Study of biological effects of varying mixtures of Cf-252 and gamma radiation on the acute radiation syndromes: relevance to clinical radiotherapy of radioresistant cancer.

PURPOSE: Data for the 30 day bone marrow syndrome (BM-50) and the 6-10 day gastrointestinal (GI-50) syndrome for a one and two fraction schedule and acute and low dose rate irradiation using pure and mixed Cf-252 and photon radiation are presented. METHODS AND MATERIALS: The radiations of Cf-252 is a mixture of neutrons and gamma rays. We total body irradiated Balb/c mice of both sexes with acute Co-60, low dose rate Cs-137 and Cf-252 using a 1 x and 2 x schedule. For low linear energy transfer radiations of Co-60 or Cs-137 there was expected to be an increase in the dose to produce the gastrointestinal and bone marrow syndromes with minimal change for Cf-252 neutrons. However, the radiations from Cf-252 are approximately 65% neutrons and approximately 35% photons and hence some repair may be expected. We further altered the proportion of photons in the Cf-252 radiation field by mixing Cs-137 with the Cf-252 sources and total body irradiated the mice to determine the effects on the syndromes. We determined the effects of mixing Cf-252 neutrons with different proportions of photons on the radiation syndromes. RESULTS: There was increase in BM-50 and GI-50 doses with fractionated or low dose rate photon irradiations and the dose modifying factors were 1.3-1.4 for the GI syndrome and 1.2 for the bone marrow syndrome. For Cf-252 there was minimal fractionation effect for the GI-50 syndrome, which increased by a 1.1 for x 1 vs. x 2 fractions; for the BM-50 syndrome it rose by a 1.1 factor. For LDR Cs-137 the dose for the GI-50 syndrome rose by a 2.2 fold. For mixed neutron-photon radiation of 0%, 15%, 35%, and 65% eta/gamma mixtures, the dose to produce the BM-50 and GI-50 endpoints dropped sharply from 0 to 35% neutrons and remained flat thereafter. CONCLUSION: For major tissues such as the bone marrow and G-I tract, Cf-252 behaved as high linear energy transfer for mixtures of neutrons and gamma rays of approximately 35% neutrons when the radiation were delivered simultaneously at the low dose rates studied. There was little or no additional contribution to the effectiveness of the mixed radiations if neutrons contributed 35% or more of the dose.

Schedule in Cf-252 neutron brachytherapy: complications after delayed implant therapy for cervical cancer in a phase II trial.

The objective of this study was to review severe complication frequency in a protocol study using a defined prescribed dose combined with fractionated whole pelvis radiotherapy to 40-45 Gy. The method used a dose of Cf neutrons to 35 Gy equivalents (relative biological effectiveness or RBE adjusted) to a total tumor dose of 80 Gy-eq in one to four implant sessions. Compliance was excellent, and most patients received two implants to 35 (0.4) (SE) Gy-eq in two sessions plus external radiation to a total point A or paracervical region dose of 80 (0.3) Gy-eqs. In patients who received delayed implants, the severe complication rate (pelvic necrosis, fistulas) was significantly greater (40% versus 3%). We postulate that neutron brachytherapy caused tumors to regress rapidly and completely, which allowed the neutron dose to adjacent radiosensitive organs (bladder, rectum, sigmoid colon, and bowel) to become excessive. The delayed Cf implant apparently contributed to the greater risk for normal tissue complications.

Megavoltage grid total body irradiation of C3Hf/SED mice.

The effect of a grid on whole-body megavoltage radiation tolerance in C3Hf/SED mice was studied. Adult mice were irradiated beneath a 50% megavoltage grid. LD50 (50% lethality) values were measured at ten and 30 days. LD50/30 day increased by a factor of 1.5 for mice receiving both single and two fraction irradiation beneath the grid. LD50/ten day increased by factors of 1.1 to 1.2 for single, two, and five fraction irradiation beneath the grid.

Regeneration in cervix cancer after 252Cf neutron brachytherapy.

Regeneration of clonogens in human cervical cancer was assessed by the pathological evaluation of the hysterectomy specimen after intracavitary 252Cf neutron brachytherapy implants separated by varying time intervals followed by extrafascial hysterectomy. In this study, patients with bulky/barrel shaped Stage IB cervical cancers received 252Cf implants plus approximately 45 Gy of whole pelvis linear accelerator radiotherapy in approximately 25 fractions in 5 weeks followed by hysterectomy 4-6 weeks after radiotherapy. The specimens were studied grossly and microscopically for residual tumor. It was found that the fraction of positive specimens increased with elapsed time interval between implants. These findings support the hypothesis that there is repopulation of surviving clonogens with increased time interval between the implants. The observation also supports current concerns that rapid depopulation of tumor can lead to rapid repopulation, that is, rapid shrinkage of tumor can alter the physiological environment such that clonogens can rapidly regenerate.

