bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐52: Inclusion of KV CBCT Dose in the Patient Treatment Plans and Evaluation of Dose to Normal Tissue and Critical Organs
Authors: Alaei P , Spezi E , Downes P , Jarvis R , Radu E , Reynolds M
Published: August 2010

Purpose: Daily kilovoltage cone beam CT (kV CBCT) patient localization adds to the dose to organs at risk and normal tissues near the planning target volume (PTV). This dose, which is highly dependent on the techniques used for imaging, is routinely ignored at the time of treatment planning and delivery. Adding this dose to the treatment plan will give a more accurate indication of the dose to normal tissues and critical organs. Method and Materials: The kV CBCT beam from the Elekta XVI system has been modeled in Pinnacle treatment planning system and the accuracy of the model has been verified by phantom measurements. A number of head and neck IMRT treatment plans have been selected and the dose from the daily CBCT procedure has been added to the treatment plans. The effect of this dose on the DVH of all organs has been studied. Results: The modeling provides an agreement of 3% or better between measured and computed profiles within the field. Utilizing the standard preset of the Elekta XVI system for head and neck CBCT, the dose from each scan is added to the treatment plan. The computed dose agrees with that reported in the literature for the head and neck presets. The magnitude of this dose, however, depends on the technique used. Therefore, the dose as a result of using a different technique has also been calculated. Conclusion: This work demonstrates the feasibility of adding the dose from kV CBCT to the patient treatment plans. Similar work in the past has been done using the MV CBCT but this is the first time the kV dose is added to plans. Accounting for this dose at the time of treatment planning will help to optimize the plan accordingly, avoiding possible overdose of critical organs.
SU‐GG‐J‐67: Evaluating Dynamic Magnetic Resonance Imaging Using a New Design of Phantom: Validation with Fast Megavoltage Fluoroscopic Imaging
Authors: Chang Z , Cai J , Wang Z , Yin F
Published: August 2010

Purpose: To devlope a reliable and economic phantom for motion management study and investigate its feasibility in evaluating dynamic MRI. Method and Materials: Experiments was performed using an in‐house developed phantom that consists of a platform, a low‐elastic thread and a motion phantom driven by a motor in various modes. A small cylinder object was placed on the platform as an imaging object. The design allows metallic motor to be away from the MRI scanner and thereby immunizes the interferences between them. To test its reproducibility, the phantom was setup separately for three times and imaged using fluoroscopy with the same motion mode with an amplitude of 18mm and a period of 5 seconds. An EPID detector was used for fluoroscopy with a high temporal resolution (8 frames/second). Because of free of distortion and fast imaging, fluoroscopy is considered as reference. After this, the phantom was tested with MRI and fluoroscopy with five different motion modes, each with a different period from 4–6 seconds and amplitude from 16–20mm. MR images were acquired on a 1.5T GE scanner with the sequence of FIESTA, (flip angle 50°, matrix 198×128, FOV 30cm, TR 3.2ms, TE 1.0ms, slice thickness 5mm, 2.5 frames/second). Results: The reproducibility test shows consistent agreement among the three measurements. A quantitative analysis yields an average standard deviation (SD) of trajectory profiles of 0.28mm, ∼1.5% of the amplitude. Comparison between MRI and fluoroscopy for five different modes shows that the trajectory profiles by MRI are generally consistent with references. The discrepancies measured by average SDs are from 0.31–0.5mm, relatively small compared with amplitudes from 16–20mm. Conclusion: A reliable and economic motion phantom is developed and successfully used to evaluate dynamic MRI. As a general tool, the phantom can be used to assess motion management of other modalities including 4DCT and PET.
SU‐GG‐J‐85: A Method Incorporating 4DCT Data for Evaluating the Dosimetric Effects of Respiratory Motion in Single Arc IMAT
Authors: Kuo H , Mah D , Wu A , Chuang K , Hong L , Yaparpalvi R , Spierer M , Kalnicki S
Published: August 2010

Purpose: The purpose of this work was to introduce a method to investigate the effect of the breathing motion in a single arc IMAT. We also investigated the role of plan complexity on the dosimetric impact of the respiratory motion in the delivery of VMAT. Method and Materials: The patient's motion model was built from deformable registration over 4DCT images. IMAT plans (one moderately modulated, another highly modulated) were partitioned into 10 (skip & shoot arc) sub‐plans, which were delivered to each of 10 corresponding CT phase image. The dose distribution was re‐warped with a deformation map into a reference phase CT image. The organ dose was derived from the weighted sum over all of the phases. Results: The moderately modulated plan had an average leaf movement of 386 mm and mean leaf gap of 37.9 mm. The highly modulated plan had a maximum leaf movement of 625 mm and leaf gap of 17.2 mm For a patient with a maximum motion displacement of ∼15 mm, the dosimetric impact is rather small and can be ignored for both of moderately and highly modulated IMAT, irrespective of number of fractions. Specifically, highly modulated plans only increased the degradation of D95 of the DVH curves for a single fraction by 2% in the CTV and 9% in the PTV compared to the mean value from a 25 fraction plan. Conclusion: Although single Arc IMAT has less flexible intensity modulation per beam direction, in the treatment of the lesion within the throax‐ abdominal site, less interplay between the organ motion and the dynamic movement gave it an advantage over the conventional IMRT techniques.
SU‐GG‐J‐92: Motion Control Consistency with Abdominal Compression Device from Daily 4D CBCT
Authors: Cui Y , Harrison A , Xiao Y
Published: August 2010

