bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐T‐514: Full 3D Heterogeneous Dose Calculation for Total Body Irradiation: A Comparison Study Between Different Treatment Planning Systems
Authors: Lavallee M , Gingras L , Aubin S , Cote C , Chretien M , Beaulieu L
Published: July 2008

Purpose: To realise a full 3D heterogeneous dose calculation for total body irradiation (TBI) cases treated with a translating couch technique and to compare different treatment planning tools. Method and Materials: A retrospective study was performed on 7 patients. Dose distributions obtained with Pinnacle3 v.7.9u (Philips Medical Systems) were compared with those calculated with our actual TBI planning system Theraplan Plus (TPP) by MDS Nordion/Nucletron. Two different Pinnacle3 models were studied: standard beam commissioning (std_Pinnacle3) and TBI commissioning (TBI_Pinnacle3). For the later case, the commissioning was adapted for TBI and its special conditions (extended SSD of 190cm, large field, acrylic beam spoiler, and out of field dose (OFD)). Results: The retrospective study on 7 patients showed significant differences between TPP, std_Pinnacle3 and TBI_Pinnacle3 dose distributions. Relative homogeneous mid‐line doses were compared. Differences up to 12% were obtained and a systematic overestimation of 5% was found in patients extremities (e.g.: head and legs) between TPP and TBI_Pinnacle3. Average dose underestimation of 3% was observed between std_Pinnacle3 and TBI_Pinnacle3. Differences in patient extremities are attributed to the OFD contribution which is not correctly computed in TPP and std_Pinnacle3. Dose comparison outside the patient mid‐line showed greater differences (up to 20%) between models. Because only TBI_Pinnacle3 takes into account the beam spoiler effect, other models underestimate shallow doses. An accurate 3D heterogeneous dose calculation is possible with TBI_Pinnacle3 model. Results showed major differences (homogeneous versus heterogeneous) in high and low density regions as bones and lungs. Dose overestimation of 5% was observed in bone regions and dose underestimation of 5% to 10% was observed in lung regions. Conclusion: Those results are of major interest since, depending on the treatment planning system and its beam commissioning, it could lead to significant dose misevaluation. Heterogeneous dose calculation should be performed with TBI specific beam commissioning.
SU‐GG‐T‐519: Commissioning of the Commercial Planning System for the Electron Arc Treatment
Authors: Kang S , Cheong K , Hwang T , Kim S , Kim K , Oh D , Bae H
Published: July 2008

Purpose: Most commercial radiation treatment planning systems do not provide the planning mode for the electron arc treatment which most linear accelerators have. We have commissioned a new exclusive physics machine for pseudo electron arc planning and checked the validity with phantom measurements. Method and Materials: With an electron arc aperture tray under Varian 21‐EX, minimum beam data including depth doses, lateral profiles and output factors were measured and transferred into a Pinnacle3 for commissioning. An acrylic cylindrical phantom wrapped with 1 cm‐thick bolus was used for planning and measurement. Multiple static beams with 5 degrees interval were adopted for the pseudo arc planning and delivered via dynamic electron arc mode of the Varian linac. For the evaluation of the pseudo arc planning, measurements were made with MOSFET detectors placed at five different points beneath the bolus and on the surface. Results: Pinnacle3 was commissioned successfully for the electron arc treatments with a fixed field of 6×25 cm2 on the Varian 21‐EX. The extended distance from the beam‐shaping‐edge of the electron arc aperture to the surface makes the beam characteristics totally different from those for the usual electron beams. The MOSFET measurements agreed with the calculation to within 5% except the ends of the arc where 16.5% of discrepancy was obtained. Conclusion: Without the electron arc planning function, multiple static beams can be exploited successfully for the electron arc treatment on the commercial planning system. However, a new physics machine for the exclusive electron arc therapy should be commissioned because of the totally different characteristics of the electron beam for arc therapy. In‐vivo dosimetry is a necessity for the plan evaluation.
SU‐GG‐T‐524: Initialization Strategy and Concurrent Imaging for Single 360 Degree Arc Intensity Modulated Treatment Delivery
Authors: McNutt T , Tryggestad E , Susil R , Ford E , Bzdusek K , Sandin C , Wong J
Published: July 2008

Purpose: Single 360 degree arc treatment with variable MU per degree and changing MLC apertures provides an efficient means for delivering highly conformal radiation therapy. Additionally, the treatment geometry is amenable to CT image acquisition during the delivery enabling verification of patient position. The challenge with the technique is finding the optimal set of apertures over the arc. Aperture based optimization (MLC leaf positions) is the natural approach, but suffers for complex targets if the initial starting condition is simply the fields exposing the target around the arc. The problem occurs when the optimal solution would have the MLC closing off a larger portion of the target requiring large positional changes from the initial condition to the optimal position. In this case gradient based optimizations fall short in that the derivative of the dose distribution with respect to the leaf position is flat for locations further from the leaf tip. In order to remedy this problem, improved initialization of the initial MLC positions around the arc based on the target geometry are proposed. Method and Materials: A research version of the Pinnacle3 RTPS was used to plan the single arc delivery. The approach uses 36 equispaced beams over a 360 degree arc, and optimizes the plan using a single MLC aperture for each beam and the direct machine parameter optimization (DMPO) technique in the system. The Elekta Synergy linear accelerator was used to deliver the treatment and for cone beam CT acquisition. Results: Initial results show dose conformality similar to that of traditional intensity modulated radiotherapy with the 360 degree delivery using geometry based pre‐initialization of the apertures. Additionally, kilovolt image acquisition during delivery was possible. Scattered radiation and the interplay between image acquisition frequency and the pulse rate of the treatment beam influence the image quality but not significantly.
SU‐GG‐T‐529: Pre‐Clinical Evaluation of a 4D Tracking DmMLC‐Based Delivery to Lung Tumor
Authors: Liu Y , Guo B , Lin L , Papanikolaou N
Published: July 2008

