Photobiomodulation of a flowable matrix in a human skin ex vivo model demonstrates energy-based enhancement of engraftment integration and remodeling

The use of dermal substitutes to treat skin defects such as ulcers has shown promising results, suggesting a potential role for skin substitutes for treating acute and chronic wounds. One of the main drawbacks with the use of dermal substitutes is the length of time from engraftment to graft take, plus the risk of contamination and failure due to this prolonged integration. Therefore, the use of adjuvant energy-based therapeutic modalities to augment and accelerate the rate of biointegration by dermal substitute engraftments is a desirable outcome. The photobiomodulation (PBM) therapy modulates the repair process, by stimulating cellular proliferation and angiogenesis. Here, we evaluated the effect of PBM on a collagen-glycosaminoglycan flowable wound matrix (FWM) in an ex vivo human skin wound model. PBM resulted in accelerated rate of re-epithelialization and organization of matrix as seen by structural arrangement of collagen fibers, and a subsequent increased expression of alpha-smooth muscle actin (α-SMA) and vascular endothelial growth factor A (VEGF-A) leading to an overall improved healing process. The use of PBM promoted a beneficial effect on the rate of integration and healing of FWM. We therefore propose that the adjuvant use of PBM may have utility in enhancing engraftment and tissue repair and be of value in clinical practice.

Experimental model for low level laser therapy on ischemic random skin flap in rats

PURPOSE: To develop an experimental model to be used in the study of low level Laser therapy on viability of random skin flap in rats. METHODS: The sample was 24 Wistar-EPM rats. The random skin flap measured 10 x 4 cm and a plastic sheet was interposed between the flap and donor site. Group 1 (control) underwent sham irradiation with diode laser (830 nm). Group 2 was submitted to laser irradiation with diode laser (830 nm). The animals were submitted to Laser therapy with 36 J/cm² energy density (72 seconds) immediately after the surgery and on the four subsequent days. The probe was usually held in contact with the skin flap surface on a point at 2.5 cm cranial from the flap base. On the seventh postoperative day, the percentage of necrotic area was measured and calculated. RESULTS: Group 1 reached an average necrotic area of 48.86%, Group 2 - 23.14%. After the statistic analysis, compared with the control group, Group 2 showed a statistically significant increase in survival area (p<0.001). CONCLUSION: The experimental model proved to be reliable to be used in the study of effects of low level laser therapy in random skin flap in rats.

Helium-neon laser in viability of random skin flap in rats

BACKGROUND AND OBJECTIVES

The purpose of this study was to determine the role of helium-neon (He-Ne) laser random skin flap viability in rats.

STUDY DESIGN/MATERIALS AND METHODS

Experimentally controlled randomized study. Forty-eight Wistar-EPM rats were used, weighed, and divided into 4 groups with 12 rats each. The random skin flap was performed measuring 10 x 4 cm, with a plastic sheet interposed between the flap and the donor site. The Group 1 (control) underwent sham irradiation with He-Ne laser. The Group 2 was submitted to laser irradiation, using the punctual contact technique on the skin flap surface. The Group 3 was submitted to laser irradiation surrounding the skin flap, and the Group 4 was submitted to laser irradiation both on the skin flap surface and around it. The experimental groups were submitted to He-Ne laser irradiation with 3 J/cm(2) energy density immediately after the surgery and for the four subsequent days. The percentage of necrotic area of the four groups was calculated at the 7th post-operative day, through a paper-template method.

RESULTS

Group 1 reached an average necrotic area of 48.86%; Group 2, 38.67%; Group 3, 35.34%; and Group 4, 22.61%. After the statistic analysis, results showed that all experimental groups reached statistically significant values when compared to the control group, and Group 4 was the best one, when compared to all groups of this study (P<0.001).

CONCLUSION

The He-Ne laser irradiation was efficient to increase random skin flap viability in rats.

