Penn-Ohio and Ohio Valley River Chapters of AAPM Fall Symposium Abstracts Catalog Application of risk-based analysis methods to radiotherapy quality management

The increasing complexity of modern radiation therapy planning and delivery challenges traditional prescriptive Quality Management methods, such as many of those included in guidelines published by organizations such as the AAPM, ESTRO and IAEA. These prescriptive guidelines have traditionally focused on monitoring all aspects of the functional performance of radiotherapy equipment by comparing parameters against tolerances set at strict but achievable values. In modern radiotherapy, the number of devices, systems, and processes involved in planning and delivery lead to dramatically increasing numbers and sophistication of necessary tests and measurements to fully cover the modern radiotherapy process. There is thus a need to prioritize Quality Management (QM) activities in a way that strikes a balance between being practical in the clinical environment and optimally beneficial to patients. A systematic understanding of the likelihood and clinical impact of possible errors throughout a course of radiotherapy (RT) is needed to direct limited QM resources efficiently to produce maximum safety and quality of patient care. Task Group 100 of the AAPM has taken a broad view of these issues and has developed a framework for designing QM activities, and hence allocating resources, based on estimates of failure modes, risk assessment and clinical outcome through the RT planning and delivery process. Toward this goal, the task group has chosen the specific radiotherapy processes “intensity modulated radiation therapy (IMRT)” for analysis. The goal of this work is to apply modern risk-based analysis techniques to this complex RT processes in order to demonstrate to the RT community that these techniques may help determine more effective and safe ways to enhance the safety and quality of our treatment processes. The TG has performed a Failure Modes and Effects Analysis (FMEA) for this processes, and determined, by consensus, the most and least risky steps of these processes. This report describes the methodology and nomenclature developed, and presents the Process Maps, FMEAs, Fault Trees and QM programs developed, and finally makes suggestions on how this information can be used in the clinic. A Priori Determination of Dose Uncertainties in IMRT Planning and Delivery Jatinder R Palta Ph.D. University of Florida, Gainesville, Florida Abstract: The uncertainties in dose delivered to a patient arise from each step of the overall process of radiation therapy, which starts with image acquisition and ends with the dose delivery. The enhanced capabilities and functionalities of 3D RTP systems present a challenge for radiation therapy staff to maintain the quality, safety, and reliability of radiotherapy without resorting to extensive efforts in quality assurance (QA). Increased complexity of advanced technologies is inevitably associated with larger possible uncertainties, which can potentially result in unfavorable clinical consequences. This has been addressed by the development of patient specific QA; a process that is onerous, resource intensive, and not comprehensive. There are well documented clinical cases in which even a detailed QA procedure is unable to resolve large discrepancies between measured and calculated dose distributions. This observation can only be attributed to a complex interplay of uncertainties in the treatment planning and delivery process that are not accounted for in the RT process. We have developed an analytical model that incorporates all clinically significant dosimetric and spatial uncertainties in IMRT and a priori predicts overall uncertainty associated with any IMRT treatment plan. The ability to accurately predict these discrepancies at the time of the planning allows clinicians to objectively evaluate each IMRT plan and discard plans that have potentially large uncertainties. Furthermore, the minimization of overall uncertainty in treatment planning can be used as a critical element of IMRT multi-criteria optimization in the future. In summary, this analytical model has the potential to increase the safety and efficacy of IMRT, while at the same time, minimize the effort expended in time-consuming and onerous patient specific QA measurements. The uncertainties in dose delivered to a patient arise from each step of the overall process of radiation therapy, which starts with image acquisition and ends with the dose delivery. The enhanced capabilities and functionalities of 3D RTP systems present a challenge for radiation therapy staff to maintain the quality, safety, and reliability of radiotherapy without resorting to extensive efforts in quality assurance (QA). Increased complexity of advanced technologies is inevitably associated with larger possible uncertainties, which can potentially result in unfavorable clinical consequences. This has been addressed by the development of patient specific QA; a process that