bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐23: Artificial Neural Networks Approach For Clinical Portal Dose Image Comparison
Authors: Tran M , McCurdy B , Pistorius S
Published: July 2007

Purpose: This work uses Artificial Neural Networks (ANN) to compare measured portal images with their corresponding predicted images in order to determine the underlying problems causing any differences. Materials and Methods: In external beam radiation therapy, a dose may be incorrectly administered to the patient due to patient set‐up errors and/or treatment delivery errors. In this work we focus on incorrect dosage due solely to geometric patient set‐up errors, consisting of in‐plane rotation, out‐of‐plane rotation, two‐dimensional translations, and magnification. Using an anthropomorphic pelvic phantom on a Varian Medical Systems linear accelerator with an aS1000 EPID, sets of images that emulate these errors were obtained. The angle (about the z axis) was varied from 0 ° to ± 45 ° in (2 ° – 5 °) increments, and the translational distance was varied from 0 mm to ± 60 mm in (2 mm – 20 mm) increments. A two‐layered, backpropagation ANN unit was created with 10 neurons in the hidden layer and 5 outputs. The difference images were analyzed using PCA and were input to the network, which was trained to classify the images according to their error types, and then tested for its robustness and generalization ability. Results: Preliminary results demonstrate that ANN unit is capable of classifying clinical difference images that it has not seen before. It was found that the unit performed best when presented with images containing in‐plane rotational errors. Conclusions: A reduction in patient set‐up errors is of paramount importance, since they can result in substantial dose reduction in the tumour and increase dose to the surrounding normal tissues. Preliminary results demonstrate that the ANN unit is adequate as an automatic tool for on‐line verification of patient set‐up errors. Modifications to the network architecture and a larger training set will hopefully improve the current results.
SU‐FF‐J‐24: Toward Real‐Time Tracking of HDR Source Position Using Emission Imaging with a Collimator and Flat‐Panel Detector
Authors: Bowsher J , Song H , Yin FF
Published: July 2007

Purpose: High dose rate (HDR) brachytherapy delivers rapidly a large, highly spatially varying dose. Consequently, precise quality assurance of source location and dwell time is important. Here, we propose that, with no additional radiation exposure to the patient, the same flat‐panel X‐ray detector (FPD) used for anatomical imaging during simulation can also be used for real‐time emission imaging of Ir‐192 brachytherapy source location. Method and Materials: A standard parallel‐hole, low‐energy, gamma‐camera collimator (weight 34 lbs) was placed on a FPD, in order to preferably accept those Ir‐192‐emitted photons which are directed perpendicular to the FPD surface. A 10 Ci Ir‐192 source was advanced in 2‐cm steps through a catheter positioned 20 cm from the collimator/FPD. FPD images where acquired continuously with 6 seconds per frame. Measurements were obtained with 3 different thicknesses (0, 10 cm, and 20 cm) of solid water between the Ir‐192 source and the collimator/FPD. Results: A hot spot corresponding to Ir‐192 source location was clearly resolved, well above noise, in all images, even with 20 cm solid water. There were penetration patterns corresponding to collimator septal thickness. Imaged source locations tracked the 2 cm steps of the source. Conclusion: A standard gamma‐camera collimator provides directional selection of Ir‐192‐emitted photons that is sufficient to determine source location. The commercial FPD considered provides ample signal‐to‐noise ratio for imaging Ir‐192‐emitted HDR photons on the few‐second time scale investigated. Thus HDR source location — along the 2 dimensions parallel to the FPD surface — can be determined by positioning a collimator over the same FPD used for transmission anatomical imaging.
SU‐FF‐J‐27: Target Localization Verification for Partial Breast Irradiation with An EPID in Cine Mode
Authors: Berbeco R , Ionascu D , Park S , Lyatskaya Y
Published: July 2007

Purpose: In partial breast irradiation (PBI), even if the target is well defined, and positioned precisely at the beginning of each treatment session, there are no assurances that it will remain so during irradiation. We propose tracking the PBI target using an electronic portal imaging device (EPID) in cine mode. Method and Materials: Phantom studies have been conducted using a breast phantom and diode detector. We quantified the dose enhancement to a point on the surface of the contra‐lateral breast when the EPID is left extended during treatment. Measurements of the dose enhancement were made for multiple field sizes, beam energies and EPID positions. Additional measurements were made of the dose enhancement to the contra‐lateral breast with the medial field included. To preliminarily assess the visibility of targets in the breast, images were taken with a wire fiducial in the field. Additional images were taken with the phantom set in a sinusoidal motion. Results: For a PBI field, the dose enhancement (DE) is 19% for 6 MV and 23% for 10 MV for Source‐to‐Detector Distance (SDD) = 130 cm, compared to 4% and 4.5%, respectively, for SDD = 155 cm. When the dose to the surface of the contra‐lateral breast from the medial field is included in the calculation, the dose enhancement is below 2% for both energies for SDD greater than 142 cm. For a WBI field, DE is below 2% for both energies for SDD greater than 147 cm. In the cine EPID images, visualization of the target can be improved with simple image processing techniques Conclusions: The cine EPID technique may be employed safely to monitor WBI and PBI treatments.

