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Physics Standards - External Beam Therapy
 

Version : December 2, 1999



  1. INTRODUCTION

    Radiation therapy involves the use of ionizing radiations in the treatment of patients with cancer and occasionally non-malignant conditions. The success of radiation therapy depends, in large measure, on the accuracy of delivery of specified absorbed doses of ionizing radiations to selected targets, in both tumors and normal tissues. These standards have been developed by the American College of Radiation Oncology (ACRO) to assist the radiation oncology physicist to ensure accurate and safe delivery of external beam radiation therapy. Since the practice of radiation oncology physics occurs in a variety of settings, the judgement of a Qualified Medical Physicist should be used to apply these standards to individual practices.

    Therapeutic doses of ionizing radiations shall only be prescribed by a physician who possesses the appropriate training and experience in the application of this modality. In the interest of patient and personnel safety, delivery of ionizing radiations as a therapeutic modality demands strict attention to the training and experience of all personnel associated with this process as well as to the equipment used in this process and actual dose delivery.

    The clinical practice of therapeutic radiological physics includes calibration of radiation beams generated by radiation treatment units; definition of the operational characteristics of said radiation treatment units; and establishment of dosimetric system(s) based upon the aforementioned calibration and operational characteristics. It also includes the modeling of radiation beams for the purposes of treatment planning and documentation, as well as review of the technical aspects of the treatment delivery system(s) in order to ensure that the radiation dose is being delivered in a safe and accurate manner. These responsibilities shall be clearly defined in a departmental policy and procedure manual.

  2. PERSONNEL

    For patient and staff safety considerations, all facilities that utilize a dual photon or multi-modality megavoltage linear accelerator, shall employ a full-time Qualified Medical Physicist.

    Facilities that only offer low-energy photon beam treatments may employ a part-time Qualified Medical Physicist. He/she shall provide on-site physics support at least once each week during normal clinic treatment hours. Such facilities shall follow documented procedures, which include mechanisms to ensure independent checks by physicists of dose calculations before 3 fractions (or 20% of the total dose, whichever is less) have been delivered. In addition, the policies and procedures of such facilities shall identify certain patient groups, (i.e., patients being treated with single fractions, or with unusual techniques, or with large radiation doses) whose monitor unit (MU) and/or time calculations must be reviewed by a Qualified Medical Physicist prior to the first treatment. Electronic transmission of data and telephone consultation should be utilized in such circumstances, if the physicist is not on-site, subject to the ACMP Standard for Telemedicine as it Pertains to the Practice of Medical Physics in Radiation Oncology.

    Staffing of physics support personnel should be commensurate with the volume and level of complexity of radiation therapy services offered within any given practice/facility. Additional support personnel are required for research, administration, education, and training programs.

    All physics support staff should be appropriately trained. Each and every trainee shall be supervised and all work preformed thereby shall be reviewed by a Qualified Medical Physicist or his/her designee. In-house radiation therapy equipment service engineers should participate in the manufacturers' training programs. Ideally, medical dosimetrists should be certified by the Medical Dosimetry Certification Board

    Prior to the introduction of a new modality, such as conformal treatment planning, total body irradiation, intraoperative radiation therapy, stereotactic radiosurgery, and dedicated special purpose treatment units, the radiation oncology physicist should be consulted so that adjustments to staffing can be made for specialized procedures.


    1. Qualifications & Credentialing

      A Qualified Medical Physicist is an individual who is competent to practice independently in the subfield(s) of medical physics in which he or she is certified as evidenced by certification and, where appropriate, state licensure. The ACRO regards board certification in the appropriate medical physics subfield(s) and state licensure, in those states where licensure exists, as appropriate qualifications for designation of an individual as a Qualified Medical Physicist. The following boards certify medical physicists to practice in the subfield of therapeutic radiological physics, which is also known as radiation oncology physics:


      1. American Board of Medical Physics;

      2. American Board of Radiology;

      3. Canadian College of Physicists in Medicine.


      The subfields of medical physics are Therapeutic Radiological Physics, Diagnostic Radiological Physics, Medical Nuclear Physics, and Radiological Physics. Therapeutic radiological physics is that branch of medical physics which deals with (1) the therapeutic application of Roentgen rays, gamma rays, electron and charged particle rays, neutrons, and radiations from sealed radioisotope sources, and (2) the equipment associated with their production and use.

