C. Clifton Ling

By Kenneth Cashon, MS, Timothy Showalter, MD, MPH and Theodore Phillips, MD, FASTRO

On June 1, 2017, Kenneth Cashon, MS, Timothy Showalter, MD, MPH, and Theodore Phillips, MD, FASTRO, interviewed C. Clifton Ling, PhD. Dr. Ling is regarded as an important contributor to medical physics and radiation oncology. He received the ASTRO Gold medal in 2006 and the AAPM Coolidge Gold Medal Award in 2004.

Kenneth Cashon: Dr. Ling, I appreciate you coming and being a part of this.

C. Clifton Ling: Please call me Clif.

Kenneth Cashon: All right, Clif. Dr. Showalter and I are on the ASTRO History Committee, and we’re very excited about doing this interview for the committee. So it’s an honor. We’re really glad that we could interview you today and to learn more about you. For me, I’ve read your papers and I know you. I’ve met you a couple of times but haven’t worked with you, so this is pretty exciting for us. I appreciate it.

C. Clifton Ling: It’s an honor for me as well.

Kenneth Cashon: First of all, let’s get to know you a little bit - where you’re from, where you were born, when you came to America. Things like that.

C. Clifton Ling: I was born during the Second World War. As the Chinese people were pushed westward, I was born in Guilin in the southwestern part of China, which is a very scenic spot that many tourists go to to-day. Then we moved to Chongqing which was the wartime capital of China, and stayed there until the end of the war. Then my folks moved to Shanghai.

But then the Civil War broke out, and so we left Shanghai for Hong Kong, and that’s where I grew up. We were basically refugees among many others who escaped to Hong Kong with living conditions which were pretty meager. I went to grade school there, and then to a Catholic-run secondary school called La Salle, taught by the La Salle Brothers. After that I immigrated to the United States for my college education.

Theodore Phillips: What did your parents do Clif?

C. Clifton Ling: My father was trained as a lawyer. He actually went to the first law school in the new Republic of China. Subsequently he joined the diplomatic corps of the Chinese government. But when we were in Hong Kong he was just trying to make a living by brokering deals in import/export commerce. My mother was a housewife. So I grew up in an environment that was non-academic.

Kenneth Cashon: Were you interested in physics, or science, or math as a child? Is that something you’ve always been interested in?

C. Clifton Ling: I was not particularly interested in science or arts. La Salle basically provides a balanced curriculum: English and Chinese literature, mathematics, history, geography and basic sciences. So it was a comprehensive secondary education, but one does not choose which subjects to study. I was fairly good in all the subjects and I wasn’t sure what I was going to do. After high school, some of my friends had come to the United States. It was a trendy thing and so I followed. It should be interesting to note that I was going to Arkansas A&M in 1962. But when I got to San Francisco a friend said “you don’t want to go to Arkansas, they discriminate against colored people.” I don’t know whether it’s true, but I didn’t go and stayed in San Francisco instead. I went to the University of San Francisco, in their evening school. During the day I worked to earn money to pay for my expenses.

Kenneth Cashon: You might have met Bill Clinton if you went to Arkansas.

C. Clifton Ling: I was supposed to go to Arkansas A&M which is in College Station.

Kenneth Cashon: So you went to the University of San Francisco. Did you immediately start to study in their undergraduate physics program?

C. Clifton Ling: Well, I did not choose a major as a freshman. In fact, I didn’t know what I was going to major in, and how I got into physics is an interesting anecdote. Some friends and I were just sort of talking about what major one should study, and I asked what they thought was the most difficult subject? They said physics. So I decided to study physics, sort of as a dare.   

Kenneth Cashon: So purely out of the challenge of it, it sounds like.

C. Clifton Ling: Right. After one semester in USF I went to Oregon State and majored in physics. Then it was trendy to go to graduate school after college, so I applied to various universities and did my graduate studies at the University of Washington, Seattle.

Kenneth Cashon: And did you have any background on medical physics in your training there or none?

