bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐EE‐A4‐04: 4D CT Image‐Based Modeling the Deformation and Sliding Motion of Lungs
Authors: Xie Y , Chao M , Xing L
Published: July 2008

Purpose: To develop a novel method for registration of different phases of 4D CT with consideration of lung volume deformation and sliding motion. Method and Materials: Sliding motion of the lung against chest wall during breathing presents a challenging problem in image registration. The motion range of diaphragm during respiration is about 3 cm and the displacement vectors of tissue on the two sides of pleura are discontinuous. To register different phases of 4D CT, the lungs on these phases were first automatically segmented. A Scale Invariance Feature Transformation (SIFT) descriptor was used to find feature points shared by the template phase and target phases on the lung contours. A Fourier transformation of displacements of featured points was carried out. The low spatial frequency component of the displacement represents the sliding motion, whereas the high frequency component of the Fourier transformation represents the contribution from deformation and can be modeled by a conventional deformable model. After shifting the lungs on the target phase according to the filtered sliding displacements, a thin plate spline (TPS) deformable registration was applied between the template phase and shifted phases to obtain the displacement vector for each voxel. Results: We calculated the average diaphragm sliding distance between phase 1 and other phases with and without inclusion of lung sliding using patient data. It is demonstrated that the accuracy of the proposed method is three times better than that of conventional TPS method. With inclusion of sliding motion, the overlapped ratio of tumor contour is increased to 84.3% as compared to 78.0% using conventional approach. Conclusion: A hybrid method of deformable registration in spatial domain and low‐pass filter in frequency domain seems to model the lung breathing motion well. The combination provides a robust and computationally efficient method for registration of 4D CT thoracic images.
TU‐E‐350‐01: New Member Symposium/Meet the Experts
Authors: Herman M
Published: July 2008

The New Members Symposium will provide an introduction to the AAPM, our current officers, council chairs and operations. AAPM leaders will remain at the symposium to continue informal discussions following the brief opening presentations.

The New Members Symposium is followed directly by the Meet the Experts sessions in the same room. Bill Hendee, Gary Barnes, Dan Low and Jim Hevezi, all individuals with many years of experience will address current issues and lead discussions on many medical physics aspects of Imaging Research, Imaging Clinical, Therapy Research and Therapy clinical.

Educational Objectives:

1. To introduce new members to the AAPM leadership and operations.

2. To provide discussions with experts in medical physics
TU‐FF‐A1‐02: IMRT Verification with 3 Min/plan, 50 Plans/week, 1 Therapist and Only EPID Dosimetry
Authors: McDermott LN , Mans A , Wendling M , Stroom J , van Herk M , Mijnheer BJ
Published: July 2008

Purpose: To provide an overview of 3 years' clinical experience with EPID dosimetry as our only form of plan‐specific IMRT verification, used for all curative patient treatments. Method and Materials: Dose is checked in 2D per field (back‐projected to the isocentric plane perpendicular to the beam) or in 3D per plan (summed back‐projected images to a volume). The algorithm includes corrections for EPID and patient scatter, attenuation (using CT data) and the inverse square law. Open images for each field are used to calculate the attenuation. For cases with large inhomogeneous regions (e.g. lung), plans are re‐calculated with inhomogeneity corrections “off” and compared with an adjusted dose reconstruction. With γ = 1 for 3.0% (of isocentre dose) and 3.0 mm differences, an alert is raised if or . Results: This year, 50 (IMRT) plans per week are verified by 1 therapist. Physicists perform the initial EPID dose calibration and are available in case errors arise. Checks are performed in vivo, except one‐fraction treatments and large fields (> EPID), which are verified by EPID in a phantom. Typical total analysis time is 3 minutes (3 fractions in vivo). Between 2 and 4 serious errors have been prevented per year, i.e. plans changed based on discrepancies in 2D, or if necessary, 3D dose distributions. Conclusion: As the sole form of plan verification for a large radiotherapy department, the combination of in vivo and pre‐treatment EPID dosimetry allows a holistic approach to IMRT verification. Three years of clinical experience has proven the system to be highly efficient, sufficiently accurate and provides a safety net as the final check that all patients are correctly treated. EPID dosimetry solves time and management problems, and should become ubiquitous throughout radiotherapy centres worldwide.
TU‐FF‐A1‐03: Dosimetric Effect of Target Degradation On Helical TomoTherapy Treatment Plans
Authors: Staton R , Langen K , Meeks S
Published: July 2008

Purpose: On a TomoTherapy HiArt system, x‐ray target replacement is required every 9–12 months due to target degradation. Near the end of target life, the target thins and causes a softening of the beam profile at the lateral edges of the beam. The purpose of this study is to evaluate the dosimetric effects of this target degradation on recalculated helical tomotherapy treatment plans. Method and Materials: A measured beam profile near the end of target life was used to create a modified beam profile model. The model was then incorporated into the treatment plan sinograms for recalculation. The plans were calculated using a research version of the planned adaptive treatment planning software from TomoTherapy, Inc. Three plans were evaluated in this study: prostate, partial breast, and head and neck. The D50 of organs at risk (OARs), the D95 for planning target volumes (PTVs), and the local dose difference were used to evaluate the changes in the modified treatment plans. Results: For the prostate and head neck treatment plans, the D50s for OARs and the D95s for PTVs were within 1% for the original and recalculated treatment plans. The largest differences were found for the partial breast plan. The D95 for the breast PTV decreased by 1.8 % for the recalculated treatment plan. The maximum local dose difference inside the PTV was 6 cGy (3% of the prescription dose of 200 cGy). The absolute difference in the D50s for the heart and the ipsilateral lung were less than 0.5 cGy. Conclusion: The dosimetric effects of target degradation on calculated helical tomotherapy treatment plans were found to be small, less than 2% for DVH changes and less than 3% for local dose differences. Conflict of Interest: M. D. Anderson Cancer Center Orlando holds a research grant from TomoTherapy, Inc.
TU‐FF‐A1‐04: Dosimetric Effect of Setup Errors On NPC IMRT Treatments
Authors: Ng C , Wong G , Kwong D , Chiu A
Published: July 2008

