bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐P‐06: Use of a Website for Support of a Clinical Rotation in Radiation Oncology Physics
Authors: Starkschall G , Beddar S , Johnson J , Kudchadker R , Lawyer A , Tung S , Zhang S
Published: July 2007

Purpose: The purpose of the present work is to demonstrate how a website can be incorporated into the support of a clinical rotation course in radiation oncology physics in a graduate medical physics training program. Materials and Methods: A website was developed consisting of a home page with a list of contacts and a class schedule. Linked to this home page were websites for specific clinical rotations. On each rotation website were listed specific objectives and tasks with links to appropriate teaching materials, examinations, and forms. Results: Use of the website simplified management of the clinical rotation course and made all course materials easily accessible to all the students. Conclusions: Success with the website supporting the clinical rotation course has encouraged the development of websites for additional courses in our graduate program.
SU‐FF‐T‐11: A Dosimetric Study of the Effect of Respiratory Motion On Whole Breast Radiation Therapy
Authors: Cao J , Roeske J , Schumra S , Salama J , Shoushtari A , Boyer A , Martel M
Published: July 2007

Purpose: Study the effect of respiratory motion on whole breast radiotherapy for three treatment planning techniques: conventional wedged technique (CWT), segment IMRT (SIMRT) and beamlet IMRT (BIMRT). Investigate the relationship between the dosimetric coverage difference introduced by respiration and breast motion. Method and Materials: Eight patients with early stage breast cancer underwent free breathing (FB) CT simulation for whole breast radiotherapy. Two additional CT scans were obtained at the end of inspiration (EI) and end of expiration (EE). The FB scan was used to develop three plans using CWT, SIMRT and BIMRT. Each plan was copied and applied to EI and EE scans. The dose volume histograms were compared and statistical methods were used to investigate the relationship between dosimetric coverage and breast motion. Results: Medial and lateral markers of EI scans moved an average of 8 mm and 3mm, respectively. Both medial and lateral radiopaque markers of EE scans moved an average of 2 mm. For CWT and SIMRT, the percentage of CTV volume receiving 95% of the prescription dose V95% remained almost constant. BIMRT was relatively sensitive to respiratory motion. The average difference comparing FB and EI for the eight patients was 4.3% (V95%) and 7.4% (V100%). FB dose coverage remained almost the same as EE. A linear relationship with marker motion was found in the V100% difference between FB and EI. Conclusion: This study shows CWT and SIMRT are less sensitive to respiratory motion than the BIMRT. A linear model was found to relate the dosimetric coverage difference introduced by respiration with the breast motion. With this model, the dosimetric coverage difference could be evaluated during CT simulation. Based on the studies, we recommend BIMRT is not used for whole breast radiotherapy unless respiration control is used and SIMRT could be used without control.
SU‐FF‐T‐20: A Method to Achieve Uniform Dose Distributions in Small Animal Subcutaneous Tumors
Authors: Cui J
Published: July 2007

Purpose: In the current radiotherapy paradigm, a major treatment planning goal is target dose uniformity. However, a boost dose to as large a fraction as possible of the target volume (partial target boosting) may improve local control without increasing the risk of normal tissue injury. We are investigating the feasibility of using 6 MV photon beam from Varian 2100 Linac to deliver controlled, non‐uniform dose distributions to subcutaneous small animal tumors. The focus here is to achieve dose uniformity as the first step. Methods: A superficial structure was created near the thigh of a healthy mouse to simulate a subcutaneous tumor. It had a maximum dimension of 9mm and density equal to water. The fast Monte Carlo code, Dose Planning Method, (DPM) was coupled to our research treatment planning system, CERR (Computational Environment for Radiotherapy Research), to conduct the planning study. The mouse was placed on the in‐house microRT system. Different boluses and beam arrangements were tested. Results: By computing and evaluating the different plans using 2, 4, and 7mm boluses, it was found that 4mm bolus was enough to provide buildup. Two slightly‐angled (35° and 240°) or parallel‐opposed (60° and 240°) beams can achieve a tumor dose with 3% RMS, the minimum and maximum dose as 0.89Gy and 1.05Gy respectively, for the mean dose 1Gy. This suggested that the uniform dose distributions can be delivered. Conclusions: 6MV photon beam is capable of delivering uniform dose on a superficial tumor of 9mm. Thus it is achievable to deliver a non‐uniform dose on the tumor, provided accurate positioning and beam collimation, to facilitate the investigation of tumor response to heterogeneous dose. The microRT hardware and CERR planning system are a useful platform for this study. Conflict of Interests: This research was partially supported by a grant from Varian Medical Systems, Inc.
SU‐FF‐T‐24: A Monte Carlo Study of the Out‐Of‐Field Dose From IMRT
Authors: Kry S , Salehpour M , Titt U , Stovall M , White R , Followill D
Published: July 2007

