[Technical parameters to decrease the radiation dose from conventional and digital radiographs]. / Éléments technologiques permettant de réduire la dose en radiologie conventionnelle et numérique.

Reducing radiation dose while maintaining adequate image quality on conventional and digital radiographs requires optimal use of the unit. Additional filtration avoids unnecessary tissue exposure and improves photon transmission. Automatic exposure control may reduce exposure and dose. The volume of tissue imaged must be limited by the use of diaphragms and shutters or compression. Sensitive detectors with increased photon detection also contribute to reduce dose. Radiographic films combined to rare-earth screens also afford a good photon-conversion efficiency. Large area flat panel amorphous silicon x-ray sensors may also reduce dose up to 50% compared to films. Finally, calculation of the Kerma-area product independent of the source distance constitutes an important indicator of radiation dose.

[Hypofractionated stereotactic radiotherapy for brain metastases]. / Place de l'irradiation stéréotaxique hypofractionnée dans le traitement des métastases cérébrales.

PURPOSE: A survey of the literature has been performed to find arguments in order to help the choice between radiosurgery and hypofractionated stereotactic radiotherapy in the treatment of brain metastases. PATIENTS AND METHODS: A comparison of two groups of brain metastases treated with hypofractionated stereotactic radiotherapy or radiosurgery, with or without WBRT was performed. Hypofractionated stereotactic radiotherapy: there were eight series including 448 patients published from 2000 to 2009; treated with 5-6 MV X-Rays, non invasive head immobilization, a margin 2 to 10mm; 24 to 40Gy in three to five fractions; a 5 to 8 days duration in six series and 15-16 days in two other series. WBRT (30%) ; radiosurgery: there were 12 series (1994 to 2005) including 2157 patients; an invasive head immobilization, no margin; doses from 10 to 25 Gy; six series over 12 had Gamma Knife radiosurgery and six had Linacs X-Rays. WBRT (30 Gy/10 F/12 days) associated to radiosurgery in several series. The following parameters were compared: median GTV, median survival, 1-year survival rate, local control rate, necrosis and WBRT rates. RESULTS: Hypofractionated stereotactic radiotherapy series: the parameters were respectively: 0,52-4,47 cm(3) (median 2,8 cm(3)); 5-16 months (median 8,7 months); 68,2-93% (median 82,5%); necrosis rate 3,1%; associated WBRT 30%. Radiosurgery series: the parameters were respectively: 1,3 to 5,5 cm(3) (median 2 cm(3)); 5,5 to 22 months (median 11 months); 71 to 95% (median 85%); 0,5 to 6% (median 2,4%); associated WBRT 58%. Results seem similar in the two groups: Hypofractionated stereotactic radiotherapy with non invasive immobilization could theoretically treat all brain metastases sizes except lesions<10 mm (500 mm(3)). In large volumes,>4200 mm(3) GTV, the toxicity of hypofractionated stereotactic radiotherapy was not reported, thus it was difficult to compare its results with the published reports of radiosurgery toxicity. WBRT was a confusing parameter. Obviously, this initial survey has important limitations, specifically its methodology. CONCLUSION: Radiosurgery and hypofractionated stereotactic radiotherapy could be used to treat brain metastases with GTV>500 mm(3) and < or = 4200 mm(3) (Ø 20mm); for GTV<500 mm(3) (Ø 10mm) an invasive procedure with radiosurgery is necessary. For GTV>4200 mm(3) (Ø 20mm), hypofractionated stereotactic radiotherapy could be proposed, provided further studies, using 4 to 6 Gy fractions, a duration less or equal to 10-12 days and a margin of 2mm will be performed.

[Quality assurance of enhanced dynamic wedge using the aS500-II, EPID]. / Etudes et contrôle de qualité des filtres dynamiques à l'aide de l'imageur portal aS500-II (Varian).

