Oral

presentations

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GENE DELETION IN MURINE TUMOURS DETECTED BY DNA FINGERPRINTING

MECHANISMS OF REPAIR OF APURINIC/APYRIMIDINIC (AP) SITES IN DNA BY HUMAN CELL EXTRACTS.

D. Tarin, Sylvia Kocialkowski, Mary M McMenamin University of Oxford

A. PRICE & T.LINDAHL, IMPERIAL CANCER RESEARCH FUND, CLARE HALL LABORATORIES, SOUTH MIMMS, HERTS.

Genetic fingerprinting has been used in this study to search for genetic alterations involved in tumour formation and metastasis. Fingerprints are patterns of bands obtained when Southern blots of genomic DNA are probed with labelled minisatellite probes. They are specific for a given individual and identical in all normal tissues. We have compared the fingerprints of tumours of several organs and metastases in C3H/Avy mice with that of each host. These mice are extremely susceptible to the mammary Infected animals all develop these tumours, tumour virus. 30% of which are spontaneously metastatic. Virus-free animals frequently develop hepatomas but rarely mammary tumours. As C3H/Avy is an inbred line, all animals have very similar fingerprints, which has facilitated analysis. We have examined 12 mammary tumours and 15 hepatomas and in all of these have observed the absence, or substantial reduction, of a single band of approximately 6kb, present in normal tissue. So far we have not observed additional abnormalities in metastases. The deletion of a similar allele in tumours of different organs and aetiologies suggested that the locus is involved in the control of normal cell proliferation and behaviour. Attempts to clone related sequences are now in progress. The contribution of this approach is that it enables simultaneous examination of many loci and is concerned only with naturally-occurring lesions which, by definition, must be free of artifacts induced by experimental manipulation.

DNA is subject to the introduction of many forms of damage which produce potentially cytotoxic or mutagenic lesions requiring efficient repair. AP sites are among the commonest spontaneous lesions, but are also important consequences of therapeutic modalities such as alkylating agents and ionising radiation, both directly and via the repair of DNA base damage. In prokaryotes and eukaryotes, AP sites are repaired by a highly conserved pathway of DNA glycosylases, AP endonucleases, DNA polymerases and DNA ligases. An essential intermediate step of this pathway is the excision of the terminal 5'-dRp residue resulting from the action of AP endonucleases. In E. coli this step is catalysed by a DNA deoxyribophosphodiesterase (dRpase). We have fractionated human cell extracts by gel filtration and hydrophobic chromatography to determine what activities are responsible for this step in eukaryotes. The major activity is a Mg2+-dependent enzyme of about 45 kDa, localised to the cell nucleus, which catalyses the hydrolysis of the phosphodiester bond 3' to the terminal 5'-dRp residue, has no 5'-phosphatase or 5'->3' exonuclease activity and is separate from the major AP endonuclease. This enzyme is closely analogous in function and charactenstics to the E. co#i dRpase. The terminal 5'-dRp residue can also be removed by the major nuclear 5'->3 exonuclease, DNase IV, as part of a small oligonucleotide and by nonenzymatic 5-elimination promoted by polyamines or basic proteins, but these processes are less efficient than the action of the human dRpase. Thus, this step of the base excision repair pathway appears subject to evolutionary conservation. Further understanding of the mechanisms of repair of DNA lesions caused by common cancer therapeutic agents, and a search for inhibitors of repair enzymes, may allow for improvements in the specificity and efficacy of cancer therapies.

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PULSED-FIELD GEL ELECTROPHORESIS - A NEW MOLECULAR ASSAY OF DNA DAMAGE

DNA DOUBLE STRAND BREAK REJOINING IN HUMAN TUMOURS OF DIFFERING RADIOSENSmVITY.

S.J. Whitaker and T.J. McMillan, Institute of Cancer Research, Sutton, Surrey.

Gillian Ross and Robert Brown. Radiation and Medical Oncology, Glasgow University.

