The relative biological effectiveness of cyclotron fast neutrons for early and late damage to the small intestine of the mouse

The r.b.e. of fast fission neutrons (2 MeV) for chronic radiation damage of the large bowel of rats after single dose and fractionated irradiation

Late damage in the rectum of rats was studied after local irradiation with 2 MeV fast fission neutrons and the results were compared with those for 300 kV X-rays. A similarity between latency times, and between clinical, gross pathological and histological appearances of the rectal obstruction after the two types of radiation was observed. The r.b.e. evaluated from ED 50/200 days values was 1.8 for single doses, 2.1 for two fractions and 3 for five fractions and these are similar to r.b.e.s from other investigations of chronic intestinal radiation damage. Using linear quadratic analysis, a limiting r.b.e. of 5 was obtained. The beta-values are similar for both radiation qualities. Because of the high gamma-contamination (25 per cent) in the RENT I beam a possible correction of the r.b.e. for neutrons only, assuming interaction, is discussed.

Late effects of irradiation in mouse jejunum

The response of mouse jejunum at intervals up to 1 year after single 'priming' doses of X-rays has been assessed by crypt survival after retreatment with single doses of X-rays and morphometric analysis of changes in the intestinal submucosa. The first 'priming' dose was given as a single dose to the whole abdomen. To assess crypt survival, groups of mice were retreated to the whole body with a range of test doses 2, 6 or 12 months later, while other groups of mice were given only the priming doses. These data were compared to crypt survival in mice not previously irradiated. The crypt dose-survival curves in mice re-irradiated at all three intervals after priming irradiation were displaced to higher doses in pre-treated than in non-pre-treated mice and were characterized by higher D0 values. Misonidazole given before the test exposure reversed this effect so that the dose survival curve for crypts in pre-treated mice were superimposed on that for mice not previously irradiated, suggesting that the increase in isoeffect dose and the change in the D0 in previously exposed mice was due to crypt hypoxia. Quantification of the area of the submucosa showed that its area was increased at all three times after the priming doses and was a result of collagen deposition and oedema. Thus, the hypoxia in the crypts was probably secondary to these changes. Deaths began at 6-7 months after priming irradiation and were due to intestinal obstruction and stenosis. Thus, as in other tissues, two phases of injury can be assayed in the intestine of experimental animals.

Pathologic effects of fractionated fast neutrons or photons on the pancreas, pylorus and duodenum of dogs

Thirty-nine adult male Beagles received either fast neutron or photon irradiation to the right thorax to determine the relative biological effectiveness (RBE) of fast neutrons on normal pulmonary tissue. The right anterior abdomen was included in the field of radiation. Twenty-four dogs (six/group) received fast neutrons with an average energy of 15 MeV to total doses of 1000, 1500, 2250 or 3375 rad in four fractions per week for six weeks. Fifteen dogs received 3000, 4500 or 6750 rad of photons (five/group) in an identical fractionation pattern. All neutron irradiated dogs receiving 3375 and 2250 rad and one receiving 1500 rad developed clinical signs of pancreatic, hepatic and gastrointestinal disturbances. The liver enzymes of these dogs became elevated and they died or were euthanatized in extremis 47-367 days after irradiation. Only one 6750 rad photon dog developed similar signs and died 708 days post-irradiation. Five neutron and 10 photon exposed dogs died of other causes. Neutron-induced lesions in the stomach and duodenum included hemorrhages, erosions, ulcerations and fibrosis. Ulcers perforated the GI tract of five dogs. Pancreatic lesions included degranulation and necrosis of acinar cells, fibrosis ans atrophy. Islet cells were not obviously damaged. All lesions were associated with degenerative and occlusive vascular changes. The RBE of fast neutrons, assessed by clinical signs, gross and microscopic pathology, is approximately 3-4.5 for pancreas and about 4.5 for pylorus and duodenum.

RBE values for colo-rectal injury after caesium 137 gamma-ray and neutron irradiation. I. Single doses

Colo-rectal damage in mice has been assessed after caesium gamma irradiation and 3 MeV neutrons given as single doses. Several assays were used, including body weight changes, faecal deformity and lethality. Dose response curves have been constructed for each assay at different times after irradiation, ranging from 10 days to 16 months. The data have been analysed in terms of the time course of expression of damage and the RBE for neutrons. An initial loss of weight at 10-20 days was presumably related to epithelial denudation, but a dose-dependent weight reduction (compared with controls) persisted over the animal's life span. Mice died progressively after localised pelvic gamma irradiation; there was no sharp demarcation between an early and late phase of lethal injury. Death resulted from intestinal stricture or stenosis. The time course for lethality was qualitatively different after neutrons, with little progression of damage between 5 and 11 months. Faecal deformity was detectable as a higher proportion of small pellets when the rectum became constricted by fibrosis. No significant faecal deformity was observed before 6 months after which time dose response curves could be obtained. The RBE for early damage (assessed at 1-3 months) was 2.2-2.7. This fell to 1.7-1.9 for late damage (determined at 10-15 months) over the range of neutron doses of 7.5-12 Gy. The need for sublethal assays allowing for sequential evaluation of radiation damage within the same animal is stressed, as is the need to compare RBE values from early and late endpoints at equivalent neutron doses.

