Wishing you success!
Roles and responsibilities of medical physicists in oncology radiation therapy
Author: Fu Yuchuan (ychfu@hotmail.com) Source: Original Updated Date: 2005-10-26
Briefly: Medical physicists are indispensable and important members of oncology radiation therapy. Especially with the rapid development of tumor radiation therapy equipment and technology in recent years, the role of physicists in ensuring radiation safety, improving the level of therapeutic technology, and providing patients with high-quality services is becoming more and more important.
Roles and responsibilities of medical physicists in oncology radiation therapy
Medical physicists are indispensable and important members of oncology radiation therapy. Especially with the rapid development of tumor radiation therapy equipment and technology in recent years, the role of physicists in ensuring radiation safety, improving the level of treatment technology, and providing high-quality services for patients is becoming more and more important [1]. In Europe and the United States hospitals in the oncology radiotherapy department, physicists as a profession has a long history, the number of physicists engaged in the profession is also due to the development of equipment and precision radiotherapy technology continues to increase, and at the same time the responsibility is also increasingly heavy.
In oncologic radiation therapy, the radiation oncologist will undoubtedly be responsible for the entire course of radiation therapy, and based on this role, it is his or her responsibility to identify an appropriate and competent physics team in which the duties of the different personnel (including physicists, dosimetrists, or others) are clearly designated. Without adequate physical support, it is impossible to provide a high standard of treatment and service to patients [2]. The physiatrist, in turn, must lead the physics team and be responsible for all physical data and processes applied to the patient, whether or not these processes are performed directly by the physiatrist himself.
Every radiotherapy department needs to continually improve its treatments, which means that new treatment techniques and tools need to be introduced on a continuous basis, while selectively retaining the original treatment programs. Physicists all play an important role in this process. For example, in the last 30 years, the development of gas pedal technology, CT imaging, three-dimensional treatment planning, conformal and dynamic therapy, remote rear-loaded brachytherapy, intensity-modulated radiation therapy, and stereotactic therapy and other new technologies have appeared and developed one after another [3], all of which have continued to change the content of the physicists' work and the scope of their duties. Since the oncology radiology departments of each clinical hospital have different treatment equipment, different treatment levels and different programs, the specific tasks and responsibilities of physicists working in different hospitals vary. In oncology radiotherapy departments with most advanced radiotherapy equipment, the specific tasks of the physicists in this profession include the following aspects.
1. Radiotherapy equipment
Modern radiotherapy equipment includes tele-irradiation equipment, brachytherapy equipment, and simulators. Considering the rapid development of radiotherapy equipment, the types of diseases targeted and the relatively high price, the physicist has the responsibility to choose the radiotherapy equipment to be purchased by the unit in terms of performance and price ratio, to make their own recommendations on how to carry out the treatment program, and to propose the manufacturer's equipment needs to meet the specifications and conditions. This not only requires the physicist to keep abreast of the latest radiation therapy techniques, but also to be aware of the scope and limitations of the various techniques and tools, and to have an understanding of the complexity of the process of implementing these techniques.
The installation of radiation therapy equipment is generally done by the manufacturer, but then the acceptance testing of that equipment and the measurement of machine data is the job of the medical physicist. For each type of radiotherapy equipment a formal acceptance inspection entry can be made, with the guiding principle being that any equipment used for patient care must be tested to ensure that it meets the requirements for use and safety standards. For example, for linear gas pedals, the following tests are required: radiation protection measurements, checking the symmetry of the independent collimators, consistency of the central axes of the various parts, the effect of rotation of the frame and head on the position of the isocenter, testing of the energy of the X-rays, the flatness and symmetry of the field [4], testing of the energy of the electron beams, the flatness and symmetry of the field, monitoring of the stability of the ionization chamber and testing of linearity, and so on. linearity of the ionization chamber, and so on. Each test has different contents, steps and indexes, and can be completed one by one in the form of a table.
