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Since 1995, the brachytherapy dosimetry protocols follow the methodology recommended by the Task Group 43. This methodology, which has the advantage of being fast, is based on several approximations that are not always valid in clinical conditions. Model-based dose calculation algorithms have recently emerged in treatment planning stations and are considered as a major evolution by allowing for consideration of the patient's finite dimensions, tissue heterogeneities and the presence of high atomic number materials in applicators. In 2012, a report from the American Association of Physicists in Medicine Radiation Therapy Task Group 186 reviews these models and makes recommendations for their clinical implementation. This review focuses on the use of model-based dose calculation algorithms in the context of iridium 192 treatments. After a description of these algorithms and their clinical implementation, a summary of the main questions raised by these new methods is performed. Considerations regarding the choice of the medium used for the dose specification and the recommended methodology for assigning materials characteristics are especially described. In the last part, recent concrete examples from the literature illustrate the capabilities of these new algorithms on clinical cases.

In order to reduce the incidence of major accidents during external radiotherapy treatment, "never events" checklists have been incorporated into the "record and verify" system. This article details this process. Prospects for improvement are also proposed, including a peer-to-peer audit on the use of checklists and the availability of the radiotherapy information system manufacturer to collaborate in this process to secure the patients' journey.

Background and Purpose The aim of this study was to investigate the role of radiation dose received to the circle of Willis (WC) during radiation therapy (RT) and of potential dose-response modifiers on the risk of stroke after treatment of childhood cancer. Methods We evaluated the risk factors for stroke in a cohort of 3172 5-year survivors of childhood cancer who were followed up for a median time of 26 years. Radiation doses to the WC and brain structures were estimated for each of the 2202 children who received RT. Results Fifty-four patients experienced a confirmed stroke; 39 were ischemic. Patients not receiving RT had a stroke risk similar to that of the general population, whereas those who received RT had an 8.5-fold increased risk (95% confidence interval [CI]: 6.3-11.0). The excess of incidence of stroke increased yearly. The dose of radiation to the WC, rather than to other brain structures, was found to be the best predictor of stroke. The relative risk was 15.7 (95% CI: 4.9-50.2) for doses of 40 Gy or more. At 45 years of age, the cumulative stroke incidence was 11.3% (95% CI: 7.1%-17.7%) in patients who received 10 Gy or more to the WC, compared with 1% expected from general population data. Radiation doses received to the heart and neck also increased the risk. Surgery for childhood brain cancer was linked to hemorrhagic strokes in these patients. Conclusion The WC should be considered as a major organ at risk during RT for childhood brain cancers. The incidence of radiation-induced ischemic stroke strongly increases with long-term follow-up.

Aims In locally advanced cervical cancer, the dose delivered results from the sum of external beam radiotherapy and brachytherapy, and is limited by the surrounding organs at risk. The balance between both techniques influences the total dose delivered to the high-risk clinical target volume (HR-CTV). The aim of the present study was to compare the ability of reaching different planning aims after external beam radiotherapy pelvic doses of 45 Gy in 25 fractions or 50.4 Gy in 28 fractions, both considered as standard prescriptions. Materials and methods The optimised plans of 120 patients treated with pelvic chemoradiation followed by magnetic resonance image-guided intracavitary brachytherapy were reviewed. The doses per pulse were calculated, and the number of pulses required to reach the planning aims, or a limiting dose constraint to organs at risk, was calculated. All doses were converted to 2-Gy equivalents. Three scenarios were applied consisting of different sets of planning aims: 85 and 60 Gy for the HR-CTV and the intermediate-risk CTV (IR-CTV) D90 (minimal dose received by 90% of the volume) in scenario 1, 90 and 60 Gy, respectively, for scenarios 2 and 3. For organs at risk, dose constraints were 90, 75 and 75 Gy to the bladder, rectum and sigmoid D2cm 3 , respectively, in scenarios 1 and 2, and 80, 65 and 70 Gy in scenario 3. Results A similar HR-CTV D90 could have been reached in scenarios 1 and 2 according to both pelvic doses. In scenario 3, a higher mean HR-CTV could have been reached in the 45 Gy arm (83.5 ± 8.0 versus 82.4 ± 8.0, P 3 of organs at risk was systematically and significantly increased after a delivery of 50.4 Gy to the pelvis, from 0.9 to 2.89 Gy. The proportions of plans reaching planning aims were 85.8, 72.5 and 42.5% after 45 Gy and 85.5, 67.5 and 33.3% after 50.4 Gy according to scenarios 1, 2 and 3, respectively. According to scenario 3, 50.4 Gy, the reachable HR-CTV D90 was higher in 30% of the cases, by 2 Gy in two cases. Those cases were unpredictable and due to unfavourable organs at risk topography and poor response to external beam radiotherapy. Conclusion The delivery of 45 Gy in 25 fractions to the pelvis before brachytherapy warrants a higher probability to reach brachytherapy planning aims, in comparison with 50.4 Gy in 28 fractions.

International audience; Background and purpose The dose effect-effect relationship for cardiac diseases following radiotherapy suffers from uncertainties. Three dimensional coronary artery (CA) dose calculation after mediastinal Hodgkin lymphoma radiotherapy was performed, using the patient's coronary CT angiography (CCTA), and the relationship between the coronary arteries’ radiation doses and the risk of stenosis was estimated. Materials and methods Radiotherapy simulation CT scans and CCTAs of patients treated for a mediastinal Hodgkin lymphoma were used to merge thoracic and detailed cardiovascular anatomies. Radiation treatment parameters were used to estimate CA radiation doses. Twenty-one patients without coronary stenosis (controls) were matched with twelve patients with stenosis (cases). CA segments were considered as sub-volumes of interest. Radiation doses to stenotic segments were compared with those received by normal segments (from cases and controls) using a logistic regression. Results In eleven cases out of twelve, the highest of the coronary dose distribution was on a damaged segment. Logistic regression with CA segments yielded an odds ratio associated with the risk of coronary stenosis of 1.049 per additional gray with the CA segment median dose (95% confidence interval, 1.004–1.095; p-value

Since 1995, the brachytherapy dosimetry protocols follow the methodology recommended by the Task Group 43. This methodology, which has the advantage of being fast, is based on several approximations that are not always valid in clinical conditions. Model-based dose calculation algorithms have recently emerged in treatment planning stations and are considered as a major evolution by allowing for consideration of the patient's finite dimensions, tissue heterogeneities and the presence of high atomic number materials in applicators. In 2012, a report from the American Association of Physicists in Medicine Radiation Therapy Task Group 186 reviews these models and makes recommendations for their clinical implementation. This review focuses on the use of model-based dose calculation algorithms in the context of iridium 192 treatments. After a description of these algorithms and their clinical implementation, a summary of the main questions raised by these new methods is performed. Considerations regarding the choice of the medium used for the dose specification and the recommended methodology for assigning materials characteristics are especially described. In the last part, recent concrete examples from the literature illustrate the capabilities of these new algorithms on clinical cases.

