Volume 33, Issue 6, June 2006
Index of content:
- Therapy Continuing Education Course: Room 230A
- CE: Monte Carlo ‐ I: Machine and Source Modelling
33(2006); http://dx.doi.org/10.1118/1.2241393View Description Hide Description
In this presentation, we will discuss source modeling and beam commissioning for Monte Carlotreatment planning. We will review the current status of Monte Carlo simulations of clinical photon and electron beams and the theories and methodologies used in particle phase space representation and reconstruction for Monte Carlo dose calculation. We will discuss the sensitivity of beam characterization to simulation details, such as beam energy, angle, intensity, and details of the treatment head design. We will review different source models for photon and electron beam characterization and discuss the accuracy and efficiency tradeoffs between full phase space and simplified source models. We will describe the methods and software that have been developed for source modeling and beam commissioning for the clinical implementation of the Monte Carlo method for treatment planning and beam delivery verification. We will present different methods for source parameterization based on simulated phase space data and a standard set of measured beam data including in‐air and in‐phantom output factors and in‐phantom dose distributions.
1. Describe the Monte Carlo method for clinical photon and electron beam simulations.
2. Review theories and methodologies for phase space representation and reconstruction.
3. Present different source models for Monte Carlo dose calculation.
4. Describe different methods for source parameterization and beam commissioning.
- CE: TG‐43 Update
33(2006); http://dx.doi.org/10.1118/1.2241400View Description Hide Description
Since publication of the 2004 update to the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report (AAPM TG‐ 43U1), several new low‐energy photon‐emitting brachytherapy sources have become available. Many of these sources have satisfied the AAPM prerequisites for routine clinical use as of January 10th, 2005, and are posted on the Joint AAPM/RPC Brachytherapy Seed Registry. Consequently, the AAPM has prepared this supplement to the 2004 AAPM TG‐43 update. This paper presents the AAPM‐approved consensus datasets for these sources, and includes the following 125I sources: Amersham model 6733, Draximage model LS‐1, Implant Sciences model 3500, IBt model 1251L, IsoAid model IAI‐125A, Mentor model SL‐125/SH‐125, and SourceTech Medical model STM1251. The Best Medical model 2335 103Pd source is also included. While the methodology used to determine these datasets is identical to that published in the AAPM TG‐ 43U1 report, additional information and discussion are presented here on some questions that arose since the publication of the TG‐43U1 report. Specifically details of interpolation and extrapolation methods are described further. Despite these small changes, additions, and clarifications, the overall methodology, the procedures for developing consensus datasets and the dose calculation formalism remain the same as in the TG‐43U1 report. Thus, the AAPM recommends that the consensus datasets and resultant source‐specific dose‐rate distributions included in this supplement be adopted by all end users for clinical treatment planning of low‐energy photon‐emitting brachytherapy sources. Adoption of these recommendations may result in changes to patient dose calculations, and these changes should be carefully evaluated and reviewed with the radiationoncologist prior to implementation of the current protocol.
- CE: Informatics Systems Overview
33(2006); http://dx.doi.org/10.1118/1.2241492View Description Hide Description
Due to the increasing complexity of radiation therapy, government regulations, and legal liability, computerized radiationoncology information systems are becoming a necessity. Selection of an information system involves understanding of both computer software and hardware issues. Topics such as network infrastructure, software interfaces, and hardware interfaces, which are not part of the normal physics training, must be understood by the medical physicist. As the person with the most technical training in the radiationoncology department they will be called upon to do one or more of the following; specify a system, setup and installation, troubleshoot the system when things go wrong. This course will identify both hardware and software issues to consider when either first implementing a computerized information system or changing to an electronic treatment record. An overview/summary of the commercially available Record & Verify systems will also be presented.
