bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐182: The Secondary Electron Distribution of Goldnanoparticle in Proton Therapy
Authors: Gao JunFang
Published: July 2008

Purpose: We simulate the secondary electron distribution qualitatively in low energy (0.1∼5 MeV) proton irradiation on single gold nanosphere and nanorod separately. A preliminary dose enhancement of gold nanoparticles (NPs) in proton therapy is also performed. Method and Materials: Three scenarios were studied. First one, proton beams were used to irradiate nanosphere with diameter of 100 nm. The beams passed through the center of NP. Only 10 protons were tracked for visualization in this case. The second one was similar to the first one except protons shooting the surface. In the third one, 100 protons shot nanosphere with diameter of 50 nm and nanorod with diameter of 10 nm and length of 100 nm individually. Beside this, we simulated a proton therapy in clinical use. The concentration of 7.5% gold nanosphere solution was mounted in water phantom. Results: 1), if the proton energy is less than 0.5 MeV, elastic scattering and electron capture are dominant. If the proton energy is higher than 1.0 MeV, ionization is dominant and more secondary electrons are generated in nanosphere. 2), if the proton beam shoot the nanosphere surface region, most secondary electrons will go out side the NP. 3), nanrod is more effective to produce secondary electrons than nanosphere. 4), about 20% dose enhancement was observed in one proton therapy lab where proton mean energy is 63.5 MeV. Conclusion: In the low energy gold NP proton therapy, a lot of secondary electrons are produced. This motivated us in doing similar study in higher energy proton cases. The enhancement in dose and RBE around NP is possible in proton therapy.
SU‐GG‐J‐184: Performance Optimization of the Integrated Acquisition Mode (synchronised and Not Synchronised to Beam Pulses) of the Varian AS500‐II, EPID
Authors: Al Kattar Z
Published: July 2008

Purpose: To better understand the image acquisition operation of an EPID and to evaluate the dosimeter properties in conformational radiotherapy and in treatments with enhanced dynamic wedges. Method and Materials: The Work presented rests on the study of the Varian EPID: aS500‐II and the Image Acquisition system IAS3. We are interested in integrated image acquisition mode. From a functional point of view, in this mode, the frame acquisition either is synchronized, or not synchronized to the beam pulses of the accelerator. We investigated the influence of various parameters of acquisition: “NPF (Number of Pulse by Frame), NRP (Number of Rows per Pulse) and FCT (Frame Cycle Time)” on the gray level, the speed of acquisition and the noise in the image, according to the energy of the X‐ray beams (6 and 15 MV) and the Clinac 2100 C/D dose rate. Results: In synchronized mode, the response of the EPID is dependent on the pulse frequency of the accelerator. The value of the pixel is proportional to the number of pulses per frame; the increase in the dose rate introduces a deceleration of the variation of gray level and instability of the response. The speed of acquisition is inversely proportional to the number of pulse per frame and the noise lies between 0.2% and 0.5%. A dysfunction and saturation are detected when the dose per frame exceeds 1.53 UM/frame. In the integrated mode not synchronized to beam pulses, only one parameter the “FCT” influences the pixel value. The pixel value is directly proportional to this parameter. We determined the rules to avoid saturation in the two acquisition modes. Conclusion: The choice of the acquisition parameters in the integrated mode is essential for the complete detection of radiations and especially to use this detector as a dosimeter.
SU‐GG‐J‐185: Towards in Vivo Dose Validation Using Real‐Time Physiologically Constrained Deformable Image Registration
Authors: Xia J , Muyan‐Özçelik P , Owens J , Palta J , Samant S
Published: July 2008

Purpose: To develop an adaptive radiotherapy (ART) strategy based on in vivo dose verification using volumetric imaging, real‐time physiologically constrained deformable image registration (PC‐DIR) and high performance computation (HPC). Method and Materials: Comparison of delivered and planned dose distributions for patients undergoing radiation therapy, especially IMRT, can be used to estimate treatment outcome, and develop a successful ART strategy that accounts for patient positioning errors, organ deformation, physiological changes (i.e. tumor shrinkage, edema), and incorporating this back into the treatment planning. Using 4DCT imaging, we have developed a ART methodology based on 1) PC‐DIR for auto‐contouring; 2) automated internal target volume generation; 3) probability density function (PDF) for specific structures; and 4) graphics processor unit (GPU) based HPC for real‐time computation using NVIDIA 8800GTX. Results: Compared with the same algorithm without the PC constraint, PC‐DIR resulted in superior performance with up to 91% reduction in inverse consistency errors. The computer generated ITV yielded contours typically within 3mm of physician drawn contours, and also served as a check of physician drawn ITVs. The PDF was constructed for the ITV to determine the dose distribution based on spatial probability using time averaging over a respiratory cycle. GPU based registrations of 256×256×64 imaging volumes required 3.6 sec for 100 iterations, a 56X speedup compared with conventional CPU computing (i.e. dual core 2.4GHz CPU). Dose remapping and dose volume histogram computations were near real‐time (⩽3sec). Conclusion: We have developed key elements of a clinically implementable ART strategy, which include real‐time computations using GPU, and accurate and robust registrations based on PC‐DIR. These elements incorporate 4DCT imaging coupled with GPU based PC‐DIR and frequent conebeam CT (CBCT) verification. This methodology can exploit ongoing improvement in GPU hardware performance and CBCT image quality.
SU‐GG‐J‐187: Tracking with Motion Models That Adapt to Patients and Physiological Events in Image‐Guided Therapy
Authors: Siddique S , Jaffray D
Published: July 2008