      The clinical privileges of a radiation oncology physicist must be set forth either in a job description or through the medical staff membership process in the appropriate category. The medical physicist must meet any qualifications imposed by state and/or local radiation control agencies in order to practice radiation oncology physics and/or to provide oversight of the establishment and/or conduct of the physics quality management program (QMP).

    2. B. Professional Relationships


      1. Accountability

        A Qualified Medical Physicist shall be accountable directly to the Medical Director of radiation oncology. Where physicists are employed in a setting which precludes direct reporting to the Medical Director regarding administrative matters, the physicist should be accountable to the appropriate administrative representative.

      2. Authority

        The senior Qualified Medical Physicist shall direct the radiation oncology physics program, which includes the technical direction of medical dosimetrists, therapy equipment service engineers, and other physics support staff. Responsibilities and reporting status of support staff shall be clearly defined by the physicist.


      Responsibilities

      Radiation oncology physicists are primarily and professionally engaged in the design, optimization and technical evaluation of radiation treatment plans as well as ensuring precise and accurate radiation dose delivery. They are also responsible for radiation protection of patients and staff. Their role may include clinical, research, and educational duties. The responsibilities of the radiation oncology physicist shall be clearly defined.


      1. Availability

        The radiation oncology physicist shall be available, when necessary, for consultation with the Radiation Oncologist and to provide advice or direction to technical staff when radiation treatments are being planned or when patients are being treated. Where possible, the radiation oncology physicist should be present to observe and/or help supervise complicated simulations and/or treatment set-ups.

      2. Calculations

        The radiation oncology physicist(s) shall specify and monitor method(s) to calculate MUs or treatment times and ensure independent review(s) of such calculations. Any individual having appropriate training and experience may perform the initial calculation(s). Independent review of said calculation(s) shall be performed by the radiation oncology physicist within a specified period of time.

      3. Chart Review

        The radiation oncology physicist shall develop and maintain a method for the regular (usually weekly) and systematic review of the charts of all patients under radiation treatment. The radiation oncology physicist shall perform a final chart review at the end of the course of radiation treatment in order to confirm that the prescribed dose has been delivered, and to document the total doses delivered to critical structures.

      4. Dosimetry

        The modeling of radiation beams for either planning or documentation purposes is generally performed with the aid of a treatment planning computer system. The radiation oncology physicist(s) are responsible for data input into the planning system, which should be based upon measured beam data for the radiation beam(s) in question, and for output from the planning system(s). The output should be tested and documented on a regular periodic basis. The output should agree within the manufacturer's specifications for the treatment planning system and/or published standards such as those found in the report of AAPM TG-40. The radiation oncology physicist(s) are responsible for understanding the calculation algorithm and should document those conditions for which the algorithm and measured data are in disagreement by more than 5%. The output of the planning system should be periodically tested by comparisons to direct measurements of the radiation beams. The radiation oncology physicist(s) shall ensure that all users of the treatment planning system receive appropriate training.

        The purpose of the dosimetry system is to ensure accurate delivery of the prescribed radiation dose in every case. Generally, patient-specific data (i.e., depths, external patient contours, details of internal anatomy, etc.) are utilized in calculation of parameters for delivery of the prescribed dose. Data from CT and/or MRI are frequently used to specify certain patient-specific anatomic details. The spatial and physical accuracy of all individual devices used to provide patient-specific information should be known by the radiation oncology physicist and should be monitored according to established protocols. As a minimum, the radiation oncology physics staff can test the various imaging devices using phantoms with known characteristics.

        The radiation oncology physicist shall cause to be established a dosimetry system for each and every available radiation treatment beam. Said dosimetry system(s) shall include calibration of each beam and parameterization of each beam such that all factors that are required to meet the requirements of the treatment prescription(s) are established. Said factors include dose parameters as functions of depth and field size, off axis parameters, and beam modifier (e.g., tray, wedge filter, etc.) factors. These factors shall be based upon direct measurements taken from each radiation beam.

        The dosimetry system shall be initially established via initial beam specification and calibration and shall be maintained thereafter through daily, monthly and annual checks and calibrations. All unusual applications of the dosimetry system shall be confirmed by measurement(s) prior to actual clinical use. All repairs of the treatment unit that may impact the dosimetry system shall be reviewed by the radiation oncology physicist prior to returning the unit to clinical use.