Purpose: To investigate the effectiveness of abdominal compression in tumor motion control for lung cancer radiotherapy. To study the motion control consistency during radiation treatment course through 4D reconstruction of daily cone beam computed tomography(CBCT) images. Method and Materials: Patients with lung tumor were scanned with 4D helical CT and the tumor motion was evaluated in left‐right(LR), superior‐inferior(SI), and anterior‐posterior(AP) directions. Patients with tumor motion greater than 1cm in any of the three directions and who could not tolerate the active breathing control(ABC) were treated with abdominal compression. Kilovoltage(kV) CBCT image was acquired for each treatment fraction to correct patient setup. The CBCT imaging data were then reconstructed using a respiratory‐correlated technique to derive 4D CBCT images with 10 different phases of breathing cycle. Daily tumor motion with abdominal compression was evaluated from the 4D CBCT by recording the tumor center position relative to the treatment isocenter in each phase. Three patient data (1 upper lobe tumor and 2 middle lobe tumors) were included in this study and 4 consecutive treatment fractions for each patient were studied. The extent of tumor motion was compared between different treatment fractions to assess the daily variation of motion control with abdominal compression. Results: Mean value and standard deviation(SD) of tumor motions from all patients and treatment fractions studied were 3.1mm±0.9mm (mean±SD), 6.8mm±1.7mm, and 5.3mm±1.8mm in LR, SI, and AP directions respectively. The variation of tumor motion extent of same patient between different fractions was 1.1mm±0.7mm, 2.0mm±1.9mm, and 2.3mm±2.0mm, in LR, SI, and AP directions respectively. Conclusion: Tumor motions which were greater than lcm with free‐breathing were reduced to less than 1cm with abdominal compression. Variation of motion control during treatment course was significant relative to the tumor motion in the patients and treatment fractions studied.
SU‐GG‐J‐102: The Effect of Inter‐Fraction Setup Error on Single Fraction, Cumulative, and Biological Effective Doses in Head‐And‐Neck Radiotherapy
Authors: Pinnaduwage D , Yom S , Quivey J , Chen J
Published: August 2010

Purpose: To compare the effect of inter‐fraction setup error in head‐and‐neck radiotherapy patients on a) dose from a single fraction, b) cumulative dose, and c) cumulative dose corrected for the biological effect of variable dose/fraction. Method and Materials: Intensity Modulated Radiation Therapy plans are copied and trials created by shifting the isocenter to simulate setup error. The dose from each shift is calculated in the Pinnacle treatment planning system (Philips, Cleveland, OH). Cumulative dose is found by summing the dose from each fraction. Cumulative biological effective dose (BED) at each point is found by summing the BED for each fraction. The BED‐corrected cumulative dose is defined as the dose producing the same cumulative BED when delivered in constant fractions as the variable dose/fraction treatment. Results: A 33‐fraction treatment was simulated. assuming 6 fractions with a 5 mm patient shift in each of the left, anterior, and superior directions and 5 fractions with a 5 mm shift in each of the right, posterior, and inferior directions. This example represents large daily shifts but a small mean shift. The spinal cord, parotid, and CTV α/β ratios were set to 0.87, 3, and 10.5 Gy. The maximum single fraction spinal cord dose was 14% greater than the original. The cumulative and BED‐corrected doses were 1.4% and 2.5% greater than original. The largest single fraction parotid mean dose was 37% greater than original. The cumulative and BED‐corrected doses were respectively 1.5–3.5% and 2.5–4.8% greater. The CTV V100% was 98.7% in the original plan, 91.5% for the worst single fraction, and 98.7% for both the BED‐corrected and cumulative doses. Conclusion: Cumulative doses to normal structures increase slightly if corrected by the BED due to inter‐fraction motion. BED‐corrected doses suggest that large daily shifts may be acceptable if mean shifts over time are small.
SU‐GG‐J‐104: Inclusion of Effects of Image Registration Errors in Accumulated Dose Distributions
Authors: McQuaid D , Sharp G , Bortfeld T
Published: August 2010

Purpose: To consider the effects of image‐registration error in dose accumulation across different geometry instances and to display the resultant errors in a meaningful and useful way. Method and Materials: 4DCT phases acquired of a lung cancer patient were non‐rigidly registered by a B‐spline interpolation method (www.plastimatch.org) to the first phase chosen as a reference geometry. Dose was calculated on each phase and warped back to the reference phase by linear interpolation. The error in the deformation values at each voxel were assumed to be independent of that of neighboring voxels or of adjacent phases. This allows an error instance to be simulated by randomly perturbing the deformation used in dose accumulation by a value sampled from a Gaussian distribution for each voxel. The dose was accumulated for each instance and thirty instances were simulated to sample the total error distribution. Three methods of assigning the standard deviation of the error distribution to each voxel were considered: (i) fixed value of 3mm; (ii) intensity‐matching method: the local value is scaled by a distance to agreement metric calculated by comparing the registered phase image with the reference image; and (iii) vector‐discrepancy method: the local value is scaled by evaluating the invertability of the deformation maps. The effects of the simulated error were visualized by a spread of the accumulated isodose contours. Results: The vector‐discrepancy method resulted in the representation of reduced errors in the posterior region of the target where the extra image detail provided by the ribs and vertebrae increased the accuracy of the registration. Differences between the intensity‐matching method and fixed‐error method were less noticeable. Conclusion: A method of including image registration error in dose accumulation has been developed. Further work is required to compare results to a gold standard on a number of image datasets.
SU‐GG‐J‐114: A Graphical Tool for Assessing Margin Definition from Daily Deformations
Authors: Apte A , Al‐Lozi R , Pereira G , Matthew J , Mansur D , Deasy J , El Naqa I
Published: August 2010

