From childhood to adulthood: long-term outcome of medulloblastoma patients. The Institut Curie experience (1980-2000).

Medulloblastoma patients treated at the Institute Curie between 1980 and 2000 were reviewed. Only patients whose primary treatment included craniospinal radiation were considered. Surviving patients were identified and evaluated by means of self-report questionnaires using the Health Utility Index (HUI). Psychosocial functioning, employment, and other health-related indicators were recorded. Seventy-three patients were treated during the study period. At a median follow-up from diagnosis of 14.4 years, 49 patients were alive and 45 surviving patients could be contacted. Late sequelae were frequent, particularly neurological deficits (71%) and endocrine complications (52%). Impairments of psychosocial functioning, including employment, driving capacity, independent living, and marital status, were identified in most patients. Most long-term medulloblastoma survivors suffer persistent deficits in several domains, with a significant impact on their psychosocial functioning. These findings reinforce the importance of early intervention programs for all survivors in order to reduce the psychosocial impacts of their disease.

The relevance of image quality indices for dose optimization in abdominal multi-detector row CT in children: experimental assessment with pediatric phantoms.

This study assessed and compared various image quality indices in order to manage the dose of pediatric abdominal MDCT protocols and to provide guidance on dose reduction. PMMA phantoms representing average body diameters at birth, 1 year, 5 years, 10 years and 15 years of age were scanned in a four-channel MDCT with a standard pediatric abdominal CT protocol. Image noise (SD, standard deviation of CT number), noise derivative (ND, derivative of the function of noise with respect to dose) and contrast-to-noise ratio (CNR) were measured. The 'relative' low-contrast detectability (rLCD) was introduced as a new quantity to adjust LCD to the various phantom diameters on the basis of the LCD(1%) assessed in a Catphan phantom and a constant central absorbed dose. The required variations of CTDIvol(16) with respect to phantom size were analyzed in order to maintain each image quality index constant. The use of a fixed SD or CNR level leads to major dose ratios between extreme patient sizes (factor 22.7 to 44 for SD, 31.7 to 51.5 for CNR(2.8%)), whereas fixed ND and rLCD result in acceptable dose ratios ranging between factors of 2.9 and 3.9 between extreme phantom diameters. For a 5-9 mm rLCD1(%), adjusted ND values range between -0.84 and -0.11 HU mGy(-1). Our data provide guidance on dose reduction on the basis of patient dimensions and the required rLCD (e.g., to get a constant 7 mm rLCD(1%) for abdominal diameters of 10, 13, 16, 20 and 25 cm, tube current-time product should be adjusted in order to obtain CTDIvol(16) values of 6.2, 7.2, 8.8, 11.6 and 17.7 mGy, respectively).

[Conformal radiotherapy to 76Gy in localized prostate cancer. Therapeutic modalities and preliminary results]. / Radiothérapie conformationnelle à 76Gy des cancers localisés de la prostate. Modalités thérapeutiques et résultats préliminaires.

PURPOSE: To describe therapeutic modalities for localized prostate cancer treated by conformal radiation to 76Gy with or without androgen ablation. To evaluate the preliminary results in terms of survival, biological control and toxicity. PATIENTS AND METHOD: Between January 1998 and June 2001, 321 patients with localized prostate cancer were irradiated at institut Curie. Tumors were stratified into the three Memorial Sloan-Kettering Cancer Center prognostic groups (1998) for analysis: favorable risk group (FG) 23%, intermediate risk group (IG) 36.5%, unfavorable risk group (UG) 40.5%. Androgen deprivation, mainly neoadjuvant, less or equal to one year was prescribed to 93.8% of patients (72.6% less or equal to six months). Planning target volume prescription doses were: prostate: 76Gy, seminal vesicles: 56 to 76Gy, and pelvic lymph nodes: 44Gy to 16.8% of patients. RESULTS: The five-year actuarial overall survival was 94% (95% IC: 90-97%). The median post-therapeutic follow-up was 36 months (nine to 60 months). The 48-month actuarial rates of biochemical control for the three prognostic groups were statistically different according to both the American Society for Therapeutic Radiology and Oncology consensus (ASTRO 1997) and the Fox Chase Cancer Center definitions of biochemical failure (FCCC 2000) with respectively 87 and 94% for FG, 78 and 84% for IG, 54 and 58% for UG (P<10(-6) and P<10(-8)). At time of our analysis, late post-treatment rectal and bladder bleedings were 17,4 and 13,6%, respectively. According to a 1-4 scale adapted from M.D. Anderson Cancer Center criteria: rectal bleedings were grade 1 (9.6%), grade 2 (6.2%) and grade 3 (1.6%). Bladder bleedings were grade 2 (13%) and grade 3 (0.6%). Analysis of rectal bleeding risk factors showed significant correlations with pelvic lymph nodes irradiation for grade 2 and 3, (P=0.02), and for all grades, a correlation with smaller rectal wall volumes (P=0.03), and greater percentages of rectal wall irradiated to higher doses: 65, 70, 72 and 75Gy (P=0.02, P=0.01, P=0.0007 and P=0.003, respectively). CONCLUSIONS: These results are comparable to those previously reported with the same follow-up. Impact of dose escalation with short androgen deprivation on local control, survival and complications needs longer follow-up and further analysis.

