bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐394: Start‐Up Characteristics of Elekta SLi‐Linacs: Minimum Number of MU Required for IMRT
Authors: Steenhuijsen J
Published: July 2006

Purpose: On Elekta SLi‐linacs steering of flatness and symmetry starts after a user‐definable delay of 0.5 to 1 s after beam‐on, which equals 5 to 10 MU at 600 MU/min. The impact of start‐up characteristics of Elekta SLi linacs on dose delivery with small segments during IMRT was investigated and the minimum number of monitor units needed per segment was quantified. Method and Materials: Linearity of the ionisation monitor was quantified by taking ionisation chamber readings for 10×10 cm2 6MV and 10 MV photon beams over the range 1–200 MU. By using the Wellhöfer Beam Imaging System (BIS) dosimetric images of 820×820 pixels of the beam were acquired during the first 10 monitor units for 5 gantry angles (−180°, −90°, 0°, 90°, 180°). Every 120ms images were taken of a 40×40 cm2 field. All data are compared to the reference value after delivery of 10 MU, which is regarded to be the steady‐state value. Results: Deviations in ionisation monitor readings were less than 0.5% for segments larger than 2 MU. For segments of 1MU readings were 1.5% less than expected. Values for symmetry and flatness of the beams were very large during the first MU but decreased within 2MU to twice the steady‐state value at 10 MU. The integrated symmetry (defined as the symmetry of the integrated dose distribution) and integrated flatness decreased within 4MU to twice the steady‐state value. Neither gantry angle nor energy had influence on these results. Conclusion: During IMRT segments of 4MU can be safely used for all gantry angles. Errors in dose are smaller than 1% and errors in symmetry and flatness are less than twice that of 10 MU segments.
SU‐FF‐T‐396: Stereotactic Peripherial Brachytherapy and Image Guidance for the Breast
Authors: Rivard MJ , Bricault RJ , Melhus CS , Sioshansi P
Published: July 2006

Purpose: Breast brachytherapy may be applied peripherally without piercing the skin as currently performed with interstitial and MammoSite applications. By virtue of being a protruding and deformable organ, the breast lends itself to peripheral brachytherapy by non‐invasive applicators. A delivery system was made (Advanced Radiation Therapy, Billerica, MA) to implement this developmental treatment modality using real‐time mammographic image guidance for stereotactic applicator positioning and CTV localization. In this design, therapeutic dose to the lumpectomy cavity is delivered by externally placing opposing plaque‐like applicators at multiple orientations to provide conformity while not exceeding the skin toxicity threshold. An initial assessment of this system was performed to determine clinical feasibility. Materials & Methods: The applicator geometry comprises two curved plates which slightly compress the breast to minimize slab thickness irradiated by the parallel‐opposed plaque. Within the applicator are a series of parallel catheters spaced 1 cm apart. For a thickness of 6 cm, the breast geometry and applicators were simulated using analytical (Pinnacle3 treatment planning system) and Monte Carlo (MCNP v5) techniques. A breast phantom was used for CT‐based treatment planning; however, standard‐of‐care for brachytherapy dosimetry algorithms assume an infinite water phantom. CTV ellipsoids ranged from 2×4×4 cm3 to 3×6×6 cm3. Sources were positioned within the catheters to create a circular loading region (5 to 9 cm diam.) towards providing uniform CTV coverage. Dose homogeneity index (DHI) was determined for the skin. Results & Discussion: Average ratio of skin‐to‐tumor dose was < 0.9. Pinnacle and MCNP results indicated that DHI ∼ unity for the CTVs studied. Dose to lungs, heart, and other critical organs was typically < 2%. These simulation results suggest that this technique may be an attractive APBI option. Conflict of Interest Statement: Advanced Radiation Therapy provided the applicator used in this study.
SU‐FF‐T‐400: Supine Craniospinal Irradiation Using Electronic Portal Imaging
Authors: Heaton R , Guscott H , Lau M
Published: July 2006

Purpose: The traditional prone patient position for craniospinal irradiation [CSI] is not suitable for paediatric patients requiring anaesthetics. A new supine CSI technique was developed to implement crucial features of the prone technique—the ability to palpate the spine and pre‐treatment verification of junctions. Methods and Material: Fourteen patients have been treated using a custom treatment board, which indexes to the CT and Varian Exact™ couch. Patient were immobilized with a thermoplastic head‐and‐shoulder mask secured to the board. Three‐dimensional CT based plans were developed with the collimator of lateral opposed cranial fields rotated to match the beam divergence of the posterior spine field. The fields junction along a common line running through the mid‐sagittal plane.