Purpose: To investigate the resulting dosimetry error, change in TCP and NTCP from random and systematic setup errors for IMRT treatment of NPC. Method and Materials: The IMRT plans of 16 NPC patients treated with SIB technique were analyzed. Random setup errors were simulated by convolving the fluence of each field with Gaussian distributions of σ equal to 2 or 3 mm. Leaf motion calculation was then performed on the convolved fluence and the corresponding dose calculated. Translational setup errors were simulated by translating the isocenter in the x, y and z direction by 2 and 3 mm respectively. Patient pitch, yaw and roll of up to 3° were simulated by collimator, couch and gantry rotations. The dose distributions were computed after the change. For the original plan and altered plans, DVHs were generated for GTV and the following: L/R optic nerves, brainstem and spinal cord. Dosimetric indices, such as EUD, TCP and NTCP were computed and compared. Results: TCP is not significantly affected by setup errors. For 3 mm random error, the average decrease in TCP was 1.1%. For systematic errors, the average decrease in TCP was <1%. Average change in NTCP for brainstem and spinal cord was found to be with ±1% for both random and systematic setup errors. However, systematic setup errors results in a substantial increase in NTCP for the optic nerves, especially when isocenter is shifted craniocaudally. The average increase of NTCP from 3 mm shift is 22.2%. Patient yaw also resulted in the greatest increase in NTCP amongst rotational setup errors. Conclusion: Our results indicate that both random and systematic setup errors have little effect on TCP. Change in NTCP for brainstem and spinal cord were also negligible for our cases. Nevertheless, the optic nerves are very sensitive to systematic setup errors.
TU‐FF‐A2‐02: Dual‐Fields Rotational Total Skin Electron Irradiation/therapy
Authors: Xu M , Sethi A , Glasgow GP , Gao M , Ke Y , Rusu I , Roeske J , Chi A , Garza R
Published: July 2008

Purpose: We have developed a new technique for rotational total skin electron therapy (RTSET). The technique combines the rotational method of McGill University with the Stanford University angled dual‐fields method. We report dosimetry characteristics and in‐vivo dosimetry. Method and Materials: Patients stand on a rotational (0.9 rpm) platform at an extended SSD (332cm) with field‐size 133‐cm by 133‐cm. The gantry is angled 70° and 110° so that beam points above patient's head and below patient's feet, respectively, in order to minimize contaminant x‐ray dose. A “high‐dose‐rate” mode (600 MU/min) on a Varian‐21EX delivers a 6 MeV‐electron beam. Daily treatments require only about 0.5 h, one‐half of which is used for patient set‐up. Shields are used for eyes, nails, and toes. Dosimetry measurements include static dose‐rate at extended SSD, rotational dose‐rate for a rotating patient/phantom, and a power law correction for SSD variation. In‐vivo dose measurements are performed using XV‐films and MOSFET. Films strips are attached firmly on patient's skin to avoid any air gaps. Results: We obtained MU = Dose/(0.0751*0.39 *(332/SSD)2.25). Therefore, a prescription dose of 125cGy at 325cm SSD required 4068 MU or 7.5 revolutions. The dose distribution along the vertical direction was measured by a parallel‐plate ionization chamber in a phantom. For a patient prescribed 116cGy daily, the average measured surface dose with film was 110cGy, within 5% of prescribed dose. In‐vivo MOSFET on a patient prescribed 125cGy daily, measured doses were distributed from 99% to 102% from the prescribed dose of 125cGy. Conclusion: The dual‐field RTSET offers combined advantages of shorter beam‐on time, uniform dose distribution, larger treatment fields, and less x‐ray contamination than other techniques. Our in‐vivo measurements revealed that delivered dose matched prescribed dose to < 5% and dose uniformity was within 6% variation.
TU‐FF‐A3‐01: Analysis of Dose to Patient, Spouse/caretaker, and Staff, From An Implanted Trackable Radioactive Fiducial for Use in the Radiation Treatment of Prostate Cancer
Authors: Neustadter D , Corn B
Published: July 2008