C. Clifton Ling: None. At the University of Washington I initially wanted to study theoretical physics because of the two Nobel Prize laureates TD Lee and CN Yang, who proved that parity is not conserved, are of Chinese decent. But after the first semester, I immediately discovered I was too dumb to be a theorist. So I picked up screwdrivers and Allen wrenches and eventually received my PhD in nuclear physics. 

Kenneth Cashon: So you went on and started working at Memorial Sloan as a fellow. Is that where you started picking up medical physics training?

C. Clifton Ling: When I graduated from the University of Washington, there were very few good jobs for nuclear physicists. Through the ad pages in Physics Today I learned that Chuck Kelsey of University of Wisconsin was recruiting medical physics postdocs, and Edward Epp of Memorial Sloan-Kettering was recruiting physicists to work in his lab. I received offers from both institutions. I eventually came to Memorial because they offered $8,000 instead of $6,000 offered by the University of Wisconsin.

Kenneth Cashon: Smart.

C. Clifton Ling: Except that I didn’t know New York City is so expensive. So I don’t know whether it was a good decision or not. I ended up at Memorial Sloan-Kettering, but not in medical physics. It was actually in the Laboratory of Physical Biology, with Ed Epp as the chief. Ted, you probably know Ed Epp.

Theodore Phillips: I know Ed very well. He was doing high dose rate research, which I was doing at that time.

C. Clifton Ling: I got involved in high dose rate radio-biophysics research, specifically depleting oxygen with high dose radiation and tried to avoid the hypoxic effect. I think that’s what you were doing as well, right, Ted?

Theodore Phillips: We were doing those kinds of experiments with a LINAC down in Santa Barbara.

C. Clifton Ling: Yes, and there was a guy by the name of Ralph Worsnop. Is that right?

Theodore Phillips: Yes. Ralph worked with us in those experiments. Right. He is a physicist.

C. Clifton Ling: So working at Epp’s lab I was basically forced to learn radiation biology, working with bacteria, bacteriophage, and mammalian cells to understand the effect of radiation on biological systems. 

As to how I got into medical physics, that’s also serendipity. During my time in his lab, Ed Epp was being recruited to head up medical physics in Mass General. So when Ed asked if I wanted to come along, I said I’ve never heard of medical physics - what is that? He assured me that I will learn, so I went to Mass General. Some very good physicists were already at Mass General, both in clinical and in research, and they basically taught me.

Theodore Phillips: Who were they, Clift? Who was there?

C. Clifton Ling: It was an interesting group of people. Some of the people you may have heard about. Michael Goitein, to me one of the smartest medical physicists I’ve ever met. There was Arthur Boyer and then there was Lynn Verhey. Ted, you subsequently recruited Lynn to UCSF. Another young faculty was Peter Biggs from MIT. Two very experienced clinical physicists were Karen Doppke and Miriam Gitterman. It was an interesting group.

Kenneth Cashon: That’s kind of a rock star and all-star team right there.  

C. Clifton Ling: So I learned medical physics from scratch while I was in Mass General. After 5 years at MGH, I had gained the fundamentals in it, but I wouldn’t at that point call myself a really seasoned clinical medical physicist. When I decide to depart, I felt that I have to because at MGH there was always some senior person watching over me so I didn’t make any errors. So I left Mass General because I wanted to be more independent, sort of learning through my own mistakes.

Kenneth Cashon: So were you more like a junior physicist?

C. Clifton Ling: At first I was an assistant medical physicist at MGH and an assistant professor at Harvard Medical School. When I left I was an associate medical physicist at MGH and an assistant professor at Harvard.

Theodore Phillips and Kenneth Cashon: Where did you go?

C. Clifton Ling: I went to George Washington University Hospital, working with another physicist and a dosimetrist. Actually that was a very important part of my career development because I really learned clinical physics. For example, I would go to the simulator when the therapists had trouble doing complex set-ups, e.g. matching the supraclav and internal mammary fields for breast treatment. I did minor maintenance and repair on the LINACs because there were no engineers. Only for major troubles, I would call the engineering group which supported the clinic.