[Chordomas of the base of the skull and upper cervical spine. 100 patients irradiated by a 3D conformal technique combining photon and proton beams]. / Les chordomes de la base du crâne et du rachis cervical haut. A propos d'une série de 100 patients irradiés selon une technique conformationnelle 3D par une association de faisceaux de photons et de protons.

OBJECTIVE: To define prognostic factors for local control and survival in 100 consecutive patients treated by fractionated photon and proton radiation for chordoma of the skull base and upper cervical spine. PATIENTS AND METHODS: Between December 1995 and August 2002, 100 patients (median age: 53 years, range: 8-85, M/F sex-ratio: 3/2), were treated by a combination of high-energy photons and protons. The proton component was delivered by the 201 MeV proton beam of the Centre de Protonthérapie d'Orsay (CPO). The median total dose delivered to the gross tumour volume was 67 Cobalt Gray Equivalent (CGE) (range: 60-71). A complete surgery, incomplete surgery or a biopsy was performed before the radiotherapy in 16, 75 and 9 cases, respectively. RESULTS: With a median follow-up of 31 months (range: 1-87), 25 tumours failed locally. The 2 and 4-year local control rates were 86.3% (+/-3.9%) and 53.8% (+/-7.5%), respectively. According to multivariate analysis, less than 95% of the tumour volume encompassed by the 95% isodose line (P=0.048; RR: 3.4 IC95% [1.01-11.8]) and a minimal dose less than 56 CGE (p=0.042; RR: 2.3 IC95% [1.03-5.2]) were independent prognostic factors of local control. Ten patients died. The 2 and 5-year overall survival rates were 94.3% (+/-2.5%) and 80.5% (+/-7.2%). According to multivariate analysis, a controlled tumour (P=0.005; RR: 21 IC95% [2.2-200]) was the lonely independent favourable prognostic factor for overall survival. CONCLUSION: In chordomas of the skull base and upper cervical spine treated by surgical resection followed by high-dose photon and proton irradiation, local control is mainly dependent on the quality of radiation, especially dose-uniformity within the gross tumour volume. Special attention must be paid to minimise underdosed areas due to the close proximity of critical structures and possibly escalate dose-constraints to tumour targets in future studies, in view of the low toxicity observed to date.

The sliding slit test for dynamic IMRT: a useful tool for adjustment of MLC related parameters.

For treatments with dynamic intensity modulated radiotherapy (IMRT), the adjustment of multileaf collimator (MLC) parameters affecting both the optimization algorithm and dose distributions is crucial. The main parameters characterizing the MLC are the transmission (T) and the dosimetric leaf separation (DLS). The aim of this study is twofold: a methodology based on the 'sliding slit' test is proposed to determine (T, DLS) combinations inducing the best conformity between calculations and measurements. Secondly, the effects of the MLC adjustment on measured dose and on optimization are presented for different configurations as the chair test and for the patient dosimetric quality control (DQC). Tests were performed with a Varian 23EX linac operated at 20 MV and equipped with a 120 leaf Millenium dynamic collimator. The treatment planning system was CadPlan/Helios (version 6.3.6). Results demonstrated that the sliding width (SW) strongly depends on the (T, DLS) combinations, and the measured dose is a linear function of the SW. Different (T, DLS) combinations induced a good agreement between calculations and measurements. The influence of the MLC calibration was found to be particularly important on the 'sliding slit' test (11.8% for a gap change of 0.8 mm) but not so much on the chair test and on the DQC. To detect small variations in leaf adjustment and to ensure consistency between calculation and actual dose delivered to patients, a daily check called IMRT MU check is proposed.