Purpose: A fiducial tracking system based on a novel radioactive tracking technology is being developed for realtime target tracking in external beam radiation therapy. In this study we calculate the radiation dose to the patient, the spouse/caretaker, and the medical staff that would result from a 50uCi Ir192 radioactive fiducial marker permanently implanted in the prostate of a radiation therapy patient. Method and Materials: The local dose to the surrounding tissue was calculated using a Monte Carlo simulation. The equivalent whole body dose to the patient was calculated by summing the equivalent doses to the sensitive organs using standard organ weighting factors. The exposure of the spouse/caretaker was calculated according to the NRC guidelines. The exposure of the medical staff was calculated based on estimates of proximity to the patient and time spent in the vicinity of the patient. Results: The lifetime local dose to the surrounding tissue is below 40Gy at 4mm and below 10Gy at 6mm. The lifetime whole body equivalent dose to the patient is 32mSv. The lifetime dose to the spouse/caretaker is 0.2mSv, and the annual exposure of the medical staff is 0.1mSv for a doctor performing implantations and 0.17mSv for a radiation therapist positioning patients for therapy. Conclusion: The local dose to the tissue surrounding the implant, which is irradiated during therapy, is not expected to have any clinically significant effect. The equivalent lifetime whole body dose to the patient is insignificant in comparison to the whole body dose received from the therapy itself. The radiation exposure of the spouse/caretaker and medical staff is well below the recommended limits. We conclude that with respect to radiation exposure, there is no contraindication to applying this novel system in the radiation treatment of prostate cancer. Conflict of Interest: Research sponsored by Navotek Medical Ltd.
TU‐FF‐A3‐04: Intrafraction Motion of Prostate in Cyberknife Hypofractionated Radiotherapy
Authors: Xie Y , Djajaputra D , King C , Hossain S , Ma L , Xing L
Published: July 2008

Purpose: To report the characteristics of prostate motion as tracked using implanted fiducials during hypofractionated radiotherapy with CyberKnife. Method and Materials: Twenty one patients with prostate cancer who were treated with CyberKnife between January 2005 and September 2007 were selected for this retrospective study. The CyberKnife uses a stereoscopic X‐ray system to obtain the position of the prostate target through the monitoring of implanted gold fiducial markers. If there is a significant deviation, the treatment is paused while the patient is repositioned by moving the couch. The deviations calculated from X‐ray images acquired within the time interval between two consecutive couch motions constitute a data set. Results: A total of 427 data sets and 4439 time stamps of X‐ray images were analyzed. The average duration for each data set is 697 s. The spread of prostate position increases as the time elapses. At 30 s, a motion larger than 2 mm exists in about 5% of data sets. The percentage is increased to 8%, 11%, and 14% at 60 s, 90 s, and 120 s, respectively. A similar trend exists for other values of prostate motion. Conclusion: With proper monitoring during treatment, the prostate shifts observed among the patients can be kept well within the tracking range of the CyberKnife. On average the sampling interval of ∼40 s between consecutive X‐rays is adequate to ensure sub‐millimeter tracking. However, there is significant movement variation among patients and higher sampling rate is necessary in some patients.
TU‐FF‐A3‐05: Optimizing KV Fluoro Acquisition for Prostate Intrafraction Motion Evaluation
Authors: Adamson J , Wu Q
Published: July 2008

Purpose: Commercially available gantry mounted kV imagers are currently restricted to manual fluoroscopy acquisitions with fixed mAs & frame rate, limiting use of fluoroscopy for prostate intrafraction motion measurement. For consideration in future acquisition improvements, we investigate the parameters required to optimize the 3D accuracy of prostate intrafraction localization while minimizing imaging dose. Method and Materials: Prostate intrafraction motion is measured at our clinic using simultaneous kV fluoroscopy to visualize implanted markers for a hypofractionated radiotherapy protocol. For a 5‐beam step‐and‐shoot IMRT delivery we compare the current technique with acquiring images between MLC segments. Effects of imaging frequency and of including acquisitions during gantry rotation were also considered. The 3D localization accuracy was evaluated using simulations with existing sagittal cine‐MRI images from 6 patients consisting of 490 motion tracks for ∼8 minutes/track. Dose was evaluated using surface and central axis measurements on a 30‐cm diameter acrylic phantom, assuming adequate mAs values to achieve 80% registration success rate. Results: Simulations with the cine‐MRI data showed that 3D accuracy is acceptable even for low imaging frequencies: 95% of measurements were within 1.0 mm when imaging every 30s, and within 1.2 mm for 60s. 3D accuracy is adequate when imaging between MLC segments only (95% within 1.0 mm, 98% within 1.6 mm), with minor improvement when acquiring also during gantry rotation (95% within 1.0 mm, 98% within 1.5 mm). Maximum dose was lowered to 1.4 mGy when imaging only between MLC segments with gantry dependant mAs, compared to 3.3 mGy for the current technique and 21.1 mGy for a CBCT. Conclusion: Optimal intrafraction fluoroscopy measurement is achieved with adjustable acquisition frame rate, synchronization with MV beam delivery (acquisition between segments), and programmable gantry dependent mAs, resulting in high 3D accuracy and low imaging dose. Conflict of Interest: Partially supported by NIH Grant CA118037.
TU‐FF‐A4‐01: Virtual Simulator Design for Collision Prevention During External Radiotherapy Planning
Authors: Kum O , Kim S , Han Y
Published: July 2008