Pulsed-field gel electrophoresis (PFGE) is a recent innovation which allows separation of large DNA molecules. Here it has been explored as a measure of DNA strand breakage induced by ionising radiation. When PFGE is performed after neutral pH (7.5) cell lysis it is specific for DNA double-strand breaks (dsb's). 14C-thymidine pre-labelled cells are encapsulated in agarose plugs and irradiated on ice to measure initial dsb induction or at 370C with incubation for repair assays. Following cell lysis the plugs are loaded into the electrophoresis gel and the level of dsb is inferred from the fraction of total DNA extracted from the plugs. When run for 4 days damage is detectable from doses as low as lGy. The amount of initial dsb was found to vary within one human tumour cell line when irradiated under oxygenated and hypoxic conditions. An OER of 2.0 was found on clonogenic assay (at a surviving fraction of 0.1). By PFGE the OER was 4 with dsb induction frequencies of approximately 5 dsb/bp/Gy (oxic) and 1.2 dsb/bp/Gy (hypoxic). Also a higher level of induced dsb's were seen in a radiosensitive neuroblastoma line (HX-142) than in the radioresistant bladder line (RT-112). The rate of dsb rejoining has been measured in 3 human tumour lines. After 2OGy irradiation dsb's were

The molecular basis of the dffferences In radlosensitivity observed In human tumours at clinically relevant doses (2Gy) remains unclear.We have Investigated the ability of human tumour cells of widely differing cellular radlosensitivity (neuroblastoma;ovarian carcinoma;glloma) to rejoin DNA double strand breaks(dsb).This is a class of radiation-induced DNA lesions whose fate correlates closely with cell death.

The plasmid reconstitution assay measures the ability of nuclear protein extracts derived from human cells to rejoin a recominant plasmid DNA molecule, bearing selectable marker genes, In which dsb of defined chemistry have been produced by enzymatic digestionAccurate repair enables the plasmid molecule to confer ampicillin resistance and LacZ gene function on JM83 E.coll transformants.Data has been pooled from a minimum of 3 Independent nuclear extract preparations on each of 4 human tumour lines.No significant difference has been detected In maximal rejoining of cohesive dsb, or fidelity of repair, between neuroblastoma and giloma cell lines.The possibility of differential repair Induction Is being examined.

repaired with half-times of 30-45 minutes. The amount of dsb's unrepaired varied from 10% to 50% but this was not reflected by differences in cellular sensitivity. PFGE is becoming the most sensitive and widely applicable assay for DNA dsb induction and repair in human tumour cells.

it Is suggested that radiosensitive tumours may differ In induction of DNA damage at critical sites, or be less tolerant of a residual, post-repair level of genomic damage than most epithelial tumours.These areas are the subject of continuing investigation.

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DEVELOPMENT OF A RAT TUMOUR SYSTEM FOR VASCULAR STUDIES IN WHICH THE MICROCIRCULATION ORIGINATES FROM A SINGLE ARTERY AND VEIN. G M Tozerl, K M Shaffil, and V J Cunningham2 ICRC Gray Laboratory, Mount Vernon Hospital, Northwood, Middlesex. 2MRC Cyclotron Unit, Hammersmith Hospital, London.

NUCLEOID ANALYSIS AS A PREDICTOR OF RESPONSE TO RADIOTHERAPY IN PATIENTS WITH MUSCLE INVASIVE BLADDER CANCER.

T H Lynch, P Anderson, B waymont, R P Beaney, A T M Vaughan and D M A. Wallace. Queen Elizabeth Hospital, Birmingham and Loyola

University Medical School, Chicago. Flow Cytometric Nucleoid Analysis (FCNA) is a technique used by cell biologists to detect radiation damage to cells in vitro. Nucleoids contain supercoiLed DNA attached to the nuclear protein matrix and those extracted from cells which have been exposed to radiation are larger than those extracted from non-irradiated cells. The purpose of this study is to determine if the technique of FCNA can be applied to patients with muscle invasive transitional cell carcinoma of the bladder to predict tumour radiosensitivity.

