFF images was extracted, calibrated, corrected and analyzed with in‐house developed software. Results: The differences between eMC and the measurements were found to be within the gamma‐criteria of 2% dose and 2mm distance‐to‐agreement, including in the areas under the Cerrobend cutout. These differences decrease with increasing electron beam energy. Compared to the commonly used electron Pencil Beam algorithm, eMC produced significantly more accurate dose distributions for all regions of the irregular field, as well as under the cutout. Conclusions: The new CMS XiO eMC algorithm is capable of calculating dose distributions for highly irregular fields with an accuracy expected from photon beam calculation algorithms. Additional tests are under way to verify the performance of eMC for inhomogeneous medium and the calculation of dose output for a range of clinical electron fields.

SU‐D‐BRA‐02: Penumbra Measurement for a Flattening‐Filter‐Free Artiste Linear Accelerator

Purpose: The primary benefit of removing the flattening filter of a linear accelerator is to increase the dose rate by a factor of 3 to 6. Additionally, change in scatter conditions in the head of the accelerator may also decrease the penumbra, which could lead to better target conformality. The purpose of this work is to evaluate this effect on a Siemens Artiste linear accelerator. Methods: Profiles of 10 ×10 cm2 flat and flattening‐filter‐free (FFF) fields were measured in water using a scanning diode with 0.3 mm steps. The penumbra created by both the 160‐leaf multileaf collimator (MLC) and the backup jaw (Y‐jaw) was measured. The profile of the FFF beam was renormalized so that for both flat and FFF beams, the penumbra was defined as the distance between the points with 20% and 80% of the central flat beam dose. The penumbra was measured every 5 cm along the major axes and around the central axis at four depths from 1.5 to 20 cm. Results: The average penumbra defined by the MLC and Y‐jaw was 4.9 mm and 5.9 mm, respectively for the flat beam, and 4.9 mm and 5.2 mm for the FFF beam. The flat beam penumbra increased with depth from 4.6 to 9.2 mm and 5.5 to 10.1 mm for the MLC and Y‐jaw respectively. The corresponding increase for the FFF beam penumbra was 4.6 to 9.2 mm and 4.6 to 8.8 mm. The average paired difference was &lt;0.1 mm for the MLC and 0.8 mm for the Y‐jaw. Conclusion: The MLC penumbra was not affected by removing the flattening filter, while the decreased scattering in the FFF beam reduced the Y‐jaw penumbra by 0.8 mm. Removing the flattening filter does not clinically significantly improve the way the MLC can conform to the target.This research was partially supported by Siemens Medical Solutions.

SU-GG-T-130: Rotational IMRT Delivery Using a Siemens Artiste in Flattening-Filter-Free, High Dose-Rate Mode

Purpose: To demonstrate the ability to deliver unflattened (high dose rate), modulated arc plans using the Siemens Artiste linear accelerator using prototype linac firmware developed by Siemens and prototype TPS software developed by Prowess. Method and Materials: Prototype Prowess treatment planning software was used to develop a set of high dose rate (1,000 mu/min) modulated arc plans for four treatment sites ‐ head/neck, lung, prostate and breast. A step‐and‐shoot plan (SS) was also created for delivery efficiency comparison to arc‐based plans. The same planning criteria were used for all plans to ensure their ‘equivalence’. With the linear accelerator converted to the experimental state, all plans were delivered to a solid water phantom. Dose was measured using an ion chamber for point dose measurements and film for evaluation of relative dose distribution with a gamma criteria of 3%/3mm. Delivery times were collected to assess delivery efficiency. Results: Plans developed using all arc modalities were successfully delivered for all cases. The maximum difference between measured and calculated doses was 3.08% for ion chamber measurements and the minimum 3%/3mm gamma agreement was 87% of pixels. All arc treatments were delivered in less time than the corresponding SS plans, with the lungSBRT plans being delivered in 5 minutes for a 20 Gy prescription. Conclusion: Unflattened, modulated arc delivery is possible using prototype firmware on a Siemens Artiste machine and the Prowess treatment planning system accurately predicted doses for such deliveries. Modulated arc delivery in combination with unflat (high dose rate i.e. 1,000+ mu/min) mode may allow for very efficient delivery of highly conformai isodose distributions. Conflict of Interest: This work is funded by a grant from Siemens Oncology.

SU‐GG‐J‐33: Localizing a Moving Tumor Using MV‐CBCT

Purpose: To evaluate mega‐voltage cone‐beam computed tomography (MV‐CBCT) imaging of moving tumors. Method and Materials: Five patients treated for early stage non‐small cell lung cancer using stereotactic body radiation therapy (SBRT) were analyzed. Simulation images were obtained with a Siemens Sensation Open 4D‐CT scanner. The Internal Target Volume (ITV) comprised of the tumor in each phase and on the free‐breathing CT was created. Daily localization was performed with MV‐CBCT on a Siemens Artiste linear accelerator with the in‐line kView system, using a 4.2 MeV electron beam incident on a carbon target without flattening filter to increase the yield of low energy photons. The tumor was contoured on each daily CB image. The size of the ITV contours on the planning CT and MV‐CBCT was compared in the anterior‐posterior (AP), left‐right (LR) and superior‐inferior (SI) directions. Results: In the majority of cases the standard deviation of the MV‐CBCT contour size from day to day was less than 2 mm. The average difference between the planning CT and MV‐CBCT contours varies widely from patient to patient. The largest difference (10.1 mm) was seen in the SI direction for a patient for whom breathing motion was large (18 mm), and the contrast between the tumor and its surroundings in the expected tumor position during the full‐inhale phase was reduced. The second largest difference (7.2 mm) was seen in the SI direction in a patient for whom the proximity of the tumor to a large blood vessel also reduced the contrast. Conclusion: There is a possibility of inaccurate registration between the planning CT and MV‐CBCT and less effective localization when the contrast is adversely affected because of large tumor motion or proximity to other structures. This should be taken into account in the Planning Target Volume margin. Research partially supported by Siemens Medical Solutions.

SU-GG-T-582: Comparison of Dose Based and Biological Based Treatment Planning Systems for the Siemens Artiste Linear Accelerator

Purpose: To compare the performance of the biological-based treatment planning system (TPS) CMS Monaco with the dose-based TPS CMS XiO, for treatment of head and neck patients on the Siemens Artiste Linear Accelerator. Method and Materials: Three head and neck patients treated on the Artiste and planned with XiO were replanned using Monaco. The Monaco plans were developed using the same clinical objectives concerning the prescription dose to the target and the maximum allowed dose to the organs at risk. The XiO plans were optimized using the Superposition algorithm employing dose-volume and minimum/maximum dose constraints. The Monaco plans were optimized with the Monte Carlo algorithm using biological cost functions. Minimum, maximum and mean doses were compared as well as the equivalent uniform dose (EUD), total number of segments and monitor units (MU) required. The plans were delivered onto the Sun Nuclear MapCheck diode array with a 3%/3mm distance to agreement criterion. Results: Target coverage was similar in both plans. The average reduction in the Monaco mean dose was 4.7, 1.7, 9.3 and 11.2 Gy for the spinal cord, brainstem and, right and left parotid, respectively, compared to the XiO plans. The number of segments was comparable for two patients and was reduced by 63 for the third patient. The number of MU's for the Monaco plans were greater in all three cases. Conclusion: The three plans developed with Monaco were deemed to be clinically acceptable and were dosimetrically equivalent or superior to plans developed using XiO. The Monaco plans had superior organ at risk sparing whilst maintaining the same target coverage achieved with the XiO system.