This work was funded, in part, by a grant from Varian Medical Systems, Inc.
SU‐FF‐J‐28: A Software Tool for On‐Line Real‐Time Verification of Gated Delivery Using Megavoltage Fluoroscopy
Authors: Tai A , Christensen J , Khamene A , Bayouth J , Boettger T , Celi J , Li X
Published: July 2007

Purpose: To test and to explore the application of a software tool developed for on‐line real‐time treatment verification for 4D/gated radiation delivery using megavoltage fluoroscopy (MVF) acquired with treatment beams. Method and Materials: MVF images were acquired with a flat panel detector installed on a Siemens Linac using 6MV photon beams for phantoms with moving structures and for thoracic cancer patients. A previously developed software, RTReg4D, was used to register acquired MVF with digitally reconstructed radiographs (DRRs) from 4DCT. The MVF frame grabber can be synchronized with the gating signal from Anzai gating device to capture target motion in selected gating window. The isocenter and target contours were transferred from a planning system into RTReg4D and were overlaid on the MVF images, verifying whether the target with residual motion is adequately covered during the gated delivery. Appropriate actions can be initiated should the verification fail. Results: The software tool can effectively and accurately register MVF images with DRRs. The MVF images acquired with a dose as low as 1 cGy were adequate for the registration. In addition, the registration can be performed between the averaged MVF frame of all frames acquired within gating window and the corresponding DRR, further reducing dose required. The accuracy of registration can be better than 3 mm. The entire process is fast. Conclusion: MVF achieves adequate image quality at a low dose. It is practically feasible to use the software tool with MVF for real‐time (prior or during) treatment verification of 4D/gated radiation delivery.

Conflict of Interest: This work is sponsored in part by Siemens OCS.
SU‐FF‐J‐31: Comparison of Image Registration Tools Used for Daily KV Imaging‐Based Patient Set‐Up
Authors: Lindsay P , Choi B , Bucci M , Zhang L , Dong L , Kudchadker R , Zhu X , Balter P
Published: July 2007

Purpose: To assess daily set‐up of thoracic patients, based on kV images and kV cone‐beam CT (CBCT), and to compare different tools for analysis of kV images. Method and Materials: Nine thoracic patients who had daily kV imaging as a part of their routine treatment were evaluated. A total of 205 images (18–26 images per patient) were available for analysis. Patients were set up daily to skin marks, and orthogonal kV images were acquired. Shifts used for patient treatment were determined by side‐by‐side visual inspection of images in a commercial R&V system. Weekly CBCT images were obtained, and patient alignment was done using an in‐house 3D‐3D rigid registration tool. All images were retrospectively analyzed by a single observer using in‐house 2D‐3D image registration tools. In this software, split windows and shifting of the reference image were used to determine the shifts. Results: The standard deviation of the shifts actually made, for all 9 patients, were 3.8, 4.5, and 4.6 mm (L/R, S/I and A/P respectively). The standard deviation of the differences between actual shifts and those obtained retrospectively by manual 2D‐3D matching were 2.7, 3.0, and 2.7 mm (L/R, S/I and A/P respectively). The standard deviation of the differences between manual kV shifts and CBCT were 2.3, 2.5, and 1.5 mm (L/R, S/I and A/P respectively). The largest systematic difference observed was between manual 2D‐3D and CBCT shifts (1.0 mm in the A/P direction). Conclusion: This study demonstrates that PTV margins are non‐zero and need to be determined even when using daily kV imaging. The differences between different manual methods of evaluating daily patient images are smaller than the actual shifts made, but still substantial. Reduction of this variation, through use of better tools, training, or improvements in image quality, may improve patient set‐up and allow for further margin reduction.
SU‐FF‐J‐33: Image Guided Radiotherapy in Prostate Localization: A Comparison of Ultrasound Modalities to Implanted Seed Markers and Assessment of Intrafractional Prostate Motion
Authors: Weyers B , Wu C , Goddu S , Michalski J
Published: July 2007

Purpose: To compare 2D (BAT) and 3D (IBeam) ultrasounds with seed markers (SM) for prostate localization, and to assess intrafractional prostate motion during external beam radiotherapy (EBRT). Method and Materials: Prior to daily prostate localization with SM, patients underwent localization with two ultrasound systems for one week and with one ultrasound system for remaining treatments. Ultrasound shifts were prospectively recorded and patients were shifted as per SM alignment. The differences in lateral (LR), craniocaudal (CC) and anterior‐posterior (AP) directions were compared assuming SM revealed the true position of the prostate. Intrafraction motion of the prostate was assessed by repeating the SM after EBRT treatment on four fractions. Results: From 20 patients, 455 I‐Beam and 343 BAT ultrasound scans were compared to SM localizations. I‐Beam had a mean error ± sd of 0.6±3.3mm in the LR direction, 2.2±4.8mm (CC) and 0.2±3.8mm (AP). BAT had a mean error ± sd of 0.0±3.8mm (LR), 0.8±4.5mm (CC), and −1.5±4.3mm (AP). Deviations >5mm occurred in 11%, 32% and 18% in the LR, CC and AP directions respectively for I‐Beam, and 11%, 24% and 23% respectively for BAT. Deviations >1cm occurred in 7% in the CC direction for I‐Beam. Intrafraction prostate motion is minimal with a mean displacement ⩽1.5mm. The greatest movement is in the AP direction with 4% of patients having >5mm displacement. Conclusion: Target localization with two US systems provide different results than SM localization. Our data suggest that PTV margin guidelines for BAT and I‐Beam should be greater than those for SM. The US margin requirements may also need to be greater than if no daily localization is performed. In addition, intrafractional prostate motion is minimal with large displacements occurring in <5% of patients. We have adopted seed markers for daily prostate localization at our institution.
SU‐FF‐J‐34: Influence of Volumes of Prostate, Rectum and Bladder On Treatment Planning CT‐Day On Inter‐Fraction Motion of Prostate During BAT Image‐Guided IMRT
Authors: Reddy N , Nori D , Sartin W , Maiorano S , Modena J , Mazur A , Osian A , Sood B , Ravi A , Sampath S
Published: July 2007