Purpose: To calculate the out‐of‐field dose resulting from intensity‐modulated radiation therapy (IMRT) using Monte Carlo. Out‐of‐field radiation poses a health risk to the patient as it may induce late effects such as secondary malignancies. While this dose can be measured, measurements are time consuming and are specific to the irradiation conditions and patient examined. In contrast, Monte Carlo modeling can be flexible and applied to an arbitrary condition or patient, and may offer reasonable accuracy. Method and Materials: MCNPX was used to create a Monte Carlo model of a Varian 2100 accelerator and treatment vault. Step‐and‐shoot IMRT of the prostate was simulated at 6 MV and 18 MV. The simulated patient was an anthropomorphic phantom, the CT of which was converted to MCNPX format using Scan2MCNP. The dose from photons and the dose equivalent from neutrons were calculated at various organ locations throughout the phantom. These calculated doses were compared to measured doses that were previously published, based on the same anthropomorphic phantom and IMRT treatments. Results: The Monte Carlo model was able to accurately predict the out‐of‐field photon dose at both 6 MV and 18 MV. At 6 MV, the average absolute out‐of‐field photon dose was 14% different than measurement, while at 18 MV the average absolute out‐of‐field photon dose was 13% different than measurement. There have been a wide range of published neutron dose equivalents in phantom and our calculated neutron dose equivalents were consistent with these values. Conclusion: Using Monte Carlo it was possible to calculate the out‐of‐field dose equivalent resulting from complex therapies incident on a complex phantom. Such a Monte Carlo model would therefore be a useful tool for evaluating the out‐of‐field dose received by patients undergoing radiotherapy.
SU‐FF‐T‐27: A Multi‐Vendor Compatible Respiratory Motion Visualization Device for Use with Kilovoltage Imaging, the “Hubie”
Authors: Hubenschmidt J , Bradley J , Goddu S , Low D , Mutic S , Santanam L , Parikh P
Published: July 2007

Purpose: Creation of a simple robust tool to use in conjunction with onboard fluoroscopic imaging of the patient in treatment position that will allow daily review of target motion relative to the expected motion used to plan treatment. This tool is needed to circumvent software incompatibilities in a multi‐vendor environment. Method and Materials: The procedure creates a radio‐opaque outline of the treatment aperture and physically attaches it the kV detector surface so as to project the aperture on subseuent fluoroscopic images. The patients need to have a treatment target that is visible on fluoroscopy or have an implanted radiopaque fiducial marker. A DRR is printed showing the planned tumor or fiducial range of motion as a projected structure outline. The outline will be used to evaluate the absolute position of the tumor or marker relative to the intended location. The motion range is outlined with a radiopaque wire, and 5 wire crosses are placed for alignment and scale verification. The wired DRR is attached to the kV detector and the patient is imaged with fluoroscopy; displaying the expected motion range (wire outline) against the projected tumor or fiducial marker motion. The wire outline position and scale are checked against a virtual reticule. Results: Using the methods described above it is possible to visualize a moving target just prior to treatment as well as the treatment location. Care must be taken to ensure not only accurate placement of the outline but also that the correct structure is outlined for the current patient. Conclusion: The procedure outlined here creates a flexible process that is non machine, software or manufacturer dependant. The procedure is sensitive to user error and is dependant on the manufacturing and placement accuracy of the device.
SU‐FF‐T‐32: A Novel Continuum Mechanics Approach Towards Multiscale, Stochastic Tumor Modeling Based On Multimodality Imaging
Authors: Titz B , Jorabchi K , Suresh K , Jeraj R
Published: July 2007

Purpose: Current tumor simulation models describe either microscopic or macroscopic behavior and do not efficiently use information available on both levels. Furthermore, they are based on simplifying assumptions rather than observable data. To overcome both these deficiencies, we incorporated an existing microscopic, stochastic tumor model based on radiobiological properties and PET/CT imaging data into a multiscale tumor model. Method and Materials: In the microscopic model, biological parameters accounting for micro‐ and macroscopic tumor characteristics complement anatomical information, thereby enabling simulating tumor development voxel‐by‐voxel. Resulting changes in voxel density and microenvironmental conditions are passed on to the superior tissue level where a finite element analysis method is used to determine tumor deformation based on a thermo‐elastic continuum mechanics analogy. Deformation tensors are then applied to the initial input geometry to calculate the final morphology in image space, allowing for comparison to clinical data. Results: Simulation results based on murine squamous cell carcinoma xenograft μPET/CT data show good qualitative agreement with tumor behavior pre‐ and post‐radiotherapy. Due to tight integration between the simulation levels, relevant biological properties are conserved to within 2% error. Since biological parameters are monitored at a voxel level, this approach is computationally superior to classic single‐cell‐based models. However, a limitation of voxel discretization is that growth may be discontinuous across adjacent voxels, causing residual stresses within the tumor that are easily detectable during the simulation. Conclusion: Our results indicate the ability of the proposed model as a platform to simulate tumor behavior while allowing for integration of and comparison to (pre‐) clinical data. All required input variables can be directly accessed through experiments and multimodality imaging. Tensiometric properties and anatomical constraints influencing mechanical interaction of the tumor can be easily added, allowing for a calibration in future investigation of more complex clinical cases to improve reliability.
SU‐FF‐T‐43: A Simplified Framework for CT Simulation of Left Breast Patients Using Deep Inspiration Breath‐Hold (DIBH)
Authors: Guan H , Pradhan D , Hammoud R , Kim J , Movsas B
Published: July 2007