[Phenomenological statistics of laser irradiation related metabolic changes in guinea pig livers]

In the past, dosimetric investigations on which hyperthermal therapy radiation planning for minimally invasive treatment of tumours were based were often limited to tissue coagulation. While heatshock proteins identified by biochemical basic research provided a fundamental knowledge of the thermal processes of tissue reactions between 42 degrees C and ca. 45 degrees C, the resulting understanding was insufficient to serve as a basis for radiation planning. For this reason, the Arrhenius formalism has so far been used as a good approximation for the complex description of the hyperthermal tissue reactions, with the activation energy being employed as statistic energy threshold for irreversible tissue coagulation. Our investigations were aimed at elucidating whether this formalism could be kept reproducible for tissue damage as temporal accumulation with an implicit biochemically balanced feedback mechanism, i.e. below the coagulation threshold. In our experiments we chose the fluorescence-technical measurement of the NADH concentration as a vital parameter to obtain a more informative statement in a preliminary phenomenological approach. The two most striking differences--as compared with the vitality measurement from the Arrhenius formalism--are the negligible variations in the damage integral (as compared with the phenomenological metabolic reactions acquired by cyclic heating), and the conclusion that the Arrhenius formalism as quasi-linear correlation between metabolic dynamics and tissue damage, will not hold.

Microvascular reconstruction of the hypopharynx: defect classification, treatment algorithm, and functional outcome based on 165 consecutive cases

The objectives of this study were three-fold: to develop a scheme for classification of hypopharyngeal defects, to establish a reconstructive algorithm based on this system, and to assess the functional outcome of such reconstruction. This study is a retrospective review of a 14-year experience with 165 consecutive microvascular reconstructions of the hypopharynx in 160 patients. The average patient age was 59 years (95 percent CI, 37 to 81). Thirty-four patients were operated on for recurrent disease; 71 had preoperative radiotherapy. Partial defects were reconstructed with radial forearm flaps (n = 52); circumferential defects were reconstructed with jejunum (n = 90); and extensive, noncircumferential longitudinal defects were reconstructed with rectus abdominis flaps (n = 23). The overall free flap success rate was 98 percent. Six flaps required reexploration, two of which were salvaged. The incidence of fistula was 7 percent and stricture, 4 percent. Preoperative radiotherapy was significantly associated with risk of recipient site complications (OR, 2.3; 95 percent CI, 1.0 to 5.0). Follow-up data were available on 95 percent of patients: 53 percent were able to tolerate an unrestricted diet, 23 percent a soft diet, 12 percent liquids only, and 12 percent were limited to tube feedings. The treatment algorithm for microvascular hypopharyngeal reconstruction is based on the type of defect with partial defects with radial forearm flaps, circumferential defects reconstructed with free jejunal flaps, and extensive, multilevel defects reconstructed with rectus abdominis myocutaneous flaps. Microvascular reconstruction of pharyngeal defects is highly successful with few postoperative complications. With appropriate flap selection, functional outcome can be optimized.

Intensity modulated versus non-intensity modulated radiotherapy in the treatment of the left breast and upper internal mammary lymph node chain: a comparative planning study

BACKGROUND AND PURPOSE

To compare and evaluate intensity modulated (IMRT) and non-intensity modulated radiotherapy techniques in the treatment of the left breast and upper internal mammary lymph node chain.

MATERIALS AND METHODS

The breast, upper internal mammary chain (IMC), heart and lungs were delineated on a computed tomography (CT)-scan for 12 patients. Three different treatment plans were created: (1) tangential photon fields with oblique IMC electron-photon fields with manually optimized beam weights and wedges, (2) wide split tangential photon fields with a heart block and computer optimized wedge angles, and (3) IMRT tangential photon fields. For the IMRT technique, an inverse planning program (KonRad) generated the intensity profiles and a clinical three-dimensional treatment planning system (U-MPlan) optimized the segment weights. U-MPlan calculated the dose distribution for all three techniques. The normal tissue complication probabilities (NTCPs) for the organs at risk (ORs) were calculated for comparison.