Purpose: Estimating the proper margins for the planned target volume (PTV) could be a challenging task in cases where the organ undergoes significant changes during the course of radiotherapy treatment. This is practically the case in stomach lymphoma, where the stomach can change significantly from day to day. A common practice is to add a constant l–2cm margin isotropically around the tumor volume based on planning CT scan. This might lead to some portions of stomach being under dosed or surrounding normal structures over‐dosed. The purpose of this work is to develop a tool that utilizes information from daily images to aid localization of these deformations and guide estimations of proper margins. Method and Materials: In this work, the stomach volume for each treatment fraction was delineated manually over the course of 6 weeks of fractionated treatment using daily Tomotherapy Mega voltage CT (MVCT) images from three patients. A software tool was developed to aid tracking variations in shape during therapy and record estimates of the probability by which an organ spends at any particular place. Accordingly, plots of estimated tumor coverage and excess irradiated normal tissue volumes as a function of margin could be generated. Results: Estimated stomach volumes for these cases were 429.2±67.7, 383.0±66.6, and 294.1±27.7 cc. Plots of tumor coverage and excess irradiated volume were created for each case. It was observed that with a margin of 1.5 cm over the original stomach, the entire union volume was covered. This margin resulted in about 500–800 cc of excess volume being irradiated for the three test cases. Conclusions: This work presented a new tool for visualization and quantification of daily deformations for isotropic and anisotropic margin definition guidance.
SU‐GG‐J‐139: Quantitative PET Imaging of Heterogeneous Tumors: The Dosimetric Effect of Patient Motion on Image‐Based Dose Painting Plans
Authors: McCall K , Bowen S , Jaskowiak C , McNall M , Rice S , Jeraj R
Published: August 2010

Purpose: Dose‐painting requires accurate quantification of tumor characteristics and precise localization of molecular targets within tumors. Imaging with PET provides surrogate markers of molecular activity within sub‐tumor volumes; however, quantification is limited by many physical factors, including patient motion during image‐acquisition. We have evaluated the dosimetric impact of neglecting respiration‐motion management during PET image‐acquisition. Methods and Materials: PET/CT images were used to generate dose‐painting plans of 60Gy base‐dose to the entire tumor volume (PTV) and 10Gy boost‐dose redistributed within sub‐regions of elevated metabolic activity. Spatial distributions of metabolic activity were derived from: (1) heterogeneous phantoms with variable amplitudes of respiration‐motion, and (2) respiration‐gated and non‐gated [18F]FDG PET images of lung‐cancer patients. For each phantom and patient, a reference plan was generated from PET image where minimal motion occurred. For lung patients, these reference plans corresponded to respiration‐gated PET of the end‐exhalation phase. “Motion‐blurred” dose‐painting plans were generated from non‐gated PET images; however, the PTV contour, boost volume, and integral dose were kept constant. Results: Phantom studies characterized the relationship between dosimetric errors and amplitude of motion. For typical respiration‐motion (2cm superior‐inferior, 1cm anterior‐posterior) 10% of PTV voxels showed dose errors exceeding 3Gy (30% of boost‐dose). Errors were reduced below 3Gy, when motion amplitude was lcm or less. For lung‐cancer patients, the use of motion‐blurred images resulted in dosimetric errors (exceeding 3Gy) within 5% of PTV voxels. Additionally, dose differences up to ±10Gy were observed. Conclusion: Respiration‐motion during PET acquisition resulted in dosimetric errors throughout PTV for dose‐painting plans in phantoms and lung‐cancer patients. Magnitudes of these errors were correlated to the amplitude of residual motion within PET images. Motion‐management techniques (e.g. gated acquisition, 4D‐PET) are necessary to reduce uncertainty in defining heterogeneous dose‐distributions and improve efficacy of image‐based dose‐painting.
SU‐GG‐J‐141: Development of a Novel Multipurpose Specimen Slicing‐Imaging Platform
Authors: Wen J , Ma D , Hoefert J , Yang F , Lu W , Parikh P
Published: August 2010

Purpose: To develop an automated system that slices and images surgical specimens for volume reconstruction. Methods and materials: In order to correlate radiographic images with pathologic tumor volumes, a technique that can cut different tissue structures with minimal specimen deformation is required. Thus a high precision cutting surface with ultra‐low cutting forces is needed for this application. A specially designed rotary wire saw using a closed‐loop, diamond coated cutting wire rolled by a motor‐driven pulley was used for this purpose. This motor was computer controlled for variable cutting speed. The sample was held in paraffin or gelatin with a Styrofoam mold and was driven by a computer‐controlled linear slide that fed the sample to the wire saw. After each slice, a CCD camera was used for imaging the cut surface. The image resolution can be adjusted steplessly from 1 m/pixel to 5 m/pixel with the field of view varying from 3.2 × 4.4 mm to 16 × 22 mm. Raster scanning was employed when studying large samples. Different animal tissue samples including kidney, liver, heart and shank were used to evaluate the cutting device, i.e., the consistency of slice thickness and the evenness of the slice surface. The relationship between tissue loss and 3D volume reconstruction was also studied. Results: Slice thickness was measured by both caliper measurements and pixel counting on corners. Both the single slice thickness variation and the overall slice thickness variation were within 5% agreement by both measurements. Surface roughness was similar to microtome slices. The kerf loss was consistently 0.28mm ±0.01mm and had a very small disturbance on 3D model reconstruction. Conclusion: 3D volume reconstruction using this automated technique closely approximates the specimen volume and can be used for correlating radiologic volumes with pathologic volumes.
SU‐GG‐J‐159: Dosimetric Consequences of Rotational Setup Errors Using Direct Simulation in a Treatment Planning System for Fractionated Stereotactic Radiotherapy (SRT)
Authors: Peng J , Chen Y , Liu C , Kahler D , Li J
Published: August 2010