In order to reduce the incidence of major accidents during external radiotherapy treatment, "never events" checklists have been incorporated into the "record and verify" system. This article details this process. Prospects for improvement are also proposed, including a peer-to-peer audit on the use of checklists and the availability of the radiotherapy information system manufacturer to collaborate in this process to secure the patients' journey.

Objectif de l’etude Etudier les facteurs predictifs d’une pathologie cerebrovasculaire apres cancer de l’enfant. Materiel et methode Il s’agissait d’un etude de cohorte French Childhood Cancer Survivor Study (FCCSS) : 7018 survivants a 5 ans d’un cancer de l’enfant traite avant 2001, dont 1193 pour une tumeur cerebrale, et suivis 24 ans en moyenne, par l’acces aux dossiers medicaux et aux donnees du Systeme national d’information interregimes de l’assurance maladie (Sniiram), ainsi qu’au moyen de l’envoi d’autoquestionnaires. Les radiotherapies recues par 4176 sujets, dont 1016, pour une tumeur cerebrale, ont ete reconstituees a l’aide de fantomes anthropomorphiques, et les doses de radiation recues au niveau des arteres cerebrales et d’autres structures d’interet ont ete estimees. Resultats Un total de 145 sujets a ete atteint d’un accident vasculaire cerebral, dont 72 apres une tumeur cerebrale et 134 apres la radiotherapie. Le type d’accident vasculaire cerebral n’a pas pu etre defini pour 24 patients, il etait ischemique pour 77 et hemorragique pour 44. Il n’a pas ete possible d’identifier de drogue ou de categorie de drogue augmentant le risque d’accident vasculaire cerebral. Dans une analyse multifactorielle, celui-ci etait plus important chez les sujets atteints d’une neurofibromatose de type I (NF1), et augmentait avec la dose de radiation recue au niveau des arteres cerebrales, le coefficient de risque etant plus eleve pour les accidents vasculaires cerebraux ischemiques, ainsi qu’avec la radiotherapie thoracique ou abdominale. Il n’a pas ete possible de mettre en evidence de role de la chirurgie des tumeurs cerebrales, que ce soit propre ou par interaction avec la radiotherapie, mais seuls 206 sujets traites pour une tumeur cerebrale n’avaient pas eu de chirurgie. Les sujets qui avaient recu de la radiotherapie, mais 30 Gy ou plus sur seulement moins de 5 % de la longueur des arteres cerebrales principales avaient un risque d’accident vasculaire cerebral augmente d’un facteur 2,8 (1,3–5,5). En revanche, il n’y avait pas d’evidence claire pour un role des doses faibles de rayonnements ionisants de un ou quelques Gy. Conclusion Cette etude n’a pas permis de mettre en evidence de role de la chimiotherapie ou de la chirurgie dans le risque de tumeur cerebrale, mais a permis de preciser et de quantifier le role de la radiotherapie cerebrale.

The use of image-guided brachytherapy has led to a significant change in application techniques and improvements in treatment planning. Today, 3D imaging has replaced orthogonal radiographs for a large number of treatments, providing a possibility of an optimization adapted to the anatomy of each patient. When properly selected and implemented, this imaging provides accurate 3D information of volumes and brachytherapy device, allowing moving from a dose to points assessment to a dose/volume evaluation. This article describes the contribution of different imaging modalities for the different brachytherapy techniques: gynecological brachytherapy, interstitial brachytherapy (breast, penis, etc.) and prostate brachytherapy. It reminds recommendations for the establishment of protocols of images acquisition and 3D reconstruction of brachytherapy devices (applicators, plastic tubes, needles, etc.).

Resume Objectif Evaluer le gain dosimetrique d’une irradiation de la glande mammaire avec le module d’optimisation avec presegmentation (OAPS, DosiSoft™) par rapport a une irradiation tridimensionnelle conformationnelle standard. Patients et methodes Vingt patientes atteintes d’un cancer du sein, droit pour neuf, gauche pour 11, traitees par chirurgie conservatrice, ont ete selectionnees avec differents volumes mammaires (le volume median etait de 537 cm 3 [100–1049 cm 3 ]). Deux planifications dosimetriques ont ete realisees et comparees pour chaque patiente : (i) tridimensionnelle conformationnelle et (ii) avec modulation d’intensite avec champ dans le champ avec le module OAPS, apres delineation manuelle de la glande mammaire, delineation automatique d’un volume de compensation (volumes cibles) et des organes a risque (cœur, poumons). Le gain dosimetrique a ete evalue en fonction de l’indice de conformite de distribution de dose pour les volumes cibles, de la dose moyenne et le V30 Gy (volume recevant 30 Gy) pour le cœur, et de la dose moyenne, et les V20 Gy (volume recevant 20 Gy) et V30 Gy pour le poumon. Resultats La planification OAPS permet d’ameliorer l’homogeneite de la distribution de dose mammaire avec un indice de conformite de distribution de dose moyen de 0,978 contre 0,897 en radiotherapie tridimensionnelle conformationnelle ( p p p Conclusion Le module OAPS, developpe en partenariat avec la societe DosiSoft™ est une methode originale de planification et d’irradiation de la glande mammaire, automatisee, rapide et simple, qui permet d’augmenter l’indice de conformite tout en epargnant les organes a risque.

Resume Objectif de l’etude Evaluer la toxicite aigue de la radiotherapie conformationnelle avec modulation d’intensite dans le traitement adjuvant postoperatoire des sarcomes retroperitoneaux. Patients et methodes Les dossiers des patients operes d’un sarcome retroperitoneal puis irradies avec modulation d’intensite ont ete retrospectivement revus. Resultats Les patients etaient atteints de lesions primitives pour sept et de rechutes pour sept. Tous ont beneficie d’une resection macroscopiquement complete. Toutes les tumeurs etaient des liposarcomes, de taille mediane de 21 cm (extremes : 15–45), le volume cible previsionnel median etait de 580 cm 3 (extremes : 329–1172) et la dose mediane prescrite de 50,4 Gy (extremes : 45–54). Le suivi median est de 11,5 mois (extremes : 2–21,4). La toxicite aigue a ete moderee : une toxicite digestive aigue de grade 1–2 est survenue chez 12 des 14 patients (86 %), mais il n’y a eu aucune perte de poids de plus de 5 % et aucune interruption de traitement. Sur le plan digestif, deux mois apres la fin de la radiotherapie, il n’etait plus releve qu’un cas de toxicite de grade 1 (7 %). Il n’y a eu qu’un cas de toxicite de grade 3 (douleur abdominale transitoire) pendant le suivi. Trois tumeurs ont rechute, deux uniquement en dehors de la region irradiee et une a la fois en zone irradiee et non irradiee. Conclusion La toxicite aigue de la radiotherapie conformationnelle avec modulation d’intensite est faible. Un suivi plus long est necessaire pour evaluer la toxicite a long terme, principalement digestive et renale, et le risque de cancer radio-induit.