[Constraints and dosage for prostate cancer patients treated with conformal radiotherapy and intensity modulated radiation therapy]. / Choix des contraintes et amélioration dosimétrique d'une radiothérapie conformationnelle du cancer de la prostate modulée en intensité pendant une partie du traitement.

PURPOSE: Intensity modulated radiation therapy (IMRT) is based on a methodology called inverse planning. Starting from dosimetric objectives, constraints of optimization are fixed and given to the inverse planning system, which in turn calculates the modulated intensity to apply to each beam. Since the algorithms allow the constraints to be violated, the results of optimization may differ from the initial dosimetric objectives. Consequently, the user is compelled to adapt the choice of the constraints according to the type of modulation and until satisfactory results are found. The purpose of this work is to present our experience in the choice of these constraints for prostate cancer treatments, as we moved from conformal radiotherapy to IMRT. Treatments were performed with a Varian 23EX linac and calculations were realized with the Varian CadPlan-Helios planning system. PATIENTS AND METHODS: The approach used for the first 12 patients treated at institut Curie with IMRT from June 2002 was analysed. The treatment always consisted of a combination of conformal radiotherapy with and without intensity modulation. RESULTS AND CONCLUSION: Results showed that, a larger fraction of the treatment performed with IMRT induced a better sparing of the organs at risk for the same homogeneous dose distribution to the target volume. Apart from the dose-volume constraint for the rectum, a fixed set of constraints, slightly more restrictive than the dosimetric objectives, could be used for all patients. Compared with conformal radiotherapy, the conformation factor for IMRT increased up to 16%. A specific study was undertaken in view of treatments completely performed with IMRT. The optimal technique consisted in performing separated IMRT plans for the two target volumes, the prostate volume and the prostate plus seminal vesicles volume respectively. Another satisfactory possibility was to define new constraints on two separated planning target volumes, prostate and seminal vesicles. This last approach is now routinely implemented for our IMRT patients.

Combination of photon and proton radiation therapy for chordomas and chondrosarcomas of the skull base: the Centre de Protonthérapie D'Orsay experience.

PURPOSE: Prospective analysis of local tumor control, survival, and treatment complications in 44 consecutive patients treated with fractionated photon and proton radiation for a chordoma or chondrosarcoma of the skull base. METHODS AND MATERIALS: Between December 1995 and December 1998, 45 patients with a median age of 55 years (14-85) were treated using a 201-MeV proton beam at the Centre de Protonthérapie d'Orsay, 34 for a chordoma and 11 for a chondrosarcoma. Irradiation combined high-energy photons and protons. Photons represented two-thirds of the total dose and protons one-third. The median total dose delivered within the gross tumor volume was 67 cobalt Gray equivalent (CGE) (range: 60-70). RESULTS: With a mean follow-up of 30.5 months (range: 2-56), the 3-year local control rates for chordomas and chondrosarcomas were 83.1% and 90%, respectively, and 3-year overall survival rates were 91% and 90%, respectively. Eight patients (18%) failed locally (7 within the clinical tumor volume and 1 unknown). Four patients died of tumor and 2 others of intercurrent disease. In univariate analysis, young age at time of radiotherapy influenced local control positively (p < 0.03), but not in multivariate analysis. Only 2 patients presented Grade 3 or 4 complications. CONCLUSION: In skull-base chordomas and chondrosarcomas, the combination of photons with a proton boost of one-third the total dose offers an excellent chance of cure at the price of an acceptable toxicity. These results should be confirmed with a longer follow-up.

Experimental determination and verification of the parameters used in a proton pencil beam algorithm.

We present an experimental procedure for the determination and the verification under practical conditions of physical and computational parameters used in our proton pencil beam algorithm. The calculation of the dose delivered by a single pencil beam relies on a measured spread-out Bragg peak, and the description of its radial spread at depth features simple specific parameters accounting individually for the influence of the beam line as a whole, the beam energy modulation, the compensator, and the patient medium. For determining the experimental values of the physical parameters related to proton scattering, we utilized a simple relation between Gaussian radial spreads and the width of lateral penumbras. The contribution from the beam line has been extracted from lateral penumbra measurements in air: a linear variation with the distance collimator-point has been observed. Analytically predicted radial spreads within the patient were in good agreement with experimental values in water under various reference conditions. Results indicated no significant influence of the beam energy modulation. Using measurements in presence of Plexiglas slabs, a simple assumption on the effective source of scattering due to the compensator has been stated, leading to accurate radial spread calculations. Dose measurements in presence of complexly shaped compensators have been used to assess the performances of the algorithm supplied with the adequate physical parameters. One of these compensators has also been used, together with a reference configuration, for investigating a set of computational parameters decreasing the calculation time while maintaining a high level of accuracy. Faster dose computations have been performed for algorithm evaluation in the presence of geometrical and patient compensators, and have shown good agreement with the measured dose distributions.

