You can move the table, collimator, XY jaws, and gantry in the right direction without entering the treatment room if you familiarize yourself with the IEC scale convention of your machine. I have mostly used Varian machines during my career in medical physics and recently commissioned a Varian Trilogy linear accelerator at our cancer center. During commissioning, it became necessary (for productivity’s sake) to move the jaws, table, gantry and collimator from outside treatment room. Normally, Varian machines conform to either the Varian standard, Varian IEC (601-2-1) or IEC1217. Our Trilogy coordinates, movements and scales follow the Varian IEC (601-2-1) scale. Therefore, here are a few tips on this Varian IEC 601-2-1 scale that I generated during the commissioning of my machine. For a better understanding, these “tips” are explained in question and answer format. However, since some of us may not know what IEC stands for, here is a short paragraph taken from the IEC website before proceeding to the main topic:
IEC (International Electronic Commissioning) is the world’s leading organization that prepares and publishes International Standards for all electrical, electronic and related technologies. Wherever you find electricity and electronics, you find the IEC supporting safety and performance, the environment, electrical energy efficiency and renewable energies. The IEC also manages conformity assessment systems that certify that equipment, systems or components conform to its International Standards.
Out of the four components (the couch, jaws, collimator and gantry), we cover the couch and the gantry in this post and will discuss the jaws and the collimator in next post.
Couch: Vertical Movement
The couch vertical is at 8.5 cm. You need to move the table 4 cm upward toward the ceiling. At what do you set the new vertical position of the table from outside the treatment room: 12.5 cm or 4.5 cm?
Click on this link for the answer. Depending on your screen resolution, you may have to scroll up to see the answer window.
The couch vertical is at 2.5 cm. You need to move the table 4 cm upward toward the ceiling. At what do you set the vertical position of the table from outside the treatment room: 6.5, -1.5 or 998.5 cm?
Click on this link for the answer.
Tip: Table vertical position is at 0 degrees at iso-center. Moving the couch toward the floor down from iso-center, the number increases on this coordinate axes. If you move the couch toward the ceiling up from iso-center, the number decreases from 1000.
Couch: Lateral Movement
The couch lateral position is at 4.5 cm. You need to move the table 4 cm toward the right of the gantry if you face the gantry. What do you set the new lateral position of the table from outside the treatment room: 8.5 cm or -8.5 cm?
Click on this link for the answer.
The couch lateral position is at 2.5 cm. You need to move the table 8 cm toward left of the gantry if you face the gantry. What do you set the new lateral position of the table from outside the treatment room: -5.5 cm or 994.5 cm?
Click on this link for the answer.
Tip: Table lateral position is at 0 degrees at iso-center. When moving the couch toward the right (facing the gantry) from iso-center, the number increases on this coordinate axes. If you move the couch toward left (facing the gantry) from iso-center, the number decreases from 1000.
Couch: Longitudinal Movement
The couch longitudinal is at 55 cm. You need to move the couch 24 cm toward the gantry. What do you set the new longitudinal position of the table from outside the treatment room: 79 cm or 31 cm?
Click on this link for the answer.
The couch longitudinal is at 105 cm. You need to move the couch 50 cm away from the gantry. What do you set the new longitudinal position of the table from outside the treatment room: -55 cm or 55 cm?
Click on this link for the answer.
Tip: Table longitudinal Position increases if the couch moves towards the gantry and decreases if the couch moves away from the gantry.
The gantry is at 115 degrees. You need to move gantry 90 CCW. What do you set the position of the gantry from outside the treatment room: -25, 25, 205, or 335 degrees.
Click on this link for the answer.
The gantry is at 15 degrees. You need to move gantry 90 CW. What do you set the position of the gantry from outside the treatment room: -75, 105, or 255 degrees.
Click on this link for the answer.
Tip: The gantry on the Varian IEC 601-2-1 scale is at 0 degrees when the gantry is up at vertical position. The degree increases as gantry rotates CW. It goes to 90 degrees when the gantry is to the right (facing the gantry), to 180 degree when gantry is down at vertical position, to 270 degree when gantry is to the left (facing the gantry) and increases as it rotates CW to 359.9 and then 0 degree up at vertical position. Reversely, the angle decreases as gantry rotates CCW.
- Varian resources
- S C Lillicrap et. al. “Radiotherapy equipment standards from the International Electrotechnical Commission” BJR 71 (1998), 1225-1228.