Purpose: We presented a simplified framework for deep inspiration breath hold (DIBH) in AAPM 2006. This study presents the implementation of the framework for patient simulation using AcQSim CT simulator. Materials and methods: An aqua‐plastic mask band of 1.0–1.5in was made before simulation while the patient was instructed in DIBH for 30s or longer. The mask band was set near the umbilicus and the RPM marker box was set ∼1cm superior or inferior to the mask. The DIBH signal was also displayed on a monitor set close to patient, which was a duplicate display of patient's signal in the RPM computer. The patient can physically achieve DIBH by the mask band. She can also visually guide herself for stable breathing amplitude. The CT images were acquired in spiral rather than in gated axial mode such that much faster scanning can be made. The RPM system was simply used to monitor the breathing and in case patients cannot hold her breath, the spiral scanning can be manually terminated and then resumed for the next breath hold. For each patient, two sets of CT were acquired, one in DIBH and the other in free breathing. Patient tattoo was made while the patient was in DIBH. Results: The framework was successfully applied for the simulation of three left breast patients. During the simulation, two patients can hold their breath for ∼60s or longer with very stable amplitudes, such that CT scanning can be made in spiral rather than in the gated axial mode in just one breath hold. The DIBH CT images have less motion artifacts compared to the free breathing CT images. Conclusion: The system can be reliably applied for the simulation of left breast patients with DIBH. A modern multislice CT simulator can be more efficient to make the DIBH scanning.
SU‐FF‐T‐44: A Simplified PC‐Based Helical Tomotherapy Planning System
Authors: Shaw R , Kao M , Steidley K , Xu D
Published: July 2007

Purpose: A simplified helical‐tomotherapy independent planning system (SHIPS) has been developed for independent verification of the TomoTherapy Hi‐ART (TomoTherapy Inc. Madison, WI) treatment scheme and to provide an alternative method to produce helical tomotherapy plans. The SHIPS program is designed to be simple, so the program can run on a desktop PC, and straightforward, so the delivery scheme is intuitive. Presented here are relationships/equations SHIPS uses to produce delivery parameters and treatment sinogram. Methods and Materials:SHIPS requires the user to input the patient geometry and contours as geometric shapes, e.g. cylinders and ellipsoids. Simplifying the geometry makes the structures in the treatment sinogram more perceptible and speeds the contouring process. The user specifies pitch, field size, and prescribed dose. SHIPS calculates the couch travel length, the number of rotations, couch travel speed, MU, and time of treatment. The required rotation period can be calculated using the prescription, depth to a point of interest, and measured beam data (depth dose output factors, and profile data). The treatment sinogram is created using geometry information, treatment parameters, beam data, and the prescription. SHIPS treatment parameters are compared against values produced from the Hi‐ART system, forty plans are observed. Results: The average deviation of the SHIPS calculated couch travel distance, time of treatment, couch speed, and number of monitor units to the Hi‐ART's values are, respectively, 0.08%, 0.05%, 0.37%, and 0.74%. Simulated imbedded targets(e.g. prostate) and external/convex(e.g. breast) are presented examples of SHIPS treatment plans. The SHIPS treatment plan calculation is less than 30 seconds. Conclusion: SHIPS bypasses the Hi‐ART's optimizer, producing independently derived plans. Running SHIPS in parallel with the Hi‐ART's treatment planner provides quality assurance of the entire treatment planning process. Additionally SHIPS can challenge how much inverse planning the Hi‐ART system requires and can be used for basic forward planning.
SU‐FF‐T‐166: Dose Measurement to ICD Outside the Treatment Fields Using Optically Stimulated Luminescence
Authors: Chan M , Dauer L , Burman C
Published: July 2007

Purpose: To determine relative sensitivity factors for optically stimulated luminescence (OSL) dosimeters (microStar™ DOT, Landauer), as a function of distance from the field edge, to be applied when measuring dose at any out‐of‐field point. Method and Materials: OSL dosimeters have been used to measure the radiation dose to patient's implantable cardioverter defibrillator (ICD) outside the treatment fields. ICDs have a thin outer case made of 0.4–0.6 mm thick titanium (∼2‐mm tissue equivalent) and are usually implanted 3‐mm underneath skin. Approximate 5‐mm bolus thickness is about the equivalent depth of the sensitive electronics. The responses of the dosimeters with and without bolus were measured per unit dose to water at off‐axis distances up to 15‐cm. Doses were measured by an ionization chamber located at various depths for 6 and 15 MV using a Varian Clinac‐iX linear accelerator. The relative sensitivity of the OSL dosimeters was determined as the ratio of the sensitivity at each off‐axis distance to that at central axis. Results: The OSL results were compared with those of other detectors in our previous studies [1]. The detector sensitivity as a function of distance from the field edge changed little for LiF TLD (∼2%) and OSL (∼7%); decreased by 12% and 17% for the ISORAD photon diode (Sun Nuclear Corp.); increased 11% and 14% for the skin QED diode (Sun Nuclear Corp.) for 6 MV and 15 MV, respectively. Conclusions: Compared to other detectors studied, OSL dosimeter has the closest out‐of‐field dosimetric characteristics to TLD. OSL dosimeters should be calibrated out‐of‐field and preferably with bolus equal in thickness to the depth of interest. This can be readily performed at each institution.
SU‐FF‐T‐167: Dose Perturbation From Head Frame at Gamma Knife Stereotactic Radiosurgery
Authors: Xiong W , Huang D , Qin L , Lee L , Feng J , Morris K , Calugaru E , Li J , Burman C
Published: July 2007