RESULTS

The average root mean square deviation of the differential dose-volume histogram of the breast planning target volume was 4.6, 3.9 and 3.5% and the average mean dose to the IMC was 97.2, 108.0 and 99.6% for the oblique electron, wide split tangent and IMRT techniques, respectively. The average NTCP for the ORs (i.e. heart and lungs) were comparable between the oblique electron and IMRT techniques (<or=0.7%). The wide split tangent technique resulted in higher NTCP values (>or=2%) for the ORs.

CONCLUSIONS

The lowest NTCP values were found with the oblique electron and the IMRT techniques. The IMRT technique had the best breast and IMC target coverage.

Submandibular gland transfer: a new method of preventing radiation-induced xerostomia

OBJECTIVE

Radiation-induced xerostomia is a significant morbidity of radiation therapy in the management of patients with head and neck cancers. We have recently reported a method of transfer of one submandibular gland to the submental space in a small pilot series of eligible surgical patients. The submental space was shielded during postoperative radiation therapy. The transferred gland continued to function after the completion of radiation therapy and none of the patients developed xerostomia. The purpose of this article is to present the technique of submandibular gland transfer in detail and to evaluate the postoperative survival and function of the transferred submandibular glands.

DESIGN

Prospective clinical trial.

METHODS

The submandibular gland was transferred on eligible patients as part of their surgical intervention. The patients were followed clinically, with salivary flow and radioisotope studies.

RESULTS

We performed the surgical transfer of the submandibular salivary gland in 24 of 25 patients placed on the protocol. All the glands survived transfer and functioned well postoperatively as demonstrated on the salivary flow and the radioisotope studies. The surgical transfer was relatively simple and added 45 minutes to the surgical procedure. There were no complications attributed to the submandibular gland transfer.

CONCLUSIONS

We have successfully demonstrated that the submandibular gland can be surgically transferred to the submental space with its function preserved. The gland seems to continue functioning even after radiation therapy with the appropriate shielding. This surgical transfer procedure has the potential to change the way we currently manage patients with head and neck cancer.

Effect of radiation on skin expansion and skin flap viability in pigs

The aim of the present study was to investigate the effect of radiation treatment both on skin tissue expansion with the chronic inflation of subcutaneous expanders and on skin flap viability in surgically delayed and expanded skin in the pig. One flank in each of six pigs (initially weighing 17 +/- 1.8 kg) was randomly assigned for radiation treatment, and the contralateral flank served as a nonirradiated control. Three mirror-image, 8 x 10 cm, rectangular templates were marked on each flank; these templates were randomly assigned to the construction of a delayed skin flap (group A), a skin flap raised on expanded skin (group B), or a skin flap raised on expanded skin with a capsulectomy before flap surgery (group C). Radiation treatment was performed using sequential radiation with three fractions per week (810 cGy/fraction) for 2 weeks, with a total dose of 4,860 cGy. Twelve weeks after radiation treatment, skin expanders (8 x 10 cm) were installed subcutaneously in the locations assigned for skin expansion. Skin expansion by the inflation of subcutaneous skin expanders with saline twice weekly was started 8 weeks later and lasted for 3 weeks. Two weeks after surgical delay and the last skin expansion, 8 x 20 cm skin flaps were raised on the locations assigned for delayed skin flaps, expanded skin flaps, and expanded skin flaps with a capsulectomy. Skin flap viability was assessed 24 hours later using a fluorescein dye-staining technique. Skin expansion by the inflation of subcutaneous expanders with saline was slower (p < 0.05) in the radiated skin (39 +/- 6 ml/filling) than in the nonirradiated control skin (51 +/- 6 ml/filling). Radiation reduced the overall area of expanded skin by 23 percent (p < 0.05) compared with the control. Radiation treatment also reduced skin viability by 36 percent (p < 0.05) in the delayed skin flaps, 27 percent (p = 0.10) in the expanded skin flaps, and 36 percent (p < 0.05) in the expanded skin flaps with a capsulectomy when compared with their contralateral, nonirradiated controls. There were no significant differences in skin viability among these three types of skin flaps within the radiated and nonirradiated groups. Taken together, these observations indicate that radiation treatment reduced the effectiveness of the surgical delay procedure, the amount of subcutaneous skin expansion (by an increase in skin area), and skin flap viability. However, a capsulectomy alone did not affect the viability of skin flaps raised on expanded skin.

