Volume 34, Issue 6, June 2007
Index of content:
- Therapy Continuing Education Course: Ballroom A
- CE‐Therapy: Shielding I: New NCRP Report: General Report Background and Formulation
34(2007); http://dx.doi.org/10.1118/1.2761192View Description Hide Description
This Report was prepared through a joint effort of the AAPM Task Group 57 and the NCRP Scientific Committee 46‐13. It addresses the structural shielding design and evaluation for medical use of megavoltage x rays and gamma rays for radiotherapy and supersedes related material in NCRP Report No. 49, which was issued in 1976.
This first presentation will review the general formalisms used for primary and secondary barrier designs at energies below and above the 10MeV maximum energy that was considered by the old Report 49. While most of the formalisms and data can be found in the published literature, the goal of the report was to bring together in one work all the required methods for shielding modern radiotherapy accelerators. This overview will be followed on the second day by a review of the methods and equipment that are necessary to survey the final facility and then the equations and data presented will be used extensively in the third day's presentation to work a number of detailed example calculations.
1. Understand the history and rationale behind this report,
2. Understand the appropriate use of the equations and data for calculating shielding for medical accelerators,
3. Understand the limitations of the proposed methods.
- CE‐Therapy: Shielding II: Practical Examples, Including IMRT, TBI, SRS
34(2007); http://dx.doi.org/10.1118/1.2761202View Description Hide Description
NCRP Report No. 151(December 2005), titled “Structural Shielding Design and Evaluation for Megavoltage X‐ and Gamma‐Ray Radiotherapy Facilities”, presents updated methods and data for radiation therapy room shielding design. These calculation methods are applied in examples representing the more common shielding design situations. A radiation therapy vault with a maze barrier and intended for use with IMRT and TBI procedures is the principal example. Detailed calculations of the barriers and door shielding structures are presented. Procedures for evaluating compliance with the NRC licensing constraint on dose equivalent in‐any‐one‐hour are presented. An example of a high‐energy room where photoneutron production is of concern is presented with focus on assessing the dose equivalent at the entrance and the maze door design.
Objectives: Learn by worked examples (1) how to apply the methods and data presented in NCRP 151 for designing high energy therapy vault barriers; (2) how to determine prospectively if the barrier design is adequate to satisfy the public areas “2 mrem in‐any‐one‐hour” constraint when it is applicable.
- CE‐Therapy: Daily Localization — II: EPID, MVCT
34(2007); http://dx.doi.org/10.1118/1.2761303View Description Hide Description
The Mega‐Voltage Cone‐Beam CT (MVCBCT) system provides a 3D image of the patient anatomy in the actual treatment position that can be tightly aligned to the planning CT, allowing daily verification and correction of the patient position moments before the dose delivery. Integrated onto a linear accelerator, the system consists of a new a‐Si flat panel adapted for MV imaging and a workflow application allowing the automatic acquisition of projection images at low dose rate, CBCTimage reconstruction,CT to CBCTimage registration and couch position adjustment. MVCBCT provides accurate electron density and allows studies of dosimetrical impact of setup error, anatomical changes or in presence of implanted metallic objects.
This lecture will provide an overview of the physics characteristics of MV and MV CBCTimaging, acquisition and reconstruction,image registration, alignment precision and quality assurance procedures. A description of the workflow and a survey of the clinical applications, indications and protocols will be presented. Finally, current challenges and future developments will be addressed.
1. Understand the basics of MV Cone‐Beam CTimaging.
2. Understand the possibilities of daily 3D Imaging for patient alignment and other applications.
3. Understand the clinical roles of Image‐Guided(IGRT) and Dose‐ Guided (DGRT) Radiation Therapy.
This work was supported by Siemens Oncology Care Systems.
- CE‐Therapy: Functional/Molecular Imaging: PET for Planning/Assessment
34(2007); http://dx.doi.org/10.1118/1.2761316View Description Hide Description
Purpose:Positron Emission Tomography(PET)images show physiological and biological information through the in vivo distribution of radioactive, positron‐emitting agents. PETimaging shows focal and distributed regions of cancer and its metastases. Initial PET uses in oncology include diagnosis and staging, which are important for determining treatment decisions. Current PET uses now include target definition for radiation planning followed by PET‐based assessment of treatment. Hybrid PET‐CT devices are beginning to be used as radiation treatment simulators. Method and Materials: F‐18‐labled Fluoro‐deoxyglucose (F‐18 FDG) is the most commonly used PETimaging agent. FDG shows regions of active glucose metabolism, such as local cancer, metastases, non‐cancer inflammation, and normal glucose use. Non‐FDG PET agents can be more specific in cell targeting (binding), and can image different aspects of tumor biology, like hypoxia (FMISO, CuATSM) and cell proliferation (FLT) Results:PETimaging has coarse spatial resolution compared to CT and MR. PET's clinical use is valued because of its great sensitivity for cancer detection. Voxel intensity and image fidelity depend on equipment design, patient size, anatomic site, and imaging study parameters. PET‐CT units enable CT‐based attenuation corrections and inclusion of CTinformation in a registered PET‐CT dataset. The Standardized Uptake Value (SUV) is a normalized intensity measure for quantitative indication of disease, and can be used to identify disease or possibly for target delineation, with certain limitations. While FDG remains the most promising agent for tumor detection, other, biologically more specific agents (e.g., FMISO, CuATSM for hypoxia imaging or FLT for cell proliferationimaging) might be more appropriate for target delineation and treatment assessment. Conclusion: This course reviews PET‐CT hybrid scanning devices, uses of FDG and non‐FDG PET for oncologyimaging, and quantitative aspects for PET‐based radiation target definition and treatment assessment. Example images demonstrate the potential contributions and limitations of FDG and non‐ FDG PEToncologyimaging. This review course is intended for both imaging and radiationoncology physicists.