      5. Equipment

        The radiation oncology physicist shall participate in the specification, selection, and acceptance of radiation-producing machines, accessories, and computerized treatment planning systems. The physics staff should also supervise arrangements for proper maintenance of this equipment. The radiation oncology physicist will periodically evaluate all equipment for continued utility, appropriateness, reliable performance, age, and condition and make recommendations regarding practical life span, obsolescence, and replacement.

        The radiation oncology physicist shall determine the need for, specify, and have access to dosimetric and treatment planning equipment including, but not limited to, the following:


        1. Measurement instruments to calibrate all treatment equipment and patient monitoring devices. Such instruments shall include ionization chambers/electrometers used as local standards and field instruments, readout devices, constancy check instruments, and phantoms;

        2. Computerized treatment planning systems;

        3. Computerized water phantom system with appropriate ionization chambers and diodes;

        4. Film densitometry system;

        5. Patient dose monitoring systems (e.g., diodes and thermoluminescent dosimeters [TLDs]);

        6. Radiation protection measurement devices;

        7. Appropriate quality assurance test tools for radiation therapy equipment.


      6. Quality Management

        The radiation oncology physicist(s) shall develop and maintain a quality management program (QMP) for the dosimetry system(s) and all applications pertinent thereto. Said QMP shall define explicit evaluation criteria intended to ensure that the prescribed dose is delivered in a safe, consistent and accurate manner. The radiation oncology physicist(s) shall provide the Medical Director with regular (at least annual) written reports of these activities.

        Quality management of radiation therapy equipment is primarily an ongoing evaluation of functional performance characteristics. Accordingly, the radiation oncology physicist shall develop, implement, supervise, and periodically review all QMP policies and procedures that pertain to radiation therapy equipment. The radiation oncology physicist is responsible for the design, implementation and periodic review of all aspects of the QMP that involve the use of radiotherapy equipment.

      7. Documentation

        The radiation oncology physicist(s) shall produce and maintain documentation of the following:


        1. Calibration and periodic testing of the local standard system(s);

        2. Periodic intercomparisons (and other checks) of other dose measuring equipment;

        3. Performance characteristics of all radiation treatment units and simulator(s) in comparison with previous measurements and with the manufacturer's specifications;

        4. Calibration(s) of all available radiation beams;

        5. Parameterization of the characteristics of each available radiation beam with identification of any and all changes from previous characteristics;

        6. Periodic testing of MU and/or time calculation system(s);

        7. Input data for the radiation treatment planning system(s);

        8. Initial and all subsequent tests of the treatment planning computer system(s);

        9. Technical standards applicable to new procedures and the results obtained in ensuring that any new procedure meets these standards;

        10. Activities of the facility/practice safety program(s);

        11. Periodic reports to the Medical Director of radiation oncology and to the practice/facility administration describing the performance of the radiation therapy simulator(s), treatment unit(s), dosimetry system(s) and applications thereof;

        12. All reports which pertain to the safe and accurate operation of the radiation therapy simulator(s), treatment unit(s), dosimetry system(s) and applications thereof.


      8. Conference Participation

        The radiation oncology physicist(s) shall participate in chart rounds and should participate in other conferences, such as new patient or treatment planning conferences.

      9. Professional Development

        A Qualified Medical Physicist should be in compliance with published standards for continuing professional education for medical physicists. Each radiation oncology physicist is expected to remain current with respect to technical developments, standards of practice, professional issues, and changes in regulatory requirements.


  3. QUALITY MANAGEMENT

    Quality management (QM) in radiation oncology physics encompasses those procedures that ensure a consistent, accurate and safe fulfillment of the dose prescription. Each individual radiation therapy facility is responsible for its own quality management program (QMP) for radiation oncology. Radiation oncology physicist(s) must be included in this program.

    The goal of the QMP for external beam radiation therapy equipment is to ensure that the performance characteristics, as defined by physical parameters established during commissioning of the equipment, remain within acceptable limits. Procedures shall be established to verify that the performance of the equipment meets the manufacturer's specifications and to establish baseline performance values for new or refurbished equipment, or for any equipment following major repair. Once a baseline standard has been established, a protocol for periodic QM tests shall be developed for the purpose of monitoring performance. The protocol for QM testing should recommend the testing equipment to be used, the frequency of measurements, the techniques to be followed, suggested performance criteria, action levels, and routes of notification. QM test procedures should be able to measure parameter changes smaller than tolerance or action levels.