Resume Objectif de l’etude Etudier la dose delivree lors de l’acquisition d’images par le systeme d’imagerie par tomographie conique de haute energie (MVCBCT) MVision® embarque sur un accelerateur Oncor Impression® (Siemens™). Materiel et methodes L’acquisition d’images par tomographie conique de haute energie a ete modelisee dans un systeme de planification de traitement par 67 faisceaux de photons de 6 MV. Une etude a ete realisee afin de : comparer les doses calculee et mesuree au centre d’un fantome cylindrique ; comparer les distributions de dose calculee et mesuree dans le fantome Alderson-Rando pelvis ; etudier l’influence de l’acquisition d’images par tomographie conique de haute energie, pour le repositionnement d’un patient traite pour un cancer prostatique par irradiation conformationnelle tridimensionnelle de 74 Gy, sur les histogrammes dose–volume (HDV) pour le traitement et sept tomographies coniques de haute energie (j1–3 puis chaque semaine) et pour le traitement et 37 tomographies coniques de haute energie (une par jour de traitement). Resultats L’ecart entre les doses calculee et mesuree au centre du fantome cylindrique etait inferieur a 3 %. Un ecart maximum de 7 % entre la distribution de dose calculee dans le fantome Rando et les doses mesurees normalisees a l’isocentre des faisceaux a ete observe (ecart moyen inferieur a 4 %). La dose delivree a l’isocentre etait de l’ordre de 3,7 cGy pour un protocole « 5 unites moniteur », avec une dose maximale de l’ordre de 6 cGy. Dans le cas du patient considere, la realisation de 37 tomographies coniques de haute energie correspondait a une dose moyenne additionnelle au volume-cible previsionnel (PTV) de 1,2 Gy pour un protocole « 5 unites moniteur », avec une influence significative sur les histogrammes dose–volume. Conclusion Au regard de cette etude, il apparait que les doses delivrees lors d’une utilisation frequente de la tomographie conique de haute energie doivent etre obligatoirement prises en compte par l’oncologue radiotherapeute dans l’evaluation de la dose therapeutique delivree au volume-cible et aux organes a risque.

Resume Objectif de l’etude Ce travail presente la mise en place d’un protocole de controle qualite d’un systeme d’imagerie cone beam megavoltage (MVCB) embarque sur un accelerateur lineaire Oncor (Siemens) 6 MV. Materiel et methodes Plusieurs parametres ont ete controles sur le systeme MVCB : (1) calibration geometrique initiale du systeme ; (2) qualite des images (distorsion geometrique, uniformite, resolution spatiale, resolution a bas contraste) pour differents protocoles d’acquisitions ; (3) correspondance entre l’intensite des voxels et les densites electroniques ; (4) dose delivree lors de la realisation d’un MVCB. Ces tests ont ete realises principalement avec deux fantomes cylindriques specifiques au controle qualite (CQ) d’un systeme MVCB, fournis par la societe Siemens, ainsi qu’avec les fantomes Catphan 600 (The Phantom Laboratory) et QuasarTM Multipurpose Body (Modus Medical Devices Inc). Resultats Les resultats des controles de la qualite des images etaient dans les tolerances retenues. L’utilisation du fantome Catphan 600 s’est revelee inadaptee pour le CQ des images MVCB. Ces tests ont egalement mis en evidence la necessite de corriger les images MVCB du phenomene de durcissement du faisceau dans le cas d’une utilisation a des fins de calcul de dose. Conclusion Les caracteristiques initiales du systeme d’imagerie MVCB ont ete etablies. Ces tests ont egalement permis d’evaluer l’influence de divers parametres sur la qualite des images et la dose associee delivree lors de leur acquisition, ainsi que de souligner les corrections supplementaires necessaires pour une utilisation des images MVCB a des fins de calcul de dose.

Ces dernieres annees ont vu se developper des techniques d’irradiation performantes telles que la radiotherapie conformationnelle tridimensionnelle et la radiotherapie avec modulation d’intensite (RCMI), La precision avec laquelle ces techniques permettent de delivrer la dose a rehausse l’importance d’une localisation et d’une definition les plus exactes possibles des volumes d’interet. Pour repondre a cette exigence, de nouvelles technologies regroupees sous l’appellation de la radiotherapie guidee par l’image (IGRT pour « image-guided radiation therapy») se sont developpees et peuvent etre utilisees dans deux principales phases d’un traitement par radiotherapie externe: 1) la preparation du traitement par la definition du volume cible; 2) la realisation du traitement par le repositionnement du patient et la localisation du volume cible. Dans cet article, nous presenterons plus particulierement differentes techniques d’IGRT pouvant etre utilisees lors de la deuxieme phase: l’imagerie utilisant un faisceau de rayons X (kV ou MV) comme le systeme ExacTrac® ou le systeme associe au CyberKnife™, l’imagerie tomodensitometrique ou la tomographie conique, et l’imagerie non irradiante comme la detection des balises de radiofrequence ou le « tracking » de la surface du patient utilisant la video.

Resume Objectif de l'etude La mise en œuvre d'une radiotherapie conformationnelle fait generalement appel a des logiciels de simulation virtuelle. Une part de la qualite du traitement etant liee a la precision de la balistique, il est imperatif de controler ces logiciels avant utilisation clinique. Les tests presentes ont ete realises sur le systeme de planification de traitement ISOgrayTM (DOSIsoft), comprenant les modules de delineation (IMAgo) et de simulation virtuelle (SIMAgo). Materiel et methodes Les controles les plus pertinents, selon notre experience clinique, ont ete selectionnes a partir de protocoles internationaux. Ces tests ont porte principalement sur les outils de mesure et de delineation, sur les fonctionnalites de simulation virtuelle, et ont ete realises a l'aide de trois fantomes : les fantomes QuasarTM Multi-Purpose Body et Multi-Leaf Collimator Beam Geometry (Modus Medical Devices Inc.) et un fantome cubique developpe a l'hopital Tenon. Resultats Les tests realises n'ont pas mis de problemes en evidence et ont permis de souligner la necessite de garder un regard critique sur les resultats affiches par un logiciel de simulation virtuelle. Le contraste de visualisation utilise lors de la delineation, l'epaisseur des coupes scanner, le mode de calcul et d'affichage des volumes tridimensionnels utilises par le logiciel sont autant de facteurs pouvant introduire des incertitudes dans les resultats obtenus. Conclusion Une procedure d'assurance qualite pour logiciels de simulation virtuelle a ete ecrite et appliquee a une serie d'images scanographiques. Des tests similaires sont a effectuer periodiquement et au moins a chaque changement de version majeure.