It was a very small clinic and I attended chart rounds every week. So I really was learning the ins and out of clinical medical physics, and I thought that it was a very important part of my development because I began to master the multiple elements of radiation therapy and how medical physics should support it.

Kenneth Cashon: Who were you working under there that kind of mentored you?

C. Clifton Ling: Well, I was the chief physicist.

Kenneth Cashon: Oh, boy. Okay.

C. Clifton Ling: I was quite worried initially, as I did not consider myself an experienced clinical medical physicist. The chief physician was Charles Rogers - a very nice guy, very experienced - we basically worked with each other and I managed to survive those six years.

Theodore Phillips: Wasn’t Charlie Rogers interested in neutron therapy at that time, Clif?

C. Clifton Ling: Yes, Charlie came to George Washington as chief of radiation oncology and principle investigator of MANTA, which stands for Middle Atlantic Neutron Treatment Association. MANTA had a neutron machine with which they were doing clinical trials in neutron therapy. But soon after I went there, the grant that supported the research ended and the MANTA program was closed.

Kenneth Cashon: Were you doing any research at that time on your own or just clinical work?

C. Clifton Ling: Yes, I was trying to do both clinical work and research. Some of my research was based on my collaborative work at MGH with Bill Shipley related to I-125 implants. George Washington awarded me a starter grant to study low-dose-rate radiobiology, which led to a funded NCI grant after a couple or three years. With the NCI grant I established a lab in George Washington working on low dose rate radiobiology. Concerning brachytherapy dosimetry, I was continuing to study I-125 implant dosimetry, particularly as it relates to the anisotropic fluence distribution from I-125 seeds. I also started to evaluate the effect of the shields in the Flectcher-Suit applicators used in intracavitary GYN implants. Some of that research may still have implication for the practice of brachytherapy, I think.

Kenneth Cashon: Definitely.

Theodore Phillips: Clift, you had an interaction with Jim Mitchell at that time. Is that correct? You guys were doing some experiments together I sort of remember. How did that come about?

C. Clifton Ling: Because of the NCI grant, I had money in my budget to recruit a postdoc to George Washington to work in the lab. And, I was lucky to be able recruit a recent PhD from Bill Dewey’s lab at Colorado State. Jim Mitchell, also from Colorado State, was joining the NCI Radiotherapy Branch around that time. So I was introduced to Jim, and he and I did some work together on the interaction of low dose rate radiation and hyperthermia, which resulted in a couple of publications. Jim and I are good friends since then.

Theodore Phillips: Who was the postdoc?

C. Clifton Ling: Ira Spiro. 

Theodore Phillips: Oh, Ira Spiro.

C. Clifton Ling: You may not know him.

Theodore Phillips: Oh, I know him. He subsequently turned out to be a very important person.

C. Clifton Ling: Yes. He worked in my lab for a few years, then we received a second NCI grant. While I was the PI, he became the PI because I was leaving Washington for UCSF. While working on that grant he also attended the medical school at George Washington, and then was recruited by Herman Suit to go to Mass General. He did some good work with Herman, I believe, in the treatment of sarcoma.

Theodore Phillips: Yes.

C. Clifton Ling: So that was how I got to know Jim Mitchell and then did some work with him. I remember you were at NCI at a sabbatical at that time as well.

Theodore Phillips: Yes.

C. Clifton Ling: That’s when I was being recruited to UCSF. Do you remember the interview I had with you at NCI?

Theodore Phillips: Yes.

C. Clifton Ling: You interviewed me while counting mammalian cell colonies with a Coulter counter.

Theodore Phillips: Yes. Do you want to go ahead and tell us what happened next?

Kenneth Cashon: Yes. So you went on to UCSF at that time?