- Correspondense – BJR 72 (1999), 623
- Radiotherapy equipment-Coordinates, movements and scales. AS?NZS 4495:1997, IEC 1217:1996
Staffing in radiation oncology practices has always been plagued with administrative issues. The process of radiation therapy consists of a series of steps and often involves a number of different individuals. Each practice should establish a staffing program consistent with patient care, administrative, research and other responsibilities. It is recognized that talent, training and work preferences may vary from individual to individual; therefore, it is appropriate to factor these aspects into a staffing program. Since the 1980′s many organizations have published benchmarks for radiation therapy staffing. Among these organizations are AAPM, ACR, ACRO, AAMD, ASRT and a few private market research institutions. These reports provide benchmarks for the staffing of not only medical physicists, but also dosimetrists, radiation therapists, and nurses. It is worth noting that some of these reports were generated before computer information system technology became a part of radiation treatment systems. We believe that development of benchmarks for staffing in radiation therapy practices is very important and directly affects the quality of patient care and safety. Until we finalize this study, here are some recent staffing levels in radiation therapy practices as published by the ACR for the purpose of radiation oncology program accreditation.
According to the ACR, for accreditation purposes “the facility’s staffing levels for radiation oncologists, physicists, radiation therapists and dosimetrists are compared to the accredited facility averages and averages for the facility’s stratum as defined in the following table. The table allows facilities to identify personnel and equipment utilization issues. Staffing recommendations may be part of the final report; however, variations from these levels generally do not result in withholding of accreditation unless inadequate staffing levels result in non-compliance with ACR Practice Guidelines and Technical Standards and/or compromise patient safety.”
We will post more articles on this topic in a timely fashion and encourage our readers to send us their thoughts and comments on this issue.
Report number 162, Self Assessment of Radiation Safety Programs, is the latest report published in March 2010 by the NCRP (National Council on Radiation Protection and Measurement). It is an informative report for all of us and is particularly relevant for all physicists who are also responsible for the radiation safety program at their institution. Self Assessment of Radiation Safety Programs is defined by the NCRP as:
“Self assessment is a process by which an organization evaluates its compliance with external regulatory requirement and commitments and with its own internal radiation safety program requirements. It is a proactive component of an effective management plan for a radiation safety program. This report will cover the types of assessments, their purposes, and the processes for conducting them. It will discuss the frequency, the program areas to be assessed, the documentation, and the follow-up of assessments. The report will also discuss guidance for the scheduling and resolution of corrective actions.”
The report provides information and guidance on the following topics:
- Definition and purposes of self assessment;
- Types of self assessment (i.e., performance based, risk based, compliance based, task, process and program level, formal and informal);
- Responsibilities for establishing self-assessment programs including upper management, line management, the radiation safety committee, radiation safety program personnel including the radiation safety manager or radiation safety officer, and the workers;
-Self assessment program planning for an institution, including determining the purpose and type of self assessment, selecting the program elements to be assessed, allocating the necessary resources, and developing a self assessment program review plan;
- Qualification and selection of individuals performing the self assessments;
- Self assessment methods and techniques including evaluation of radiation safety program survey and monitoring results, workplace observations, interviews, document reviews, checklists, review of metrics, and questionnaires;
- Types of deficiencies that can be identified in the self-assessment process, ranging from the minor ones that are most likely to be found to those that are more serious;
- Identification of noteworthy practices;
- Planning an individual self assessment including the program elements to be assessed, the schedule for performing the self assessment, and the types of self assessment to be used;
- Conducting the self assessment including the entrance meeting, performing the assessment activities, daily team conferences, upper management briefings, exit meeting, and documentation;
- Documenting the self assessment including writing reports, report approval, communicating the results, and legal consideration; and
- Developing corrective-action plans including tracking and resolution of corrective actions and reviewing the effectiveness of the corrective-action program.
In a recent newsletter of the Health Physics Society (Volume XXXVIII Number 4 April 2010), it was noted that David Myers, an HPS member, worked on NCRP Report 162. In the newsletter, he provides more information about the latest report and its importance to the radiation safety programs of all institutions. The report can be purchased through the NCRP web site for $50 or $40 in pdf format.
The rapid advances in nuclear medicine have made it essential for medical physicists to have a strong understanding of the field, its relevant technologies and clinical applications. With the increasing utilization of nuclear medicine in patient care, more and more medical physicists–whether to prepare for the boards or to understand new challenges in the workplace–are looking to increase their knowledge of nuclear medicine. We have fielded a few emails from readers regarding books and resources on nuclear medicine, so we have put together a listing of resources we feel are helpful to those looking for one or two nuclear medicine reference. And, as always, we welcome reader feedback: share your thoughts on our selections. Did we miss any books on our list? Leave a comment to let us know! Read more
Our Radiation Oncologist recently showed me a pelvis CT image of a male patient who had undergone bilateral hip replacement with forged titanium alloy implants. The patient had early stage prostate cancer, and the doctor wanted to treat this patient with IMRT. The difficulty was to delineate the prostate, seminal vesicles and other organs at risk because of the streak artifacts in the CT images due to high-Z material in the patient. The question came up about how this kind of artifact can be removed or minimized so that the target organ, as well as the organs at risk and other organs can be delineated for treatment planning. I did some research and was able to come up with some good articles on this topic. I am summarizing my findings below for those who are interested to learn or as a reference for those who may have such cases in the clinic.