[Biological mechanisms of late effects of ionizing radiations]

The daily practice of radiation oncology is increasingly influenced by the late tolerance of normal tissues. The treatment decision must be based on detailed arguments and the physician's duty to extensively inform his patients is emphasised every day. The incidence and severity of radiation-induced sequelae and late complications can be reduced by decreasing the total dose to the normal tissues, and by decreasing the dose protraction, provided that the interval between fractions remains longer than 6 to 8 hours. This approach yields a selective protection of late responding normal tissues, since tumours are less sensitive to the effects of fractionation. Despite its own limitations, the linear- quadratic model is nowadays the standard method to compare the biological effects of different radiation treatments.

Chronic radiation damage in the rat rectum: an analysis of the influences of fractionation, time and volume

PURPOSE

Analysis of four different sets of experiments performed by the G.S.F. group in Munich investigating the late tolerance of the rat rectum to external or intracavitary irradiation.

MATERIAL AND METHODS

The endpoint was late rectal stenosis in female Wistar rats. The raw data were fitted to the linear-quadratic model by means of a likelihood maximization method (Direct Analysis). The model was altered to allow for repopulation, incomplete repair, and varying irradiated lengths of the rectum.

RESULTS

Fractionation sensitivity was high or intermediate (alpha/beta ratio values [95% confidence limits] ranging from 2.67 [0.86, 4.80] to 6.65 [2.21, 11.73] Gy). Significant repopulation occurred when treatments were longer than 5 days (Dprolif equal to 0.61 [0.20, 1.47] and 1.08 [0.58, 1.90] Gy/day, in fractions of 4 Gy). Another interpretation is that radiosensitivity changed during treatment. Repair half-time estimates ranged between 1.84 [1.52, 2.34] and 5.02 [2.83, 21.7] h. Finally, the present analysis indicated that the smallest surviving compartment capable of tissue rescue was about 1/50 to 1/100 of a 1 cm high cylinder of the rectum wall.

CONCLUSIONS

The radiobiological features of late stenosis in the rats are consistent with combined injuries of early and late responding components of the rectal wall. This raises some concerns about the possible danger of hyperfractionated treatments, where the beneficial impact of fraction size reduction may be obviated for interfraction intervals that are too short. Also, accelerated irradiation may result in more late complications because of increased early reactions.

Quantitative clinical radiobiology

Based on a series of recent papers, a status is given of our current ability to quantify the radiobiology of human tumors and normal tissues. Progress has been made in the methods of analysis. This includes the introduction of 'direct' (maximum likelihood) analysis, incorporation of latent-time in the analyses, and statistical approaches to allow for the many factors of importance in predicting tumor-control probability or normal-tissue complications. Quantitative clinical radiobiology of normal tissues is reviewed with emphasis on fractionation sensitivity, repair kinetics, regeneration, latency, and the steepness of dose-response curves. In addition, combined modality treatment, functional endpoints, and the search for a correlation between the occurrence of different endpoints in the same individual are discussed. For tumors, quantitative analyses of fractionation sensitivity, repair kinetics, reoxygenation, and regeneration are reviewed. Other factors influencing local control are: tumor volume, histopathologic differentiation and hemoglobin concentration. Also, the steepness of the dose-response curve for tumors is discussed. Radiobiological strategies for improving radiotherapy are discussed with emphasis on non-standard fractionation and individualization of treatment schedules.