Purpose: The aim of this study is to provide a pre‐clinical evaluation of four‐dimensional tracking radiation therapy to lung tumor using a prototype tracking system. The evaluation was based on films dosimetric analysis, time delay measurements and treatment planning DVH analysis by using two types of dynamic phantoms. Method and Materials: The key component of the 4DTRT system was a prototype of TrackBeam. It consists of an image processing tools and a first‐of‐its‐kind dual‐layer micro MLC. DmMLC has two layers of orthogonal leaves which provide advantages in speed and conformality when forming beam aperture for tracking. The TrackBeam was mounted to a Varian Linac and connected to a workstation which process the online MV fluence and controls each leaf's motion. A Quasar dynamic phantom was used for radiographic film irradiation with 4DTRT and also 3DCRT. The phantom has a Gafchromic film insert and a gold marker in the insert. It can move in Sinusoid mode as well as real patient respiratory cycle. Another tissue‐equivalent thorax dynamic phantom was used for DVH analysis after a phantom‐based 3DCRT planning and a 4DTRT planning developed respectively. Results: The synchronization of marker motion and the DmMLC leaf motion was achieved within less than 0.05 seconds. The films analysis indicated that total 29.91% over the tolerance of 5% and 5.09% of over the tolerance of 5% when the 3DCRT and 4DTRT films compared to a static film. The DVH comparisons indicate 4DTRT reduces significant dose to the Ring from 75% (80% volume) to 60% (50% volume). 4DTRT also reduces considerable amount dose to the total lung from 33% (30% volume) to 22% (22%). Conclusion: The 4D tracking using MLC provides a feasible solution delivering conformal dose to lung tumor and spare the surrounding tissue. Conflict of Interest: The work was partially supported by Initia‐RT medical device.
SU‐GG‐T‐532: Dosimetric Comparison of Proton Delivery Techniques: Double‐Scattering and Uniform‐Scanning
Authors: Slopsema R , Lin L , McKenzie C , Yeung D , Li Z , Hsi W , Palta J
Published: July 2008

Purpose: To compare proton dose distributions generated with double‐scattering to uniform‐scanning for different clinical sites. Method and Materials: The ‘universal nozzle’ developed by IBA incorporates several delivery modes. In double‐scattering (DS) a flattening filter scatters the proton beam into a flat circular profile. In uniform‐scanning (US) two dipole magnets scan the beam into a rectangular profile. US covers larger volumes both laterally and in depth, and has dosimetric characteristics that are different from US. This study deals with cases that can be treated with either US or DS. Eclipse (Varian) treatment planning is commissioned for both delivery modes. Comparison of water‐phantom calculations to measurements validates the treatment‐planning algorithm. We compare the dose for the following sites: prostate (2 cases), head‐and‐neck (4 cases), cranio‐spinal (3 cases). Dose‐volume‐histograms are used to evaluate target coverage and dose to critical structures. Results: The US in‐air penumbra is typically smaller because of less scattering material in the beam path. For a range of 15.0g/cm2, modulation of 8.0g/cm2, and air gap of 12.0cm, the 80%–20% penumbra at 11.0cm depth is 4.4mm in US and 6.9mm in DS. In addition, the US distal fall‐off is sharper because of reduced energy straggling in the treatment head. For a range of 5.0 (28.0) cm in water the 80%–20% fall‐off is 2.7mm (5.5mm) in US, compared to 4.0mm (6.0mm) in DS. For deep seated tumors (prostate) the sharper in‐air dose distribution in US is washed out by in‐patient scatter, resulting in no significant benefit. For targets at shallow and intermediate depth, located next to a critical structure, the sharper fall‐off in US allows for better target coverage and less dose to the critical structure. Conclusion: The sharper lateral and distal penumbra in uniform scanning are beneficial when the target volume abuts a critical structure. For deep‐seated tumors this advantage diminishes.
SU‐GG‐T‐539: Carbon Fiber Couch Effect On Skin Doses as a Function of Photon Energy
Authors: Mihaylov I , Moros E , Corry P , Penagaricano J
Published: July 2008

