Volume 36, Issue 6, June 2009
Index of content:
- Therapy Continuing Education Course: Ballroom D
- CE ‐ Therapy: Quality Assurance for IGRT
36(2009); http://dx.doi.org/10.1118/1.3182192View Description Hide Description
Image‐guidedradiation treatment(IGRT) is now widely available and implemented for routine clinical use in many clinics, allowing unprecedented level of precision and accuracy in treatment delivery. These systems bring a substantial change in clinical practice for all the disciplines involved in radiation medicine. One can now correct patient position immediately prior to administration of radiotherapy by registering IGRTimages to a reference CT scan, generally the same that has been used for treatment planning. Modern IGRT systems not only display two‐dimensional bony anatomy and airways, like portal imaging, but also three‐dimensional datasets representing the internal anatomy of the patient, implanted markers, soft tissue, and sometimes the target to be irradiated. Growing experience with IGRT has demonstrated the ability to verify, on a daily basis, the position of internal anatomy structures, such as the tumour or its surrogates, the spinal cord, and other organs at risk with respect to the treatment beam geometry for several anatomical sites. It is therefore logical to use IGRT daily for on‐line correction of patient translations and rotations, and to compare successive IGRTimages to monitor changes of internal anatomy through the course of therapy. Nevertheless, introducing IGRT within busy radiation therapy clinics requires thoughtful commissioning and quality assurance (QA) protocols, and judicious modification of existing radiation therapy processes and protocols. While the modes of use of these novel systems will continue to evolve, their performance needs to be of the highest level, as they will be depended upon in the treatment process; indeed, increasing the precision of radiotherapy delivery may lead to reduced margins and therefore allow further dose escalation.
There are two key features of IGRT systems that require particular attention: geometric accuracy and image quality. First, the chosen IGRT system often does not share a common central axis with the megavoltage treatment beam; therefore, the geometric relation of the IGRT datasets to the megavoltage treatment beam must be assessed and monitored to ensure adequate localization, scaling, and geometric accuracy. Second, image quality metrics define the ability of the IGRT system to consistently produce an image of sufficient quality to localize the structures of interest, through either manual au automatic registration of IGRTimages to the reference planning CT scan. A well‐planned QA program integrates closely the IGRT system procedures with linac procedures described in accepted QA standards such as the report of the AAPM task group 40 report.
This lecture will present a brief review of IGRT systems, including kilovoltage and megavoltage cone‐beam CT, ultrasound, CT on rails, Tomotherapy, and projection radiography. The emphasis will be on QA issues germane to these systems and the clinical processes relying on their use. QA checks and phantoms will be suggested, and some QA metrics, with their associated tolerance levels based on clinical experience will be presented. Successful strategies for clinical implementation of IGRT will also be discussed.
1. Understand the technical and process issues related to IGRT systems
2. Present a QA program for IGRT systems focusing on geometric accuracy and image quality
3. Users will tailor their program according to the clinical use of the device.
- CE ‐ Therapy: Stereotactic Cranial RS/RT
MO‐B‐BRD‐01: Quality Assurance in Stereotactic Radiosurgery and Fractionated Stereotactic Radiotherapy36(2009); http://dx.doi.org/10.1118/1.3182199View Description Hide Description
In the 50‐plus years since it was first introduced, stereotactic radiosurgery, high‐dose irradiation of cranial neoplasms delivered in a single fraction, has become a standard of care in the treatmentbraintumors, vascular malformations, functional disorders, and pain. Modern radiosurgery can be performed non‐invasively and on an outpatient basis, yet with an extremely high degree of accuracy. Within the past ten years, the field of radiosurgery has seen numerous technological enhancements, including: the development of dedicated devices for stereotactic delivery, the use of relocatable frames to facilitate fractionated delivery, the development of image guided and “frameless” approaches, and the application to extracranial tumor sites. Each of these developments is accompanied by its own challenges in assuring targeting and dosimetric accuracy. In this presentation we review the technologies for stereotactic localization and treatment of cranial targets with particular emphasis on the quality assurance aspects associated with establishing and maintaining a clinical radiosurgery program.
1. Differentiate how radiation is delivered for Gamma Knife and Linac‐based (conventional and robotic)stereotactic radiosurgery.
2. Define the treatment planning parameters for Gamma Knife and Linac‐based stereotactic radiosurgery.
3. Discuss measures for assuring accuracy in stereotactic localization and dose delivery for Gamma Knife and Linac‐based stereotactic radiosurgery.
