[Repositioning accuracy of cerebral fractionated stereotactic radiotherapy using CT scanning]. / Evaluation par tomodensitométrie du repositionnement en radiothérapie stéréotaxique fractionnée cérébrale.

PURPOSE: To evaluate the accuracy of patient repositioning in fractionated cerebral stereotactic radiotherapy using a Brain Lab stereotactic cranial mask in conjunction with standard dental fixation. PATIENTS AND METHODS: Fifty planning and checking CT scans were performed in 25 patients. The check CT scan was performed before or after one of the three sessions of treatment. Coregistration to the planning CT scan was used to assess alignment of the isocentre to the reference markers. The relative position of the PTV with regard to isocentre allowed us to determine its total displacement (3D vector). RESULTS: Mean isocentre translations (+/-SD) taking into account direction were -0.01+/-0.7, -0.2+/-1.3 and 0.07+/-0.5mm in mediolateral, craniocaudal and anteroposterior directions respectively. Mean rotations (+/- SD) were -0.02+/-0.6, -0.08+/-0.3 and -0.1+/-0.3 degree in mediolateral, craniocaudal and anteroposterior axes respectively. Mean overall PTV displacement was 1.8+/-1.5mm. PTV displacement was smaller than 2 and 3mm in 19/25 and 23/25 patients respectively. CONCLUSION: The accuracy of patient positioning using a stereotactic cranial mask system is similar to those reported in the literature and shows a satisfactory reproducibility with a standard dental fixation.

[Volume-effect and radiotherapy [II]. Part II: volume-effect and normal tissue]. / Effet volume en radiothérapie [II]. Deuxième partie : volume et tolérance des tissus sains.

The first part of our work has focused on the relationship between tumor volume and tumor control. Indeed, it is well known that the importance of irradiated volume could be a main parameter of radiation-induced complications. Numerous mathematical models have described the correlation between the irradiated volume and the risk of adverse effects. These models should predict the complication rate of each treatment planning. At the present time late effects have been the most studied. In this report we firstly propose a review of different mathematical models described for volume effect. Secondly, we will discuss whether these theoretical considerations can influence our view of radiation treatment planning optimization.

[Volume-effect in radiation therapy part one: volume-effect and tumour]. / L'effet volume en radiothérapie première partie: effet volume et tumeur.

Volume is an important parameter of radiation therapy. Local control is inversely related to tumor size and the complication rate increases with the importance of the irradiated volume. Although the effect of irradiated volume has been widely reported since the beginning of radiotherapy, it has been less studied than other radiation parameters such as dose, fractionation, or treatment duration. One of the first organ system in which the adverse effect of increased volume was well defined is the skin. Over the last twenty years, numerous mathematical models have been developed for different organs. In this report we will discuss the relation between irradiated volume and tumor control. In a second article we will study the impact of irradiated volume on radiation adverse effects.

Nicotinic acetylcholine receptor ligands differently affect cytochrome oxidase in the Honeybee brain.

The objective of this study was to determine if nicotinic receptor antagonists known for their ability to impair memory in the honeybee could induce changes in brain metabolism. We tested the effect of antagonists [hexamethonium, mecamylamine, alpha-bungarotoxin (alpha-BTX)] and agonist (nicotine) brain injections on cytochrome oxidase (CO) histochemistry. Within as little as 30 min following nicotine injection, an increase of the staining was observed in almost all the structures analyzed. The increase was limited to the alpha-lobe after alpha-BTX injection. In contrast, the antagonists hexamethonium and mecamylamine reduced CO staining in this structure that seems to be involved in information retrieval. These results suggest that the decrease of metabolism in the alpha-lobe obtained with hexamethonium and mecamylamine injections could be related to the impairment of retrieval processes previously observed with these drugs.

Functional cytochrome oxidase histochemistry in the honeybee brain.

The variations of neural metabolism induced by surgical and chemical treatments were studied in the honeybee brain by the means of cytochrome oxidase (CO) histochemistry. CO staining is considerably reduced in the alpha-lobe by antennal input deprivation. Chemical stimulation (50 mM K(+)) was linked to an increase of CO staining in antennal lobes (AL) and to a decrease in the basal ring of calyces (Cal). Application of the nicotinic ligand imidacloprid (10(-4) M) resulted in increased CO labelling within 30 min in all the structures analysed. Treatment with a lower concentration (10(-8) M) resulted in reduced staining in Cal and central body (CB). We conclude that CO histochemistry can be used to identify the target structures of cholinergic ligands in the honeybee brain.