is onerous, resource intensive, and not comprehensive. There are well documented clinical cases in which even a detailed QA procedure is unable to resolve large discrepancies between measured and calculated dose distributions. This observation can only be attributed to a complex interplay of uncertainties in the treatment planning and delivery process that are not accounted for in the RT process. We have developed an analytical model that incorporates all clinically significant dosimetric and spatial uncertainties in IMRT and a priori predicts overall uncertainty associated with any IMRT treatment plan. The ability to accurately predict these discrepancies at the time of the planning allows clinicians to objectively evaluate each IMRT plan and discard plans that have potentially large uncertainties. Furthermore, the minimization of overall uncertainty in treatment planning can be used as a critical element of IMRT multi-criteria optimization in the future. In summary, this analytical model has the potential to increase the safety and efficacy of IMRT, while at the same time, minimize the effort expended in time-consuming and onerous patient specific QA measurements. Learning Objectives: • Understand the sources of uncertainties in IMRT planning and delivery • Learn to evaluate the impact of spatial and dosimetric uncertainties in the IMRT process. Commissioning and clinical use of the Novalis TX for SRS and SBRT treatments Indrin Chetty, Ph. D. Henry Ford Hospital, Detroit The general outline will be as follows: · Introduction of the Novalis technology and the HFHS experience. · Overview of Novalis TX (NTX) and it's use in IGRT related to SRS and SBRT. · Commissioning of NTX: measurements and experiments needed for clinical implementation. This will include a review of literature. · Example studies performed at HFHS for clinical implementation. · Clinical work flow on NTX for SRS and SBRT example from HFHS. Transitioning from 3D IMRT to 4D IMRT and Role of Image-Guidance Ping Xia, Ph.D. Cleveland Clinic, Cleveland, Ohio The transition from 3D-IMRT to 4D-IMRT is mandated by clinical necessary as we are treating tumors embedded in the moving organs and/or patients with anatomic changes during the course of radiotherapy. If we do not incorporate organ motion and anatomical changes into our patient management strategy we may not be able to achieve a high tumor control probability (TCP) without introducing unacceptable normal tissue complications probabilities (NTCP). IGRT and 4DCT allows us to explicitly incorporate the time variables into 3D-IMRT, referred to as 4D-IMRT. 4D-IMRT requires efficient IGRT tools and other tools (such as fast dose calculation engines and efficient contouring tools) facilitate for adaptive radiotherapy. This refresher course will focus on how to apply currently available technologies to implement the transition from 3D-IMRT to 4D-IMRT. Using three specific clinical sites (head and neck, prostate, and lung) as examples, we will discuss challenges and technical strategies in clinical implementation of 4D-IMRT. Optically Stimulated Luminescence (OSL) Dosimetry in Medical Physics Clifford J. Yahnke, Ph.D. Landauer, Inc. Optically Stimulated Luminescence (OSL) is a dosimetry technique that has been used in a variety of applications for over 20 years. Landauer, Inc. has been using this technique with Al2O3:C to monitor radiation workers and their environments since 1998. This same technology is currently being used in medicine to measure the dose to patients from mammography, fluoroscopy, CT, and radiation oncology procedures. This talk will consist of two parts: 1) a summary of the physics of OSL, and 2) an examination of its use in medical physics where it is enjoying a growing adoption at clinics throughout the US. An overview of the features and advantages of OSL as documented in peer-reviewed publications will be presented. This review will include primal dosimeter characteristics such as energy, angle, linearity, dose-rate, modality, and temperature dependence followed by a discussion of how these characteristics affect clinical use. Finally, a brief introduction to the microStar Dosimetry system and its operational advantages will be presented. Augmenting 4D PET with deformable image registration Darek Michalski, Ph.D. University of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania Purpose/Objective: Application of the deformation maps derived from 4D CT scans to 4D PET scans for spatio-temporal additivity of the metabolic PET signal to improve the resultant image quality. A software based solution is for combined PET/CT scanners. Material/Methods: Quantitative use of the positron emission tomography (PET) scans to aid in diagnosing, staging and tumor response evaluation for various cancer sites is frequently affected by a variety of factors such as tumor size and tumor motion, which may decrease the signal to noise ratio. This is apparent for gated four-dimensional PET scans. The 4DPET and 4DCT images were acquired on the hybrid PET/CT GE Discovery scanner