PURPOSE: The work presented herein rests on the study of the Varian EPID aS500-II and the Image Acquisition system IAS3. We assessed the dosimetric performance of this EPID for measurements and quality assurance of enhanced dynamic wedge profiles and wedge factors. MATERIALS AND METHODS: We evaluated the dosimeter properties using the integrated asynchronous mode of acquisition in treatments with enhanced dynamic wedges (EDW). We studied the performance, stability and the reproducibility in measurements of the transmission factors and profiles of the fields with dynamic wedges. EPID profiles were compared to the "Profiler Sun Nuclear" diode array and PTW ion chamber. Analytical functions were developed in order to correct EDW profiles. The dependence of EPID measurements on wedge direction, beam dimensions and source to EPID distance was assessed. RESULTS: The backscatter produced by the "exact arm" was evaluated; EPID profiles depended on the EDW direction and on the detector source distance. Wedge factors were determined using this detector and compared to the ion chamber response, differences were all within 1 %. Two empirical correction functions were developed to produce EPID wedge profiles that correspond to diode for all wedge angles and energies depending on the wedge direction. CONCLUSION: The EPID is highly suited to regular measurement of EDW due to the reproducibility of the EPID-measured wedge factors and profiles.

[Electronic tissue compensation for breast external radiotherapy: use of digital reconstructive radiography]. / Compensation électronique dans les traitements de cancer du sein par irradiation: utilisation des radiographies numériques reconstruites (digital reconstruct radiograph [DRR]).

PURPOSE: In case of external breast radiotherapy, the usual treatment consists of two tangential beams homogeneously attenuated by a dynamic or physics wedge in order to obtain the most homogeneous dose distribution as possible. Depending of the shape and size of the breast volume, we may observe with this technique dose heterogeneity over 20% from the recommendation of the International Committee on Radiation Units and Measurements (95-107%). We propose to study breast treatment planning by compensating tissues thickness in order to decrease dose heterogeneity observed on the dose distribution for conventional treatment. MATERIALS AND METHODS: We have segmented the initial tangential beams used for this kind of treatment into several smaller beams. Their shape was adapted to the distribution of the greys level on the DRR image. Therefore, we have compensated the thickness gradient and we have given the right dose to the right thickness group. RESULTS: Dose distribution performed with this method shows an improvement of the dose homogeneity in the three space dimensions and a decrease of the maximal dose between 5 and 10% over the ICRU recommendation. CONCLUSION: This technique allows us to perform breast irradiation on a single photon energy linac even if the treated volume presents important thickness gradient. However, in case of large breast, this method is not able to reduce the overdosage at the entry of the volume due to inappropriate photon energy relative to the breast thickness.

[Progress in radiation therapy and integration in Tenon hospital (AP-HP) of new advances in routine practices of radiotherapy for non-small-cell lung cancer]. / Evolution de la radiothérapie externe et intégration à l'hôpital Tenon (AP-HP) des innovations technologiques récentes dans la pratique de la radiothérapie externe des carcinomes bronchiques non à petites cellules.

Much progress has been made in recent years in administration modalities for external radiotherapy of non-small-cell lung carcinoma. Three-dimensional conformal radiotherapy with or without intensity modulation, with respiratory gated radio-therapy (4D radiotherapy), and image-guided radiotherapy (IGRT) can be considered as a third revolution in radiation therapy after total dose fractionation and the development of megavoltage radiation therapy equipment. We describe progress in the three-dimensional radiotherapy technique and the integration of this technique in the department of Radiation Oncology at Tenon hospital (AP-HP).

[Impact of computed tomography (CT) and 18F-deoxyglucose-coincidence detection emission tomography (FDG-CDET) image fusion for optimisation of conformal radiotherapy in non-small-cell lung cancers]. / Tomographie par émission de positons et détection en coïncidence (TEDC) et recalage d'images de simulation virtuelle par tomodensitométrie. Impact sur la planification de la radiothérapie conformationnelle des cancers bronchiques non à petites cellules.