Resume Au cours de la derniere decennie, les evolutions technologiques en radiotherapie ont permis le developpement de techniques d'irradiation performantes telles que la radiotherapie conformationnelle tridimensionnelle et la radiotherapie avec modulation d'intensite (RCMI). Les exigences rigoureuses de ces techniques d'irradiation concernant la localisation precise des volumes cibles et des organes a risque ont conduit au developpement d'un grand nombre de techniques de positionnement du patient et/ou de tracking guidees par l'image. Avec l'introduction des nouvelles modalites d'imagerie dans la salle de traitement, la realisation d'une radiotherapie adaptative devient possible. Dans cet article, nous presentons les nouvelles techniques de la radiotherapie guidee par l'image (IGRT) et de la radiotherapie adaptative (ART). Les developpements technologiques et cliniques de la IGRT sont effectues dans les domaines suivants : 1) l'imagerie biologique pour une meilleure definition du volume cible ; 2) techniques d'imagerie quadridimensionnelle pour la modelisation des mouvements des organes ; 3) systemes d'imagerie embarques sur les appareils de traitement pour le positionnement du patient ; 4) la planification et l'irradiation incorporant les informations provenant de ces nouvelles techniques d'imagerie. Ce volume de Cancer–Radiotherapie etant dedie aux tumeurs pulmonaires, des exemples d'utilisation de ces nouvelles technologies pour ces localisations seront apportes quand elles s'y pretent.

The development of sophisticated conformal radiation therapy techniques for prostate cancer, such as intensity-modulated radiotherapy, implies precise and accurate targeting. Inter- and intrafraction prostate motion can be significant and should be characterized, unless the target volume may occasionally be missed. Indeed, bony landmark-based portal imaging does not provide the positional information for soft-tissue targets (prostate and seminal vesicles) or critical organs (rectum and bladder). In this article, we describe various prostate localization systems used before or during the fraction: rectal balloon, intraprostatic fiducials, ultrasound-based localization, integrated CT/linear accelerator system, megavoltage or kilovoltage cone-beam CT, Calypso 4D localization system tomotherapy, Cyberknife and Exactrac X-Ray 6D. The clinical benefit in using such prostate localization tools is not proven by randomized studies and the feasibility has just been established for some of these techniques. Nevertheless, these systems should improve local control by a more accurate delivery of an increased prescribed dose in a reduced planning target volume.

The development of conformal radiotherapy techniques (CRT) and intensity modulated CRT requires an accurate delineation of target structures and organs at risk. Thus, additional information provided by anatomical and/or functional imaging modalities can be used for volume of interest determination combined with traditionally used Computed Tomography imaging (CT): for instance, functional or morphological Magnetic Resonance Imaging (f MRI or m MRI) or Positron Emission Tomography (PET). A prerequisite to the simultaneous use of this information is image registration. Due to the differences between the images and the information they provide, a quality control of image registration process for radiotherapy is mandatory. The purpose of this article is to present the difficulties in implementing such controls and to show the necessity for a clinical validation on patient's images. The last part of this work presents the possible interest in using f MRI to help radio-oncologists in the treatment planning for gliomas associated to image coregistration and quality control considerations.

Target localization has become increasingly important in the advent of IMRT, as treatment margins are reduced and target doses are increased with high-dose gradients outside this target volume. The in-room CT on rails-LINAC system allows CT imaging while the patient remains immobilized in the treatment position just prior to treatment. The anatomic inter- and intra-fractional variations can be therefore quantified during a course of treatment. The position of the tumour can be checked and corrected before the fraction. In case of modification of tumour shape, a re-planning of the treatment is also feasible. However, several issues remain: the integration with routine clinical treatment due to a lack of software tools, the frequency of imaging, and the cost-efficiency ratio. The clinical experience is yet very limited but CT-image-guided radiotherapy appears promising for prostate, brain and spinal tumours.

Resume Objectif de l’etude. – L’objectif de ce travail a ete d’etablir les parametres optimum d’acquisition, de calcul et de fabrication du compensateur tridimensionnel en s’appuyant sur un environnement faisant appel a la simulation virtuelle et a la dosimetrie tridimensionnelle. Materiels et methodes. – Les materiels utilises sont un scanographe simulateur helicoidal (PQ 5000–Marconi), un systeme de simulation virtuelle (AcQsim version 4–Marconi), un systeme de dosimetrie (Dosigray), un accelerateur lineaire Saturne 43 (Varian, CGR), un decoupeur automatique de compensateur (Autimo 2,5 D–HEK), un explorateur de faisceau (wellhofer), un fantome homogene de forme geometrique simple afin de simuler l’obliquite de la surface du corps du patient. Le materiau compensateur choisi est l’etain sous forme de billes, car il assure une bonne modulation des profils en presence de forts gradients de dose. Le plan de compensation a ete calcule sur 80 % du profil de dose. Les profils des epaisseurs des compensateurs ont ete calcules en faisant varier les parametres d’acquisition (epaisseur des coupes ((e), pas de la spirale (p)), les parametres de calcul (coefficient d’attenuation lineaire, bixel b)), et les parametres de fabrication (diametre de la fraise (f), specificite de l’appareil de decoupe). Resultats et Conclusion. – Cette etude preliminaire, nous a permis de definir les parametres optimums pour la realisation d’un compensateur. Nous avons observe que l’epaisseur de coupe, la taille du bixel et le diametre de fraise sont les parametres qui agissent le plus sur l’homogeneite des profils calcules et mesures. En theorie, nous pouvons considerer que les valeurs ideales sont e = 3 mm, b = 3 mm et f = 3 mm. Cependant, pour aboutir a des temps de fabrication compatibles avec la routine clinique, les parametres choisis sont e = 5 mm, b = 6 mm et f = 6 mm. Les compensateurs peuvent etre utilises sur tous les types d’accelerateurs et a un cout modere. Il faut cependant etre tres rigoureux sur le processus de realisation du compensateur et precis dans l’alignement de celui-ci sur l’axe du faisceau.

