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Purpose. A national survey was performed to assess patient dose indicators based on clinical indication and on patient morphology for most common adult computed tomography (CT) examinations in France. Methods. Seventeen groups of clinical indications (GCIs) for diagnostic CT in adult patients were considered based on their frequency and on image quality requirements. Data was collected for 15-30 consecutive examinations performed between 2015 and 2017, per CT scanner and GCI. Distributions of total examination Dose-Length Product (DLP) and Volume CT Dose Index (CTDIvol) were assessed for each GCI as a function of patient gender or patient Body Mass Index (BMI) for head/neck and trunk examinations, respectively. Results. 6610 examinations were analysed. Median total exam DLP values were higher for men compared to women patients for head and neck examinations: difference ranged from 6% for ear trauma indication (577 vs 543 mGy•cm, p=0.01) to 35% for brain tumour GCI (1472 vs 1093 mGy•cm, p<0.01). For trunk examinations, total exam DLP increased consistently with patient's BMI. For normal-BMI patients, median CTDIvol and DLP differed significantly between different GCIs for single-phase CT of the chest (3 mGy and 112 mGy•cm, respectively, for chronic obstructive pulmonary disease group vs 5.8 mGy and 207 mGy•cm for pulmonary embolism group, p<0.05) and of the abdomen-pelvis (5.6 mGy and 284 mGy•cm, respectively, in renal colic group vs 9.5 mGy and 463 mGy•cm in occlusive syndrome group, p<0.05). Conclusion. This study provides morphological-and clinical-based patient dose indicators in CT as a practical tool for clinical practices optimisation.

This study assessed and compared various image quality indices in order to manage the dose of pediatric abdominal MDCT protocols and to provide guidance on dose reduction. PMMA phantoms representing average body diameters at birth, 1 year, 5 years, 10 years and 15 years of age were scanned in a four-channel MDCT with a standard pediatric abdominal CT protocol. Image noise (SD, standard deviation of CT number), noise derivative (ND, derivative of the function of noise with respect to dose) and contrast-to-noise ratio (CNR) were measured. The 'relative' low-contrast detectability (rLCD) was introduced as a new quantity to adjust LCD to the various phantom diameters on the basis of the LCD(1%) assessed in a Catphan phantom and a constant central absorbed dose. The required variations of CTDIvol(16) with respect to phantom size were analyzed in order to maintain each image quality index constant. The use of a fixed SD or CNR level leads to major dose ratios between extreme patient sizes (factor 22.7 to 44 for SD, 31.7 to 51.5 for CNR(2.8%)), whereas fixed ND and rLCD result in acceptable dose ratios ranging between factors of 2.9 and 3.9 between extreme phantom diameters. For a 5-9 mm rLCD1(%), adjusted ND values range between -0.84 and -0.11 HU mGy(-1). Our data provide guidance on dose reduction on the basis of patient dimensions and the required rLCD (e.g., to get a constant 7 mm rLCD(1%) for abdominal diameters of 10, 13, 16, 20 and 25 cm, tube current-time product should be adjusted in order to obtain CTDIvol(16) values of 6.2, 7.2, 8.8, 11.6 and 17.7 mGy, respectively).

In France, as in most countries, strict strategies were implemented in cancer hospitals to reduce the spread of coronavirus , but to maintain as much as possible the capacity of oncology health services [1,2]. These strategies included the reduction of elective services, an emphasis on remote visits, and the use of personal protective equipment [3][4][5][6][7]. International radiation therapy (RT) academic societies proposed to restrict the indications for treatment [8], to delay as long as possible the start of nonurgent treatments and to prefer hypofractionated regimens [9][10][11][12][13][14][15][16]. To our knowledge, none of these recommendations anticipated how to handle the load of delayed treatments after the lockdown. However, the successful management of cancer treatments during lockdown undoubtedly correlates with the successful management of post-lockdown activity overload.The Institut Curie has one of the largest RT departments in Europe. It is spread over three separate sites in the Paris area and has a total of eleven LINACs (six in Paris, four in Saint-Cloud and one in Orsay) and three treatment rooms for proton therapy in Orsay. In 2019, 5,860 patients were treated and the average number of treatment essions per month delivered was 8931, comprising 4183 sessions in Paris, 3303 in Saint-Cloud and 1445 in Orsay. In order to comply with the international recommendations mentioned above, several measures had to be applied in our department to protect both patients and operators from the risk of contamination. The challenges of post-crisis management following the COVID-19 pandemic therefore had to be anticipated. Here, we propose some key considerations to prepare for the post-lockdown period by pre-

This study was designed to measure organ absorbed doses from multi-detector row computed tomography (MDCT) on pediatric anthropomorphic phantoms, calculate the corresponding effective doses, and assess the influence of automatic exposure control (AEC) in terms of organ dose variations. Four anthropomorphic phantoms (phantoms represent the equivalent of a newborn, 1-, 5-, and 10-y-old child) were scanned with a four-channel MDCT coupled with a z-axis-based AEC system. Two CT torso protocols were compared: a first protocol without AEC and constant tube current-time product and a second protocol with AEC using age-adjusted noise indices. Organ absorbed doses were monitored by thermoluminescent dosimeters (LiF: Mg, Cu, P). Effective doses were calculated according to the tissue weighting factors of the International Commission on Radiological Protection (). For fixed mA acquisitions, organ doses normalized to the volume CT dose index in a 16-cm head phantom (CTDIvol16) ranged from 0.6 to 1.5 and effective doses ranged from 8.4 to 13.5 mSv. For the newborn-equivalent phantom, the AEC-modulated scan showed almost no significant dose variation compared to the fixed mA scan. For the 1-, 5- and 10-y equivalent phantoms, the use of AEC induced a significant dose decrease on chest organs (ranging from 61 to 31% for thyroid, 37 to 21% for lung, 34 to 17% for esophagus, and 39 to 10% for breast). However, AEC also induced a significant dose increase (ranging from 28 to 48% for salivary glands, 22 to 51% for bladder, and 24 to 70% for ovaries) related to the high density of skull base and pelvic bones. These dose increases should be considered before using AEC as a dose optimization tool in children.

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