- CE ‐ Therapy: Panel Session: kV and MV CBCT
TU‐A‐BRD‐01: KV and MV Cone‐Beam CT Imaging for Daily Localization: Commissioning, QA, Clinical Use, and Limitations36(2009); http://dx.doi.org/10.1118/1.3182307View Description Hide Description
Three‐dimensional conformal radiotherapy (3D‐CRT), intensity‐modulated radiotherapy(IMRT), and stereotactic body radiotherapy(SBRT) allow for the generation of highly conformal dose distributions for patients with tumor volumes wrapped around or adjacent to critical structures. As a consequence of steep dose gradients between the target and organs‐at‐risk, precise localization of the target volume and surrounding normal tissue is essential. However, variations in patient setup and organ motion are limiting factors in the accurate delivery of radiation treatment with a high degree of precision. Recent online image‐guided RT techniques using kilo‐Voltage cone‐beam CT (kV‐CBCT) and Mega‐Voltage CBCT (MV‐CBCT) are now offering the opportunity to overcome these limitations and greatly improve treatment localization accuracy. These IGRT techniques using the latest imaging technologies represent an improvement over traditional techniques such as 2D portal imaging. It allows for the use of volumetric online imaging to account for organ motion and setup variation by providing multiple anatomical views of the patient during the full course of RT treatment. The selection of imaging modality and system to use in support of a treatment protocol is often a compromise between image quality, efficiency, availability, and dose. The objective of this educational session is to review the current kV‐CBCT and MV‐CBCT imaging systems and their evolution for daily localization including
1. Commissioning, image quality, dose, registration process, and acquisition modes
2. Clinical integration
3. QA, stability over time, and downtime
4. Standard clinical applications
5. Novel clinical applications
6. Technology evolution and future directions
- CE ‐ Therapy: Panel Session: The Management of Motion: Technologies and Practical Limitations
36(2009); http://dx.doi.org/10.1118/1.3182443View Description Hide Description
The current climate of rapid technological evolution is reflected in newer and better methods to modulate and direct radiation beams for cancer therapy. This Continuing Education lecture focuses on one aspect of this evolution, locating and targeting moving tumors. The two processes — locating and targeting tumors— are somewhat independent and in principle different implementations of these processes can be interchanged. Advanced localization and targeting methods have an impact on treatment planning, and also present new challenges for quality assurance (QA), that of verifying real‐time delivery. Some methods to locate and target moving tumors with radiation beams are currently FDA approved for clinical use — and this availability and implementation will increase with time. Extensions of current capabilities will be the integration of higher order dimensionality into the estimate of the patient pose and real‐time reoptimization and adaption of delivery to the dynamically changing anatomy of cancer patients.
1. To describe the technology available to determine real‐time target position
2. To review the systems for real‐time target‐beam alignment
3. To discuss the practical considerations of real‐time target tracking systems
Research sponsored by Accuray, Calypso, Cyberheart, GE, NIH/NCI, Philips and Varian.
36(2009); http://dx.doi.org/10.1118/1.3182444View Description Hide Description
The breathing‐induced motion adversely affects the radiotherapy process for pulmonary tumors at all stages. During the conventional 3D imaging, motion causes artifacts that lead to erroneous anatomical information that propagates as a systematic error during planning and delivery. For planning, the standard approach to insure tumor coverage in the presence of geometrical uncertainties is to surround the target with a safety region. The pitfall of the margin expansion approach is that additional high doses are delivered to the normal tissue adjacent to the target, thus increasing the chances of radiation‐induced disease, while also limiting tumordose escalation and, subsequently, the potential for better tumorcontrol. The advent of 4D computed tomography (4D CT) represented a significant step forward toward improved imaging accuracy for regions affected by the respiratory motion due to the ability of reconstructing multiple image sets corresponding to various points during the breathing cycle. The information from the 4D CT is first used to better identify the target region at various stages over the breathing cycle and the extent of motion. Next, the more complete imaging data has to be factored into the planning process. To this end, depending on the treatment delivery strategy, one or more treatment plans are designed for each breathing instance for which data is available. Dose computations are performed on multiple datasets (usually termed as 4D dose calculations), and the cumulative dose is then used to assess the plan quality similar to the conventional 3D planning. The accumulation of doses on a reference image dataset is accomplished by using deformable image registration, which maps corresponding image voxels from one dataset to the reference dataset. To date, several approaches have been developed to fulfill this task. The amount of data available from 4D scans increases significantly the amount of time and effort needed for treatment planning. However, studies have suggested that the dose accumulation process could be reduced to planning on certain datasets only, while preserving at an acceptable level the accuracy that would otherwise be achieved through a full 4D dose computation. Multiple centers have employed the 4D planning approach to study the changes in doses as a result of 4D treatment planning and addressed the clinical significance of the changes observed.