1. Understand basic network infrastructure for both local area networks (LAN) and wide area networks (WAN).
2. Understand interfaces to both hospital information systems and various radiationoncology devices.
3. Understand differences in network requirements for both single department and multi‐department institutions.
4. Understand what is required when migrating from a paper treatment record to an electronic treatment record.
5. Be able to generate specifications for a radiationoncology information system.
6. Understand the personnel requirements for implementing and maintaining a radiationoncology information system.
Conflict of Interest Statement
Michael Herman — Research sponsored by Varian Medical Systems Corporation.
- CE: NCI Talk on Funding
33(2006); http://dx.doi.org/10.1118/1.2241669View Description Hide Description
The National Institutes of Health is composed of 27 Institutes and Centers, with the National Cancer Institute (NCI) being the oldest and the National Institute of Biomedical Imaging and Bioengineering (NIBIB) the youngest. Medical physicists have a major stake in the pursuits of these institutes since they have a large influence on everything from the research that is funded to the clinical protocols and methods that are employed in both therapy and diagnosis.
Yet these institutes are themselves experiencing very significant extrinsic and intrinsic factors that affect the ways that they interact with the medical community. A partial list would include: the NIH budget in the post‐doubling period; the creation of NIH‐wide Roadmap Initiatives and NCI‐wide Enterprise Initiatives; the adaptation of the NIBIB to the other Institutes; budget set‐asides for the war on terrorism; the dawning of translational research methods; the blurring of boundaries between disciplines; and an increasing role for industry, to name a few.
The ramifications of these changes will be explored with regard to the institute budgets, priorities and relationships; and the presentation will outline some of the current research agendas and the mechanisms which are used to implement them.
1. Understand the structure and processes involved in NIH funded research.
2. Understand the issues surrounding the NIH budget.
3. Understand how to develop a research proposal.
- CE: Pediatric RT Issues
33(2006); http://dx.doi.org/10.1118/1.2241676View Description Hide Description
Most Medical Physicists working in radiotherapy departments see few pediatric patients. This is because, fortunately, children get cancer at a rate about 30 times smaller than adults. Children have not smoked, abused alcohol, or been exposed to environmental carcinogens for decades, and of course, have not fallen victim to the aging process. Children get very different cancers than adults. Breast or prostate cancers, typical in adults, are rarely seen in children but instead a variety of tumors occur in children that are rarely seen in adults; examples are germinomas, ependymomas and primitive neuroectodermal tumors, which require treatment of the child's brain or neuroblastoma, requiring treatment in the abdomen. The treatment of children with cancer using radiation therapy is one of the most challenging planning and delivery problems facing the physicist. This is because bones, brain, breast tissue, and other organs are more sensitive in children than in adults while the required tumordose is frequently above 50 Gy. Because most therapy departments treat mostly adults, when the rare 8 year‐old patient comes to the department for treatment, the physicist may not understand the clinical issues of his disease which drive the planning and delivery decisions. There is a new set of dose constraints different from the adult patient, which, depending on the site of treatment, may require changing the routine beam arrangement for that site. Additionally, children are more prone than adults to developing secondary cancers after radiation. This fact has important implications for the choice of delivery techniques, especially when considering IMRT. For bilateral retinoblastoma, an irradiated child has a 50% chance of developing a second cancer by age 50.
In this presentation, an overview of childhood cancers and their corresponding treatment techniques will be given. These can be some of the most complex treatments that are delivered in the radiation therapy department. These cancers include Leukemia treated with total body irradiation, medulloblastoma, treated with craniospinal irradiation plus a conformal boost to the posterior fossa, neuroblastoma, requiring focal abdominal irradiation to avoid kidney, liver, and vertebral body damage, retinoblastoma, requiring treatment to an eye while minimizing dose to surrounding tissues, and a variety of other tumors which occur anywhere in the body. Case studies will be presented showing the treatment technique and resulting dosimetry, highlighting the objectives for tumor coverage and organ‐at‐risk sparing. Practical issues that have to be faced when treating children will also be discussed such as daily sedation and immobilization. Finally, most children with cancer are treating within a clinical trial administered by the Children's Oncology Group. Examples of the protocol physics requirements will be discussed as well as the physicist's responsibility for providing data to the Quality Assurance Review Center. The presenter is Chief of Physics at one of only two radiotherapy departments in the country that treat exclusively children (Chidlrens Hospital Los Angeles).
