[Brachytherapy in France in 2020: State of the art and perspectives from the Groupe curiethérapie de la SFRO]. / Curiethérapie en France en 2020 : synthèse et perspectives du Groupe curiethérapie de la Société française de radiothérapie oncologique.

Because of its principle and its high proof level clinical results, brachytherapy represents a specific irradiation technique for the treatment of primary tumors as well as some local relapses in pre-irradiated area. After a glory period between the 80's and 90's, brachytherapy has progressively lost its attractiveness. In order to provide a practical solution to this deleterious situation, it is important that guardianships, health care payers, patient associations, specialist doctors and radiation oncologists understand the reasons leading to this harmful state as well as the risks concerned. A teaching judged insufficient, non-adapted value and an aging image of brachytherapy represent the three main reasons of this degradation and constitute the three most important challenges conditioning its maintain in the anticancer treatment arsenal. An adapted communication with radiation oncologists themselves but also with the other scientific societies remains crucial as well as with guardianship and patient associations. It is central that brachytherapy could be recognized in order to make it stronger and accessible for all the patients who could need it.

Independent 6D quality assurance of stereotactic radiotherapy repositioning on linacs.

PURPOSE: A high level of accuracy while positioning the patient is mandatory for frameless stereotactic radiotherapy (SRT), as large doses in multiple fractions can be delivered near organs at risk. The objective of this study is to propose an end-to-end quality assurance method to verify that submillimetre alignment can be achieved with stereotactic conventional linacs. METHODS: We used a TrueBeam® linear accelerator equipped with a 6DOF robotic couch. The "ISO Cube" phantom was used with a homemade stand designed to generate known translational and rotational offsets. A reference CT scan was performed with straight alignment of the phantom. The procedure introduced 1.6° angular offset for the couch pitch and roll, at various gantry angles. The couch base was also moved between 0° and 270°. We compared the results with the daily machine performance check tests (MPC, Varian). RESULTS: The mean isocentre size, MV and kV imager offsets were found to agree to within 0.1mm, 0.1mm and 0.3mm respectively, and were in close agreement between the methods. For a total four months data collection period, the mean deviation between requested and measured 6DOF couch shifts was 0.6mm and 0.2°. Errors on field size were smaller than 1mm for 97.7% of the 324 data points. CONCLUSION: Results demonstrate that the linac equipped with a 6DOF robotic positioner and CBCT imaging satisfies requirements for SRT. Our methodology, based on a modified Winston-Lutz quality control, allowed us to quantitatively assess end-to-end accuracy of a linac in order to safely deliver SRT.

Second malignancies after permanent implant prostate cancer brachytherapy: A single-institution study of 675 patients treated between 1999 and 2003.

PURPOSE: To analyse the rate of secondary malignancies observed in a series of 675 prostate cancer patients who underwent a permanent implant brachytherapy between 1999 and 2003, and to compare the incidence with the expected rate in a matched general French population. MATERIAL AND METHODS: The cohort included low-risk patients and a selection of "favourable-intermediate" risk patients. All patients were homogeneously treated using an intraoperative dynamic planning prostate brachytherapy technique, with loose 125-iodine seeds and a prescription dose of 145Gy. The mean follow-up was 132 months. RESULTS: The 10-year overall survival for the entire cohort was 92% (95% confidence interval [CI]: 90-94). The 10-year relapse-free survival rate was 82% (95% CI: 79-85). Overall, 61 second cancers were registered. When comparing with a matched general French population, the standard incidence ratio (SIR) for bladder cancer was 1.02 (95% CI: 0.46-1.93). For colorectal cancer, the SIR was 0.45 (95% CI: 0.19-0.89). For lung cancer, the SIR was 0.38 (95% CI: 0.17-0.76). The SIR for all cancers was 0.61 (95% CI: 0.47-0.79). When excluding secondary colorectal and lung cancers (both with low SIRs in this series), the SIR for all cancers was 1.06 (95% CI: 0.77-1.29). CONCLUSION: With a mean follow-up of more than 11 years, this series does not detect any excess risk of second cancers associated with permanent implant prostate brachytherapy. However, due to power limitation, a small increase in the risk of secondary malignancies cannot be totally ruled out.

Long-term results of permanent implant prostate cancer brachytherapy: A single-institution study of 675 patients treated between 1999 and 2003.