C. Clifton Ling: Yes, I was being recruited to UCSF. Again it was in part because of Ira Spiro. Bill Dewey, Ira’s PhD supervisor, has relocated to UCSF and was chairing the search committee for the chief of physics. Bill, through Ira, encouraged me to apply. As Ted Phillips was doing a sabbatical at NCI, my initial interview was with Dewey, the Acting Chair Glenn Sheline, MD, and other members on the search committee and in the department. After that interview, they told me that I had to be interviewed by Ted Phillips. I said, where is Ted? They said, well, he is in Bethesda. So, I came back to Washington, D.C. and went to NCI to be interviewed by you, Ted.

Kenneth Cashon: I’m supposing it went well.

C. Clifton Ling: I guess.

Theodore Phillips: It did.

C. Clifton Ling: So that’s how I went to UCSF.

Kenneth Cashon: Well, tell us a little bit about the highlights of your time at UCSF and maybe your role in developing that strong program.

C. Clifton Ling: Well, compared to George Washington, UCSF is a much bigger operation. I already said at George Washington we initially have two medical physicists, one dosimetrist, and no engineers. Because I received two NCI funded grants and started a lab, my group eventually grew to seven persons, including those working in the lab. When I went to UCSF, I believe at the time, Ted, we had like 30 or more people in the physics group. There were six medical physics faculty. So I had some growing up to do, if you will, in terms of managing a larger group of people and interacting with very smart clinical colleagues like Ted Phillips, Glenn Sheline, Karen Fu etc. Dave Larson arrived the same time as a faculty. So, it was very challenging, but I think that I was not a total failure. I managed to persuade Ted to get rid of all the radium. I also remember persuading Ted to discontinue the use of “given dose”.  

Kenneth Cashon: Who?

C. Clifton Ling: I bet Ken and Tim don’t know what given dose is, do you?

Kenneth Cashon: I do. I had a cobalt when I was at the university, in fact.

Timothy Showalter: Yes. I was there.

C. Clifton Ling: So I was trying to modernize some of the physics aspect of the department. I reorganized the physics group into a number of sections, each with a faculty as section head. The idea was to delegate responsibilities to the other faculty in managing the clinical physics workload. The faculty members included Vernon Smith, Keith Weaver, Michael Schell, Paul Stauffer and others.   

Theodore Phillips: But you were very successful in getting grants, as I remember. I’ve never seen anyone who is so good at getting grants and getting them funded in both biology and physics. Can you tell us a little bit about why you were so successful?

C. Clifton Ling: Well, in a sense I was lucky in learning radiation biology at MSK, and later be able to combine it with medical physics. I think there were very few people who had both a background in medical physics and radiation biology. Although I do not consider myself to be a card-carrying radiation biologist, I did know something about radiation biology.

My first grant, as I said, was on radiobiology of low dose rate radiation. And, as Ted mentioned, in Ed Epp’s lab I dealt with very high dose rate radiation. When I came to UCSF I brought two NCI funded grants with me, one on radiobiology and the other on brachytherapy physics. Now, at UCSF, in the radiobiology lab there were very strong faculty, headed by Bill Dewey, and included Gloria Li, Helen Stone, Karen Fu. And I think, Ted, you also pursued some radiobiological research.

Theodore Phillips: Yes.

C. Clifton Ling: I already mentioned Ira Spiro at George Washington. He was key in my subsequent radiobiology research because he recognized the importance of molecular biology for the future development of radiobiology. He persuaded me to go “molecular” and learn molecular biology to be competitive in obtaining NCI grants. 

When I came to UCSF, at the time, Ted, there was no molecular biology in the lab. Now, for whatever reason, Alok Chatterjee of the Lawrence Radiation Laboratory visited us and told me that DOE was soliciting proposals on radon research because radon’s alpha particles cause lung cancer. That started me to explore how to study that topic. By chance I was introduced to William Lee, MD PhD, a postdoc in the lab of Mike Bishop (who subsequently received the Nobel Prize laureate for the discovery of the oncogene). Bill Lee in turn introduced me to the concept of cooperating oncogenes, based on experimental work done in MIT. So, we came upon the idea to transfect mammalian cells with one oncogene and try to use radiation to cause the second oncogenic event, then maybe we can study the mechanism of radiation-induced carcinogenesis, as it relates to radon.   