Purpose: To investigate the possible dose perturbation from head frame which is attached to patient skull to provide precise location of target in brain and is not considered during dose calculation in Gamma Knife SRS. Method and Materials: An EGS4 based Monte Carlo simulation was applied to Gamma Knife SRS. In the simulation, the geometries of the stationary collimator and the helmet collimator were reconstructed exactly according to Gamma Knife Model C. The materials of the collimators were selected as close to the original materials as possible. All particles were traced through the stationary collimator and the helmet collimator until they pass the inner surface of the helmet or were absorbed. Patient's geometries were rebuilt from CT data. The dose was calculated using Monte Carlo simulation with and without presence of head frame using identical beam parameters. DVH was compared in a small volume around the iso‐center. Results: For patient's data, Monte Carlo results showed that although the 50% to 90% isodose lines remained almost the same with and without the presence of head frame, the maximum distance between two 10% isodose lines could be as far as 1.5 mm. The dose with head frame was about 1.3% lower than the dose without head frame. The dose difference varied from 1% to 2% among five patients. Conclusion: The head frame may have significant impact on peripheral dose distribution as well as absolute dose. Since Automatic Positioning System is applied on Gamma Knife unit, average shot number for each patient has been increased to produce a conformal dose distribution to match the irregular tumor volume. Regular position check can't exclude the possibility that some shots are affected by the head frame. The dose perturbation from head frame should be considered in dose calculation.
SU‐FF‐T‐176: Dosimetric Effects of Metallic Hip Implants On Image Guided Radiation Therapy
Authors: Hwang A , Ludlum E , Xia P
Published: July 2007

Purpose: Image guided radiation therapy allows us to track the prostate location daily, and to compensate for prostate movement by shifting the treatment isocenter. For patients with metallic hip prostheses, this may result in dosimetric errors due to the presence of high Z materials in the fields. The purpose of this work is to determine whether shifting the isocenter to compensate for prostate motion delivers the proper dose in patients with hip prostheses. Method and Materials: A retrospective study was performed using IMRT plans for five prostate cancer patients with hip prostheses. For each patient, six copies of the contours defining the prostate were created, and shifted 1.5 cm (representing the worst case scenario) in the anterior‐posterior, superior‐inferior, or lateral direction to simulate prostate movement. The dose to the shifted prostate was calculated using the original treatment plan with an isocenter shift corresponding to the change in the prostate position. Results: Without compensating for prostate movement, a 1.5 cm displacement in prostate position has significant dosimetric effects, resulting in an average decrease in the dose delivered to 95% of the prostate (D95%) by 33%. We found that for patients without hip prostheses, shifting the isocenter to track prostate motion reduces the change in D95% to under 1%. The presence of hip prostheses did not have a significant effect, except in a case using lateral beams in a patient with bilateral prostheses. In that particular case, D95% decreased 5% even when an isocenter shift was used to compensate for prostate motion. Conclusion: In IMRT treatment of prostate cancer, it is possible to compensate for prostate motion by simply shifting the isocenter without creating a new treatment plan, even in patients with hip prostheses. The effect of hip prostheses can be minimized by avoiding beam angles that pass through the prostheses.
SU‐FF‐T‐180: Dosimetric Guidance On Using Brachytherapy (LDR Or HDR) to Offset a Flawed Permanent Prostate Implant
Authors: Zaider M
Published: July 2007

Purpose: To provide practical dosimetric advice on mending suboptimal permanent implants using low dose‐rate (LDR) or high dose‐rate (HDR) brachytherapy (BRT). The problem is to make the combination of the two radiation treatments (the initial, flawed one and the compensatory boost) clinically isoeffective with the planned dose. Methods: The device of isoeffective dose (IED) is the appropriate tool for this purpose as it accounts for the physical (temporal distribution of dose) and biological (radiosensitivity, repair kinetics, proliferation rate) treatment setting. Results: I give, as a function of separation time from the initial, flawed treatment, and stratified by risk group representative values for the additional dose (LDR or HDR) needed to make the combined treatment isoeffective with a prescription of 144 Gy of permanently‐implanted seeds. Conclusions: While the IED concept, within the constraints stated in the presentation, is rigorously valid, its practical implementation depends importantly on the relevant radiobiological parameters, and in this respect the reader is urged to use his own critical judgment.
SU‐FF‐T‐184: Dosimetric Verification of a Novel TBI Technique Using Segmented Radiation Fields
Authors: Amin M , Heaton R , van Prooijen M , Norrlinger B , Cheung F , Islam M
Published: July 2007

Purpose: To evaluate the dosimetric performance of a novel CT planning based total body irradiation (TBI) technique, which utilizes a conventional linear accelerator in a standard bunker and employs segmented beams for dose uniformity. Methods and Materials: An extended distance TBI technique at ∼180 cm SSD has been developed for a conventional linear accelerator using a custom couch aligned along the plane of gantry rotation. Up to 3 abutting fields are used to cover the patient, with divergence matching achieved through a combination of gantry angles and couch shifts. Treatment planning was performed using a full body CT scan and standard beam models within the Pinnacle 7.6C TPS. The dosimetric verification consisted of: (i) pre‐treatment patient specific dose measurements in phantoms and (ii) in‐vivo dosimetry using MOSFET and films. Similar to the process of IMRT verification measurements, treatment plans were transferred to a 40×40×20 cm3 phantom and compared to ionization chamber dose measurements in the same geometry. In‐vivo dosimetry measurements were performed using paired MOSFET detectors (at entrance and exit) at the level of the umbilicus and at the level of the mediastinum. Junction doses were assessed by in‐vivo exit dosimetry using films on the couch. Results: Dose measurements in phantom for 11 clinical TBI patients were found to agree with Pinnacle to within (0.96±0.71)%, with a maximum deviation of 2.08%. The average agreement between the in‐vivo dose measurements and calculated values were found to be within (0.44±4.33)%, with a maximum deviation of 10.7%. No significant dose differences were observed along the junctions. Conclusion: This work validates the accuracy of dose delivery for this novel TBI technique, developed with Pinnacle 7.6C. The segmented fields and the matching of divergent field edges provide adequate dose uniformity throughout the treatment volume.
SU‐FF‐T‐215: Evaluation of IMRT Delivery Differences for Varian and Elekta Accelerators
Authors: Rothley D , Miller R
Published: July 2007