Purpose: Motion estimation is an important problem in radiotherapy and minimally invasive surgery. The motion of targets during an image‐guided procedure varies not only across patients but also across treatment fractions for any given patient. Moreover, targets are susceptible to physiological dynamics that produce involuntary and unexpected motion such as that due to bowel gas motion and coughs. A generic motion model alone does not suffice. This study seeks to improve the robustness of motion estimation by developing motion models that adapt to patients and physiological events that dictate the dynamics of targets. Method and Materials: The task of tracking a fiducial in the thorax is considered. Two cases are examined: (i)Adapting to patients—A prior is defined over a dynamic model for the fiducial. A small set of samples from the respiratory cycle of a patient is used to compute a posterior for the dynamic model, and predict future locations and associated uncertainties using Gaussian Process Regression (GPR). This method is evaluated on patient data obtained from the Cyberknife® Synchrony system. (ii)Adapting to physiological events—A metric based on the Kulback‐Liebler divergence between the predicted and observed distributions of the location of the fiducial is used to identify physiological events and update the dynamic model. The method is evaluated on a simulated cough sequence. Results: Using a generic prior and only a few samples, the method was able to produce posterior models that were adapted to the patients with the accuracy of the predictions being proportional to the number of samples used. The method was able to identify the cough and adapt the model accordingly. Conclusion: The proposed method can:(i)predict using a generic prior that adapts to patients and physiological events and (ii)report the associated uncertainty and relative entropy.
SU‐GG‐J‐188: Treatment Verification of Hypo‐Fractionated Lung Radiotherapy Using Cine EPID
Authors: Mackenzie A , Jiang S
Published: July 2008

Purpose: To develop an online method of monitoring hypo‐fractionated lung treatment. Method and Materials: For hypo‐fractionated 3D conformal lung treatment, tumors are often small and visible with the use of an electronic portal imaging device (EPID). Portal images in cine mode were acquired from a Varian Trilogy machine to assess tumor position. This assessment was done using a modified, normalized cross‐correlation function which utilized both EPID cine and the digitally reconstructed radiographs (DRR). The modifications to the established cross‐correlation equation were made in order adapt this function to the spatial and geometrical properties of these images. The output of the algorithm was then used to find the displacement of the tumor from its intended position relative to the beam aperture, and thus monitor the accuracy of treatment. Results: Preliminary results from two patients show a mean correlation of 0.6 for an adaptive search region parameterized by the cross‐sectional length of the treatment beam. The highest correlations were found both near the center of the tumor and occasionally in other regions which strongly resembled the tumor. High scores also appear to be associated with treatment field geometry. We developed a sorting algorithm to pick the true position based on the correlation score and location. This method generated few false positives for visible tumors. Substantial spatial precision was observed for different fractions of the same field. Conclusion: The modified, normalized cross‐correlation procedure developed here has shown great potential for verifying treatment on patients with tumors visible on EPID. This method can produce verification results well within the time of treatment. With small improvements such as weighting, filtering, and sufficient computing resources, this algorithm could potentially be used to stop the treatment when beam moves out of beam aperture.
SU‐GG‐J‐196: Vascular Occlusion by Acoustically Vaporized Droplets for Potential Targeted Enhancement of Thermal Therapies
Authors: Fabiilli M , Haworth K , Zhang M , Fowlkes J , Kripfgans O , Roberts W , Ives K , Carson P
Published: July 2008

Purpose: Acoustic droplet vaporization (ADV) of perfluorocarbon droplets with boiling points below ambient temperature shows promise for spatially and temporally targeted vascular occlusion. Vascular occlusion of a tumor or other target tissue can decrease the local heat dissipation relative to adjacent normal tissues during less directed or slow thermal therapies, such as RF or ultrasonic ablation. Also, encapsulated drugs can be released with the occluding bubbles into the target tissues. Method and Materials: In six canines, in vivo gray scale imaging and color flow and pulse wave (PW) Doppler imaging were employed with low concentration droplet injections to identify exteriorized target arteries or tissues, avoiding major adjacent veins. Short tone bursts at 3.5 MHz with 0.25% duty cycle were used during bolus passage to vaporize droplets with concentrations comparable to clinical ultrasound contrast agent recommendations. Studies included multiple intracardiac (IC) and intravenous (IV) injections, the latter with lipid, rather than albumin, shell. Results: Bubble production by ADV in arteries or tissues is easily visible in gray scale images. Both IC and IV injections repeatedly produced ADV at will in the renal or segmental artery, each injection and ADV generating vascular occlusion as seen by gray scale and Doppler imaging. Mean cortex occlusion was ∼85% by colored microspheres in the targeted kidney or renal pole with an ∼10 min half life per droplet dose. Cardiopulmonary symptoms occurred in some IC injections. ADV was successful in a canine prostate using an intercavitary imaging array for ADV and targeting. Conclusion: Keys to the new, consistent success with both IC and IV injections include adequate concentrations of droplets, use of frequencies with ADV threshold well below those for cavitation, and reliable targeting. Conflict of Interest: This work was supported in part by NIH RO1EB00281.
SU‐GG‐P‐02: The Role of Medical Physicists in the Revised International Radiation Safety Standards
Authors: Borras C
Published: July 2008