[Fractionated radiotherapy of intracranial meningiomas: 15 years' experience at the Bordeaux University Hospital Center]. / Radiothérapie fractionnée des méningiomes intracrâniens: 15 ans d'expérience au centre hospitalier universitaire de Bordeaux.

PURPOSE: To evaluate the long-term results of external fractionated radiation therapy (RT) in the treatment of intracranial meningiomas. PATIENTS AND METHODS: From January 1981 to December 1996, 156 patients with intracranial meningiomas were treated with external fractionated RT. Median age was 57. Indications for radiation therapy were as follows: (1) completely excised histologically aggressive tumors (12 patients); (2) incomplete surgical resection (37 patients); (3) medically inoperable or basilar tumors where operation would involve considerable danger or permanent neurological damage (77 patients); and, (4) tumor recurrences (30 patients). Most patients were irradiated with 6 to 9 MV photon beams. A three to four-field technique with coned-down portals was used. Since 1993, 71 patients had a three dimensional dosimetry. Doses were calculated on the 95% or 98% isodoses, all fields were treated every day, five days a week, for a median total dose of 50 Gy (1.8 Gy/Fraction). RESULTS: Median follow-up from radiation therapy was 40 months. Acute tolerance was excellent; an early clinical improvement during radiation therapy was noted in 19 patients (17.8%). Clinical improvement or stabilization was observed in 130 patients (83.4%). Radiologically, local control was obtained in 124 cases (79.4%) and tumor recurrences occurred in 21 cases (ten progressions in the treated volume, five borderline, six new locations). Overall and cause specific-survival rates were 75% and 89% at five years, and 45 and 76% at 10 years, respectively. CONCLUSION: These results reassess the role of fractionated RT in the treatment of intracranial meningiomas. Long-term tolerance is excellent for a majority of patients. The study of recurrences confirms the importance of the definition of the target volume, and asks questions about total given doses.

[Fractionated irradiation of cerebellopontine angle neurinoma: 12 years' experience of the Bordeaux University Hospital Center]. / Irradiation fractionnée des neurinomes de l'angle pontocérébelleux: 12 ans d'expérience au centre hospitalier universitaire de Bordeaux.

PURPOSE: To evaluate retrospectively the long-term results of fractionated radiation therapy (RT) in cerebello-pontine angle neurinomas (CPA). METHODS AND MATERIAL: From January 1986 to October 1995, 29 patients with stage III and IV neurinomas were treated with external fractionated RT. One patient was irradiated on both sides and indications for RT were as follows: (1) general contraindications for surgery (16 patients); (2) hearing preservation in bilateral neurinomas after controlateral tumor exeresis (six patients); (3) partial tumor removal (five patients); and, (4) non-surgical recurrence (three patients). A three to four fields technique with coplanar static beams and conformal cerobend blocks was used; doses were calculated on a 95 to 98% isodoses and were given five days a week for a median total dose of 51 Gy (1.8 Gy/fraction). Most patients were irradiated with 6 to 10 MV photons). RESULTS: Median follow-up was 66 months (seven to 120 months). Seven patients died, two with progressive disease, five from non-tumoral causes. Tumor shrinkage was observed in 13 patients (43.3%), stable disease in 14 (46.6%), and tumor progression in three. Two patients underwent total tumor removal after RT (one stable and one growing tumor). Hearing was preserved in four out of six patients. No patient experienced facial or trigeminal neuropathy. CONCLUSION: Fractionated RT is a well tolerated and efficacious treatment of large non-surgical CPA neurinomas.

[Practice of virtual simulation at the Saint-André hospital]. / Pratique de la simulation virtuelle à l'hôpital Saint-André.

