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Results for “Radiation Tolerance”

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PubMed1982

Implications of the quadratic cell survival curve and human skin radiation "tolerance doses" on fractionation and superfractionation dose selection.

An analysis of early published multifraction orthovoltage human acute skin irradiation tolerance isoeffect doses is presented. It indicates that human acute skin radiation reactions may result from the repetition, with each dose fraction, of a cell survival curve of the form: S = e-(alpha D + beta D2) The analysis also shows no need for an independent proliferation related time factor for skin, for daily treatments of six weeks or less in duration. The value obtained for the constant beta/alpha for orthovoltage irradiation from these data is 2.9 x 10(-3) rad-1 for the cell line determining acute skin tolerance. A radiation isoeffect relationship, based on the quadractic cell survival curve, is introduced for human skin. This relationship has some advantages over the nominal standard dose (NSD). First, its use is not restricted to tolerance level reactions. Second, a modification of the relationship, which is also introduced, may be employed in the selection of doses per treatment when irradiation dose fractions are administered at short intervals where repair of sublethal injury is incomplete.

Cell Survival↗
PubMed2001

Impact of pulmonary metastases of the R1H-tumour on radiation tolerance of rat lung.

PURPOSE: The aim was to investigate the influence of pulmonary metastases of the rhabdomyosarcoma R1H on the radiation response of the lung of the WAG/Rij rat. MATERIAL AND METHODS: Three groups of animals were investigated: metastases-free animals treated with fractionated irradiation of the lungs; metastases-bearing animals receiving no irradiation; and metastases-bearing animals treated with fractionated irradiation initiated 14, 21 or 28 days after induction of pulmonary metastases of the R1H-tumour by i.v. injection of viable tumour cells. Metastases were thus treated at various well-defined sizes. Total doses of 20-60Gy were applied in fractions of 2 Gy within 11 days. Complication rate and survival time were used as endpoints. RESULTS: About 2 months after onset of irradiation treatment, animals had to be sacrificed because of severe respiratory distress either caused by irradiation-induced lung damage (median 57 days, range 36-77 days), or because of development of lung metastases (65, 20-160 days). A decrease of the ED(50) (dose required to induce lethal lung damage in 50% of irradiated animals) was determined for metastases-bearing animals. This effect increased with metastatic volume. CONCLUSIONS: The results suggest that the presence of tumours in the lung decreased the lung tolerance to radiation. This effect can hardly be explained by a reduction in functional lung volume by metastatic volume.

Animals↗
PubMed1989

Radiation tolerance of the cervical spinal cord.

The incidence of permanent injury to the spinal cord as a complication of radiation therapy generally correlates positively with total radiation dosage. However, several reports in the literature have indicated that fraction size is also an important factor in the development or nondevelopment of late injuries in normal tissue. To determine the effect of fraction size on the incidence of radiation-induced spinal cord injuries, we reviewed 144 cases of head and neck cancer treated at our institution between 1971 and 1980 with radiation greater than 5600 cGy to a portion of the cervical spinal cord. Most of these patients received greater than or equal to 6000 cGy, with fraction sizes ranging from 133 cGy to 200 cGy. Fifty-three of the 144 patients have been followed up for 2 years or more. Nearly half of these (26 patients) received greater than 6000 cGy with fraction sizes of 133 cGy to 180 cGy. Only 1 of the 53 (1.9%) has sustained permanent spinal cord injury; 20 months after completion of radiation treatments he developed Brown-Séquard syndrome. Our experience suggests that radiation injuries to the spinal cord correlate not only with total radiation dosage, but also with fraction size; low fraction sizes appear to decrease the incidence of such injuries.

Head and Neck Neoplasms↗
PubMedDate not supplied

[Formal kinetic treatment of the possible role of proteins in DNA radiation tolerance, protection and sensitization].

