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      The role of medical physicists in developing stereotactic radiosurgery : Role of medical physicists in SRS

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          Abstract

          This article is a tribute to the pioneering medical physicists over the last 50 years who have participated in the research, development, and commercialization of stereotactic radiosurgery (SRS) and stereotactic radiotherapy utilizing a wide range of technology. The authors have described the evolution of SRS through the eyes of physicists from its beginnings with the Gamma Knife in 1951 to proton and charged particle therapy; modification of commercial linacs to accommodate high precision SRS setups; the multitude of accessories that have enabled fine tuning patients for relocalization, immobilization, and repositioning with submillimeter accuracy; and finally the emerging technology of SBRT. A major theme of the article is the expanding role of the medical physicist from that of advisor to the neurosurgeon to the current role as a primary driver of new technology that has already led to an adaptation of cranial SRS to other sites in the body, including, spine, liver, and lung. SRS continues to be at the forefront of the impetus to provide technological precision for radiation therapy and has demonstrated a host of downstream benefits in improving delivery strategies for conventional therapy as well. While this is not intended to be a comprehensive history, and the authors could not delineate every contribution by all of those working in the pursuit of SRS development, including physicians, engineers, radiobiologists, and the rest of the therapy and dosimetry staff in this important and dynamic radiation therapy modality, it is clear that physicists have had a substantial role in the development of SRS and theyincreasingly play a leading role in furthering SRS technology.

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          Most cited references137

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          Radiological use of fast protons.

          R R Wilson (1946)
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            Stereotactic hypofractionated high-dose irradiation for stage I nonsmall cell lung carcinoma: clinical outcomes in 245 subjects in a Japanese multiinstitutional study.

            Stereotactic irradiation (STI) has been actively performed using various methods to achieve better local control of Stage I nonsmall cell lung carcinoma (NSCLC) in Japan. The authors retrospectively evaluated results from a Japanese multiinstitutional study. Patients with Stage I NSCLC (n = 245; median age, 76 years; T1N0M0, n = 155; T2N0M0, n = 90) were treated with hypofractionated high-dose STI in 13 institutions. Stereotactic three-dimensional treatment was performed using noncoplanar dynamic arcs or multiple static ports. A total dose of 18-75 gray (Gy) at the isocenter was administered in 1-22 fractions. The median calculated biologic effective dose (BED) was 108 Gy (range, 57-180 Gy). During follow-up (median, 24 months; range, 7-78 months), pulmonary complications of National Cancer Institute-Common Toxicity Criteria Grade > 2 were observed in only 6 patients (2.4%). Local progression occurred in 33 patients (14.5%), and the local recurrence rate was 8.1% for BED > or = 100 Gy compared with 26.4% for or = 100 Gy compared with 69.4% for or = 100 Gy compared with or = 100 Gy) were excellent, and were potentially comparable to those of surgery. (c) 2004 American Cancer Society.
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              Cone-beam computed tomography with a flat-panel imager: magnitude and effects of x-ray scatter.

              A system for cone-beam computed tomography (CBCT) based on a flat-panel imager (FPI) is used to examine the magnitude and effects of x-ray scatter in FPI-CBCT volume reconstructions. The system is being developed for application in image-guided therapies and has previously demonstrated spatial resolution and soft-tissue visibility comparable or superior to a conventional CT scanner under conditions of low x-ray scatter. For larger objects consistent with imaging of human anatomy (e.g., the pelvis) and for increased cone angle (i.e., larger volumetric reconstructions), however, the effects of x-ray scatter become significant. The magnitude of x-ray scatter with which the FPI-CBCT system must contend is quantified in terms of the scatter-to-primary energy fluence ratio (SPR) and scatter intensity profiles in the detector plane, each measured as a function of object size and cone angle. For large objects and cone angles (e.g., a pelvis imaged with a cone angle of 6 degrees), SPR in excess of 100% is observed. Associated with such levels of x-ray scatter are cup and streak artifacts as well as reduced accuracy in reconstruction values, quantified herein across a range of SPR consistent with the clinical setting. The effect of x-ray scatter on the contrast, noise, and contrast-to-noise ratio (CNR) in FPI-CBCT reconstructions was measured as a function of SPR and compared to predictions of a simple analytical model. The results quantify the degree to which elevated SPR degrades the CNR. For example, FPI-CBCT images of a breast-equivalent insert in water were degraded in CNR by nearly a factor of 2 for SPR ranging from approximately 2% to 120%. The analytical model for CNR provides a quantitative understanding of the relationship between CNR, dose, and spatial resolution and allows knowledgeable selection of the acquisition and reconstruction parameters that, for a given SPR, are required to restore the CNR to values achieved under conditions of low x-ray scatter. For example, for SPR = 100%, the CNR in FPI-CBCT images can be fully restored by: (1) increasing the dose by a factor of 4 (at full spatial resolution); (2) increasing dose and slice thickness by a factor of 2; or (3) increasing slice thickness by a factor of 4 (with no increase in dose). Other reconstruction parameters, such as transaxial resolution length and reconstruction filter, can be similarly adjusted to achieve CNR equal to that obtained in the scatter-free case.
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                Author and article information

                Journal
                Medical Physics
                Med. Phys.
                Wiley
                00942405
                September 2008
                August 26 2008
                August 26 2008
                : 35
                : 9
                : 4262-4277
                Article
                10.1118/1.2969268
                18841876
                dea0d930-6a94-4dc8-95f8-6fb24e38e191
                © 2008

                http://doi.wiley.com/10.1002/tdm_license_1

                http://creativecommons.org/licenses/by/3.0/

                http://doi.wiley.com/10.1002/tdm_license_1.1

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