AAPM MEDICAL PHYSICS PRACTICE GUIDELINE 5.b: Commissioning and QA of treatment planning dose calculations—Megavoltage photon and electron beams

Abstract

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines:• Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. While must is the term to be used in the guidelines, if an entity that adopts the guideline has shall as the preferred term, the AAPM considers that must and shall have the same meaning. • Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

AAPM Medical Physics Practice Guideline 8.b: Linear accelerator performance tests

“…Given that clinical treatment decisions are primarily based on dose calculations done in a TPS, it is best to compare ongoing linac dosimetric performance to the site's well-commissioned clinical TPS models or TPS calculations following the principles established in MPPG 5. 27 This ensures that the link between what the physician approves in the TPS and what the linac actually delivers is validated. Therefore, monitoring any dosimetric deviation of the linac from the same beams calculated in the TPS is of primary interest.…”

“…For field sizes below 3 × 3 cm, see MPPG 9, IAEA Report 483, and TG-155. 40,51,52 Note: The committee recognizes that the threshold for modeling error established by MPPG 5 27 is 2% for off axis factors. Since the goal is to ensure the linac is producing the same beam that is calculated in the TPS, it is appropriate to retain the same 2% threshold.…”

“…Monthly, jaw positions must be tested against the readout for at least two settings across the clinical range of motion, including the smallest field used clinically (including the smallest allowed field size used in jaw tracking), which is the smallest field that has been calculated in the TPS and verified as accurate according to the methodology outlined in MPPG 5. 27 This check should be performed using the actual radiation field, such as irradiating film, an EPID, or other device, but can be a visual check with the light field as long as the light field and radiation field have been recently verified as congruent (test M5). Each individual jaw size must be accurate within 2 mm or a cumulative deviation of all jaws that would create a 2% change in field size dependent output factors, whichever is smaller.…”

“…This test should be similar to the E2E test from MPPG 5,Table 8. 27 Any deviation of 3% or more must be investigated to determine if improvements can be made that would allow better agreement. More rigorous testing as described above should be pursued, if feasible.…”

Effects of surface curvature on electron Monte Carlo (eMC) calculation results

“…Many resources recommend that electron beam dosimetry be performed in water or solid‐water phantoms, which have a flat surface 1–6 . However, many clinical fields used in electron radiotherapy are directed onto surfaces that exhibit curvature in two or three dimensions.…”