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D Lefkopoulos

Publications and source records attributed to D Lefkopoulos.

At least 37 records · Page 2Linked to original sources
PubMed2000

Dose-volume analysis of different stereotactic radiotherapy mono-isocentric techniques.

Several stereotactic irradiation techniques, using Linacs with the patient in lying and sitting position and a Gamma Knife Unit, were compared with regard to mono-isocentric three-dimensional dose distributions. Three types of target volumes, a sphere and two ellipsoids, were used for the comparisons. All three targets were centered on a real head, reconstructed from transversal CT scans. The ARTEMIS 3D Treatment Planning System, developed by the Tenon Hospital, Paris, was used for the dosimetry and the dose-volume histogram (DVH) calculation. For the comparative study, several quantitative parameters were used, derived from the dose-volume histogram calculation. Differential DVHs were plotted for each target volume and beam arrangement. Irradiation techniques were compared by deriving quantitative parameters from the DVHs such as mean and integral dose delivered to the target and normal tissue irradiated, as well as by the relative volume of the examined areas. All techniques used in this study produced very similar dose distributions. The small differences confirm the capability of the studied techniques to produce the same irradiation effects. By changing from the spherical target shape to a more elliptical shape, more of the normal tissue was irradiated with higher doses. For elliptical cases we therefore identified a need for more conformal stereotactic planning.

Brain Neoplasms↗
PubMed1999

Study of ill-conditioning of Linac stereotactic irradiation subspaces using singular values decomposition analysis.

A Linac stereotactic irradiation space is characterized by different angular separations of beams because of the geometry of the stereotactic irradiation. The regions of the stereotactic space characterized by low angular separations are one of the causes of ill-conditioning of the stereotactic irradiation inverse problem. The singular value decomposition (SVD) is a powerful mathematical analysis that permits the measurement of the ill-conditioning of the stereotactic irradiation problem. This study examines the ill-conditioning of the stereotactic irradiation space, provoked by the different angular separations of beams, using the SVD analysis. We subdivided the maximum irradiation space (MIS: (AA)AP x (AA)RL = 180 degrees x 180 degrees) into irradiation subspaces (ISSs), each characterized by its own angular separation. We studied the influence of ISSs on the SVD analysis and the evolution of the reconstruction quality of well defined three-dimensional dose matrices in each configuration. The more the ISS is characterized by low angular separation the more the condition number and the reconstruction inaccuracy are increased. Based on the above results we created two reduced irradiation spaces (RIS: (AA)AP x (AA)RL = 180 degrees x 140 degrees and (AA)AP x (AA)RL = 180 degrees x 120 degrees) and compared the reconstruction quality of the RISs with respect to the MIS. The more an irradiation space is free of low angular separations the more the irradiation space contains useful singular components.

Humans↗
PubMed1999

A computerized dosimetric database for conformal stereotactic irradiations.

An innovative computerized dosimetric database (DDB) is proposed to enable the analysis of the stereotactic radiosurgical dose distributions; it contains relationships between the irradiation parameters and the dose-volume data. Dose-volume data provide guidance to the physicist-physician team by facilitating the initialization of the irradiation parameters and the treatment planning. The presented DDB contains dose-volume data such as the 70% isodose widths and the 70%-30% isodose penumbra along the right-left, anterior-posterior, and superior-inferior directions as a function of the irradiation parameters defined by the user. In order to demonstrate the usefulness of the DDB, the effects of the collimator diameter, the number of arcs, and their length on the shape of the prescription isodose surface are shown and are related to practical considerations for the treatment plan. However, the presented DDB is one example that can be generated by the DDB system. The planner can define as many different DDBs as he/she wishes, which can then be used for different investigations. This type of DDB enables us to investigate the irradiation technique used, to compare different irradiation techniques, to inspect the feasibility of planning different lesion types, or to define some dosimetric rules. The DDB provides useful interactive guidelines for the treatment planning process and replaces the voluminous dosimetric atlas. It has now been in clinical use for a year in a conformal procedure which automatically proposes collimator diameters, arc positions, and lengths allowing rapid conformal planning.

Algorithms↗
PubMed1998

Single-fraction stereotactic radiotherapy: a dose-response analysis of arteriovenous malformation obliteration.