Purpose: To study the relationship between prostate volume/location, bladder and rectum volumes on treatment‐planning CT‐day and prostate shift in XYZ directions on treatment‐days. Method and Materials: Prostate, SV, bladder and rectum (rectosigmoid‐flexure to anorectal‐verge), were contoured on CT‐images. Isocenter was 6 cm posterior to the tip of pubic‐arch and 1 cm inferior to the pubic‐brim. IMRT plans were prepared. Contours were exported to BAT‐system. Patients were positioned on couch using skin marks. US‐probe was used to obtain US‐images of prostate, bladder and rectum and aligned with CT‐images. Shifts in XYZ directions as recommended by BAT‐system were made and recorded. 4698 couch‐shifts for 42 patients were analyzed to study a correlation between prostate shifts vs. bladder and rectum volumes and prostate volume/location on CT‐day. Spatial location of prostate was defined as distance of prostate base to isocenter. Dose to 50% of bladder vs. volume was also studied. Pearson's correlation coefficient r, and P values were used for statistical analysis. Results: Mean and range of volumes (cc): bladder: 179, 42–582, rectum: 108, 28–223 and prostate: 55, 21–154. Mean prostate shifts (cm, ±SD): R/L (X): −0.047±0.16, AP/PA (Y): 0.14±0.3 and S/I (Z): 0.19±0.26. Lateral, AP/PA and S/I shifts were not correlated with volumes of bladder, rectum and prostate; bladder and prostate; and bladder and rectum, (P>0.2), respectively. Smaller the rectal volume (P<0.001) or diameter (P<0.05) of rectum, larger was the anterior shift and vice‐versa. Smaller the prostate base distance to isocenter or volume, larger was superior shift and vice‐versa (P<0.05). Dose to bladder decreased with increase in volume up to 300cc, reaching a plateau with further increase in volume (P<0.001). Conclusions: Prostate location/volume and rectal‐volume, but not bladder‐volume on CT‐day influence prostate position. Bladder with 200–300cc volume, but not full bladder, would be optimum for patient comfort, minimizing bladder dose and US‐image quality.
SU‐FF‐J‐47: A Feasibility Study Using a CCD‐Based EPID for Digital Tomosynthesis
Authors: Sarkar V , Shi C , Rassiah‐Szegedi P , Stathakis S , Papanikolaou N
Published: July 2007

Purpose: To investigate the feasibility of using digital tomosynthesis to extract volume data from images produced by a CCD‐based electronic portal imaging device (EPID). Method and Materials: A simple phantom geometry was created by placing several contrasting material amongst layers of 1cm thick bolus. Nine images of the phantom were acquired using the CCD‐based EPID mounted on a Varian 2100 C/D linear accelerator. Images were taken from 340° to 20° in 5° steps using 1 MU per image. A more realistic case using a humanoid phantom and implantable tumor makers was investigated. The acquired data was post‐processed using a shift‐and‐add algorithm implemented in an in‐house developed software. The processing of the images allows the reconstruction of coronal slices at various depths in the phantom for positional verification. Results: The results from the reconstructed digital tomosynthesis images in the bolus phantom demonstrate that the objects at the plane of the tomosynthesis are in focus while other structures that were out of plane were blurred. Reconstructed images using implantable tumor markers in an anthropomorphic phantom were comparable to the ones reconstructed by a treatment planning system from megavoltage CT data. Conclusion: While structures not on the reconstructed plane are not completely taken out of the image, they are blurred enough that it is obvious whether they are on the reconstructed level or not. The results obtained from this experiment confirm the viability of using this low‐dose technique to obtain CT‐quality planar images that can be used for patient positioning and daily target localization.
SU‐FF‐J‐53: Evaluation of Image‐Guidance Strategies in the Treatment of Localized Prostate Cancers
Authors: Lee C , Kupelian P , Langen K , Zeidan O , Meeks S
Published: July 2007

