The requirement of an independent verification of the monitor units (MU) or time calculated to deliver the prescribed dose to a patient has been a mainstay of radiationoncology quality assurance. The need for and value of such a verification was obvious when calculations were performed by hand using look-up tables, and the verification was achieved by a second person independently repeating the calculation. However, in a modern clinic using CT/MR/PET simulation, computerized 3D treatment planning, heterogeneity corrections, and complex calculation algorithms such as convolution/superposition and Monte Carlo, the purpose of and methodology for the MU verification have come into question. In addition, since the verification is often performed using a simpler geometrical model and calculation algorithm than the primary calculation, exact or almost exact agreement between the two can no longer be expected. Guidelines are needed to help the physicist set clinically reasonable action levels for agreement. This report addresses the following charges of the task group: (1) To re-evaluate the purpose and methods of the “independent second check” for monitor unit calculations for non-IMRT radiation treatment in light of the complexities of modern-day treatment planning. (2) To present recommendations on how to perform verification of monitor unit calculations in a modern clinic. (3) To provide recommendations on establishing action levels for agreement between primary calculations and verification, and to provide guidance in addressing discrepancies outside the action levels. These recommendations are to be used as guidelines only and shall not be interpreted as requirements.
II. OBJECTIVE OF THE VERIFICATION CALCULATION
II.A. Types of error
II.B. Potential errors
III. LIMITATIONS OF THE VERIFICATION CALCULATION
IV. ASPECTS OF A MU VERIFICATION PROGRAM
IV.A. MU verification and patient plan quality assurance
IV.B. Commissioning of a verification system
IV.C. Independence of verification calculation
IV.D. Potential advantages of a measurement-based verification algorithm
V. RECOMMENDED METHODS OF MU VERIFICATION
V.A. Comparison point selection
V.B. Differences in primary verification and calculation methods
V.C. Manual verification methods
V.D. Computer-based MU verification programs
V.E. Verification TPS
V.F. Verification by measurement
V.G. Stereotactic therapy
VI. ACTION LEVELS AND REMEDIAL ACTIONS
VI.A. Action levels for MU disagreement
VI.B. Remediation of MU discrepancies
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