But to do that I needed to hire someone with molecular biology background who would transfect the oncogene into mammalian cells. I was able to hire a postdoc and began to perform studies and generate preliminary data for our grant application to the Department of Energy. The grant was funded. 

Theodore Phillips: So who was the postdoc?

C. Clifton Ling: Brian Endlich. I don’t know whether you remember him.

Theodore Phillips: Yes, I remember him.

C. Clifton Ling: Brian subsequently relocated to New York city and we continued that line of research using the alpha particles from the cyclotron at MSKCC.

Theodore Phillips: Why did you decide to go to Memorial? That was the biggest tragedy of my life.

Kenneth Cashon: Good question.

C. Clifton Ling: I don’t know whether you remember John Laughlin who has been at Memorial since the early 1950s and was chair at Memorial until the 1980s. He was stepping down because at Memorial, one had to retire as chair at a certain age. I received a letter from the search committee asking me to suggest names. I wrote back and suggested Michael Goitein, Mark Henkelmann, and several other brilliant medical physicists.   

They probably were unsuccessful in recruiting the best candidates for a year or so. Then Steve Leibel suggested that I be considered, I think. You remember Steve, Ted?

Theodore Phillips: Oh, yes.

C. Clifton Ling: Steve was at UCSF the same time I was, but was appointed Radiation Oncology Vice Chair at Memorial around 1987-88. He probably suggested to Zvi Fuks, Chair of Radiation Oncology and of the search committee, to take a look at this guy Clift Ling at USCF. Actually, Ted, you came to my office and said that you got a call from Zvi Fuks, and that they wanted me to interview for Laughlin’s position. In reply, I think I said something like - “Ted, do you think I should go? I haven’t been here for long, only two or three years. If you don’t think I should consider MSK, I would be happy to remain here.” Ted, do you remember what you said to me?

Theodore Phillips: Not exactly, but I probably said you should go for it. It’s the biggest job in physics.

C. Clifton Ling: Not exactly. You said: “you cannot turn down a job that you haven’t been offered”.

Theodore Phillips: That’s a quote from Shelly Wolfe.

C. Clifton Ling: Is that right?

Theodore Phillips: Yes.   

C. Clifton Ling: So it sounded like you think I should go get interviewed. A couple of weeks after my interview at MSK, you were in my office again and said that Fuks called again, and wanted me to go for a second visit. And I said, Ted, why is he calling you, if they want me to visit? I asked you the same question: “do you want me to go back for a second visit?” You gave the same quote from Shelly Wolfe: “you can’t turn down a job that you haven’t been offered.” So I went for a second visit, and then they offered me the job. Anyhow, that’s how I came to Memorial.

Theodore Phillips: Can tell us a little bit about that job? It was kind of unique in radiation physics, the job at Memorial, because it was a separate department. Could you tell us about that?

C. Clifton Ling: Yes. The first person who interviewed me at MSK was Sam Hellman, who was physician-in-chief at the time, shortly before he became Dean of the Medical School at the University of Chicago. I do not recall much from that interview except that he told me that “this is the best medical physics job in the whole world”. This is in part because medical physics is an independent department which makes it rather unique. The chair of medical physics reports directly to the physician-in-chief, the chief medical officer, in the same reporting role as the chairs of radiation oncology and radiology. In terms of clinical support, medical physics provides services to both radiation oncology and radiology, which include MRI, diagnostic radiology and nuclear medicine. The department also provides center-wide support in radiation safety and biomedical engineering.

When I first came to Memorial, the number of people in the physics department probably was 110 or 120, which is a sizable operation. Organizationally, it is very different from other institutions. MD Anderson had a similar organization some time ago; but when Bob Shalek retired, they changed the structure so that the radiation oncology physics would report through radiation oncology and the radiological physics through the radiology departments, respectively.  