Part of the radiotherapy equipment through the acceptance test can directly start clinical use, but there are some can not be used directly, need to obtain more data, such as linear gas pedal for clinical use, must be through the scale [4], measurement of the treatment planning system needs all the beam parameters and machine parameters and enter them into the treatment planning system, and then test the treatment planning system calculated dose distribution with the actual measurement of the dose distribution, and then check the treatment planning system to see if the dose distribution is the same as the actual measurement of the dose distribution, and then the treatment planning system to see if the dose distribution is the same as the actual measurement of the dose distribution. dose distribution calculated by the treatment planning system is consistent with the actual measurements, these are the work of the physicist. Only machines authorized by the physicist can be used to treat patients.
Quality assurance (QA) of radiotherapy equipment is essential for a clinical organization to perform high quality radiotherapy services [2]. Each radiotherapy equipment needs to have QA elements that should be done on a daily basis, QA elements that should be done on a monthly basis, and QA elements that should be done on an annual basis, which should be listed in a document and implemented by personnel on a time schedule, one by one. Some routine QA tasks can be done either by the physiatrist or by the dosimetrist, but the physiatrist must create QA content entries and steps to guide the process and check the final results.
2. Radiation Treatment Planning Aspects
First, acceptance inspections of the hardware and software of the radiation treatment planning system, data measurements, and routine system and data maintenance need to be performed by physicists [5][6]. The inspection of the hardware system consists of checking the accuracy and linearity of the digital input and output devices; the inspection of the software system is the selection of a range of treatment conditions and checking the accuracy of the calculated data compared to the measured data under these conditions, e.g., comparison of the various calculations and measurements that can be made in a three-dimensional tank. Another important aspect is the examination of the various algorithms in the treatment planning system, e.g. their accuracy, constraints and characteristics, etc. Here the role of the medical physicist is to ensure that the treatment planning system is used correctly.
Secondly, the radiation treatment planning process definitely requires the involvement of a physicist. Although the radiation oncologist has overall responsibility for the patient's treatment plan, the radiation oncologist and the physicist*** work together to complete the specific treatment plan because the design and optimization of many of the options in the treatment planning process involve complex physical concepts. The general pattern is as follows: ① the radiation oncologist decides whether to do CT examination or MR examination or both according to the patient's condition, and determines the localization mode and localization point of CT simulation; ② the physicist inputs the CT image data and MR image data into the treatment planning system; ③ if the MR image data is available, the physicist firstly performs the fusion of the CT image and MR image, and then performs the external contours on the CT image If there are MR image data, the physicists will first fuse the CT image and MR image, and then outline the outer contour and important organs on the CT image; ④ The radiation oncologist will outline the target area, discuss with the physicists about how to set up the shooting field, and outline the shape of the block in the shooting field on the DRR image. doctor's treatment plan; ⑥ Finally, the doctor decides whether the treatment plan is acceptable or not and signs the medical record to approve it. Both radiation oncologists and physicists are supposed to work closely together during the whole process. In many treatment centers, the general treatment planning is done by the dosimetrist, which also needs to follow the above steps, and the physicists mainly play a supervisory and guiding role, when it comes to complex treatment plans.
Additionally, the physiatrist has another important task, which is the quality assurance of the treatment plan. All the treatment plan after the doctor's approval, on the one hand, need to be output to the control of the treatment equipment in the computer to control the actual treatment process, on the other hand need to be output to the patient's medical record, both of these outputs are required to be very accurate, physicists need to check each of the contents, to ensure that the plan output, the control of the output and the patient's medical record of the three data is the same; in addition, because the radiation therapy is generally In addition, because radiation therapy is usually carried out in separate sessions, in order to check whether each treatment is carried out according to the plan, the therapist needs to fill in the daily treatment according to the form, such as the date, the actual dose output in each field, etc., and the physicists check these records every week or so, and correct any problems in a timely manner. In order to minimize errors, the above checks usually need to be double-checked by two physios.
