In their article, Michael Goitein, Antony Lomax, and Eros Pedroni describe how beams of 250-MeV protons can produce radiation dose distributions that conform to the shapes of tumors much more precisely than those from 6- to 10-MeV x rays. The authors also describe how, due to the sharply defined depths of penetration, the doses to normal organs surrounding the tumor may be kept well below tolerance levels. As a result, the reader is led to believe that proton-beam installations dedicated to radiation therapy could significantly affect a cancer patient’s life expectancy and quality of life. Several clinical considerations throw this hypothesis into doubt, to say nothing of the economics. But first, permit us to point out the fundamental flaw in the authors’ argument.
Surgery is the primary treatment for more than 80% of all cancers at most hospitals, and for good reasons. For example, when treating esophageal cancer, it is standard practice for a surgeon to resect several centimeters of apparently normal tissue above and below the cancerous region to assure that microscopic disease has not been left behind. Subsequent pathological staging provides guidelines about the likely course of the disease and whether follow-up treatments will be required. Despite what would appear to be an aggressive and definitive approach, the five-year survival rate for esophageal cancer patients is around 15%. The results for other, more common cancers are not so dismal: about 60% for the colon and 80% for the bladder. In the context of surgical experience, one must wonder how the millimeter precision of proton-beam dose distributions will benefit the patient.
Albeit more traumatic than radiation therapy, surgery presents the family physician with the status of the patient’s cancer in a matter of days, and the need for adjuvant therapies can be decided early on. The authors suggest that the results of well-established clinical protocols, many of which include radiation, can be improved by the precisely defined dose distributions provided by proton beams. However, before this highly complex and expensive modality receives widespread adoption, clinical data must show marked and statistically significant improvements in the life expectancies of most cancer patients.
Radiation therapy plays a primary or competing treatment role in at least six cancers that make up more than 23% of all new cases; it also is used in supportive therapy for many others. Along with surgery and chemotherapy, radiation therapy is a critical component in the current armamentarium for the treatment of cancer. As for the future of the therapeutic applications of ionizing radiation, clinical trials over the past decade suggest that a plateau has been reached and that the impact of new modalities such as proton beams and intensity-modulated radiation therapy (IMRT) on overall cancer mortality will be difficult to detect. As the cost of health care continues to rise at an alarming rate, consideration of the cost/benefit ratios for newly introduced technologies increases in importance. Are 250-MeV proton-beam facilities likely to show a favorable reduction in this ratio for cancer patients? Based on the results of more than 20 years of proton-beam therapy compared with those achieved by conventional x rays, we think not.
Goitein and his colleagues present some data on clinical experience that are difficult to interpret in the context of their article. However, the reader should appreciate that, whether by prostatectomy or conventional x-ray therapy, the 5- and 10-year relative survival rates (relative to age-matched men who die of other causes) for early-stage prostate cancer are 90–98% and 80%–90%, respectively. The authors present a sketchy overview and some results unrelated to those obtained by more conventional treatments. Except for prostate and lung, the other disease sites mentioned make up but a small percentage of all new cases. How can the authors justify the expenditure of tens of millions of dollars for equipment, to say nothing of high operating costs, for the treatment of these rare tumors? (Perhaps by the establishment of a few national referral centers, but that is another issue.) In their one-sentence discussion of disease-free survival for lung cancer (83%) at Loma Linda University Medical Center, the authors failed to mention the time period involved. Surgical management of stage-I non—small-cell lung cancer currently achieves five-year survival rates of 50–60%. It is difficult to understand why radiation would be so strikingly superior to surgery for this highly malignant disease. Perhaps the time elapsed since treatment at Loma Linda is considerably shorter than five years.
The authors are to be commended for a clear and comprehensive description of how cyclotrons, originally used to study nuclear structure and interactions, were redeployed to treat cancer. Goitein and his coauthors show how radiation dose distributions can be made to conform to the complex shapes of tumors and thereby permit delivery of higher doses. We wish that these refinements were all it would take to reduce cancer mortality. Unfortunately, the majority of cancer deaths are due to metastases from malignant cells that have stealthily diffused into adjacent tissues and into organs far from the primary. Radiation therapy has been researched and developed for nearly a century, and improvements in radiation source technology have most certainly contributed to the increased life expectancy of cancer patients over that time. Two questions remain: How much more can we reasonably expect from further improvements in dose distributions? And how much are we willing to pay for them?