Dose calculation and verification of intensity modulation generated by dynamic multileaf collimators.

While the development of inverse planning tools for optimizing dose distributions has come to a level of maturity, intensity modulation has not yet been widely implemented in clinical use because of problems related to its practical delivery and a lack of verification tools and quality assurance (QA) procedures. One of the prerequisites is a dose calculation algorithm that achieves good accuracy. The purpose of this work was twofold. A primary-scatter separation dose model has been extended to account for intensity modulation generated by a dynamic multileaf collimator (MLC). Then the calculation procedures have been tested by comparison with carefully carried out experiments. Intensity modulation is being accounted for by means of a 2D (two-dimensional) matrix of correction factors that modifies the spatial fluence distribution, incident to the patient. The dose calculation for the corresponding open field is then affected by those correction factors. They are used in order to weight separately the primary and the scatter component of the dose at a given point. In order to verify that the calculated dose distributions are in good agreement with measurements on our machine, we have designed a set of test intensity distributions and performed measurements with 6 and 20 MV photons on a Varian Clinac 2300C/D linear accelerator equipped with a 40 leaf pair dynamic MLC. Comparison between calculated and measured dose distributions for a number of representative cases shows, in general, good agreement (within 3% of the normalization in low dose gradient regions and within 3 mm distance-to-dose in high dose gradient regions). For absolute dose calculations (monitor unit calculations), comparison between calculation and measurement reveals good agreement (within 2%) for all tested cases (with the condition that the prescription point is not located on a high dose gradient region).

[Radiotherapy of cancer of the breast. Technical problems and new approaches]. / Radiothérapie du cancer du sein. Problèmes techniques et nouvelles approches.

Technical problems often arise during irradiation to the breast, chest wall, and regional lymph nodes. The following are among the most frequently encountered problems: avoidance of normal tissues (heart and lungs) during chest wall, internal mammary nodes, and large breast irradiations; dose heterogeneity in large breasts; under- or overdosage at field junctions (breast medial tangent and internal mammary fields in particular). Various technical solutions have been offered: modified treatment positions, field inclinations, and conformal irradiation. Many are currently under evaluation. These new technical approaches in breast cancer irradiation require modern facilities for imaging, simulation, and dosimetry, which help to individually design treatment planning.

[Conformal radiotherapy: principles and classification]. / La radiothérapie conformationnelle: principes et classification.

'Conformal radiotherapy' is the name fixed by usage and given to a new form of radiotherapy resulting from the technological improvements observed during, the last ten years. While this terminology is now widely used, no precise definition can be found in the literature. Conformal radiotherapy refers to an approach in which the dose distribution is more closely 'conformed' or adapted to the actual shape of the target volume. However, the achievement of a consensus on a more specific definition is hampered by various difficulties, namely in characterizing the degree of 'conformality'. We have therefore suggested a classification scheme be established on the basis of the tools and the procedures actually used for all steps of the process, i.e., from prescription to treatment completion. Our classification consists of four levels: schematically, at level 0, there is no conformation (rectangular fields); at level 1, a simple conformation takes place, on the basis of conventional 2D imaging; at level 2, a 3D reconstruction of the structures is used for a more accurate conformation; and level 3 includes research and advanced dynamic techniques. We have used our personal experience, contacts with colleagues and data from the literature to analyze all the steps of the planning process, and to define the tools and procedures relevant to a given level. The corresponding tables have been discussed and approved at the European level within the Dynarad concerted action. It is proposed that the term 'conformal radiotherapy' be restricted to procedures where all steps are at least at level 2.

[Radiotherapy using a combination of photons and protons for locally aggressive intracranial tumors. Preliminary results of protocol CPO 94-C1]. / Radiothérapie des tumeurs intracrâniennes localement agressives par une combinaison de photons et de protons. Résultats préliminaires du protocole CPO 94-C1.