Kenneth Cashon: All right. So just to transition into the current and start getting out of the history part of this, I’m kind of curious about your thoughts on -- well, I guess it’s still some history. But what do you think as far as developments in radiation oncology and what you’ve done during your career? I think of 3D calculations, 3D therapy, and I think of IMRT. What do you think are some of the more significant developments in radiation oncology that you specifically might have played a role in developing, I guess?

C. Clifton Ling: Well, I witnessed a number of development that transformed radiation oncology practice over the last 4 decades. One important development was imaging. The development of CT (and subsequently MRI and PET) was very important for modern radiotherapy, and crucial to 3DCRT. Another significant facilitator is the computer, and the increase in computation power. When I came into the field, treatment planning was basically done by hand. MGH then purchased an Artronix PC12 computer. But still the patient’s contour was acquired using lead wires, and the structures were guess-timated from radiographs by the physicians, and then the computer did dose distribution calculation. 

So, Ted, you would remember when I came to San Francisco we were beginning the 3DCRT era. UCSF had its own system, and eventually I believe UCSF purchased the UM plan developed at the University of Michigan.

Theodore Phillips: Correct.

C. Clifton Ling: When I came to Memorial, Memorial has its own treatment planning system. Radhe Mohan was the chief of the computer service in charge of developing a 3DCRT treatment planning system, which was a very important development. After that, the multi-leaf collimators became available, which I think people cannot do without today. Right?

Kenneth Cashon: Yes.

C. Clifton Ling: So when I came to Memorial there was no multileaf collimator. There was some manually operated multi-leaf collimators in Japan, and Scandatronics in Sweden was developing the first commercial multi-leaf collimator. We were trying to convince Varian to develop multi-leaf collimators. Initially unwilling, they eventually produced a computer-controlled multi-leaf collimator system. Several years later, EPID, which stands for electronic portal imager, arrived on the scene, replacing portal films. And finally, we have kV imagers that were mounted on the gantry to generate cone-beam CT images.

Now, each incremental sub-system is controlled by its own computer with a separate display screen, and the various computers need to communicate with each other. So, as more and more subsystems were added to the linac, eventually the treatment process becomes very complex, with the radiation therapists having to monitor up to half a dozen computer screens at the same time. I think this situation led to Varian’s development of the TrueBeam, which basically has a master-computer that centrally controls all the functioning nodes, both imaging and for radiation-delivery.   

Of course, IMRT was implemented in the 1990’s, and evolved into VMAT or RapidArc as a more efficient method to deliver intensity-modulated treatment. So that is a very brief summary of what I experienced in the development of radiotherapy techniques as it is practiced today.

Theodore Phillips: What role do you think Mark Carol and his development of the system with the air-operated multileaf that was attached to another machine, do you think that stimulated Varian into doing the right thing - the fact that he had an add-on system that actually did it before Varian did it?

C. Clifton Ling: Well, I’m not privy to some of the information. But I definitely think that Mark Carol contributed, as NOMOS was the first to implement IMRT clinically, although the concept originated from Sweden’s Anders Brahme. After Brahme published his seminal paper in the 1980s, many groups started to develop research programs on IMRT algorithms and methodology, including MD Anderson and the Heidelberg group in Germany. Because the PEACOCK system of NOMOS was the first to deliver IMRT clinically, they were very instrumental in pushing the field forward. Eventually when the capability for delivering IMRT with dynamic or step-and-shoot MLC was developed, those methods were adopted as they are more efficient and easier to use. 

Theodore Phillips: Yes. It was like EMI was destroyed by GE, NOMOS was destroyed by Varian.

C. Clifton Ling: Yes. Well, I always say that competition is good because it pushes the field forward.

Theodore Phillips: That’s right.

Kenneth Cashon: That leads into a discussion about you working with Varian. I see you are part of the Varian team. Consequently, it was during that time when RapidArc started coming into the scene. Tell us about your role in working with companies like Varian and how that played out with your career.

C. Clifton Ling: When I decided that I would step down as chair, I was going to discontinue the administrative part of my duties which you may understand is time consuming and somewhat of a headache - to deal with administration and supervise the many staff members. By then, the medical physics department has grown to about 180 people.   

