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Stereotactic radiosurgery (SRS) has proven itself as an effective tool in the treatment of intracranial lesions. Image-guided high dose single fraction treatments have the potential to deliver ablative doses to tumours; however, treatment times can be long. Flattening filter free (FFF) beams are available on most modern linacs and offer a higher dose rate compared to conventional flattened beams which should reduce treatment times. This study aimed to compare 6 MV FFF and 10 MV FFF to a 6 MV flattened beam for single fraction dynamic conformal arc SRS for a Varian Truebeam linac.
Materials and methods:
In total, 21 individual clinical treatment plans for 21 brain metastases treated with 6 MV were retrospectively replanned using both 6 MV FFF and 10 MV FFF. Plan quality and efficiency metrics were evaluated by analysing dose coverage, dose conformity, dose gradients, dose to normal brain, beam-on-time (BOT), treatment time and monitor units.
FFF resulted in a significant reduction in median BOT for both 6 MV FFF (57·9%; p < 0·001) and 10 MV FFF (76·3%; p < 0·001) which led to reductions in treatment times of 16·8 and 21·5% respectively. However, 6 MV FFF showed superior normal brain dose sparing (p < 0·001) and dose gradient (p < 0·001) compared to 10 MV FFF. No differences were observed for conformity.
6 MV FFF offers a significant reduction in average treatment time compared to 6 MV (3·7 minutes; p = 0·002) while maintaining plan quality.
It is largely through the work of David Lewis-Williams that San rock art has come to be understood so well, as a complex symbolic and metaphoric representation of San religious beliefs and practices. The purpose of this volume is to demonstrate the depth and wide geographical impact of Lewis-Williams’ contribution, with particular emphasis on the use of theory and methodology drawn from ethnography that he has used with inspirational effect in understanding the meaning and context of rock art in various parts of the world. Seeing and Knowing explores how to understand and learn from rock art with and without ethnography. Because many of the chapters are based on solid fieldwork and ethnographic research, they offer a new body of work that provides the evidence for differentiation between knowing and simply seeing. This volume is unique in that it focuses exclusively on rock art and ethnography, and covers such a wide geographic range of examples on this topic, from southern Africa, to Scandinavia, to the United States. Many of the chapters explore studies in rock art regions of the world where variation and constancy can be observed and explored across distances both in space and in time. The editors have entitled the book Seeing and Knowing to echo Lewis-Williams’ Believing and Seeing published almost thirty years ago; they say ‘seeing’ again because looking at rock art is and will always be central, and then what is seen when human eyes and minds look; they say ‘knowing’ in recognition that, by his work and by his example, archaeologists now know a little more than they knew before. Even so, as Lewis-Williams will be the first to say, we still know only a fraction.