bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐401: Development of Specific Treatment Plan Based On Physical Lattice Structure for Stereotactic Radiosurgery
Authors: Choi K , Oh S , Suh T , Lee J , Choe B , Kim M , Chung H
Published: June 2005

Purpose: The stereotactic radiosurgery (SRS) describes a method of delivering a high dose of radiation to a small target volume in the brain, generally in a single fraction, while the dose delivered to the surrounding normal tissue should be minimized. To perform automatic plan of the SRS, a new method of multi‐isocenter/shot linear accelerator (linac) and gamma knife (GK) radiosurgery treatment plan was developed, based on a physical lattice structure in target. Method and Materials: The optimal radiosurgical plan had constructed by many beam parameters in a linear accelerator or gamma knife‐based radiation therapy. In this work, one isocenter/shot was modeled as a sphere, which is equal to the circular collimator/helmet hole size because the dimension of the 50% isodose level in the dose profile is similar to its size. In computer‐aided system, it accomplished first an automatic arrangement of multi‐isocenter/shot considering two parameters such as positions and collimator/helmet sizes for each isocenter/shot. Simultaneously, an irregularly shaped target was approximated by cubic structures through computation of voxel units. The treatment planning method by the technique was evaluated as a dose distribution by dose volume histograms (DVHs), dose conformity, and dose homogeneity to targets. Results: For irregularly shaped targets, the new method performed the optimal multi‐isocenter packing, and it only took a few seconds in computer‐aided system. The targets were included in a more than 50% isodose curve. The dose conformity was ordinarily acceptable levels and the dose homogeneity was always less than 2.0, satisfying for various targets referred to Radiation Therapy Oncology Group (RTOG) SRS criteria. Conclusion: This approach using new method could be an efficient radiosurgical plan used two beam parameters both the irregularly shaped targets and different modality techniques such as linac and GK for SRS.
SU‐FF‐T‐405: Impact of Tissue Heterogeneities Upon Dose Delivery to Lung Lesions and Comparison of BrainSCAN Treatment Planning System Dose Calculations
Authors: Schell M , Clark D , Reynolds D , Liu H , O'Dell W , Yu Y , Okunieff P
Published: June 2005

Purpose: Tissue heterogeneity changes result in a build down/build up of the recoil electron fluence at heterogeneity interfaces. The use of stereotactic radiosurgery beams on small lung lesions can compromise the dose delivery to lesions ranging from 6 mm up through 30 mm in diameter, since the dimensions of the lesions are comparable to the range of the secondary electrons in lung and air. Dose perturbations are evaluated for a range of lesion diameters in lung equivalent phantom material. Method and Materials: Lesion diameters of 6.4, 12.5, 19.7, and 25.4 mm of unit density were inserted into lung equivalent material. The dose distributions were measured with film densitometry and calculated with the dose calculation engine of the ADAC Pinnacle system. The Pinnacle treatment planning system uses the adaptive convolution superposition algorithm, which rigorously reproduces x‐ray beam attenuation, and the electron fluence changes at tissue heterogeneity interfaces. Results: The physical density of the lung equivalent phantom material is 0.30 g/cm3 in contrast to water and normal tissue at 1.0 g/cm3. The spherical tumor phantoms were irradiated with beam margins of 0, 7, 10, and 25 mm. Dose volume histogram analysis was performed to develop a DVH surface map of the dose delivery to each lesion as a function of margin size. It was determined that a 7 mm margin for all lesion diameters delivers a minimum tumor dose of 94 % of the prescribed isocenter dose for all lesion diameters. The DVH analysis and film dosimetry were also compared with the dose calculations of the BrainSCAN planning system. Conclusion: These measurements and calculations confirm the clinical feasibility of stereotactic irradiations of lung lesions with minimal compromise of the tumor dose. Research supported by BrainLAB, AG Munich, Germany.
SU‐FF‐T‐408: Regular Lesions Stereotactic Treatment: Physical and Dosimetrical Comparison Between Circular and Mini/micro Multileaf Collimators
Authors: Sardo A , Madon E , Richetto V , Trevisiol E , Pellegrini R , Cirio R , Donetti M , Giordanengo S , Iliescu A , Marchetto F , Peroni C , Urgesi A
Published: June 2005