PURPOSE: To analyse long-term overall survival, relapse-free survival and late toxicities in a series of 675 patients treated between 1999 and 2003, with a median follow-up of 132 months. PATIENTS AND METHODS: The cohort included low-risk patients and a selection of "favourable-intermediate" risk patients. All patients were homogeneously treated using an intraoperative dynamic planning prostate brachytherapy technique, with loose 125 iodine seeds. Hormone therapy, consisting most often of an anti-androgen alone, was given in 393 patients (58%). RESULTS: The 10-year overall survival was 92% (95% confidence interval [CI]: 90-94) without a significant difference between the low and the select intermediate-risk groups (P=0.17). The 10-year relapse-free survival rate for the entire cohort was 82% (95% CI: 79-85), and was significantly higher in the low-risk group than in the intermediate one (87 vs 71%; P<0.0001). Twenty-six percent of the relapses observed in this series occurred after more than 10 years of follow-up. The 10-year cumulative incidence of grade 3-4 urinary toxicity (whatever the delay and the recovery) was 5.78%. The cumulative incidence of grades 3-4 rectal toxicity in the present series was 1.65% at 10 years. As for sexual toxicity, 61% of our patients retained an erectile capacity at 10 years (with or without oral medication), with age being a major factor. CONCLUSION: With a median follow-up of more than 11 years, this series appears to confirm the excellent long-term results of low-dose rate prostate brachytherapy, both in terms of survival and in terms of toxicity.

Dose reduction with adaptive statistical iterative reconstruction for paediatric CT: phantom study and clinical experience on chest and abdomen CT.

OBJECTIVES: To assess the benefit and limits of iterative reconstruction of paediatric chest and abdominal computed tomography (CT). METHODS: The study compared adaptive statistical iterative reconstruction (ASIR) with filtered back projection (FBP) on 64-channel MDCT. A phantom study was first performed using variable tube potential, tube current and ASIR settings. The assessed image quality indices were the signal-to-noise ratio (SNR), the noise power spectrum, low contrast detectability (LCD) and spatial resolution. A clinical retrospective study of 26 children (M:F = 14/12, mean age: 4 years, range: 1-9 years) was secondarily performed allowing comparison of 18 chest and 14 abdominal CT pairs, one with a routine CT dose and FBP reconstruction, and the other with 30 % lower dose and 40 % ASIR reconstruction. Two radiologists independently compared the images for overall image quality, noise, sharpness and artefacts, and measured image noise. RESULTS: The phantom study demonstrated a significant increase in SNR without impairment of the LCD or spatial resolution, except for tube current values below 30-50 mA. On clinical images, no significant difference was observed between FBP and reduced dose ASIR images. CONCLUSION: Iterative reconstruction allows at least 30 % dose reduction in paediatric chest and abdominal CT, without impairment of image quality. KEY POINTS: • Iterative reconstruction helps lower radiation exposure levels in children undergoing CT. • Adaptive statistical iterative reconstruction (ASIR) significantly increases SNR without impairing spatial resolution. • For abdomen and chest CT, ASIR allows at least a 30 % dose reduction.

Comparison of organs' shapes with geometric and Zernike 3D moments.

The morphological similarity of organs is studied with feature vectors based on geometric and Zernike 3D moments. It is particularly investigated if outliers and average models can be identified. For this purpose, the relative proximity to the mean feature vector is defined, principal coordinate and clustering analyses are also performed. To study the consistency and usefulness of this approach, 17 livers and 76 hearts voxel models from several sources are considered. In the liver case, models with similar morphological feature are identified. For the limited amount of studied cases, the liver of the ICRP male voxel model is identified as a better surrogate than the female one. For hearts, the clustering analysis shows that three heart shapes represent about 80% of the morphological variations. The relative proximity and clustering analysis rather consistently identify outliers and average models. For the two cases, identification of outliers and surrogate of average models is rather robust. However, deeper classification of morphological feature is subject to caution and can only be performed after cross analysis of at least two kinds of feature vectors. Finally, the Zernike moments contain all the information needed to re-construct the studied objects and thus appear as a promising tool to derive statistical organ shapes.

[Brachytherapy dose calculation]. / Calcul de la distribution de dose en curiethérapie.

Brachytherapy dose distribution calculation has evolved from the simple use of charts to the TG-43 formalism. It depends on the physical and geometrical characteristics of each source, the position of the source relatively to the calculation point and on the medium composition. Its principles and limitations are presented as well as the different dosimetric systems associated with implementing rules and the definition of the prescribed dose. The new generation of algorithms and their contributions are discussed.

