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ble implications for treatment planning we have generated composite CTVs boost dose of 10 Gy), ependimoma of the IV ventricle (isocenter dose of 13 using contrast enhanced T1-MR images, multivoxel CSI images, Gy), brain stem astrocytoma (isocenter do.~e of 13 Gy), meningioma of the BOLD/Carbogen Images, and Perfusion Images. clivus (isocenter dose of 14 Gy), and meningioma of the cerebello-pontine Results : Ten CT-MR image sets were used to compare auto-fusions of angle CPA (isocenter dose of 10.3 Gy). Both IMRS and DCARS treatment these image sets to previously obtained expert manual fusions. On aver- plans were performed with the BrainSCAN treatment planning system age, the auto-fused and manually fused images were within an average (TPS) (BrainLab). Five dynamically conformed arcs were compared to 7-10 2.69:L-0.77 mm translational shift and within 0.72!-0.24 degrees and IM fixed fields. The target volumes ranged from 3.1 to 15.2 cc. The brain 0.67:L-0.16 degrees of rotational displacement around two perpendicular stem and optic nerves were considered the organs at risk (OARs). Maxi- axes. Our composite CTVs show that the possible target volume for radia- mum dose to OARs was 10 Gy. For comparison purposes the following tion therapy may well include areas that are not indicated on standard post dosimetric parameters were used: V9Gy (volume receiving 9 Gy) and contrast enhanced T1-MR images. V5Gy (volume receiving 5 Gy), conformity index (CI, treated volume/tumor (~onclusions : Our treatment planning examples demonstrate that the T1 volume) and homogeneity index (Ht, maximum dose/minimum dose within enhanced volume defined by standard MR imaging differ considerably from the target). the physiologic tumor volume defined using CSI (metabolic activity), BOLD Results: As reported in the table below, IMRS improved CI and HI mostly in (hypoxia), and pMRI (angiogenesis). we are currently conducting a clinical the irregular shaped lesions near the brain stem compared to DCARS. In trail to determine whether failure patterns can be predicted using physio- the other intracranial target sites, especially those small sized and regular logic tumor imaging on patients whose treatment plan has been designed shaped in the brain stem and in the CPA region, DCARS was better for using contrast enhanced T1-MR and T2-MR images and adding standard most dosimetric parameters. margins. Acknowledgement: Supported in part by a research grant from Pineal IV ventricle Brain-stem Clives CPA ADAC/Philips Rad. Onc. Systems. DCARS IMRS DCARS IMRS DCARS IMRS DCARS IMRS DCARS IMRS

Ct 2.09 1.77 1.99 1.81 1.96 2.79 3.54 2.43 2.17 2.90 HI 1.15 1.36 1.16 1.24 1.12 1.13 1.75 1.66 1.05 1.05

1019 Poster VgGy 0.07 0.00 2.92 2.66 1.65 2.30 1.92 2.02 0.54 0.56 Radiotherapy for glioma during pregnancy: foetal doses vary V5Gy 1.08 0.10 5.52 6.52 3.54 5.70 6.86 8.27 1.77 2.09 according to energy and type of l inear acce le ra to r In bold, best results. Y. Haba 1, N. Twyman 2, S. Thomas "?, P. Dendy 2-, N. Burner I Conclusions: Both DCARS and IMRS are able to deliver high doses with

optimal conformation standards. DCARS, however, should be preferred for 1Addenbrooke's Hospital, Department of Onco/ogy, Cambridge, United small, spherical lesions away from critical structures, while IMRS should be Kingdom considered for treating irregularly shaped tesions close to critical structures 2Addenbrooke's Hospital, Department of Medical Physics, Cambridge, such as the brain stem or optic pathways. United Kingdom