In this presentation, we will discuss the rationale for 4D treatment planning, review the methods available for cumulative dose computation, identify potential sources of error specific to the 4D planning approach, and discuss the clinical importance of the dosimetric changes resulting from 4D‐based treatment planning.
1. Understand the rationale for accounting for respiratory motion during treatment planning.
2. Understand the principles of cumulative dose computation.
3. Learn about the clinical importance of the changes induced by the respiratory motion.
36(2009); http://dx.doi.org/10.1118/1.3182445View Description Hide Description
Respiratory gated radiotherapy holds promise to reduce the incidence and severity of normal tissue complications and to increase local control through dose escalation for lungcancer patients. In this lecture, we discuss the current status, existing problems, and potential solutions for applying gating techniques to lungcancertreatment. First, the motion artifacts in CT simulation are discussed and the 4D CT scan technique is recommended for treatment simulation of lungcancer patients under gated radiotherapy. Second, we discuss two currently available forms of gated radiotherapy: internal (fluoroscopic) gating and external (optical) gating. Internal gating utilizes internal tumor motion surrogates such as implanted fiducial markers while external gating uses external respiratory surrogates such as markers placed on the surface of the patient's abdomen. The major strengths of external gating are that it is non‐invasive, is relatively easy and does not require any radiationdose for imaging. However, the relationship between the tumor motion and the surrogate signal may change over time, inter‐ and intra‐fractionally. The major strength of the internal gating systems is the precise and real‐time localization of the tumor position during the treatment. The two major weaknesses of internal gating are the risk of pneumothorax for implantation of markers in lung and the high imagingdose required for fluoroscopic tracking. Third, we discuss the potential solutions and future development of gated radiotherapy for lungtreatment. We propose the combination of external and internal surrogates (hybrid gating) to solve the imaging dos problem and the direct fluoroscopic tracking of lung mass to avoid seed implantation. Other related issues are also discussed.
- CE ‐ Therapy: Panel Session: The Future of NIH Research Funding
36(2009); http://dx.doi.org/10.1118/1.3182589View Description Hide Description
The National Institute of Health (NIH) is the most important source for fundingmedical physics research in the US. Consequently it has a profound impact on careers in medical physics. Most medical physicists rely on NIH funding to support their research ideas and launch or maintain research projects. While innovative research ideas are a pre‐requisite to attract funding, it is also important to understand the mechanisms of grant application.
For this year the NIH has made significant changes to its grant review and submission process. These changes were driven by three aims:
1. Engage the Best Reviewers
Reviewing grant applications can be a huge burden for scientists. Consequently, new reviewers will be given additional flexibility regarding their tour of duty. Further, efforts will be undertaken to improve retention of standing review members. Studies will be conducted on the feasibility of using high‐bandwidth support for review meetings to provide greater flexibility and alternatives for in‐person meetings.
2. Improve the Quality and Transparency of Review
A new criterion‐based scoring on a 1‐7 scale, using structured critiques, will be introduced. The reviewers will provide feedback through scores and critiques for each criterion in a structured summary statement. Streamlined applications will receive a preliminary score. Applications will be shortened significantly to for example a 12‐page research plan for an R01 application.
3. Ensure Balanced and Fair Reviews across Scientific Fields and Career Stages, and Reduce Administrative Burden
To ensure that the largest number of high quality and meritorious applications receive funding earlier and to improve system efficiency, NIH is considering separate percentiling of new and resubmitted applications and permitting one amended application. NIH is establishing an Early Stage Investigator designation for which clustering of applications is considered. The same approach will be considered for clinical research applications.
This educational session is divided into three presentations followed by a panel discussion with questions from the audience. It will address newcomers and established researchers. The presentations will cover the following topics:
1. “Overall strategies for successful NIH grant applications.”
2. “Imminent changes in the NIH grant submission and review.”
3. “Impact of the changes from an applicant's point of view.”
1. Understand the new NIH grant submission and review process
2. Understand the imminent changes in the NIH grant submission and review process