The junction was confirmed using a 2 mm radio‐opaque marker placed daily on the anterior surface of patient's mask at the intersection of inferior border of cranial fields. Pre‐treatment electronic portal images of the lateral cranial and posterior spinal field borders were captured and assessed to confirm the position of the field junction, with discrepancies greater than 2.0mm corrected prior to treatment delivery. Results: This new supine CSI technique has improved patient comfort, treatment set‐up reproducibility and stability. It mirrors the prone technique in matching field junctions and maintaining the ability to palpate the spine. Standard EPI measuring tools facilitate the assessment of marker position relative to the field edge and patient anatomy. Conclusion: Supine CSI has increased patient safety through improved airway access in the event of respiratory distress. Supine positioning facilitates alternative distraction devices, such as video entertainment, reducing the need for anaesthetics in the paediatric population. The couch indexing system has allowed a more accurate monitoring of treatment set‐up, as demonstrated by a decrease in postplanning shielding modifications. The supine technique is preferred for patient comfort, precise junction match, and demonstrated reproducibility.
SU‐FF‐T‐401: Surface Dose Measurement in 6 MeV X‐Ray Beam Using Radiographic Film and TLD
Authors: Al‐Ghamdi H , Maalej N
Published: July 2006

Purpose: The purpose of this study was to estimate and compare the surface dose in 6 MV x‐ray beam using TLDs, radiographic film and parallel plate ionization chamber. Method and Materials:_ The surface dose measurements were performed in a 6 MV x‐ray beam of a medical accelerator (Varian 2100 C/D) with X‐Omat V (Ready Pack) radiographic film, LiF thermoluminescence dosimeters (TLD‐100) and parallel plate ionization chamber (PTW) for 10×10 cm field size. The film was placed perpendicular to the beam axis at the surface and at different depths of a solid water phantom, placed 100 cm from the source (SSD=100). The film was calibrated to convert optical density to dose. For TLD measurements, five TLDs were inserted in the center of 2 mm thick Perspex plate and placed at different depths in a solid water phantom. Each TLD was individually calibrated. A Parallel Plate Chamber was placed in a solid water phantom at different depths and the doses were extrapolated to estimate the surface dose. Results: The estimated surface dose with radiographic film was found 17.4% ± 3% and with the TLD technique was found 23% ± 3% relative to maximum dose. The corresponding parallel plate ionization chamber extrapolated dose was 17.8 % ± 2% relative to maximum dose. Conclusion: Radiographic film measurement of surface dose showed good agreement with the parallel plat ionization chamber in this study. With TLD‐100, the measured surface dose was higher than chamber and film measurements due to the positioning of the TLD in the phantom and the inaccuracy of the effective point of measurement.
SU‐FF‐T‐404: Techniques and Procedures Developed to Improve the Quality of Total Body Irradiation
Authors: Cai Y , Hu Z , Chu J
Published: July 2006

Purpose: Half‐standing position has been used in our clinic for Total Body Irradiation (TBI) treatment for better patient comfort and dose uniformity. Several compensation techniques and diodes calibration procedures were developed to improve the quality of total body irradiation (TBI) treatment. Methods and Materials: A frame was designed to stand on the linac couch and to hold the Cerrobend lung blocks. The blocks were mounted on a polystyrene board, which was screwed on the frame. The position of the blocks could be adjusted with the vertical movement and certain rotation of the board. It could then be fine tuned by moving the couch vertically and laterally. The source to patient's mid‐plane distance is 400 cm, and the block to patient's mid‐plane distance is 200 cm. An house‐made rice bag was used to compensate the thickness of the patient's neck, and the linac jaws were partially closed during the treatment to compensate the dose to patient's lower legs. The dose distribution was monitored by in‐vivo diodes, which were calibrated at Dmax with treatment distance. Result: Since the blocks were halfway in‐between the source and the patient's midplane, they were not heavy and their penumbra was small. It was easy for therapists to positioning the blocks. The thickness of the neck was well compensated by the rice bag, the deviation of the dose measured at the neck to the prescription was reduced from 8–9% to 2–3%. The Dmax dose measured at the prescription site was in good agreement with the calculated Dmax dose. The differences were usually within 5%. No corrections of the diode's readings were necessary for the variation of patients' separations. Conclution: The TBI technique provides a simple and efficient method to deliver high quality treatments.
SU‐FF‐T‐406: Testing of ATC Method 2 for Supporting QA of Cooperative Group Advanced Technology Clinical Trials Requiring Digital Data Submission
Authors: Bosch W , O'Leary S , Matthews J , Frouhar V , Palta J , Field G , Pho L , Purdy J
Published: July 2006

Purpose: To test the readiness of a system of software (“ATC Method 2‐v.2.3”) developed by the Resource Center for Emerging Technologies (RCET) for supporting QA of cooperative group clinical trials within the Advanced Technology QA Consortium (ATC). Method and Materials: ATC Method 2‐v.2.3 includes WebSys client and server for secure data upload/download/archiving of volumetric imaging and radiotherapy treatment planning data, a web‐based Rapid Image Viewer (RIV) tool, and web‐based tools for server administration. The software was implemented on a test server at the Image‐guided Therapy QA Center (ITC), and underwent rigorous testing by ITC personnel. Tests conducted included examination of user interface behavior, as well as systematic comparison of submitted/retrieved copies of 16 representative test data sets (in DICOM and RTOG Data Exchange format) from nine different treatment planning system vendors. Results: Evaluation tests of version 2.3 of the ATC Method 2 software identified improvements in the usability of software over the previous version, and provided general suggestions for further improvement. These tests also identified specific input that led to failure of the WebSys client, usability issues in the RIV tool, database changes needed to support case identifiers in ATC trails, and corrections needed in handling certain DICOM objects. These test results have contributed to improvements in version 2.4 of this software in preparation for its use to support clinical trials. Version 2.4 is expected to be ready for testing beginning March 2006. The National Cancer Institute of Canada (NCIC) Clinical Trials Group (CTG) will participate in the new round of testing. Conclusion: Since this software is intended to play a major role in QA of data submitted for future ATC‐supported clinical trials, rigorous testing is essential to its ongoing development. Future testing is expected to benefit from collaborative efforts of NCIC CTG.