PURPOSE: From October 1993 through July 1998, 48 assessable adult patients with non-resectable aggressive intracranial tumors were treated by a combination of high dose photon + proton therapy at the Centre de Protonthérapie d'Orsay. PATIENTS AND METHODS: Grade 1 and 4 gliomas were excluded. Patients benefited from a 3D dose calculation based on high-definition CT and MRI, a stereotactic positioning using implanted fiducial markers and a thermoplastic mask. Mean tumor dose ranged between 63 and 67 Gy delivered in five weekly sessions of 1.8 Gy in most patients, according to the histological types (doses in Co Gy Equivalent, with a mean proton-RBE of 1.1). RESULTS: With a median 18-month follow-up (range: four-58 months), local control in tumors located in the envelopes and in the skull base was 97% (33/34), and in parenchymal tumors, 43% (6/14) only. Two patients (5%) presented with a clinically severe radiation-induced necrosis (temporal lobe and chiasm). CONCLUSION: In our experience, high-dose radiation combining photons and protons is a safe and highly efficient procedure in selected malignancies of the skull base and envelopes.

[3D automatic expansion: clinical application]. / L'expansion 3D automatique: application clinique.

The determination of the various volumes (GTV: gross target volume, CTV: clinical target volume, PTV: planned target volume) recommended by the ICRU 50 report is a critical step in conformal treatment planning, since treatment optimisation procedures and documentation rely on accurate dose-volume histograms. The shape and the size of the CTV vary with the computer algorithm, the patient image acquisition parameters, the definition of the GTV and the margins surrounding it. The automatic expansion programs included in commercially available treatment planning system require careful validation and control before and during their routine use by the clinicians. Significant differences have been observed between 2D- and 3D-based expansions, with a usual underestimation of the PTV by 2D algorithms.

[Use of a multileaf collimator for the production of intensity-modulated beams]. / Utilisation d'un collimateur multilames pour la production de faisceaux modulés en intensité.

In external radiotherapy, the use of intensity modulated fields has been proposed for tissue and non-homogeneity compensation or for the generation of conformal dose distributions. Multileaf collimators can be employed dynamically for the modulation of the X-ray field in two dimensions. Efficient dynamic collimation became possible due to advances in computer and linear accelerator technology. It presents a number of advantages over conventional methods such as the use of compensators. We have developed a program which calculates, from a given intensity distribution, the motion of the MLC leaves as a function of monitor units, and we have applied it on a Varian linear accelerator with a 40 pair multileaf collimator. The analysis of the experimental results demonstrates the feasibility and the potential of the method.

[Dosimetry of small-size photon beams]. / Dosimétrie des faisceaux de photons de faibles dimensions.

A high performance standard radiotherapy treatment unit could be used to perform stereotactic radiosurgery. The dosimetric aspects of stereotactic irradiation with small size photon beams (energies from 5 to 25 MV produced by electron linear accelerator or gamma-rays produced by cobalt-60 treatment unit) are analyzed. The diameter of circular beams used are 5 to 40 millimeters wide at the isocenter of the treatment unit. The dosimetry of small x-ray fields is complicated by two factors: the relationship between detector size and field size dimensions, and the lack of lateral electron equilibrium. The large dose gradients outside the beam's central axis require dosimetry techniques with higher spatial resolution. To determine the best dosimetry system for measurements at the beam's small focal point, particularly for measurement of the field size dependent on output factors, several different detectors were investigated: ionization chamber, silicon diode, diamond detector, thermoluminescent dosimeter, and film. Ionization chamber, which presents a sensitive volume smaller than 0.02 cm3, is the most commonly recommended detector for field diameter above 8 mm. Current representative examples of dosimetric measurements for different x-ray energies, including percent depth dose, tissue maximum ratios, beam profiles (off axis ratios), and output factors, are presented and discussed. As well, the dosimetric characteristics of small photon beams are detailed.

A simple method for 3D lesion reconstruction from two projected angiographic images: implementation to a stereotactic radiotherapy treatment planning system.