Purpose: Collision avoidance of the treatment accelerator components such as gantry, table, collimators, jaws, and fixation devices with the patient is one of the biggest concerns in external treatment planning. Most commercial treatment planning systems do not include collision prevention simulation step. On the other hand, a fool‐proof collision‐map, lookup table, and simpler analytical method guard only against the most apparent collisions. Thus, a comprehensive virtual simulator design for collision avoidance is very useful for external radiotherapy planning. Method and Materials: An accurate modeling of the treatment accelerator is possible with geometric data. Three‐dimensional patient modeling is also possible from the patient's CT data. Since each component in the data bank is described as an independent mesh modeling based on the type of associated polygons, relative position changes can be described easily for the device dynamics simulation. The relative motions of the gantry and the treatment table are collected from the treatment plan and the graphical user interface generates the events at the given time intervals. This visual system is incorporated with the treatment planning simulation system. Results: The quality verification of our virtual simulator for the potential collision has been performed with two combinations of treatment table and gantry rotations where a collision is eminent based on the visual assessment. The planner can search for beam paths with minimal critical structure interference before extensive optimization process. A database of CT and MR scans for all tumor sites is being built, which provide useful information to map all potential collision possibilities for all treatment isocenters. Conclusion: The important benefits of this virtual simulator is the replacement of the conventional laborious procedures required for the expensive hardware simulator unit, the efficiency increment, the accuracy improvement of radiation treatment procedure, and the cost reduction in terms of time and physical patient's presence.
WE‐E‐AUD C‐06: 4D Imaging of Lung Cancer Patients Treated with Stereotactic Body Radiotherapy (SBRT): Assessment of Target Volumes
Authors: Ouyang I , Wen N , Chen Q , Babij D , Aref I , Ajlouni M , Movsas B , Chetty IJ
Published: July 2008

Purpose: To compare target volumes assessed via 4D and free‐breathing CT scans for patients treated with peripheral lung lesions. Method and Materials: The target volumes of five lung cancer patients imaged using 4D‐CT and treated with hypo‐fractionated SBRT (12 Gy/Fxn × 4Fxn) were retrospectively analyzed. For each patient 6‐to‐8 CT datasets were acquired between inhale and exhale respiratory phases on a Philips 16 slice 4D‐CT scanner. The GTV was segmented on each dataset using a maximum‐intensity‐projection (MIP) method and an ITV (ITV4D), representing the composite of GTVs, was formed. The ITV4D was expanded uniformly 5mm to generate a PTV (PTV4D). The GTV was also contoured on the free‐breathing scan and expanded using population‐based margins of 5mm and 10mm in the axial and longitudinal planes, respectively, to form a free‐breathing‐based PTV (PTVFB), following RTOG ♯0236. Finally, a target volume defined as a composite of GTVs contoured on only the inhale and exhale datasets was generated to form the ITVInh_Exh. Results: For three of five patient images, PTV4D was substantially larger than PTVFB (average increase of 33%; max.=65%). In one case the volumes were equivalent and in the remaining case PTV4D was 11% smaller than PTVFB. Significant shape changes were also observed in some instances between PTV4D and PTVFB suggesting that PTVFB was improperly designed. The ITVInh_Exh was smaller than the ITV4D in all cases (mean=31%; max.= 78%, smaller) suggesting that the inhale and exhale breathing phases sometimes fail to capture the largest extents of tumor motion in the respiratory cycle. Conclusion: Results suggest that, based on 4D imaging, the use of population‐based margin expansions may not adequately account for tumor motion of peripheral lung tumors. This may be of increased consequence in the SBRT setting, where the overall effects of motion may be escalated given the small number of fractions.

Acknowledgement_NIH‐R01‐CA106770.
WE‐E‐332‐02: Dosimetric Characterization of a Cone Beam O‐Arm Imaging System
Authors: Weir V , Zhang J , Fajardo L , Hsiung H , Ritenour E
Published: July 2008

Purpose: The O‐arm is a cone beam imaging system designed primarily to support orthopedic surgery as well as for image‐guided and vascular surgery. Using a gantry that can be opened or closed, the O‐arm can function as a 2D fluoroscopy device or collect 3D volumetric imaging data like a CT system. Our clinical applications of the O‐arm in spine surgical procedures, assessment of pedicle screw position, kyphoplasty procedures, and etc show that the O‐arm 3D mode provides enhanced imaging information in the surgical procedure compared to radiographs or fluoroscopy alone. However, the radiation dose of the O‐arm has remained uninvestigated. This study is to investigate patient dose and scatter radiation from an O‐arm and compare the results to those from a CT scanner and a conventional C‐arm. Method and Materials: The patient dose was measured using a 0.6 cc Farmer ion chamber and 30 cm long CT head and body phantoms. Scatter radiation was measured at several locations around the O‐arm, at 1m, 2m and 3m distances from the iso‐center of the O‐arm, in both the 2D fluoroscopic mode and the 3D mode with a Radcal 10×5−180 pancake ion chamber using a 30 cm long CTDI body phantom as the source of scatter. The same measurements were made for an OEC C‐arm and a 64 slice CT scanner, respectively. Results: The results show that under identical technical conditions and with the same scan length, the O‐arm 3D mode delivers radiation dose to patients and scatter dose to personnel that is comparable to that of the 64 slice CT scanner. The O‐arm 2D mode produces similar scatter radiation as a conventional GE OEC fluoroscopic C‐arm system. Conclusion: Our study demonstrated that the O‐arm had comparable radiation dose to patients and radiologists as CT and C‐arm systems.
WE‐E‐332‐06: Estimated Cumulative Effective Dose From PET/CT in Pediatric Patients with Malignancies
Authors: Zhang D , Chawla S , Nagata K , Federman N , Soujanya N , Boechat I , Angel E , McNitt‐Gray M
Published: July 2008