Purpose: To compare different image‐guidance (IG) strategies in the alignment of prostate cancer patients. Using data from patients that were treated with daily IG, the remaining set‐up errors for several different strategies were retrospectively calculated. Method and Materials: Alignment data from 74 patients treated with helical tomotherapy were analyzed, resulting in a dataset of 2252 fractions during which a megavoltage CT image was used for image‐guidance. Given the daily positional adjustments, a variety of protocols differing in imaging frequency and methodology were studied retrospectively. The residual set‐up errors on days imaging would not have been performed were determined for each protocol. Results: As expected, systematic errors were effectively reduced with increasing imaging frequency. However, the random errors were unaffected. Even when image guidance was performed every other day with a running mean of the prior displacements, residual set‐up errors exceeding 5 mm occurred in 24% of instances. This frequency increases to about 40% if setup errors larger than 3 mm are scored. Conclusion: Set‐up errors increased with decreasing frequency of image guidance. However, residual errors are still significant even at the 5 mm level if the patient is imaged every other day. This suggests that it is beneficial to use daily IG in the set up of prostate cancer patients during a course of external beam radiotherapy. Conflict of Interest: This study was funded in part by TomoTherapy Inc., Madison, WI.
SU‐FF‐J‐56: Patient Dose From Kilo‐Voltage Cone Beam Computed Tomography (kV‐CBCT) Imaging
Authors: Li F , Yang Y , Heron D , Chen H , Komanduri K , Saw C , Huq M
Published: July 2007

Purpose: To investigate patient dose from on‐board imager‐based kV‐CBCT. Method and Materials: Radiation doses from kV‐CBCT were measured using TLDs at different locations in three anthropomorphic‐phantoms (H&N, chest and pelvis) and patients retrospectively. kV‐CBCT scans were performed in standard settings (125 kV, 80 mA and 25 ms) using a Varian Trilogy linear accelerator. Both full‐fan (FOV=24 cm) and half‐fan (FOV=40 cm) modes were evaluated for H&N case while only half‐fan (FOV=45 cm) technique was studied for chest and pelvic cases. The skin dose in both phantoms and patients were measured at 4 locations: anterior, posterior, Rt‐Lat, and Lt‐Lat. Doses measured in the phantoms included different critical organs. The dosimeters used were high sensitivity TLD‐100H and only those with standard‐deviations less than 3% and sensitivity within ±3% were selected for this study. Each TLD was individually calibrated using an ion chamber under the irradiation condition. Phantom data was averaged from 3 separate measurements and patient data was averaged from 5 measurements in each category. Results: The skin dose for H&N cases were 9–10cGy for half‐fan mode in both the phantom and patients. The dose for brain and brainstem were 7.1cGy and 7.6cGy, respectively. The doses in same locations were 2–3cGy lower if the full‐fan mode is used. The skin dose for chest cases was 8–10cGy and were same for the phantom and patient measurements. Measured mean lung dose was 8.5cGy and spinal cord dose was 6.2cGy. For pelvis, measured skin dose was 2.9–4.2cGy and the prostate and rectum dose were 2.9cGy. Conclusions: For pelvic cases, kV‐CBCT dose was comparable or less than that from portal imaging. For chest and H&N cases the dose can be two times higher than that for the pelvis cases. Daily CBCT may lead to extra 400cGy to skin and 250cGy to spinal cord in 40 fractions.
SU‐FF‐J‐59: Evaluation of Daily Tumor Localization Shifts in the H&N Region Based On Bony Anatomy and Soft‐Tissue Implanted Markers
Authors: Zeidan O , Kupelian P , Langen K , Manon R , Meeks S
Published: July 2007

Purpose: To evaluate tumor localization in H&N patients with implanted markers based on co‐registered MVCT and KVCT images using bony anatomy and marker‐based alignments Method and Materials: Daily MVCT images from a tomotherapy unit were acquired for a total of 35 fractions for a patient with two implanted gold markers in the base of tongue. The MVCT and KVCT image sets were retrospectively aligned (MVCT with respect to KVCT) based on two alignment criteria: (1) marker‐based alignment. (2) Alignment to the cervical vertebral bony anatomy. Shifts from each alignment method were recorded and analyzed. Results: We found insignificant inter‐marker distance variation or migration through the course of treatment. Relative shifts (differences between bony anatomy and marker‐based shifts) in the vertical and lateral directions between the two methods yielded a maximum of 7 mm (in one direction). A histogram of the relative shifts showed that ∼14% of the relative shifts in the vertical direction and ∼ 43% of the relative shifts in the lateral direction differ by more than 3mm. There was no obvious temporal trend in the daily shifts throughout the course of treatment. However, the data shows that the standard deviation of the shifts based on markers is nearly twice that of bony anatomy based shifts, indicating more interfraction positional variability with respect to the CT planning images. Conclusion: Daily MVCT imaging for a base‐of‐tongue cancer patient revealed significant difference in tumor localization between marker‐based and bony‐based registration with KVCT in the H&N. Dosimetric evaluation of these two localization methods is necessary to determine the most clinically beneficial alignment approach. Conflict of Interest: Our group holds a research grant from TomoTherapy, Inc.
SU‐FF‐J‐61: Inter‐Observer Image Quality Analysis of Megavoltage Cone Beam‐CT Versus Megavoltage Fan Beam‐CT
Authors: Meadows J , Bichay T , Chen C , Schippers D
Published: July 2007