Purpose: The 1996 version of the International Basic Safety Standards for the Protection against Ionizing Radiation and for the Safety of Radiation Sources (BSS) [IAEA Safety series 115], used world‐wide as the basis for radiation protection legislation/regulations, is being revised by several cosponsoring international organizations to be consistent with the new ICRP Recommendations. This paper will focus on major changes regarding medical exposures and the role of medical physicists. Method and Materials: The current BSS draft is including, for the first time, the term “medical physicist”, replacing the expressions in the previous version: “expert” in “radiotherapy physics”, “radiodiagnostic physics” and/or “nuclear medicine physics”. This step is crucial towards the recognition by the International Labor Organization of medical physicists as health professionals, a pre‐requisite in many countries for hiring medical physicists in hospitals. The draft is also expanding the medical physicist's role in medical exposures, now a “principal party” together with the “radiological medical practitioner” and the “employer, owner and/or administrator”. Results: Medical physicists are responsible for imaging, calibration, dosimetry and quality assurance requirements. “For therapeutic uses of radiation”, these activities shall “be conducted by or under the supervision of a medical physicist with competence in the relevant field (radiation oncology or nuclear medicine)”. “For diagnostic and image‐guided interventional uses of radiation”, they shall be “fulfilled by, or under the oversight of or with the advice of, a medical physicist with competence in the relevant field”; the degree of involvement “determined by the omplexity of the particular use of radiation and the ensuing radiation risks”.

Conclusion: The AAPM should play a prominent role in the BSS revision process through two mechanisms: the IOMP, the international organization representing medical physics globally, and the official delegation of the US, which, as any member state of the cosponsoring organizations, has to approve the standards.
SU‐GG‐T‐01: Measurement of Dose Difference in Breast HDR Brachytherpay Using MOSFET Detectors
Authors: Oh S , Suh T , Kim S
Published: July 2008

A few years ago, MammoSite was developed to perform breast HDR brachytherapy easily and accurately. The MammoSite was consisted of balloon and catheter, and contrast was injected into the balloon through the catheter at treatment. The real dose do not agreed well with the calculated dose by treatment planning system because of the contrast in the balloon and the lack of backscatter. In this study, we experimentally estimated dose discrepancies due to contrast and lack of backscatter in breast HDR brachytherapy with MammoSite. Using MOSFET detectors and a breast simulating phantom, the dose discrepancies between calculation condition (no contrast and with backscatter) and delivery condition (contrast and without backscatter) were measured according to contrast concentration (0, 10, and 20% volume ratio), balloon size (35 cc and 60 cc), and source to detector distance (SDD) ranging from 25 to 50 mm. Each measurement was made with three MOSFET detectors to increase measurement stability. The source was Ir‐192 isotope from Nucletron HDR unit. The dose discrepancies from calculation condition due to both contrast and lack of backscatter combined ranged from about −7% to −30% in studied cases. It was found the effect of contrast was more significant with backscatter material than without. In all cases, the effect of backscatter was dominant to that of contrast (about −7% to −24%). Significant dose discrepancies existed between the calculation and the real treatment condition due to contrast and lack of backscatter. Therefore, skin dose is expected to be less than calculated. A table with which dose discrepancy can be determined will be provided using measured data of this study.
SU‐GG‐T‐05: MOSFET In‐Vivo Dosimetry for Colorectal Cancer Patients Treated with Shielded Brachytherapy
Authors: Furstoss C , Yan X , Reniers B , Poon E , Hallil A , Verhaegen F
Published: July 2008

Purpose: To investigate the suitability of MOSFET detectors as in‐vivo dosimeters for shielded colorectal brachytherapy. Method and Materials: A silicone applicator used in colorectal brachytherapy treatments was located at the middle of a water tank with an source in one catheter and two MOSFETs in two other ones. The dose was measured as a function of the distance and the angle from the source without and with a shielding rod in the applicator. In order to correct the measurement of the detector over‐response, the MOSFET energy dependence was calculated by the Monte Carlo (MC) code MCNPX2.5 and a correction factor was determined for each measurement point. Then, the measured corrected doses were compared to TG‐43 calculations for measurements without shielding and an in‐house dose‐kernel superposition method based on MC dose calculations for measurements with shielding. Results: The calculated MOSFET energy dependence shows an over‐response below 200 keV with a maximum at 40 keV by a factor 6.4 due to the dominant contribution from the photoelectric effect in Si02. Without shielding, the comparison between the measured dose and the dose calculated with TG‐43 shows a good agreement with a ±5% relative difference. With shielding, the comparison between the measured and the calculated dose gives a relative difference between 10% and 15% for the measurement point in the catheter at 90° from the source, and between 5% and 10% when the MOSFET is behind the shielding. Conclusion: For colorectal cancer patients the application of an energy response correction factor leads to good agreement between MOSFET measured and calculated doses when the shielding is not inserted. With the shielding, the discrepancy between measurement and calculation is higher, between 5% and 15%.
SU‐GG‐T‐133: TomoTherapy for Post‐Mastectomy Radiotherapy (PMRT): TLD Chest Wall Dose Measurements
Authors: Ito S , Parker B , Cheek D , Levine R , Gibbons J , Hogstrom K
Published: July 2008