Purpose: To evaluate the dosimetric effect of a carbon fiber couch (CFC) on delivered skin dose as a function of photon energy. Method and Materials: A carbon fiber couch (BrainLab) was incorporated into a commercial TPS (Pinnacle) through auto‐contouring. A retrospective investigation on 2 lung and 2 prostate patient plans was performed. Targets and OARs, together with a skin contour of 0.3 cm thickness in contact with the CFC, were outlined in each plan. For each patient two sets of treatment plans were generated: 1) set of four plans with 4‐, 5‐, 7‐, and 9‐fields, all with 6MV beams, and 2) set of four plans, identical to the first set except that the CFC was intersected by 18MV beams. IMRT optimization was performed for each plan. Both sets of plans for each patient were normalized such that 95% of the PTV was covered by the same dose, escalated to the maximum allowed by the OAR constraints. CFC effect as function of beam energy was tallied by the highest dose to 2 cm2 of skin. The observed skin doses range from 20% to more then 87% of the prescription doses. Results: If 18MV rather than 6MV energies are used in the beams traversing the CFC the skin dose reduction ranges from 12% to more than 45%. An additional sparing for some OARs was also observed for the prostate cases, while the opposite was observed for the lung case. Conclusion: The results indicate that mixed energy 6MV/18MV (18MV for the beams passing through the CFC) IMRT plans would result in a substantial skin sparing of more than 45% compared to IMRT plans with only 6MV beams. The high skin doses in some cases (87% of the prescription) suggest that in hypofractionated SRS/SRT the CFC skin effect needs to be considered.
SU‐GG‐T‐540: Impact of Biological Optimization On Plan Quality: An Evaluation of a Commercial Treatment Planning System
Authors: Semenenko V , Qi S , Li X
Published: July 2008

Purpose: To evaluate the impact of biological optimization implemented in the new commercial IMRT treatment planning system (TPS) Monaco (CMS, St. Louis, MO) on plan quality as compared to a traditional TPS employing dose‐based optimization (XiO, CMS, St. Louis, MO). Method and Materials: Clinically used IMRT treatment plans for selected head and neck, prostate, and brain cases generated using XiO (version 4.3.3) were compared with corresponding plans generated using Monaco (version 1.0.0). The same CT data, contours, isocenter, number of beams (7–9), beam angles, and calculation grid spacing (2 mm) as in the original XiO plans were used for the Monaco treatment planning. Biological cost functions were used with parameter values suggested in a Monaco training manual as initial guesses. Iterative adjustment of isoconstraint values followed by re‐optimization was continued until approximately 95% coverage of each target volume by a prescription dose was achieved. A Monte Carlo algorithm with 3% variance was used for final dose calculation in Monaco. Dose calculations in XiO were performed using a fast superposition algorithm. Results: Monaco plans tend to result in smaller values of the mean dose and generalized equivalent uniform dose (gEUD) for OARs (15 out of 17 OARs in all plans combined) and greater mean doses and gEUD for targets (4/5). Maximum doses to normal structures are sometimes greater in Monaco compared to XiO (6/17) as a consequence of larger hot spots in target volumes. Dose heterogeneity was increased for all but one target in Monaco plans. Conclusion: The biologically based Monaco TPS has the potential to generate superior IMRT treatment plans compared to the dose‐based XiO TPS, as judged by better or equivalent target coverage accompanied by reduction in normal tissue exposure. However, greater dose inhomogeneity in the target must be accepted in most cases.
SU‐GG‐T‐545: Dosimetric Verification of RapidArc Treatment Delivery Using the Delta4 Phantom
Authors: Korreman S , Medin J , Wiberg I , Bocanek J , Archambault Y , Cozzi L
Published: July 2008

Purpose: Recently, Varian Medical Systems have introduced a new treatment technique, in which dose is delivered over one gantry rotation with variable MLC positions, dose rate and gantry speed, RapidArc. A preclinical RapidArc installation was carried out on a Varian Clinac at our institution. We report dosimetric verification of reproducibility and consistency of RapidArc delivery using the Delta4 phantom (Scandidos, SE). Method and materials: 9 treatment plans generated in the Eclipse preclinical version of the RapidArc optimizer (H&N, prostate and lung) were delivered using a Clinac equipped with RadidArc delivery capability. The delivered dose was measured using the Scandidos Delta4 phantom. The measured dose distributions were compared with doses calculated in Eclipse. All plans were delivered three times consecutively, and the first run was used as reference for constancy checks. The temporal resolution of the delivery was analysed by investigating the arc segments between control points separately (177 control points per rotation). Gamma analysis (3%/3mmDTA) was used to quantify correspondence between dose distributions. Results: Overall, good agreement was observed between measured and calculated doses, generally with gamma values <1 in >95% of measured points. Comparison of the accumulated doses for two consecutive runs of a plan showed gamma values <1 in all measured points. The segment‐by‐segment analysis showed discrepancies between two consecutive runs, with >90% gamma values <1 in around 50–60% of the segments (gamma dose criterium 3%; <1–2 mGy for single segments). Segments with large dose deviations were typically counter‐balanced by following segments with large deviations of the opposite sign. The segment discrepancies cancelled out in the accumulated dose. Conclusion: The delivery of RapidArc beam delivery corresponded well with calculated dose distributions for different cases. The delivery was reproducible, and was carried out with high stability of the accelerator performance.

