[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.

[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.

[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.

[Routine use of electronic portal imaging. Positioning verification in 922 successive pelvic fields]. / Utilisation en routine du portal imaging électronique. Vérification de mise en place de 922 champs pelviens successifs.

Treatment reproducibility is a major criterion of quality assurance in radiation therapy. During each course, the same dose should be delivered in the same volume of irradiation. Today, portal imaging devices can be used routinely to check and correct patient positioning before much of the daily irradiation has been delivered. In this study we used the Portal Vision Varian (PVV) system during pelvic irradiation in 16 patients. This device can automatically acquire portal images in the first seconds of each course. Observed discrepancies are directly classified by the radiation oncologist according to their type (cranio-caudal, lateral, antero-posterior) and severity (correction of patient positioning is necessary or not). In case of error, patient positioning is corrected before the end of irradiation. Of the 922 portals analysed with PVV, 901 could be analysed (97%). Two hundred and ninety-nine positioning discrepancies were observed (33%) with 59 of them leading to correction (6%). Most of the time, these errors concerned antero-posterior portals. Finally, each patient had an average of 18 to 19 discrepancies which were mainly of no importance for treatment quality. Nevertheless, real errors leading to correction were observed in 14 patients (88%) with an average of four per patient. In some patients many errors occurred, while in others only a few. These shifts were not related to patient weight and thickness but probably a portal dimension. In summary, we think that during pelvic irradiation a portal imaging device should be used daily to improve treatment quality. This system can help the radiation oncologist to discover many positioning errors (an average of four) in the majority of patients (88%) and to correct them before the end of irradiation.

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.