Supported by NIH U24 Grant CA81647.
SU‐FF‐T‐407: Testing the Accuracy and Usefulness of the Portal Vision Dosimetry System for Large‐Volume and Complex‐Geometry IMRT
Authors: Nalichowski A , Rosca F , Kadam D , Zygmanski P
Published: July 2006

Purpose: To test a commercial EPID dosimetry system for the accuracy and usefulness for head&neck, whole‐pelvis, mesothelioma IMRT QA.

Materials and Methods: Portal Vision (PV) dosimetry system was configured and experimentally used as intended by the manufacturer (Varian) for 6MV 2100Ex. Additional data analysis software was developed. Collimator angle=90deg and the smallest possible SDD=105cm and were selected to maximize the functional area of the EPID. EPID responses were calculated by Eclipse and compared to the experimentally determined responses in two ways: by comparing individual images and 3D‐response reconstructions for cumulative plans (home‐built software).

To account for the PV arm sag during gantry rotation, and the need to shift the detector, raw PV images were automatically magnified and registered with calculated images. 3D‐response reconstructions for the measured and calculated images were performed by: backprojecting the images and applying attenuation and phantom scatter in a homogeneous virtual patient. Patient beam configuration and depths to isocenter were used. Results: PV dosimetry for large/complex targets is difficult and time‐consuming due to practical limitations (detector size, arm sag, manual shifting). Experimental response images show strong tongue&groove effects and elevated values outside of the field edges compared to Eclipse. Response discrepancies inside treatment fields cause (±2–3%) discrepancies in cumulative plan. Discrepancies outside of field edges cause systematic shift up to (5–7%) in cumulative plan, because fluences are split into 2–3 narrower subfields in the delivery. The observed discrepancies are consistent with but stronger than ion chamber measurements in solid water. The reason may be the small 1cm‐buildup and therefore larger PV sensitivity to MLC scatter and T&G. Conclusions: Neither MLC scatter nor T&G are modeled in Eclipse. Their contributions may be significant for large/complex IMRT due to the increased MLC blockage. PV dosimetry may capture these effects, but caution is indicated in interpretation.
SU‐FF‐T‐408: TG21 In‐Air Measurements of Elekta Gamma Knife Dose Volumes
Authors: Griffin S , DeWerd L
Published: July 2006

Purpose: To implement TG21 dosimetry protocols and in‐air measurements to determine the dose rate of fields resulting from the 18mm and 14mm helmets of an Elekta Gamma Knife (GK) unit. Methods and Materials: An air ionization chamber with a collecting volume of 0.007cm3 was used to make in‐air measurements at the physical isocenter of a GK unit. The isocenter was determined and the chamber was positioned in air using a chamber holder and laser positioning system. The dose rate to water was determined using the TG21 formulism designed for use with Co‐ 60 teletherapy machines. Only a measurement taken at the isocenter of the machine is required. Certain chamber‐specific correction factors and a chamber calibration factor are also used. The clinical dose rate is determined by Elekta from measurements taken in an 8cm radius spherical phantom. For comparison this clinical dose rate can be corrected out of phantom using tissue‐air ratios. The experimentally determined dose rate is then compared with to the corrected clinical dose rate. Results: The dose rate for the 18mm and 14mm helmets determined using TG21 is within 1% of the Elekta‐provided clinical dose rate after correction out of phantom. The dose rate was also experimentally determined for the 8mm and 4mm helmets. The experimental dose rate is low for these helmets due to the field fall off within the chamber volume. Conclusion: TG21 in‐air measurements may be performed with the GK unit providing the field size is large enough to appear as a uniform field to the ionization chamber. These measurements allow GK dosimetry to be performed with an established dosimetry protocol and without complications arising from phantom material. This will allow further developments of in‐air calibration methods appropriate for the 8mm and 4mm fields of GK units to be compared to a well established standard.
SU‐FF‐T‐409: The Computational Environment for Radiotherapy Research: New Tools for Multi‐Modality Imaging, Treatment Plan Comparisons, and Plan Evaluations
Authors: Deasy J , Khullar D , Apte A , Hope A , Alaly J , Clark V , El Naqa I , Spezi E
Published: July 2006