PURPOSE: Stereotactic radiotherapy delivered in a high-dose single fraction is an effective technique to obliterate intracranial arteriovenous malformations (AVM). To attempt to analyze the relationships between dose, volume, and obliteration rates, we studied a group of patients treated using single-isocenter treatment plans. METHODS AND MATERIALS: From May 1986 to December 1989, 100 consecutive patients with angiographically proven AVM had stereotactic radiotherapy delivered as a high-dose single fraction using a single-isocenter technique. Distribution according to Spetzler-Martin grade was as follows: 79 grade 1-3, three grade 4, 0 grade 5, and 18 grade 6. The target volume was spheroid in 74 cases, ellipsoid in 11, and large and irregular in 15. The targeted volume of the nidus was estimated using two-dimensional stereotactic angiographic data and, calculated as an ovoid-shaped lesion, was 1900 +/- 230 mm3 (median 968 mm3; range 62-11, 250 mm3). The mean minimum target dose (Dmin) was 19 +/- 0.6 Gy (median 20 Gy; range: 3-31.5). The mean volume within the isodose which corresponded to the minimum target dose was 2500 +/- 300 mm3 (median 1200 mm3; range 75-14 900 mm3). The mean maximum dose (Dmax) was 34.5 +/- 0.5 Gy (median 35 Gy; range 15-45). The mean angiographic follow-up was 42 +/- 2.3 months (median 37.5; range 7-117). RESULTS: The absolute obliteration rate was 51%. The 5-year actuarial obliteration rate was 62.5 +/- 7%. After univariate analysis, AVM obliteration was influenced by previous surgery (p = 0.0007), Dmin by steps of 5 Gy (p = 0.005), targeted volume of the nidus (< or = 968 mm3 vs. >968 mm3; p = 0.015), and grade according to Spetzler-Martin (grade 1-3 vs. grade 4-6; p = 0.011). After multivariate analysis, the independent factors influencing AVM obliteration were the Dmin [relative risk (RR) 1.9; 95% confidence interval (CI) 1.4-2.5; p < 0.0001] and grade distribution according to Spetzler-Martin (RR 1.4; 95% CI 1.1-1.7; p = 0.010). Delayed complications were observed in eight patients. The 5-year actuarial rate of delayed complications was 7.4%. CONCLUSION: After stereotactic radiotherapy delivered in a single high dose using a single-isocenter technique, the success rate for complete obliteration is independently correlated to Dmin but does not seem to be influenced by Dmax and the targeted volume of the nidus.

Adolescent↗
PubMed1998

Use of a general inverse technique for the conformational stereotactic treatment of complex intracranial lesions.

PURPOSE: The stereotactic irradiation of intracranial lesions constitutes an excellent example of conformational therapy whose purpose is to adapt the dose envelope to the target volume with great precision and at the same time to deliver as low a dose as possible to the healthy tissues. We propose the mathematical analysis of the singular values decomposition (SVD) as an inverse planning process to find the optimal minibeam weightings that permit the calculation of the most conformational dose distribution. METHODS: For the radiosurgical treatment of complex lesions, we realize a division of the lesion into several elliptic volumes using the "Associated Target Methodology." This division allows the definition of an irradiation configuration: the number of isocenters, the position of the isocenters, and the diameter of each collimator. For this defined irradiation configuration, we use SVD to find the optimal minibeam weightings. This analysis enables us to understand better the ill-conditioning of the multi-isocentric irradiation and the influence of irradiation parameters on the process of reconstruction minibeam weightings. RESULTS: In this paper, the SVD analysis and the reconstruction technique have been evaluated for the first time on practical cases. We present, as an example, a complex lesion compartmentalized into 3 subvolumes according to our Associated Target Methodology. This analysis allows us to study the ill-conditioning of the example and proposes a large number of solutions from among which we have to choose the most conformational physical solution. This choice is based on the dose-volume histograms. CONCLUSION: We use the SVD procedure as a computer-aided planning system and obtain good solutions, i.e., healthy tissue protection and lesion coverage similar to or better than an experimented planner solution.

Brain Neoplasms↗
PubMed1998

Failure in radiosurgery treatment of cerebral arteriovenous malformations.