[The mutual effect of ultrasound stimulation and exogenous ATP on myocardial protection during cardiac arrest]

We have reported that ultrasound stimulations have a protective effect toward ischemic insult upon myocardial cells during cardioplegic arrest. However, the exact mechanism of ultrasound stimulation was not known. To elucidate this mechanism, we investigated the effect of ultrasound stimulation (UI) and/or 0.1 mMATP added to the cardioplegic solution (A) on ventricular function and adenine nucleotide changes in isolated perfused rat hearts. The hearts were perfused by working heart mode for 10 min. to determine baseline values of hemodynamic variables and they received infusion of cardioplegic solutions, followed by 20 min cardiac arrest with myocardial temperature 37 degrees C. Subsequently to the ischemic arrest, aerobic reperfusion was continued for 30 min. In group I, neither UI was irrigated nor ATP was added to cardioplegic solution. In group II and IV, ATP was added and in group III and IV, UI (1010 KHz, 0.25 W/cm2) was irrigated during cardiac arrest. Myocardial ATP was measured by Luciferase method. Myocardial ATP content after 20 min of cardiac arrest showed 12.4, 25.3, 14.5 and 32.5 (nmol/mg protein) in group I, II, III, and IV respectively, whereas it was 32.6 at the pre-ischemic cardiac arrest. The recovery of aortic output after 30 min of reperfusion revealed 30.9%, 78.9%, 79.6%, 85.4%. These data suggested the ATP depletion during cardiac arrest was attenuated by the UI and exogeneous ATP, resulted in the high recovery level of ventricular function during reperfusion.

A generalized formulation of the 'incomplete-repair' model for cell survival and tissue response to fractionated low dose-rate irradiation

A generalized equation for cell survival or tissue effects after fractionated low dose-rate irradiations, when there is incomplete repair between fractions and significant repair during fractions, is derived in terms of the h- and g-functions of the 'incomplete-repair' (IR) model. This model was developed originally from the concept of 'dose equivalent of incomplete repair', assuming that the repair of radiation damage is an exponential function of time and that the cell survival curve can be described adequately by the linear quadratic (LQ) formalism. The generalized incomplete-repair equation is shown to be equivalent to an expression derived by Dale et al. (1988) for analysis of tissue effects of fractionated irradiations at varying dose rates. The model is critically dependent on alpha/beta, repair half-time, treatment time and interfraction interval, and should therefore be regarded primarily as a tool for the analysis of fractionation and dose-rate effects in carefully designed radiobiological experiments, although it should also be useful in exploring, in a general way, the feasibility of clinical treatment protocols using fractionated low dose-rate treatments.

Predicted dose-latency relationships for early- and late-responding hierarchical tissues

Theoretical dose-latency relationships for the time to manifestation of radiation injury in a hierarchical (type H) tissue were investigated using mathematical modelling. Observable tissue injury was assumed to correspond to depletion of cells in the functional compartment to a critical level. The results illustrate that the latent times of an early-responding type H tissue can be dose-dependent, although the difference between the maximum and minimum latent times is fairly small; the dose-dependence occurs because the dose affects the rate at which cells enter the functional compartment from the proliferative compartment while the functional cells are initially shed from the tissue at a rate that is independent of dose, resulting in a net dose-dependence of functional cell loss. Dose-dependent latent times were also obtained for a hypothetical late-responding type H tissue, but the dose-dependence was much more pronounced than for the acutely responding tissue; the difference in latent times was nearly 3 months over a dose range of a few Gy. This illustrates that the experimentally observed dose-latency relationships for late-responding normal tissues, which have unknown renewal characteristics, are not inconsistent with the hypothesis that those tissues have a hierarchical tissue structure similar to that of early-responding tissues. The dose-latency relationship for early responses was influenced most strongly by the characteristics of the transit cells, whereas for the late responses it depended mainly on the characteristics of the stem cells. Residual injury in both early and late-responding tissues can be modelled on the basis of permanent depletion of the stem cell compartment, e.g. via depletion of the number of tissue-renewal units.