Research sponsored by Varian Medical Systems, Inc.
SU‐GG‐T‐553: Dosimetry Impact of Radiation Beams Due to Presence of Calypso Electromagnetic Array
Authors: Li S , Enke C
Published: July 2008

Purpose: The 4D Calypso systems are used for accurately localizing and continuously tracking the targets in prostate treatments. An electromagnetic array composed of low density materials is positioned over the patient during radiation treatment delivery to excite the Beacon transponders, which are permanently implanted in targets, and sense their motions. This study is to investigate and verify the attenuation of photon beams due to presence of the array. Method and Materials: A solid water phantom was used to simulate the radiation treatment. The array was positioned at distant of 18cm to isocenter and aligned to ceiling laser. The 0.3cc cylinder chamber was used for measurement of the attenuation for field size of 5×5cm2 and 10×10cm2 and 0.015cc pinpoint chamber for field size of 2×2 cm2 and IMRT fields. For each field, chambers were at depth of 8cm, 10cm, and 12cm respectively and the 6MV beams delivered 200MUs at gantry angles of 0, 10, 20, 30, and 40 degree. Each measurement was repeated twice. The attenuation was evaluated by comparison of dose measured at isocenter with and without the array. Results: The measurements show that the attenuation from beams normal to the array ranges from 1% to 2%. This result is consistent to conclusion provided in Calypso user manual (<2% at 6 cm depth), but disagrees with another published results (<0.5%, Med Phys, 30(6), 1473 (2003)). The results demonstrate that attenuations increase with gantry angle and are larger than 2% at 40 degree for field size of 10×10cm2. Measurements with IMRT beams show that the attenuations are less than 2% at gantry angle less that 20 degree and could be as high as 3% at 40 degree. Conclusion: To minimize the array impact to radiation delivery, the large oblique angle should be avoided for the beams incident to the array.
SU‐HH‐AUD C‐02: Carbon Foam Collimators for Proton Therapy
Authors: Charara Y , Ramsey C , Townsend L
Published: July 2008

Purpose: The purpose of this study was to test the effectiveness of a new collimating material made of carbon foam and low‐density polyethylene. The hypothesis is that the carbon foam material will produce fewer neutrons and be more affordable to manufacture than conventional materials. The study includes comparison with spallations produced from a tungsten target and a combination between a new material and tungsten, as well as the effect of the products in Tissue Equivalent Plastic, and the energy deposition contribution to the total dose. The study also includes incorporating a new Multi‐leaf Collimator concept. Method and Materials The collimation material developed in this study is based on a space radiation shielding materials NASA project, and it is a low density Polyethylene that was impregnated into Carbon Foam (PELowFOAM). The material has a density of 1.071 g/cm3, a hydrogen atomic composition of 10.5% and a carbon atomic composition of 89.5%. Monte Carlo analyses for neutron and secondary protons production was performed (using HETC‐HEDS). Results: The number of neutrons produced with Tungsten is 65.78 % of the primary proton beam. PELowFoam and PELowFoam with tungsten produce almost 3.5 times fewer neutrons than tungsten alone. Secondary protons produced are not of concern. Almost 45.43 % of the primary beam deposited its energy as a scattering neutron into the Tissue equivalent Plastic. This number is alarming and needs to definitely be taken into consideration. Conclusion: A novel material was tested that is made of low density polyethylene impregnated in carbon foam to be used for collimating proton beams instead of using high Z materials like tungsten. Out of the three materials, tungsten performed the worst producing 66% of the primary beam in the form of neutrons, while the PELowFoam produced about 16% neutrons, and the PELowFoam combined with tungsten produced about 19% neutrons.
MO‐B‐AUD C‐01: Proton Therapy
Authors: Smith A , Paganetti H
Published: July 2008

The clinical advantages of proton beams have become widely recognized and there has recently been a significant increase in interest for building additional proton therapy facilities. There are currently over 25 institutions worldwide treating patients with proton beams and over 55,000 patients have been treated. There are at least 25 new facilities in various stages of planning and building. However, the fraction of patients treated with protons each year remains extremely small compared to the total number of cancer patients treated with external beam photons and electrons. The advantage of proton beams lies primarily in their excellent dose localization as compared to that which can be achieved using photon beams. Due to the Bragg peak characteristic in the depth dose of proton beams, the integral dose from proton therapy is, in general, about two times less that that for photon treatments. This allows higher doses to be delivered to target volumes, resulting in increased probabilities of local control, and lower doses delivered to critical normal tissues, resulting in decreased probabilities of treatment‐related morbidity. There are many challenges associated with increasing the accessibility of proton therapy not the least of which is the very limited number of clinical staff with knowledge of and training in proton therapy. The aim of the present Continuing Education Course is to provide a basic understanding of the rationale for proton therapy, physics of proton beams, technology of proton beam acceleration and transport, delivery of proton treatments, proton treatment planning and clinical results of proton therapy.