Purpose: To estimate the cumulative effective dose to pediatric patients with malignancy from regularly PET/CT scans. Method and Materials: We retrospectively reviewed 248 PET/CT studies performed on 78 pediatric patients with malignancies who were being periodically scanned for evaluation of disease progression. To estimate the effective dose from the CT portion of the exam, we used the ImPACT CT Patient Dosimetry Calculator software package which provides estimates based on patient specific scan parameters (scanner, kVp, mAs, collimation, scan coverage and so on). To estimate effective dose from the PET portion of the study, OLINDA software (Vanderbilt University) was used which provides estimates based on patient specific FDG doses. Since estimations from both parts were based on adult models, effective doses were adjusted for patient age according to published values. Results: The average effective dose from a single CT scan was 20.3mSv, ranging from 2.7 to 54.2 mSv. For the PET study the average effective dose was 4.6mSv, ranging from 0.4 to 7.7mSv. For a combined PET/CT study the average was 24.8 mSv, ranging from 6.2 to 60.7mSv. The average cumulative effective dose per patient from combined PET/CT studies was 78.9mSv, ranging from 6.2 to 399 mSv. Radiation doses varied significantly depending on the number of studies as well as the number of additional CT scans performed. Conclusion: Effective doses from combined PET/CT studies for pediatric patients with malignancies may be significant. While some of these patients will go on to radiation therapy, many will not. While PET/CT remains an important non‐invasive diagnostic, staging, and surveillance modality, the decision to use PET/CT should be made with particular awareness to the cumulative radiation dose, potential dose reduction options (such as further reducing tube currents) and the overall benefit of this exam.
WE‐E‐332‐07: Workloads for High Dose Rate Brachytherapy Facilities
Authors: Glasgow G , Rusu I , Albuquerque K
Published: July 2008

Purpose: Neither NCRP Report 147, Structural Shielding Design… Facilities nor NCRP Report 151, Structural Shielding Design… Facilities address high dose rate (HDR) brachytherapy facility shielding. From a review of HDR patients treated at a major medical center, we report yearly patient census, treatment times, and workloads, compare them to literature data, and observe the consequences for HDR facility design. Method and Materials: For shielding calculations for an HDR vault, the yearly workload is defined as the product of the air kerma strength (Gy m2/h) at 1 m and the time (h) the source is used yearly. For a conventional 10 Ci HDR Ir‐192 source, 0.04 Gy m2/h is commonly used. Limited literature data on HDR workloads varies between 4 Gy/Yr to 15 Gy/Yr. From a two year (2006, 2007) review of patient treated with HDR, we identify patient treatment dates, anatomic sites, prescribed absorbed doses, fractions, and total treatment times. From these data we extract yearly patient census, workloads by anatomic site and total yearly workloads. Results: By anatomic site, of 41 patients treated yearly, 14 were vagina, 13 uterus, 7 breast, 3 base of tongue, 2 sarcoma, and 2 head and neck. The average total number of fractions yearly was 232. Excluding quality assurance procedures, the average total yearly treatment time was 16.4 h and the average yearly workload at 1 m was 0.655 Gy/Yr, about 0.013 Gy/Week. These data are well below suggested literature values. This workload is less than 20% of the yearly workload of 4 Gy assuming 200 patients per year and a total yearly treatment time of 100 h used in this HDR facility's design. Conclusion: Using current popular HDR treatment methodologies, workloads of 1 to 2 Gy/Yr likely are sufficient for HDR facility design, potentially reducing shielding costs.
WE‐E‐342‐02: (Part II) 50 Years of Women in Medical Physics — Symposium organized by the AAPM Minority Recruitment Subcommittee
Authors: Borras C , Martel M , Vickers S , Brateman L , Okuno E , Gueye P
Published: July 2008

The AAPM celebrates past and current contributions of distinguished female scientists to medical physics in the areas of radiology, nuclear medicine and radiation therapy, as well as in some non‐traditional areas of medical physics, such as mechanics, optics and electromagnetism. The impact of female medical physicists' work at the scientific, educational and professional levels will be analyzed and key individuals will be recognized. Among the twenty female charter members, the achievement of at least three of them was extraordinarily. Mary Louise Meurk won the AAPM Award for Achievement in Medical Physics; Edith Quimby, the AAPM William D. Coolidge Award, and Rosalyn A. Yalow, the Nobel Prize in Physiology or Medicine! Many more women joined the AAPM after them. Some were elected to lead the organization. Among the AAPM female officers, there have been two presidents, one secretary and six treasurers. Women have been very active in medical physics world‐wide. In Europe, the majority of medical physicists in clinical settings are women. The symposium will present an overview of the advancement of several medical physics applications in both diagnosis and therapy and will introduce novel methods of physics teaching such as explaining the physics of soccer. The future of the profession and the impact of the increasing number of women joining it will be addressed.
TH‐A‐350‐01: Putting the A Into ADCL, the Role of the Calibration Laboratory Accreditation Sub‐Committee
Authors: McEwen M , Stevens D , Slowey T , Seuntjens J
Published: July 2008

The Calibration Laboratory Accreditation Subcommittee (CLA) of the AAPM oversees the accreditation of the ADCLs (Accredited Dosimetry Calibration Laboratories) who provide calibration services to clinical users in North America and around the world. The AAPM accreditation is similar to other accreditation programs that use the international standard for calibration and testing laboratories (ISO17025) but with additional focus on technical competencies through a strict set of AAPM‐developed Criteria. The purpose of this accreditation is to provide users with the highest level of confidence in equipment calibrations which form the basis for radiation treatments in the clinic.