Purpose: To compare measured and calculated skin doses in post‐mastectomy radiation therapy (PMRT) of the chest wall (CW) treated with the TomoTherapy Hi‐Art system. Method and Materials: In‐vivo dosimetry has been used to assess CW skin dose at a single point for multiple fractions of 9 patients. On the first treatment day, a radiation therapist marked a point on the CW near the mastectomy scar and took pictures of the mark placement. A thin packet of TLD LiF powder was taped over the mark prior to megavoltage CT alignment and dose delivery. Following treatment, TLD readout was performed using a REXON TLD reader, with TL being converted to dose using a 6‐MV calibration curve. In the Pinnacle TPS, a Point of Interest (POI) was added at the location of the mark by comparing the pictures with 3D skin rendering. Calculated POI dose was obtained and compared to measured dose. Results: The number of daily TLD measurements acquired throughout the course of treatment ranged from 5 to 25 per patient. Overall for the 9 patients, the TLD measured (delivered) dose was less than the calculated (TPS) dose by 3.7±4.2%. This results in approximately 7% of the patients receiving less than 90% of the calculated dose. Reasons for the delivered dose being low are under investigation, but are likely due to inaccuracies in the TPS dose calculation, CW respiratory motion, and air gap between the bolus and patient. Conclusion: In‐vivo TLD measurements are useful in evaluating the dose delivered by TomoTherapy for PMRT of the CW. Understanding the reasons for the dose differences could allow improvement to our existing technique. Conflict of Interest: This work funded in part by a research grant with TomoTherapy, Inc.
SU‐GG‐T‐136: Real Time Delivery Verification Using Exit Detector Data
Authors: Chen Q , Reitz G , Finley S , Westerly D , Koenigs C , Ruchala K , Olivera G
Published: July 2008

Purpose: TomoTherapy® treatment systems have exit MV detectors that record the radiation fluence during treatment. This information can be used in real time to verify delivered dose. Method and Materials: We developed a method that can extract the MLC leaf open time from the detector data without relying on the patient CT or pre‐measured database proposed by previous researchers. Because each leaf has penumbra, an open leaf will contribute signals to the detectors that correspond to adjacent leaves. Therefore, a closed leaf could be reported as open if its adjacent leaf is open. To eliminate the impact of the penumbra, we model the penumbra with a point‐spread‐function and apply an iterative deconvolution procedure to remove the penumbra. The iterative method successfully removes the penumbra without introducing ringing artifacts. The MLC leaf open time is then extracted with a simple thresholding method. To verify the algorithm, we install optical sensor on each MLC leaf that reports the leaf position. The leaf open time extracted from exit detector is compared to the optical sensor report. Results: The leaf open time extracted from the exit detector showed good agreement with the optical sensor under a variety of conditions, such as different attenuation phantom and different delivery sinogram. The detector measured leaf open time agrees with the optical sensor within 0.2 ms and a standard deviation of 3.6 ms. The impact of these uncertainties to the dose calculation is estimated to be around 0.2%. The algorithm is optimized so that it can run on the onboard computer in the machine to process the detector data in real time. Conclusion: The exit detectors in TomoTherapy® treatment systems can provide us information of leaf behavior during delivery. Together with the monitor chambers of the linac, the actual delivered dose to patient can be calculated.
SU‐GG‐T‐150: Commissioning and Validation of a Novel Measurement‐Based IMRT QA Method, Incorporating Dose Recalculation On Patient CT Data
Authors: McCurdy B , Mueller L , Backman E , Venkataraman S , Fleming E , Asuni G , Jensen M , Ur‐Rehman F , Pistorius S
Published: July 2008

Purpose: A novel measurement‐based IMRT QA method was tested which provides an accurate reconstruction of the 3D dose distribution in the patient model. This approach is a significant improvement over current QA methods since it allows direct and independent comparison of the doses calculated by the treatment planning system (TPS), including the 3D spatial dose distribution overlaid on CT data and contoured structures, as well as DVHs. Method and Materials: The challenging RPC Head and Neck phantom was used for initial evaluation. A 6 MV, 7 field, 79 segment, step and shoot plan was developed satisfying required dose metrics. A 2D‐array of dose chambers (MatriXX, IBA Dosimetry) was mounted on a linear accelerator. This device captured the delivered IMRT plan fluence in a pretreatment QA context. The measurement data were read directly by the control software (COMPASS, IBA Dosimetry), which also provides the ability to import patient plan data from the TPS. The COMPASS software also includes a dose calculation engine and head fluence model. Beam commissioning procedures analogous to those of a TPS were required. Reconstructed dose and DVHs were compared to those calculated by the TPS. Results: The beam model in the COMPASS software was able to predict percentage depth dose and X and Y profiles (Dmax, 5, 10, 20 cm depths) for MLC‐defined apertures ranging from 1×1–20×20 cm∧2 to within 1.5% (percentage depth‐dose), 2.0% (in‐field profiles), and 2.5% (out‐of‐field profiles). The reconstructed doses in the RPC Head & Neck phantom were within −3 to +4% of those in the treatment planning system. DVHs compared to within 1%. Conclusion: A novel measurement‐based IMRT QA method was tested. Reconstructed doses were overlaid on CT data and contoured structures, to enable a clinically relevant understanding of delivered under‐ or over‐doseages as compared to the TPS plan. Research partially sponsored by IBA Dosimetry.
SU‐GG‐T‐152: Applying Imaging Detector Data for Daily Monitoring of Dose Output in Helical Tomotherapy
Authors: Verellen D , Tournel K , Linthout N , Van de Vondel I , Duchateau M , Lelie S , Storme G
Published: July 2008