Purpose: CERR (a Computational Environment for Radiotherapy Research) is an open‐source Matlab‐based set of tools for conducting radiotherapy research which has been available for several years. In order to make CERR as useful as possible to radiotherapy researchers, we have added multi‐modality imaging support as we as new dosimetric and radiobiological plan review tools. Method: The existing DICOM Import tool box in CERR was upgraded with capability to import PET, MR and SPECT DICOM images. While MR and PET are single frame image sets, CERR seamlessly imports multiframe SPECT DICOM. Automated and interactive registration tools were developed. A new metric selection GUI provides user ability to select a variety of metrics and save a ‘plan evaluation set' for later use. When adding an individual metric, the user can select applicable parameters as well as information about criteria, including passing and marginal values, and priority. The metrics can then be compared on a graphical display or a report can be generated which lists passed/marginal/failed for all criteria and displays a score for each dose distribution. Several new dose comparison tools have been added, including: (1) side‐by‐side dose comparison views, (2) dose subtraction views for up to three dose distributions compared to a reference distribution, and (3) a 3‐D slicer view which paints differences on coordinate system or transparent anatomic structure surfaces. Results: CERR continues to undergo continuous development to provide a wide range of tools for image‐guided research. The latest release can be downloaded from www.radium.wustl.edu/cerr. CERR can be used freely only for research work. Conclusions: New CERR tools can facilitate research in adaptive and 4‐D treatment planning.

This research was partially supported by NIH grant CA85181 and a grant from TomoTherapy, Inc.
SU‐FF‐T‐410: The Credentialing Process for the NSABP B‐39/RTOG 0413 Partial Breast Irradiation Trial
Authors: Lowenstein J , Davis C , Roll J , Harris I , Hall F , Followill D , Ibbott G
Published: July 2006

Purpose: Develop a credentialing process for the NSABP B‐39/RTOG 0413 Partial Breast Irradiation (PBI) trial. Method: NSABP B‐39/RTOG 0413, a Phase III trial comparing whole breast irradiation versus PBI (3D conformal radiation therapy (3D‐CRT), MammoSite® and multi‐catheter brachytherapy). For each PBI technique, an institution, radiation oncologist and physicist team must be credentialed. The credentialing verifies that all personnel involved with treatment planning have read the protocol prior to enrolling patients to limit the number of deviations. Credentialing also allows feedback to the team prior to patient treatment to correct any mistakes. Each institution must complete online the knowledge assessment and facility questionnaires and download a PBI technique CT benchmark case. Results: Teams at 308 distinct institutions have submitted applications for credentialing for at least one PBI technique. 733 radiation oncologists applied for 3D‐CRT credentialing, 490 radiation oncologists for MammoSite® and 151 radiation oncologists for multicatheter. Of those applications, 79% became credentialed for 3D‐CRT, 69% for MammoSite®, and 56% for multi‐catheter. Reasons for which a radiation oncologist failed to become credentialed included; incomplete application, incorrect answers on knowledge assessment, treatment planning system could not submit data electronically, and the CT benchmark was not planned per protocol. The first patient enrolled by each institution received a rapid review prior to patient treatment. The next 4 cases received a timely review. These reviews included a dosimetric and clinical review. Currently, this protocol has accrued 880 patients, of which 328 treated with 3D‐CRT, 82 treated with MammoSite, and 31 treated with multi‐catheter brachytherapy. Of the 441 patients treated to date on the PBI arm there have been no dosimetric deviations. Conclusion: The PBI credentialing process has been successful in educating participating facilities and helping to minimize dosimetry errors.

Work was supported by PHS grants CA10953 and CA081647 awarded by NCI.
SU‐FF‐T‐415: The Effect of MLC Geometry On Monte Carlo Simulated Beam Output for IMRT
Authors: Lin T , Fan J , Li J , Chen Z , Luo W , Ma C
Published: July 2006

Purpose: This work studies the effect of detailed multileaf collimator (MLC) geometry on beam output for small MLC segments in Monte Carlo dose calculation for IMRT planning and quality assurance. Method and Materials: An analytical examination of the geometrical structures between the linac extrafocal source and the isocenter plane was evaluated. The main source, a small extended source, can contribute almost the same to every point at the isocenter plane while the extrafocal source, at the level of the flattening filter, may be partially blocked by the MLC leaves. The Siemens MLC geometry, with 7.7cm thick leaves was used to investigate the blocking effect. The flattening filter is 18.3cm above the MLC and the isocenter is 64 cm away from the MLC. The Monte Carlo method is an accurate method to predict the deliver doses to the patient; however, the beam output variation due to the detailed MLC geometry may introduce uncertainties in the Monte Carlo dose calculation. Results: A 1×1 cm opening at the isocenter plane 2.5cm away from the central axis can project a 0.24×0.33 cm area on the secondary source plane. While in Monte Carlo calculations, a 0.33×0.33 cm area is used. In order to precisely predict the effect of MLC blockage on beam output, a multiple Gaussian source at the secondary source plane (S. Jiang et al, Med. Phys. 28, 55, 2001) was used in this work. The integral scatter contribution from the real case differs from that used in Monte Carlo calculation by about 1.0%. This means the Monte Carlo method will predict a 1.0 % higher accumulated dose due to the overestimation of the exstrafocal source. Conclusion: Small (1–2%) uncertainties on the IMRT dose distribution calculated by the Monto Carlo method are predicted using reconstructed intensity maps rather than using detailed MLC geometry.
SU‐FF‐T‐417: The Effect of Target Volume Depth On Surface Dose for Inverse Planned IMRT Treatments of Head and Neck Cancers
Authors: Parker W , Poli E , Evans M , Campos L Lucente , Podgorsak E
Published: July 2006