Purpose: To analyze and evaluate treatment delivery time, total number of MU, and number of control points with similar IMRT plans delivered both on Varian 21EX and Elekta Synergy accelerators. Comparison of maximum dose based on a minimum volume of 2ccs was also reviewed. Method and Materials: Prostate and breast plans with similar +/−5% angles and using the same step and shoot technique were chosen for this study. These plans were created with the Pinnacle v7.4 DMPO planning system. The total MU, time (normalized for minor differences in dose rate delivery) and number of control points needed to execute these IMRT plans was compared. Maximum dose was evaluated utilizing the treatment planning software statistics and DVH. Results: The Synergy took slightly more time to deliver a similar IMRT plan than the 21EX. The 80 Elekta leaves moved more slowly than the 120 Varian leaves but the most time consuming element was the fact that the Elekta diaphragms moved for each segment. Although the carriage shifts laterally for Varian 120 leaf MLC delivery for very large fields necessitating more time, this was not needed for any of the cases studied. Conclusion: The advantage of the diagraphm movement is that larger field sizes may be delivered with the Elekta MLC without splitting beams. The movement is necessary to block the inherent leaf gaps due to the MLC limitation. Because of the slightly longer treatment time with the Elekta, patient selection and patient movement must be considered. The study did not account for time for any imaging including port films or CBCT for localization. Both accelerators produced clinically acceptable treatment plans for delivery.
SU‐FF‐T‐233: Feasibility Study of Linac‐Based Intensity Modulated Total Marrow Irradiation (IM‐TMI)
Authors: Aydogan B , Roeske J
Published: July 2007

Purpose: Standard total body irradiation (TBI) techniques are associated with both acute and chronic toxicities due to the large volume of normal tissue irradiated. Additionally, inhomogeneous dose distributions are known to be the cause of failures and relapses in the treatment of leukemia and lymphoma. The goal of this study is to investigate the feasibility of linac‐based intensity modulated total marrow irradiation (IM‐TMI) and to discuss the challenges associated with its clinical implementation. Methods: To evaluate the feasibility of linac‐based IM‐TMI, we performed an exploratory treatment planning using the CT scan of a TBI patient. Active bone marrow sites were defined and contoured as the clinical target volume (CTV) and a margin was added to create the planning target volume (PTV). Dose limiting organs included the lenses, lungs, liver, kidneys, and heart. IMRT plans were created using the Eclipse/Helios inverse planning system (Varian Inc., Palos Alto, CA) to deliver a total dose of 12 Gy. Dose volume histograms (DVHs) were calculated and subsequently compared with standard TBI‐DVHs. Results: IM‐TMI resulted in a significant reduction in the volume of normal tissue irradiated compared with conventional TBI. The median lung doses were 7.3 Gy and 8.8 Gy, while the maximum lung doses were 12.9 Gy and 15.5 Gy for IM‐TMI and conventional TBI, respectively. The maximum dose to the lenses was 7 fold less using the IM‐TMI approach. Similar results were also observed for liver, kidney, heart, small bowel, and spleen. Moreover, IM‐TMI resulted in a more homogeneous dose to the PTV with a median dose of 12.3 Gy vs. 10.5 Gy using standard TBI. Conclusions: Our results demonstrate that linac‐based IM‐TMI is capable of delivering a conformal dose to the target volume while reducing the dose to the surrounding normal tissue. Such an approach may improve the overall efficacy of TBI.
SU‐FF‐T‐234: Fetal Dose Estimates for Radiotherapy During Pregnancy — Case Report of a Young Woman with Medulloblastoma
Authors: Baumann R , Bremer M , Warszawski A
Published: July 2007

Purpose: To determine clinically the fetal dose from irradiation of head and neck during pregnancy by a young woman using phantom measurements. Method: A 30 years old woman with medulloblastoma should receive a cranio spinal axis irradiation during pregnancy. Phantom measurements should show if the irradiation of head and neck as a first step of the radiotherapy is possible. Fetal dose was estimated with measurements at an Alderson‐phantom using thermoluminescent dosimeters (TLDs). Irradiation of typical fields (26×24 cm2, 8×8 cm2, 6 MV photons) were simulated, measuring points were used as in the AAPM report no 50. A special shielding was developed to reduce the dose at the foetus. Results: For single doses of 2 Gy the measurements at the phantom results in maximal doses between 6.04 mGy and 1.86 mGy for the large fields (0.95 mGy to 0.39 mGy for the smaller boost fields) at different points between fundus and pubis without any shielding. Using a specially designed shielding the doses were reduced to 3.90 mGy and 1.16 mGy. For a planned total dose for the patient of 30 + 24 Gy the fetal dose should be 0.03 Gy to 0.11 Gy without and 0.02 Gy to 0.07 Gy with the shielding. In vivo measurements during radiotherapy confirmed these values for a single irradiation. Conclusion: Irradiation during pregnancy should be avoided if anyway possible. To reduce the fetal dose a specially designed shielding should be used. Also for irradiation in the region of head and neck in any case measurements should be done to estimate the fetal dose before starting radiotherapy.
SU‐FF‐T‐240: Hair Sparing IMRT for Whole Brain with Simultaneous Integrated Boosts
Authors: Mallah J , Mihailidis D , Plants B , Fischer T
Published: July 2007