Purpose: Use of strict scoring criteria to study the inter‐observer variability of image quality between megavoltage cone‐beam cat scan (MV CBCT) and megavoltage helical fan‐beam computed tomography (TomoTherapy). Method and Materials: A Siemens MVCB QA phantom was utilized for all image acquisitions. Sections 2 and 4 of this phantom contain low contrast objects, and section 3 contains a line pair array for spatial resolution determination. The phantom was imaged on a 20‐slice Siemens SOMATOM® Sensation Open (CT‐Sim) as the “gold standard” for image quality. The phantom was also imaged on a TomoTherapy machine utilizing the three available imaging modes of fine, normal, and coarse. The imaging was repeated on a Siemens OnCor Avant‐Garde linear accelerator utilizing the MVCB‐CT option. Five observers were asked to score each image modality. A scoring scheme and rules were developed to allow all of the observers to use the same criteria to judge these image attributes. Each image was processed using a constant region of interest (ROI) and fixed window and level to reduce scoring bias. Results: The outcome was consistent among the observers concerning spatial resolution. There was a decrease in perceived resolution in the z‐axis compared to the x‐y directions for all three imaging units The Siemens MVCB scored higher compared to TomoTherapy in the z‐axis, but scored lower in the x‐y plane. The observer scoring for low contrast detection was most consistent in the phantom containing high‐density objects (1.56–1.02 g/cc) compared to lower density (1.09–1.02 g/cc). A comparison was made between low contrast scoring and quantitative contrast ratio. Conclusion: The results show consistent scoring of image spatial resolution by multiple observers regardless of modality. The largest variation occurred when scoring the lowest density objects. A noticeable trend was established between contrast ratio and observer scoring. Conflict of Interest: Partially supported by Siemens.
SU‐FF‐J‐67: Tomotherapy MVXCT Numbers Versus RLSP for Various Ions and Materials
Authors: Moyers M , Sun S , Sardesai M , Rightnar S , Sharma A , Rusek A , Sivertz M
Published: July 2007

Purpose: Optimization of ion radiotherapy and spacecraft shielding is critically dependent upon the relative linear stopping power (RLSP) of each material through which an ion would pass. In radiotherapy, RLSPs for patient tissues are usually obtained by converting kilovoltage x ray computed tomography (KVXCT) numbers; however, some registration and immobilization devices, implant materials, and dosimetry phantoms do not lie on the standard KVXCT number to RLSP conversion curve. KVXCT imaging is also prone to artifacts created by high atomic number and density materials. Ion computed tomography (ICT) could reduce these problems but these systems currently exist only in the research stage and, for abdominal scanning, would require energies and field sizes greater than available with current therapy accelerators and beam delivery systems. Megavoltage x ray computed tomography (MVXCT) may offer an alternative imaging scheme. Methods and Materials: The RLSPs for twenty‐two materials were measured using a parallel plate ionization chamber and scanning water phantom in proton, carbon ion, and iron ion beams. These same materials were scanned using both KVXCT and MVXCT. Results and Discussion: The MVXCT versus RLSP functions for the three ions were almost identical. The functions were approximately bi‐linear but the change in slope was smaller than for the KVXCT curves and deviations between measured and fit data were smaller. Conclusions: An MVXCT number to ion RLSP conversion function has been generated for use in treatment planning. Although the function does not account for the effect of ion nuclear interactions, MVXCT numbers can be used to predict the range of ions and may serve as an intermediate step until ICT is developed. Experiments may now be performed to compare KVXCT and MVXCT based treatment planning in the presence of artifacts and non‐tissue like materials.

This work was partially supported by NASA grant NAG‐1943 and NMTB grant DAMD17‐97‐2‐7016.
SU‐FF‐J‐68: Dosimetric Comparison of Patient‐Specific Margins Vs. Uniform Margins for Prostate IMRT Treatments
Authors: Yoo S , Das S , Kim S , Koontz B , Lee W , Light K , Yin F
Published: July 2007

Purpose: To evaluate the dosimetric improvement of IMRT treatment plans generated with patient‐specific margins compared to uniform margins for prostate cancer patients. Methods and Materials: For 13 prostate cancer patients who underwent IMRT treatment, daily cone‐beam computed tomography (CBCT) scans were acquired during the first week, followed by weekly scans (total of 85 scans) for the remainder of the treatment. Both prostate and seminal vesicles were retrospectively segmented on all CBCTs. The patient‐specific planning target volume (PTVPS) was defined based on a composite volume of both prostate and seminal vesicles from the first four daily CBCTs and the planning CT. A 3‐mm margin was added around the composite volume to obtain PTVPS. As a comparison, we also generated a PTV in the planning CT with a uniform margin (PTVUni) of 10‐mm in all directions, except 5‐mm posteriorly, around the prostate and seminal vesicles. An IMRT plan for each PTV was generated for each patient. Evaluation plans based on each of weekly CBCT were generated to gauge the DVHs resulting from these IMRT plans to the patient volumes segmented on weekly CBCTs. Results: Evaluation plans generated with PTVPS in place of PTVUni resulted in average improvements of 1.4% and 2.8% for V95 of prostate and seminal vesicles, respectively, and average reduction of 7.0% and 4.7% for V50 of bladder and rectum, respectively. Out of 85 weekly CBCT evaluation plans for each PTV, 7.1% of cases showed improvement for V95 of prostate with PTVUni, 40.0% for V95 of seminal vesicles, 28.2% for V50 of bladder and 29.4% for V50 of rectum. Conclusions: Patient‐specific margins, designed using multiple scans, appear to provide little dosimetric benefit with respect to target coverage over a standard uniform margin formulation; sparing critical structures is improved to a greater degree.

