Steven J. Goetsch

Calibration of 192Ir high-dose-rate afterloading systems

A method is described for calibration of 192Ir high-dose-rate (HDR) brachytherapy afterloading systems. Since NIST does not offer calibration of ionization chambers with the gamma-ray spectrum of iridium-192, an interpolation procedure is employed, using calibrations above (137Cs, 662 keV) and below (250 kVcp, 146-keV x rays) the exposure-weighted average 192Ir energy of 397 keV. The same total wall + cap thickness must be used for both calibrations, and for the 192Ir measurements. A wall + cap thickness of 0.3 g/cm2 is recommended to assure charged particle equilibrium and to exclude secondary electrons emitted from the source encapsulation. Procedures are described for determining the corrections for source-chamber distance and room scatter during the source calibration in inverse-square-law geometry. A new well-type ionization chamber has been designed specifically for convenient routine use with the HDR afterloading system. It can be calibrated by means of a previously calibrated 192Ir source, and offers a simple means for verifying the decay rate and for calibrating 192Ir replacement sources.

Anniversary Paper: The role of medical physicists in developing stereotactic radiosurgery

This article is a tribute to the pioneering medical physicists over the last 50years 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.

SURFACE DOSE RATE CALIBRATION OF SR-90 PLANE OPHTHALMIC APPLICATORS

Calibration of an imported strontium-90 ophthalmic applicator at the U.S. National Bureau of Standards (now the National Institute of Standards and Technology) has disclose a significant discrepancy in dose rate calibration (32%-35%) with that quoted by the manufacturer. The University of Wisconsin has investigated this discrepancy and found that both laboratories use similar techniques and a version of the Bragg-Gray equation to yield dose rate estimates. Experimental results indicate a strong relationship between the size of the collecting electrode used in the extrapolation chamber and the resulting estimate of absorbed dose rate. Calibration of these applicators is reviewed and suggestions for improvement and further research are proposed.

The role of medical physicists in developing stereotactic radiosurgery

This article is a tribute to the pioneering medical physicists over the last 50years 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.

Stereotactic radiosurgery and stereotactic body radiation therapy

Early History of stereotactic Radiation Therapy Historic Development of Stereotactic Radiosurgery and Stereotactic Body Radiation Therapy, Steven J. Goetsch Stereotactic Radiation Therapy Delivery Systems Gamma Knife, Steven J. Goetsch Conventional Medical Linear Accelerators Adapted for Stereotactic Radiation Therapy, William H. Hinson and Timothy D. Solberg Dedicated Linear Accelerators for Stereotactic Radiation Therapy, Malika Ouzidane, Joshua Evans, and Toufik Djemil Light Ion Beam Programs for Stereotactic Radiosurgery and Stereotactic Radiation Therapy, Michael F. Moyers, Marc R. Bussiere, and Richard P. Levy Small Animal Irradiators for Stereotactic Radiation Therapy, Ke Sheng, Patricia Lindsay, and John Wong Stereotactic Radiation Therapy, Precision Patient Positioning, and Immobilization Developing Stereotactic Frames for Cranial Treatment, Habeeb Saleh and Bassel Kassas Frames for Extracranial Treatment, D. Michael Lovelock Motion Management, Krishni Wijesooriya, Rohini George, and Mihaela Rosu Image-Guided Radiation Therapy and Frameless Stereotactic Radiation Therapy, Ryan McMahon and Fang-Fang Yin Stereotactic Radiation Therapy Treatment Planning and Dosimetry Stereotactic Treatment Planning, Bill J. Salter, Brian Wang, and Vikren Sarkar Small-Field Dosimetry for Stereotactic Radiosurgery and Radiotherapy, Kamil M. Yenice, Yevgeniy Vinogradskiy, Moyed Miften, Sonja Dieterich, and Indra J. Das New directions in stereotactic radiation therapy Radiation Biology of Stereotactic Radiotherapy, Igor Barani, Zachary Seymour, Ruben Fragoso, and Andrew Vaughan Clinical Outcomes Using Stereotactic Body Radiation Therapy and Stereotactic Radiosurgery, Megan E. Daly, Anthony L. Michaud, and Kyle E. Rusthoven The Future of Stereotactic Radiosurgery, Joshua Evans, Cedric Yu, Michael Wright, Edwin Crandley, and David Wilson Index

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

This article is a tribute to the pioneering medical physicists over the last 50years 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.

Calibration and use of the Wisconsin kVp Test Cassette

The Ardran-Crooks kVp test cassette is widely used in diagnostic radiology to provide a rapid, simple, noninvasive measurement of x-ray tube potential. A modified version of this cassette called the Wisconsin kVp Test Cassette was introduced commercially in the U. S. in 1972. Since then, the method of calibration of these cassettes has changed significantly. Wisconsin kVp Test Cassettes calibrated by the manufacturer prior to August 1982 may yield underestimates of kVp measurements, particularly when using the 90-110 and 110-130 kVp regions with single-phase units. In August 1982 significant improvements in the calibration methods were implemented. The resultant change in calibration is demonstrated by data from the Centers for Radiological Physics. Present calibration methods are believed to be accurate within the greater of +/- 2 kVp or 2% of actual peak tube potential. Proper use of the cassette is necessary to achieve this level of accuracy.