Purpose: In Tomotherapy dose is dependant on the output and shape of the beam (‘cone’). Variations in these can have huge influences on IMRT‐treatments and daily monitoring is required, but time consuming using conventional methods. Method and Materials: A software package was developed to run independently on the system and retrieve the integrated CT‐detector and dose‐chamber data. The ability to monitor daily output changes was tested by using static fields and ionization chamber(IC). To validate the link between output, cone and daily patient QA a dedicated IMRT‐plan containing disjunctive targets was used and a regression model was built to check the effect variations of cone and output have on this. Results : Results show that the in‐house tool can be used to monitor output and cone shape on tomotherapy in a fast and reliable way. Furthermore, the system has the ability of separating effects of output and cone in one single measurement. The static beam measurements using IC show a correspondence within 2% after elimination of the cone effect. Using a 6D‐linear regression the software can predict IMRT‐ionization chamber measurements within 0.7%. Early results show that the model's instabilities model could predict problems such as target failure prematurely. Conclusion : The in‐house developed software tool based on direct detector and dose‐chamber monitoring can be used to monitor output‐ and cone‐variation in 1 procedure. By using a regression the tool can also replace IMRT‐QA measurements. Combined, this allows for daily QA‐time reduction from 50 to 5 minutes.
SU‐GG‐T‐153: Scaling the Prescription Dose: How Accurate Is the Varian Delivery System?
Authors: Sterling D , Sakhalkar H , Oldham M
Published: July 2008

Purpose: The prescribed dose of an IMRT treatment plan may need to be scaled without changing any other parameters of the plan (e.g. relative fluence‐maps). Examples include changing the prescription as ordered by the physician, or rescaling the dose to avoid overexposure of a dosimeter. In these instances, it may be advantageous and most efficient to rescale the dose without recalculating fluence maps and leaf‐sequencing, as is possible with the Varian delivery system. This work investigates the dosimetric consequences of such dose‐scaling. Method and Materials: A complex 9‐field IMRT treatment plan was created in the Eclipse planning system to meet the RPC head‐and‐neck IMRT credentialing test, which prescribes a dose of 6.6Gy to the primary PTV. A modified RPC head phantom incorporating a PRESAGE 3D dosimeter required a maximum dose of 4Gy to the PTV to avoid over exposure. The prescription dose was correspondingly scaled in the Eclipse system without changing any other aspects of the plan. Other plans were also created scaling the prescription dose to deliver 10 Gy, 4 Gy, 3 Gy, 2 Gy and 1 Gy to the primary PTV. These plans were delivered to the MapCHECK QA device to determine dosimetric errors. DynaLog files were collected to investigate changes in leaf positioning errors and beam hold‐offs. Results: As the prescription dose was decreased, the number of beam hold‐offs and the error in leaf position increased. Reducing the prescription dose by a factor of 6.6 resulted in an average leaf position error of 0.5 mm and caused 17.5% of MapCHECK diodes to fail a relative dose difference threshold of 0.3% with a maximum relative dose difference of 2.2%. Conclusion: These results indicate that scaling the dose prescription by <40% has a negligible effect on dosimetric measurements. However, reducing the prescription dose by >40% can introduce significant errors to measurements.
SU‐GG‐T‐156: Patient Specific QA Results for Step and Shoot and Sliding Window Deliveries of IMRT Beams as Implemented by Two Treatment Planning Systems
Authors: Villarreal‐Barajas J , Breitman K , Smith W
Published: July 2008