OBJECTIVE: The aim of this study was to retrospectively analyze the reasons for the failure of radiosurgical treatment of cerebral arteriovenous malformations (AVMs). METHODS: Seventeen cases of noncured AVMs were reviewed 3 years after radiosurgical treatment. Follow-up ranged from 33 to 54 months (mean, 44.3 mo). Lesion dimensions varied from 9 to 55 mm (mean, 29.2 mm). The lesions were located in critical or near-critical brain regions. Angiography was performed under Talairach's stereotactic conditions. Two large AVMs bled 36 and 39 months after receiving irradiation, respectively. These two AVMs had been incompletely irradiated. RESULTS: Retrospectively, in four cases (23.5%) we observed errors in determining AVM target shape and size because of inaccurate definition of the nidus and/or because of stereoangiographic incompleteness (absence of external carotid artery injections). In five large and/or irregularly shaped AVMs (29.4%), a strategy of partial volume irradiation had been used. In one patient (5.8%), we observed the recanalization of previously embolized AVMs. In another case (5.8%), the target had been partially missed. The AVMs in one case (5.8%) had been treated with an ineffective peripheral dose. In one (5.8%), the failure occurred because of the lesion angio-architecture. In four cases (23.5%), no evident reasons for failure were determined. CONCLUSION: The results of this study suggest the necessity of complete irradiation of the nidus. The strategy of partial volume irradiation might be avoided, even if it necessitates lowering the doses to treat large AVMs. Accuracy in the target determination is required, and complete stereoangiography is necessary.

Adult↗
PubMed1996

Treatment of brain arteriovenous malformations by embolization and radiosurgery.

Embolization was used to reduce the size of brain arteriovenous malformations (AVMs) prior to radiosurgical treatment in 125 patients who were poor surgical candidates or had refused surgery. Of these patients, 81% had suffered hemorrhage, and 22.4% had undergone treatment at another institution. According to the Spetzler-Martin scale, the AVMs were Grade II in 9.6%, Grade III in 31.2%, Grade IV in 30.4%, and Grades V to VI in 28.8% of the cases. Most embolizations were performed using cyanoacrylate delivered by flow-guided microcatheters. Radiosurgery was performed using a linear accelerator in 62 patients treated by the authors, and 34 patients were treated at other institutions using various methods. Embolization produced total occlusion in 11.2% of AVMs and reduced 76% of AVMs enough to allow radiosurgery. Radiosurgery produced total occlusion in 65% of the partially embolized AVMs (79% when the residual nidus was < 2 cm in diameter). Embolizations resulted in a mortality rate of 1.6% and a morbidity rate of 12.8%. No complications were associated with radiosurgery. The hemorrhage rate for partially embolized AVMs was 3% per year. No patient with a completely occluded AVM experienced rehemorrhage. Angiographic follow-up review of AVMs embolized with cyanoacrylate demonstrated a 11.8% revascularization rate, occurring within 1 year. It is concluded that after partial embolization with cyanoacrylate, the risk of hemorrhage from the residual nidus is comparable to the natural history of AVMs and that the residual nidus can be irradiated with results almost as good as for a native AVM of the same size.

Adolescent↗
PubMed1995

A modified 60C teletherapy unit for total body irradiation.

PURPOSE: A modified teletherapy unit to achieve total body irradiation with a vertical beam in a conventional treatment room. METHODS AND MATERIALS: A standard 60C teletherapy unit has been modified to achieve total body irradiation with a vertical beam in a conventional treatment room. Patients are treated in prone and supine positions. Removal of the adjustable collimator assembly of this standard machine provides a circular field of 196 cm in diameter at 167 cm from the source. Second, the machine has been elevated by about 50 cm on a metallic base to enlarge irradiation field to obtain 248 cm in diameter at 210 cm from the source, and to encompass tall patients under better conditions. A special lead conical beam flattening filter, 10-mm thick at the center, was designed to compensate the spatial inhomogeneity of the beam. An instantaneous dose rate of 6.10(-2) Gy/min is attained at the L4 level (midplane) in an average 20-cm thick patient with a source activity of 5099 RHM (air kerma rate of 44.8 Gy.h-1.m2). Between February 2, 1984 and December 27, 1990, 244 total body irradiations were performed either by single dose (n = 69, 10 Gy were given to midplane at L4 level in about 6 to 8 h, 8 Gy to the lungs), or by fractionated dose (n = 175, 12 Gy were given in 6 fractions over 3 consecutive days to midplane at L4 level, 9 Gy to the lungs). RESULTS: The dose distribution is similar than the ones obtained by a linear accelerator with patients lying on their sides. CONCLUSION: Patients were treated in a comfortable and highly reproductible position. Organ shielding was easily achievable. This could be a less expensive and reasonable alternative to linear accelerator.