Purpose: The comparison of stereotactic treatments for small spherical and ellipsoidal intracranial lesions using three different collimators with single isocenter: the standard circular collimators and two dynamic multileaf collimators (DMLC) with 3 mm and 5 mm leaf thickness, micro and mini DMLC respectively. Method and Materials: Spherical and ellipsoidal lesions of different sizes were designed to evaluate treatments with collimators under consideration. For spherical lesions with diameter from 15 mm up to 35 mm a treatment with 9 arcs of 140 degrees was performed. For ellipsoidal lesions treated with circular collimators, different combinations of treatment variables were studied to achieve 80% isodose surface conformation: number of arcs, gantry start/stop angles, couch angles and arc spacing. This treatment was matched up to 9 arcs with the two DMLCs. For the comparison geometrical (penumbra, difference between the target volume and 80% isodose volume and conformal indexes) and radiobiological (EUD, TCP and NTCP) parameters were used. Results: Circular collimators and micro DMLC behave similarly with spherical targets in terms of conformal indexes and TCP/NTCP, but EUD and 20% isodose volume are greater for micro DMLC. In the case of ellipsoidal target TCP/NTCP are comparable, EUD is greater for micro DMLC but conformal indexes are higher for circular collimators. The 20% isodose volume is less with micro DMLC; the difference, however, is entirely due to the wider penumbra along the deformation axis with circular collimators. The same considerations are valid for targets with diameters ⩾ 35 mm, where mini DMLC becomes competitive versus circular collimator. Conclusion: The analysis shows that micro and mini DMLC are more functional for non spherical lesions. Circular collimators however are widely used and yield sharper dose fall off along directions perpendicular to the deformation axis and thus are preferable in the case of neighbourhood of organs at risk.
SU‐FF‐T‐409: Study of the Technology of Pin‐Point CT Imaging Guide System
Authors: Tsai J , Cardarelli G , Hiatt J , Shearer D , Bradford C , DiPetrillo T , Puthawala Y , Remis M , Wazer D
Published: June 2005

Purpose: The Pin‐PointTM is a technology for promoting accurate access to a designate target in the CT room, especially during biopsy procedures. This study is to confirm its capability by an independent methodology for clinical implementation. Method and Materials: The Pin‐Point system (FigA) is based on CT imaging with an invisible frame system and instant 3‐D image reconstruction in the laser (needle insertion) plane as illustrated in FigB. Two (yam and daikon) phantoms were used for the studies. The center portion of the phantoms was cut into ten 4mm thick slices. Simulated tumors were created on each slice using barium paste. Organs at risk (OAR) were carved with various shape cavities. BBs were attached as reference points (FigC). Target searching and their correlation to the neighboring OARs were explored. An optimal “reference point R” was defined to serve as navigation for the laser‐guided needle for start location, direction, and the needle depth to reach the targets and avoid OARs. Results: FigD demonstrates the needle reaching the tumor as navigated by the Pin‐Point system. We oriented the guiding laser beam and pushed its path depth from point R to the tumor edge. Next the phantom slices were studied to determine needle positioning relative to the target and OARs, and compared with the foregoing CT image. The agreement is shown in FigD. FigE illustrates the optimal needle trajectory to ‘tumor A’, by‐passing the OARs. FigF illustrates pre‐warning of OARs. FigG displays the possibility of excessive needle penetration. Conclusion: Pin‐Point system was accurate for correct tumor access without jeopardizing the nearby OARs. Our study proves valuable for the search of designated tumors and avoiding critical structures. In addition, its feasibility for further application to linac based stereotactic radiosurgery as frameless setup should be studied.
SU‐FF‐T‐412: The Feasibility of Using Tomotherapy Hi‐Art Machine for Stereotactic Radiosurgery
Authors: Jaradat H , Tome W , Mehta M
Published: June 2005

Purpose: To study the feasibility of treating multiple‐brain metastass with stereotactic radiosurgery using the tomotherapy Hi‐Art machine, and to compare tomotherapy stereotactic radiosurgery treatment plans with conventional linac‐based stereotactic radiosurgery plans. Method and Materials: Five previously treated patients with multiple brain metastases ranging from 1 to 5 metastases were selected for the study. These five patients were treated with linac stereotactic radiosurgery. The same structures and prescription doses used for linac radiosurgery were also used to produce stereotactic radiosurgery treatment plans on the tomotherapy planning system. In order to compare the tomotherapy plans to the linac‐based plans, the homogeneity of the target volumes, as well as the PITV, the volume of normal brain tissue receiving at least 10Gy and treatment time were considered. Results: Analysis of the five plans shows that the target dose uniformity, target dose conformality, and the treatment time for each plan is much improved for tomotherapy. The plans show that on average using tomotherapy planning system increases the dose uniformity by 70%, increases the target‐dose conformality by 42% while it reduces the normal tissue volume receiving at least 10 Gy by about 40% for large metastases. On the other hand, for metastases smaller than 1cc tomotherapy increases the 10.0 Gy volume over that for a conventional linac plan by about 60%. Conclusion: These results show that tomotherapy could be used for treating patients with multiple brain metastases using stereotactic radiosurgey.
SU‐FF‐T‐413: The Impact of Heterogeneity Correction On Tumor Dosimetry for Lung Cancer Stereotactic Body Radiation Therapy
Authors: Ding M , Newman F , Stuhr K
Published: June 2005