PURPOSE: Prospective evaluation of a virtual simulation technique. PATIENTS AND METHODS: From September 1993 to February 1997, 343 patients underwent radiation therapy using this technique. Treated sites were mostly: brain (132), rectum (59), lung (43), and prostate (28). A CT-scan was performed on a patient in treatment position. Twenty-five to 70 jointive slices widely encompassed the treated volume. The target volume (CTV according to ICRU 50) and often critical organs were controured, slice by slice, by the radiation oncologist. Beams covering the CTV plus a security margin (PTV) were placed on the "virtual patient". Digital radiographs were reconstructed (DRR) as simulator radiographs for each field. Thus, the good coverage of PTV was assessed. Fields and beam arrangements were further optimized. Definitive isocenter was then placed using a classical simulator. Perfect matching of DRR and actual simulator radiographs had to be obtained. RESULTS: Nineteen patients presented grade 3, and 1 grade 4 acute radiation effects. With a median follow-up of 18 months, five patients suffered from grade 3, and one from grade 4 complications. Fifty-five patients had tumor recurrence in the treated volume, and 19 had marginal relapse. CONCLUSION: In our department, virtual simulation has become a routine technique of treatment planning for deep-seated tumors. This technique remains time-consuming for radiation oncologists: about 2 hours. But it stimulates reflexion on anatomy, tumor extension pathways, target volumes; and is becoming an excellent pedagogical tool.

Fractionated radiation therapy in the treatment of intracranial meningiomas: local control, functional efficacy, and tolerance in 91 patients.

PURPOSE: To evaluate efficacy and tolerance of external fractionated radiation therapy (RT) in the treatment of intracranial meningiomas. METHODS AND MATERIALS: From January 1981 to September 1993, 91 patients with intracranial meningiomas were treated with fractionated RT. Indications were as follows: (a) incomplete surgical resection, 29 patients; (b) tumor recurrences without considering the amount of the second resection, if performed, 14 patients; (c) completely excised angioblastic, aggressive benign, and anaplastic tumors, 8 patients; (d) medically inoperable and basilar tumors where operation would involve considerable danger or permanent neurological damage, 44 patients. Most patients were irradiated with 6 to 9 MV photon beams. A three- to four-field technique with coned-down portals was used. Doses were calculated on the 95% isodose and were given 5 days a week for a median total dose of 52 Gy (1.80 Gy/fraction). RESULTS: Median follow-up from radiation therapy was 40 months. Acute tolerance was excellent, but there were six late delayed injuries. Tumor recurrences occurred in six cases. Six patients died from their tumor or RT complications, 19 from nontumoral reasons. Three, 5- and 10-year survival rates were 82, 71, and 40%, respectively. The most significant prognostic factor was age: 5-year survival rate was 86% for patients less than 65 years and 37% for patients more than 65. However, there were no differences in recurrence-free survival rates between patients younger than 65 and the oldest ones. Of 60 symptomatic patients with neurological deficits, 43 had neurological improvement (72%), beginning in some cases within 15 to 20 days after starting RT. CONCLUSION: These results reassess the role of fractionated RT in the treatment of meningiomas, and stress on its efficacy, especially on cranial nerves palsies, without severe toxicity in most cases.

Radiotoxic model for three-dimensional treatment planning. Part 1: Theoretical basis.

Since recent treatment planning systems calculate volumetric dose distribution, an objective evaluation of potential toxicity in the main critical organs may be helpful in treatment optimization. Modeling the toxicity of radiotherapy must at least account for: (a) specific risks in every critical organ; (b) total dose and dose per fraction; (c) partial irradiation of critical organs; (d) heterogeneous dose distribution. The Radiation Damage Factor formula is aimed at estimating the delayed toxicity of a given treatment plan on every critical organ concerned. The formulation uses a double exponential function: RDF = 100 e-Ke-(a+bd)DVc, where: D is the total dose, and d the dose per fraction; a and b are coefficients representing the radiosensitivity of the critical organ, according to the linear-quadratic model, with a/b = alpha/beta. K represents the theoretical critical unit content of the organ, these critical units being groups of functionally related stem cells. The avoidance of a complication depends on the ability of surviving critical units to preserve organ function. V is the ratio:irradiated volume/total volume of the organ. Exponent c accounts for tissue organization: c is equal to or near 1 in "parallel organs" like the liver or the lung, where localized hot spots are tolerated; c is lower in "series organs" like the spinal cord where hot spots, even in a small portion, are dangerous. Heterogeneous irradiation, summarized by dose cumulative-volume histograms, is accounted for by calculating step by step the dose D' considered as having an equivalent effect when given in the largest irradiated volume ratio. Preliminary calibration of the RDF formula is attempted for radiation myelitis and radiation hepatitis.