Purpose: To determine dose‐delivery errors resulting from systematic rotational setup errors for fractionated stereotactic radiotherapy (SRT) using direct simulation in a treatment planning system (TPS). Methods and materials: Ten patients who received IMRT of brain tumors were studied. Simulation of systematic rotation was done by applying a 3×3 rotation matrix to the original images and contours. Combined rotational errors of ±1°, ±3°, ±5° and ±7° and residual translation errors of 1 mm along each axis were simulated. The rotated images were re‐imported into the TPS and the dose effects were evaluated by re‐computing the dose distributions. Target volumes receiving ≥ 100% (V100Rx), 93% (V93Rx), and 110% (V110Rx) of the prescription dose level and the volumes of the 6 organs at risk (OARs) receiving more than the tolerance dose levels were evaluated. Results: The accuracy of the image rotation algorithm was validated using the image registration package within the TPS and was found to be within 0.5 mm/0.2° in translation/rotation transformation, respectively, and the volumes of the rotated contours are within 2% of the original contours. A systematic reduction in CTV coverage was observed, with the mean V100Rx of the CTV to be 99.3±0.5% (original), 98.4±1.2% (±1°), 95.8±3.0% (±3°), 90.0±7.3% (±5°), and 81.4±13.1% (±7°). In most cases, OAR doses fell within the tolerance levels. However, for two cases where D0.1cc (dose to 0.1 cm3) of the brain stem received close to the dose limit in the original plan, even a ±1° rotations had made D0.1cc > 55Gy, which exceeded our dose limit. Conclusions: We conclude that for rotations less than ±3°, no action level is required; however, cases presenting extreme rotations and high doses in the brain stem should be investigated as routine practice. This procedure allows easy evaluation of dosimetric consequences when systematic rotational errors are present in patient setup.
SU‐GG‐J‐160: Monte Carlo Optimization of a Three‐Stage Compton Camera for Prompt Gamma Imaging and Spectroscopy: Materials and Geometry
Authors: Robertson D , Peterson S , Polf J
Published: August 2010

Purpose: Prompt gamma photons emitted from biological tissues under proton irradiation carry dosimetric and spectroscopic information that can provide treatment verification and indicate biological response. We optimize the materials and geometry of a three‐stage Compton camera for prompt gamma detection and to calculate the efficiency of such a detector. Method and Materials: A three‐stage Compton camera was modeled in Geant4 as a series of parallel square detector stages. The assembly was placed 15 cm from an isotropic point source of mono‐energetic gamma‐rays. The primary energies considered were 2.33, 4.44, and 6.13 MeV, which are characteristic emission energies of Nitrogen, Carbon, and Oxygen. Certain detector arrangements were characterized over the energy range from 0–1 MeV in 0.25‐MeV increments and from 1–10 MeV in 0.5‐MeV increments. The scintillating materials evaluated in this study include germanium, BGO (Bi4Ge3O12), NaI, Xenon, and LaBr3. For each material, the thickness of each stage was optimized to produce the maximum number of relevant interactions. Results: For the primary and secondary stages, each material exhibits peak production of single Compton‐scatter events at thicknesses ranging from 2 cm for BGO to 4 cm for Xenon. Transportation efficiency, or the fraction of interacting photons that enter the next stage, decreases linearly with thickness. Peak efficiencies for the primary and secondary stages vary from 15–25% per stage, depending on energy and material. In the final stage, all interactions are used, making detection efficiency an increasing function of thickness. At 10 cm thickness, BGO detection efficiency approaches 80%, while germanium and LaBr3 exhibit 70% efficiency. Conclusion: The most important contributors to detection efficiency are thickness and material. The most efficient detector configurations are BGO‐Germanium‐BGO, with a peak efficiency of 2.25×10−3 at 2 MeV, and Germanium‐Germanium‐BGO, which is the most efficient detector below 1.5 MeV and above 4 MeV.
SU‐GG‐T‐174: Comparison of Structure Contouring Efficiency and Dose‐Volume Histograms (DVH) of Pinnacle3 and Eclipse Treatment Planning Systems for Prostate IMRT
Authors: Reddy N , Ravi A , Chang H , Lange C , Nori D
Published: August 2010

