Peter Wootton, medical physicist and professor emeritus of radiation oncology at the University of Washington, Seattle (UW), died at his home in Bellevue, Washington, on 3 May 2004 after a 3½-year battle with pancreatic cancer.
Peter was born on 30 April 1924 in Peterborough, England. He attended Birmingham University, where he received a BSc in physics with honors in 1944. After serving in His Majesty’s Antisubmarine Establishment, he took a position as a radiation physicist at the Royal Infirmary in Glasgow, Scotland. In 1951, he came to the US as an instructor in medical physics at the University of Texas M.D. Anderson Cancer Center, where he worked with Robert Shalek and Gilbert Fletcher on the calculation of radiation dose from radium and cobalt-60 in water and tissue.
When Peter left M.D. Anderson in 1953 to take a position at Swedish Hospital’s Tumor Institute (now the Swedish Cancer Institute) in Seattle, he was the only full-time medical physicist in the Northwest. At that time, radiation therapy and medical physics were considered part of radiology. The Tumor Institute, a separate facility devoted to radiation oncology, was a rare exception, perhaps unique in the US.
In 1964, Peter joined the faculty of UW’s radiology department, which followed the more common model of combining radiation therapy and medical physics with diagnostic radiology. He served as head of the department’s medical physics division. In 1978, that division was incorporated into a new radiation oncology department, and Peter continued as division head until his retirement in 1995.
Peter was deeply committed to the service of cancer treatment. In 1966, he started a medical physics service, known as the Regional Medical Physics program, at UW. The service evolved into a freestanding institution, now called the Northwest Medical Physics Center, which still provides medical physics services to radiation therapy facilities throughout the Northwest.
Peter worked closely with radiation oncologist Robert Parker while at Swedish Hospital, and later at UW, where Parker became chairman of the new radiation oncology department, in the investigation of high-pressure oxygen as an enhancement to radiation therapy. The procedure is based on the so-called oxygen effect, in which the response of some kinds of tumors to radiation increases with increased oxygenation of the tissues. Conversely, tumors poorly infused with oxygen are more resistant to radiation. The oxygen enhancement ratio (OER) is the ratio of radiation dose required for a given endpoint under oxygen-deficient conditions to that required for the same endpoint under oxygen-rich conditions. The OER for a typical high-energy photon therapy beam is 2.5–3.0, which makes oxygen one of the most powerful radiation sensitizers known. Despite heroic efforts, it was not possible in a clinical setting to increase the perfusion of tumors sufficiently to take advantage of this effect.
The oxygen effect is somewhat less pronounced for fast neutrons than for photons (the OER for neutrons is only about 1.5–1.8), so the use of fast neutrons for cancer treatment has been explored for many decades. Because normal tissue is already typically much better perfused with oxygen than tumor, the lower OER for neutrons gives an enhancement of tumoricidal effect relative to normal tissue, and not just a scaling of the required dose. In 1971, clinical trials of neutron radiotherapy, using the NPL cyclotron, began at UW’s Nuclear Physics Laboratory. Peter directed the medical physics component of that project.
When the National Cancer Institute decided to expand its facilities for investigation of particle-beam radiotherapy, Peter worked with George Laramore, then an assistant professor at UW, on a proposal for a dedicated cyclotron-based neutron therapy facility at UW. Peter directed the construction phase, and his visionary approach resulted in a unique structure representing a significant step forward in radiotherapy facility design. Peter insisted on the importance of a multileaf collimator for neutron therapy, even though it was well beyond the state of the art even for x-ray therapy.
His judgment was borne out later in clinical trials. The UW facility saw significantly less adverse normal tissue response than the other neutron therapy facilities without multileaf collimators, even though the dosimetric characteristics of the various neutron beams appeared to be very close. Today, 20 years after it first began operating, the UW clinical neutron therapy facility continues to be the state of the art in neutron therapy and serves a worldwide patient base.
Peter pursued clinical aspects of fast neutron therapy with an interest in the possible application of boron neutron capture therapy. He advocated the use of sodium activation as an assessment of potential boron capture dose enhancement, and worked with Ruedi Risler—whom he hired as technical director of the clinical neutron therapy facility—on the measurements. That therapy is still limited by the unavailability of drugs that would deliver sufficient boron to tumor sites.
As a teacher, Peter was superb. He supervised many master’s students, several PhD students, and a series of postdoctoral trainees. He served as a mentor to numerous others who have benefited greatly from his personal and professional qualities.
When the American Association of Physicists in Medicine was incorporated in 1965, Peter was a member of the initial board of directors and a signatory of the organization’s articles of incorporation. He served a yearlong term as AAPM president in 1978.
For as long as he was able, following his retirement, Peter participated in weekly physics conferences at the UW radiation oncology department. His experience, wisdom, and insight were invaluable and are greatly missed.