After I announced that I was stepping down, I got a call the very next day from Tim Guertin, the CEO of Varian at the time. I have known Tim from way back, in collaborating with him on the development of MLC, IMRT, among other things. Tim asked if I would work Varian. But as I still have obligations on NCI funded research, we negotiated for me to work for Varian on a part-time basis.

Concerning RapidArc, I had nothing to do with its development. It was the brainchild of Karl Otto of Canada, and his algorithm was licensed to and implemented by Varian. After I joined Varian, Tim told me that they will soon release a product called RapidArc, but that nobody at Varian knows how to perform machine QA for it.

Kenneth Cashon: Right.

C. Clifton Ling: I was put in a position to do some real work, because I have not done hands-on QA methods for a long time. I went back to read all the IMRT QA papers, and thought about how to extend them to RapidArc. Anyhow, to make the long story short, we managed to develop the machine QA process for RapidArc in a relatively short time. The method is still being used today, I think.

Kenneth Cashon: Absolutely. In fact, I use it every month on my monthly to do my MLC tests. We refer to that paper in those tests all the time, in fact. In fact that’s where it leads to a question about, you know, many of the community-based physicists that I work with of course know your work and what you did academically. Actually I didn’t know how much radiobiology work you had done, but you know more recently this work with RapidArc. It makes me want to ask what’s your feelings about the relationships with academic physicists and community-based physicists and I guess how they’re trained. There was a question earlier about is the MS level physicist enough for the field today or should it be PhD. Maybe comment on residencies and things like that.

C. Clifton Ling: I believe that both PhD and MS physicists have a role in the practice of medical physics. I already said that after my five years at Mass General I did not think that I was really a mature clinical physicist. Although I spent five years in a very prominent institution and I was supposed to know all those things, it was only after two or three years as a sort of solo physicist, because I was the senior of the two physicists, that I learned to be more confident in my understanding of the practice of medical physics as applied to radiotherapy.

Relative to medical physics residency, I think a two-year residency is totally inadequate to prepare a person to be an independent medical physicist. I believe that after the residency they would understand clinical medical physics to a certain extent, but need another period of time, say 2-3 years of total immersion in the clinic for them to really feel confident that they can function independently. My views are in part based on my own experience and what I observed first hand from the training program at MSK in the last decades. Even after two years of rotation through the various sections in the clinical physics service, the graduating residents are not really mature enough to go to a private practice and be on their own. And, Ken, the practice of medical physics has become much more complex than when I got into the field.

Kenneth Cashon: Yes, exactly.

C. Clifton Ling: You need more training rather than less. So, the people who come out after a 2 year residency are not quite there yet.

Theodore Phillips: Do they have to work a little bit, a year or two, before they take their boards or can they take their boards right away? Clinically, you have to work another year before you take the board. So what’s the situation in physics?

C. Clifton Ling: I’m not sure. Ken, do you know?

Kenneth Cashon: Yes. You can take the written part almost right away, and then you have to work a couple of years - I think it’s two or three years - before you -- under someone and be able to take the rest of the written and the oral part. But, like you said, there are certain things. This field is driven nowadays I think by computers, and networking, and a constant learning of new technology. I feel like I spent a lot of my career doing that instead of physics and it’s sometimes frustrating.

When you think about what we’re doing in medical physics in radiation oncology, let me just put your fortune teller hat on, what do you envision is the future of what we’re doing in radiation oncology? In like five to ten years, what do you think might be different or we might be focused more on?

C. Clifton Ling: Well, one thing that I’m working on is proton therapy. I think proton therapy (PT) will have a major role in the future. Until recently, most proton therapy has been delivered using the so-called “passive scattering” method. The most advanced form of PT, intensity-modulated PT (IMPT) is just beginning to be used clinically and significant development has yet to occur to fully realize the potential of this most powerful method of radiotherapy.