INTRODUCTION: The most used imaging modality for diagnosis and localisation of arteriovenous malformations (AVMs) treated with stereotactic radiotherapy is angiography. The fact that the angiographic images are projected images imposes the need of the 3D reconstruction of the lesion. This, together with the 3D head anatomy from CT images could provide all the necessary information for stereotactic treatment planning. We have developed a method to combine the complementary information provided by angiography and 2D computerized tomography, matching the reconstructed AVM structure with the reconstructed head of the patient. MATERIALS AND METHODS: The ISIS treatment planning system, developed at Institute Curie, has been used for image acquisition, stereotactic localisation and 3D visualisation. A series of CT slices are introduced in the system as well as two orthogonal angiographic projected images of the lesion. A simple computer program has been developed for the 3D reconstruction of the lesion and for the superposition of the target contour on the CT slices of the head. RESULTS AND CONCLUSIONS: In our approach we consider that the reconstruction can be made if the AVM is approximated with a number of adjacent ellipses. We assessed the method comparing the values of the reconstructed and the actual volumes of the target using linear regression analysis. For treatment planning purposes we overlapped the reconstructed AVM on the CT slices of the head. The above feature is to our knowledge a feature that the majority of the commercial stereotactic radiotherapy treatment planning system could not provide. The implementation of the method into ISIS TPS shows that we can reliably approximate and visualize the target volume.

Dosimetric and cytogenetic studies of multiple radiation-induced meningiomas for a single patient.

No criteria are currently available to determine the spontaneous or radiation-induced origin of a malignant tumor occurring in a previously irradiated area. This study presents the dosimetric and cytogenetic analysis of meningiomas diagnosed in irradiated brain areas from a single patient and a discussion of the karyotypes of spontaneous meningiomas and radiation-induced tumors published in the literature.

Automatic three-dimensional expansion of structures applied to determination of the clinical target volume in conformal radiotherapy.

PURPOSE: A method is provided for the automatic calculation of the Clinical Target Volume (CTV) by automatic three dimensional (3D) expansion of the Gross Tumor Volume (GTV), keeping a constant margin M in all directions and taking into account anatomic obstacles. METHODS AND MATERIALS: Our model uses a description of the GTV from contours (polygons) defined in a series of parallel slices obtained from Computed Tomography (CT) or Magnetic Resonance Imaging (MRI). Each slice is considered sequentially, including those slices located apart from the GTV at a distance smaller than M. In the current slice a two-dimensional (2D) expansion is performed by transforming each vertex of the polygon into a circle with a radius equal to M, and each segment into a rectangle with a height equal to 2M. A cartesian millimetric grid is then "projected" onto the slice and a specific value is assigned at each point depending if the point is internal to the 2D expansion. The influence in the current slice of any slice located at a distance delta z smaller than M is taken into account by applying a 2D expansion using a margin [formula: see text]. Additional contours representative of various "barriers" stopping the expansion process can also be defined. RESULTS: The method has been applied to cylindrical and spherical structures and has proven to be successful, provided that the slice thickness is small enough. For usual slice thicknesses and margins, it gives a slight overestimation of the additional volume (around 5%) due to the choice that the calculated target volume would not be less than the expected volume. It has been shown that for a spherical volume, a 2D expansion performed slice by slice leads to a volume up to 80% smaller than that obtained by 3D expansion. CONCLUSIONS: This tool, which mimics the tumor cell spreading process, has been integrated in our treatment-planning software and used clinically for conformal radiotherapy of brain and prostatic tumors. It has been found to be extremely useful, not only saving time but also allowing a precise determination of the CTV which would be impossible to do manually.

Potential of T2 relaxation time measurements for early detection of radiation injury to the brain: experimental study in pigs.

PURPOSE: To investigate the MR T2 relaxation time and histologic changes after a single-fraction 25-Gy dose of radiation to the brain of pigs. METHODS: The right hemisphere of 10 Meishan pigs was irradiated with a single dose of 25 GY at the 90% isodose, using a 12-MeV electron beam. T2 relaxation time was measured within three regions of interest in the brain: those that had received 90%, 70%, and 40% of the total dose, respectively. T2 kinetics over time was compared with histologic studies. RESULTS: Brain T2 values were noted to increase within the irradiated areas. T2 kinetics were analyzed in three phases: an immediate transient phase and two long-lasting phases. These two long-lasting phases were correlated with the detection of ventricular compression and necrosis, respectively. The T2 increase within the 90% region of interest was 19%, 22%, and 26% for phases I, II, and III, respectively. T2 measurements within other regions of interest were not significant. CONCLUSION: Although our results suggest a dose threshold for T2 variations, brain T2 values increased after irradiation at a level at which disease could not be seen on conventional MR images. This illustrates the value of using conventional MR imaging in a quantitative manner to assess molecular tissue abnormalities at earlier stages of developing diseases.