The efficiency of the tumour blood supply is an important determinant of the outcome of tumour therapy. Chemical manipulation of tumour blood flow for therapeutic benefit is therefore of considerable interest. However, results from these studies are often conflicting or difficult to interpret. A system, based on that described by Grantham et al. (1973)3, has been developed for growing rat tumours within silicon chambers such that only a single artery and vein (r. epigastric a. and v. ) supply the tumour with blood. This will be used for a systematic investigation of the response of tumour vasculature to vasoactive agents. A system for cannulating and suturing blood vessels around the tumour site is described such that agents can be administered either systemically or directly to the tumour via the single artery.

We have analysed tumour specimens from 100 patients with invasive bladder cancer. Tunour samples were received from either transurethral resection samples or urine. All specimens were analysed fresh without any form of fixative. Single cell suspensions were prepared and irradiated with a cobalt 60 gamna source and analyzed on the Flow Cytometer. The degree of nuclear expansion is compared to the subsequent local tunour response at 3 and 6 months following radiotherapy.

Blood flow to the P22 tumour in BD9 rats has been measured using the uptake into the tumour of the readily diffusible tracer iodo-antipyrine labelled with 14C for autoradiography (14C-IAP) or 125I (125I-IAP) for external y-counting. Blood flow to tumours growing in silicon chambers has been found to be similar to that for tumours growing in the subcutaneous site without chambers (0.42 ± 0.07 mls g-1 min-1). Autoradiography enabled the regional distribution of blood flow within tumours to be determined. External y-counting enabled blood flow measurements to be made repeatedly in the same animal. It also provided a means for correcting blood flow measurements for artefacts introduced into the calculations by the use of plastic cannulae for blood sampling.

We have initial results on follow-up in 30 patients at three and six months after completion of radical radiotherapy. These reveal that radiosensitivity in-vitro as determined by nucleoid expansion correlates well with the clinical response of the patient to treatment. 85% of those with an expansion greater than 10% were clear of tumour whereas 80% of those with an expansion less than 10% had residual disease as determined cystoscopically. This technique can be applied using voided urine or TUR samples of tumour and gives a result within hours. It may therefore be of

Preliminary blood flow measurements in these tumours are encouraging for a future study into methods for manipulation of tumour blood flow for therapeutic benefit.

practical benefit in seLecting patients for radical radiotherapy as opposed to other treatment modalities.

3Grantham, F.H. et al (1973) J. Natl. Cancer Inst. 50: 1381-1383 This work is supported by the Cancer Research Campaign

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08 Immunodetection of hypoxic cells in solid experimental tumours

DETECTION OF ALLELE LOSS IN OVARIAN CANCER

R.J. Hodgkiss, E. Kelleher, G.D. Wilson, M.R.L Stratford & tJ. Parrick Cancer Research Campaign Gray Laboratory, Mount Vernon Hospital, Northwood, Middlesex. tDept. of Chemistry, Brunel University, Uxbridge, Middlesex. The presence of hypoxic cells in poorly vascularised regions of tumours may contribute to failures of radiotherapy to achieve local control. A clinical test for hypoxia could facilitate the selection of patients most likely to benefit from adjuvants to radiotherapy such as hypoxic cell sensitizers and normobaric or hyperbaric oxygen. Hypoxic cells can be identified in experimental tumours by administration of a 2-nitroimidazole (NITP) which has an immunologically recognisable side-chain (theophylline). Bioreductive binding of the nitroimidazole to cellular macromolecules immobilizes the side-chain, which can then be quantified by immunofluorescent staining and flow cytometry of cell suspensions. Studies carried out in vitro show the oxygen-dependence of metabolic binding to cells is similar to that of radiosensitivity with 'K' values of 1400 ppm and 3800 ppm respectively. The probe is of low toxicity in vivo and has little effect of body temperature, breathing rate and blood flow. Cells from disaggregated tumours contain less of the bound probe if the mice were breathing carbogen (95% 02) at the time of administration of NITP compared with air (21% 02). Simultaneous fluorescent DNA staining allows the distribution of hypoxia throughout the cell cycle, and in diploid (normal) and aneuploid (tumour) cells to be analysed. The spatial distribution of NITP in tumours can be demonstrated by immunohistochemical staining of frozen sections. The probe is bound in the outer cells in tumour cords, typically, 5-6 cell diameters from blood vessels and binding does not extend into necrotic material. Immunohistochemical staining for Budr shows that the labelled cells, actively synthesising DNA, are located much closer to the blood vessels than the hypoxic cells. This work is supported by the Cancer Research Campaign '

