Evaluation of past experience with fast neutron teletherapy and its implications for future applications

Modern radiation treatment planning and delivery--from Röntgen to real time

The field of radiation oncology has advanced exponentially since the discovery of X-rays just over 100 years ago. With the advent of three-dimensional treatment planning, the therapeutic index was increased by dose escalation and more accurate shielding of normal tissues. Now, even greater advances are under way with IMRT, image-guided radiation therapy, delineation and control of organ motion, and real-time imaging. Similarly, the use of particle therapies such as protons has the potential to effect even more accurate dose distributions. Clinical studies investigating these modalities will likely further increase the efficacy of radiation in years to come.

Fast neutron radiation therapy for unresectable squamous cell carcinomas of the head and neck: the results of a randomized RTOG study

Forty patients with advanced, unresectable squamous cell carcinomas of the head and neck were entered on a prospective, randomized study comparing fast neutron radiation therapy with conventional photon radiation therapy. Twenty-six patients were randomized to neutrons, and 14 patients were randomized to photons. The randomization was purposefully unbalanced in favor of the experimental treatment. The complete response rate for the neutron-treated group of patients was 52%. The complete response rate for the photon-treated group of patients was 17%. The difference is statistically significant at the p = .04 level. The two-year survival rates for the neutron-treated group and the photon-treated group were 25 and 0%, respectively. The major complication rates were not statistically significantly different for the two groups (18% for neutrons, and 33% for photons).

The changing role of radiation oncology in cancer management

Radiation therapy has made major contributions to the improved quality of care for the cancer patient. This quality improvement has derived not only from a greater understanding of the natural history of the disease process but also from a more critical evaluation of the results of clinical treatment. Today, clinical radiation therapy stands on a firm foundation of basic understanding of ionizing radiations and its effect on tissue, the biology of the effect in normal tissues and tumor. This explosive growth in knowledge relative to radiation therapy physics, clinical treatment planning, the utilization of computers in radiation therapy as well as basic information in radiation biology and how it might be implemented in clinical situations are well known. Data will be presented to illustrate how major and important applications of basic physics and biologic data in clinical practice are beginning to influence the changing character of cancer management. These new techniques, now being implemented in general clinical practice, offer major potential opportunities toward improving the expectation for cure of many cancers, not cured in the past.

Fast neutron beam radiation therapy in the United States

Following a 30-year hiatus after Dr. Stone's work in the 1930's and 1940's, clinical trials with fast neutrons were restarted in the United States in 1972. Approximately 2500 patients have been treated with neutrons since that time. Three hundred and seven patients with squamous cell carcinomas of the head and neck were entered on an RTOG-coordinated randomized study comparing standard photon irradiation with mixed beam radiation therapy. No significant differences were noted in the local control, survival or complication rates. One hundred and sixty patients were entered on a randomized glioblastoma study. Although there were no significant differences in median survival, autopsy results showed greater tumor effect on the neutron-treated tumors. Twenty-six patients were treated for transitional cell carcinomas of the bladder with either preoperative mixed beam irradiation or mixed beam irradiation alone. Both the local control rates and survival rates compare favorably with photon radiation therapy. The future of fast neutron beam radiation therapy in the United States is discussed.

Particle radiation therapy: current status and future potential

Radiation therapy with "heavy" particles offers potential biological and physical advantages compared to irradiation with low LET photons. Clinical studies are in progress with proton beams, which have dosimetric advantages, and fast neutron beams, which have potential biologic advantages. Clinical studies with negative pi mesons and heavy nuclei, which have combined dosimetric and biologic advantages are about to start.

Fractionated dose of 35-MEV fast neutrons and hypoxic tumor cell survival curve

The determination of the RBE for the MANTA fast neutrons produced by NRL is inprogress, with the model system using tumor cell population kinetic response patterns assayed in vitro after irradiation in vivo. Ascites tumor cells BW-5147 were irradiated with a clinically usable fast neutron beam from the NRL cyclotron, which is produced by accelrating deuterons to 35 MeV and using htem to bombard a thick berylliumtarget. The comparison of dose-effect relationships was made for doses ranging from30 to 1000 rads. The doses required for an isoeffect on BW-5147 hypoxic tumor cell survival and impairment of its reproductive capacity from fast neutron exposure were not different wheither it was given a single dose or the same dose given in three fractions separated by long recovery periods in situ. No intracellular repair of sublethal injury when the dose was given in three fractions, although the hypoxic BWp5147 tumor cells haveno effective reoxygenation or repopulation in this time interval. The RBE for the fast neutron beam is 4 relative to x rays for fractionated doses at the surviving fractionlevel of 0.6-0.7, while the RBE IS 2.5 FOR SINGLE DOSES. However, at a surviving fraction of 0.1, the RBE is 1.9 for single and 2.8 for fractionated doses. Analysis of thedaily cell population rate or mitotic delay between the two types of radiations at a similiar level of survival.

Experimentally determined tissue air ratios and scatter air ratios for collimated beams of 14 mev neutrons

Tissue air ratios (TAR) and scatter air ratios (SAR) for collimated beams of 14 MeV neutrons were determined from depth dose curves measured in air and water using a tissue equivalent proportional counter. Central axis depth dose data were obtained as a function of field size and depth in a water phantom for an SSD or 125 cm. The collimator was composed of steel and polyethylene and was continuously variable from a 3 times 3 cm to a 20 times 20 cm field size at 125 cm SSD. The field scans for this collimator were flat within plus or minus 2 per cent over 80 per cent of the field dimension in air and were reduced to 20 per cent of the central axis dose at 1-2 field radii in air. Relative depth dose data in air and phantom were measured with an accuracy of plus or minus 2 per cent and were used for the TAR and SAR calculations. The resulting scatter air ratios for 14 MeV neutrons have roughly the same characteristics as 60-Co SAR, but are 60 per cent larger at maximum build-up and reach that maximum at about 60 per cent of the peak depth for 60-Co for all field sizes. The effects of collimator throat scatter on the central axis depth dose characteristics of this particular collimator design are discussed in detail using the measured tissue and scatter air ratios.