Purpose: Stereotactic body radiation therapy (SBRT) for non‐small cell lung cancer has been shown to limit toxicity. Heterogeneity correction on lung cancer radiotherapy has not been recommended by RTOG. In this study, dosimetric difference between the SBRT plans with/without heterogeneity correction is analyzed. Method and Materials: Nine lung cancer patients treated with SBRT techniques using a 6 MV Novalis system were selected. Using the path length algorithm in BrainLAB treatment planning system, all the treatment plans were applied the heterogeneity correction. With same beam parameters, we performed the plans without the heterogeneity correction, and compared the dosimetric difference to the treatment plans. The heterogeneity correction factors (Kc) at iso‐center, target coverage, heterogeneity index (HI), and conformity index (CI) were used in the comparison. Results: The average of Kc at isocenter for 14 planning target volumes (PTV) was 1.002±0.02, only three Kc values (1.07, 0.985, 0.981) were relatively off to the average. Except one case, the other 13 target coverage values of the plans with the heterogeneity correction were better than those without the correction. The maximum difference of the target coverage was ∼7%. All the HI values of the plans with the heterogeneity correction were better than those without the correction. The maximum difference of the HI reached 300%. The difference of the CI between the compared plans was within ∼10%. The CIs of the plans without correction were better than those corrected. For one case — the tumor located in the lung base, the impact of heterogeneity correction was significant. Conclusion: The impact of heterogeneity correction for tumor dosimetry on SBRT for lung cancer is case depended. For most primary lung tumors the difference between the plans with/without heterogeneity correction is clinically insignificant. For the tumors near the interface of different mass density, the heterogeneity correction is necessary.
SU‐FF‐T‐414: Transfer of Brain Tumor Patients From Leksell Gamma Knife to BrainLAB Novalis
Authors: Djemil T , Suh J , Neyman G , Weinhous M , Ouzidane M
Published: June 2005

Purpose: To identify and resolve issues associated with transferring brain tumor patients, after placement of Leksell frame (LF) and the completion of MRI and CT scans for Gamma Knife (GK) radiosurgery, to linac‐based stereotactic radiosurgery (SRS) with BrainLAB Novalis. Method and Materials: Three patients were studied. These patients could not technically be treated with GK radiosurgery given the technical limitations posed by frame placement or tumor location. CT and MRI scans were transferred to the BrainLAB treatment planning system (TPS), BrainSCAN. Treatment plans were then generated and evaluated. Systematic and potential issues were identified. Compatibility of the LF and the BrainLab system was evaluated. Imaging issues were investigated, and time restriction considerations to have the patient treated the same day were addressed. Results: The LF is compatible with the Novalis system using a special adapter. The MRI scans presented no issues. CT imaging may constitute an issue since the Leksell localizer box is shorter than the BrainLab box. Depending on the frame placement on the patient head, part of the anatomy may not be localized by BrainSCAN and cannot be used. While the GK TPS can extrapolate parts of the anatomy, BrainSCAN cannot. As a result, planning options are limited (novertex beams/arcs). In this case, a new CT scan with the LF and the BrainLAB localizer is required. Once imaging issues are resolved, a plan, quality assurance, evaluation and treatment can be completed the same day. Conclusion: Patients scheduled for GK radiosugery can be efficiently transferred to Novalis the same day of the procedure when tumor location or frame placement does not allow GK radiosurgery. The issues associated with the transfer are manageable and allow same day treatment with the Novalis system.
MO‐B‐I‐618‐01: Recent Advances and State‐Of‐The‐Art in Screen‐Film Receptors and Film Processing
Authors: Dickerson R
Published: June 2005

Purpose: This presentation discusses recent advances in film/screen radiography. These include a high‐resolution high‐contrast film/screen system for mammography, as well as a high‐speed high‐resolution film/screen system that provides improved image quality and opportunities for dose reduction, compared to an existing state‐of‐the‐art, general purpose film/screen system. A description of the technical aspects and system design of these new systems is given. The new film features novel silver‐halide microcrystals and is dual coated using a split E‐layer coating format featuring gradient crossover control. Without sacrificing image quality, the new system can be exposed with existing intensifying screens and provides significant dose reductions. Method and Materials: This paper describes details of the system's design and performance. The film includes: 1) a dual‐layer coating structure that provides high‐speed and high‐resolution imaging of chest and orthopedic imaging; 2) high sensitivity silver‐halide microcrystals that provide high contrast and high resolution. Modulation transfer function (MTF) measurements were used to describe the resolution of various film/screen combinations using this new radiographic film and they are compared to existing state‐of‐the‐art film/screen systems. Results: Inverse square sensitometry and MTF measurements, as well as phantom and clinical radiographs using this new film/screen system, demonstrate several benefits. A significant dose reduction is possible without reducing image quality by using standard intensifying screens. In addition, significant image quality improvements are possible in orthopedic imaging using high‐resolution extremity‐intensifying screens at conventional radiation doses. Conclusions: We have designed, built, and implemented a novel film/screen system for general‐purpose radiography that provides high‐resolution images with a potential for dose reduction or MTF improvement. Initial clinical evaluation of the system demonstrates a 2X reduction in dose without sacrificing image quality. In addition, significant resolution improvements are possible at the conventional radiation doses.
MO‐C‐T‐6E‐04: Einstein 1905 and Beyond: The “Revolutionary” Paper, Plus Four, Plus Five
Authors: Rigden J
Published: June 2005

In the short duration of six months, one week, and two days, Einstein, in 1905, wrote five papers that stand today at the bedrock of physics. Only one of these papers was, according to Einstein himself, revolutionary. This paper, on the nature of light, made him the father of quantum physics. In the other four papers, Einstein clearly eschewed trivialities as he demonstrated the reality of atoms and examined their dimensions (the reality of atoms was still debated in 1905), put the laws of thermodynamics on a new footing as he established the validity of the kinetic theory, enhanced the significance of the speed of light, and purged the basic concepts of space, time, mass, and energy of profound fallacies. But Einstein did not retire after 1905. He continued a career that, in sum, stands alone in the annals of physics.
MO‐D‐I‐618‐01: Estimating Medical Physicist FTE Using the 2003 Abt Survey and Procedure Volumes in Radiation Therapy
Authors: Herman M , Klein E , Mills M , Boyer A
Published: June 2005