Purpose: To test the hypothesis that structure contouring precision and DVH for Prostate‐PTV, rectum and bladder would be the same for Pinnacle and Eclipse treatment planning systems (TPS). Materials and Methods: DVH for 51 patients each planned with Pinnacle3 and Eclipse TPS and treated with Elekta‐Synergy and Varian Linacs, respectively, was compared. Patients and treatment planners were different for Pinnacle and Eclipse. Beams numbers, angles, energy (6X) and Radiation Oncologists were the same. Prostate, SV, rectum and bladder were contoured from CT‐images with 0.5 mm separation. Prescription was 45‐Gy to prostate+SV (CTV) and 36‐Gy boost to prostate. Margins for CTV and prostate were 0.5‐cm superiorly and posteriorly, and 1‐cm in other dimensions to create PTV and Prostate‐PTV, respectively. Dose‐volume constraints (DVC) were to cover 95% PTVs with 95% prescription dose and keep respective doses to 70%, 50% and 30% rectum and bladder to less than 30%, 50% and 70% of 81‐Gy. Pearson's correlation coefficient ‘r’ and two‐sample ‘t’ test were used for statistical analysis. Results: Structure‐contouring efficiency was the same between TPS. Mean‐volumes (±SD, cm3) of prostate (53.9±20.4 vs. 52.8±23.8), SV (13.3±6.6 vs. 11.5±6.6), prostate‐PTV (159.7±42.4 vs. 144.9±46.6), rectum (106.6±34.8 vs. 120.5±47.7) and bladder (191.8±103.9 vs. 177.2±81.3) were the same for Pinnacle and Eclipse patients, respectively, (P >0.1). Percent of 81‐Gy delivered to 95% prostate‐PTV was higher with Pinnacle (97.63±0.71) than Eclipse (96.12±0.997) TPS (P<0.001). Consequently, mean‐dose (Gy) delivered to rectum (36.1±2.7 vs. 31.5±4.8, P<0.001) and bladder (32.9±7.5 vs. 29.7±7.5, P<0.05) was higher with Pinnacle than Eclipse TPS, respectively. Conclusions: Structure‐contouring efficiency, prescriptions and DVC‐guidelines being the same, there is great potential for delivering significantly different doses to targets and normal tissues. Although these doses are within the DVC‐guidelines, clinical outcomes and normal tissue toxicities could be different. This may also be true for RTOG trials where DVC‐guidelines are general.
SU‐GG‐T‐175: Dosimetric Evaluation of the Use of Air or Water Filled Endorectal Balloons for Prostate IMRT Patients
Authors: Kudchadker R , Nguyen Q , Vu K , Wootton L , Vassiliev O , Choi S , Frank S , Johnson J , Kuban D , Lee A
Published: August 2010

Purpose: Prostate cancer patients undergoing intensity modulated radiation therapy (IMRT) are typically treated without endorectal balloon in our clinic. On occasion, there is a clinical need to use endorectal balloons. The purpose of this study is to evaluate the dosimetric advantages and disadvantages of using water or air in endorectal balloons. Materials and Methods: In an IRB approved protocol, water filled endorectal balloons were inserted into the rectum of 7 prostate patients. The patients were imaged in the supine position with full bladder and endorectal balloon. The Pinnacle treatment planning system (TPS) was used for planning. The prostate, seminal vesicles, rectum, anterior rectal wall and bladder were contoured on all patients. A second plan was generated by converting the water into air by overriding the density of the water. Dose distributions and dose volume histograms were evaluated. To verify Pinnacle dose computation at the rectum‐prostate (air‐tissue) interface, the treatment plans were recomputed using Monte Carlo for the air balloons. Monitor units required to deliver the two plans were also compared. Results: Mean dosimetric parameters for air vs water were; Rectum: V70 ‐ 9.7% vs 11.6%; V60 ‐ 17.3% vs 17.2%; V40; V40 ‐ 34.7% vs 30.9%; Bladder: V70 ‐ 6.5% vs 6.4%; Maximum dose: 8003 cGy vs 7953 cGy. Mean monitor units for the air vs water plans were 803 MU vs 710 MU. Conclusions: The dosimetric parameters for rectum and bladder for air and water balloons were similar (<5%) indicating that either could potentially be used. The water‐filled balloon plans required significantly less MU's as compared to the air balloons and required less planning time to meet dosimetric criteria and constraints when compared to air‐filled endorectal balloons. Monte Carlo calculations agreed better with Pinnacle water balloon plans than air balloon plans.
SU‐GG‐T‐179: Dosimetric Analysis of Simultaneous Integrated Boost with Step and Shoot IMRT
Authors: Ravindran P , Balukrishna S , Viswanathan P
Published: August 2010

Purpose: In this work, the dosimetric parameters of Simultaneous Integrated Boost treatment with step‐and‐shoot IMRT were analysed. Method & Materials: Treatment plans of eight patients, who were treated for locally advanced head and neck squamous cell carcinoma, were included in the analysis. The homogeneity index for target volumes was estimated. The dose to critical organs‐ spinal cord, brainstem and parotids were analysed. The hot spots in the cord and the brainstem, the serial organs, were analysed by considering the maximum dose to 2% volume and for parotid, volume that receives 30Gy or more was considered. Results: For the cord and the brainstem the objectives of <45Gy and <54Gy respectively were well met and, V30 < 50% for at least one parotid was also met. Conclusion: Treatment of HNSCC with SIB using static multi‐segmental IMRT also could provide desirable homogeneity in dose distribution and enable adequate sparing of organs at risk.
SU‐GG‐T‐198: A Pitfall in IMRT Verification: The Jaw Position
Authors: Lin C , Huang Y
Published: August 2010