Cobalt Radioisotopes↗
PubMed1995

Conservative versus nonconservative treatment of epidermoid carcinoma of the anal canal for tumors longer than or equal to 5 centimeters. A retrospective comparison.

BACKGROUND: The role of radiotherapy alone in the sterilization of anal canal epidermoid carcinomas of 5 cm or more remains to be assessed. Thus, the outcomes of patients treated with radiotherapy alone (RT) versus those treated with preoperative radiotherapy and surgery (RS) were compared retrospectively. METHODS: Between 1972 and 1990, 185 patients were treated with curative intent either with RT alone (n = 147) or with RS (n = 38). The Mean tumor length was 6.18 +/- 1.14 cm and was significantly longer in the RS group (6.55 +/- 1.29 cm) than in the RT group (6.08 +/- 1.08 cm) (P = 0.02). The median follow-up was 77 +/- 57 months and 93 +/- 60 months (P = 0.23) for the RT and RS groups, respectively. For the RT group, the first course of radiotherapy was 40 to 45 Gy in the pelvis for 4 to 5 weeks; after a rest of 4 to 6 weeks, radiotherapy was boosted an additional 15 to 20 Gy for 2 weeks. The RS patients received 40 to 45 Gy in the pelvis for 4 to 5 weeks, then received surgery after a median period of 54 days. RESULTS: The overall 10-year cancer specific survival rates were 58% in the RT group and 66% in the RS group (P = 0.48). The T-stage 10-year cancer specific survival rates were 68% in the RT group and 67% in the RS group for T2 tumors (P = 0.96); 57% in the RT group and 53% in the RS group for T3 tumors (P = 0.85); and 42% in the RT group and 40% in the RS group for T4 tumors (P = 0.05). In the RS group, the local control rate was 75% (3/4) for T2 tumors; 74% (17/23) for T3 tumors; and 82% (9/11) for T4 tumors. In the RT group, the local control rate was 77% (34/44) for T2 tumors; 70% (58/82) for T3 tumors; and 60% (12/20) for T4 tumors. In the RT group, the anal conservation rate was 61% (27/44) for T2 tumors, 59% (48/82) for T3 tumors, and 55% (11/20) for T4 tumors. Local tumoral control and a functioning anus were present in 72 out of 147 (49%) patients [52% (23/44) for T2 patients, 52% (43/82) for T3 tumors, and 30% (6/20) for T4 patients]. In the RS group, the grade 3 complication rate was 9% (13/146) and in the RS group, 5% (2/38). CONCLUSION: For patients with T4 tumors, preoperative radiotherapy and surgery seemed to be better in terms of survival and local tumor control rate, but the difference was not significant probably because the number of patients in the RS group was small. For these large tumors, the treatment should probably be more aggressive, combining chemotherapy and radiation therapy, but the increase of local control in relation with the addition of cytotoxic chemotherapy to irradiation is not proved.

Adult↗
PubMed1995

Epidermoid carcinoma of the anal margin: 17 cases treated with curative-intent radiation therapy.

Between 1973 and 1991, 17 patients with epidermoid carcinoma of the anal margin without evidence of distant metastasis were treated with curative-intent radiation therapy (RT). There were nine T1-tumors, six T2-, one T3- and one T4-tumor; two patients presented with inguinal node involvement: one N1 and one N3. Nine patients underwent prior incomplete local excision (six with microscopic involvement of surgical margins and two with macroscopic residual disease). The radiation dose to the tumor was 60-70 Gy; the radiation dose to the inguinal lymph nodes was 40-45 Gy in N0, and 50-60 Gy for involved inguinal nodes. The 5- and 10-year cancer-specific survival rates were 86.2% and 77.5%, respectively. The same probabilities were 100% and 100% for T1-tumors, 60% and 40% for T2-tumors. Severe complications occurred in two patients, one anal radionecrosis requiring a colostomy and one permanent anal incontinence after local excision, which was non-related to irradiation. For the cured patients, the sphincter preservation rate after 5 years was 82% (9/11). In univariate analysis and in Cox multivariate analysis, the cancer-specific survival rate was influenced by one factor: the tumor size.