UNLABELLED: To report a retrospective study concerning the impact of fused 18F-fluorodeoxy-D-glucose (FDG)-hybrid positron emission tomography (PET) and computed tomography (CT) images on three-dimensional conformal radiation therapy (3D-CRT) planning for patients with non-small-cell lung cancer (NSCLC). PATIENTS AND METHODS: One hundred and one patients consecutively treated for stages I-III NSCLC were studied. Each patient underwent CT and FDG-hybrid PET for simulation treatment in the same radiation treatment position. Images were coregistered using five fiducial markers. Target volume delineation was initially performed on the CT images and the corresponding FDG-PET data were subsequently used as an overlay to the CT data to define target volume. RESULTS: FDG-PET identified previously undetected distant metastatic disease in 8 patients making them ineligible for curative CRT (one patient presented some positive uptakes corresponding to concomitant pulmonary tuberculosis). Another patient was ineligible for curative treatment because fused CT/PET images demonstrated excessively extensive intrathoracic disease. The gross tumor volume (GTV) was decreased by CT/PET image fusion in 21 patients (23%) and was increased in 24 patients (26%). The GTV reduction was > or = 25% in 7 patients because CT/PET image fusion reduced pulmonary GTV in 6 patients (3 patients with atelectasis) and mediastinal nodal GTV in 1 patient. The GTV increase was > or = 25% in 14 patients due to an increase of the pulmonary GTV in 11 patients (4 patients with atelectasis) and detection of occult mediastinal lymph node involvement in 3 patients. Among 81 patients receiving a total dose > or = 60 Gy at ICRU point, after CT/PET image fusion, the percentage of total lung volume receiving more than 20 Gy (VL20) increased in 15 cases and decreased in 22 cases. The percentage of total heart volume receiving more than 36 Gy increased in 8 patients and decreased in 14 patients. The spinal cord volume receiving at least 45 Gy (2 patients) decreased. After multivariate analysis, one single independent factor made significant effect of FDG/PET on the modification of the size of the GTV: tumor with atelectasis (P = 0.0001). Conclusion. - Our study confirms that integrated hybrid PET/CT in the treatment position and coregistered images have an impact on treatment planning and management of patients with NSCLC. FDG images using dedicated PET scanners with modern image fusion techniques and respiration-gated acquisition protocols could improve CT/PET image coregistration. However, prospective studies with histological correlation are necessary and the impact on treatment outcome remains to be demonstrated.

[Impact of computed tomography (CT) and 18F-deoxyglucose positron emission tomography (FDG-PET) image fusion for conformal radiotherapy in esophageal carcinoma]. / Tomographie par émission de positons et fusion d'images de simulation virtuelle par tomodensitométrie. Impact sur la planification de la radiothérapie conformationnelle des cancers de l'oesophage.

PURPOSE: To study the impact of fused (18)F-fluoro-deoxy-D-glucose (FDG)-hybrid positron emission tomography (PET) and computed tomography (CT) images on conformal radiation therapy (CRT) planning for patients with esophageal carcinoma. PATIENTS AND METHODS: Thirty-four patients with esophageal carcinoma were referred for concomitant radiotherapy and chemotherapy with radical intent. Each patient underwent CT and FDG-hybrid PET for simulation treatment in the same radiation treatment position. PET-images were coregistered using five fiducial markers. Target delineation was initially performed on CT images and the corresponding PET data were subsequently used as an overlay to CT data to define the target volume. RESULTS: FDG-PET identified previously undetected distant metastatic disease in 2 patients, making them ineligible for curative CRT. The Gross Tumor Volume (GTV) was decreased by CT and FDG image fusion in 12 patients (35%) and was increased in 7 patients (20.5%). The GTV reduction was >or=25% in 4 patients due to reduction of the length of the esophageal tumor. The GTV increase was >or=25% with FDG-PET in 2 patients due to the detection of occult mediastinal lymph node involvement in one patient and an increased length of the esophageal tumor in the other patient. Modifications of the GTV affected the planning treatment volume (PTV) in 18 patients. Modifications of delineation of GTV and displacement of the isocenter of PTV by FDG-PET also affected the percentage of total lung volume receiving more than 20 Gy (VL20) in 25 patients (74%), with a dose reduction in 12 patients and a dose increase in 13 patients. CONCLUSION: In our study, CT and FDG-PET image fusion appeared to have an impact on treatment planning and management of patients with esophageal carcinoma related to modifications of GTV. The impact on treatment outcome remains to be demonstrated.

[Dosimetric validation of compensator for their use in clinical routine, in conformation radiotherapy]. / Validation dosimétrique des compensateurs physiques pour leur utilisation clinique en radiothérapie conformationnelle.