1. Improve understanding about childhood cancer and treatment with radiation.
2. Understand treatment planning and delivery issues specific to children.
3. Understand physicist responsibility for clinical trial participation.
- CE: Heterogeneity Corrections in the IMRT Era
33(2006); http://dx.doi.org/10.1118/1.2241828View Description Hide Description
Intensity modulated radiation therapy(IMRT) has revolutionized the treatment planning process. We are now able to produce treatment plans for complex target shapes that have remarkable dose conformity while respecting the tolerance doses to critical structures. Although the emphasis has been given in the implementation of faster, more efficient, and more comprehensive optimization algorithms to solve the inverse problem, little has been done in the dose calculation aspect of the planning process. The convolution/superposition algorithm is the most popular photondose engine used in treatment planning, while the Monte Carlo algorithm although available, remains a futuristic option.
In this presentation we will discuss the algorithms that have historically been used for treatment planning with photon beams with emphasis on the convolution and Monte Carlo based methodologies and their application in IMRT planning. Clinical examples will also be presented to demonstrate the use and outcome of dose calculations in homogeneous and heterogeneous media.
1. Review of dose calculation algorithms for photon beams.
2. Demonstrate the effect of dose algorithm selection in IMRT planning.
- CE: A Medical Physicist's Guide to the IEC
33(2006); http://dx.doi.org/10.1118/1.2241834View Description Hide Description
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes international standards for all electrical, electronic and related technologies. These serve as a basis for national standardization and as references when drafting international tenders and contracts.
Through its members, the National Committees of participating countries, the IEC promotes international cooperation on all questions of electrotechnical standardization. The IEC embraces all electrotechnologies including radiology and radiationoncology, as well as associated general disciplines such as terminology and symbols, electromagnetic compatibility, measurement and performance, dependability, design and development, safety and the environment.
IEC standards are developed by its technical committees, of which TC 62 addresses electrical equipment in medical practice. Within TC 62, Subcommittee 62C deals with equipment for radiation therapy, nuclear medicine and dosimetry. And within the subcommittee, Working Groups are responsible for writing IEC standards and technical reports. These standards dictate how electrical equipment shall be built, primarily from the standpoint of safety, although some technical reports address performance issues. For example, recent standards, or amendments to existing standards, have defined the coordinate systems to be used by radiotherapy equipment (forcing all manufacturers to change in one way or another to comply); specified the allowable leakage through multileaf collimators; and strengthened requirements for treatment planning systems. At this writing, WG‐1 is revising the performance standard for linear accelerators.
Membership on a Working Group is through a National Committee. The US National Committee is responsible for coordinating distribution of IEC drafts for review, collecting and submitting comments and votes, and recommending participation at meetings. IEC standards are too complex and carry too much significance for one person to manage, so the US has established a technical advisory group (TAG) to support the US representatives to the working groups. The role of the US TAG is to contribute to the preparation of these documents and ultimately advise the USNC how to vote on the final approval of the documents.
The US TAG consists of nine members supported by AAPM, ASTRO and ACR, but includes another 8 members representing industry and the regulators. TAG meetings are generally scheduled shortly before meetings of WG‐1, to prepare the US position on documents to be discussed. On occasion, conference calls are used, but generally TAG meetings are face‐to‐face, to facilitate discussion.
To summarize: This is a valuable activity that is critical to assure that radiation therapy equipment design properly balances the safety of patients, staff and the public; the desires for new capabilities; and practical and efficient use. Maintaining a medical physics presence on IEC committees and working groups is essential to ensure that economic issues and regulatory pressures do not dictate equipment design.
1. Become familiar with the structure of the IEC and the working groups that develop standards.
2. Appreciate the significance of IEC standards and their influence on the design of radiationoncology equipment.
3. Learn about several specific IEC standards and how they have affected the design of equipment in use today.