Purpose: To estimate radiation therapy medical physicist FTE needs based on procedure numbers and published medical physicist work survey data. Method and Materials: A spreadsheet was developed to combine procedure volumes requiring medical physicist effort with procedural time values extracted from the 2003 Abt survey and a previous survey on medical physics costs (Herman et. al. JACMP, 2003) and included: Patient Procedures: Median procedural time efforts and annual volumes for CPT codes 77295, 77300–77370. Commissioning and QA: Annualized time for commissioning and QA per major clinical system. Education: Contact teaching time for medical residents, allied health and medical physics trainees with a preparation multiplier of 3 for didactic courses. Research: A 10% factor was used, recognizing that development work varies considerably between practices. Administration: A value between 10 and 15% was recommended by ACR. FTE needs were summarized for a 3 machine practice (800 new patients), IMRT (250 pts per year), HDR(50), Radiosurgery(60), prostate implants(40) and TBI(30). Physician residents and one medical physics trainee are taught. Results: A total of 9.4 FTE was calculated based on: Patient Procedures — 6.67, Commissioning and QA − 1.04 Education: − 0.11, Research: − 0.78, Administration: − 0.78. With shared duties, no specials and an efficient electronic record, for example, the FTE could be reduced to 7.3 FTE. Conclusion: A medical physics staffing complement of between 7.3 and 9.4 FTE is suggested by a model based on workloads from the 2003 Abt and procedure volumes in a clinic with 800 new patients. The range is due to the sharing of duties (with other professionals), efficiency and the absence of some procedures. The number of hours committed by the medical physicist for procedural effort versus non procedural effort must be evaluated/validated against one's specific practice to make proper use of data from the Abt.
MO‐D‐I‐618‐02: Survey of Quality Performance Status in Radiation Oncology Departments
Authors: Schmanke K , Schmanke T , Kitch M , Schuster R
Published: June 2005

Purpose: To survey quality assurance performance in both hospital‐based and free‐standing radiation oncology departments. Method and Materials: Consisted of an online survey of 15 questions that was also mailed to 425 radiation oncology departments, covering topics ranging from peer review and issues, departmental processes and equipment, state reportable events, TG‐40 recommendations and accredidation status. Results: We received 56 responses for a 13% response rate. Of these, 73% were from hospital‐based and 27% from free‐standing clinics. 80% reported conducting physician peer‐review meetings, and discussed issues such as high risk/low volume procedures, unplanned treatment breaks (48%), mortality (41%), and reaccurences in adjacent and previously irradiated fields (31%). 93% reported knowing what is a state‐reportable event, and 83% had conducted a root‐cause analysis for a state‐reportable event. 85% of the responders reported using Continues Quality Improvement (CQI) methods within the department and 50% cross‐departmentally in an effort to improve the treatment processes. Tracking of quality indicators included patient satisfaction (95%), treatment misadministration (80%), physics check prior to 3rd treatment (73%), number of simulations and starts (48%), pateint wait time (36%), chart consistancy (30%), port film repeat rate (30%), machine overides (29%) and block re‐cuts (7%). However, only 41% reported being accredidited by either the ACR or ACRO. In addition, 50% of respondants reported knowing the AAPM TG‐40 guidelines, and only 32% of respondants tracked compliance with TG‐40 recommendations. Conclusion: The results represent a small sample size so must be interpreted cautiously. Overall responses indicate a lack of consistancy between departments in managing quality assurance issues. Responses also indicate a disregard for AAPM TG‐40 reccomendations, and an overall lack of interest in accredidation.
MO‐D‐I‐618‐03: A Web‐Based Lead Apparel Management System for Medical Enterprises
Authors: Oshiro T , Cagnon C , Rael B , Shah S , Urquidi J , Melendez J
Published: June 2005

Purpose: Accrediting bodies often require facilities to have a system for managing radiation protective apparel. In larger hospitals and medical enterprises, the standardization and monitoring of radiation protective apparel becomes increasingly difficult. The purpose of this work was to develop a web‐based infrastructure for inventory control of radiation protective (lead) apparel across a large‐scale hospital system. Method and Materials: A centralized database was developed and made accessible by a departmental website using Active Server Pages (ASP). Unique identifiers were assigned and entered into the database for the current apparel inventory. Quality control (QC) records — including lead patency checks were also integrated into the system. An automated email notification system was implemented for overdue QC tests. Web‐based education modules were posted and an enterprise wide policy was formed to identify staff responsibilities and quality control methodology. Results: Responsible individuals were assigned to monitor local section inventory changes and ensure proper care of apparel. Quality checks, unique identification and centralized ordering of apparel were coordinated through the Medical Physics office. For the four major enterprise sections, (two hospitals — with inpatient and outpatient centers) over 1081 different pieces of lead apparel were uniquely identified, inventoried and inspected. The web‐based system allowed staff and managers across the enterprise to access current inventory and latest quality control results for apparel in their section. Reminders of overdue checks are sent out monthly with no user interaction. Conclusion: The web‐based information system is effective at dissemination of information throughout a medical enterprise. Centralized systems of inventory control and quality assurance testing reduce redundancy throughout departments. Assigning unique identifiers has the potential to reduce conflicts in inventory management and provides a system to return apparel that has been accidentally moved. Policy formation encourages this integration throughout the enterprise.
MO‐D‐I‐609‐02: Performance Evaluation of Magnetic Field Homogeneity in MRI
Authors: Chen H , Roby J , Li J , Gao J , Clarke G
Published: June 2005