Adult↗
PubMed1995

[Radiosurgery by linear accelerators in the treatment of 84 arteriovenous malformations].

We have treated in 1990 and 1991, 84 arteriovenous malformations (AVMs) by radiosurgery. Irradiation was realized by 5 to 7 arcs with 15 MV X rays circular minibeams of a GE-CGR Saturne 43 Linac diameter, at 100 cm 6 to 20 mm; the Betti arm chair and the Talairach frame. The prescribed peripheral dose containing the nidus was 25 Gy corresponding to the 60-70% isodose range (100% was the maximum dose). For the irradiation planning we used the 'associated targets methodology' and the ARTEMIS-3D TPS, both of which have been developped in the radiotherapy departement of the Tenon hospital. Evaluation was performed in February 1995, the follow-up range was 38 to 62 months. In 1990, 46 cases were treated for cure and were all evaluable, whereas in 1991, among the 38 irradiated cases one patient was not evaluable because of lack of arteriographic control. Thus this series consisted in 84 evaluable cases. The overall obliteration rate was 65/84 (78%), partial obliteration was seen in 18/84 (21%) and no change in 1 case. According to AVM volume, obliteration rate was: AVMs < 4200 mm3: 82% (46/56). For lesions > 4200 mm3 it was 68% (19/28). In one isocenter irradiation, the obliteration rate was 42/47 (89%); whereas it was 23/37 (62%) in multi-isocenters treatments. The obliteration rate was better for not previously treated cases: 39/44 (89%) than for previously treated nidus (mostly embolisation) 65% (26/40). In 23 spheroid AVMs obliteration rate was 87% (20/23) in 43 ellipsoid AVMs the obliteration rate was 77% (33/43); and in irregular rounded nidus, it was 67% (12/18). The peripheral dose of 25 Gys has been used in 78 cases (93%), the obliteration rate was 63/78 (81%); in 6 other cases treated with 15-23.5 Gy, it was 2/6 (33%). We observed two recurrences of haemorrhage at 4 and 6 months after radiosurgery (recurrent haemorrhage rate 2/84 = 2.4%) with total neurological recovery in one of the two patients. One patient died of myocardial infarctus 11 months after radiosurgery (there was a partial obliteration of his AVM at 8 months after radiosurgery). There was no AVM related death. One patient developed an epilepsy.

Aged↗
PubMed1994

Epidermoid carcinoma of the anal canal. Results of curative-intent radiation therapy in a series of 270 patients.