The CLA is currently working towards obtaining recognition by the National Cooperation for Laboratory Accreditation (NACLA) that the accreditation program satisfies the ISO standard 17011. This standard covers accrediting bodies and one of its requirements is that AAPM develop a pool of trained assessors. The main of aim, therefore, of this presentation is to give potential assessors (who could be members of the AAPM outside of the CLA) an introduction to the accreditation process with particular focus on on‐site assessments. Accreditation by the CLA requires a site visit every four years in which every aspect of the laboratories performance (as related to calibration services) is assessed. Quality manuals and procedures are reviewed and sample calibrations witnessed to verify that the laboratories are continuing to provide the high quality of service demanded by the AAPM Criteria.

Although this lecture is aimed specifically at a small sub‐group of AAPM members there is much in the discussion of quality systems and the audit process that would of value to a wider audience. The details may be different but the approach set out here (e.g. development and review of Quality Systems, gathering of objective evidence) can be applied to a variety of QA applications in clinics and elsewhere.

Since it is not possible to cover the whole accreditation process in one lecture those interested in becoming assessors for the CLA should contact the lead author prior to the meeting for additional material to review.

Educational Objectives:

1. Understand the role of the CLA in the accreditation of the ADCLs.

2. Understand the requirements of the AAPM Criteria for Accreditation.

3. Understand the steps in the accreditation process.

4. Understand how an accreditation audit should be carried out.
TH‐SAMS‐AUD B‐01: Introduction To: Quality Assurance for Advanced RT Technologies—The Challenge for RT Clinical Trials
Authors: Olch A
Published: July 2008

We as medical physicists have a crucial role to play in ensuring that all patients on radiotherapy protocols are treated comparably. Without this comparability, the validity of outcome results from the pooled patient data may be jeopardized. Advances in radiation therapy technology and delivery techniques have naturally led to the desire to incorporate such new tools into clinical trials, yet standardized quality assurance (QA) procedures are not fully developed and widely practiced. Although several task groups within the AAPM have been formed to set standards for QA for these new technologies, a major challenge is to conduct clinical trials that involve both the old and new technologies without overwhelming individual physicists with additional testing. National and international multi‐institutional clinical trials uniquely challenge the medical physics community to maintain comparability while at the same time requiring or permitting patient treatments that incorporate advanced technologies such as IMRT, image guided radiotherapy, image fusion, and other techniques.

The AAPM Working Group on Clinical Trials presents this continuing education symposium in order to discuss the efforts underway to design QA methods for advanced radiotherapy technologies especially in the context of clinical trials with the intent to address the issue of comparability and standardization of protocol data. We will present the work of Task Group 113, an important player in these efforts, on providing guidance as to physics practice standards for QA for radiotherapy clinical trials. The task group's recommendations on QA procedures and reporting methods are intended to facilitate highly consistent protocol treatments and data submission.

The Working Group on clinical trials has identified several topics that pose significant challenges with respect to consistency of physics practices: dose calculations with heterogeneity corrections, localization verification, image fusion techniques, and the treatment of moving targets. In this course, the history and the current state of the art will be described for each topic. The discussion about these areas should be of interest whether or not one is involved in clinical trials.

Educational Objectives:

1. Understand the quality assurance issues facing Medical Physicists using advanced technologies and how these relate to clinical trial data validity.

2. Learn what Task Group 113 is doing to address the accuracy and consistency of data we send to quality assurance review centers.

3. Understand the problems and potential solutions to controversies in quality assurance measures for image fusion, target motion, patient localization, and heterogeneity corrections.
TH‐SAMS‐AUD B‐03: Requirements for Addressing Respiratory Motion in Cooperative Group Clinical Trials (SAM Session)
Authors: Ibbott G
Published: July 2008

In mid‐2006, the National Cancer Institute (NCI) published updated guidelines for the use of intensity‐modulated radiation therapy (IMRT) on clinical trials, specifically when the target volume included the thoracic region or other areas in which respiratory motion could have a significant effect. In addition to requiring heterogeneity corrections, the NCI now requires that the clinical protocol address the localization and immobilization of both the patient and the tumor. Imaging must be performed in a manner that provides a representation of the target volume without motion artifact. Procedures must be defined to document reproducible daily position of the patient and target. Some form of credentialing is required.

The Radiological Physics Center (RPC) has been enlisted to participate in the credentialing process for institutions participating in certain cooperative group trials in which respiratory motion is an issue. To accomplish this, the RPC has constructed several phantoms that mimic the thoracic and abdominal region, and which can be placed on a moving platform to simulate respiratory motion. The combination of phantom and moving platform have been used to evaluate compensation techniques for respiratory motion at several institutions. The techniques employed and the results of these measurements will be described as well as those reported in the literature.