Purpose To report the application of the global risk analysis (GRA) in the pulsed-dose rate (PDR) brachytherapy workflow. Material and Methods Analyses were led by a multidisciplinary working group established within the unit with the guidance of a quality engineer. First, a mapping of hazardous situations was developed as a result of interactions between the patient workflow for a treatment using PDR brachytherapy split into 51 sub-phases with a comprehensive list of the hazards that he/she faces (44). Interactions, when relevant, were sorted by level of priority: to be treated immediately, secondarily (the group is not entitled to treat the situation), or later (safe situation). Secondly, for each high priority dangerous situation, scenarios were developed to anticipate their potential consequences. Criticality was assessed, using likelihood and severity scales and a matrix, which allocated risks into categories: acceptable (C1), tolerable under control (C2) and unacceptable (C3). Then, corrective actions were proposed and planned when relevant, after assessment of their feasibility with a scale of effort. Finally, the criticality of the scenarios was reevaluated, taking into account the implementation of these actions, leading to a residual risk mapping, which could trigger additional proposals of actions. Results Two thousand one hundred and eighty-four potential interactions between the list of hazards and the workflow were analyzed. Mapping of dangerous situations identified 213 relevant interactions, from which 61 were considered with high priority. One hundred and twenty-six scenarios were generated: 68 with a low criticality (74.3%), 58 with an intermediate score (25.7%). No scenario with the highest criticality was individualized. Twenty-one corrective actions were planned. Mapping of residual risk resulted in the disappearance of most C2 risks, leaving 5 C2 scenarios (4%), for which four monitoring indicators were implemented in addition to the corrected actions decided on. Conclusion The implementation of the GRA appeared feasible, and led to implement 21 corrective actions, based on scenarios and not on incidents.

Resume L’obtention de distributions de dose d’intensite modulee se fait par planification inverse, ce qui necessite un algorithme d’inversion et une fonction objectif qui peut etre physique ou biologique ; les fonctions objectif biologiques ayant pour but de quantifier la probabilite de l’issue favorable du traitement. L’algorithme d’inversion analytique utilise se fonde sur l’analyse mathematique de la decomposition en valeurs singulieres et propose autant de solutions qu’il y a de faisceaux elementaires. A partir de la probabilite de controle tumoral, des probabilites de complications des tissus sains et de la probabilite de controle sans complications, trois fonctions d’evaluation biologiques des solutions sont definies et comparees par la difference des moindres carres entre les distributions de dose prescrite et obtenue. La configuration dˈirradiation utilisee est simplifiee : prescription de Brahme (modele bidimensionnel d’une irradiation pour cancer de la prostate) et neuf faisceaux (unidimensionnels). La determination par critere biologique de la solution optimale permet d’augmenter la dose moyenne dans la tumeur ainsi que son homogeneite par rapport a l’optimisation physique. A l’inverse, les organes a risque sont alors moins proteges. L’imposition de contraintes pertinentes permet alors d’obtenir des distributions de dose satisfaisantes. Certaines limitations apparaissent au niveau de la validite des modeles et des donnees utilises, ce qui pour l’instant nous semble exclure l’utilisation en routine clinique d’une optimisation uniquement biologique. La disponibilite future de nouvelles donnees biologiques permettra le developpement et notamment l’utilisation clinique de l’optimisation biologique.

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.

Resume Objectif de l’etude. – Evaluer les consequences dosimetriques de la definition automatique de l’isodose de prescription basee sur la couverture de la lesion. Une serie de 124 malformations arterioveineuses a ete analysee. La qualite de ces planifications est quantifiee par l’ecart-type de l’histogramme dose–volume differentiel dans la lesion. Materiels et methodes. – Nous avons defini deux protocoles quantitatifs de definition automatique d’isodose de prescription a partir d’indices bases sur la couverture de la lesion en utilisant la definition volumique de la couverture (90 % du volume lesionnel), la definition basee sur les isodoses proposee par le Radiation Therapy Oncology Group (RTOG) (isodose de prescription egale a l’isodose minimale dans la lesion divisee par 0,9). Resultats. – Nous avons evalue les planifications obtenues pour ces deux protocoles en calculant differents indices dose–volume. Ces indices sont presentes en fonction de l’ecart-type de l’histogramme dose–volume differentiel dans la lesion afin de quantifier les consequences de leurs variations pour cette serie representative de planifications. La marge toleree par notre equipe est telle que la somme des facteurs de sous-dosage lesionnel et de surdosage des tissus sains reste inferieure a 1. Le protocole base sur la couverture volumique a donne des resultats situes dans cette marge. Celui utilisant la definition RTOG a genere des indices de conformation pouvant etre superieurs a 1. Conclusion. – La dose absolue doit etre decidee en tenant compte des indices dose–volume examines et des donnees cliniques. Un protocole de definition automatique d’isodose de prescription utilisant une couverture lesionnelle volumique semble plus judicieusement adapte aux planifications conformationnelles des malformations arterioveineuses en conditions stereotaxiques vues les variations observees au niveau du surdosage des tissus sains.

Resume Ces dernieres annees, la radiotherapie conformationnelle avec des faisceaux d'intensite uniforme a ete utilisee avec succes pour ameliorer la conformation de la distribution de dose dans le volume cible et dans les structures critiques. Cependant, plusieurs situations cliniques existent (volume cible complexe et structures critiques proches du volume cible) pour lesquelles cette technique ne peut pas fournir les distributions de dose souhaitees. De nouvelles techniques utilisant des faisceaux d'intensite modulee sont necessaires pour cela. La planification dosimetrique de ces faisceaux exige des systemes d'optimisation constitues de deux composantes: un algorithme d'inversion et un modele d'optimisation decrivant les criteres physiques ou biologiques a respecter. Nous presentons dans cet expose ces systemes d'optimisation en discutant chacune des deux composantes. Nous abordons le role des differents parametres d'irradiation tels que le nombre de faisceaux et l'energie des rayons X dans la procedure d'optimisation. Enfin, nous presentons quelques exemples realises par notre equipe.

Resume La definition des criteres et d'une methodologie plus structuree pour l'evaluation quantitative des plans de traitements en radiotherapie conformationnelle stereotaxique est presentee. Pour l'evaluation quantitative des planifications dosimetriques, nous avons adapte l'analyse receiver operating characteristics (ROC), procedure d'evaluation utilisee en imagerie medicale. L'adaptation est basee sur des donnees provenant des histogrammes dose-volume. Pour le choix de l'isodose de prescription d'un plan de traitement donne, trois techniques, chacune utilisant un critere dosimetrique different, ont ete definies. Nous avons utilise l'analyse ROC pour choisir le meilleur plan de traitement parmi les plans proposes pour un patient et son isodose de prescription. L'etude a montre l'interet de l'analyse ROC basee sur les histogrammes dose-volume pour l'evaluation quantitative des plans d'irradiation.

Resume L'objectif de ce travail etait de presenter un algorithme d'optimisation inverse qui determine la modulation d'intensite des faisceaux permettant de realiser une distribution de dose conformationnelle. Cet algorithme est base sur l'analyse mathematique de decomposition en valeurs singulieres. Il a ete integre dans le systeme a trois dimensions (3D) de planification dosimetrique Dosigray. La dose est calculee en separant le rayonnement primaire du rayonnement diffuse. Nous avons presente, dans le cas d'un cancer de la prostate, les profils d'intensite modulee et les distributions de dose optimales resultant du logiciel d'optimisation inverse developpe et integre dans un systeme de planification dosimetrique. Nous avons obtenu une region de fortes doses conformee geometriquement au volume cible et qui evite les structures critiques avoisinantes. Cette premiere etude a montre la faisabilite de l'utilisation de la decomposition en valeurs singulieres pour generer des distributions de dose conformationnelles dans un environnement clinique.