Educational Objectives:

1. Understanding of the physical characteristics of proton beams and interactions in tissues.

2. Understanding of the beam production and treatment delivery technology for proton beams.

3. Understanding of the clinical commissioning of proton therapy beams.

4. Understanding of the basic principles of proton treatment planning.

5. Understanding of the clinical results for proton therapy.
MO‐E‐332‐04: Comparison of Dose‐Area‐Product (DAP) and Fluoroscopy Time Between a Mobile and a Fixed C‐Arm Unit for Electrophysiology (EP) Procedures
Authors: Dohatcu A , Bednarek D , Rudin S
Published: July 2008

Purpose: To determine if there is a difference in dose‐area‐product (DAP) or fluoroscopy time between electrophysiology (EP) procedures performed using a mobile and a fixed C‐arm fluoroscopic unit. Method and Materials: DAP and fluoroscopy‐time data was logged for 800 EP procedures performed using a mobile C‐arm unit from 2003 to 2005. In early 2006, a fixed C‐arm unit was installed and the same data logged for over 200 procedures. The procedures were sorted into five categories: 1. electrophysiology studies, 2. radiofrequency ablations, 3. pacemaker and implantable‐cardiac‐defibrillator implants, 4. biventricular interventions, and 5. lead changes. For each category, the distributions of DAP and time were compared and the average, median and range of values determined. Results: The median fluoroscopy time more than doubled for all procedure categories when using the fixed unit. Median DAP increased significantly for procedures 3 and 4, but remained nearly the same for procedures 1, 2 and 5. In all cases, the procedures were successfully completed without evidence of compromising patient care for either unit. However, the cardiologists were much more conservative in their use of fluoroscopy for the mobile unit due to its heat loading limitations and, also, they worked quicker because of their impression that the older mobile C‐arm gave more radiation dose to themselves and the patient. In addition, fluoroscopy at 15 frames per second was used on the fixed unit versus 7 frames per second on the mobile unit. Conclusion: Although the DAP and fluoroscopy time generally was higher for the fixed installation, it should not be concluded that the mobile unit is to be preferred. Rather, these results point out the importance of physician training and dose monitoring, not only to track patient radiation risk, but also to provide physician feedback.

(*Support: NIH Grant R01‐NS43924).
TU‐A‐350‐01: Electron Monte Carlo: Clinical Impact
Authors: Ma C
Published: July 2008

This presentation will facilitate participants with the clinical application of Monte Carlo dose calculation algorithms in radiotherapy treatment planning and dosimetry verification. Following a brief introduction to the clinical implementation and commissioning of the Monte Carlo dose calculation software detailed discussions will be given on the actual and potential impact of Monte Carlo dose calculation algorithms on conventional electron beam therapy and advanced mixed beam treatments.

Comparisons of patient treatment plans generated using conventional dose calculation algorithms and Monte Carlo methods will be made with an emphasis on the causes of the dose discrepancies. Further discussions will be conducted on the use of Monte Carlo dose calculation as a radiotherapy treatment QA tool to validate individual patient plans and as an investigation tool to improve target dose conformity and normal tissue sparing using novel treatment techniques.

Educational Objectives:

1. To describe clinical implement and commissioning of Monte Carlo dose calculation algorithms for radiotherapy treatment planning.

2. To discuss the impact of Monte Carlo dose calculation in electron therapy and advanced mixed beam therapy treatment planning.

3. To describe the applications of Monte Carlo dose calculation in treatment planning and beam delivery QA for advanced radiotherapy treatments.
TU‐A‐350‐02: Monte Carlo Dose Calculation for Clinical IMRT Treatment Planning
Authors: Siebers J
Published: July 2008

Monte Carlo (MC) dose calculation algorithms are now available in some commercial treatment planning systems for applications in photon beam IMRT planning. This course will examine the various stages of a MC IMRT dose calculation, including methods for particle sourcing, fluence modulation, and patient dose computation dose. The use MC as a QA tool to validate commercial IMRT dose calculation algorithms and its use as a QA tool to validate 3D dose distributions for individual IMRT plans will be reviewed. To this end, large‐scale comparison of clinical IMRT plans created with a commercial planning system with MC dose re‐calculation will be presented. Advantages of using MC algorithms directly in the IMRT optimization loop to circumvent optimization convergence errors and strategies to reduce MC dose calculation time when used within an optimization framework will be discussed.

Educational Objectives:

1. To understand the stages of a Monte Carlo dose calculation when applied to clinical IMRT treatment planning.

2. To illustrate the role of Monte Carlo for IMRT treatment planning quality assurance.

3. To evaluate the dose accuracy of a commercial non‐Monte Carlo IMRT dose calculation algorithms with respect to Monte Carlo dose computations.

4. To demonstrate methods for Monte Carlo‐based clinical IMRT dose optimization.

The author is supported in part by NCI Grant P01 CA116602, by Philips Medical Systems and by Varian Medical Systems.
TU‐A‐AUD A‐01: LINAC and MLC QA for IMRT
Authors: LoSasso T , Xia P
Published: July 2008

Intensity‐modulated radiotherapy (IMRT) is now common in many therapy centers. Quality assurance (QA) procedures for a linear accelerator (linac) and multi‐leaf collimator (MLC) designed for conventional static fields do not address the unique dosimetric issues pertinent to IMRT planning and delivery. IMRT portals are composed of many irregular, small, off‐center, and abutting field segments throughout the target volume, each delivering only a few MU. In these regards, emphasis should be placed on beam stability for small MU and leaf position accuracy with gantry rotation. At the same time, the target volume, shielded by the MLC for much of the treatment, sees a larger transmitted dose, especially for MLC with rounded leaf ends, The impact of delivery technique, segmented (step and shoot) or dynamic (sliding window), on the required leaf position tolerance is not fully appreciated and will be addressed. While the mechanics and software of the various linacs and MLC distinguish them, there are many aspects of QA in common. This course will discuss: (1) the specific QA related to the MLC design; (2) additional QA for linear accelerators pertinent to the small MU and small field sizes used in IMRT; (3) tools and procedures often used to perform these QA tasks; (4) specific QA issues for different IMRT delivery methods.

