Luc Dewit

Target volumes in radiotherapy for high-grade malignant glioma of the brain.

Delineation of the clinical target volume (CTV) in radiation treatment planning of high-grade glioma is a controversial issue. The use of computerized tomography (CT) and magnetic resonance imaging (MRI) has greatly improved the accuracy of tumor localization in three-dimensional planning. This review aims at critically analyzing available literature data in which tumor extent of high-grade glioma has been assessed using CT and/or MRI and relating this to postmortem observations. Attention is given to the pattern of tumor spread at initial presentation and to tumor recurrence pattern after external beam irradiation. Special emphasis is given to the site of tumor regrowth after radiation treatment in relation to the boundaries of the CTV. Guidelines for delineating CTV will be inferred from this information, taking data on radiation effects on the normal brain into account.

Ionizing radiation enhances platelet adhesion to the extracellular matrix of human endothelial cells by an increase in the release of von Willebrand factor.

The effect of radiation on the secretion of von Willebrand factor by endothelial cells was studied in a three-compartment culture system. The release of von Willebrand factor was significantly increased at 48 h after a single gamma-radiation dose of 20 Gy in both the luminal and abluminal direction by 23 (P < 0.05) and 41% (P < 0.02), respectively. To establish whether the enhanced production of von Willebrand factor affected the thrombogenicity of the extracellular matrix, platelet adhesion to the matrix produced by a monolayer of cultured endothelial cells during 48 h after irradiation was analyzed in a perfusion chamber at high shear rate (1300 s-1). Platelet adhesion was significantly increased by irradiation both in the presence and in the absence of plasmatic von Willebrand factor by 65 (P < 0.05) and 34.5% (P < 0.005), respectively. Incubation of the perfusate with a monoclonal antibody that blocks the binding of von Willebrand factor to platelet GPIb (CLB-RAg 35) resulted in an almost complete inhibition of platelet adhesion. These data indicate that radiation enhances platelet adhesion to the the extracellular matrix by an increase in the release of von Willebrand factor by endothelial cells. This event may be important in early radiation-induced vascular pathology.

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.

Radiosensitization by cisplatin of RIF1 tumour cells in vitro

The ability of cis-diamminedichloroplatinum (II) (c-DDP) to enhance radiation-induced cell killing was tested on oxic RIF1 tumour cells in monolayer culture. Marked radiosensitization of the survivors of a 1 h drug treatment was found with all c-DDP doses tested, with enhancement ratios increasing from 1.2 to 2.2 with increasing drug dose. Isobologram analyses showed that the interactions of c-DDP with X-rays were supra-additive. To test whether part of the enhancement was due to a selection of subpopulations, the diploid and tetraploid RIF1 cells, which normally coexist in culture, were separated by unit gravity velocity sedimentation, and by developing diploid and tetraploid clones. Both methods showed that there was little difference in either drug sensitivity or radiation sensitivity between diploid and tetraploid cells. DNA histograms obtained by flow cytometry showed little or no cycle progression during the 1 h drug treatment. These data indicate that the radiosensitization was not the result of the drug exposure leaving cells in a radiosensitive phase. The observed radiosensitization, therefore, appears to have resulted from a true drug/X-ray interaction.

Repair of sublethal radiation injury after multiple small doses in mouse kidney: An estimate of flexure dose

Functional kidney damage in mice was measured after a series of fractionated X-irradiations. Doses per fraction of 0.75-12.5 Gy were given as 2, 5, 10, 30, 40, 60, or 80 equal doses in a total treatment time of 4 weeks. Renal function (measured by clearance of 51CrEDTA or hematocrit levels) deteriorated progressively, in a dose related manner, from 20 to 46 weeks after the start of treatment. The changes in renal function versus time were fitted by a polynomial regression through all data and interpolated values for 51CrEDTA clearance were then calculated at 30 and 40 weeks after treatment. Steep dose response curves were obtained and these were used to calculate isoeffective doses for the different fractionation schedules. There was a marked increase in total isoeffective doses from 2-30 fractions and these data were well described by a linear quadratic (L.Q.) expression for damage with an alpha/beta ratio of 2.3 +/- 0.2 Gy. There was only a slight increase in the total isoeffect dose as the size of the dose per fraction was decreased below 2 Gy and the measured isoeffect doses after 40 to 80 fractions were lower than predicted on the basis of an L.Q. model assuming complete repair between successive irradiations. The flexure dose for mouse kidneys irradiated 3 times per day was, effectively, 1 to 2 Gy and hyperfractionation using lower doses per fraction did not lead to significant, additional repair.

Early and late damage in the mouse rectum after irradiation andcis-diamminedichloroplatinum(II)

Summary The effects of radiation and cis -diamminedichloroplatinum(II) (c-DDP) in the mouse rectum were assessedusing two functional endpoints (anal discharge/diarrhoea and body weight changes), one lethal endpoint (obstructive rectal stenosis) and a microscopic endpoint (semiquantitative histological scoring). After irradiation, anal discharge, diarrhoea and lethal rectal stenosis were found to be the result of submucosal fibrosis with a secondary mucosal ulcer due to mechanical damage by the faeces. Weight loss at both early and late times after irradiation seemed to be related to epithelial cellular depletion. c-DDP, when given in combination with X-rays, did not enhance the incidence of late anal discharge, diarrhoea or rectal stenosis. Using an arbitrary semiquantitative scale for measuring the degree and extent of late rectal injury, c-DDP sometimes seemed to postpone the expression of radiation damage in the rectum. This effect, however, might also be the result only of interexperimental variation. An increase by c-DDP in the early body weight loss after irradiation was also observed which could be explained by an additive effect in the rectal epithelium.