If the patient's treatment plan is an Intensity Modulated Radiation Therapy (IMRT) plan, a specialized quality assurance process is required for it. Each radiation therapy department may develop quality assurance components for IMRT based on the equipment available in the department. For example, for an IMRT treatment plan, the treatment plan can be applied to a solid water body model, and the isodose distribution of each field in this body model is calculated; at the same time, the isodose distribution of each field is actually measured with a Mapcheck, in which each field consists of dozens or even hundreds of subfields. The calculated values are compared with the measured values, and if 80% of the points have a dose error of 5% or less, then the plan is approved and the next step in the treatment can be taken. Alternatively, a small cavity ionization chamber is used to measure the absolute dose at a given point, and EDR2 film is used to measure the isodose distribution in a given plane, which is then compared to the calculated results. If a radiation therapy department has IMRT treatment planning systems from two different manufacturers, quality assurance can be performed using a method known as hybrid plan validation. This is done by applying the IMRT plan generated by one system to a solid water body model and calculating the isodose distribution for each field of fire in this body model; at the same time, dose distribution calculations in the solid water body model are performed in the other treatment planning system using the same beam conditions, and the results of the calculations from the two systems are compared, and the difference in the results of the isocenter dose calculations should be less than 5 percent. This method is similar to the method of QA validation with an independent dose calculation system.
3. Training and Research Efforts
Because of the inherent complexity and rapid advances in radiation therapy technology, every radiation therapy department requires not only a team of physicists capable of meeting the clinical tasks, but also the ongoing training of its personnel. Such training includes not only routine clinical training but also the progressive mastery of new techniques and treatment modalities. First, for new entrants to the field of medical physics to work as physicists, there must be a reasonable period of clinical training, and there must be a process of familiarization with many of the practical aspects of clinical work; second, the introduction of a new treatment modality into a radiotherapy department, such as whole-body irradiation, electron beam irradiation, three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, stereotactic radiosurgery, low-energy source implantable internal irradiation, high dose rate internal irradiation, etc., it is important for the physicists to master the treatment technology itself on the one hand, and to understand the treatment equipment used to carry out the treatment technology on the other hand, as well as to formulate the corresponding operation procedures and quality assurance program for this treatment equipment, and to comprehensively develop the various functions of this equipment. Therefore, the vocational training of medical physicists should be a long-term process of continuing education and self-training. This will ensure that the therapy equipment is in good working condition and provide the best technical support for the diagnosis and treatment of patients. In addition, the physiatrist has the responsibility of training the dosimetrists and therapists in the unit in the physical aspects of their knowledge.
The rapid development of a variety of high, precise, pointed technology in modern society is also concentrated in the development and application of modern radiation therapy equipment, such as electronic technology, precision instruments, computer networks, graphic image processing, automatic control technology and so on. In the process of improving radiation therapy technology and developing new treatment equipment, especially in their design and clinical application, medical physicists have played an important role. And research involving all aspects of the field of medical physics is a source of continuous development of radiation therapy techniques. Striving for excellence in radiation therapy technology itself is also part of the role of the medical physicist. Not every physical support work in the process of radiation therapy for tumors has to be done by the physicists themselves, and some of the specific technical work can be done by the dosimetrists and checked by the physicists. In this way the physicist can have some time to carry out some research work to improve the level of treatment technology and develop new treatment means.
The roles and responsibilities of each medical physicist in oncology radiation therapy depend very strongly on the types of equipment and treatment programs available in his or her radiation therapy department, and also on the number of physicists in the department, and some physicists are also burdened with teaching and administrative tasks, so it is difficult to make an exhaustive generalization. However, they all share the same goal of assisting the oncology radiologist in delivering the prescribed dose correctly and efficiently to the focal target area, improving and developing clinical treatment techniques, and providing a high standard of care for patients.
References
[1] AAPM, The role of a physicist in radiation oncology. report No. 38. colchester, VT:AIDC, 1993.
[2] ISCRO. Radiation oncology in integrated cancer management: report of the Inter-Society Council for Radiation Oncology. Reston, VA: American College of Radiology, 1991. .
[3] Faiz M. Khan, The physics of radiation therapy, Third Edition, Lippincott Williams & Wilkins, 2003.
[4] Peter R. Almond, et.al. AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams, Med. Phys., Vol. 26, 1847-1870, 1999.
[5] Van Dyk J, Barnett R, Cygler J, etal. Commissioning and QA of treatment planning computers. Int J Radiat Oncol Biol Phys, 26, 261-273, 1993.
< p>[6] Benedick Fraass, et.al. American Association of Physicists in Medicine Radiation Therapy Committee Task Group 53: Quality assurance for clinical radiotherapy treatment planning, Med. Phys., Vol. 25, 1773-1829, 1992.