BACKGROUND: Epidermoid carcinoma of the anal canal is an uncommon disease, and most institutions have only a small series of patients. The current study of a large series of patients treated with radiation therapy in a single institution evaluates the outcome, prognostic factors, and the late complications for these patients. METHODS: From 1972 to 1991, 270 patients with anal canal epidermoid carcinoma without evident distant metastasis were irradiated with curative intent in the Radiotherapy Department of Tenon Hospital. The sex ratio was 1 man/5.7 women, with a mean age of 67.5 years. The histology included 59.6% well-differentiated epidermoid carcinoma, 32.2% moderately or poorly differentiated epidermoid carcinoma, and 8.2% cloacogenic. The T-classification was: T1: 8.5%; T2: 51.1%; T3: 30.4%; T4: 10%. Abnormal inguinal lymph nodes were present in 12.5% of the patients. Patients were irradiated by external beam. They received a first course of photon irradiation consisting of (mostly 18 mV or 25 mVl; some Co60 or 6 mV) 40-45 Gy (box technique) in the pelvis for 4-5 weeks. After a rest of 4-6 weeks, a second course of 15-20 gy in 2 weeks was given through a perineal field by an electron beam of suitable energy. When rectal involvement was important, a four-field, small box technique was used. Fourteen patients were given a booster irradiation of 30 Gy by interstitial brachytherapy (Iridium 192 sources), and four patients were treated with interstitial brachytherapy alone, to a mean dose of 62.5 Gy. RESULTS: At 5 and 10 years, determinate survival rates were: T1: 86% and 86%; T2: 86.2% and 82.5%; T3: 60.1% and 56.8%; T4: 45% and 45%, respectively. The overall local control rate was 80%. The overall anal conservation rate was 67%. In 154 patients (57%), the anus had maintained its normal function. At 5 and 10 years, determinate survival was 76% and 73.7%, respectively, for N0 and 53.5 and 53.5% for clinically involved inguinal lymph nodes. According to the log-rank test, survival comparisons between T2 and T3 classifications and of tumor sizes less than or equal to 4 cm in length and greater than or equal to 5 cm in length were significant (P = 0.0001 and P < 0.0001, respectively). The presence of clinical abnormal inguinal lymph nodes had a significant negative influence on survival rates (P = 0.047). Multivariate analysis indicated that T-classification and tumor size in centimeters were the only predictive variables. Nonpredictive variables included nodal status, histology, age, total dose, overall treatment time, and irradiation technique. The grade 3 complication rate requiring surgical treatment was 27/270 (10%), considering all patients (27/190 represents a 14% rate for patients who had local tumor control after radiation therapy alone without secondary salvage amputation). There was no significant relationship between complication rate and the aforementioned variables. Because of the homogeneity of the irradiation doses, no significant relationship was found between dose, local control rate, or complication rate. CONCLUSIONS: After radiation therapy, recognizing the distinction between tumor sizes of less than or equal to 4 cm in length and more than 4 cm in length (which is not considered in TNM Classification criteria [International Union Against Cancer, 1987]) could help to improve treatment strategies. For tumors more than 4 cm in length and/or with clinically involved lymph nodes, the treatment should be more extensive with combined chemotherapy and radiation therapy, but the increased local control with the addition of cytotoxic chemotherapy to irradiation has not been proven.

Adult↗
PubMed1994

Total-body irradiation and cataract incidence: a randomized comparison of two instantaneous dose rates.

PURPOSE: To assess the influence of instantaneous total-body irradiation dose rate in hematological malignancies, we randomized 157 patients according to different instantaneous dose rates. METHODS AND MATERIALS: Between December 10, 1986 and December 31, 1989 157 patients have undergone a total-body irradiation before bone-marrow transplantation according to two different techniques: either in one fraction (1000 cGy given to the midplane at the level of L4, and 800 cGy to the lungs) or in six fractions (1200 cGy over 3 consecutive days to the midplane at the level of L4, and 900 cGy to the lungs). Patients were randomized according to two instantaneous dose rates, called LOW and HIGH, in single-dose (6 vs. 15 cGy/min) and fractionated (3 vs. 6 cGy/min) TBI groups; there were 77 cases for the LOW and 80 for the HIGH groups, with 57 patients receiving single-dose (28 LOW, 29 HIGH) and 100 patients receiving fractionated total-body irradiation (49 LOW, 51 HIGH). RESULTS: As of July 1992, 16 (10%) of 157 patients developed cataracts after 17 to 46 months, with an estimated incidence of 23% at 5 years. Four (5%) of 77 patients in the LOW group, 12 (15%) of 80 patients in the HIGH group developed cataracts, with 5-year estimated incidences of 12% and 34%, respectively (p = 0.03). Ten (18%) of 57 patients in the single-dose group, and 6 (6%) of 100 patients in the fractionated group developed cataracts, with 5-year estimated incidences of 39% and 13%, respectively (p = 0.02). When the subgroups were considered, in the single-dose group, 3 (11%) of 28 LOW patients, and 7 (24%) of 29 HIGH patients developed cataracts, with 5-year estimated incidences of 24% and 53%, respectively; in the fractionated group, 1 (2%) of 49 LOW patients, and 5 (10%) of 51 HIGH patients developed cataracts, with 5-year estimated incidences of 4% and 22%, respectively (single-dose LOW vs. single-dose HIGH vs. fractionated LOW vs. fractionated HIGH, p = 0.006). There was no statistically significant difference in terms of 5-year estimated cataract incidence between the patients receiving steroids and those not (30% vs. 25%, p = 0.22). Multivariate analyses revealed that the instantaneous dose rate was the only independent factor influencing the cataractogenesis (p = 0.04). CONCLUSION: We conclude that the total-body irradiation regimen (instantaneous dose rate and/or fractionation) may have an influence on the development of cataracts following bone-marrow transplantation.