    A review should be performed annually to evaluate the effectiveness of the QMP. A written report of said review should be prepared for the Medical Director and administration.


    1. Measurement Equipment

      A program must be in place to ensure accuracy and precision of all measurement equipment used for calibration and constancy checks of treatment machines as well as all instruments used for patient dosimetry. The program must document procedures for instrument calibration to ensure traceability to accredited calibration facilities and to affirm instrument precision and accuracy.

      Redundancy in dose calibration equipment is recommended to ensure consistency and constancy of instrument calibration.

    2. Calibration of Treatment Machines and Independent Verification of Output.

      Protocols for the calibration of treatment machines shall follow procedures currently published by the AAPM.

      An independent check of the machine output for each radiation beam shall be performed annually to verify that the treatment unit calibration is consistent with national standards. The independent check should be performed by either:


      1. A qualified radiation oncology physicist who did not perform the annual output calibration, using a dosimetry system other than the one that was used during the annual calibration,

      2. Using an independent TLD system designed to measure radiation doses with accuracy of five percent (5%) or better.


    3. Simulators, Imaging Equipment, and treatment Devices

      Simulators, CT scanners and MR scanners used for planning radiation treatment should be encompassed by the QMP. Other treatment aids (e.g., block cutting devices, block mounting procedures, attachment holders, etc.) should also be included as part of the QMP.

    4. Treatment Planning Computer Systems

      Treatment planning computer systems must undergo rigorous acceptance tests and commissioning to ensure that the calculated output satisfactorily agrees with measured beam data for a series of test cases and to ensure that the hardware and software was installed properly. All users must receive proper training. A documented in-service program should be provided for new users when appropriate and for all users following major software modifications.

      Periodic tests of the treatment planning computer system(s)must be implemented in order to:


      1. Ensure accuracy of dose calculation algorithms;

      2. Ensure that any software modifications (including editing of beam data files) were correctly implemented and that beam data were not thereby corrupted;

      3. Ensure that any hardware changes were properly installed;

      4. Verify that all users have received proper training and are proficient in the use of the system(s).


  4. SAFETY

    The radiation oncology physicist(s) shall develop and maintain a program to ensure that patients are treated in a safe environment and that staff work in a safe environment. Such a program should contain elements that address electrical, mechanical and irradiation issues. In areas outside the training and/or expertise of the radiation oncology physicist(s), he/she shall seek expert help from sources such as the appropriate safety officer, the appropriate engineer, and/or various vendor service engineers.


    1. Electrical & Mechanical Safety

      A program for assessing potential safety hazards and for checking the integrity of mechanical and electrical patient care devices shall be implemented and documented. Periodic inspections of patient dose monitoring devices, treatment machines, simulators, and all attachments to these machines (e.g., portal imaging devices, head holders, bite blocks, compensators, multileaf collimators, wedges, etc.) should be performed.

    2. Radiation Safety

      Each individual radiation therapy practice/facility is responsible for ensuring the existence of a radiation safety program. Said program shall include all radiation therapy simulators as well as all radiation treatment units. The radiation oncology physicist(s) shall, as a minimum, be responsible for ensuring that the simulator(s) and radiation treatment units are operated in a manner consistent with the radiation safety program, with federal and/or state regulations, and with the As Low As Reasonably Achievable (ALARA) concept.


  5. NEW PROCEDURES

    The practice of radiation oncology often involves the implementation of new procedures and technologies, so the radiation oncology physicist must, in conjunction with the Medical Director, define basic standards of practice and develop a reasonably prudent course of action to determine the quality and safety of any new procedures prior to implementation thereof. In those cases where the radiation oncology physicist requires assistance, consultation with experienced colleagues is encouraged. When newly published techniques or procedures are being implemented for the first time within the practice/facility, the radiation oncology physicist should undertake a systematic literature review, make appropriate site visits, observe procedures, and participate under the supervision of colleagues who are familiar with the procedure. The QMP associated with any new procedure should be periodically reviewed and updated.

 
 
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