1. Describe FDG PETimaging and oncologic indications.
2. Review the uses and limitations of PETimages in radiation treatment.
3. Describe the SUV and other threshold parameters for target delineation.
4. Review non‐FDG PETimaging of tumor biology.
5. Discuss quantitative aspects of PETimaging for treatment assessment.
Conflict of Interest: (JDB) Research sponsored in part by Varian Medical Systems.
- CE‐Therapy: Imaging for Assessment/New Technologies
34(2007); http://dx.doi.org/10.1118/1.2761467View Description Hide Description
The clinical value of in vivo functional and physiological imaging (perfusion, diffusion, and diffusiontensorimaging (DTI)) for assessment of therapeutic responses has been demonstrated in recent years. In vivo functional and physiological imaging can provide early prediction for treatment outcomes and complications, compared to conventional clinical methods and anatomic imaging. The advantage of early assessment is to allow for re‐optimizing individual patients' treatment plans, including decisions of total dose, modifying risks of critical normal tissue, and optimizing use of concomitant therapies. Clinical applications of perfusion, diffusion and diffusiontensorimaging are increasing rapidly.
This lecture will provide an overview of physiological origins of perfusion, diffusion and diffusiontensorimaging, as well as clinical applications, typical imaging acquisition protocols, and image processing methods. The limitations of these techniques will also be discussed.
1. Understand the physiological origins of perfusion, diffusion and diffusiontensorimaging;
2. Understand typical imaging acquisition protocols and basic image processing methods;
3. Understand clinical applications and limitations.
34(2007); http://dx.doi.org/10.1118/1.2761468View Description Hide Description
- CE‐Therapy: Functional/Molecular Imaging: MRI for Planning/Assessment
34(2007); http://dx.doi.org/10.1118/1.2761482View Description Hide Description
Newer radiation therapy (RT) modalities and devices are able to deliver radiation more precisely and accurately to irregular three‐dimensional target volumes and have generated renewed interest in optimized targeting and dosing with the goal to increase radiation effectiveness while reducing side effects. These RT approaches offer great potential in redefining the value of RT in certain disease sites. However, the more conformal and precise the RT delivery the more important becomes the definition of target volumes, placing a premium on definition of the tumor's spatial location, its extent, heterogeneity and possible spread in order to direct more or less dose to appropriate areas while sparing as much normal tissue as possible. CT and MRI have provided the morphological information used for target definition and treatment planning for several decades. They describe the anatomic relationship of the tumor and surrounding structures well but fail to provide biologic information. In addition, they have oftentimes proven nonspecific in assessing treatment related changes.
Recently introduced advanced MR‐based techniques have shown promise as a means of providing information on the tumor's biological characteristics. Three‐dimensional Proton Magnetic Resonance Spectroscopy Imaging(MRSI) provides information on cellular metabolism, energetics and hypoxia through its ability to distinguish signals from cellular metabolites allowing the detection of tumor suggestive metabolism relative to surrounding same organ tissues. Diffusion Weighted Imaging (DWI) provides additional information on cellularity, cell membrane permeability, intra‐ and extracellular diffusion, and tissue architecture and integrity. Perfusion Weighted Imaging (PWI) provides insight into overall blood volume, tissue microvasculature and angiogenesis as well as vessel permeability. These imaging modalities complement each other greatly as they provide metabolic, physiologic and functional information relative to the underlying anatomy.
Two major disease sites have been studied at UCSF with respect to the potential and actual incorporation of advanced MRimaging into the treatment planning process for RT: prostate cancer and brain gliomas. Brain gliomas have traditionally proved difficult to image using standard means due to their literally “non‐visible” infiltrative behavior and heterogeneous composition. The extent and location of prostate cancer are similarly difficult to determine without the aid of particularly MRSI because although MRI has good sensitivity it has relatively low specificity.
The combination of these metabolic and physiologic modalities with standard anatomic MR modalities will enhance our current understanding of tumor biology, heterogeneity and extent and will provide guidance as to how to optimize current treatment approaches. In addition to assisting in image guidance for RT, these imaging tools show promise for assessing and predicting therapeutic response and to help distinguish treatment effect from tumor progression. The latter becomes even more important in light of the increasing use of combined radiation and chemotherapeutic or molecularly targeted treatment approaches.
Educational objectives are to become familiar with the application of advanced Magnetic Resonance Imaging(MRI) techniques to Radiation therapy of brain and prostate cancer patients. Specifically, to understand the current technology, molecular information attainable, and to become familiar with current and future clinical applications.