Purpose: To investigate inclusion of the hair‐sparing limitation of scalp dose as a secondary objective in a protocol for whole brain IMRT treatment along with high dose simultaneous integrated boosts (SIB) added to help control gross brain metastases. Methods and Materials: Three patients were selected to simulate a variety of brain tumors using artificial GTVs. The target doses were 54 Gy or 45 Gy for the boosts, and 27 Gy for the remainder of the whole brain, in 15 fx. To implement hair sparing, a 5 mm thick hair shell within the patient contour was created. Typical planning objectives for the hair shell were a max DVH constraint of 1250 cGy to 50% volume, and a max dose objective of 2300 cGy. Planning was done using Phillips Pinnacle3 (V7.4f) software configured for step‐and‐shoot treatment on a Siemens Primus unit with 6‐MV photons. Results: The high‐dose boost regions were found to require at least 5 beams but did not substantially degrade the whole brain DVH or hair DVH. However, for a PTV near the surface it was not possible to keep the hair dose low. The DVH may appear acceptable in such cases, but dose on the inner side of the 5 mm region will not cause hair loss, while a patch of high dose on the surface will. Conclusions: IMRT can provide a clinically viable avenue for hair‐sparing whole brain treatment with SIB to higher primary tumor doses. A specific region of interest that would represent the “hair sparing” region might need to be defined and be assigned a specific dose limiting objective during the optimization process. We found that hair‐sparing cannot successfully be satisfied for primary targets situated closer to the surface.
SU‐FF‐T‐246: Implementation of Helical CT Source in DOSXYZnrc/EGSnrc Monte Carlo Code
Authors: Kim S , Yoshizumi T , Yin F
Published: July 2007

Purpose: To implement and verify a new source type — phase‐space source in helical mode in DOSXYZnrc/EGSnrc Monte Carlo (MC) code. Method and Materials: To implement a new source type — “phase space source in helical mode” in DOSXYZnrc/EGSnrc, we modified the mortran and macro files related with DOSXYZnrc user code; dosxyznrc.mortan, srcxyznrc.mortran and srcxyznrc.macro. This source was implemented based on the source type 8 in DOSXYZnrc (isource=8: phase‐space source from multiple directions). Different with other researcher's approach (i.e. random sampling of possible particle locations with coordinate transformation in a spiral band) we introduced a step method which calculates the isocenter displacement in each step with a new parameter of table travel distance into srcxyznrc.mortran file. Conceptually this is easier to be comprehended and implementation is simpler. Accompanying with modifying the DOSXYZnrc source code, we also changed the GUI tcl/tk files of DOSXYZnrc to make users easy to build input files for MC simulations. To validate this new source geometrically, we established the Monte Carlo model of GE lightspeed RT using BEAMnrc/EGSnrc and simulated the helical beams to PMMA cylinder phantom using DOSXYZnrc. We have tested our source model with various pitch sizes and we have used DOSXYZ_SHOW to check whether the helical irradiation field is correct or not. Results: By performing the distance measurements of isocenters in an axial irradiation field using DOSXYZ_SHOW, we found that the source model worked well without any geometrical errors. Conclusion: In this study, we have implemented a new source model — phase‐space source in helical mode in DOSXYZnrc/EGSnrc Monte Carlo (MC) code and verified the model using DOSXYZ_SHOW. In future, we will perform the dosimetric evaluations of this source with physical measurements.
SU‐FF‐T‐250: Improved Patient Treatment with Leksell Gamma Knife Automatic Positioning System
Authors: Goetsch S
Published: July 2007

Purpose: To determine whether the implementation of the Automatic Positioning System for the Leksell Gamma Knife leads to better and more conformal treatment plans than the use of the earlier manual positioning system. Method and Materials: Treatment plans from a Gamma Knife Center with an 11 year history of use of the manual positioning Model U Gamma Knife (2482 treatments) and a one year history with the Model 4C with APS (233 treatments) were retrospectively examined. The labor‐saving feature of the new device was expected to encourage more elaborate planning with smaller helmet sizes, leading to increased number of shots and better Conformality Index. Treatment of patients with non‐malignant tumors in patients with long life expectancy were examined statistically, as well as metastatic tumors. Results: The total number of shots per patient for all treatments increased from 7.3 to 10.8. Acoustic neuromas were treated with 10.8 shots with the new APS system versus 6.5 with the old system, while target coverage increased from 97.7% to 98.7% and Conformality Index improved from 1.89 to 1.50, all significant at p<0.05. Meningiomas showed similar increase in shots (from 9.3 to 14.9), improvement in coverage from 96.0% to 97.8% and improvement in Conformality Index from 1.81 to 1.55. Metastatic tumors were treated with more shots and better coverage while the CI was slightly decreased. Conclusion: The burden of all new technology, especially when it is costly, is to demonstrate evidence based improvements in treatment. The Leksell APS system simultaneously reduces error rate through a Record and Verify system while encouraging planners to create more elaborate plans without straining staff resources or patient tolerance. It is too early to demonstrate better patient outcome but the trend is encouraging.
SU‐FF‐T‐252: Improvement of Localization Accuracy by Using 3D Cone Beam CT for Stereotactic Body Radiation Therapy of Liver, Lung and Spine Lesions
Authors: Wang Z , Nelson J , Yoo S , Wu Q J , Kirkpatrick J , Larrier N , Meyer J , Willett C , Yin F
Published: July 2007