Milner. B.1,Haites, N.", Kelly, K.1, McKenzie, S.,1 Hall, M.0, Kitchener, H.a, Parkin, D.'and Johnston, A.' MED. GENETICS1/OBS. & GYNAE.E, Foresterhill, ABERDEEN. DNA has been analysed from 44 ovarian tumours, of which 22 were malignant and 12 were of borderline malignancy. Using a panel of chromosome 17 probes tumour and normal DNA have been compared in a 'loss of heterozygosity' study. All malignant tumours proved to be informative for at least two of these chromosomal markers, demonstrating allele loss as shown in the table below.

DNA probe pYNZ22 pYNH37.3

pMCT35.1 pBHP53 pTHH59

No. of tumours showing loss

(17pl3.3) (17pl3.3) (17pI3. 1) (17p13.1) (17q23-qter)

12/22 1/1 4/8 2/9 10/17

(55%) (100%) (50%) (22%) (59%)

None of the benign or borderline tumours were seen to lose alleles at these loci, apart from one benign tumour which appeared to have lost a copy of pBHP53. Steps are currently being taken to characterize in all tumours, the sequence of the p53 gene, which maps to chromosome 17p, using PCR amplification and direct sequencing. Work has also been started to assess the allele loss status for chromosome 18 and other candidate anti-oncogene loci in the same tumours. Loss of chromosome lBq material has been found to be common in other cancers, including breast and colon cancer.

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A NEW ANTIBODY-PHOTOSENSITISER CONJUGATE; EXPERIMENTAL

EVIDENCE FOR USE AGAINST LOCALLY RECURRENT CANCERS.

IMPROVED PHARMACOKINETICS OF BIOREDUCTIVE PRODRUG RB 6145 COMPARED TO THE ACTIVE AZIRIDINYL NITROMIDAZOLE RSU 1069: A MAJOR CONTRIBUTION TOWARDS FAVOURABLE ANTITUMOUR SELECTIVITY.

J W Dawson, J Morgan, H Barr, B R Davidson, F Savage, A J MacRobert, C Dean, P B Boulos. University College London.

Paul Workman* and Michael Binger, MRC Clinical Oncology and Radiotherapeutics Unit, MRC Centre, Hills Road, Cambridge CB2 2QH, U.K.

Adjuvant therapies have been unsuccessful in eradicating residual cells following 'curative' resection of colorectal and breast cancers. Photodynamic therapy has been widely used to treat cancer but is limited by poor selectivity of photosensitiser for tumour and cutaneous side-effects. The tumour localisation and cytotoxicity of a photosensitiser conjugated to a monoclonal antibody (MAb) has been investigated in vitro and in vivo to determine whether this is a suitable technique for the elimination of micro-deposits of cancer.