Clinical study of relative biological effectiveness for cervical carcinoma treated by 252Cf neutrons and assessed by histological tumour eradication.

Clinical data of the University of Kentucky trial using californium (252Cf), or caesium (137Cs), are reviewed for dose-response based on the endpoint of tumour eradication estimated from hysterectomy specimens obtained 4-6 weeks after preoperative irradiation. These data are used to assess the relative biological effectiveness (RBE) for 252Cf neutrons compared with 137Cs gamma radiation. Tumours treated were of common stage but were of bulky or barrel shape suitable for "radiosurgical" therapy. Dose-response curves were constructed, and additional data from the literature used to analyse the curve shape. The photon dose-response curve is complex on a logarithmic plot, whereas the 252Cf neutron curve is exponential. This indicates that the RBE can be different depending on the number of implants, schedule and size of dose delivered per session. The RBE values were approximately 8.0 at low doses or for multiple implants but they may rise to approximately 16 at larger doses or for single 252Cf implants.

Relative biological effectiveness (RBE) of p(26) + Be neutrons from the King Faisal Specialist Hospital and Research Centre CS-30 cyclotron measured by testis weight loss.

Testis weight loss of C3H and Swiss-Webster (SW) mice was used as endpoint to determine the relative biological effectiveness (RBE) of p(26) + Be fast neutrons with respect to Co-60 gamma irradiation. Percent weight loss versus dose curves showed two components. Comparing first component effects, the RBE was 3.4 (C3H) and 3.7 (SW); when the second component was used, the RBE was 2.6 and 2.7 (C3H), and 3.5 (SW). When percent weight loss was plotted versus log dose, parallel lines were obtained, giving an RBE of 3.9 and 4.1 (C3H), and 4.2 (SW). Results were compared with published values and RBE as a function of fast neutron energy was plotted. A good correlation was found. Discrepancies seem to be mostly due to the use of different baseline radiation. When a constant correction is made, most of the values fit a single line. The possibility of using this approach as a substitute for international comparisons is discussed.

Sperm shape abnormalities in mice exposed to californium-252 radiation.

Male mice of the B6C3F1 hybrid strain were whole-body irradiated with different doses of 252Cf/60Co. They were killed 35 days later and spermatozoa from cauda epididymides were stained with eosin-Y. The air-dried smears were examined under light microscope for sperm shape abnormalities. There was an increase in the frequency of abnormal sperm in all the treated groups compared to controls. The RBE for the mixed neutron and gamma radiation of 252Cf was 2.6. The RBE for the neutron component was 3.4. The increased frequency of abnormal sperm was associated with a concomitant decrease in testis weight in the irradiated animals.

Specimen histology after one or two preoperative CF-252 implants for bulky stage IB cervical cancer.

Using hysterectomy specimens obtained 1 month after Cf-252 neutron brachytherapy plus fractionated radiotherapy, we determined the fraction of positive and negative specimens with neutron dose for bulky Stage IB cervical cancers. The specimens obtained and studied after an initial Cf-252 insertion when the sources were newer and less decayed were more frequently negative for histological evidence of cancer than after the sources had decayed and 2 insertions were needed. After two insertions to deliver a therapeutic dose preoperatively the specimens were more frequently positive. When a larger initial dose was delivered to the tumor a larger proportion of negative specimens was noted. The size of neutron dose fraction was important to local tumor clearance and to rendering the specimens negative as well as schedule in use.

Cf-252 leukemogenesis in the C57BL mouse.

Radiation-induced leukemia/lymphomas were induced in C57BL mice using four weekly acute 60Co fractionated irradiation exposures (to 188 cGy, or graded doses of low dose rate (LDR) Cf-252 irradiation given in fractionated exposure sessions at four weekly intervals. The acute 60Co radiation produced 84% thymic lymphomas with a median survival time (MST) of 162 days for mice developing tumors. Mice were exposed to Cf-252 n + gamma radiation in graded doses of 50, 62.5, 80, 112, and 188 cGy per week repeated 4X. Mice exposed to Cf-252 radiation developed thymic lymphomas on a much delayed time schedule. Mice irradiated at 50-80 cGy Cf-252 were killed after the 60Co induced thymoma mice had died to detect tumors. At Cf-252 doses of 112 or 188 rads 79 or 70% of mice, respectively, developed thymic lymphomas and had similar survival times which gave an estimated leukemogenesis RBEn of approximately 1.0-2.0. These studies show that for Cf-252 n + gamma radiation, compared to 60Co for leukemogenic efficiency, had a much longer latent period, and had a low RBE (1.0-2.0) at the large doses per fraction used in these studies. Under the experimental fractionated conditions tested, Cf-252 neutrons were leukemogenic, but only slightly more so than fractionated 60Co.