Purpose: To present the patient specific QA results for step and shoot (SS) and sliding window (SW) deliveries of IMRT beams as implemented by two treatment planning systems (TPS). Method and Materials: From a sample of our clinical practice 648 (108 cases) Eclipse AAA_7_5_‐18‐SW and 464 (66 cases) Pinnacle 7.4f ‐SS IMRT beams were evaluated using the MapCheck diode array system. The planar dose measurements at 5 or 10 cm depth in water were compared with the predictions from both TPS. A 3 % −3mm distance to agreement (DTA) criteria was used to score the percent of passing points (PPP) for each individual field. The samples for both TPS were composed of 75 % of Head and Neck cases, 15% prostates and 10 % other sites. Results: The distribution of the PPP showed that 83% and 85% of the evaluated beams were above the 95 % PPP for Eclipse and Pinnacle respectively. Between 90 and 95 % the PPP were 15% and 14% and below 90% the PPP were 1.9 % and 1.7 % for Eclipse and Pinnacle respectively. The passing rates for Eclipse‐SW are significantly improved when the first 20 Eclipse‐SW cases (130 beams) are not considered for this comparison. The Eclipse‐SW PPP above 95% increases to 91.1 %. The patterns of failure observed for the two TPS were distinctively different with Pinnacle‐SS exhibiting clusters of hot points (measurements higher than calculations) while Eclipse‐SW showed cold points aligned in the direction of the MLC leaves movement. Conclusion: The results from our patient specific IMRT QA using the Eclipse‐SW delivery system exhibited a better agreement when compared with our previous experience using Pinnacle‐SS. A detail analysis is required in order to assess the clinical significance of the different failure patterns observed between these two TPS.
SU‐GG‐T‐157: Commission of 2.5 Mm ModuLeaf MLC for Stereotactic Radiation Therapy
Authors: Li K , Kong X , Wang J , Gupta N , Weldon M , Zhang H , Zhang D , Mayr N
Published: July 2008

Purpose: Improvements of MLC technology in radiotherapy, including smaller leaf sizes, allow greater accuracy in delivering radiation doses to the target with better conformality. For example, the high ablative doses used in hypo‐fractionated stereotactic body radiotherapy (SBRT) require high precision in dose delivery, thus high precision in commissioning the MLC system to verifiy MLC accuracy. The purpose of this study was to evaluate the procedure and challenges in the commissioning and application of 2.5‐mm small‐leaf MLC. Method and Materials: Siemens' newly‐developed Moduleaf MLC (MMLC) with 2.5mm leaf‐size was commissioned for SBRT. Step‐by‐step QA and application procedures for SBRT commission guidelines were followed. Error tolerance and QA results were analyzed through the entire commission process from beam data preparation, to treatment planning system commission, to treatment plan verification. The commission was divided into 3 phases: mechanical commission, software commission, and comprehensive commission. Isocenter accuracy was assured for mechanical precision. For software commission, the effect of small field factor was analyzed. In comprehensive phase, a single field and a head‐and‐neck case were tested with the QA standard. Results: The commission and clinical implementation of 2.5mm MMLC were described in this study, with provided guidelines for QA procedures from beam data collection and modeling to treatment planning methodology. The accuracy of the MLC mechanic isocenter was within 0.2 mm. At the same time, the treatment modalities with or without the flatten filter were compared, and they were consistent to each other except for the dose‐rate effect. Different MMLC clinical protocols, from SBRT to head‐and‐neck and intracranial treatments, have been suggested. Conclusion: After strictly following the physical QA requirements, we successfully commissioned the new mounted‐on 2.5mm MMLC for SRS/SBRT. In the follow‐up studies, clinical applications with MMLC will be further compared to other on‐site SRS systems, including Gamma‐Knife, and Tomotherapy system.
SU‐GG‐T‐162: Correlations Between Potential Setup Errors and Dose Gradients When Verifying Patient Specific DQA Plans of IMRT
Authors: Park J , Chung J , Park Y , Kim H , Choi C , Park C , Ha S , Kim I , Ye S
Published: July 2008

Purpose: Fourteen cases out of 150 IMRT DQA (dose quality assurance) plans showed measured dose differences of particular fields > ±10%. We investigated the relationship between potential setup errors, and dose gradients and dose differences. Method and Materials: A 0.125 cc ion‐chamber and a home‐made cylindrical phantom were used for verifying patient specific DQA plans of IMRT. We investigated dose gradients within ±3 mm from a verification point along x, y, z axes of 5 DQA plans where dose differences of any fields were within ±5% and of 14 DQA plans where at least one of fields had dose differences of > ±10% at planed delivery dose larger than 10 cGy. Reflecting potential setup errors, we moved the verification point along the axis of the steepest dose gradient and searched the point that dose differences of any fields were within ±10%. Results: For the DQA plans of dose differences < ±5%, the average dose variation along x, y, z axis was 0.6%, 0.6%, 0.3%, respectively. The same variation for the DQA plans of dose differences > ±10% was 1.6% (3.5 cGy), 1.2% (2.5 cGy), 0.8% (1.8 cGy), respectively. The correlation between those variations of the two groups was statistically significant (p‐value: 0.034). Except six cases of 14 DQA plans, all fields showed dose differences smaller than ±8% by shifting the ion‐chamber less than 3 mm from the original location. The average of all field dose differences was reduced from 4.7% to 3.6% after shifting. Conclusion: Due to steep dose gradients, small setup errors less than 3 mm significantly affect the measured doses of individual fields, of which dose differences could be larger than ±10%. Such a large difference at a particular field can occur, even the total dose difference is less than ±3%.
SU‐GG‐T‐166: Quality Assurance for SRS/SRT IMRT
Authors: Guo F , Chen Z , Deng J , Fan Y , Nath R
Published: July 2008