Educational Objectives:

1. Understand different IMRT delivery methods and their specific QA issues.

2. Understand effect of QA on the IMRT delivery accuracy.

3. Understand the importance of proper commissioning of the planning system to avoid confusion with dose delivery issues.
TU‐B‐352‐02: Assessing Tumor Response to Therapy Over Time
Authors: Bullitt E
Published: July 2008

Monitoring the efficacy of brain tumor therapy is a clinical dilemma. Results of biopsy provide the most reliable indicator but biopsy is too invasive for frequent use. The clinical standard of practice is to perform serial magnetic resonance scans and to assess changes to tumor “size” as seen on gadolinium enhanced images, with “size” measured in one, two, or three dimensions. This review discusses the advantages and disadvantages of the three measurement methods as well as some of the effects of voxel size on the calculation. Problems inherent to the use of gadolinium enhanced images include the effect of steroids and the confounding appearance of radiation necrosis. New treatment methods, such as administration of anti‐VEGF agents, may even cause disappearance of gadolinium enhancement while the tumor continues to grow. The limitations of the “tumor size” approach have led multiple groups to explore alternative methods of assessing tumor activity. We briefly explore some of these alternative methods to assessing tumor growth and treatment response.

Educational Objectives:

1. Understand the clinical standard of practice of monitoring brain tumor therapy from T1 gadolinium enhanced images.

2. Understand the different common approaches to assessing tumor activity and their strengths/limitations.

3. Understand the limitations inherent to various approaches.
TU‐C‐350‐02: Professional Services: What Can the AAPM Do to Support Your Practice?
Authors: Sherouse G
Published: July 2008

The Professional Services Committee (PROFS) is a relatively new node in the AAPM's Committee Tree, created by gathering together some previously free‐floating entities that all have in common that they represent services to the membership in nominal support of professional practice. These include the newsletter, insurance, the Placement Service, and the Professional (salary) Survey. In addition, PROFS also serves as a home for some critical infrastructure including subcommittees charged with gathering workforce statistics and with validating the results of the Professional Survey.

PROFS is the right platform for addition of new member‐directed services to the membership in support of professional practice. The last three bullets in the current Rules describing the charge of PROFS are.

• Create and operate a career services booth at the Association annual meeting.

• Educate the membership on issues related to practice development and business management support.

• Offer programs and services of value to the membership that support the careers of medical physicists, such as malpractice insurance, legal and contractual guidance, business education, employment counseling, marketing techniques and compensation negotiation.

We're currently underachieving at most of this, and both Vice Chair Mark Davidson and I are anxious to try to fill some of the void with your help. In this presentation I'll briefly review the structure of PROFS and the work of the current subcommittees. But I'll move pretty quickly to the question of what PROFS can be and what our priorities ought to be in the coming year, and will solicit audience feedback about that.

It should be no surprise that an overarching theme of my presentation will be that if you want help from the AAPM, you've got to volunteer to be part of the effort. Requests from members for new services from subcommittees or task groups in PROFS are always welcome, and the potential for funding of new projects is high, but a suggestion is way more likely to be implemented if the request is accompanied by a draft charge and a list of 6 willing and enthusiastic volunteer members.
TU‐C‐AUD A‐02: Middleware for the Clinic — Taking Small Steps Towards Implementing New Technologies Into Routine Practice
Authors: Dong L
Published: July 2008

New products from vendors may not work immediately in many clinics due to a variety of reasons. One of the main reasons, however, is due to the fact that most clinics are in a multi‐vendor environment. The workflow demonstrated by the vendor may not completely work in a multi‐vendor / hospital‐specific environment. Similarly, new technologies are not perfect; they often require supplementary workflow solutions to accomplish the main goal. Often in time, vendor's support is limited. Simply waiting for the next product release is not always working. As the technology leader in a radiation oncology team, medical physicists should be actively involved in the technology implementation process, which can be hospital‐specific. However, there are common steps in achieving the goal of technology integration. The first step is often involved in identifying why things are not working. This trouble‐shooting process may require the assistant from vendors or friends in other hospitals. Once the main problem is identified, value‐adding new ideas should be sought as alternative solutions. After an alternative solution is judged feasible, resources need to be identified to implement it in the clinic. This resource‐seeking process may require you to “sell” your idea to your chief physicist, the vendor, or other members of the radiation oncology team. It is important to get buy‐ins in the clinic before you invest time significantly. Successful clinical implementation often relies on the key clinical issues identified. Technologies used for such implementation do not need to be complicated, definitely not a complete overhaul of the existing workflow. While inventing a technical solution may not be easy, the biggest challenge is to take it live in your clinic. In addition, continuous support, improvement and adapting to changes are required. It is worth mentioning that many of these middleware solutions can be short‐lived. The goal is not to insist “in‐house” solutions. Rather, the eventual goal is the clinical efficacy for your clinic. Examples of in‐house solutions will be discussed to illustrate these processes and experience will be shared among other presenters.