Cure rates and tumor resistance in cured mice after nitrosourea treatment of EMT6 ascites tumors.

Single-dose BCNU or chlorozotocin (CLZ) treatment of EMT6 mammary carcinoma tumors of the BALB/c mouse has only a transient effect on tumor growth, after which tumors follow control growth patterns. To test the hypothesis that drug access to tumor cells might be a factor in cell killing, we adapted the EMT6/KY tumor to ascites form. Injection of 10(5) EMT6/KY cells i.p. kills BALB/c mice with a mean survival time of 13.0 +/- 1.0 days. We have surveyed several nitrosoureas for their effects on the EMT6/KY ascites tumor after intraperitoneal injection of the drugs. Cure rates and percent increase in life span were used as endpoints. Also, we tested for induced host tumor resistance (TR) in cured mice, by challenging survivors with live EMT6 cells. Highest cure rates were obtained for treatment on days 2, 3, or 4 after inocula of 10(5) cells: CLZ (10 mg/kg), 83.3%; cis-acid (20 mg/kg), 75%, and CCNU (30 mg/kg), 70%. Other nitrosoureas, i.e. BCNU, PCNU, GANU, STZN, FCNU, ACNU, MeCCNU, NSC-88104 produced lower cure rates. Cured mice surviving challenges of 10(6) EMT6 cells were considered TR. TR mice did not correlate with cure rates for the 3 nitrosoureas giving high cure rates. As percent of survivors, TR mice were (for day 3 treatment): FCNU, 100%, BCNU, 100.0% and CLZ, 50.0%. Thus, cure rates and TR seem to depend on the structure of the nitrosourea, but through different mechanisms.

Chemotherapeutic effects of 13 nitrosoureas on the LSA lymphoma ascites tumor of the C57BL mouse.

The LSA lymphoma of the C57BL/ym mouse has been used to test 13 nitrosoureas for cure of advanced tumors and for induced tumor resistance (ITR) of surviving animals. Tumors were initiated by intraperitoneal inoculation of 10(6) LSA cells. Controls died in 8-9 days. Five-day old tumors were defined as advanced tumors, and treatment consisted of a single dose of a nitrosourea to groups of 10 male mice, 8-9 weeks old, for each compound. The nitrosoureas used were: BCNU (NSC-40992), CCNU (NSC-79037), MeCCNU (NSC-95441), chlorozotocin (CLZ) (NSC-178248), streptozotocin (STZN) (NSC-85998) CNU (NSC-47547), FCNU (NSC-87974), GANU (NSC-254174), ACNU (NSC-245382), PCNU (NSC-95466), cis-acid (NSC-153174), 153174), NSC-88104, and GCNU (NSC-114460). The major endpoint assessed was tumor cure and was grouped as follows: (1) high (greater than or equal to 80%), achieved with BCNU, MeCCNU, CCNU, CLZ, ACNU, FCNU, PCNU, and cis-acid; (2) medium (40- less than 80%), obtained with GANU, NSC-88104, and GCNU, and (3) low or nil (less than 40%), shown by CNU and STZN. The second endpoint was treatment-induced ITR. Cured mice, i.e., those surviving over 30 days after death of controls were challenged with 10(5) LSA live cells, and survivors from this challenge were challenged with 10(7) LSA cells 1 month later. Survivors from both inocula were considered highly immune (HI). High percentages of HI mice (greater than or equal to 80%) were obtained from mice cured with MeCCNU, CCNU, ACNU, FCNU, PCNU, and NSC-88104. STZN produced 0.0% cures; the other nitrosoureas showed 33.3-75% HI mice. Cure rates and ITR appeared to be agent- and structure-related. Cure alone did not lead to the resistant state.

Heterotransplantation of human cervix cancers in radiation-conditioned or nonconditioned athymic mice.