Objectifs Rapporter les resultats cliniques et la toxicite tardive chez des patientes atteintes de cancer du col uterin localement evolue apres chimioradiotherapie concomitante suivie de curietherapie endocavitaire adaptative guidee par l’image. Materiels et methodes Les donnees de patientes atteintes de lesions de stade IB1N + -IVA du col uterin ont ete retrospectivement analysees. Apres radiotherapie externe pelvienne et ou non lombo-aortique, toutes ont recu une curietherapie endocavitaire adaptative guidee par l’image de debit de dose pulse suivant les recommandations du Groupe europeen de curietherapie–European Society for Therapeutic Radiology and Oncology (Gec-ESTRO). Resultats Deux cent vingt-cinq patientes ont ete incluses. Soixante-cinq pour cent des lesions ont ete classees au moins IIB selon les recommandations de la Federation de gynecologie-obstetrique (Figo). Quatre-vingt-cinq pour cent ont recu une chimiotherapie concomitante. Les doses delivrees a 90 % des volumes cibles anatomocliniques de haut risque et de risque intermediaire etaient respectivement de 80,4 ± 10,3 Gy et de 67,7 ± 6,1 Gy. Apres un suivi median de 38,8 mois, les taux de controle local et de survie globale a 3 ans etaient respectivement de 86,4 et 76,1 %. Un effet deletere du stade tumoral sur le taux de controle local a ete note (de 92,0 % pour les cancers de stade 1B a 66,7 % pour ceux de stade IVA, p = 0,038), parallele a une diminution de la D90 (dose dans 90 % du volume cible anatomoclinique de haut risque) avec le stade tumoral (de 84,6 Gy a 65,4 Gy). Les taux de controle local a 3 ans variaient significativement avec cette D90 : 95,6 % a 3 ans si 85 Gy ou plus, 88,8 % entre 80 et 85 Gy, et 80 % si moins de 80 Gy (p = 0,018). Quatorze patientes ont souffert d’une toxicite tardive de grade 3–4 gastro-intestinale ou urinaire, ce qui correspond a une incidence de 6,6 % a 3 ans. Conclusion La chimioradiotherapie concomitante suivie de curietherapie endocavitaire adaptative guidee par l’image fournit des taux de controle local eleves avec une toxicite limitee. La necessite d’atteindre des doses elevees pour obtenir le controle local rend la curietherapie interstitielle necessaire pour les tumeurs localement evoluees.

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.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).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; p0.0001] 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%.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.

Resume Onze ans apres le debut des irradiations intracrâniennes en conditions stereotaxiques par le groupe Salt (Saint-Anne — Lariboisiere — Tenon) sous l'egide de Betti, il nous a semble utile de faire le point sur la methodologie de planification du groupe Salt de 1997. A ce jour, nous avons traite 693 patients dont une majorite avait une malformation arterioveineuse (90 %) et a recu un traitement non fractionne. La realisation de l'irradiation elle-meme a peu change. La localisation du volume cible est realisee en neurochirurgie a Sainte-Anne. L'ensemble de l'imagerie stereotaxique est envoye par le reseau numeris, dans le service de radiotherapie de l'hopital Tenon. La planification est realisee a l'aide d'un SPT Artemis 3D/Dosigray. La conformation ou le remplissage du volume lesionnel est realisee par compartimentage selon la « methodologie des foyers associes a en plusieurs subvolumes spheriques ou elliptiques ajustes, interactivement sur les representations graphiques 3D de la lesion. L'optimisation directe de l'espace d'irradiation se fait en agissant sur le nombre d'arcs, leur position angulaire, les angles de debut et de fin de chaque arc tels qu'ils sont fournis par la base de donnees dosimetriques. La distribution de dose calculee va etre evaluee selon un certain nombre de parametres quantitatifs. La deuxieme methode d'optimisation fait appel a la modulation de l'intensite du faisceau au cours des arcs. Elle est basee sur la theorie mathematique des problemes inverses et l'analyse SVD (singular value decomposition) des procedures d'irradiation. Les accelerateurs lineaires actuels ne permettent pas encore la modulation d'intensite d'une arctherapie. Pour realiser cela, nous transformons les profils de forme irreguliere en profils rectangulaires de ponderation modulee. Toute planification optimisee doit etre evaluee avant la mise en œuvre. Les criteres d'evaluation reposent sur l'analyse par histogrammes dose-volume differentiels et cumulatifs de la distribution de dose. Les histogrammes dose-volume permettent d'etudier dans la lesion et a l'exterieur, les volumes de « sous- a et de « surdosage a en fonction d'une isodose peripherique choisie. Nous avons mis au point des parametres quantitatifs permettant d'evaluer les planifications: le facteur conformationnel et l'indice d'homogeneite. L'ensemble de cette methodologie d'optimisation de la planification s'adresse aux irradiations non fractionnees, ou plurifractionnees, intra ou extracrâniennes.

✓ 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.

The use of image-guided brachytherapy has led to a significant change in application techniques and improvements in treatment planning. Today, 3D imaging has replaced orthogonal radiographs for a large number of treatments, providing a possibility of an optimization adapted to the anatomy of each patient. When properly selected and implemented, this imaging provides accurate 3D information of volumes and brachytherapy device, allowing moving from a dose to points assessment to a dose/volume evaluation. This article describes the contribution of different imaging modalities for the different brachytherapy techniques: gynecological brachytherapy, interstitial brachytherapy (breast, penis, etc.) and prostate brachytherapy. It reminds recommendations for the establishment of protocols of images acquisition and 3D reconstruction of brachytherapy devices (applicators, plastic tubes, needles, etc.).

Objectif de l’etude La curietherapie adaptative guidee par l’image est une technique de haute precision qui autorise escalade de dose et adaptation a la reponse tumorale. Des etudes monocentriques ont permis d’etablir des relations dose–volume reponse. Celles-ci sont cependant grevees d’intervalles de confiance larges. L’objectif etait d’affiner ces estimations en effectuant une meta-regression sur donnees publiees. Materiels et methode L’eligibilite etait limitee aux series rapportant des resultats selon les recommandations du Groupe europeen de curietherapie – European Society for Therapeutic Radiology and Oncology (Gec-ESTRO). En se basant sur le modele Probit, les taux de controle local evalues a 2 a 3 ans, ont ete confrontes aux doses recues par 90 % du volume (D90) moyennes converties en equivalent 2 Gy (α/β = 10 Gy). L’impact de chaque serie a ete pondere en fonction du nombre de patientes incluses. Resultats Une recherche exhaustive a permis d’identifier 13 series rapportant les donnees de 1299 patientes. Les D90 moyennes du volume cible anatomoclinique a haut risque (CTVHR) variaient de 70,9 a 93,1 Gy. Le modele probit a montre une forte relation entre la D90 et la probabilite d’obtenir le controle local ( p p = 0,009). Le seuil de 60 Gy etait associe a une probabilite de controle local de 79,4 % (60,2 a 86,0 %). Conclusion Les relations d’effet dose–volume ont ete entre les D90 et la probabilite d’obtenir un controle local confirmees et affinees. Des etudes basees sur donnees individuelles sont necessaires pour developper des nomogrammes prenant en compte donnees dosimetriques et cofacteurs cliniques.