PURPOSE: The aim of this work was to establish the acquisition, calculation and 3D compensator manufacturing optimum parameters. This methodology is based on virtual simulation and 3D dosimetry. MATERIALS AND METHODS: The material used is a helicoidal CT (PQ 5000-Marconi), a virtual simulation system (AcQsim version 4-Marconi), a Treatment Planning System (Dosigray), a linear accelerator Saturne 43 (Varian, CGR), an automated milling system for compensator filters (Autimo 2.5 D-HEK), a water tank phantom (wellhofer) and an homogeneous phantom with simple patterns in order to simulate the obliquity surface of patient body. The compensator was composed by granulate tin because this material ensures a good profile modulation. The compensation plane has been calculated at 80% to dose profile. The compensator thickness profile has been calculated with different acquisition (slice thickness, pitch factor), calculation (attenuation coefficient, bixel) and fabrication parameters (drill diameter, specification of milling system). RESULTS: After this preliminary study, we have defined the optimum parameters for the compensator realization. We have observed that the slice thickness, bixel size and drill diameter are the parameters that mainly affect the profiles homogeneity. The choice of parameters with smaller dimensions S = 3 mm; B = 3 mm, F = 3 mm, improve the profiles homogeneity. Though, for manufacture times compatible with the clinical routine, the selected parameters are S = 5 mm, B = 6 mm and F = 6 mm. Compensator can be used for any type of Linac. However, one must pay attention on their realization and their positioning on the beam central axis.

[Physical and methodological aspects of multimodality imaging and principles of treatment planning in 3D conformal radiotherapy]. / Aspects physiques et méthodologiques de l'imagerie multimodalités et principes de planification dosimétrique pour la radiothérapie conformationnelle tridimensionnelle.

The recent evolutions of the imaging modalities, the dose calculation models, the linear accelerators and the portal imaging permit to improve the quality of the conformal radiation therapy treatment planning. With DICOM protocols, the acquired imaging data coming from different modalities are treated by performant image fusion algorithms and yield more precise target volumes and organs at risk. The transformation of the clinical target volumes (CTV) to planning target volumes (PTV) can be realised using advanced probabilistic techniques based on clinical experience. The treatment plans evaluation is based on the dose volume histograms. Their precision and clinical relevance are improved by the multi-modality imaging and the advanced dose calculation models. The introduction of the inverse planning systems permitting to realise modulated intensity radiation therapy generates highly conformal dose distributions. All the previously cited complex techniques require the application of rigorous quality assurance programs.

[Breast-conserving surgery and irradiation for early breast cancer: value of surgical clips in the surgical cavity]. / Association radiochirurgicale conservatrice des cancers du sein de petit volume: intérêt des clips chirurgicaux dans le lit de tumorectomie.

PURPOSE: To evaluate, qualitatively and quantitatively, the role of surgical clips in planning the tumor bed electron or brachytherapy boost in patients undergoing breast-conserving surgery and radiotherapy. PATIENTS AND METHODS: In 60 patients with breast cancer stage I or II, the excision cavity boundaries were marked by clips at surgery. Patients received a boost with brachytherapy (n = 51) or electron beam (n = 9) after whole breast irradiation. The boost target volume was first planned using clinical, mammography and operative information and its accuracy evaluated by screening the surgical clips and, if necessary, adjusting the field to encompass all clips and to include the scar. Dosimetry was retrospectively performed for each brachytherapy patient and for each surgical clip. RESULTS: It was necessary to modify the target volume field in 11 cases (18%). The average dose received by the surgical clips was 116.1% of the dose delivered to the reference isodose (median: 101.75%, range: 16-457%). However, dose heterogeneity was important in the same patient and between patients. CONCLUSION: Delineation of the boost target volume with surgical clips is more accurate than with clinical landmarks alone but this technique does not allow measurements of the clip-chest wall and clip-skin distances. Virtual simulation with CT-scan cuts is recommended for optimising boost planning.

[Importance of quantitative evaluation in the planning of the stereotactic irradiation of complex cAVMs]. / Importance de l'évaluation quantitative dans la pratique clinique et planification des irradiations en conditions stéréotaxiques des MAVc complexes.

BACKGROUND AND PURPOSE: The purpose was to present the successive steps of dosimetric planning and the different means used to allow the choice of the best solution among several planning projects considering the anatomical and clinical features of arteriovenous malformation. Method. Four successive steps were: A study of these factors for 5 different plannings of a clinical case using different isocenters is presented and the results are discussed. CONCLUSION: For complex arteriovenous malformations several hours are often necessary to permit physicians/radiotherapists to elaborate planning which is often a compromise among several solutions.

[Automatic definition of prescription isodose for stereotaxic radiation of arteriovenous malformations]. / Définition automatique de l'isodose de prescription pour les irradiations stéréotaxiques de malformations artérioveineuses.