Purpose: By verifying the consistency between the planning dose and the delivered dose for each segment, we try to figure out the cause of the high dose regions outside the treatment field which only shown in measured dose, but not in the treatment plan. Method and Materials: Our treatment planning system is ADAC Pinnacle version 8.0m. The IMRT plan is transferred to IMP AC oncology management system version 8.3 to drive the LINACs. Instead of taking an overall two dimensional dose distribution, we took the fluence maps for each beam by using Kodak XV films on two ELEKTA Precise LINACs and one ELEKTA Synergy. Results: High dose regions are obviously in only one Precise LINAC and always perpendicular to MLC leakages. By comparing the fluence maps between treatment plan and verification film segment by segment, we find it occurs on the MLC 0.8 cm gap which is designed to prevent one side MLCs to collide with the opposite MLCs. The gap should be blocked by the primary jaw and MLC directional backup jaw. However, because of the machine limitation, the primary jaws are not allowed to cross the central line, the gap is simply blocked by the MLC directional backup jaw only (3cm tungsten) occasionally and slight transmission doses are generated (about 15%). If the backup jaw goes to the wrong position and does not block the MLC gap, a high dose region occurs during dose delivery, but not shown in plan. Conclusion: When the backup jaw position is not compatible with treatment plan, the unanticipated high dose region emerges not only outside of the field but also inside the field. Even if one checks the jaw position by any open field, this situation sometimes occurs. The best way is to recalibrate the jaw mechanical parameters and recheck the incorrect segment.
SU‐GG‐T‐278: Clinical Dosimetry of Photon Sources Used in Brachytherapy: Need for ISO Standardization, Based on and Extending the AAPM TG‐43U1 Formalism by Calibration in Terms of Absorbed Dose to Water
Authors: Quast U , Kaulich T , Ahnesjö A , Álvarez‐Romero J , Donnarieix D , Hensley F , Maigne L , Medich D , Mourtada F , Pradhan A , Zakaria G
Published: August 2010

Purpose: By calibrating brachytherapy (BT) sources to the TG‐43U1 reference position at 1cm in water, named the nominal absorbed dose‐rate to water, Ḋw,1, accuracy and precision for patient treatment will be increased. Traceability must be provided to Ḋw,1 ‐primary‐standards; which soon become available. Methods and Materials: Efforts have been made in discussions with fellow scientists from many countries, by reviewing concerned literature, and similarities are drawn from documents (e.g. extending TG‐43U1). Results: From the study of primary photon interaction mechanisms, a need was recognized to classify BT‐photon radiation qualities as: high‐energy >100keV, medium energy 40keV to 100keV, and low energy <40keV. It was further recognized that Monte Carlo simulation based primary and scatter dose separation provides characterization for radionuclide BT‐sources and electronic X‐ray BT‐sources, for BT‐detectors and BT‐phantoms. A need was felt for developing reference data‐sets and calibration data of BT‐sources, ‐detectors and ‐phantoms, through which the end‐user medical‐physicist could critically evaluate the data supplied by the manufacturer by using established methods, prior to clinical application. Plastic scintillators appeared to be a choice of detector as future high precision transfer‐standard and high resolution, fast, direct reading dosemeter for detailed quality assurance of BT‐sources, ‐software, ‐planning, and ‐verification. Conclusion: There is the need for international standardization of clinical dosimetry in photon radiation brachytherapy similar to that described in ISO‐21439 (2009) for beta radiation BT‐sources. Based on AAPM TG‐43U1, this planned ISO‐standard will provide guidance for clinical BT‐dosimetry in terms of absorbed dose to water and for estimating the uncertainty of this quantity. Most standardized procedures can be given by referring to AAPM‐ and ESTRO‐reports. Recommendations will be prepared to replace the reference air‐kerma‐rate (air‐kerma strength) by the nominal absorbed dose‐rate to water as basic dosimetric quantity, to increase brachytherapy accuracy and precision and to become consistent with external beam radiotherapy.
SU‐GG‐T‐279: Current Practice in Small Radiosurgery Field Dosimetry — Preliminary Results from 21 Centers Participating in the International Leksell Gamma Knife Calibration Survey
Authors: Novotny J , Desrosiers M , Bhatnagar J , Novotny J , Bednarz G , Huq M , Puhl J , Seltzer S
Published: August 2010

Purpose: To investigate current practice in calibration of small Leksell Gamma Knife (LGK) radiosurgery fields and measure output of the surveyed LGK units using alanine dosimeter. Methods and Materials: Each participant of the project received a LGK calibration questionnaire addressing following information: LGK model, calibration protocol used, phantom used, ion chamber used, LGK calibration personnel, independent verification of calibration and collimator relative output factor values. Alanine dosimeters evaluated with a Bruker ECS106 Electron Paramagnetic Resonance spectrometer using the protocol described in the NIST Ionizing Radiation Division Quality System Manual were used to measure the dose rate of the surveyed LGK units. Results: To date, 21 LGK units have participated in this project (North America 9, Europe 5 and Asia 7).The calibration protocols used for surveyed sites were: AAPM TG21 9 sites, IAEA TRS277 1 site and IAEA TRS398 11 sites. ELEKTA ABS spherical phantom was used in 18 cases and ELEKTA solid water phantom in 3 cases. Following ion chambers were used for LGK calibration: PTW 31010 (0.125 cm3) 9 times, Exradin A16 (0.070 cm3) 2 times, PTW 31006 (0.125 cm3) 1 times, Capintec A1SL1 (0.070 cm3) 2 times, Wellhoffer IC‐10 (0.125 cm3) 1 time, Exradin A1SL 1 time and Exradin A14SL 1 time. Calibration of LGK units was performed by an on‐site physicist in 15 cases and by ELEKTA physicist in 6 cases. Independent verification was done in 8 cases out of total 21 surveyed units. All LGK units surveyed are currently using the ELEKTA default values for collimator relative output factors. Conclusions: The range of dose planned to measured ratio was 0.972 – 1.030 demonstrating reasonably good LGK calibration consistency. Mean absolute value percentage deviation between planned and measured dose was 1.34 – 0.84 %. This project is ongoing and more information will be provided at its conclusion.
SU‐GG‐T‐296: Experience on Using Modified CHECKMATE for Hi‐Art Tomotherapy Daily QA
Authors: Li W , Liu L
Published: August 2010