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.

The aim of this study was to determine therapy-related risk factors for the development of melanoma after hemangioma. A cohort study was conducted among 4620 patients treated before 16 years of age for skin hemangioma in France. A nested case-control study was also conducted on 13 patients who developed a melanoma (cases) matched with five controls in cohort according to sex, age at the hemangioma diagnostic, the calendar year of occurrence of the hemangioma, and follow-up. The radiation dose received at the site of the melanoma and at the same site in controls was estimated, and named 'local dose'. A total of 13 melanomas were registered during an average follow-up of overall 35 years, the risk of developing melanoma after a hemangioma treatment was 2.5-fold higher [95% confidence interval (CI): 1.4-4.1] compared with that of the general population, this ratio being only 0.8 (95% CI: 0.05-3.6) in 896 patients who did not receive radiotherapy, but 3.0 (95% CI: 1.6-5.1) after radiotherapy. When adjusting on sex, age, and year of the treatment and follow-up duration, melanoma risk was 11.9 (95% CI: 1.4-123) times higher in patients treated with ytrium 90 than in the ones who did not received radiotherapy. In the case-control study, the risk of melanoma was not linked to the local radiation dose. Indeed, the increase in melanoma risk was observed even for very low local doses. Compared with the corresponding skin areas in patients who did not receive radiotherapy, the ones having received less than 0.001 Gy had a melanoma risk of 3.9 (95% CI: 0.5-32) and those who received more than 0.01 Gy had a risk of 6.9 (0.5-99). This study suggests that radiation therapy of skin hemangioma increases the risk of further melanoma, but we were not able to evidence a relation with the local dose. Nevertheless, childhood treated for hemangioma should be considered at risk for developing melanoma and suspicious pigmented lesions should be carefully evaluated even far from treated areas.

To assess the acute toxicity of intensity modulated radiotherapy as post-operative adjuvant treatment for retroperitoneal sarcoma.Patients who received adjuvant intensity modulated radiotherapy from January 2009 to September 2010 were retrospectively reviewed.Fourteen patients entered the study (seven primary tumours and seven relapses). All tumours were liposarcoma and had macroscopically complete resection, epiploplasty was systematically realized. Median tumour size was 21 cm (range: 15-45), median planning target volume was 580 cm(3) (range: 329-1172) and median prescribed dose was 50.4 Gy (range: 45-54). Median follow-up was 11.5 months (range: 2-21.4). Acute toxicity was mild: acute digestive toxicity grade 1-2 occurred in 12/14 patients (86%). However, there was no weight loss of more than 5% during radiotherapy and no treatment interruption was required. Two months after completion of radiotherapy, digestive toxicity grade 1 remained present in 1/14 patients (7%). One case of grade 3 toxicity occurred during follow-up (transient abdominal pain). Three relapses occurred: two were outside treaded volume and one was both in and outside treated volume.Intensity modulated radiotherapy in the postoperative setting of retroperitoneal sarcoma provides low acute toxicity. Longer follow-up is needed to assess late toxicity, especially for bowel, kidney and radio-induced malignancies.

Pupose Peripheral dose from bremsstrahlung and scattered electrons in high-energy electron beams in external radiotherapy remains poorly studied. The purpose of this work is to assess peripheral dose outside applicators at the patient level. Methods and materials Commissioning was performed for 6, 9, 12 and 18 MeV electron beams on three linear accelerators Varian 2300 C/D (Varian applicator), Siemens Primus KD2 (Deva applicator) and Siemens Oncor (applicator EA3). The peripheral dose was measured in a water phantom as a function of off-axis distance from 5 cm to 65 cm from the field edge for SSD = 100 cm. Thermoluminescent TLD-700 powder dosimeters were used. Measurements were made at both 1 cm and 10 cm depths, using applicator sizes from 6 × 6cm2 to 20 × 20 cm2, the results assuming that the TLD signal is proportional to the dose. Results Whatever the field size, a peak dose spot appeared at 15 cm from the field edge for Siemens applicators. For Siemens Primus with an applicator size of 10 × 10 cm2, this peak reached 2,1%, 1%, 0,9% and 1,3% of Dmax for 6, 9, 12 and 18 MeV electron beams, respectively, doubled for 6 × 6 cm2 field size. For Siemens Oncor, with the above applicator size, this peak dose reached 0,8%, 1,2% and 1,3% of Dmax for 6, 9 and 12MeV, respectively, doubled for 20 × 20cm2. In contrast for Varian 2300 C/D, the doses at 15 cm from field edge were 0,3%, 0,6% and 1,1% of Dmax for 6,12 and 18 MeV, respectively. No peak dose spot was evidenced for Varian applicator. The doses measured at 10 cm depth were 2–3 times lower than doses at 1 cm depth for out off- field distances from 5 cm to 35 cm, and were 4–7 times lower for larger distances. Conclusion This work analyzes peripheral doses for different electron beams energies and three different applicator types. It shows that depending on beam energy, applicator size and type, the peak dose at 15 cm from field edge ranges from 0,3–2,7% of the Dmax. Measurements made at 10 cm depth show that, depending on beam energy and applicator size and collimator size, the dose at 15 cm from field edge is 0,07–0,2% of Dmax. Although the debate on signal to dose conversion coefficients for mixed fields is still ongoing, our results should be considered because, to date, peripheral dose with electron beams are not fully accounted for by TPS.

International audience; The aim of this study is to define criteria for accurate representation of the thyroid in human models used to represent external beam radiotherapy (EBRT) patients and evaluate the relationship between the volume of this organ and clinical and anthropometric characteristics. From CT images, we segmented the thyroid gland and calculated its volume for a population of 188 EBRT patients of both sexes, with ages ranging from 1 to 89 years. To evaluate uncertainties linked to measured volumes, experimental studies on the Livermore anthropomorphic phantom were performed. For our population of EBRT patients, we observed that in children, thyroid volume increased rapidly with age, from about 3 cm(3) at 2 years to about 16 cm(3) at 20. In adults, the mean thyroid gland volume was 23.5 ± 9 cm(3) for males and 17.5 ± 8 cm(3) for females. According to anthropometric parameters, the best fit for children was obtained by modeling the log of thyroid volume as a linear function of body surface area (BSA) (p < 0.0001) and age (p = 0.04) and for adults, as a linear function of BSA (p < 0.0001) and gender (p = 0.01). This work enabled us to demonstrate that BSA was the best indicator of thyroid volume for both males and females. These results should be taken into account when modeling the volume of the thyroid in human models used to represent EBRT patients for dosimetry in retrospective studies of the relationship between the estimated dose to the thyroid and long-term follow-up data on EBRT patients.