Purpose: Poor main (Bo) magnetic field homogeneity (MFH) leads to artifacts in MR images. The ACR MRI QC Manual mandates annual checks of MFH, suggesting tests using spectral line widths (FWHM) and phase‐difference (Δφ)maps. A new method for determining MFH is proposed and compared with standard methods using three different phantoms. Method and Materials: Small receiver bandwidth (BW) in the presence of poor MFH leads to geometric distortions because gradients are reduced to the level of the Bo inhomogeneities. The proposed bandwidth‐difference (ΔBW) method compares the distortion for small and large BW acquisitions to determine the MFH. Data were acquired using a 3T system and FFE pulse sequence scanned twice with BW's of 50 Hz and 501Hz, respectively. MFH was measured from the shift of landmarks between the two BW acquisitions. Data were compared with data from the FWHM and Δφ methods. Results: Measured FWHM = 0.06 ppm@13.5cm DSV for the manufacturer's phantom, 0.27 ppm over the 19cm(diam) × 15cm(length) ACR phantom and 0.07ppm@27.9cm DSV in our spherical homogeneity phantom. The Δφ images showed pronounced areas of poor MFH near the corners of the ACR phantom, which were not evident in the other phantoms. The ΔBW method could not be used in phantoms without landmarks, but in the ACR phantom MFH was measured to be 0.43 ppm in the axial direction and 0.86 ppm in the saggital direction. In the spherical phantom ΔBW measurements show MFH=0.16 ppm@15.3 cm DSV to 0.32 ppm@18.83cm DSV. Conclusion: Spectral line width measurements of MFH on spherical phantoms can be useful however the acquired data are only for one DSV. The ΔBW method produces measurements of MFH at various DSV values that can be obtained from a single set of phantom images.
MO‐D‐I‐609‐04: In Vitro Stability of a Liposome‐Based Multimodal Contrast Agent: A CT and MR Imaging Study
Authors: Zheng J , Allen C , Jaffray D
Published: June 2005

Purpose: To investigate the stability of a liposome‐based multimodal contrast agent for computed tomography (CT) and magnetic resonance (MR) imaging in the presence of various environmental conditions in vitro using both imaging and chemical analysis techniques. Method and Materials: Liposomes encapsulating iohexol and gadoteridol were dialyzed in an 8000 molecular weight cut‐off dialysis bag against 250‐fold excess of physiological buffer and fetal bovine serum (FBS) at 37°C. The liposome‐based contrast agent was also irradiated to clinically relevant single doses ranging from 0.5 Gy to 32 Gy delivered at a rate of 3.9 Gy/min (6MV, photon beam, medical linear accelerator) at 37°C in physiological buffer and FBS. The same samples were imaged in a purpose‐built multimodal phantom using CT (120 kV, 200 mA) and MR (1.5T, TR/TE = 450/9) before and after either dialysis or irradiation. The mean CT and MR signal differential was measured over circular regions of interest. Chemical detection of iohexol and gadoteridol concentrations was performed using high performance liquid chromatography and inductively coupled plasma atomic emission spectrometry respectively. Results: Partial release of the encapsulated agents occurred during dialysis due to differences in osmotic pressure and volume distribution (in the presence and absence of blood proteins). This small degree of agent leakage caused the MR signal to slightly increase and the CT signal to slightly decrease. In addition, the imaging properties of the system were found to remain unchanged when clinically relevant radiation doses were applied. Conclusion: The liposome‐based multimodal contrast agent remained substantially stable under osmotic pressure and distribution volume changes, in the presence of blood proteins and clinically relevant radiation doses. This investigation showed the feasibility of employing this system for blood pool CT and MR imaging over the course of a radiation treatment.
MO‐E‐T‐618‐05: Monte Carlo Study of the Effect of the Tissue Composition On the Dosimetric Data Used for Low Energy Photons
Authors: Reniers B
Published: June 2005