Response of human organs to single (or fractionated equivalent) doses of irradiation

Characteristics of the kinetics of radiation response of human tissues and organs are exemplified by effects in the testis and the ovary. Also, published dose-incidence curves for specified levels of injury in bone marrow, liver, bladder and lung are characterised in terms of single doses as well as single-dose equivalents calculated from fractionated doses using the alpha/beta equation. It is shown that these curves, analysed using a Poisson model, have slopes characterised by D0-equivalents ranging between 1.25 and 2.5 Gy. These values are higher or within the range of values reported in general for single-dose survival curves of human cells in primary culture (range of D0 values 0.7-1.8 Gy). This indicates that single-cell responses together with other complicating biological and statistical sources of heterogeneity under discussion, could form a basis for explaining the steepness of dose-incidence curves for organ injury after fractionated doses. With local organ irradiation, increase in the single-dose equivalent by 3-10 per cent would increase the complication rate from 5 per cent to 10 per cent. Higher dosage increases (by up to two times) apply to fractionated doses.

Fractionation parameters for human tissues and tumors

Time-dose factors such as fractionation sensitivity (alpha/beta) can sometimes be estimated from clinical data, when there is a wide variation in dose, fraction size, treatment time, etc. This report summarizes estimates of fractionation parameters derived from clinical results. Consistent with the animal data, alpha/beta is higher for acutely responding than for late-responding normal tissues. While many human tumors seem to be characterized by high alpha/beta values, there are exceptions (e.g. melanomas). Repair kinetics may be slower in human than in rodent skin and mucosa, but there are no hard and fast estimates of the repair halftime. Regeneration in head and neck tumors is equivalent to a daily dose of 1 Gy or less, while in the mucosa it is equivalent to approximately 1.8 Gy/day.

[Postradiation changes of active ion transport systems of the CNS. The effect of superlethal doses of ionizing radiation on the Na,K pump in surviving brain slices]

Active potassium ion transport in surviving sections of rat brain was irreversibly inhibited 6 min, 1 h and 6 h following whole-body single X irradiation. At the same time, the accumulation of products of lipid peroxidation and phospholipase hydrolysis was followed up during the development of radiation pathology. The relationship was noted between the postirradiation changes in the physicochemical status of lipids of the membrane and the impairment of its transport function.

Invasive bladder cancer. Strategies for cure and bladder preservation

At the present time, standard therapy for invasive bladder cancer includes radical cystectomy and urinary diversion. Clearly, there is a population of patients who can be rendered tumor free by combinations of irradiation and chemotherapy, or irradiation and surgery. These patients may not require total cystectomy to be cured. Only time and experience will tell which treatment regimens can provide both cure and preservation of the urinary bladder.

[Postradiation changes in the systems of active ion transport in the CNS. Potassium ion reaccumulation by surviving brain slices]

The data are reported concerning the effects of ionizing radiation (0.155 C/kg, 0.206 C/kg, and 0.31 C/kg), A2 phospholipase and short-chain fatty acids that are indicative of an essential contribution of a membrane lipid component to the effect of radiation on Na-K pump of the neuron and the universality of the mechanisms of action of ionizing radiation on organisms differing in radiosensitivity.

On the problem of the characterization of late effects by a linear-quadratic survival function. I. Theoretical and radiobiological aspects

Radiobiological data have been used for an analysis of acute and late tissue responses on the basis of a linear-quadratic survival function SLQ = exp(-alpha d -beta d2). Isoeffect curves of late effects exhibit a steeper slope than those for the corresponding acute effects, and, therefore, late effects may become an essential aspect in the radiotherapy of many kinds of tumours. In this communication, the theoretical and radiobiological view will be presented, whereas in a second part clinical applications will play a dominant role: Thus a statistical analysis of clinical observations has revealed that the volume factor of the irradiated tissue represents an important factor with regard to the characteristic average latency period, when clinical effects will become manifested.