Purpose: Investigate proper QA procedures, standards, and difficulties for IMRT SRS/SRT, which has high dose proscription (⩾10 Gy for a fraction) and high dose rate (600–1000 MU/minute). Under these situations, the films, diodes, or electron portal imaging devices (EPIDs) all have some limitations, such as dose saturation and dose rate dependence. Method and Materials: Our initial QA procedure is staying with conventional ion chamber plus film, to which each field is exposed to get around the saturation problem. SRS/SRT Patient IMRT plans were generated with Eclipse Treatment Planning System (Varian Medical Systems, Mountain View, CA). The plans then were copied to a verification plan with a polystyrene QA phantom. The generated QA plan was delivered with the same gantry, collimator, and couch angles from the patient plan. Point dose was measured at isocenter with Capintec PR‐05P (Capintec, Inc. Ramsey, New. Jersey, USA) and compared with the calculated value from the Eclipse TPS. At the same time, each field was filmed with EDR2 film (Kodak Inc., Rochester, NY). The film was processed and compared with the exported dose map from Eclipse TPS by Vidar scanner (Vidar Systems, Herndon, VA) and RIT113 software (Radiological Imaging Technology, Colorado Springs, CO). Results: The planned point dose agreed well with the measurements. For five plans, the ratios of measured dose over the planned dose are from 97.0% to 98.0%, with an average of 97.7%. The individual film also agrees with the exported two‐dimensional dose distribution, respectively. This IMRT QA procedure takes about 2–3 hours for each patient. Conclusion: Despite the problems arising from high dose and dose rate, conventional procedure of ion chamber plus film (EDR2) is reliable for SRS/SRT IMRT QA. Other QA methods, such as EPIDs, MapCheck, and ion chamber arrays, need to be investigated for quicker and reliable verification.
SU‐GG‐T‐172: Compensator Based Intensity Modulated Radiation Therapy Dosimetry Using EDR2 Film
Authors: Srivastava R , De Wagter C
Published: July 2008

Purpose: Radiographic EDR2 film is the most commonly used radiographic film for dose distribution measurement, quality assurance and treatment plan verification. The compensator is an alternative way to deliver intensity modulated treatment. The EDR2 film reliability was investigated for dosimetry and QA of compensator based IMRT. Method and Materials: MC‐96 was used to fabricate the compensator blocks (10, 20, 30 and 50 mm thickness). For this study 6 and 25 MV photon beam qualities from an Elekta SL‐25 were used. The transmission factors of the blocks were measured with a Farmer type ion chamber of 0.6cc for a 10×10cm field size. The film was placed at isocentric distance between the slabs of a polystyrene phantom in a perpendicular geometry. To determine the effect of block thickness on the dose response of EDR2 film for both beam energies, dose measurements were made for various field sizes and offsets and compared to Farmer chamber measurements. To obtain a similar exposure of the film, transmission factors were applied to adjust the MUs. An inverse pyramid intensity modulated beam, achieved with a compensator block, was dosimetrically investigated to assess the value of the EDR2 film in a more clinical setting. Results and Discussion: The film showed a systematic under‐response of maximally 1.3% for a 50mm thick block and 25 MV (10×10 cm) beam, which is within the 3% overall uncertainty of film dosimetry for perpendicular geometry. The field offset measurement showed also a film under‐response in the order of 1.3% in the direction towards the gun, which might be due to spectral changes related to the beam bending system. The cross‐sectional dose profiles by compensator blocks showed that the film is within 1.2% to the diamond detector. EDR2 film can be safely and easily used as a 2D dose detector in compensator based IMRT.
SU‐GG‐T‐175: Analysis of Inter‐ and Intra‐Fraction Breathing Patterns Using the Varian Real Time Position Management System
Authors: Whitaker M , Whitaker J , Todd S , Kenny M , Hagekyriakou J , Kron T
Published: July 2008

Purpose: To analyse respiratory waveforms for key parameters that may be used to characterise patients' breathing patterns for the purpose of distinguishing between patients, tailoring gated treatment for individuals and determining the suitability of patients for gated radiotherapy. Method and Materials: The Varian Real time Position Management (RPM) system was used to record the breathing waveforms of three volunteers. The RPM marker was placed on the volunteers': chest, sternum and abdomen. Waveforms were captured for 1min on several days in each position, and a 5min waveform captured in the sternum position. From the resulting waveforms, four key parameters were determined using customised software, and compared between inter‐ and intra‐fraction measurements. Also, the breathing waveforms of three patients were captured for 1min over several days and analysed similarly. Results: The key parameters investigated were: frequency of breathing, maximum amplitude of inhale and exhale, asymmetry of the breathing pattern and the maximum potential duty cycle of both inhale and exhale. The intra‐fractional differences were smaller than the inter‐fraction differences for the volunteers, although this was not the case for the patients. The frequency of breathing ranged from 8 to 16, and 4 to 12 for the patients and volunteers respectively. The maximum amplitudes were noticeably different between the volunteers for both inhale and exhale, although the patient group showed marked differences only on the maximum exhale amplitude. The volunteers' and patients' waveforms were reasonably symmetric and the longest duty cycles were observed on the inhale for both patients and volunteers. Conclusion: The breathing patterns of the volunteers and patients indicate that the differences within a subject are smaller than the differences between subjects. We conclude that the RPM can be used to reproducibly record the waveforms from which these four key parameters may be derived to tailor gated radiotherapy for an individual.
SU‐GG‐T‐177: Determination of SOBP PDD for Therapeutic Proton Beams
Authors: Zhu TC , Karunamuni R , Slopsema R
Published: July 2008

