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The thermal cycloaromatization reactions of hex-3-ene-l,5diynes to form 1,4-didehydrobenzene intermediates were first studied in our laboratories several years ago.1"4 5678Such intermediates are now thought to play a critical role in the DNA-cleaving activity of an emerging class of powerful antitumor antibiotics. The isolation of natural products such as the esperamicins, calicheamicins, and dynemicins has stimulated numerous synthetic, mechanistic, and biological activity studies.5,6 The renaissance of research in this area has prompted us to return to the chemistry of a variety of substituted enediyne systems in the hope of discovering new types of dehydroaromatic biradical intermediates. Our first goal was the synthesis and thermal reactions of the extended enediyne system (Z,Z)-deca-3,7-diene-l,5,9-triyne (1). We present experimental evidence that heating 1 leads to 2,6didehydronaphthalene.7,8The stereospecific synthesis of the requisite dienetriynes utilized standard nickel-9 and palladium-catalyzed10,11 coupling metho-(1)

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 (MPPG) 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 radiation requires specific training, skills, and techniques as described in each document. As the review of the previous version of AAPM Professional Policy (PP)‐17 (Scope of Practice) progressed, the writing group focused on one of the main goals: to have this document accepted by regulatory and accrediting bodies. After much discussion, it was decided that this goal would be better served through a MPPG. To further advance this goal, the text was updated to reflect the rationale and processes by which the activities in the scope of practice were identified and categorized. Lastly, the AAPM Professional Council believes that this document has benefitted from public comment which is part of the MPPG process but not the AAPM Professional Policy approval process. The following terms are used in the AAPM's MPPGs: Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline.Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Proper patient positioning plays a large role in the function of TCM, and hence CTDI and SSDE. In addition, body mass distribution may affect how patients ought to be positioned within the scanner. Understanding these effects is critical in optimizing CT scanning practices.

AAPM Report 270 provides an update to the recommendations of the AAPM's "TG18" report. Report 270 provides new definitions of display types, updated testing patterns, and revised performance standards for the modern, flat-panel displays used as part of medical image acquisition and review. The focus of the AAPM report is on consistent image quality and appearance, and how to establish a quality assurance program to achieve those two goals. This work highlights some of the key takeaways of AAPM Report 270 and makes comparisons with existing recommendations from other references. It also provides guidance for establishing a display quality assurance program for different-sized institutions. Finally, it describes future challenges for display quality assurance and what work remains.