“Partially supported by Varian Medical Systems”.
SU‐FF‐J‐130: PET Free Breathing Motion Artifact Reduction Using List‐Mode Data
Authors: Zhao T , Parikh P , Hubenschmidt J , Mutic S , Dempsey J , Malinowski K , Bradley J , Low D
Published: July 2007

Purpose: To show feasibility of a method for acquiring free‐breathing thoracic PET images without breathing motion artifacts but with full statistics. Method: Data were collected using a Philips Brilliance and Siemens Biograph PET/CT scanners using list mode. Patient‐modeled tumor trajectories were provided using a custom‐fabricated 4D motion phantom. To synchronize the phantom and PET acquisition, a TTL synchronization signal was fed to the cardiac trigger channel. The trigger was activated when the phantom passed a user‐determined spatial threshold and therefore provided an irregular but well‐determined time pattern. The list mode was queried to determine the relative time of the cardiac triggers and this was used to synchronize the phantom position and the list mode data. The known phantom positions were subdivided into 10 bins of 8 mm width. PET events were selected from the list mode file according to which bin the phantom was in at the time of the PET event. This created 10 separate list mode files. Those list mode files were submitted to the commercial reconstruction software to reconstruct images using only events occurring in the corresponding bins. The reconstruction images were shifted by the known phantom displacement and summed. The subsequent image was compared against the known phantom shape to determine if the reconstruction was successful. Results: The gated reconstructions were compared against the ungated (original list mode file) reconstructions, showing significant improvement in the reconstructed phantom shape. Residual deformation was noted, consistent with the 8 mm wide gating window. Conclusions: This method suggests that the list‐mode based respiratory gating is feasible and may provide an effective method in eliminating the artifacts caused by breathing motion from PET images. The process should be supported by modern multislice PET/CT scanners. This work supported in part by NIH R01CA96679.
SU‐FF‐J‐132: A Novel Technique for Closed‐Loop Feedback Real‐Time Tracking by Controlling Dose Rate : A Parametric Study
Authors: Han‐Oh Y , Yi B , Lerma F , Berman B , Yu C
Published: July 2007

Purpose: We have developed a new technique called dose‐rate‐modulated tracking (DRMT) for closed‐feedback real‐time tumor tracking by changing the dose rate. Method and Materials: DRMT uses pre‐programmed MLC sequences that are generated using measured data for tumor motion obtained at an earlier time. Since the leaves move, their positions are programmed with schedules that are a function of the accumulated dose. The leaf trajectory on the time axis then can be changed during treatment by changing the dose rate. DRMT changes the dose rate to minimize the discrepancy between the scheduled MLC position and the target position or breathing signal on the day of treatment. If the monitored breathing is slower than that observed at simulation, the dose rate is lowered to slow down the movement of the MLC and vice versa, thereby maintaining synchrony. DRMT tumor‐tracking power was tested with sinusoidalbreathing functions and patient‐breathing signals (RPM, Varian). The tracking error (2σ) for each breathing signal was derived as a function of the system reaction time and the dose‐rate correction period. Results and Conclusions: DRMT simulation showed that for the sinusoidal‐breathing signal with 2‐cm peak‐to‐peak tumor motion, less than 0.2 cm tracking error was obtained if the system can react to a detected mismatch in less than 0.3 s and the dose rate can be adjusted in 0.36 s. Fourteen out of 26 patients were eligible for DRMT. The selection criteria were: (1) peak‐to‐peak breathing motion greater than 0.5 cm and (2) amplitude variation less than 20 % during the DRMT simulation. The tracking error for the patient data is expressed as a percentage of the motion amplitude. A tracking error of less than 20 % was achieved for 13 out of the 14 patients if the system can respond in 0 s.
SU‐FF‐P‐01: Brachytherapy Source Disposal: Survey of Available Services
Authors: McUmber A , Rudin S , Bednarek D
Published: July 2007

Purpose: To review the required procedures involving the disposal of unneeded brachytherapy sealed sources and present selection criteria with a survey of available services. Method and Materials: A total of 663 mCi of unneeded Cs‐137 in 25 sealed tube sources ranging from 7–42 mCi were required by the state regulatory agency to be removed from hospital inventory. An analysis of all steps needed for removal, packaging, and transportation of the sources to a qualified disposal site was undertaken. Criteria for selecting a commercial service were developed, including previous experience, references, insurance coverage, cost, adequate licensing, shipment design, transportation details, leak testing, and safety procedures. Results: Seven commercial brokers that were considered consisted of two general types: those with associated couriers, but unable to handle the individual sources, and those with a third‐party express shipper, though able to handle the sources during packaging. Experience varied from 2–40 years and cost varied from $5K – $22K. While all would provide copies of licenses, insurance certificates, and references, experience with medical sources, details of handling, transport, and possession transfer differed. A review of the transport and labeling regulations governing radioactive materials was made, including DOT specifications for shipping containers. A legal distinction between title transfer and possession transfer is also discussed. Finally, a calculation is made to verify the lead thickness of tube‐source containers proposed by the brokers. Conclusion: A wide range of disposal services is available, with varying abilities of vendors to transfer the sources into the shipping cask and transport them. Surprisingly, those with accompanying courier services did not offer source handling assistance, while those using a third party express shipper would provide this. No correlation between price and transportation methods was observed. Though each company was insured, an apparent lack of concern regarding shipment security was noted.
SU‐FF‐P‐03: Lessons Learned From Hurricane Katrina
Authors: Sanford R
Published: July 2007