Educational Objectives:

1. To suggest common strategies for in‐house implementation of new technologies.

2. To share experience on how to work effectively with your vendors.

3. To identify challenges in in‐house solutions.
TU‐C‐AUD A‐04: Designing and Implementing Clinical Studies Involving New Technology
Authors: Fraass B
Published: July 2008

Many of the most important advances in modern radiotherapy have been developed, implemented, tested, and/or perfected through in‐house clinical research work. Study of the possible benefits of new technology and new techniques for treatment planning and delivery is crucial if we are to learn when and how to effectively use these capabilities. This presentation will use our experience designing clinical studies of normal tissue toxicity, tumor dose escalation, use of functional imaging, and other on‐going clinical efforts to illustrate both the challenges involved in clinical studies as well as some of the methods that have proven to be helpful to our research efforts. Performing clinical studies which have appropriate goals, are designed to include adequate clinical support, and which eventually result in clinically documented improvements for our patients can be a very valuable and satisfying contribution to improved patient care.

Educational Objectives:

1. To illustrate clinical study design techniques.

2. To discuss some of the methods which help make clinical studies viable in a busy clinic.

3. To highlight some of the challenges associated with clinical research efforts.
TU‐C‐AUD B‐07: Effect of Respiratory Gating On Dose Delilvery in a Moving Target
Authors: Zhang Q , Chan R , Hale D , Tsai P
Published: July 2008

Purpose: To evaluate the effect of gating on dose delivery to a moving target. Method and Materials: A motorized platform with variable speed of 8RPM to 28RPM built to carry a 30×30cm solid water phantom and capable of delivering a 2cm range of motion in both in‐out and up‐down direction is used for the study. Retrospectively gated (4D) CT simulation is acquired on the Philips Gemini PET/CT imaging system. Acquisitions are made with phantom moving at 8, 15, 28 RPM with in‐out motion only and full motion. Waveforms are monitored by the Varian RPM system. Binning is for 10 phases equally spaced between waveform peaks. Based on the most stable range of the cycle phase range of 40%–60% for in‐out motion and 30%–50% for full motion was used for gating. Plans using single AP field, sliding window (SW) and step‐and‐shot (SS) IMRT fields are evaluated using ion chamber and film dosimetry. Results: For the in‐out motion only, the measured absolute dose at the center of the target was within 1% of the planed dose, gated or non‐gated. For full motion study, dose varies up to 2.5% for non‐gated plans and 1% for gated plans. In all motions, penumbra difference is within 2 mm for gated fields but pending on the phase range difference is significantly larger for non‐gated fields. With IMRT fields, good correlation is shown for all gated fields whereas for non‐gated cases, dose delivered deviates greatly from plan. Conclusion: With moving target, dose distribution differs greatly from plan if treatment is not gated. For IMRT fields and field with limited margins 4D treatment with optimized phase range is essential.
TU‐C‐AUD B‐08: Identification of a 3D Dosimeter Best‐Suited for Use by the RPC
Authors: Heard M , Followill D , White R , Jackson E , Salehpour M , Ibbott G
Published: July 2008

Purpose: To characterize several 3D dosimeters and identify one that is best‐suited for use by the RPC in its anthropomorphic phantoms. This study will also provide useful data to other researchers when selecting a 3D dosimeter. Method and Materials: Three different dosimeters were investigated in this study: PRESAGE™ (a polyurethane and leuko dye dosimeter), and BANG® and PAGAT polymer gels. Each dosimeter was characterized to determine the dose response, linearity, reproducibility, spatial stability, and dose resolution. Both MRI and OCT were used to identify the best‐suited imaging modality for each polymer gel formulation. Goals were established for each parameter. These were used to evaluate the dosimeters' characteristics and identify the dosimeter best‐suited for use by the RPC. Results: Each 3D dosimeter demonstrated a useful dose range up to 10 Gy. Only the BANG® dosimeter provided a linear dose response over this range. The uncertainty in the determination of the response of the dosimeter was ∼2% when imaged with OCT; however, MRI yielded uncertainties < 1%. The low uncertainties achievable with MRI resulted in improved dose resolution. OCT required shorter imaging times than MRI; OCT produced planar images in 30 seconds. The BANG and PAGAT dosimeters displayed overshoots in response adjacent to regions of high dose gradient. No response overshoots were observed in PRESAGE™ dosimeters irradiated with steep gradients. The intra and inter‐batch reproducibilities of PRESAGE™ exceed the goals established for these parameters. The spatial stability and reproducibility of the polymer gel formulations is in progress. Conclusion: This study provides a framework for evaluating 3D dosimeters and identifying one best‐suited for a particular use. This study also provides the first comparison of polymer gels characterized with both MRI and OCT.