RSU 1069 is a 'mixed-function' hypoxic cell cytotoxin and sensitizer by virtue of containing both a bioreducible nitro group and an alkylating aziridine function. This agent exhibited potent antitumour activity in mice, but clinical exposures were limited by acute gastrointestinal toxicity. Haloalkylamino prodrugs developed by Adams and colleagues maintain therapeutic effectiveness, but have reduced toxicity, and analogue RB 6145 shows particular promise for clinical development (Jenkins et al, J Med Chem 33:2603, 1990). RB 6145 releases RSU 1069 by an intramolecular reaction. Because of the importance of drug disposition behaviour, we have compared the pharmacokinetic profile of RB 6145 with that of RSU 1069 in C3H mice with id KHT tumours. A new gradient reverse-phase HPLC method was developed for the 2 drugs and their metabolites. Following a dose of 0.5 mmoles/kg, RB 6145 gave peak plasma levels of 50 tsg/ml RSU 1069, about half that seen following an equimolar dose of RSU 1069 itself. A similar 2fold decrease was seen for plasma AUC. No RB 6145 prodrug was detectable, but an oxazolidinone metabolite, formed by reaction of prodrug with HC03-, was present in equal amounts to RSU 1069. Both were cleared from plasma with the t1/2 of 25 min. Tumour levels of RSU 1069 after prodrug were around 40% of the plasma level. The peak of 6 tig/g was 1.6-fold lower than after RSU 1069 itself and the tumour AUC was 1.5 lower. More similar to the reduction in plasma exposure, the brain AUC was 1.8-fold lower. We propose that the improved antitumour specificity of RB 6145 compared to RSU 1069 may be explained in large part by the more favourable ratio of active drug exposure in tumour vis a vis plasma and brain.

The photosensitiser 'Phthalocyanine' has been conjugated to the MAbs UC39.4 and ICR2 which are targeted against the rat colorectal cancer (RCC5) and human breast and ovarian cell lines (MCF7 and OVCAR-3). In vitro cytotoxicity was assessed by incubating cultured cells with conjugate or free photosensitiser and exposure to 18J/cm2 red light. Viable cells were quantified using the Mono Tetrazolium Thiazolol reduction assay. Tumour specificity and uptake of the conjugate was assessed in a nude mouse xenograft model using quantitative photometric fluorescence analysis. In vitro cytotoxicity of the conjugate was 1000x greater than free phthalocyanine (90% cell-kill using conjugated phthalocyanine at 10-9Molar compared with free phthalocyanine at 10-6Molar) in all cell lines. Immunoreactivity assessed by non-competitive binding assay was impaired by conjugation but uptake of conjugated photosensitiser in vitro and in vivo showed tumour:normal ratios of 1000:1 (conventional PDT achieves ratios of only 2:1). The conjugate was stable in vivo and in vitro, measured by chromatography (H P LC).

Targeting a photosensitiser and illumination at operation or endoscopy may eradicate microscopic deposits of cancer and improve local recurrence.

Present address: CRC Dept of Medical Oncology, Alexander Stone Building, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD U.K.

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INHIBITORY EFFECT OF SOMATOSTATIN ANALOGUE RC-160 ON EGF AND TRANSFORMING GROWTH FACTOR ALPHA (TGF-A) STIMULATED PANCREATIC CANCER GROWTH IN VIVO NM Davies, P Kapur, J Gillespie, AV Schallyt PJ Guillou and GJ Poston, Academic Surgical Unit, St Mary's Hospital, London;*Tulane University & VA Medical Center,New Orleans. EGF and TGF-a are autocrine growth factors for pancreatic cancer which may be responsible for its' usually rapid growth. The purpose of these studies was to examine the effect of RC-160 on EGF and TGF-a stimulated growth of this cancer in vivo.