Purpose: To outline the lessons taught by Hurricane Katrina during the evacuation, cleanup, and rebuilding phases of a radiation oncology center in the hope that others may benefit from our experiences in formulating their own disaster and recovery plans. Method and Materials: Hurricane Katrina flooded 80% of the city of New Orleans including our radiation oncology department. Procedures developed prior to the storm to ensure communication among staff and patients, to minimize loss of patient and physics/dosimetry data, and to expedite recovery were put to the test. Results: Several unexpected situations arose during the evacuation, cleanup, and rebuilding phases: cell phone service was interrupted for several weeks and hospital email servers were down for months; most surviving patient and physics data were found to be remote electronic backups; securing of radioisotope sources was hampered by the loss of safe keys and the lack of functioning elevators; many patients were unable to relate their diagnoses and treatment histories to their new care providers; further equipment and data loss occurred after the primary catastrophe; vender maintenance agreements greatly decreased replacement costs of replacement computer systems; the pace of rebuilding was slowed by external influences; and extra training was required after the long closure. Conclusion: Even the most careful planning cannot account for the unexpected. But because of careful planning, both pre‐ and post‐Katrina, our flooded radiation oncology department reopened in November 2006 and remains the only flooded radiation facility to do so 18+ months after Katrina. Most of the unforeseen situations encountered can now be planned for in future disaster and recovery plans.
SU‐FF‐P‐08: Oversight Protocols in the Management of Network of Facility Sites
Authors: Saw C , Combine T , Ottino F , Quader M , Tao L , Bose S , Chen H , Huq M , Heron D
Published: July 2007

Purpose: The management of quality for a network of facility sites poses challenges for an institution. Holding regular meetings, auditing treatment facilities, and requests for documentation are some mechanisms for providing clinical and quality oversights. This presentation discusses our institution protocols in recent auditing of second dosimetric checks and request for RPC‐TLD report for analysis. Methods and Materials: Our institution consists of an integrated network of 20 community (“spoke”) and academic facilities and spread about 150 miles radius from our downtown proper (“hub”). An average of 650 external beam patients are treated daily. With the diversity amongst the facilities, a common set of standards are essential to establishing quality across the facilities. This presentation examined two protocols for this Purpose: auditing second dosimetric checks and request for RPC‐TLD reports. The established protocol recommended second dosimetric checks be performed prior to the third fraction following the start of each new treatment field or field modification consistent with AAPM TG‐40 recommendation. Ten patient treatment records were randomly selected for evaluation by six auditors quarterly. The second protocol requires all RPC‐TLD reports be forwarded to the Office of Medical Physics for analysis and reporting annually. Results: Although the non‐compliance for second dosimetric checks of patient treatment records was low, there was a trend towards non‐compliance at selective facilities. RPC‐TLD analysis showed a bell‐shape curve with the median at 0.98 for the ratio of RPC measurement to institutional stated dose values. Facilities whose dose values are outside ±5% have to repeat measurements. Conclusion: Quality oversight protocols are essential to set standards of performance for institutions having a network of facilities. Establishing oversight protocols will pose challenges for any institution and two examples are given in this presentation, where data are collected by different means.
SU‐FF‐T‐02: In Vitro Validation of Temporal Optimization Effects On Cell Survival for a Single Fraction of Radiation
Authors: Altman M , Stinauer M , Chmura S , Smith B , Aydogan B , Pelizzari C , Roeske J
Published: July 2007

Purpose: To experimentally validate how temporal modification of the applied dose pattern within a single fraction of radiation therapy affects cell survival. Method and Materials: The linear quadratic (LQ) repair‐time model predicts that, for a single fraction of dose, the degree of cell kill is dependent on the pattern of dose applied over a period of irradiation. Previously, we demonstrated that: (1) maximum cell kill is achieved using a “triangular” temporal dose pattern (delivering the highest doses during the middle of a fraction and the lowest at the beginning and end), and (2) minimum cell kill is achieved with a “V‐shaped” pattern (delivering the lowest doses at the middle of a fraction and the highest at the beginning and end). Furthermore, the model also predicted that cells with low α/β values will have a larger difference in survival based on the applied pattern of dose. Two cells lines with low α/β values (PC‐3, WiDr) and one with a high α/β value (SQ‐20b) were chosen for this study. For each cell line, one group of cells in a six‐well plate received 9 Gy in a triangular dose pattern, and the same dose was delivered to a second plate using a V‐shaped pattern. The delivery time for each dose pattern was 20 min. Cell survival was assessed using a clonogenic assay. Results: For the SQ‐20b cells, irradiation with both dose patterns resulted in only a 4.5% relative difference in cell survival (p>0.25). However, the triangle and V‐shaped patterns resulted in relative cell survival differences of 15.2% and 18.6% for both the PC‐3 (p<0.025) and WiDr (p<0.01) cell lines, respectively. Conclusion: These results verify the assertions of the modeling study in vitro, and imply that the temporal pattern of applied dose is another variable to be considered in treatment planning and delivery.
SU‐FF‐T‐07: A Comparative Analysis Between Conventional MLC Based and Solid Compensator Based IMRT Treatment Techniques. A Clinical Review After 5 Years
Authors: Khadija M , Parsai E , Feldmeier J
Published: July 2007