Introduction: This work evaluates the surface dose as a function of PTV proximity to the surface for inverse planned head‐and‐neck IMRT patients and compares the results to measurements performed for a conventional treatment technique. Methods and Materials: An anthropomorphic phantom was CT scanned in the supine treatment position with thermoplastic mask immobilization covering the entire head‐and‐neck excluding the supra‐clavicular region. A CTV including the cervical, low neck, and supra‐clavicular lymph nodes, as well a 5 mm margin was outlined. Inverse IMRT plans were generated using a 7 field coplanar technique with 6 MV photons. Plans were created for PTVs defined at 0, 5, and, 10 mm depth from the phantom surface (PTVskin, PTV5, PTV10). The treatments were delivered using a dynamic multileaf collimator sliding window technique. Measurements at up to 8 locations on the surface of the phantom and at 2 locations near the center of the PTVs were performed using TLD and MOSFET dosimeters. Results were compared to measurements performed for a conventional 3‐field geometry (opposed laterals and anterior supra‐clavicular field planned to cover the PTVskin). Results: and Discussion: The average surface dose for the IMRT plans in the neck region was measured to be 59%, 78%, and 92% of the prescription dose for the PTV10, PTV5, and PTVskin plans respectively, and likewise, 53%, 55%, and 73%, respectively in the supra‐clavicular region. Average surface doses from the conventional field arrangement were measured to be 100% and 36% of the prescription dose for the neck and supra‐clavicular region respectively. Conclusion: For the IMRT plans the surface dose increased as a function of the PTV proximity to the surface. For an equivalent prescription dose, the conventional 3‐field technique yielded a higher average skin dose in the neck region and lower dose in the supraclavicular region in comparison with the IMRT plans.
SU‐FF‐T‐428: The Use of a Commercial QA Device for Daily Output Check of a Helical Tomotherapy Unit
Authors: Alaei P , Hui S , Higgins P , Gerbi B
Published: July 2006

Helical tomotherapy radiation therapy units, due to their particular design and differences from a traditional linear accelerator, require different procedures by which to perform routine quality assurance (QA). One of the principal QA tasks that should be performed daily on any radiation therapy equipment is the output constancy check. The daily output check on a Hi‐ Art TomoTherapy unit is currently performed utilizing ionization chambers placed inside a solid water phantom. This provides a good check of output at one point but does not give any information on either energy or symmetry of the beam, unless more than one point is measured. This also has the added disadvantage that it has to be done by the physics staff. To address these issues, and to simplify the process such that it can be performed by radiation therapists, we investigated the use of a commercially available daily QA device to perform this task. The use of this device simplifies the task of daily output constancy check and allows for this measurement to be performed by the therapists, rather than the physicist(s). This device can also be used to monitor the beam energy and lateral symmetry and can potentially be used to detect errors in the couch movement or laser misalignment.
SU‐FF‐T‐431: Time Delay Study of a CT Simulator in Respiratory Gated CT Scanning
Authors: Guan H
Published: July 2006

Purpose: To evaluate the time delay in respiratory gated CT scanning and its effect to motion synchronized radiotherapy.

Materials and Methods: In this study, we presented a technique to measure the time delay of AcQSim CT simulator (Philips Medical Systems) using Varian's Real‐Time Positioning Management (RPM) system (Varian Medical Systems). A respiratory gating platform (REF 91150, Standard Imaging, Inc.) was first set at the position of amplitude maximum (Phase 0). Then a ball of 1.3 cm diameter was put on the platform and set at the CT laser. A single axial‐scan was acquired across the center of the ball without motion. Then the motion was turned on and single axial‐scans gated at different phases were acquired with a very narrow gating window. The time between the phase giving a good estimate of the ball and Phase 0 is the overall delay time. The delays were also verified using metal balls of 1.5 mm diameter initially set at the amplitude minimum (Phase 180).

Results: We found that for AcQSim CT, the overall delay for a single axial‐scan (with 1s‐scan time) is 1.75s. For multiple axial‐scans, the overall delay is 1.75s for the first scan and 0.75s for the subsequent ones. This demonstrated that the CT mechanical startup delay is 1s. After the first axial‐scan, the overall delay per scan is less because CT gantry continuously spins and no mechanical delay exists. We call the overall delay without the mechanical part the scanning delay, which basically equals to half the scan time (0.5s for 1s‐scan time) plus the gating pulse triggering delay (250 ms). Conclusion: It is the scanning delay rather than the triggering delay that should be compensated when doing motion synchronized radiotherapy. The current interface between the RPM system and the AcQSim CT does not compensate for this delay.
SU‐FF‐T‐435: Tongue and Groove Effect in Direct Aperture Optimization IMRT Plans
Authors: Earl M , Cao D , Shepard D
Published: July 2006

Purpose: Direct Aperture Optimization (DAO) is a promising new IMRT technique whereby the MLC leaves and relative weights of the apertures are simultaneously optimized. Due to the stochastic nature of the simulated annealing optimization algorithm, MLC leaves can have positions that are significantly different from their neighboring leaves. Opposed adjacent leaves with these positions can lead to a “ripple” in the dose distribution due to tongue‐and‐groove effect (TGE). In this work, we attempt to quantify the magnitude of the effect and commission the Pinnacle planning system to account for it. Method and Materials: To quantify TGE, we generated a two‐segment beam: one segment with every other leaf on one side extending well past the central axis and the other with every other opposed adjacent leaf extending well past the central axis. Jaws set to 20×20 bound both segments and both had equal monitor units. This beam was delivered to a flat phantom with a film placed at 10cm depth.