Streak artifacts in CT images are generated in conventional CT when implanted objects of high atomic number exist in the patient. The artifact and image degradation associated with the kilovoltage (kV) CT imaging in the presence of high atomic number material greatly hinders the ability to delineate tumors and certain organs, particularly in the treatment planning of a prostate patient with hip prostheses. Such a situation, therefore, precludes precise dose calculation. There are several techniques reported that, if used, can minimize such artifacts, thereby enhancing image visualization for the delineation of tumor and other organs.
1- Charmley et al. (1) suggested that the use of CT-MR image registration to define target volumes in pelvic radiotherapy in the presence of bilateral hip replacements could facilitate target definition of prostate patient with hip replacements. However, a number of factors were found to affect image quality and/or the accuracy of target definition. The standard MR couch, different from a CT or linac treatment couch, might result in different patient positions, and the presence of the metallic implants may create significant distortion.
2- Yazdia M. (2) suggested an adaptive approach to metal artifact reduction in helical computed tomography for radiation therapy planning. At that time, they may require manual image post-processing and most CT scanners available in radiation oncology department are not equipped with these features.
3- The artifact image and degradation associated with the kilovoltage (kV) CT imaging in the presence of high atomic number material is greatly reduced with Megavoltage Cone Beam Computed tomography (MV-CBCT). MV-CBCT has been used in image-guided radiotherapy (IGRT) to correct patient setup immediately before treatment. Hansen et al (3) used this technique to treat paraspinous tumors in the presence of orthopedic hardware. It allows rapid acquisition of 3D images that can be registered with the planning CT with millimeter precision and enhance image visualization by exploiting the predominantly Compton scattering of high-energy photons delivered in the MV-CBCT system. Aubin et al. (4) of the Department of Radiation Oncology at UCSF did a study with the support of Siemens Oncology Care systems on the use of Megavoltage Cone Beam CT to complement CT for target definition in pelvic radiotherapy in the presence of hip replacement. They found the MV-CBCT image could be used to clearly visualize the hip prostheses and provide sufficient soft-tissue contrast to help delineate the prostate, bladder and rectum. The artifacts on the kV CT obscure the border between the prostate and anterior wall of the rectum and the interface between the prostate base and the bladder neck. However, the MV-CBCT images were particularly useful to help delineate these structures as well as the lateral extension of the prostate in the axial plane, the seminal vesicles and the lymph nodes. Also, normal anatomy such as pelvic bones, penile bulb, bladder, femoral heads, rectum and small bowel can be delineated with higher accuracy as well. They evaluate this technique for seven patients. For each patient, the MV-CBCT images were imported into the treatment planning system and registered with the original CT using body anatomy contoured on each image set. The target volumes and organs at risk for prostate treatment were contoured using both the CT and the MV-CBCT for single hip replacement, and using only the MV-CBCT for bi-lateral hip prostheses. For the full article, click on: http://bjr.birjournals.org/cgi/reprint/79/947/918
The following two figures taken from Aubin M. at el (4) show the difference between conventional CT and MV-CBCT images:
- Chamley N. et al. The use of CT-MR image registration to define target volumes in pelvic radiotherapy in the presence of bilateral hip replacements. BJR 2005; 78:634-636.
- Yazdia M. et al. An adaptive approach to metal artifact reduction in helical computed tomography for radiation therapy planning: experimental and clinical studies. Int. J. Radiation Oncol Biol Physics 2005; 62(4): 1224-1231.
- Hansen, E.K. et al. Image guided radiotherapy using Megavoltage Cone-Beam Computer Tomography for treatment of paraspinous tumors in the presence of orthopedic hardware. Int. J. Radiation Oncol Biol Physics 2006; 66(2): 323-326.
- Aubin M. at el. Use of Megavoltage Cone-Beam CT to complement CT for target definition in pelvic radiotherapy in the presence of hip replacement. Short Communication: British Journal of Radiology 2006.