Educational Objectives:

1. Review the structure supporting cooperative group clinical trials in the US.

2. Become familiar with the NCI guidelines for the use of IMRT in clinical trials.

3. Learn about the effects of respiratory motion during thoracic treatments.

4. Understand the information derived from the RPC's moving anthropomorphic phantoms.

This research is supported by grants CA 10953 and 81647 awarded by NCI, DHHS.
TH‐SAMS‐AUD B‐04: Heterogeneity Corrections in Clinical Trials
Authors: Papanikolaou N , Klein E
Published: July 2008

Clinical trials rely on accurate dose reporting, both for the planning target volumes and organs at risk (OAR). Until recently, clinical trials have not mandated that heterogeneity corrections be applied in dose calculations. Therefore history of prescription and reported doses has been for homogenous water equivalent media. The reticence is attributed to lack of confidence in commercial treatment planning algorithms and in lack of direction as how to change prescriptions when accounting for heterogeneous media. Thorax irradiation is the most challenging example of where corrections and prescription changes are difficult but necessary. Two well reported studies, RTOG‐8808 and RTOG‐9311, required complementary parallel calculations performed. One set was the prescribed and treated homogeneous (water) based calculations, and the other was retrospective heterogeneous CT‐based calculations, but using the homogeneous based MU. The calculations demonstrated major variations in the doses that would have been reported depending if heterogeneity corrections were exclusively used. This was confirmed by dosimetric studies showing the failure of algorithms of the 1990s, particularly in regions of non‐equilibrium. As OAR, particularly lung volume, were often the limiting factor, dose calculations to the lung itself had to be accurate. High energy‐small fields had the largest deviations. The commercial introduction of superposition and Monte Carlo algorithms has remedied the situation by providing accurate calculations, provided they are implemented properly. Simultaneously, publication of AAPM's Report of TG‐65 (Inhomogeneity Corrections) gave direction to physicists as how to work with clinician partners to transition to correction based plans and change prescriptions accordingly.

Educational Objectives:

1. The history of corrections for clinical trials.

2. Progression of algorithms.

3. Methods for making the transition to using heterogeneity corrections.
TH‐A‐AUD C‐01: TomoTherapy Commissioning and QA
Authors: Staton R
Published: July 2008

Helical tomotherapy using the HiArt system can provide highly conformal dose distributions through the implementation of helically delivered intensity modulated radiation therapy (IMRT). The TomoTherapy HiArt system uses a 6 MV linear accelerator mounted on a ring gantry with a simultaneously translating couch. The system also provides image guidance via megavoltage CT. Since this design is significantly different than traditional medical linear accelerators, a unique quality assurance program must be implemented to thoroughly test the HiArt delivery system.

This course will provide an overview of the HiArt system components, acceptance testing and commissioning, beam “twinning” for recommissioning of an existing machine to match the TomoTherapy “gold” standard, and basic quality assurance recommendations. The use of ion chamber and diode arrays for patient‐specific delivery QA will also be discussed.

Educational Objectives:

1. Understand the core concepts of helical tomotherapy.

2. Understand the commissioning process for a new HiArt system and the beam “twinning” and recommissioning of an existing HiArt system.

3. Understand the machine QA procedures for helical tomotherapy.

4. Understand the helical tomotherapy patient‐specific delivery QA process, including the use of ion chamber and diode arrays.

Conflict of Interest: Our group holds a research grant from TomoTherapy, Inc.
TH‐B‐AUD A‐01: Accurate Clinical Measurements
Authors: Gibbons J , Seuntjens J
Published: July 2008

Image‐guided radiation therapy deliveries are becoming increasingly complex and their verification involves clinical measurements in situations that are no longer covered by reference dosimetry protocols or relative dosimetry procedures with simple corrections. In this era of joint imaging‐therapy developments, accurate dosimetry techniques are sometimes trivialized and important effects not understood or ignored. However, clinical measurements increasingly involve reference and relative dosimetry of complex charged particle disequilibrium configurations and their interpretation.

This presentation consists of two parts: the first part revisits principles of measurement dosimetry, definitions of detectors and phantoms, reference dosimetry for conventional beams and also discusses some new developments in reference dosimetry of non‐conventional beams. The second part of the presentation concentrates on relative dose measurements with the goal to generate 3D distributions as well as integrated measurements and derived quantities. We conclude with a discussion of relative dosimetry in special cases including the photon build‐up region as well as narrow fields.

Educational Objectives:

1. To understand the principles of clinical measurement dosimetry.

2. To get an overview of detectors and phantoms for reference and relative dosimetry.

3. To understand standard clinical reference dosimetry techniques and be exposed to some of the new developments in reference dosimetry in non‐standard beam configurations.