The investigation was supported by PHS grant CA 10953 awarded by the NCI, DHHS.
TU‐C‐351‐09: Fluoroscopic Lung Tumor Tracking
Authors: Lin T , Tang X , Sandhu A , Jiang S
Published: July 2008

Purpose: To develop algorithms that can track the invisible lung tumors by tracking relevant anatomic features in the fluoroscopic images based principle component analysis (PCA) and regression analysis. Method and Materials: For each patient 15 seconds of fluoroscopic images were taken before treatment and used as training dataset. A few regions‐of‐interest (ROIs) were manually selected in the first image frame that may contain anatomic features correlated with tumor motion. PCA was applied to reduce the dimensionality of each ROI to 3. Tumor positions were manually marked by an expert observer in all training images. Regression methods were applied to build the correlations between the tumor position and the PCA‐processed ROIs. Then the correlations were used to predict the tumor positions in the testing images. Four regression methods were considered: 1‐degree and 2‐degree linear regression, artificial neural network (ANN), and support vector machine (SVM). Their accuracy was assessed by comparing the prediction results with the reference tumor locations manually determined by the expert observer. Results: 12 sequences of fluoroscopic images have been studied retrospectively. Results are reported in terms of mean and variation of localization error. Considering all regression methods, the mean localization errors (MLE) are smaller than 1 mm for most patients and in the worst case is still smaller than 2.5 mm. Variations are smaller than 1 mm most of the time, and the largest variation is about 9 mm. 1‐degree linear regression and ANN in general perform better than the other two methods. The other two methods tend to have overfitting problems. Conclusion: Based on PCA and regression analysis, we proposed a novel method that can track the invisible lung tumor in fluoroscopic images by tracking correlated anatomic features. The method has an accuracy of 1mm in most of cases and smaller than 3mm in the worst case.
TU‐C‐351‐10: Inference of Hysteretic Respiratory Tumour Motion From External Surrogates: A State Augmentation Approach
Authors: Ruan D , Fessler J , Balter J , Berbeco R , Nishioka S , Shirato H
Published: July 2008

Purpose: To infer internal respiration‐induced tumor motion from external surrogate. To systematically resolve mapping ambiguity caused by breathing hysteresis. Method and Materials: We propose a state‐augmentation approach to capture system dynamics. Concatenating real‐time surrogate observations with their time‐delayed records describes the state information in a higher‐dimensional state space. In such space, inhale and exhale “stages” are naturally separated due to the incorporated velocity contents. Any existing inference model migrates effortlessly into this framework. We illustrate the idea with simple polynomial inference models, and derive a closed‐form solution for optimal choice of model parameters. Choice of lag length is demonstrated empirically to be robust and may be chosen offline. This approach is tested on synchronized recordings of internal tumor trajectories and external fiducial marker readouts from eight lung patients (multiple fractions and readings) with a Mitsubishi real‐time radiotherapy (RTRT) system. Internal recording is obtained by fluoroscopic tracking of implanted 1.5mm‐diameter gold ball bearings around the tumor and external surrogates measure relative abdominal skin positions. Results: Examination of trajectories in the augmented state‐space suggests the existence of a consistent and unambiguous inference map. Empirical tests with clinical data show that using state augmentation decreases the 3D RMSE from 2.01mm to 1.74mm with the linear model and 1.93mm to 1.63 with the quadratic model. Paired student‐t tests with P‐values on the order of 10e‐13 indicate statistical significance of the improvement. Conclusion: We proposed a simple state‐augmentation approach to implicitly incorporate the hysteretic internal‐external response pattern into the estimation framework with any existing inference model. For the general class of correspondence models that are linear in their parameters, closed‐form solutions for the optimal parameter values and the error evaluations are derived. Tests with clinical data demonstrate statistically significant improvement over direct models.

This work is sponsored by NIH P01‐CA59827 and Barbour Scholarship.
TU‐C‐332‐01: A Comparison of Initial Area Under Curve (IAUC) Obtained From DCE‐CT and ‐MR Imaging in Patients with Cervical Cancer
Authors: Kim S , Haider M , Milosevic M , Maheshwari E , Yeung I
Published: July 2008

Purpose: To compare the IAUC60 (initial area under curve taken up to 60 seconds) obtained from DCE‐CT and ‐MR imaging in patients with cervical cancer. Method and Materials: A group of 40 patients with cervical cancer received a DCE‐MRI scan followed by a DCE‐CT scan at the time of staging. A radiologist observer identified and contoured the tumours on CT and MR images. At least one slice was identified as the matching slice in the CT and MR images for each patient. IAUC60 obtained from tumour region was normalized by IAUC60 from muscle region for DCE‐CT and ‐MR data. Correlation study and Bland‐Altman analysis were performed to assess the relationship between the normalized IAUC60 obtained from the two imaging modalities. Regression analysis was also applied to assess the relationship between the normalized IAUC60 and the normalized transfer constant (rKtrans) for DCE‐CT data. Results: The regression analysis between the normalized IAUC60 and the normalized transfer constant (rKtrans) for DCE‐CT data resulted in a significant strong correlation (R = 0.98, P<0.0005). A significant correlation (R = 0.75, P<0.0005) was found in the correlation analysis of the normalized IAUC60 between DCE‐CT and ‐MR imaging. The Bland‐Altman plot analysis of the normalized IAUC60 resulted in the 95% limit of agreement ranging from −2.68 to 4.75 and mean difference of 1.03. Since the average of the normalized IAUC60 measurements from two modalities ranged from 1.81 to 13.73, the degree of agreement was considered to be acceptable for the use of the two modalities interchangeably. Conclusion: The comparison of the normalized IAUC60 showed that both DCE‐CT and ‐MR imaging modalities may be used interchangeably in assessing cervical cancers. The normalized IAUC60 may be considered as a reliable quantitative surrogate of the normalized transfer constant for both modalities.