Purpose: To design a method utilizing a commercially available daily QA device to check the performance of the Hi‐Art Tomotherapy unit. This method is simple for therapists to finish in a short time and also can check the output and energy of the machine as well as the laser and imaging precisions as recommended by Tomotherapy. The initial experience of using this method is also reported. Method and Materials: A CHECKMATE (Sun Nuclear Corp. Melbourne, FL) with one vented parallel‐pate chamber at the center was used. BBs were added to serve as the markers to check the imaging precision and couch position accuracy. The 10 cm square markings and the BBs were also used to check the red laser movement accuracy. A procedure was designed to deliver 20s beam on time (∼287 cGy) to the chamber with SSD = 85cm. This procedure was delivered first to check the output of the machine, then a Cerrobend plate of ∼1.6 cm thick was put on top of the device and the procedure was delivered again. The ratio between the two readings was used to represent the energy of the machine. Results were compared with the monthly QA measurements and CT detector data measured by field service engineer (FSE) when available. Results Daily couch position variation was well within 1mm limit. The output measurements were in agreement with the monthly IC measurement as well as the CT detector data used by FSE. The energy measurements were consistent with the monthly QA data. When target was deteriorating, the FSE reported data had a different trend than the morning QA data. Conclusions The modified CHECKMATE provides a reliable and fast way to do daily check for Tomotherapy machine and can be easily done by a therapist
SU‐GG‐T‐302: Measuring Pacemaker Dose: A Clinical Perspective
Authors: Studenski M , Xiao Y , Harrison A
Published: August 2010

Purpose: The number of patients presenting with pacemakers in our clinic has increased recently. Following AAPM recommendations, a treatment plan is developed that minimizes the dose to the pacemaker. The most efficient way to measure in vivo dose during treatment is to use MOSFETs or diodes which offer a simple but inaccurate (up to 25% error) method of recording. In this abstract, we analyze the dose measured by these different devices in an attempt to assess pacemaker dose. Method and Materials: Five patients with different disease sites and pacemakers were chosen. To simulate the treatment delivery, a Rando phantom was placed on the table in the patient treatment position. An ion chamber was taped to the phantom under 1 cm bolus. Two MOSFETs and a diode were placed on top of the bolus and the treatment was delivered. One cone beam CT was obtained where the pacemaker was in the field‐of‐view to quantify the MOSFET and diode reading in this situation. Results: The measurement from the ion chamber agreed well with the predicted dose from the planning system. Some errors resulted from misalignment of the phantom and ion chamber. Both the MOSFET and diode measurements agreed with the ion chamber and TPS with greater distances. Dose from CBCT was overestimated for both MOSFETs and diodes. Conclusion: The simplest and most efficient in vivo measurement is to use a MOSFET or diode. When the pacemaker is more than 20 cm from the field edge these dosimeters are appropriate. When the field is less than 20 cm away, the most accurate although inefficient method is to use an ion chamber since there is little angular or energy dependence unlike diodes or MOSFETs. Another solution would be to use TLDs or OSL dosimeters although these are not simplistic dosimeters either.
SU‐GG‐T‐313: A Procedure for Standardizing MLC Quality Assurance for Elekta Linacs
Authors: Yan K , Studenski M , Liu H , Buzurovic I , Cui Y , Shabason L , Harrison A , Yu Y , Hossain M , Xiao Y
Published: August 2010

Purpose: As specified in TG142, MLC position accuracy needs to be tested on weekly/monthly basis, with 1mm tolerance. This study focuses on developing techniques, hardware and software tools for implementation of MLC QA tests for Elekta Linacs. Material and Methods: This process was tested with an Elekta Synergy S, Beam Modulator™, which has 40 leaf pairs of 4mm width (maximum 16cm×21cm field size). Based on the machine characteristics, two picket‐fence IMRT plans were designed: one has 5 2cm×16cm strips separated by 2cm gap; the other has the same setup with individual leafs intentionally displaced by ±1mm, ±1.2mm, etc. Both plans used 6MV x‐rays and 50MU on each strip. We overcame the limitation of Xio planning system in generating picket‐fence IMRT plan by modifying leaf positions from a DICOM RT plan file. In‐house software was executed to validate the files before imported into Record and Verify system (Mosaiq) for delivery. Radiographic images were acquired using Kodak XV films. The borders of a 16cm×21cm light field were first traced on the film. These reference lines helped reduce the orientation errors during image registration. Two sets of films were exposed with full buildup. After development, each film was digitized with 0.06mm resolution using a high‐resolution scanner. The images were then imported into Matlab. In‐house code was used to detect leafs exceeding the 1mm threshold. Results: The plans were delivered smoothly. Leaf positions in the first image were used as baselines, instead of using reference leaf positions from the same exposure. This reduced systematic errors. After image registration, leafs displacing from the baseline by 16 pixels (1mm) or more were detected. Conclusion: This efficient procedure provides a sufficiently accurate test for MLC positioning reproducibility. It is a simple and straightforward procedure that can be used for routine MLC position checks.
SU‐GG‐T‐316: Measurement of Photoneutron Depth Dose Equivalent and Beam Profiles of a High‐Energy X‐Ray Beam of Varian 2100C Medical Linear Accelerator by Thermoluminescent and CR‐39 Detectors
Authors: Kehwar TS , Huq MS
Published: August 2010

