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Clinical experience in single-dose stereotactic radiotherapy of irregular complex lesions has shown that new developments in optimization procedures were necessary to improve dose distribution, making this conformal technique more efficient. We propose a conformal procedure for stereotactic radiotherapy of complex lesions treated with multiple isocenters based on the associated targets methodology. The successive steps of this conformal procedure are: a) the determination of the number of subvolumes; b) the choice of collimator diameters using a dosimetric data basis; c) the search by the inverse SVD optimizer algorithm for the optimal irradiation space and the minibeam weights for each subvolume using singular value decomposition: d) the basis of quantitative evaluation criteria for the choice of satisfactory solutions on dose-volume histograms and clinical considerations. The efficiency of the SVD optimizer to planify multi-isocentric treatments was examined in the case of an irregular lesion planified with two isocenters. The condibon number of this dual isocentric configuration showed a more ill-conditioned problem than in the monoisocentric case. Examining different reconstructed weighting vectors, we observed that optimal solutions are obtained with the first singular components and an important healthy tissue overdosage occurs when the number of singular components used in the SVD expansion increases. Our SVD optimization approach is a general procedure which can be applied to different radiotherapy techniques. [ABSTRACT FROM AUTHOR]

Dose distribution optimization algorithms are necessary in pencil-beam radiotherapy to exploit efficiently the multiple parameters of this powerful irradiation technique. We propose as an optimization technique singular value decomposition (SVD) analysis, which allows the measurement of ill conditioning of the stereotactic radiotherapy inverse problem and yields optimal weights for conformal treatment. Our approach to dose distribution optimization is to recover estimates of the minibeams weights from well-defined previsional dose matrices to study the influence of the different parameters on the stereotactic radiotherapy inverse procedure. The adjustment of the different parameters of the stereotactic irradiation to the ‘SVD optimizer’ procedure is realized taking into account the ratio of the quality reconstruction to the calculation time. It will permit a more efficient use of the SVD optimizer in clinical applications with real three-dimensional lesions. We show the efficiency of the SVD optimizer in analyzing and predicting ill conditioning in stereotactic radiotherapy and in recognizing the topography of the different beams to create an optimal vector containing the beam weights (reconstructed weighting vector). [ABSTRACT FROM AUTHOR]

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 × 6cm 2 to 20 × 20 cm 2 , 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 cm 2 , 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 cm 2 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 × 20cm 2 . 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Melanoma is a severe skin cancer related to sun exposure. Whether this malignancy is linked to exposure to ionising radiation during adulthood is still controversial. This case-control study examined the risk of melanoma following treatment for an adulthood first malignant neoplasm (FMN). Cases were patients who presented with cutaneous melanoma after a first cancer in adulthood. Controls (3 per case) were patients free of melanoma, matched for age, duration of follow-up since the FMN, type of FMN, and followed in the same institution. A total of 57 cases and 171 controls were included. In the final multivariate analysis, no risk of melanoma was associated with radiotherapy (odds ratio (OR) for 1Gy=1.01, 95% confidence interval (95%CI) 0.96–1.07) nor hormonotherapy, whereas chemotherapy use (OR=2.3, 95%CI 0.93–5.6) and having a history of familial cancer (OR=2.8, 95%CI 1.3–5.9) exhibited a nearly significant risk. In conclusion, unlike the evidence for risk of exposure to ionising radiation during childhood, we did not substantiate a risk for association of melanoma with exposure to ionising radiation during adulthood. The risk associated with chemotherapy should justify the implementation of skin surveillance for early detection of melanoma in these patients. [Copyright &y& Elsevier]

Objectif de l’étude Étudier les facteurs prédictifs d’une pathologie cérébrovasculaire après cancer de l’enfant. Matériel et méthode Il s’agissait d’un étude de cohorte French Childhood Cancer Survivor Study (FCCSS) : 7018 survivants à 5 ans d’un cancer de l’enfant traité avant 2001, dont 1193 pour une tumeur cérébrale, et suivis 24 ans en moyenne, par l’accès aux dossiers médicaux et aux données du Système national d’information interrégimes de l’assurance maladie (Sniiram), ainsi qu’au moyen de l’envoi d’autoquestionnaires. Les radiothérapies reçues par 4176 sujets, dont 1016, pour une tumeur cérébrale, ont été reconstituées à l’aide de fantômes anthropomorphiques, et les doses de radiation reçues au niveau des artères cérébrales et d’autres structures d’intérêt ont été estimées. Résultats Un total de 145 sujets a été atteint d’un accident vasculaire cérébral, dont 72 après une tumeur cérébrale et 134 après la radiothérapie. Le type d’accident vasculaire cérébral n’a pas pu être défini pour 24 patients, il était ischémique pour 77 et hémorragique pour 44. Il n’a pas été possible d’identifier de drogue ou de catégorie de drogue augmentant le risque d’accident vasculaire cérébral. Dans une analyse multifactorielle, celui-ci était plus important chez les sujets atteints d’une neurofibromatose de type I (NF1), et augmentait avec la dose de radiation reçue au niveau des artères cérébrales, le coefficient de risque étant plus élevé pour les accidents vasculaires cérébraux ischémiques, ainsi qu’avec la radiothérapie thoracique ou abdominale. Il n’a pas été possible de mettre en évidence de rôle de la chirurgie des tumeurs cérébrales, que ce soit propre ou par interaction avec la radiothérapie, mais seuls 206 sujets traités pour une tumeur cérébrale n’avaient pas eu de chirurgie. Les sujets qui avaient reçu de la radiothérapie, mais 30 Gy ou plus sur seulement moins de 5 % de la longueur des artères cérébrales principales avaient un risque d’accident vasculaire cérébral augmenté d’un facteur 2,8 (1,3–5,5). En revanche, il n’y avait pas d’évidence claire pour un rôle des doses faibles de rayonnements ionisants de un ou quelques Gy. Conclusion Cette étude n’a pas permis de mettre en évidence de rôle de la chimiothérapie ou de la chirurgie dans le risque de tumeur cérébrale, mais a permis de préciser et de quantifier le rôle de la radiothérapie cérébrale. [ABSTRACT FROM AUTHOR]