Emmanuel van der Schueren

Direct Estimation of Latent Time for Radiation Injury in Late-responding Normal Tissues: Gut, Lung, and Spinal Cord

Mixture models are proposed for simultaneous analysis of the latency and fractionation characteristics of radiation injury in late-responding normal tissues. The method is an extension of the direct analysis for quantal response data. Conceptually, the application of the mixture model is based on the biological observation that over a wide range of doses a proportion of the irradiated subjects will never express damage. Mixture models allow the time of occurrence to be utilized in the analysis. Furthermore, this type of model takes time-censored observations into account in a natural way and provides an adequate framework for modelling and analysis of effect-dependent latency. Mixture models with complete and incomplete repair are applied to dose-incidence data for four late endpoints in rodents: death from radiation-induced pneumonitis, leg paralysis after spinal-cord irradiation, and radiation-induced rectal stenosis and anal discharge. Radiation-induced pneumonitis had an effect-dependent latency. The modelling of this phenomenon correlates well with the results of histologic studies. Interestingly, the ratio of hazard rates was not constant for this endpoint. The dominating feature in the latency of radiation injury to the spinal cord was a strong dependency on dose per fraction. After correction for this effect a tendency towards a longer latent time for lower effect levels was observed. For the rectal complications, there was no difference between latency with radiation only vs. radiation combined with cis-platin.

Does tumor control decrease by prolonging overall treatment time or interrupting treatment in laryngeal cancer

PURPOSE To evaluate treatment results of radiotherapy in laryngeal cancer and to retrospectively investigate the influence of treatment interruptions on local control rates. A multivariate analysis was performed to investigate the role of overall treatment time on local control rates. MATERIAL AND METHODS From 1962 to end 1986, 864 patients with cancer of the larynx were treated with primary radiotherapy, with a variation of doses and treatment times. In 352 patients a systematic interruption of 2 weeks was done after 50 Gy (split-course). Local control rates were calculated by the actuarial method. A multivariate analysis was subsequently performed in order to identify independent variables influencing local control rates. RESULTS The univariate analysis showed that in patients treated with a split-course schedule, local control rates were significantly lower in glottic cancer (p < 0.001), with differences of 7% in T1 (p = 0.05) and 11% in T2 (p = 0.11). In node-negative supraglottic cancer a difference of 10% (p = 0.16) was observed. The multivariate analysis showed the following factors to significantly influence local control: site, total dose, total treatment time, T and N stage. Split-course treatment was not an independently significant factor, probably caused by time being a stronger factor. In subgroup analysis, the effect of total treatment time remained statistically significant in T2 glottic cancer. CONCLUSION A significant negative influence of treatment interruption was seen in glottic cancer, and a trend toward significance in node-negative supraglottic cancer in univariate analysis. A multivariate analysis showed a negative influence of prolonging treatment time in the total patient group. The effect remained significant in T2 glottic cancer in subsequent subgroup analysis, possibly due to the fact that there is little variation in tumour volume in this group. In larger tumours, where there is substantial variation in tumour volume and a higher probability of heterogeneity in radiosensitivity, the effect of dose-time variations could be more difficult to discern.

SENSITIZATION OF ULTRAVIOLET‐IRRADIATED Escherichia coli K‐12 BY DIFFERENT AGARS: INHIBITION OF A rec AND exr GENE‐DEPENDENT BRANCH OF THE uvr GENE‐DEPENDENT EXCISION‐REPAIR PROCESS

Abstract—E. coli K‐12 wild‐type cells plated immediately after UV irradiation had a much lower survival on minimal medium solidified with agar‐agar No. 3 (Oxoid), purified agar (Difco) or ionagar (Colab) than on plates solidified with laboratory‐washed Noble agar (Difco). An intermediate survival was obtained on plates solidified with unwashed Noble agar (Difco). When irradiated cells were incubated in liquid minimal medium for various times before subsequent plating on agar‐agar No. 3, their survival increased rapidly and became identical to the survival of cells plated on washed Noble agar. The same phenomenon was found with polA 1 cells, but no differences in survival on the different agars were observed with uvrB, exrA, recA or recB cells. These‐ data suggest that a repair process dependent on the uvrB, recA, recB and exrA (but not the polA) gene products is inhibited when UV irradiated E. coli K‐12 cells are plated on minimal medium solidified with agar‐agar No. 3, purified agar or ionagar. This implies that the uvr gene‐dependent excision‐repair process consists of at least two branches, one controlled by the polA gene and a second controlled by the recA, recB and exrA genes and inhibitable by a substance present in certain agars. For maximum sensitivity, experiments designed to study chemical inhibitors of repair should use agar plates that do not themselves inhibit repair.