ENZYME-DIRECTED BIOREDUCTIVE DRUG DEVELOPMENT: MOLECULAR FEATURES WHICH FAVOUR ACTIVATION OF QUINONE BIOREDUCTIVES BY DT-DIAPHORASE. Porman*, M Walton, S M Bailey and N R Suggett. MRC Clinical Oncology and Radiotherapeutics Unit, MRC Centre, Hills Road, Cambridge CB2 2QH, U.K. The development of bioreductive cytotoxins has mainly focused on screening for greater activity under hypoxic versus oxic conditions. We have proposed a different approach to rational development based on the optimization of drug structure to suit the catalytic preferences of key bioreductive enzymes which are hyperexpressed in human solid tumours. One such enzyme is DTdiaphorase [or NAD(P)H: quinone acceptor oxidoreductase, EC 1.6.99.2] which is hyperexpressed in lung, gastrointestinal and breast tumours. DT-diaphorase can reduce and thereby activate indoloquines, e.g. E09, and aziridinyl benzoquinones, e.g. diaziquone or AZQ, but we found mitomycin C to be metabolised only very slowly at physiological pH. DT-diaphorase also activates the dinitrophenyl azirndine CB 1954 and 4-nitroquinoline N-oxide but detoxifies the benzotriazine di-N-oxide SR 4233. We compared substituted derivatives of E09 and AZQ as substrates for purified rat DT-diaphorase using a cytochrome c reduction assay. In the AZO series, where the 2 ethyl moieties in the carbamate groups were replaced by alternative alkyl groups, the activity at 200 MM drug was n-butyl > iso-butyl > methyl > n-propyl > ethyl (AZQ) > secbutyl > iso-propyl. Reduction did not follow conventional Michaelis-Menten kinetics. The rates were not predicted by reduction potential or lipophilicity, suggesting the involvement of steric factors. Subtle changes to the structure also markedly alter reduction rates for E09 derivatives with DT-diaphorase. For example, opening the aziridine ring to the hydroxyethylamino metabolite or conversion to the methylaziridine results in very poor activity, whereas replacement of the aziridine ring by methoxy maintains efficient catalysis. In general, the most rapidly reduced agents were also the most toxic. We propose that an elucidation of such relationships at the molecular level should permit the design of new bioreductive agents with unique preferences for specific reductases. * Present address: CRC Dept of Medical Oncology, Alexander Stone Building, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD U.K.

36 male Syrian Golden hamsters were inoculated in both cheek pouches with H2T hamster pancreatic cancer cells and then equally randomised to 6 groups: saline; RC-160 (100ug /kg);TGF-a (IOug/kg); EGF (I0ug/kg); TGF-a+RC-160; EGF+RC160, each at the same dose as the single agent treatments. Treatments were given t.i.d. for 7 weeks by intraperitoneal injection. Tumours were measured weekly, at sacrifice tumours were weighed and analysed for DNA content. From week 4 until sacrifice both EGF and TGF-a significant -ly (p 36 months. 4 patients not achieving CR died from LACL, 3 died from second malignancy (all carcinoma bronchus). Overall 3 year actuarial survival is 67% (median follow up 25 months), 3 year relapse free survival is 80%. Treatment with hyperfractionated RT given during normal departmental working hours may have a low incidence of late morbidity provided the dose per fraction is sufficiently small to allow adequate repair between fractions.