Purpose: The goals of this study were to evaluate the clinical differences of solid and MLC based IMRT treatments. Dosimetric comparison of the dose outside the target volume at various depths was carried out. The investigation was extended to compare delivery time and monitor unit requirements for IMRT techniques. Methods and Material: The ADAC Pinnacle inverse planning system was used to generate MLC based IMRT plans. Using .decimal software, ADAC was also used to generate compensator based IMRT plans. Plans were generated for the following target volumes, prostate, adrenal gland, brain, and head and neck. The delivery time, number of monitor units and the fluence intensity maps were compared. Dose points outside the target volume were compared to determine out of target doses. Delivery of treatment plans was performed on a Rando phantom and mosfet dosimeters, gaf chromic film and TLDs were used to compare measured doses of MLC and solid IMRT treatments. Results: For the more complex plans the solid compensators resulted in 26.7% fewer monitor units and delivery time was reduce in half when compared with MLC plans. However for relatively simple IMRT plans such as prostate boosts or adrenal gland plans were the target has a relatively simple cylindrical shape the MLC plans resulted in an average of 41.6% fewer MUs and required about 16% less time to deliver than the solid compensator plans. Mosfet skin dose analysis showed that the solid compensators resulted in an average of 17.5% less dose. Conclusions: Based on the measured results it is evident that solid compensators are a viable IMRT treatment option when considering complex target arrangements that require many beams segments. For relatively simple plans which result in fewer and larger beam segments compensator based plans showed no advantage over MLC plans in regards to MUs and treatment time.
SU‐FF‐T‐12: A Fluence‐Based Algorithm for MU Calculation of Proton Beams
Authors: Zhu TC , Li Z , Karunamuni R , Yeung D , Slopsema Roelf
Published: July 2007

Purpose: We have developed an empirical algorithm to calculate patient specific monitor unit (MU) for megavoltage proton beams. Method and Materials: The algorithm is based on a well‐established formula for proton output calculation.1 It adds additional data for a broad ranges of SSD, depth, off‐axis, snout size, and especially field size defined by the cutout. Pristine percentage depth doses (PDD) of proton beams are used to determine the SOBP PDD using the beam modulation wheel input file. This algorithm adopts the concept of proton head‐scatter factor, Hp(s,r,f), to characterize the proton fluence variation with source‐to‐detector distance (f), snout size (s), and radius of circular cutout (r), which is attributed to the proton scattering in the cyclotron nozzle, snout, and Copper inserts. Results: A new quantity PSF(r) as functions of equivalent beam radius r and depth d, are introduced to account for proton phantom scattering in a water phantom per unit incident fluence. PSF is measured as BF(r)/H(r), where BF is blocking factor measured as the ratio of dose measured in water at reference depth between a circular field with radius r and an open field, and Hp is the ratio of doses measured in air (without any buildup) using a diode detector for the same conditions. Equivalent radius for an arbitrary field can be calculated using a sector‐integration of PSF(r). PSF is independent of the snout size. Conclusion: This algorithm is ideally suitable for calculating patients‐pecific MU for Monte‐Carlo or pencil‐beam based treatment planning system for protons.
SU‐FF‐T‐13: A Generalized Biologically Equivalent Dose (gBED) Model and Its Application for Radiosurgery and Hypofractionated Body Radiotherapy
Authors: Ma L , Sahgal A , Larson D , Chuang C , Petti P , Verhey L
Published: July 2007

Purpose: Vastly different dose fractionation and dose prescription schemes exist for radiosurgery and body radiotherapy of intracranial and extracranial tumors. A generalized biological equivalent dose (gBED) model has been developed to account for variations in dose fractionations and non‐uniform dose distributions for both targets and critical structures of such treatments. Method and Materials: Assuming cell survival fraction (S) can be expressed as , we derived where of the linear‐quadratic model, and vi is the ith voxel receiving the dose of di as in the calculation of the dose volume histogram. In the above gBED formula, wi is the probability‐weighted volume unit which is analogous to the voxel mass (density×volume). As a result, we derived a new histogram by plotting accumulative BEDi versus accumulative wi and we called it Dose Unit Histogram (DUH). To study DUH model, analyses were applied to a group of >20 radiosurgery and body radiotherapy cases of varying fractionations and dose volume histograms. The dependence of gBED on α/β values (ranging from 2–20) and other physical dose parameters were also investigated. Results: The normalized DUH fell consistently below the normalized DVH curves regardless of α/β values. This indicates a decreased effect to target and increased tolerance of the normal structure. For high α/β values such as 20, gBED approached to the conventional BED calculated from the mean dose of a volume. For low values of α/β such as 2, gBED was significantly different, particularly for non‐uniform target dose distributions. Conclusion: A generalized BED formula was developed and used for radiosurgery and body radiotherapy planning analysis. The formula yielded different histogram plots from conventional DVH by accounting for the variations in dose fractionation and non‐uniformity of the dose distributions.