Newer versions of Pinnacle (7.4 or greater) take into account TGE. This is modeled in the physics tool with a tongue‐and‐groove step parameter. We systematically changed this parameter and compared the resulting dose distributions to the film measurement.

We imported DAO IMRT plans into the Pinnacle planning system and compared the dose distributions with and without TGE. These were also compared with verification measurements. Results: The film displayed a 23% variation from minimum to maximum dose. The Pinnacle step parameter of 0.3cm reproduced the variation. If TGE is not accounted for in the planning, an underestimation of the absolute dose is observed for DAO IMRT plans. The magnitude of the underestimation is dependent upon the aperture shapes. Conclusions: TGE affects the dose distribution for DAO plans. Limiting the distance adjacent leaves may travel can reduce the effect of TGE.
SU‐FF‐T‐436: Tools for Integrating Monte Carlo Dose Engines with a Radiotherapy Planning System
Authors: Schreiber E , Tracton G , Chaney E
Published: July 2006

Purpose: Monte Carlo simulations represent the gold standard in radiotherapy dose calculation. While numerous tools have been developed to facilitate accelerator and patient modeling within a Monte Carlo simulation, there are few commonly available tools for interfacing a Monte Carlo dose engine with a fully‐featured treatment planning software package. We report on the development of tools to integrate a Monte Carlo dose engine with clinically useful radiotherapy planning software. Method and Materials: The initial release is configured to operate with PLanUNC, a freely available open‐source radiotherapy planning tool. The Monte Carlo integration package consists of several modular scripts and programs that act as a bridge between the treatment planning software and the Monte Carlo dose engine. Results: Using PLanUNC as a front end for the Monte Carlo, the user can develop a treatment plan, export beams and patient information to the Monte Carlo, recover the dose distribution, and analyze the results of the calculation in PLanUNC according to isodose, DVH, or EUD, as well as compare the results of the Monte Carlo simulation with results from other calculations. Conclusion: The Monte Carlo interface package facilitates the clinical use of Monte Carlo by allowing a fully‐featured radiotherapy planning suite to be used as a front end, allowing flexible treatment planning and analysis of the Monte Carlo results. The modular nature of the software makes it straightforward to adapt these tools for use with other treatment planning software packages.
SU‐FF‐T‐442: Use Of A 2D Array Of Diodes To Test The Accuracy Of MLC Leaf Position And Gap Width
Authors: Jursinic P , Kainz K , Ahunbay E , Albano K
Published: July 2006

Purpose: For MLC‐modulated IMRT fields, it is important that the leaf positioning be accurate and that the gap between opposing leaf pairs be precisely set. One test of the MLC is the “picket fence” pattern, which consists of narrow, sequentially delivered, abutting sub‐fields of radiation. Typically in current practice, a radiographic film is irradiated and visually inspected for a discontinuous radiation pattern. Here, a 2D‐array of 455 diodes (MapCheck, Sun Nuclear, Melbourne, FL) was used to detect the radiation pattern. Method and Materials: The array was oriented such that 120 diodes aligned with the center of the MLC leaves at each of their sub‐field edges. Measurements were compared against a dose distribution calculated by the XiO treatment planning system (Computerized Medical Systems, St. Louis, MO) for a picket‐fence segment pattern delivered to a flat phantom. MapCheck software was used to obtain the relative percent difference, normalized to the center diode, between the 455 diode‐measured and calculated points. Spreadsheet software was written that extracted the desired 120 sample points from the 455 measured points and performed routine data analysis in less than 30 s. Results: Four different Siemens accelerators equipped with 29‐leaf pair MLCs were measured over a two‐month period. By careful adjustment of MLC leaves, the percent difference between measurement and calculation, averaged for 120 points, could be kept within ±5% with a standard deviation of 6.0%. This standard deviation is attributable to individual MLC leaves and deviations in leaf position for various set positions across the field. The trial‐to‐trial variation is about 2% for the average difference for the 120 points. A 1‐mm leaf offset in the picket fence delivery corresponded to an average difference of about 17%. Conclusion: A rapid, quantitative method, sensitive to submillimeter changes in MLC leaf positioning and gap width has been devised.
SU‐FF‐T‐445: Use of the Monte Carlo Method as a Comprehensive Tool for SMLC and DMLC‐Based IMRT Delivery and Quality Assurance (QA)
Authors: Tyagi N , Litzenberg D , Moran J , Fraass B , Chetty I
Published: July 2006