With the upcoming ABR Physics exams this summer, we have received several questions in regards to how to prepare. If you are taking Part 1 this summer, concentrate on that; don’t concern yourself with Parts 2 and the Oral examination (just yet). That said, the first thing you will want to do is review the topics covered on Part 1 of the physics exam. Fortunately, the ABR has laid out the subjects you will be tested on in the Initial Certification Study Guide. The ABR has yet (as far as we have heard) to veer from those topics, so you will not be tested on subjects outside their study guide. In fact, the guide is quite accurate in terms of the scope of the questions you will be asked. The next thing you will want to do is gather resources that cover those topics well.
The internet is strewn with information that is helpful in prepping; the resources are scattered through the Web and take time to find. One site worth bookmarking provides lecture notes on several physics topics listed in the Initial Certification Study Guide as well as a few practice questions. Another site with lecture notes on relevant topics is the course site for Diagnostic Radiology Imaging Physics at UW. More practice question can be found here and here (though at this site, you will have to register to access the free tests).
Your main allies will be your own lecture notes and good prep books. While cross-referencing is always helpful, the following texts have been helpful to other students who took the ABR Part 1 Physics exam in the past. The first is “Review of Radiologic Physics” by Walter Huda. The book is 272 pages with over 500 practice questions, and the material covered is high-yield. The next two texts are pricey, but serve as good reference texts to have in your possession. They are “The Essential Physics of Medical Imaging” by Bushberg et al and “Medical Imaging Physics” by William Hendee and E. Russell Ritenour. We have also heard that reviewing Raphex exam questions is also key in preparing. There are still a few copies of the very old exams available for purchase on Amazon.com. You can also find copies of recent exams for free on the Web: Raphex 2006 Questions and Answers, Raphex 1998 Questions, Raphex 1997 Questions and the Raphex 1997 Answers.
Last, but certainly not least, talk to people who have taken the exam within the last few years. They will be able to tell you what the ABR has been stressing on the exam these days. Ask them how they prepped and what they found to be useful. Start early, and with the resources listed above in addition to those you locate on your own, you should be well-prepared to tackle Part 1 with ease and success.
Readers who have been us since the launch of MDPhysics.com in March 2009 know that we started with just a weblog. Shortly thereafter, we added a listing of funding opportunities, a medical physics job board as well as a calendar of medical physics events. In addition, a physics classifieds section has been in the works for awhile, and now with coding complete, we’re excited to add this new functionality to the site. As always, a direct link to the page can be found in the navigation bar at the top of the site. Classifieds listings, like job listings, are free. All ads expire after 50 days and can be removed at anytime using an access code you receive via email. Read more
AAPM’s TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams contains many details to which we should pay close attention when performing necessary measurements for the calibration of high-energy beams. One such measurement is calculating the polarity correction factor (Ppol) for ionization chambers used in electron beam dosimetry. Since polarity effects vary with beam quality and other conditions (such as cable position), one must correct for these effects by making measurements each time clinical reference dosimetry is performed. To correct an ion chamber’s raw reading for polarity effects it is necessary to take readings with both polarities applied and tabulate Ppol by the following equation: Read more
Have you ever seen radioactive material labeled with the units Roentgen – Equivalent – Beta rays/second (reb/sec)? A medical physicist recently told me he came across these units on a Strontium-90 source at his new job while he was taking inventory of radioactive materials. This particular source was labeled with its model and serial number, as usual, but its radioactivity (the strength of the source) was given in Roentgen – Equivalent – Beta rays/second (reb/sec) instead of millicuries (mCi). Since the convention is to use miC when recording source strength in the inventory log book, he was wondering how to convert these units to mCi. Since I had not worked with Sr-90, I didn’t know the answer myself. I spoke to a couple of experienced physicists I know, and surprisingly no one had the answer. Like any good scientist, this peaked my curiosity…so I did some research. I am guessing many physicists may not know the answer, so I am sharing the fruits of my labor and the result of my due diligence in this post. This is for those who, like me, are curious and are interested to learn: Read more
We were recently contacted by an individual who was studying physics at the doctoral level and was interested in switching to a career in medical physics. Switching to a career in medical physics with a Ph.D. in any branch of physics was a relatively easy task, say 20 years ago, but has become increasingly more difficult with the growing number of medical physics degree programs and the restrictions of residency admissions to those who have specifically graduated from an academic program in medical physics. It’s certainly an exciting time to be in medical physics, but it’s become difficult (albeit, not impossible) for those who have not specifically trained in medical physics to join the party. It’s worth mentioning that many past (and current) leaders in our field did not graduate from medical physics degree programs, which makes one wonder how many talented individuals with the potential to contribute to our community are unable to become medical physicists simply because they chose to study a different branch of physics instead. Read more