Primary human cervix cancers were implanted into athymic nude mice from 23 patient biopsy specimens. Tissue/tumor samples were implanted as chunks by trocar in different sites in irradiated (400 rad) or nonirradiated nude mice. Without irradiation 1 of 9 (11%) implanted tumors grew progressively and 13 of 26 (50%) implanted sites formed small implantation nodules that remained stable and usually regressed. In nude mice given 400-rad irradiation, 3 of 12 (25%) showed progressive tumor growth, 8 of 12 (67%) patient samples showed growth, and 24 of 36 (67%) implanted sites showed growth. Correlation with clinical data showed that the higher-stage and more malignant tumors were more likely to show progressive growth patterns, as was noted in three of five Stage III/IV cervix tumors grafted into 400-rad conditioned mice. Conversely, the lower-stage tumors were much less likely to show growth, and zero of nine samples with Stage I/II tumors showed progressive growth.

Treatment of primary radiogenic C57BL mouse cell leukemia/lymphoma by 1,3-bis(2-chloroethyl)-1-nitrosourea chemotherapy and adjuvant cellular therapy.

Primary radiation-induced or radiation leukemia virus (RadLV)-induced T-leukemias/lymphomas were treated in vivo in an early to advanced state by using 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). BCNU was given at various times after the tumor induction procedure. Death from RadLV lymphomas which had been initiated in 33 +/- 3 day old C57BL mice by intrathymic injection of RadLV was scored in untreated, BCNU-treated or BCNU and cellular adjuvant treated mice. Intrathymic RadLV injection in 33 +/- 3 day old mice produced tumors in 98% of injected mice. Median survival time (MST) was increased by BCNU and by BCNU plus bone marrow cell therapy whether done 33 or 47 days after RadLV. There was increased in MST from 108 days to 171 days by BCNU and bone marrow cell therapy given 33 days after tumor initiation and to 195 days when therapy was given 47 days after initiation. In radiation-induced lymphomas produced by 190 rad every week X 4 of 33 +/- 3 day old mice, spleen cell (X 1) therapy or BCNU treatment increased the MST of treated mice from 142 days to 177 days after iv spleen cells or to 195 days after iv-ip spleen cells, and this protocol produced 31% long-term cures. Cellular adjuvant therapy combined with BCNU chemotherapy was effective for curing the lymphomas but cellular adjuvant therapy alone was also highly effective for therapy.

Study of acute 60Co, low dose rate CF-252 and CS-137 radiation on LSA ascites lymphoma in vivo.

Dose response curves were determined for the LSA lymphoma for acute 60Co, low dose rate Cs-137 and Cf-252 radiations using in vivo survival time bioassay. Mean survival times increased with dose with a prominent oxygen effect noted for acute 60Co and Cs-137. OER was lowest for Cf-252 where it was approximately 1.4. The RBEn for oxic LSA cells to Cf-252 neutrons was 3.1 for acute 60Co and 4.2 for Cs-137. It was larger for hypoxic tumor and RBE was 5.3 for 60Co and 5.8 for Cs-137. Survival curves based on survival data used a multitarget dose-response model for photon radiation and exponential dose-response for Cf-252 radiation. When LSA was irradiated in advanced tumor stages in vivo, Cf-252 was much more effective than acute 60Co or LDR Cs-137 for increasing survival time. Tumor response in vivo matched the in vitro irradiated tumor data. No schedule dependence was observed for mixing of 60Co and Cf-252 radiations.

Clinical trial of 252Cf neutron brachytherapy vs. conventional radiotherapy for advanced cervical cancer.

252Cf, a neutron emitting radioactive transplutonium isotope, was tested for its efficacy against advanced bulky Stage III-IV cancers of the cervix in a clinical trial at the University of Kentucky Medical Center. Eighty-two patients were treated during 1976-1979 and followed for 5-year survival and tumor control. Three different treatment methods went on sequentially and concurrently, that is, (a) conventional whole pelvis photon with delayed 137Cs implants, (b) conventional photon therapy with delayed 252Cf implants, and (c) 252Cf implants ("early") preceding photon therapy. There were 12% 5-year survival for Stage IIIB cancers by conventional therapy, and 15% by delayed 252Cf implant therapy. For early 252Cf implant therapy there were 54% 5-year survivals with 4% complications and 65% 5-year local control, but distant metastases became a prominent delayed failure pattern.

Neutron brachytherapy is better than conventional radiotherapy in advanced cervical cancer.

Californium-252 (252Cf), a fast-neutron emitting radioisotope, was used for neutron brachytherapy (NT) of 82 patients with advanced (stage III and IV) cervical cancer. The results were compared with caesium-137 brachytherapy; both isotopes were given in combination with high-dose fractionated pelvic radiotherapy. In patients with stage IIIB disease (ie, tumour to the pelvic side-wall), 252Cf intracavitary therapy resulted in 54% 5-year survival compared with 12% in the caesium group. To be effective, Cf-NT must be given before external beam (photon) therapy.