LOW DOSE SINGLE FRACTION RADIOTHERAPY IN THE TREATMENT OF METASTATIC BONE PAIN: A PROSPECTIVE RANDOMISED TRIAL COMPARING 4GY AND 8GY SINGLE FRACTIONS. Hoskin PJ, Price P, Yamold JR, Easton D, Regan J, Austin D, Palmer S. The Royal Marsden Hospital, Sutton, Surrey. SM2 5PT. In the treatment of painful bone metastases a prospective trial from the Royal Marsden Hospital found a single dose of 8Gy to be as effective as 30Gy in 10 daily fractions. This subsequent trial compares a single dose of 8Gy with a single dose of 4Gy. Between January 1986 and January 1990, 270 patients with a clinical diagnosis of local pain due to bone metastases have been prospectively randomised to receive local irradiation with a single fraction of either 4Gy or 8Gy. The two arms of the study were balanced for age, sex, primary site and site of treatment. Pain assessment was based on a pain chart completed by the patient on the day of treatment, at weekly intervals for 4 weeks and then on weeks 8 and 12. This incorporated a 4-point scale (none, mild, moderate, severe) for pain and a record of analgesics used. Compliance with the pain chart was 81% at 2 weeks and 72% at 4 weeks. Response was defined as an improvement in pain score by one category, complete response by a pain score of zero. The actuarial response at 4 weeks was 69% after 8Gy and 44% after 4Gy (p < 0.01). However, no significant difference in complete response at 4 weeks or duration of response was seen and there was no significant difference in analgesic use between the two arms. In the first 12 weeks after treatment a higher incidence of retreatment to the same site was seen after 4Gy (20%) than after 8Gy (9%). No significant difference in response rate was seen between different primary types of tumour. In conclusion, this prospective randomised trial has shown a higher probability of pain relief after 8Gy than after 4Gy and this should be considered the optimal single dose for the relief of uncomplicated bone pain. However, a single dose of 4Gy is effective in a large proportion of patients and should be considered where there is limited radiation tolerance.

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OFFICE HOUR HYPERFRACTIONATED AND ACCELERATED RADIOTHERAPY FOR ADVANCED LARYNGEAL CARCINOMA

C.H. Macmillan, P.J. Bradley, D.A.L. Morgan Dept. of Clinical Oncology, NOTTINGHAM GENERAL HOSPITAL

RADIATION MUCOSITIS IN AIDS: AND A NEW PROPOSAL.

MAXIMISING LOCAL CONTROL BY CUSTOMIZED DOSE PRESCRIPTION FOR PELVIC TUMOURS

PAST EXPERIENCE

Hughes-Davies LT Sebag-Montefiore D Knowles S Spittle M. Middlesex Hospital London.

TAIT D.M.,* NAHUM A-+

*Dept. Radiotherapy Royal Marsden Hospital Sutton Surrey +Joint Dept Physics Institute of Cancer Research Sutton Surrey Pelvic malignancies probably exhibit steep dose-response curves and hence offer scope for improved local control. It is generally assumed that the target dose can only be increased by better conformation of the radiation fields to the shape of the target. However, dose-volume histograms (DVHs) calculated from 3D distributions in dose limiting organs such as the rectum reveal considerable inter-patient variability even for standard treatment techniques. We have analysed the rectal DVHs for 100 pelvic plans in patients recently entered into a clinical trial and computed Complication Probabilities for late Rectal damage (RCP) according to the recent Kutcher-Burman model (1), choosing parameters consistent with clinical expectations. These parameters will be refined as clinical data on late effects is accrued.

The unexpected sensitivity of oropharyngeal mucosa in patients with AIDS limits the use of radiotherapy in oral Kaposi's sarcoma. We present our experience with 23 patients. Daily fractionation is hazardous. The risk of mucositis appears to increase with time from the AIDS defining diagnosis. We have recently used weekly fractionation which is safer. 16 patients received daily treatment to the palate and 4 later required treatment to the treatment 20 evaluable yielding larynx, episodes. A range of doses were used: 1200 cGy in 3 (n=7), 1600 cGy in 4 (n=4) and 1500 cGy in 10 (n=7). Two patients were prescribed 3000 cGy in 10 for acute airway obstruction, one of whom was withdrawn at 1800cGy. Only 2/20 treatments were uncomplicated by mucositis and 9/20 (45%) led to a reaction of Patients treated within 9 grade 2 or above. months of an AIDS defining diagnosis had less severe mucositis (mean score 0.88, range 0-2) than those treated later in the course of the illness (mean score 2.0, range 0-4). 7 patients received weekly fractionation (1200-1600 cGy in 4 weeks). No mucositis was encountered. 6/7 patients had complete palliation of symptoms. Weekly fractionation is safe and effective in patients with a longstanding AIDS diagnosis. Daily fractionation may be used with caution earlier in the disease.