Purpose: Low energy photon isotopes like Iodine‐125 or Palladium‐103 are widely used for brachytherapy applications, as in the treatment of prostate, eye or very recently breast. The mean energy is approximately 30 keV for Iodine‐125 and 20 keV for Palladium‐103. In the vast majority of brachytherapy treatment planning the patient is still considered as an infinite water phantom. The real compositions of the tissues, the presence of heterogeneities or the real shape of the body are not taken into account. In this work we used Monte Carlo techniques to estimate the impact of those approximations on the calculations of the dose distributions in the patient. Method and Materials: The radial dose functions were calculated for IBt seeds using MCNP4C in different situations and in different materials including different body tissues whose compositions were taken from ICRU441. For these calculations, MCNP4C default cross section library was modified to match EPDL972. Results: The differences between radial dose functions calculated in muscle and in water can be as high as 15% at 5 cm for and 10% at 5 cm for . For breast tissue the comparison with water shows an underestimation of the radial function of up to 50% at 5 cm from a seed. The same calculations in lens tissue show on the contrary a good agreement with the radial dose function calculated in water. Moreover, due to photoelectric absorption, we show that the presence of even very limited amount of high Z elements as heterogeneities or as component of the tissue has an effect on the radial dose function and so on the dose distribution around the seeds. Conclusion: The real composition of the body tissues should not be neglected because of the large influence of high Z elements due to the high photoelectric cross section for low energy photons.
MO‐E‐T‐618‐07: Toward An Energy‐Based Dosimetry
Authors: DeWerd LA , Stump K , Culberson W , Beach S
Published: June 2005

Purpose: To present a methodology for energy‐based dosimetry for brachytherapy sources Method and Materials: Methodology for brachytherapy dosimetry is based on TG 43 formulism. For low ‐dose rate low‐energy brachytherapy sources, TG‐43 involves a measurement of the air‐kerma strength traceable to NIST using the Wide Angle Free Air Chamber (WAFAC). A Variable Aperture Free Air Chamber (VAFAC) has been constructed for making air‐kerma rate measurements with various solid angles. Both instruments provide a determination of the air‐kerma strength. In addition, spectra of these seeds can be measured both in air and liquid water by an intrinsic germanium spectrometer. We have also recently measured the total energy contained and emitted from various sources using a novel cryogenic calorimeter. This provides an absolute measurement of the power of the source. Each of these experimental processes is presented in other papers. This talk is an overview of how these measurements can be combined to yield an energy‐based dosimetry process. These measurements provide a good basis for Monte Carlo calculations. The energy standard would be used for calculation of dose or by extension, energy deposited. However, with extension to energy‐based dosimetry, a modification of treatment planning systems for a gradual shift from TG 43 formulism will be necessary. An energy‐based dosimetric formulism involves knowing the contained energy or the total emitted energy of a brachytherapy source. A review of the present dosimetry with an extension to energy‐based dosimetry will be presented for discussion. Results: It is shown that energy‐based dosimetry is feasible. The experimental parameters necessary are presented and are being measured presently. The results are very promising. Conclusion: This dosimetry schema is feasible and may be the dosimetry of the future. Moreover, this methodology provides an efficient platform upon which to base Monte Carlo dosimetry calculations.
MO‐E‐T‐617‐01: Energy and Intensity Modulated Electron Radiation Therapy Using a Monte Carlo Optimization Procedure
Authors: Leal A , Ma C , du Plessis F , Lagares JI , Li J , Quin L , Xiong W , Stathakis S , Luo W , Chen Z
Published: June 2005

Purpose: This study investigates the potential benefit of energy‐ and intensity‐modulated electron radiotherapy (MERT) for superficial treatments and the possible intensity modulation by means of a multileaf collimator (MLC). Method and Materials: Detailed Monte Carlo simulation is proposed for the pre‐ and post‐optimization dose calculation for MERT treatment planning. We have used 1 × 1 cm2 electron beamlets with different weights and energies that are optimized by an integrated inverse planner following the imposed constraints for the target and critical structures. A leaf sequencer proposes the necessary segments shaped by the MLC and then, in a second optimization, the segments are considered as new beamlets, called ‘blocklets’, by the inverse planner. Dose distributions for individual blocklets are simulated accurately by Monte Carlo taking into account the effect of bremsstrahlung leakage and MLC leaf scatter. The leaf sequencer provides the final RTP file to be read by the linac. MERT and mixed beam treatments for breast cancer have been planned following the two‐step optimization criteria. Results: The dose volume histograms (DVH) show clear improvement in the dose distribution before and after the second‐optimization. The monitor units for individual segments are adjusted to correct for the effect of leaf leakage and scatter. A photon MLC has negligible leakage but more leaf scatter compared to an electron‐specific MLC. The lung and heart doses are always less than 20 Gy and the best dose homogeneity in the target results from the two‐step optimization. Conclusion: An optimization procedure based on Monte Carlo has been developed to ensure accurate treatment planning and beam delivery with MERT. The Monte Carlo procedure is also useful in the investigation of the best collimation geometry by simulating existing photon MLCs and prototype electron‐specific MLCs.
MO‐E‐T‐617‐02: Dosimetric Evaluation of Inverse Monte Carlo‐Based Modulated Electron Beam Treatment Planning and Delivery Using a Few Leaf Electron Collimator
Authors: Al‐Yahya K , Schwartz M , Shenouda G , Verhaegen F , Freeman C , Seuntjens J
Published: June 2005