Long-term storage of eight-cell mouse embryos at - 196 degrees C

Stocks of mutant mice have been reestablished from eight-cell embryos stored in liquid nitrogen for varying periods up to 11 years, and no evidence has been found of deterioration of survival with time of storage. Also, studies on the simulated cumulative effect of background radiation during storage failed to find any detrimental effect when embryos were exposed to the equivalent of about 2000 years of background radiation. However, in some cases embryos that carry mutant genes or chromosome anomalies tend to survive the freezing and thawing procedure less well than F1 hybrid embryos. Although this effect is probably independent of storage time, recent improvements in technique upon embryonic survival are to be welcomed.

Postoperative irradiation of fresh autogenic cancellous bone grafts

Discontinuity defects were created in the mandibles of dogs and then reconstructed immediately with fresh autogenic cancellous bone grafts and Dacron-urethane prostheses. The grafts were irradiated to a total dose of 5000 rads after waiting intervals of between 3 and 12 weeks. Nonirradiated grafts served as controls. The grafts were evaluated clinically, radiographically, and histologically. There was complete incorporation of all grafts, regardless of the interval between surgery and radiotherapy. There were no soft-tissue complications. The controls were distinguishable from the irradiated grafts only by the presence of hematopoietic bone marrow. Fibrofatty marrow was observed in the irradiated grafts. Theoretical support for this technique is found in the biology of cancellous bone grafting and the pathology of radiation injury. In view of the difficulties associated with mandibular bone grafting in preoperatively irradiated patients, a new method of reconstructing selected cancer patients who require both mandibular resection and radiotherapy is suggested.

Further studies on the effect of radiation during the storage of frozen 8-cell mouse embryos at -196 degrees C

Frozen 8-cell mouse embryos were treated with radiation doses of 0, 10, 50, 100 or 200 cGy gamma-rays at a dose rate of congruent to 5 cGy/day. After thawing the embryos were scored for normal morphological appearance and for development to morulae and blastocysts after 24 h in culture. Embryos from each treatment were then separately transferred to the uteri of pseudopregnant foster mothers which were killed at Day 14 of pregnancy. There was no effect of radiation on morphological appearance, development to morulae and blastocysts, implantation rate, or on the ratio of live fetuses to the number of transferred embryos. As there appeared to be no detrimental effect of up to 200 cGy on frozen 8-cell mouse embryos and, as this is the equivalent of congruent to 2000 years of background radiation, it is concluded that normal levels of background radiation would not be a hazard to the long-term storage of mammalian embryos.

Selective enhancement of radiation response in a C3H mammary carcinoma by cisplatin

The interaction between cisplatin and radiation was studied in a C3H mammary carcinoma and its surrounding normal skin. Treatment with 6 mg/kg of cisplatin given 30 mins before irradiation enhanced the radiation response in the tumor by a factor of 1.7, whereas the same drug treatment given immediately after or 4 hrs after irradiation only enhanced the effect by a factor of 1.2--1.3. No interaction between radiation and cisplatin was observed in the surrounding skin. It is hypothesized that in the C3H mammary carcinoma the prominent radiation-modifying effect of cisplatin given before radiation is due to a radiosensitization involving hypoxic tumor cells combined with a tumor cell-destructive effect of the drug itself.

Rat heart allograft survival with donor pretreatment

Heterotopic rat heart transplants from Ag-B compatible Fischer strain donors to Lewis recipients were monitored by daily ECG. The median survival time (MST) of control grafts was 12.8 days. Pretreatment of donors with whole-body radiation, cyclophosphamide, or antilymphocyte serum resulted in MST of 19.7, 18.0, and 17.8 days, respectively. Local irradiation of the heart alone did not prolong survival beyond control values, whereas whole-body irradiation with the heart shielded did, indicating that the prolongation achieved by donor pretreatment with radiation, at least, was a systemic rather than local effect. Only slight prolongation was achieved by donor radiation in the Ag-B incompatible BN to Lewis strain combination, demonstrating the importance of histocompatibility matching for the effectiveness of donor pretreatment.