Purpose: To report on use of a thoroughly benchmarked MC dose calculation algorithm as an accurate tool for IMRT delivery and QA, in patient‐like media, where direct measurements for routine QA are impractical. Methods and material: We have developed a source model to investigate dosimetric effects related to MLC based delivery techniques such as step‐and‐shoot and sliding window using the DPM MC code. The model incorporates details of the Varian, 120‐leaf MLC and has been comprehensively verified against measurements in homogeneous and heterogeneous phantoms. As part of this development, we have investigated an efficient algorithm, using adaptive kernel density estimation for sampling phase space files. Using this accurate source model, we have studied beams that were sequenced with 1% and 10% fluence intervals for prostate, brain, head and neck and breast IMRT beams. Dose differences between SMLC and DMLC delivery types were evaluated in homogeneous and heterogeneous media (bone, lung and low‐density slabs) using DPM. We have also investigated dosimetric differences between optimized planned leaf sequences and actual delivered sequences, using machine log (Dynalog) files, which capture the physical leaf positions during delivery. Results: Benchmarking of the source model showed average agreement with measurements within 1%/2 mm. For a given fluence interval, calculated dose differences between SMLC and DMLC delivery techniques are different in homogeneous and heterogeneous media. Dose differences of up to 10% were found between plans developed with 1% and 10% fluence intervals for either SMLC or DMLC delivered sequences. Calculated dose differences of up to ±3cGy were observed between planned and delivered sequences (computed using the Dynalog files) for a prostate beam; these differences were in good agreement with film measurements. Conclusions: A well commissioned MC‐based dose algorithm provides a useful tool to study dosimetric issues related to fluence modulation and static versus dynamic delivery in IMRT.
SU‐FF‐T‐447: Utility of Film Dosimetry for Assessing TomoTherapy Treatments of Superficial PTVs
Authors: Cheek D , Hogstrom K , Gibbons J , Rosen I
Published: July 2006

Purpose: To assess the utility of film dosimetry in a cylindrical polystyrene phantom for evaluating the accuracy of dose calculated by the TomoTherapy HI⋅ART treatment planning system for superficial planning target volumes (PTVs). Method and Materials: A TomoTherapy treatment plan was developed for a superficial PTV (1‐cm deep radially by 90° azimuthally by 4.2‐cm longitudinally) contoured on a 27‐cm diameter by 37.4‐cm long cylindrical white opaque polystyrene phantom. The phantom included two removable planar film cassettes, one perpendicular to and one including the cylinder's axis. Kodak EDR2 film was cut using templates, resulting in film edges coinciding with the phantom surface (±0.25‐mm). The axial film was irradiated according to the TomoTherapy plan then the phantom was translated longitudinally and the sagittal film irradiated. The films were scanned with a Vidar film digitizer, converted to dose, and the common depth‐dose curves compared. Measured axial and sagittal dose distributions were compared with those calculated. Results: The common depth‐dose of the axial and sagittal films agreed well, although the axial film had a lower relative dose by 2.5%. Comparisons of measured and calculated dose on the axial film showed agreements to within 5% at depths greater than 3‐mm. At shallower depths, doses showed larger differences but distance‐to‐agreement values were small (<2mm). These differences could be due to planned to delivered dose alignment techniques and/or the film cutting process, which is under investigation. Conclusion: Orthogonal films irradiated in a cylindrical polystyrene phantom produced common depth‐dose curves that agreed well. Future comparisons with thermoluminescent dosimetry should confirm the utility of EDR2 film for a comprehensive study of the accuracy of the TomoTherapy treatment planning system for planning treatments of superficial PTVs normally treated with electrons.

Supported in part by a research agreement with TomoTherapy, Inc.
SU‐FF‐T‐451: Verification of a Proton Treatment‐Planning Pencil‐Beam Dose Algorithm with Monte Carlo
Authors: Titt U , Zheng Y , Zhu X , Mohan R , Newhauser W
Published: July 2006

Purpose: To verify the accuracy of a pencil beam superposition dose algorithm in heterogeneous media for proton therapy treatment planning system using Monte Carlo simulations. Method and Materials: A proton treatment planning system (ECLIPSE, Varian) was validated using dose distributions predicted with Monte Carlo (MC) simulations. The accuracy of the MC physics models was established in previous studies and the model of the therapy unit is described elsewhere (Newhauser et al, Zheng et al., separate contributions to this conference). MC simulations of proton beams with different range, field sizes and modulation widths into various phantom geometries, comprising cubic water phantoms with lung and bone equivalent material slabs, cylindrical inhomogeneities and non‐flat upstream surfaces, were carried out to compare depth dose profiles, lateral profiles, penumbral widths and field size values to predictions from the treatment planning system. Results: More than 30 different beam configurations have been investigated. Range differences, and differences in the 80%–20% penumbras larger than 2 mm were observed twice, while differences in the 50%–50% field size were smaller than 1 mm. The range differences were not related to the inhomogeneities, but are due to differences in the proton stopping powers used in the MC and TPS systems. The deviations in the penumbras were mostly seen in the 90%–10% penumbra comparisons of profiles at large depths, where contributions from multiple Coulomb scattering started to become more visible in the MC simulations, but less in the TPS predictions. Conclusions: Monte Carlo simulations proofed to be a valuable tool to verify the dose predictions in heterogeneous phantoms from a commercial treatment planning system. The treatment planning software performed well in most cases considered. This investigation helped to substantially reduce the time required for testing and the treatment planning software package and provided valuable feedback to the TPS developer.
SU‐FF‐T‐453: Verification of Head Leakage as the Primary Source of Shielded Radiation From a Tomotherapy Unit
Authors: West M , Sen A
Published: July 2006