Phase I pilot study on fast neutron teletherapy for advanced carcinomas of the head and neck region. Final report on local control rate and survival

A final report is presented on the local control rate and length of survival for 100 patients with advanced squamous cell carcinomas of the head and neck region who received fast neutron teletherapy at the University of Washington during the period 1973 through 1977. Sixty-two patients were treated with neutrons alone and 38 were treated with a combination of neutrons and photons as part of a mixed beam fractionation scheme. The overall initial complete remission rate was 68% for the mixed beam group and 44% for the group treated with neutrons alone. Initial complete remission rates for the two groups of patients are given as a function of T-stage and N-stage and acturarial curves are presented which show the time course of local control and survival for the two treatment groups. For T3 and T4 lesions the initial complete remission rate appears to be greater using the mixed beam form of treatment than using neutrons alone. Treatment to high-dose levels using neutrons alone gave rise to significantly greater morbidity--both acute and late effects--than resulted from the mixed beam form of treatment. Local control rates and survival rates are compared with similar groups of patients treated with neutrons at other institutions.

Fast neutron teletherapy for advanced carcinomas of the oral cavity and soft palate

A retrospective study was performed to determine the efficacy of using fast neutron radiation for treating advanced squamous cell carcinomas of the oral cavity and soft palate. The majority of patients were judged to have less than a 10% 5-year survival with conventional medical treatment. Fifteen patients with oral cavity tumors were treated for cure with neutrons alone and six were treated with a combination of neutrons and photons as part of a mixed beam fractionation scheme. In the neutron-only group, the complete regression rate was 33% in the mixed beam group, the rate was 50%. Five patients who had squamous cell carcinomas of the soft palate were treated for cure, one with neutrons alone and four with a mixed beam regimen. The complete regression rate was 100%. The two-year NED results are comparable with literature results for more selected groups of patients with oral cavity and soft palate tumors treated by conventional photon therapy. The acute treatment morbidity was perhaps somewhat greater in the subgroup of patients treated with neutrons alone, and this subgroup later developed a more pronounced subcutaneous fibrosis. Morbidity associated with the mixed beam treatment regimen was comparable to that associated with conventional radiotherapy.

Fast neutron teletherapy for advanced carcinoma of hypopharynx and supraglottic larynx

The results of a Phase I clinical trial using fast neutron teletherapy for advanced squamous cell carcinoma of the hypopharynx and supraglottic larynx are reported. Ten patients with hypopharyngeal tumors were treated for cure using neutrons alone and 6 patients with hypopharyngeal tumors were treated for cure using a combination of neutrons and photons as part of a mixed beam fraction scheme. In the neutron-only group, the initial complete remission rate was 4/10 (40%). The mean survival of this group of patients with initial complete remission was only 5.75 months (range 2--10) but all patients died without evidence of recurrent tumor at the primary site. In the mixed beam group, the initial complete remission rate was 5/6 (83%) but the local control rate dropped rapidly to 41 per cent when displayed on an actuarial plot. Six patients with advanced tumors of the supraglottic larynx were treated for cure, 5 with neutrons alone and one with a mixed beam regime. The initial complete remission rate was 3/6 (50%) but 2 of these patients rapidly recurred, which reduced the local control rate on an actuarial plot to 16 per cent. The relative adverse effects of the neutron-only treatment regime appear to be substantially greater than those of the mixed beam treatment regime.

Effect of roentgen, cyclotron neutron, or mixed neutron-photon fractionated irradiation of mice. LD50/4 day values

Mice were whole-body-irradiated with 5 fractions of roentgen rays in 5 days, 5 fractions of cyclotron neutrons in 5 days, or with mixed neutron-photon fractionated radiation, in the sequence n-n-x-x-x or n-x-x-x-n. The LD50/4 day values were determined. Roentgen rays and neutrons interact in the additive manner in the mixed fractionation schemes: effective dose per fraction is as predicted from the roentgen ray-only and neutron-only experiments. This essentially agrees with HENDRY et coll. (1976). However, no trend was found towards a less-than -additive effect which was observed by those authors and has also been suggested in skin response to mixed schemes (NELSON et coll. 1975).

Early assessment of normal tissue tolerance of fast neutron beam radiation therapy

Between September 10, 1973 and May 20, 1975, 94 selected patients were treated with fast neutron beams generated by bombarding an "intermediate" beryllium target with 21 MeV deuterons. The clinical material included: 58 patients with head and neck cancers; 27 patients with cerebral glioblastoma multiforme; and 9 patients with a variety of other neoplasms. Of the 67 patients treated only with neutron beams, 31 received two increments per week and 36 received three increments per week. The calculated doses in most patients were 1800 rad n gamma (neutrons + gamma components) delivered in 6 weeks. Seventeen patients were treated with two increments of neutron beams and three increments of 60Co photons weekly to calculated total doses of 780-1050 rad n gamma + 3360-3780 rad 60Co gamma delivered over 50-54 days. Ten patients were treated with neutron bean "boosts" of 300-900 rad n gamma in three to seven increments over 8-23 days following conventional radiation therapy. Treatment has been well tolerated, with only 9 of 94 patients not completing the anticipated course. In three of these, treatment was dixcontinued because of intercurrent problems. Except for those patients with glioblastoma multiforme, treatment complications have not been dose-related. In four patients, complications probably were related to persistent cancer. Neutron beam irradiaiton may have been a factor in the neurologic deterioration of five patients with glioblastoma multiforme who did not complete treatment.