4. To get an overview of relative dosimetry techniques for the purpose of 3D dose distributions

5. To be aware of the complications of measurements in electronic disequilibrium such as in the photon build‐up and for small photon fields.
TH‐B‐342‐01: X‐Ray Imaging Dose to Patients in the Era of Image‐Guided Radiation Therapy
Authors: Ding G , Price R , Coffey C
Published: July 2008

Image‐guided radiation therapy (IGRT) makes it possible to locate the treatment target before each radiation dose is delivered while the patient is in the treatment position. It not only minimizes the volume of normal tissue exposed to radiation during treatment but also ensures adequate dose to the treatment target. With the advance of technology, IGRT has emerged as the new paradigm in radiotherapy. The increased clinical availability of new emerging imaging procedures, such as cone beam CT, has resulted in a dramatic growth in its usage and therefore, IGRT procedures may also entail new risk to radiosensitive organs. Unlike diagnostic imaging in radiology, image‐guided procedures are performed much more frequently or daily. Knowledge of radiation dose to patients and accurate dosimetry of radiation dose to organs from each imaging procedure is becoming increasingly important for clinicians as information to consider in making informed decisions regarding the increased dose to radiosensitive organs. This lecture will provide an overview of the commonly used image‐guided rocedures and discuss recent advances in the accurate dosimetry for these imaging procedures, especially for emerging cone beam CT scans. The x‐ray imaging procedures in radiotherapy include megavoltage electronic portal imaging (MV EPI), kilovoltage digital radiography (kV DR), megavoltage cone‐beam CT (MV‐CBCT) and kilovoltage cone‐beam CT (kV‐CBCT).

Educational Objectives:

1. Understand the commonly used image‐guided procedures in radiation therapy and differences between diagnostic x‐ray imaging and image‐guidance imaging.

2. Obtain a prospective view about radiation doses to organs from each image‐guided procedure, especially cone beam CT.

3. Learn the large variations between dose to bone (or bone marrow) and dose to soft tissues for x‐rays at kilovoltage energy range.
TH‐C‐350‐08: Dosimetric Verification of Modulated Electron Radiotherapy Delivery Using Photon Multileaf Collimator
Authors: Jin L , Ma C , Eldib A , Fan J , Chi Z , Li J
Published: July 2008

Purpose: To investigate the dose accuracy of modulated electron radiotherapy (MERT) delivered using the photon multileaf collimator (pMLC) on a Siemens Primus accelerator. Method and Materials: A Monte Carlo based inverse treatment planning system was developed for the 3D treatment planning process. Phase space data of 6, 9, 12 and 15 MeV electron beams were accurately commissioned and used as the input source for Monte Carlo dose calculations. Treatment planning was performed based on a 3D CT data of a “breast phantom” which mimics a breast cancer patient. SSD was chosen 60 cm in the planning based on the previous investigation. Rigorous film and ion chamber dosimetry was carefully established for the MERT plan verification using the breast phantom and a solid water phantom. The MERT plan verification was done by comparing isodose distributions, dose profiles and point doses with those obtained from the Monte Carlo plan calculations. Results: The plan was delivered with 22 segments with both energy and intensity modulated. The relative isodose distributions and dose profiles between film measurements and calculations agreed each other within 1%/1mm. Absolute doses given by the ion chamber measurements in the solid water phantom showed differences from the Monte Carlo dose calculations by 1.7%, 0.5%, 1.6% and 1.5% for 6, 9, 12 and 15 MeV energy component of the plan, respectively while overall measured absolute dose accuracy is 1.37%. In addition, the dose alteration caused by the film in the lung region was identified and confirmed by recalculating the treatment plan with detailed geometry that includes both the film (thickness and density) and the breast phantom. Conclusion: Our in‐house developed Monte Carlo treatment planning system is capable of performing accurate dose calculation and treatment optimization for MERT, and the pMLC has a great potential to deliver MERT treatment plans accurately and efficiently.
TH‐C‐350‐10: Improving Accuracy of Electron Density Measurement in the Presence of Metallic Implants Using Orthovoltage Computed Tomography
Authors: Yang M , Virshup G , Mohan R , Shaw C , Zhu X , Dong L
Published: July 2008

Purpose: To evaluate the improvement in electron density measurement and metal artifact reduction using orthovoltage computed tomography (OVCT) imaging compared with conventional kilovoltage CT (KVCT). Method and Materials: We constructed a bench‐top CT imaging system with adjustable x‐ray tube voltage up to 320 kVp. A commercial tissue‐characterization phantom loaded with various tissue substitute inserts and two metal inserts — Titanium (Ti) and Aluminum (Al) were scanned using 125 kVp (KVCT) and 320 kVp (OVCT) x‐rays, respectively. The metal artifacts are evaluated in two ways — visually in the constructed axial CT image and by the deviation of estimated electron density from true electron density for uniform materials outside the metal. The stoichiometric calibration curves were obtained for both KVCT and OVCT imaging system by following the Schneider method. Results: The metal streak artifacts are seen to be reduced significantly in OVCT image than in KVCT image, especially in the area near Ti insert. The deviation of estimated electron density for the materials outside the metal are also reduced significantly by using OVCT than by using KVCT: from 42% (maximum) and 18% (root‐mean‐square) to 12% and 2.0% for heavy artifact area, and from 12% (MAX) and 3.0% (RMS) to 6.3% and 1.4% for light artifact area, respectively. The relationships between CT numbers (Hounsfield Unit) and relative electron densities (to water) are more predictable for both tissue substitutes and real biological tissues using OVCT than using KVCT. Unlike KVCT, the calibration curve for OVCT is insensitive to the tissue substitutes selected for direct electron density calibration. Conclusion: OVCT may be a good option for high precision radiotherapy treatment planning, especially for patients with metal implants and especially for charged particle therapy, such as proton therapy. Conflict of Interest: Collaborated with Varian Medical Systems.