Influence of a UvrD Mutation on Survival and Repair of X-irradiated Escherichia Coli K-12 Cells

The presence of a uvrD mutation increased the X-ray sensitivities of E. coli wild-type and polA strains, but had no effect on the sensitivities of recA and recB strains, and little effect on a lexA strain. Incubation of irradiated cells in medium containing 2,4-dinitrophenol or chloramphenicol decreased the survival of wild-type and uvrD cells, but had no effect on the survival of recA, recB and lexA strains. Alkaline sucrose gradient sedimentation studies indicated that the uvrD strain is deficient in the growth-medium-dependent (Type III) repair of DNA single-strand breaks. These results indicate that the uvrD mutation inhibits certain rec+lex+-dependent repair processes, including the growth-medium-dependent (Type III) repair of X-ray-induced DNA single-strand breaks, but does not inhibit other rec+lex+-dependent processes that are sensitive to 2,4-dinitrophenol and chloramphenicol.

INHIBITION OF THE extra GENE-DEPENDENT BRANCH OF THE DNA EXCISION REPAIR SYSTEM IN ESCHERICHIA COLI K-12 BY 2, 4-DINITROPHENOL

Abstract— Ultraviolet (UV)‐irradiated E. coli K‐12 wild‐type cells were sensitized by a post‐irradiation treatment with 10‐2M 2, 4‐dinitrophenol (DNP). This effect was not seen in strains carrying a uvr mutation, suggesting that DN P interferes with the excision repair process. The polA strain was sensitized to the same extent as the wild‐type strain, while the exrA strain was not affected by DNP treatment.

Radiation dose homogeneity in an EORTC multicenter trial on breast irradiation.

The influence of the radiation dose on local control and cosmetic outcome in breast-conserving treatment for breast cancer is investigated in EORTC trial 2288110882. In this study 50 Gy is administered to the whole breast, and the effect of an additional dose to the tumor-bearing area (boost dose) is evaluated. The purpose of this analysis is to document the dose homogeneity of the radiation dose as reported in the first 1915 treatment forms, received at the EORTC Data Center. The dose to the prescription Point (A) was within 95 and 110% of 50 Gy in all but 13 (99.3%) patients (median dose 50 Gy) and the minimum and maximum doses in the central plane of the breast were within 95% and 110% of the dose to point A in 82% of patients. The dose to the tumor excision area (point B) was within the homogeneity criteria in 97% of patients, and the boost doses were consistent with randomization in 93% of cases. These data, based on one-third of the randomized patients in trial 22881/10882, demonstrate a high level of homogeneity in radiation doses, despite a number of ambiguities in the protocol, which were efficiently clarified a few months after the beginning of the trial. This high level of consistency is a remarkable achievement given the number of centers, the number of patients, and the number of countries involved in this trial.

EXCISION REPAIR AND MUTAGENESIS ARE COMPLEX PROCESSES

ABSTRACT Excision repair in Escherichia coli has been divided into two major pathways: a growth medium-independent, polA+-dependent pathway, and a growth medium, recA+, recB+, lexA+, polC+, uvrD+-dependent pathway. The former pathway handles most of the UV radiation-induced lesions, and produces short patches of repair replication. The latter pathway can be subdivided into two branches: a uurD+-dependent branch, and a uvrD+-independent branch. Long patch repair replication appears to occur via this latter branch; it is recA+, lexA+ and poiB+-dependent, and is inhibited in buffer or by chloramphenicol (CAP). The uvrD+gene product can also function independently of recA+ if UV-irradiated cells are held in buffer for a time before plating. Thus, liquid holding recovery (LHR), an excision repair process that is observed in recA strains, is blocked by a uvrD mutation, but is enhanced by lexA and recB mutations. UV radiation-induced mutations are produced by excision repair as well as postreplication repair. In either case, they appear to occur via two subbranches of these repair systems; one controlled by recB+ and the other by uvrD+.

Involvement of uvrD, exrA, and recB Genes in the Control of the Postreplicational Repair Process

Ultraviolet radiation survival studies support the hypothesis that the uvrD, exrA and recB mutations inhibit separate branches of the postreplicational repair process.

Changes in Survival of Escherichia Coli K-12 Cells as a Function of the Medium in Which They Are X-irradiated: A Rec and Exr Gene-dependent Phenomenon

SummaryEscherichia coli K-12 wild-type cells suspended in growth medium during X-irradiation have a higher survival than cells irradiated in buffer, whether irradiated in air or nitrogen. To determine if this response was due to differences in radiochemistry during irradiation or to differences in the amount of repair, we studied the influence of the irradiation medium on the survival of several repair-deficient mutants (recA, recB, exrA, uvrB, polA1 and polA1 exrA) and on the repair of radiation-induced DNA single-strand breaks in a wild-type strain.Our studies showed that the effect of the irradiation medium on survival was dependent on the presence of functional recA, recB, and exrA genes. Sedimentation studies, however, did not show a difference in the final amount of repair of DNA single-strand breaks after X-irradiation in buffer or growth medium. Thus, the increased X-ray sensitivity resulting from irradiation in buffer appears to be due to the inhibition of some rec and exr gene-dependent repair p...