The formal-kinetic calculations have been made of the postirradiation behaviour of a "protein-DNA" water system with marked variations in protein and DNA concentrations. Protein is a strong competitive acceptor of active products of radiolysis of water and free radicals of DNA. The radioresistance of DNA in such a system and the influence of mercaptoethylamine, sensitizers and oxygen on DNA injury are discussed. The results of the calculations are compared with the data on the composition of cell nuclei and the data on the comparative radioresistance of cells, cell cycle, protective effects, and sensitization. In most cases, the results of the calculations do not contradict the experimental data. It is assumed that the protein protection may be the major factor in considering the endogenous radioresistance.

DNA↗
PubMed1998

Radiation tolerance of transverse rectus abdominis myocutaneous-free flaps used in immediate breast reconstruction.

The authors determine the effects of postoperative radiation therapy on flap and local control outcomes in patients who have undergone immediate transverse rectus abdominis myocutaneous (TRAM)-free flap reconstruction after modified radical mastectomy for locally advanced breast cancer. Details of surgery, chemotherapy, and radiation therapy for 21 patients who had undergone immediate TRAM-free flap reconstruction after modified radical mastectomy were gathered retrospectively. The outcomes examined were flap complications, overall cosmesis, and local recurrence rate. Radiation therapy was indicated for large primary tumors (T3-T4), close or positive margins, or extensive nodal disease. With a mean follow-up interval of 19 months, there have been no flap complications or losses. Cosmesis was rated as excellent by 60% of patients, good by 30%, and fair by the remaining 10%. Three patients thought that radiation had improved cosmesis, one noted worse cosmesis, and the remainder thought it had no effect on cosmesis. The local control rate was 86%. Postreconstruction irradiation of TRAM-free flaps used in immediate reconstruction for locally advanced breast cancer appears safe and cosmetically acceptable.

Adult↗
PubMed1994

Influence of combined use of nicotinamide and carbogen on rat spinal cord radiation tolerance.

The effect of combining oxygen or carbogen breathing with the systemic administration of nicotinamide (NA) on spinal cord tolerance in Ethrane anesthetised male WAG/Rij rats has been investigated. Ten fraction experiments were carried out with daily (24 h between fractions) and twice a day fractionation (8 h between fractions). Nicotinamide (500 mg/kg) was injected 1 h prior to each irradiation. In addition, a 10-fraction experiment with daily intervals was carried out in which NA was added immediately after irradiation under carbogen breathing conditions. Single dose irradiations showed a minimal decrease in ED50 from 21 Gy in oxygen conditions to 19.9 Gy in carbogen conditions and 19.4 Gy when combined with NA. In the fractionation experiments, comparing the response to irradiation in oxygen (O) and nicotinamide oxygen (NO) conditions for the 24-h interval experiment, the ED50 for O was 61.6 Gy compared with 54.5 Gy for NO. When carbogen (C) was compared with nicotinamide carbogen (NC), the ED50 for C was 62.3 Gy and 53.9 Gy for NC. When NA was administered immediately after irradiation under carbogen breathing conditions the ED50 increased to 57.8 Gy. For twice a day fractionation the modifying effect of nicotinamide was similar to that observed for daily fractionation (ED50 of 57.9 Gy for O, 57 Gy for C and 50.9 Gy for CN), when corrected for incomplete repair in between the two fractions given on 1 day.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1989

Effects of high dose intraperitoneal cytosine arabinoside on the radiation tolerance of the rat spinal cord.

The effect of intraperitoneal high dose (9 g/kg) Cytosine Arabinoside (Ara-C) on the early delayed radiation response of the rat cervical spinal cord has been studied. When given 2 hrs before irradiation, systemically administered Ara-C significantly reduces the isoeffect doses for the induction of paralysis due to white matter necrosis by a factor of approximately 1.2 for both a single irradiation treatment and for a two fraction irradiation with 24 hr interval. No effect on the latency time to develop paralysis was recorded.

Animals↗