Another topic, I think that Ted can chime in, is the promise of molecular therapy, including immunotherapy using checkpoint inhibitors. Much research is needed to incorporate these new therapies into the current standard of chemoradiation which, as I understand, still generates a lot of morbidity. Actually, Ted, you were one of the pioneers in chemoradiation therapy. Your perspective will be helpful in this area as I do not have a crystal ball in terms of clinical practice and outcome.   

In terms of contribution of medical physics, processes that improves the clinical workflow are desirable. For example, knowledge-based planning, such as Varian’s RapidPlan, can improve plan quality and reducing planning time so as to free up physicists’ time to address other issues like safety, patient comfort, and developing patient-centric processes.

Kenneth Cashon: Absolutely. So if you are going to give advice to a young, smart, medical physicist that’s about to go into a graduate program and looking forward to their career, what advice would you give them?

C. Clifton Ling: Well, I would encourage them to get a very strong grounding in the physical sciences. They need to know computer well these days. Then, an understanding of the entire clinical radiotherapy process is extremely important. It is only with that understanding that meaningful research can be performed to improve medical physics as applied to radiation oncology. In summary, acquire a very strong foundation in physical sciences, know computers, understand the clinical aspects of radiation oncology, and then do research that addresses the deficiencies that are identified.

Kenneth Cashon: Very good advice. Well, before we go on to our last five minutes of maybe some personal information, was there any other questions by the other interviewers that they’d like to address?

Timothy Showalter: Ken, can I just add one question? I was curious. Most of our conversation has been about your significant research contributions, but you’ve also played a lot of roles in leadership positions and fostering the careers of other physicists. Can you comment on what you sort of took away from that or what you learned in the process and what you’d recommend to someone who’s in a position of supervising and mentoring other physicists?

C. Clifton Ling: I have been very fortunate to be involved in many committees in AAPM and in ASTRO. Such participation provided very good environments and opportunities to interact with people from other institutions that have synergistic perspectives. I learned a lot from the AAPM committees and task groups, and from various committees in ASTRO and the Radiation Research Society. Those were very important activities that help me scientifically and to develop organization skills.

Kenneth Cashon: Well, we have about two or three more minutes. I was curious to know or at least ask you about your family.

C. Clifton Ling: Yes.

Kenneth Cashon: Maybe your children and a little bit about them.

C. Clifton Ling: I would be remiss not to mention my wife, Gloria C Li, PhD, who is a very accomplished researcher in her own right. She is quite a famous person in radiation biology, in the studies of hyperthermia, DNA repair and tumor hypoxia. She has helped me in my career, both in research and in my personal life. We have a son, a very accomplished attorney, in Los Angeles. Our older daughter is working for Apple in a management role and doing quite well. Our younger daughter is a physician, but she refused to go into radiation oncology. She leads the urgent care center of her hospital. So that is a very brief description of my family.

Kenneth Cashon: Did you not tell her that she could have weekends off if she went into radiation oncology?

C. Clifton Ling: I do not know why she did not want to go into radiation oncology; probably she heard too much about radiation from me.

Kenneth Cashon: Having so many roles and being part of a team that’s so large, how did you maintain balance as a physicist, as a father, as everything else? How did you do it?

C. Clifton Ling: To my family, I probably worked too hard at my job. But I did make time for them, I think. In fact, our children often recount things that we did together when they were growing up. But of course, it was a juggling act, not entirely easy. But I think Ted and the other people who have gone through the same path, have done similar things as I have. Anyhow, it has been a rewarding and enjoyable journey.

Kenneth Cashon: It sounds like quite the journey. Well, we’re wrapping up. Any other questions from the other interviewers that they’d like to ask? Any last minute words of wisdom that you’d like to add, Dr. Clif?

C. Clifton Ling: Well, nothing really, except that I’m honored to be interviewed by the ASTRO History Committee. I thank all of you for your time and participation.

Kenneth Cashon: It was a pleasure. We appreciate your time, we do. Thank you for all this information. It’s been incredible. It’s been very nice learning about you and your career.