In the cases where the predicted RCP was very low the target dose was increased until the RCP reached an "acceptable" 5%. We show that the resultant increase in Tumour Control Probability (TCP), predicted from a simple model of cell killing, is substantial in a significant fraction of patients. This study indicates that there is potential for increasing local control in pelvic tumours if the dose prescription is individualised on the basis of 3D dose distributions in the dose limiting normal tissues.

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THE USE OF MEGAVOLTAGE IMAGING FOR PATIENT POSITIONING REPRODUCIBILITY.

PROGNOSTIC FACTORS FOR SURVIVAL OF PATIENTS WITH SOFT

TISSUE SARCOMA.

M.H.

ROBINSON, R. EELES, C.FISHER, J. SCHOFIELD, C.L. HARMER, E. WILTSHAW, J.M. THOMAS, G. SARCOMA UNIT, ROYAL MARSDEN HOSPITAL, WESTBURY. FULHAM RD., LONDON.

T. Gildersleve D.P. Dearnaley, P.M. Evans & W. Swindell Royal Marsden Hospital, Sutton, Surrey, England. The Royal Marsden Hospital megavoltage imaging system, comprising a frame grabber for digitisation of simulator images, a scanning detector and image analysis and display facilities, has been in clinical use for nine months. We have used this system to obtain a measure of the random (day to day) set-up variation which occurs for radical irradiation at differing treatment sites, using standard Royal Marsden Hospital treatment techniques. Clinical images have been obtained on at least one third of treatment days for each patient. Positioning variability is calculated as the extent of movement of visible structures within the treatment portal with respect to the average daily position. 1. Brain (in fixation cast) 216 observations 0-1.5 mm 81.5% 1.5-3 mm 16.2% 3-4.5 mm 2.3% 4.5-6mm 0.0% 2. Abdominal Nodal ('dogleg' + 'inverted Y') 0-1.5 mm 58.7% 126 observations 1.5-3 mm 27.7% 3-4.5 mm 11.1% 4.5-6 mm 0.8% 6-9 mm 1.6% 3. Pelvis 307 observations 0-1.5 mm 64.0% 1.5-3 mm 16.9% 3-4.5 mm 14.0% 4.5-6 mm 3.6% 6-7.5 mm 1.0% 7.5-9 mm 0.3% These preliminary results suggest that margins of 3 mm for brain, and 4.5 mm for abdominal and pelvis irradiation will be sufficient to avoid target volume miss due to random set-up variation in 95% of treatments using our set-up techniques.

Determination of prognostic factors for Objective: survival of patients with soft tissue sarcoma referred to the Royal Marsden Hospital. Patients: 496 males and 366 females, median age 45 years. Fifty five per cent were situated in the extremities, head and neck, 16% retroperitoneal, 8% truncal and 18% 4%

visceral.

Malignant fibrous (23%), liposarcoma (15%), leiomyosarcoma histiocytoma and synovial (8%) predominated. Mean size(10%) was 9 cm; 507 were high grade, 98 intermediate, and 246 low grade. Methods: Logrank analysis was used to compare groups. multivariate analysis was carried out including BMDPEM time dependent covariates to study factors determining survival, time to metastasis, time to lymph nodes and time to local recurrence. Results: Overall "adequate" surgical clearance was achieved at the first operation in 157 patients, 453 eventually received radical radiotherapy and least one local recurrence. Median follow-up 3534 had at years. Three hundred and two patients have developed is metastases, 62 lymph nodes (predominantly - 40%), and rhabdomyosarcoma 309 patients have died. On univariate analysis 5 year survival was inversely correlated with age (50 - 60%) and tumour size (5cm and related to site 60%), (extremity 75%; head and neck 55%; retroperitoneal 40%; visceral 30%) and grade (low/intermediate high 55%). These findings were confirmed 75%; by multivariate analysis where a significantly reduced risk of death was associated with low grade tumours (0.37), tumours