equipped with Varian RPM system. The patient audio coaching was used during the PET and CT scans. The CT images were sorted into 6 phases corresponding to the equivalent PET bins. The CT phases were registered to phase 4 that corresponded to end of exhalation. The registration uses the Demons algorithm implemented with an image hierarchical decomposition with 3-level Gaussian pyramid. The program was written in C programming language on Linux platform. The resultant deformation fields obtained from CT scans characterized by a high anatomical resolution were resampled and interpolated with cubic B-splines to match the PET scans' dimensions. The PET images were deformed to match the bin 4 scan. Data consisted of one liver tumor case and four thoracic cancer patient. Results: The 4D PET images' dissimilarity due to their temporal differences is removed in the resultant deformed PET images. Their new spatial equivalence allows for their summation to create a new volumetric view. The CT phase-to-phase registration takes between 5 to 10 minutes including pre and post processing. The resultant PET images exhibit enhanced sharpness and contrast about the tumor, improve their visibility and decrease the background noise. Conclusions: A new synergy for combined PET/CT scanner is proposed. As 4D PET/CT gains greater acceptance in IGRT and SBRT, improved PET image quality will be highly desirable. If patient coaching and breathing reproducibility during the scan acquisition process can be maintained, this method can be applied to all cases of abdominal and thoracic 4D PET/CT scan evaluation. Dosimetric effect of intrafraction tumor motion on gated lung SBRT Bo Zhao, Ph.D. University of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania Abstract In intensity modulated radiation therapy(IMRT), it is well-known that the MLC leaf movement relative to the intrafraction tumor motion causes so-called interplay effect. This effect may worsen in case of lung stereotactic body radiotherapy treatment (SBRT) with high fractional dose, small target and high dose rate delivery. With extended treatment time experienced in gated lung SBRT, the motion pattern may change, adding complexity in determination of actual dose delivery.In intensity modulated radiation therapy(IMRT), it is well-known that the MLC leaf movement relative to the intrafraction tumor motion causes so-called interplay effect. This effect may worsen in case of lung stereotactic body radiotherapy treatment (SBRT) with high fractional dose, small target and high dose rate delivery. With extended treatment time experienced in gated lung SBRT, the motion pattern may change, adding complexity in determination of actual dose delivery. In this study we investigated the dosimetric effect of tumor motion and baseline shift in gated lung SBRT. The tumor motion data were retrieved from 6 lung patients with various target size, each with 3 fractions of stereotactic radiotherapy treatments with Cyberknife Synchrony (Accuray, Sunnyvale CA). Phase gating through external surrogate was simulated with a gating window of 5 mm. The resulting tumor motion curves within gating phases were retrieved for interplay effect evaluation. Treatment planning and dose calculation were performed on the platform of Varian Eclipse. Planning target volume (PTV) was defined as physician-contoured clinical target volume (CTV) surrounded by an isotropic 5 mm margin. Each patient was prescribed with 60Gy/3 fractions. To calculate the interplay effect, the MLC segment leaves in observance of the present tumor motion parallel to the MLC plane were shifted. The motion shift in the depth direction, perpendicular to the MLC plane, was ignored since it represents a small source to surface distance (SSD) change of ≤ 5 mm with gating. The MLC leaves were shifted for each field as a function of total MU, gantry and collimator angle, and tumor motion at each segment. The newly created MLC file was imported back to the treatment planning system for dose calculation. It was found that the deviation in PTV and CTV dose due to interplay effect is not always negligible in hypofractioned gated SBRT. Half of the patients in the study group experienced fractional dose deviation up to 20% and total dose of 10% for D95 for PTV. The maximum decrease on CTV D95 is 6% for fractional dose and 3-4% for all 3 fractions compared with static plan. Although the entire CTV volume is almost covered by prescribed dose (V100=100%) with tumor motion, qualitative comparison on the 100% isodose line distribution reveals that the CTV is on the verge of underdosing. This happens due to tumor excursion outside of the gating window, which is mostly caused by the baseline shift, i.e., the change in general trend of the motion curve during extended period of treatment time. Acceptance and Commissioning of a Novel Ionizing Radiation Emitting Isotope Hospital Detection and Notification System Suitable for Use in Radiation Counter-Terrorism. Kim Jong, Ph.D. University of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania