For commissioning a linear accelerator for clinical use, medical physicists are faced with many challenges including the need for precision, a variety of testing methods, data validation, the lack of standards, and time constraints. Since commissioning beam data are treated as a reference and ultimately used by treatment planning systems, it is vitally important that the collected data are of the highest quality to avoid dosimetric and patient treatment errors that may subsequently lead to a poor radiation outcome. Beam data commissioning should be performed with appropriate knowledge and proper tools and should be independent of the person collecting the data. To achieve this goal, Task Group 106 (TG‐106) of the Therapy Physics Committee of the American Association of Physicists in Medicine was formed to review the practical aspects as well as the physics of linear accelerator commissioning. The report provides guidelines and recommendations on the proper selection of phantoms and detectors, setting up of a phantom for data acquisition (both scanning and no‐scanning data), procedures for acquiring specific photon and electron beam parameters and methods to reduce measurement errors , beam data processing and detector size convolution for accurate profiles. The TG‐106 also provides a brief discussion on the emerging trend in Monte Carlo simulation techniques in photon and electron beam commissioning. The procedures described in this report should assist a qualified medical physicist in either measuring a complete set of beam data, or in verifying a subset of data before initial use or for periodic quality assurance measurements. By combining practical experience with theoretical discussion, this document sets a new standard for beam data commissioning.

We report measurements of the attenuation of longitudinal-acoustic phonons in amorphous ${\mathrm{SiO}}_2$ for frequencies between 76 and 440 GHz, and in the temperature range 80–300 K. The samples are chemical-vapor-deposited films grown on tungsten substrates, and the phonons are generated and detected using picosecond optical techniques. The phonon attenuation is found to depend only weakly on temperature. In the upper part of the frequency range, there is some evidence that the frequency dependence is faster than quadratic, thus indicating that the attenuation cannot be explained by classical relaxation theory. A discussion of the relation between these results and the analysis of thermal-conductivity measurements is given.