Adolescent↗
PubMed1994

The associated targets methodology and the multi-isocenters radiosurgery treatment planning system Artemis-3D.

A new radiosurgical methodology, the "associated targets methodology" has been developed and tested by our group for the irradiation of complex cerebral arteriovenous malformations using our treatment planning system Artemis-3D. For the treatment of the arteriovenous malformations we used 15 MV photons generated by a Saturne 43 Linac, eight additional collimators (6-20 mm in diameter), the Betti fixation seat and the Talairach stereotactic frame. The successive steps of the associated targets' methodology are: -the prescription of a peripheral minimal therapeutic effective dose corresponding to the 60-70% cumulated isodose range; -the compartmentalization of the target volume into several sub-volumes, each of them having its own isocenter, collimator, irradiation space and isocenter dose weight; -the 3-dimensional computation and graphics requirements, and dose volume analysis; -the optimization evaluation criteria taking into account the dose inside and outside of the lesion. Two treatment planning software versions of Artemis-3D exist; the first one was developed for the sitting position and later for the supine treatment position, the second version is a multi-modalities imagery radiosurgical treatment planning system based on more powerful computers. Different types of stereotactic frames have been integrated. Three-dimensional visualization, stereotactic CT imaging, and angiography can be used for the sitting or supine position. We started using this methodology in 1990, and treated 44 patients during that year. For 26 single isocenter arteriovenous malformations, the obliteration rate was 22/26 (85%). In the 18 multi-isocenters irradiation cases, the overall obliteration rate was 11/18 = 61%. An example of successfully irradiated complex arteriovenous malformation is discussed to illustrate the methodology. With this three-dimensional methodology we have improved the results obtained during the first period (1986 to 1989) of our radiosurgical practice in which we used a two dimensional planification approach.

Dose-Response Relationship, Radiation↗
PubMed1994

[Radiosurgical irradiation of 49 cerebral arteriovenous malformations using linear accelerator].

During 1990 we treated 49 cases of arterio-veinous malformations (AVMs) using radiosurgery. We employed 15 MV X-Ray minibeams of a Saturne 43 Linac, eight additional collimators, 6-20 mm, the O Betti armchair and the Talairach stereotactic frame. Irradiation consisted of delivering 25 Gy at the periphery of the nidus corresponding to the 60-70% peripheral isodose range. We used the "Associated Target Methodology" and the three-dimensional treatment planning system Artemis-3D, both of which have been developed in our radiotherapy department. In December 1992, 44 out of 49 patients who had been treated were available for analysis with a 2-3-year follow-up. The overall obliteration rate was 33/44 (75%). According to the number of isocenters the obliteration rate was: 22/26 (85%) for one isocenter. In 18 multi-isocenters irradiation cases overall obliteration rate was 11/18 (61%). Two isocenters were used in nine of these 18 cases, the obliteration rate was 6/9; while when three isocenters were used it was 2/4 and in five cases of four isocenters irradiation the obliteration rate was 3/5. Obliteration rate for lesions < or = 4200 mm3 was 31/37 (84%). For greater volumes (5500 mm3 to 19000 mm3; median 9200 mm3) the obliteration rate was 2/7 whereas three others were partially (75 to 90%) obliterated and two remained inchanged. Before radiosurgery 21 cases received other treatment (mostly embolizations), the obliteration rate in this group was 15/21 (71.5%) while in previously untreated AVMs it was 18/23 (78%). A control arteriography was performed between 6 to 18 months after radiosurgery in 44 patients; three others refused the arteriography but are alive and well; two others had palliative irradiation, one of whom is dead. Out of 28 AVMs checked between 6 to 12 months 17/28 were obliterated (61%). In four cases, epilepsy was the first symptom; one has not suffered a further crisis whereas three others experienced a decrease in the number of crises. Two patients had recurrence of bleeding four and six months after irradiation (recurrence rate 2/44 = 5%). There were no lasting neurological consequences.

Adolescent↗