Evidence for a renovascular component in hypertensive patients with late radiation nephropathy

PURPOSE This study was undertaken to investigate whether the hypertension observed in a subgroup of patients with progressive radiation-induced nephropathy has a renovascular component. METHODS AND MATERIALS Fifteen patients with prospectively documented renal injury after high-dose radiation treatment for various abdominal malignancies were studied, 8 of them having hypertension. 99mTc-DTPA renography and plasma renin activity measurements were performed before and after an oral dose of 50 mg captopril. In patients with a positive captopril renography, a selective angiography was performed to exclude preexisting central renal artery stenosis and to assess the type and extent of the vascular changes. RESULTS The captopril 99mTc-DTPA renography demonstrated a longer time until maximal renal activity (Tmax) compared with the baseline study in five out of eight hypertensive patients. This increase in Tmax was observed in both high-dose (40 Gy/5.5 weeks) and in low-dose (12-13 Gy/3 weeks) irradiated kidneys. No increase in Tmax was observed in the normotensive patients. In the five hypertensive cases with an increased Tmax, selective angiography demonstrated severe stenotic and tortuous changes in the small intrarenal branches of the high-dose irradiated kidneys without stenosis of the main renal artery. Captopril induced an increase in peripheral plasma renin activity in the hypertensive group, but not in the normotensive patients. CONCLUSION These data suggest a radiation-induced hypertension, mediated by the renin-angiotensin system due to damage in predominantly small renal arteries. It was possible to demonstrate hypertensive changes with a captopril 99mTc-DTPA renography, even after presumed subthreshold radiation doses for clinical radiation nephropathy.

Amelioration of Radiation Nephropathy by Acetylsalicylic Acid

This investigation was carried out to assess the amelioration by two antithrombotic drugs of radiation nephropathy in mice. Mouse kidneys were given split-dose irradiation to total doses between 17 and 22 Gy. A first group of animals was given acetylsalicylic acid (ASA) in drinking water, a second received daltroban, a thromboxane A2/prostaglandin H2 receptor antagonist, and a third received normal tap water, serving as a control. Both antithrombotic drugs were started 1 week prior to the irradiation and were given throughout the whole follow-up period. Renal function was assessed every 4 weeks from 18 weeks after the start of irradiation onwards by measuring the [51Cr] EDTA retention and haematocrit. The dose of ASA (600 mg/kg/day) caused an inhibition of thromboxane A2 and prostacyclin biosynthesis to 19 +/- 10 (mean +/- SEM) and 85 +/- 22%, respectively, as assessed by the excretion of their urinary metabolites. A significant sparing effect on the renal function after irradiation was observed in the ASA-treated animals. Using the latency time to reach 4% residual plasma activity of [51Cr] EDTA, a dose-modifying factor of 1.19 was calculated. No effect was seen with daltroban (10 mg/kg/day). Histopathological analysis of the kidneys at 12 months after irradiation demonstrated a substantially lower level of damage in the ASA-treated mice compared with daltroban-treated and radiation-only animals. These data indicate that long-term treatment with ASA is effective in reducing renal functional impairment after irradiation.

HPV-negative squamous cell carcinoma of the anal canal is unresponsive to standard treatment and frequently carries disruptive mutations in TP53

Background:Human papillomavirus (HPV), p16 expression, and TP53 mutations are known prognostic factors in head and neck squamous cell carcinoma, but their role in squamous cell carcinoma of the anal canal (SCCAC) is less well established. The objective of this study was to determine the prognostic significance of tumour HPV status, p16 and p53 expression, and mutations in TP53 in patients with SCCAC receiving (chemo)radiotherapy.Methods:Human papillomavirus DNA was determined using an INNO-LiPA-based assay in tumour tissue of 107 patients with locally advanced SCCAC. Patients were treated with radiotherapy, with or without concurrent chemotherapy consisting of a fluoropyrimidine and mitomycin C. Expression of p16 and p53 was determined using immunohistochemistry. Exons 2–11 of TP53 in tumour tissue were sequenced.Results:DNA of high-risk HPV types was detected in 93 out of 107 tumours (87%), all of which overexpressed p16 (HPV+/p16+). Of 14 HPV-negative (HPV−) tumours (13%), 10 (9%) were p16-negative (HPV−/p16−) and 4 (4%) overexpressed p16 (HPV−/p16+). Patients with HPV−/p16− disease had inferior 3-year locoregional control (LRC) (15%) compared with patients with HPV+/p16+ tumours (82%, P<0.001) and HPV−/p16+ tumours (75%, P=0.078). Similarly, 3-year overall survival (OS) was 35% (HPV−/p16−) vs 87% (HPV+/p16+, P<0.001) and 75% (HPV−/p16+, P=0.219). Disruptive mutations in TP53 were found in 80% of HPV−/p16− tumours vs 6% of HPV+/p16+ tumours (P<0.001). In multivariate analysis, HPV−/p16− status was an independent predictor of inferior LRC and OS.Conclusions:HPV− tumours are frequently TP53 mutated. HPV−/p16− status is a strong predictor for reduced LRC and OS, and alternative treatment strategies for patients with HPV−/p16− disease need to be explored.

Thyroid function 10-18 years after mantle field irradiation for Hodgkin's disease.

Thyroid function was measured in 81 patients who had been curatively irradiated on a mantle field for Hodgkins disease 10-18 years ago. 47 patients (58%) had elevated levels of thyroid stimulating hormone, indicating hypofunction of the thyroid gland, compared with 4.6% of controls (hospital visitors) matched for age and sex. The mean free thyroxine index (FTI) was significantly lower in patients than in controls, but all FTI values were still normal. Age at the time of irradiation, sex, time since irradiation and administration of chemotherapy were not significant factors in the development of thyroid dysfunction. A life-long awareness of the possibility of insidiously developing myxedema in these patients is strongly advocated.