Purpose: To measure depth‐dose‐equivalent(DDE) and beam‐profiles(BP) of photoneutrons produced by 18MV photon beam. Materials and Methods: 18MV photon beam of Varian‐2100C LINAC was used to measure DDE and BP of photoneutrons. Specially designed dry‐phantom, to accommodate Thermoluminescent(TL) and CR‐39 detectors, was used. Mixer of photons and photoneutrons, and photons were measured by TLD‐600 and LTD‐700, respectively. Glow curves were generated at calibration depth of 6MV beam of 10×10cm2 for dose range 0–400cGy. DDE measured at depths 0–20cm for 5×5–30×30cm2, while BP at dmax and 10cm in cross‐plane for 10×10cm2 and 20×20cm2. Measurements were done upto 15cm beyond the photon field edge. TLDs were read by Harshaw reader and CR‐39 by the supplier(Landauer). Factors in 10CFR20 regulation were used for DE conversion. Results: TLDs provided DE for total neutrons, while CR‐39 for total, fast plus intermediate and thermal neutrons. DDE obtained by normalizing DE with that at dmax(photons). DDE for total neutron DE, of both detectors, decrease exponentially with depth and have no statistically significant differences(p>0.05). DDE for fast plus intermediate neutrons(CR‐39) also decreases exponentially with depth, while DDE for thermal neutrons exhibit buildup region and attain maximum at depth, thereafter decreases in samilar manner as photons depth doses. Central axis DE, for all type of neutrons, at 0 and dmax increases with field size. BP at dmax and 10cm for total neutron DE, have maximum normalized values at central axis and remain almost constant within 90% photon isodose region and then decreases rapidly between 90%−20% photon isodose region. Beyond 20% to the end point of measurement the decrease is only 5%. Conclusion: Study demonstrates the way to measure DDE and BP for photoneutrons and will help to compute neutron DE in critical organs and can eliminate the fear of using high‐energy photons beams in IMRT and IGRT treatments.
SU‐GG‐T‐338: Accuracy of Superficial Dose Calculation for Breast Cancer Treatments on Tomotherapy
Authors: Green O Pechenaya , Goddu S , Rodriguez V , Cates J , Michaletz‐Lorenz M , Zoberi I
Published: August 2010

Purpose: To evaluate the effect of breathing motion and setup error on the accuracy of treatment planning surface dose calculation for breast cancer treatments on helical Tomotherapy. Method and Materials: In‐vivo dosimetry with MOSFET detectors was performed on a cohort of patients treated for breast cancer on helical Tomotherapy. The detectors were placed under the 0.5‐cm tissue‐equivalent bolus used for patient treatments. The pre‐treatment MVCT images were used to localize the MOSFET detectors. Tomotherapy's Planned Adaptive software was used to compare the measurements against both the planned surface doses at the locations of the dosimeters as well as the recalculated doses based on the MVCT scan. This allowed for evaluation of the combined impact of breathing and setup error on the surface dose contribution, and the quantification of dosimetric accuracy of the Tomotherapy treatment planning system for breast cancer patients. Results: The differences between dose values at the locations of the dosimeters from the plan and those calculated from the MVCT image were on average within 1% of each other. The average dosimetric differences between measured and calculated doses were 7.8 and 8 percent for the planned and adaptive calculated doses, respectively. Overall, the treatment planning system overestimated the dose at the skin/bolus interface. Conclusion: The treatment planning system was previously shown to overestimate dose at a 5‐mm depth by about 4%. The possible setup error is taken into account by the adaptive software since it recalculates the dose distribution based on the MVCT image associated with the treatment for which the measurement was made. Since the setup error was shown to be within 1%, it is therefore estimated that the dosimetric consequence of breathing motion may be as high as 3%.

Conflict of Interest: This work was partially supported by a grant from Tomotherapy, Inc.
SU‐GG‐T‐340: A Study of Surface Dosimetry for Breast Radiotherapy Treatments
Authors: Hill R , Kim J , Kuncic Z
Published: August 2010

Purpose: To evaluate the impact of beam modifiers and field delivery on surface dosimetry. Method and Materials: Surface and near surface doses were measured for a range of field setups typically used in breast radiotherapy treatments. Doses were measured using the Attix thin window parallel plate chamber and corrected to the effective point of measurement of this chamber.1 All measurements were performed on Varian 21EX linear accelerator using 6MV x‐rays and doses normalized to the dose at depth of 15 mm which corresponds to dmax. Measurements were made for the different beam modifiers and with both static and dynamic fields. The static fields consisted of open beams, fixed wedges and MLC shaped fields. The dynamic fields consisted of Varian EDW fields, square dynamic fields with different MLC leaf gaps (from 4 mm to 2 cm) and complex shaped MLC fields typically used for breast boost fields. Results: Surface doses for the static and dynamic open field as well as the EDW fields were all of the order of 16%. Surface doses for the square dynamic fields increased very slightly as the fixed MLC gap increased from 4 mm to 4 cm. For the fixed wedges, the surface dose decreased from 14.5 to 11.6% as the wedge angle went from 15 to 60 degrees. The doses at 1 mm depth varied between 38 to 47% in a similar pattern to the surface doses with the minimum dose occurring for the fixed wedges. Conclusion: In this work, we have shown that surface and near doses for fixed wedge fields are lower compared to dynamically field setups as typically used for breast radiotherapy patients.