Purpose: To compare treatment isocenter placement based on OBI 2D kV imaging and OBI 3D‐CBCT imaging for patients undergoing SBRT, and compare the CBCT based isocenter shifts among liver, lung and spine lesions. Material and Methods: 119 SBRT fractions were delivered to 40 lesions of 32 patients. The patients were initially localized with 2D orthogonal on‐board kV images. 3D on‐board CBCT images were then acquired to localize the isocenter for treatment. The shifts from 2D to 3D localization were recorded. Histograms, mean values and standard deviation of the isocenter shifts were calculated. Results: The isocenter shifts based on the 3D CBCT for all 119 SBRT fractions were 0.27 ± 0.25 cm, 0.19 ± 0.23 cm, and 0.23 ± 0.27 cm in the A‐P, C‐C, and M‐L direction, respectively. The mean values and standard deviations of the magnitudes of the shifts along AP, CC and ML directions were 0.30 ± 0.26 cm, 0.21 ± 0.20 cm, and 0.31 ± 0.35 cm for liver patients, 0.31 ± 0.29 cm, 0.30 ± 0.31 cm, and 0.28 ± 0.33 cm for lung patients, and 0.22 ± 0.21 cm, 0.13 ± 0.16 cm, and 0.18 ± 0.18 cm for spine patients. Conclusion: CBCT guidance enhances the setup accuracy of SBRT treatment by using 3D anatomical information.

Partly supported by Varian Research Grant.
SU‐FF‐T‐267: Intercomparison of Primary Standards at PTB and NIST for the Realization of the Unit of Absorbed Dose to Water for Beta Particle Brachytherapy Sources
Authors: Bambynek M , Soares C
Published: July 2007

Purpose: With the completion of a new primary standard (the so‐called “multi‐electrode extrapolation chamber”, MEC), PTB is now able to realize a three‐dimensional dose distribution absolutely with high spatial resolution at clinically relevant depths for beta brachytherapy sources without having to rely on an additional relative dosimetry system. The need for such a realization has mainly been for the dosimetry of eye tumor and intravascular brachytherapy sources. Together with NIST, the primary standards for the realization of the unit of absorbed dose to water for beta brachytherapy sources were compared bilaterally. Method and Materials: The primary standard of the PTB is based on an extrapolation chamber with a segmented collecting electrode, which was manufactured by means of lithography on a silicon wafer in the PTB's Clean Room Center. Due to this novel collecting electrode, simultaneous measurements at 28 measuring points with a spatial resolution of 1 mm2 are possible. After a successful internal PTB comparison, a bilateral comparison with NIST was arranged. For this purpose, a line source was constructed at PTB in an appropriate holding device and measured two‐dimensionally at a water‐equivalent depth of 2 mm. At NIST, the absorbed dose rate to water was determined absolutely at the dose rate maximum with a conventional extrapolation chamber (diameter of the collecting electrode used: 1 mm). In order to determine the position of the dose rate maximum and likewise a two‐dimensional dose distribution, further measurements were carried out with radiochromic dye film. Results: The comparison of the absorbed dose to water in the dose maximum yielded a relative difference of 6.4%, which is within the uncertainty intervals of the two laboratories. The relative combined uncertainty (1 sigma) of the PTB primary standard determined according to the GUM amounts to 3.4%, and that of NIST to 5%.
SU‐FF‐T‐276: Is It Still Necessary to Use a Beam Spoiler for Breast Radiation?
Authors: Li J , Jin L , Xiong W , Ma C
Published: July 2007

Purpose: The aim of this study is to find out whether it is still necessary to use a beam spoiler for breast treatment especially with IMRT technique. Materials and methods: Full Monte Carlo simulations were performed with and without a beam spoiler for 11 breast patients treated using 10MV photon beams and another 10 patients using 18MV photon beams with IMRT technique employed. CTV was defined as the breast volume which started from 5mm away of the skin and the build‐up‐region was defined from 2mm to 5mm depth from skin. Doses to CTV, build‐up‐region, skin and contralateral breast were compared with and without a beam spoiler. Results: Comparison of dose distributions show that the beam spoiler increases dose at the build‐up‐region where the patient surface is perpendicular to the beam and thus improves the dose homogeneity inside the breast. After the dose distributions were normalized to ensure 95% volume of CTV receives at least 95% of the prescription dose, the difference on the minimum and maximum dose of CTV is <2% for 10MV and <4% for 18MV, and the difference on the mean dose in the build‐up‐region is <3% for 10MV and <7% for 18MV. However, the mean dose of skin is increased by 5% for 10MV and 14% for 18MV on average and the maximum dose to the contralateral breast is increased by >100% by using a beam spoiler. Conclusions: The Monte Carlo simulation results show that the beam spoiler can improve dose homogeneity in the breast. But it is not clinical significant especially when the IMRT technique is used to limit the dose heterogeneity. And thus it is suggested that a beam spoiler may not be necessary when breast patient is treated using two opposite tangential 10MV or 18MV beams if the build‐up‐region is not a big concern.
SU‐FF‐T‐279: Lateral Distribution of a Proton Pencil Beam Which Is Consistent with Range Straggling
Authors: Chvetsov A , Palta J , Yeung D
Published: July 2007