To assess the potential dosimetric gain of presegmentation modulated radiotherapy (OAPS, DosiSoft™) of breast, compared to routine 3D conformal radiotherapy.Twenty patients treated with conservative surgery for breast cancer (9 right and 11 left sided) with various breast volume (median 537 cm(3); range [100-1049 cm(3)]) have been selected. For each patient, we have delineated a breast volume and a compensation volume (target volumes), as well as organs at risk (lungs and heart). Two treatment plans have been generated: one using the routine 3D conformal technique and the other with the presegmentation algorithm of DosiSoft™ (OAPS). The dose distribution were analyzed using the conformity index for target volumes, mean dose and V30 Gy for the heart, and mean dose, V20 Gy and V30 Gy for lungs.Over the 20 patients, the conformity index increased from 0.897 with routine technique to 0.978 with OAPS (P0,0001). For heart and lung, OAPS decreased irradiation (mean cardiac dose 1,3 vs 1,6 Gy [P0,0001] and pulmonary V20 Gy 6,6 vs 7,1 [P0,0001]).OAPS (DosiSoft™) is an original method of segmentation of breast. It is automatic, fast and easy, and is able to increase the conformity index, while sparing organ at risk.

Purpose of study Monte Carlo based treatment planning system are known to be more accurate than analytical methods for performing absorbed dose estimation, particularly in and near heterogeneities. However, the required computation time can still be an issue. The present study focused on the determination of the optimum statistical uncertainty in order to minimise computation time while keeping the reliability of the absorbed dose estimation in treatments planned with electron-beams. Materials and methods Three radiotherapy plans (medulloblastoma, breast and gynaecological) were used to investigate the influence of the statistical uncertainty of the absorbed dose on the target volume dose–volume histograms (spinal cord, intramammary nodes and pelvic lymph nodes, respectively). Results The study of the dose–volume histograms showed that for statistical uncertainty levels (1 S.D.) above 2 to 3%, the standard deviation of the mean dose in the target volume calculated from the dose–volume histograms increases by at least 6%, reflecting the gradual flattening of the dose–volume histograms. Conclusions This work suggests that, in clinical context, Monte Carlo based absorbed dose estimations should be performed with a maximum statistical uncertainty of 2 to 3%.

This study presents a method aimed at creating radiotherapy (RT) patient-adjustable whole-body phantoms to permit retrospective and prospective peripheral dose evaluations for enhanced patient radioprotection. Our strategy involves virtual whole-body patient models (WBPM) in different RT treatment positions for both genders and for different age groups. It includes a software tool designed to match the anatomy of the phantoms with the anatomy of the actual patients, based on the quality of patient data available. The procedure for adjusting a WBPM to patient morphology includes typical dimensions available in basic auxological tables for the French population. Adjustment is semi-automatic. Because of the complexity of the human anatomy, skilled personnel are required to validate changes made in the phantom anatomy. This research is part of a global project aimed at proposing appropriate methods and software tools capable of reconstituting the anatomy and dose evaluations in the entire body of RT patients in an adapted treatment planning system (TPS). The graphic user interface is that of a TPS adapted to obtain a comfortable working process. Such WBPM have been used to supplement patient therapy planning images, usually restricted to regions involved in treatment. Here we report, as an example, the case of a patient treated for prostate cancer whose therapy planning images were complemented by an anatomy model. Although present results are preliminary and our research is ongoing, they appear encouraging, since such patient-adjusted phantoms are crucial in the optimization of radiation protection of patients and for follow-up studies.

An evaluation of the conversion process from Hounsfield units (HU) to material composition in computerised tomography (CT) images, employed by the Monte Carlo based treatment planning system ISOgray (DOSIsoft), is presented. A boundary in the HU for the material conversion between "air" and "lung" materials was determined based on a study using 22 patients. The dosimetric consequence of the new boundary was quantitatively evaluated for a lung patient plan.

To study the dose delivered by a megavoltage cone beam computed tomography imaging system (MVCBCT) installed on a Oncor Impression linac (Siemens).The acquisition of MVCBCT images was modelled in a treatment planning system by 67 photon beams (6 MV). A study was conducted to: compare the calculated and measured dose at the centre of a cylindrical phantom; compare the calculated and measured dose distributions in the Alderson-Rando phantom (pelvis); study the influence of MVCBCT image acquisition for the repositioning of a prostate cancer patient treated by 3D conformal radiotherapy (prescribed dose of 74 Gy), on the dose-volume histograms (DVH) for the treatment plus seven MVCBCT (protocol D1-3 and weekly), treatment plus 37 MVCBCT (one for each day of treatment).The difference between calculated and measured doses at the centre of the cylindrical phantom was less than 3%. A deviation of 7% maximum was found between the dose distribution calculated in the Rando phantom and the measured doses normalized at the beam isocentre. The dose delivered at the isocentre was equal to 3,7 cGy for a "5 MU" protocol, with a maximum dose of 6 cGy. In the case of the patient considered, the acquisition of 37 MVCBCT corresponded to an additional mean dose to the PTV of 1.2 Gy for a protocol "5MU" with a significant influence on the DVH.In view of this study, it appears that the doses delivered in frequent use of MVCBCT must be taken into account by the radiation oncologist in assessing the therapeutic dose delivered to the target volume and organs at risk.

Describe the principles and report the preliminary results on dose distributions obtained with a new generation of treatment planning system (TPS) designed to provide, in addition to the dose distributions within the target-volumes, the magnitude of the doses to distant healthy tissues in the course of common radiotherapy procedures. The system is made of (1) a library of adjustable whole-body patient models in radiotherapy treatment position, allowing different patient anatomies to be simulated, (2) a global-beam model allowing the dosimetric data of the irradiation beams to be extended to the whole body and (3) a TPS modified to handle the two first modules in order to produce the dose distributions within the target-volumes and in any organ at distance. Our preliminary results indicate that in an adult male patient treated by radiotherapy for Hodgkin disease using two opposed 6 MV photon beams, the mean doses to distant organs are: 0.9 % of the target volume dose for the pituitary gland, 0.40% to 3.4% for the kidneys, 0.43% for the prostate, and at larger distance, 0.07% and 0.02 % at the level of the knees and the feet respectively. Although the development of our system is still in progress, the preliminary results are encouraging. This systematic evaluation of the low doses delivered at distance of the targetvolumes is a basic requirement for prospective studies of longterm risks of modern radiotherapy procedures.