Purpose: To investigate the potential of improving the treatment planning and delivery of treatment to superficially located tumors using energy modulated electron therapy (EMET) based on inverse techniques and Monte Carlo dose calculation algorithms. This study investigates the application of EMET using a few‐leaf electron collimator (FLEC) in head & neck, sarcoma, and breast sites in comparison with three dimensional conventional radiation therapy (3D‐CRT) and intensity modulated radiation therapy (IMRT) techniques. Method and Materials: Treatment planning was performed for a parotid case, a sarcoma case, and a breast case. Three Monte Carlo calculated plans were compared for each case: 3D‐CRT, IMRT, and 3D‐CRT in conjunction with EMET (EMET‐CRT). For all patients, dose volume histograms (DVHs) were obtained for organs of interest. For each plan, homogeneity and conformity indices of dose distributions, sparing index (SPIN50/10) that quantifies the conformity of the low isodose lines, and the whole‐body dose equivalent (WBDE) were analyzed. Results: Adding EMET delivered with the FLEC to 3D‐CRT preserves target conformity and dose homogeneity and improves sparing of normal tissues. For the head & neck case the mean dose to the contralateral parotid and brain decreased relative to IMRT by 43% to 84%, and by 57% to 71%, respectively. Improved normal tissue sparing is also quantified as an increase in sparing index of 47% and 30% for the head & neck and the breast cases, respectively. The WBDE for EMET‐CRT was reduced by up to 72% when compared with IMRT. Conclusion: EMET delivered with the FLEC could be a valuable addition to currently existing treatment techniques especially when applied to superficially located tumors that are inherently difficult to plan using IMRT. The addition of EMET systematically leads to a reduction in WBDE especially when compared with IMRT.
MO‐E‐T‐617‐03: Direct Voxel Tracking Method for Calculating Dose in Deforming Anatomy
Authors: Heath E , Seuntjens J
Published: June 2005

Purpose: Current deformable dose calculation methods rely on simple translations or interpolations ignoring radiation field perturbation effects by the deforming structures. The aim of this work is to develop a method for Monte Carlo dose calculations where the dose deposition in voxels is directly tracked as the anatomy deforms. Method and Materials: The DOSXYZnrc/EGSnrc user code was modified to track dose deposition in non‐rectangular voxels obtained by applying deformation vectors from image registration software to the reference geometry. In the geometry checking subroutines each voxel is divided into 12 planes and the distance to the nearest boundary is determined. The deformation method was tested by comparing dose deposition in a deformed phantom with a static phantom with the same dimensions. Dose distributions were compared for both a rigid phantom in which only internal boundaries are deformed and a phantom whose outer dimensions were compressed. Dose deformations due to breathing motion were investigated with the use of a mathematical lung phantom for which displacements based on a measured breathing curve were applied to simulate motion of the diaphragm. Results: Dose distributions agreed within 1% for the simple rigid phantom. In the case of the compressed phantom the dose within the phantom agreed within 0.5%. In the mathematical breathing phantom dose differences of up to 16% were noted between the exhale phase and the accumulated dose over a 4 sec breathing cycle. Conclusion: We have developed a method for calculating dose in deforming anatomy where voxel coordinates are directly tracked as the anatomy changes. The code was validated by consistency checks and can be used to verify the validity of simplified dose reconstruction procedures such as translation or interpolation. We plan to implement this method to recalculate patient treatment plans using 4D‐CT data.
MO‐E‐T‐617‐05: IMRT Planning Based On Various Photon Dose Calculation Techniques at Inhomogeneous Media
Authors: Scholz C , Oelfke U
Published: June 2005

Purpose: An EGSnrc‐based Monte Carlo dose calculation tool was established to optimize fluence levels of intensity‐modulated treatment fields. It was used to benchmark dose distributions in inhomogeneous human regions optimized with a superposition as well as a standard pencil beam algorithm in order to quantify the applicability of the dose calculation engines even during the optimization process. Method and Materials: An EGSnrc‐based Monte Carlo dose calculation tool and a previously implemented superposition dose engine were adapted to a derivative of the inverse planning tool KonRad in order to iteratively optimize fluence patterns. BEAMnrc was applied to simulate 6MV and 15MV Siemens Primus accelerators. The acquired phase space information was input to a newly generated two‐source photon/electron beam model. Excellent congruence between Monte Carlo simulations and dose measurements was achieved for homogeneous and inhomogeneous phantoms. Results: Using Monte Carlo as benchmark, the systematic and convergence error of a pencil beam and the superposition dose engine for five IMRT treatments of clinical lung and five head&neck cases were ascertained. The pencil beam overestimated the prescribed PTV dose up to 16.7%, severe deficiencies were even detected in respect to the convergence error. For the head&neck cases a significant overestimation of dose deposited at tumor‐air‐intersections was observed. The superposition algorithm mostly generates acceptable results apart from intricate lung cases, where the dose still was overestimated by up to 6%. Conclusion: Applying highly‐sophisticated dose engines as superposition or Monte Carlo yields reliable dose information for IMRT‐planning in target regions with intricate tissue inhomogeneities. Our studies showed, that in such regions superposition or Monte Carlo techniques have to be used for the optimization and the final dose calculation of intensity‐modulated treatment plans, since standard pencil beam algorithms both lead to inappropriate fluence levels during the optimization and wrongly calculate the dose.
MO‐E‐T‐617‐06: Influence of Ion Chamber Response On In‐Air Profile Measurements in Megavoltage Photon Beams
Authors: Tonkopi E , McEwen M , Kawrakow I
Published: June 2005