Purpose: We have developed a Cimmino algorithm to calculate the percentage depth dose (PDD) of spread‐out Bragg peaks (SOBP) for megavoltage proton beams. Method and Materials: For patient underwent clinical proton treatment using scattered beams, it is often desirable to determine the shape of SOBP PDD for determination of dose at points away from the beam modulation width. For patient prescription, the SOBP is often prescribed by two parameters, the range of SOBP, R, defined as the distance from the surface to the distance that corresponding to 90% of the maximum dose and the modulation width of SOBP, M, defined as the width of the uniform dose within 90% of the maximum dose. Often, the shape of the SOBP PDD is unknown and has to be calculated from the file that determines the temporal dependence of nozzle equivalent thickness (NET) profiles of the energy modulation wheel. We have developed a Cimmino algorithm to calculate the SOBP PDD from the pristine PDD by constraint the PDD to be constant within M and have a range of R. Results: SOBP PDD calculated by the Cimmino algorithm agrees reasonably well with SOBP PDD determined from the modulation wheel. They agree at most depths and are slightly different at the entrance. The difference is attributed to the difference in weighing the pristine PDD. Conclusion: This algorithm is ideally suitable for calculating SOBP PDD suitable for patient‐specific MU verification for proton beams. As a result, one no longer needs the energy modulation file output for calculation of dose at arbitrary depth.
SU‐GG‐T‐181: 4D Dosimetry in the RapidArc Treatments Using Delta4
Authors: Nilsson G , Bocanek J
Published: July 2008

Purpose: The new RapidArc™ treatment technique, also described as Volumetric Modulated Arc Therapy technique, has the potential to treat patient with improved result in target coverage and normal tissue sparring in much less time than IMRT. One important aspect of this is to ensure the quality in an efficient way, find the cause of any discrepancy and learn how to best use the various TPS parameters. Delta4, originally developed to improve IMRT QA was also designed for RapidArc /VMAT 4DRT and helical tomotherapy. Presented data is from the first test using Delta4 on RapidArc made in collaboration between ScandiDos and Varian. Method and Materials: Measurements on a Varian ClinaciX with RapidArc capability, installed in Varian Medical Systems laboratory in Baden, CH, were performed with a Delta4 QA‐device of absolute dose distribution in 4‐dimensions resolved in time and each dose pulse was tagged with independently measured gantry angle. The measured dose was grouped into the control points (every 2.2 degree) of the delivery sequence planned with Eclipse. Verification against planned data in 3D using Eclipse TPS were done as well as reproducibility studies. Results: Generally there was a very good agreement between planned data and measurement using Delta4. Gamma index (3%, 3mm) was generally better than 98%. For the reproducibility gamma index (0.5%, 0.5mm) nearly all measurement were within 100%. Reproducibility could be verified also individually for each control point. Conclusion: It was shown that Delta4 can be used very efficiently to verify RapidArc delivery; the measurement time is only as long as the delivery time and set‐up is very fast, thanks to the 3D measurement array no data is missed. Analysis can be done in a few minutes directly after measurement. QA must not become the bottle neck in RapidArc clinical implementation! Conflict of interest: Sponsored by Varian and ScandiDos.
SU‐GG‐T‐245: Consolidated Image Quality QA for Diagnostic CT and Radiotherapy Cone Beam CT
Authors: Doemer A , Gingold E , Misic V , Podder T , Yu Y , Xiao Y
Published: July 2008

Purpose: As IGRT strategies evolve from localization to adaptive planning, it becomes more important to acquire guidance images of higher quality. We utilized a CATPHAN to subject radiotherapy CBCT images acquired under various conditions to the same rigorous tests and evaluation that diagnostic CTs undergo. This study reports on the evaluation of image qualities of diagnostic CT and radiotherapy CBCT and identifies the area of quality differences between the images. Method and Materials: RT‐CBCT scans were performed on Elekta XVI using pelvis scan settings on a CATPHAN Model 600. They were then compared to results from a GE Lightspeed16 multidetector CT scanner. The phantom contained modules allowing measurement of slice thickness, spatial resolution, low contrast resolution, Hounsfield Unit (HU) sensitivity and image uniformity. HU uniformity in the axial direction and geometric distortion were also measured. Results: For low contrast resolution tests, no targets could be clearly defined in the medium resolution reconstruction on RT‐CBCT. Only three spheres could be seen with the high resolution reconstruction (not used clinically) compared to six on diagnostic CTs. Calculated thicknesses for a 1.0 mm slice varied from 1.33 to 2.45 mm. The HU sensitometry test showed large variation from accepted HU values of the targets. These variations were not linear or affected by the reconstruction method. Spatial resolution for clinical settings (medium resolution) was constant at three lp/cm and improved to ten lp/cm with the high resolution acceptance testing reconstruction. This is comparable to diagnostic CT resolution. Axial direction HU uniformity varied in a stepwise fashion as the uniformity module moved away from the CBCT isocenter. No measurable geometric distortion was found as a function of distance from isocenter. Conclusion: A consolidated CBCT QA procedure is feasible for monitoring changes in image acquisition systems over time for image quality evaluation in adaptive therapy.