PURPOSE: To evaluate dosimetric consequences generated by the automatic definition based on lesion coverage of prescription isodose. A clinical series of 124 arteriovenous malformations was analysed. Plan quality was quantified by the standard deviation of the differential dose volume histogram calculated in the lesion. MATERIAL AND METHODS: We define two quantitative protocols based on lesion coverage for the automatic definition of prescription isodose using a volumetric definition of coverage (90% of lesion volume), and an isodose-based definition proposed by RTOG (prescription isodose equals minimum isodose in the lesion divided by 0.9). RESULTS: We have evaluated the plans obtained for these two protocols, calculating several dose-volume indices. These indices are presented as a function of dose-volume histogram standard deviation in order to quantify the consequences of their variations for this representative series of plans. The margin our team tolerates is such that the sum of underdosed lesion and overdosed healthy tissues factors remains lower than one. Protocol based on volumetric coverage gives results situated within this margin. Protocol based on RTOG definition produces conformation indices that could be greater than 1. CONCLUSION: The absolute dose would be decided taking into account examined dose-volume indices and clinical data. A protocol for automatic definition of prescription isodose using volumetric lesion coverage seems to be more judiciously adapted to arteriovenous malformation conformal plans in stereotactic conditions because of variations observed in the overdosage of healthy tissues.

Linac radiosurgery for cerebral arteriovenous malformations: results in 169 patients.

PURPOSE: To present the SALT group results using Linac radiosurgery (RS) for AVM in 169 evaluable patients treated from January 1990 thru December 1993. METHODS AND MATERIALS: Median age was 33 years (range 6-68 years). Irradiation was the only treatment in 55% patients. Other treatment modalities had been used prior to RS in 45%: one or more embolizations in 36%, surgery in 6%, and embolization and surgery in 3% patients. Nidus were supratentorial in 94% patients, infratentorial in 6% patients. Circular 15 MV x-ray minibeams (6-20 mm) were delivered in coronal arcs by a GE-CGR Saturne 43 Linac. Patient set-up included a Betti arm-chair, a Talairach frame. Prescribed peripheral dose was 25 Gy on the 60%-70% isodose (max dose 100%). Arteriographic results were reassessed in December 1997 at 48 to 96 months follow-up. RESULTS: The overall obliteration rate (OR) was 64% (108/169). AVM volumes ranged from 280 to 19,920 mm(3), median 2460 mm(3). OR was 70% for AVM

[Intensity modulation by inverse planning: preliminary results]. / Modulation d'intensité par planification inverse: résultats préliminaires.

An inverse planning algorithm for determining the intensity of modulated beams that generates conformal radiotherapy dose distributions is presented. This algorithm is based on the mathematical analysis of the singular values decomposition. It is integrated in the DOSIGRAY 3D treatment planning software. The dose is calculated by the separation of the primary and scattered radiation. We presented, for a prostate cancer, the modulated intensity profiles and the optimal dose distribution obtained by the inverse optimization software developed and integrated in the treatment planning system. We obtained a region with high doses which geometrically conforms the target volume and spares the neighboring critical structures. This preliminary study showed the feasibility and the managing of the singular value decomposition to generate conformal dose distribution in a clinical environment.

[Radiodiagnosis and irradiated pregnancies]. / Radiodiagnostic et grossesses irradiées.

An X-ray examination can sometimes be performed during the first few days of pregnancy. To prevent these accidental irradiations of the fetus, women must receive specific information about radiation effects, the ten Day Rule must be respected, and the physician must choose a non irradiating technique. X-ray examination may be performed in an emergency, especially if the examination is far from the pelvis. The radiologist must optimize the constants and decrease the number of films. The dose received depends on mAs, but other parameters are necessary for calculation (film source distance, kV, filtration...). For computed tomography, slice thickness, and interval between slices are taken in account. The dose received reaches a maximum after three axial sections, but is higher for a given area, than with conventional radiography. The irradiation effects depend on the fetal dose and the stage of pregnancy. Before implantation, the fetal dose is either ineffective or induces a miscarriage. During organogenesis, between the second and 16th week, doses exceeding 500 mGy can cause death of the fetus, malformations or growth retardation. We consider that when the dose is less than 100 mGy, they are no reasons to terminate the pregnancy. MRI does not seem to be dangerous for the course of pregnancy. No studies have demonstrated any teratogenic effects with intense magnetic fields.

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.