Purpose: To investigate the influence of the ion chamber response including build‐up cap materials, on the measurements of in‐air off‐axis ratio (OAR) profiles in megavoltage photon beams using Monte Carlo (MC) stimulations with the EGSnrc system. Method and Materials: Two new techniques were developed for the calculations of OARs when the ion chamber is oriented horizontally or vertically. For a horizontally oriented chamber pre‐calculated tables of the response of an ion chamber inserted in a build‐up cap for different photon energies was used to compute the dose deposited in the air cavity on‐the‐fly within the BEAMnrc simulation. For a vertically oriented chamber the BEAMnrc code was modified so that it can be compiled into a shared library that serves as a particle source for the CAVRZnrc user code. With these BEAMnrc and CAVRZnrc changes the OAR could be calculated on the fly without intermediate phase‐space file generation. Results of the simulations were compared with experimental profiles from the 6, 10 25 MV photon beams from an Elekta Precise linac. Results: The calculated and measured in‐air profiles for all investigated beams and build‐up caps (brass, hevimet and two PMMA miniphantoms) are in a good agreement within the statistical and experimental uncertainties. The comparison between the calculated air‐kerma and OAR profiles shows 3–6% differences between air‐kerma and in‐air profiles measured with hevimet and brass caps and 0.5–1% differences for measurements with PMMA mini‐phantoms. Conclusion: The change of chamber response with distance from the central axis must be taken into account. For in‐air profiles measurements PMMA mini‐phantoms should be recommended over high‐Z material build‐up caps.
MO‐E‐T‐617‐07: Simulation of Organ Specific Secondary Neutron Dose in Proton Beam Treatments
Authors: Jiang H , Wang B , Xu X , Suit H , Paganetti H
Published: June 2005

Purpose: To determine the effective secondary neutron dose to patients undergoing proton therapy. Goal was to separate the secondary radiation generated from the proton treatment nozzle from the one generated inside the patient. Further, the secondary dose should be calculated for specific organs independently. Method and Materials: GEANT4 based Monte Carlo methods were used to study the neutron induced secondary dose deposited to healthy organs/tissues during proton therapy. A whole‐body patient model, VIP‐Man, was implemented as patient model. Two proton treatment plans for tumor in the lung tumor and paranasal sinus were applied to VIP‐Man. Internal (generated inside the patient body) and external (generated in the treatment nozzle) neutrons were studied separately. The averaged absorbed dose and neutron quality factor were deduced for each organ. The ICRP‐60 tissue weighting factors were used to calculate the whole body effective dose. Results: The magnitude of secondary dose in organs/tissues depends on the distance to the primarily irradiated volume. In general, the averaged secondary dose is at least three orders of magnitudes lower than the planned dose in GTV. The neutron quality factor is calculated as to be ∼6 since the neutron fluence includes a large fraction of thermal and low energy neutrons. Neutrons are mainly generated in the treatment nozzle. Results show that the whole body effective dose for the two proton plans is 0.162 Sv and 0.027 Sv, respectively. The statistic error of the estimated effective dose is better than 0.5% and 2% for internal and external neutrons, respectively. Conclusion: Our VIP‐Man Monte Carlo method is an effective tool for secondary dose calculations in patient geometry. Secondary dose can be calculated organ specific. Our method can be used for any treatment modality and is planned to serve as basis for more quantitative evaluation of secondary cancer risk following radiation therapy.
MO‐E‐W‐608‐01: Display Evaluation Demonstration Workshop
Authors: Samei E
Published: June 2005

The AAPM TG18 is a new initiative aimed to provide standard guidelines and procedures for acceptance testing and quality control of electronic display devices for medical applications. The recommendations, based on the newly‐designed TG18 test patterns, include detailed visual and quantitative methods and specific acceptance criteria for objective assessment of display quality using the TG18 standard test patterns and specified equipment. The display characteristics considered include luminance, luminance spatial and angular response, resolution, noise, veiling glare, reflection, color uniformity, geometrical distortions, and display artifacts. The goal of this demonstration workshop is to present a tutorial and demonstration on practical aspects of display set up and display performance evaluation based on the TG18 methodology. Representatives from the TG18 committee and from industry will be present to demonstrate and discuss display evaluation issues. Participants: Jeffrey Charette, Barcoview, LLC; Ehsan Samei, Duke University Medical Center; Noriyuki Hashimoto, Eizo Nanao Corporation; Dave Sorensen, Image Systems Corporation; Kenneth Compton, National Display Systems; Adi Abileah, Planar Systems; Hans Roehrig, University of Arizon.
TU‐A‐I‐618‐01: Evaluating Digital Mammography Systems
Authors: Berns E
Published: June 2005

This lecture is going to discuss the relevant practical issues for the medical physicist who plans on performing physics testing on full‐field digital mammography units. The lecture will be broken into parts. The first will discuss what is important in preparing for the testing that includes training recommendations, recommended and required test tools, and practical site issues. The second part will discuss important issues when performing the actual physics testing. This will include describing the actual physics tests and comparing them to screen‐film mammography, measuring patient dose, evaluating for artifacts, evaluating clinical images, and experiences from previous testing. Finally, the third part will discuss the writing of the report, technologist QC, tips for dealing with the site, the techs, and the ACR. Relevant information and examples from the different FFDM unit manufacturers will be included throughout the lecture.