Purpose: Pencil beam approach for proton beams is not accurate in the Bragg peak region because the multiple scattering theories are derived for monoenergetic particles and, therefore, can be applied only within CSDA range. We improve the pencil beam model to account for the range straggling in the Bragg peak region. Method and Materials: Depth dose distribution from a monoenergetic proton beam can be calculated by folding a CSDA depth dose distribution with a function which describes range struggling. Performing the integration numerically, we obtain that the dose distribution from a proton beam can be presented as a linear combination of the CSDA depth dose distributions with weights which are defined by range straggling distribution. For particles traveling in each CSDA approximation, we can consistently apply multiple scattering theory. The final equation for 3D proton distribution covers entire range of a proton pencil beam. Results: We have obtained an analytical expression for the 3D dose distribution from a proton pencil beam which covers entire penetration range. The equation consistently describes the depth dose distribution and the lateral spread due to range straggling in the Bragg peak region. This approach accounts also for proton loss from the beam at the end of the range. Conclusions: 3D dose distribution from a proton pencil beam can be calculated using a simple analytical formula for entire proton range. This formula is convenient for use in treatment planning with therapeutic proton beams, particularly, in the heterogeneous compositions.
SU‐FF‐T‐282: Light‐Radiation Field Coincidence for Small Stereotactic Fields
Authors: Ekstrand K , Munley M , Kearns W , Hinson W , deGuzman A
Published: July 2007

Purpose: To determine the degree of congruence between the light field and the X‐ray field for a Varian 2100 SCX linear accelerator equipped with a Varian/Zmed tertiary collimator for stereotactic radiosurgery (SRS). If this congruence is sufficiently good then it is feasible to use the light field for alignment of the system instead of using a mechanical pointer or the room lasers. Method and Materials: The SRS light field was projected onto a sheet of Kodak X‐OMAT V film enclosed in a paper ready‐pack at isocenter. A lead plug, slightly smaller in diameter than the collimated field, was placed concentric with the light field on the film pack. A 0.5 mm sheet of Cu was placed between the plug and the film pack to provide electron buildup to the film. The film was then exposed with 6 MV X rays from the linac. The developed film was scanned with a Vidar VXR‐16 densitometer and the separation between the centers of the X‐ray field and the shadow of the plug (representing the light field position) was measured. Similar films were taken of fields collimated by the accelerator jaws and by the MLC. Results: The separation between the centers of the light and radiation fields was 0.1 mm for the SRS collimator, 0.2 mm for the MLC, and 0.7 mm for the jaws. These separations follow a linear relationship with the ratio (SSD‐SDD)/SDD where SDD is the source‐to‐collimator distance and SSD is the source‐to‐film distance. Conclusion: If the light radiation congruence for the field defined by the jaws is within 1 mm then the light field with the tertiary collimator can be used in setting up the SRS system for this linear accelerator.
SU‐FF‐T‐283: LINAC Cone‐Beam‐CT Option for Treatment Planning: A Possible Approach for Dynamic Adaptive RadioTherapy?
Authors: Cossmann P , Stuessi A , von Briel C
Published: July 2007

Purpose: For image‐guided radiotherapy (IGRT) the different vendors of linear accelerators offer new kV imaging tools. These systems include — besides a radiographic and fluoroscopic mode — CT functionality. The aim of this study was to evaluate the future potential of such a cone beam CT option for therapy planning purposes allowing dynamic adaptation for target volume changes. Method and Materials: The Varian On‐Board Imager™ (OBI) Cone Beam CT (CBCT) option consists of a kV‐source and kV‐Imager mounted on robotic arms perpendicular to the MV therapy beam. In a single 360° rotation a volumetric CT data set can be acquired with a 25 or 45 cm field‐of‐view. In order to calibrate the system with regard to HU a special phantom has been designed to include the whole imager area. Removable inserts allow the measurement of central axis doses. A planning study has been carried out to determine the usability of CBCT data and compare these to with diagnostic CT date. Results: Comparisons of data between a diagnostic CT scanner and the 3D‐calibrated Cone Beam CT with regard to image quality and hounsfield units representation for an humanoid phantom (RSD Alderson) indicate good accordance. Central axis doses applied during the acquisition of one volumetric data set are between 1 and 3 cGy depending on the geometry. Results with real patient data show appropriate image quality. Relative dose distributions in CBCT‐based plans show minor differences to plans calculated using a diagnostic CT image dataset (p=0.002) and absolute dosage deviations are within 1% (p=0.001). Conclusion: This work illustrates that a properly calibrated Cone Beam CT option allows off‐line treatment planning. Furthermore the image quality is sufficient for contouring of target outlines. CBCT can serve as control CT in order to adapt the target volume and resize the treatment fields and/or optimize the treatment plan.