Purpose: To investigate the adequacy of an existing 6 MV vault for shielding and to verify that head leakage is the primary source of radiation emanating from a helical tomotherapy unit. Methods & Materials: Before installation of a helical tomotherapy unit in an existing 6 MV accelerator vault, the vendor provided isodose plot was analyzed. Estimated exposure was calculated by scaling the exposure on the plot, correcting for inverse square, and using a 6 MV TVL for 2.35 g/cm3 concrete from NCRP 49. Sinograms were generated for a rotational (20 second period) and fixed gantry (0°, 90°, 180°, 270°) to deliver radiation with all leaves closed and opened for a 5×40 cm2 field size and fixed couch position. At 26 locations the exposure rate was measured at height of isocenter with an ionization chamber. Results: The maximum exposure occurred when the accelerator was nearest to the measurement point. A maximum exposure rate of 1.75 mR/hr was measured in the accelerator control area behind 30″ concrete at a 45° angle relative to the axis of the accelerator and a distance of 5 meters. The lowest exposure rate at the same position occurred when the accelerator was at the farthest distance. Assuming 30 minutes of irradiation time per hour, the maximum exposure would be less than 1750 mR/yr. No significant differences (∼10–15%) between field settings were observed. The calculated values are higher than the measured and loosely agree with the highest measured values at each position. Conclusions: The existing vault is adequately shielded for the tomotherapy unit. Data indicate that leakage is the primary radiation source. Modulation does not affect the leakage significantly. The calculated and measured values disagree and discrepancy may be attributed to the use of a 6 MV TVL.
SU‐FF‐T‐455: Volumetric Analysis of Dose Delivered by Xoft Axxent X‐Ray Sources
Authors: Axelrod S
Published: July 2006

Purpose: To study the spatial characteristics of the dose delivered by the Xoft Axxent Electronic Brachytherapy system within a volumetric (voxel) visualization system. Further, to extend the study from tools available in treatment planning systems, which are typically limited to a single set of TG43 input data for a source type, to be able to investigate data for individual sources. Additionally, to allow for comparisons to be made between the standard or average source, and a particular source of interest via difference images, line plots, and histograms. Method and Materials: Input spatial data in the form of polar and azimuthal angular distributions, and depth dose readings acquired in the course of source characterization, were loaded into a custom LabVIEW program. This program created 3D voxel arrays for an average reference set and for individual sources, allowing two data sets in memory simultaneously. Analyses on the voxel arrays include visualization of the distributions via 2D false‐color images and line plots, scatterplots and histograms of values and cumulative values. The visualization tools can be applied to either source or reference data set or the difference between them. Results: 2D images representing slices through the volume, and line plots along chosen lines on the images, provide information on the spatial variation in either the source data or in the difference, or percent difference, between a specific source and the reference. Histograms provide quantitative results on the degree of variation between source and reference, while scatterplots provide insight into the region or characteristic causing variations. Conclusion: Volumetric analysis of the Xoft Axxent™ source is a powerful tool for understanding the dose distribution and expected variation from source to source, which can be applied to any brachytherapy source for which 3D spatial data is available.
SU‐FF‐T‐459: An Implantable Dosimeter Study of Patients with Prostate Cancer
Authors: Beyer G , Scarantino C , Mann G , Carrea T , Anscher M , Prestidge B , Black R
Published: July 2006

Purpose: A study of 30 prostate cancer patients who received implanted radiation dosimeters in conjunction with external beam radiation therapy has been completed. The purpose of the study was to compare daily measured dose to the value predicted by the treatment planning system. Method and Materials: In most patients two dosimeters were placed adjacent to the capsule of the prostate. The devices were introduced perineally using a trocar/cannula system. Polyester mesh was placed behind the sensors after insertion to prevent them from moving back down the insertion track before healing occurred. Serial CT scans were taken to gauge any migration of the devices away from the point of surgical placement. Some patients were localized on a daily basis using a kilovoltage x‐ray positioning system. The clinical protocol did not permit alteration of the therapy parameters based on sensor readings. Results: An evaluation of the dose discrepancy between measured and planned values was completed for each sensor. Additionally, the relative standard deviation of each sensor's readings was calculated (as a measure of randomness of the readings). In many patients, the relative standard deviation value exceeded 3%, which is beyond the nominal value for the sensor itself when tested in a phantom. In some patients the cumulative dose for a given treatment period disagreed with the planned dose by 5% or more. The discrepancy tended to be more pronounced for boost phases when the isodose contours were reduced in volume. Conclusions: This initial data suggests that implanted dosimeters may play a useful role in tracking dose discrepancies, both systematic and random, in patients being treated with external beam therapy for prostate cancer. Future studies will focus on the effects of daily kilovoltage x‐ray localization, using the dosimeters as fiducial markers, on the magnitude and randomness of dose discrepancies.

Supported by Sicel Technologies.