1021 Poster Cancer in pregnancy is relatively uncommon, but constitutes a major prob- Rad iosens i t i v i t y o f human g l i oma cells and relationship with lem. We report an illustrative case of a patient, 20 weeks pregnant, with a glioma specific genetic alterations grade 3 anaplastic astrocytoma. A radiotherapy planning CT scan was car- ried out and a plan prepared but not verified so that radiotherapy could have K. Van Nifterlk 1, R.H. Wesse/1, J.C.M. Vos 3, T.J.M. Hu/sebos 3, W.P. Van- been started with a minimum delay if the tumour had progressed. Sequen- derfop 2, S. Leenstra 4, L. Sta/pers 5, B.J. S/otman 1, P. Sminia 1 tial MRI scans showed no progression during the pregnancy. In the event, IVU University Medical Center, Radiation Onco/ogy, section Radiobio/ogy, she was managed conservatively, until the successful completion of her Amsterdam, The Netherlands pregnancy. The foetal x-ray exposure attributable to the planning scan is 2VU University Medical Center, Neurosurgery, Amsterdam, The Nether- less than 0.005 mGy. /ands To assess the risk to the foetus, phantom measurements were undertaken to assess the likely foetal dose, depending on the choice of photon energy 3Academic Medical Center, Human Genetics, Amsterdam, The Nether- and linear accelerator. Measurements were made on a Varian 600C, with /ands 6MV beam, an ABB accelerator at 8 & 16 MV, and on a Siemens Primus at 4Academic Medical Center, Neurosurgery, Amsterdam, The Netherlands 6 &15 MV. 5Academic Medical Center, Radiation Oncology, Amsterdam, The Nether- Doses were measured at 30, 45 and 60 cm from the head; the foetus is lands approximately at 60 cm and should not be closer than 45 cm. Doses to the position of the foetus were lowest with the 6 MV Varian accelerator, in which The aim of the study is to use genetic characteristics of the tumour and the the wave-guide lies parallel to photon beam, so that electron beam bending in vitro determined radiosensitivity as guidance in the optimization of radia- ls not required. Using this machine without additional abdominal shielding, tion therapy in human malignant gliomas. the estimated dose on the surface at 45 cm from the tumour volume was Over a period of one year, tumour specimens of 43 high grade malignant 2.2 mGy for a tumour dose of 54 Gy. Using the different accelerators the gliomas (Ill-IV) were processed to cell cultures. Early passage cell cultures dose varied between 22 mGy-59 mGy. With the Varian accelerator the dose and established human glioma cell lines were tested for their radiosensitiv- at the center of the abdomen at 60 cm was only 0.7 mGy. With the other ity, i.e. estimation of the surviving fraction after 2 Gy, either by clonogenic - accelerators the dose varied between 1.0-2.9 mGy. The energy of scattered or Sulpho Rhodamine B assay. A series of tumour samples of 17 high grade radiation was in the range 208-688 KeV, so that additional shielding is prac- malignant gliomas were analysed on genetic changes. The analyses could tical, and should reduce the foetal dose by half. be performed on the complete set of material, i.e. biopsy of the original The cancer risk up to age 15 attributable to radiation is 1 in 17,000 per mGy, tumour, the primary cell culture and blood leucocytes of the same patient. of which half will be fatal, ie 1 in 33,000 per mGy. A dose of 2.2 mGy adds Freeze-slides were prepared from all tumours and stained with H&E. Only a risk of fatal cancer by the age 15 of only 1 in 15,000. Since the addition samples with > 80% tumor cells were processed for DNA isolation. The fol- of shielding can halve the foetal dose, this risk should be reduced to 1 in lowing genetic screenings were performed: (1) Loss Of Heterozygosity 30,000. For comparison, the overall UK risk of cancer up to age 15 is 1 in (LOH) for markers on chromosome arm 10q (containing PTEN and 650. DMBT1 ); " ' (3) determination of the ampli- (2) p53 gene mutational status and Careful choice of linear accelerator for the treatment of pregnant patients is fication status of the EGFR gene. needed since this can dramatically affect foetal dose, which may be 27 First results show LOH10 in approx. 75%, p53 mutations in approx. 10 % times lower on some linear accelerators, and EGFR gene amplification in approx. 20% of the tumours.

A data base has been set up in which clinical and experimental data are col- 1020 Poster lected, with the final aim to correlate the experimental data with tumour dif- In tens i t y modulation or dynamically conformed arc rad io - ferentiation grade, genetic profile of the primary tumour and patients' follow- su rge ry for intracranlal lesions? up, i.e. time to recurrence and survival. S. Villa. L. Escude, F. Vi/a, R. Ama/te, D. Linem, $. Cana/es, R. Mira/bell /nstituto Onco/(Jgico Teknon, Radio-onco/ogia, Barcelona, Spain Supported by the Dutch Cancer Society KWF, project VU 2000-2149

Purpose: To dosimetrically assess for potential advantages of intensity modulated radiosurgery (IMRS) compared to dynamically conformed arc radiosurgery (DCARS) in intracraneal lesions for sihgle dose. Methods: Five tumor sites were chosen for comparison: pineal (isocenter