[Permanent implant prostate cancer brachytherapy: 2013 state-of-the art]. / Curiethérapie du cancer prostatique par implants permanents : le point en 2013.

With an experience of more than 25 years for the pioneers (and more than 14 years in France), permanent implant brachytherapy using iodine 125 seeds (essentially) is now recognized as a valuable alternative therapy for localized low-risk prostate cancer patients. The possible extension of the indications of exclusive brachytherapy towards selected patients in the intermediate-risk group has now been confirmed by several studies. Moreover, for the other patients in the intermediate-risk group and for the patients in the high-risk group, brachytherapy, as an addition to external radiotherapy, could represent one of the best ways to escalate the dose. Different permanent implant brachytherapy techniques have been proposed; preplanning or real-time procedure, loose or stranded seeds (or both), manual or automatic injection of the seeds. The main point here is the ability to perfectly master the procedure and to comply with the dosimetric constraints, which have been recently redefined by the international societies, such as the GEC-ESTRO group. Mid- and long-term results, which are now available in the literature, indicate relapse-free survival rates of about 90% at 5-10 years, the best results being obtained with satisfactory dosimetric data. Comparative data have shown that the incontinence and impotence rates after brachytherapy seemed to be significantly inferior to what is currently observed after surgery. However, a risk of about 3 to 5% of urinary retention is usually reported after brachytherapy, as well as an irritative urinary syndrome, which may significantly alter the quality of life of the patients, and last several months. In spite of those drawbacks, with excellent long-term results, low rates of incontinence and impotence, and emerging new indications (focal brachytherapy, salvage brachytherapy after localized failure of an external irradiation), permanent implant prostate brachytherapy can be expected to be proposed to an increasing number of patients in the next future.

The relevance of image quality indices for dose optimization in abdominal multi-detector row CT in children: experimental assessment with pediatric phantoms.

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).

[Permanent implant prostate cancer brachytherapy]. / La curiethérapie du cancer prostatique par implants permanents.

With an experience of more than 20 years for the pionneers (and more than 10 years in France), permanent implant brachytherapy using Iodin 125 seeds is now recognized as a valuable alternative therapy for localized low-risk prostate cancer patients. An extension of the indications of exclusive brachytherapy towards selected patients in the intermediate-risk group is presently under study. Moreover, for patients in the high-risk group, brachytherapy, as an addition to external radiotherapy, could represent one of the best way to escalate the dose for some patients. Various permanent implant brachytherapy techniques have been proposed; preplanning or real-time techniques, loose seeds or stranded seeds, manual or automatic injection of the seeds. The main point here is the ability to perfectly master the procedure and to comply with the dosimetric constraints which have been recently redefined by the Groupe européen de curiethérapie--European Society for Therapeutic Radiology and Oncology (GEC-ESTRO) group. Mid- and long-term results which are now available in the literature indicate relapse-free survival of about 90% at 5-10 years, the best results being obtained with satisfactory dosimetric data. Some comparative data have shown that the incontinence and impotence rates after brachytherapy seemed to be significantly inferior to what is currently observed after surgery. However, a risk of about 3-5% of urinary retention is usually reported after brachytherapy, as well as an irritative urinary syndrome which may be significant and last several months. In spite of those drawbacks, with excellent long-term results and low rates of incontinence and impotence, brachytherapy can be expected to be proposed to an increasing number of patients in France in the next future.

OEDIPE: a new graphical user interface for fast construction of numerical phantoms and MCNP calculations.

Although great efforts have been made to improve the physical phantoms used to calibrate in vivo measurement systems, these phantoms represent a single average counting geometry and usually contain a uniform distribution of the radionuclide over the tissue substitute. As a matter of fact, significant corrections must be made to phantom-based calibration factors in order to obtain absolute calibration efficiencies applicable to a given individual. The importance of these corrections is particularly crucial when considering in vivo measurements of low energy photons emitted by radionuclides deposited in the lung such as actinides. Thus, it was desirable to develop a method for calibrating in vivo measurement systems that is more sensitive to these types of variability. Previous works have demonstrated the possibility of such a calibration using the Monte Carlo technique. Our research programme extended such investigations to the reconstruction of numerical anthropomorphic phantoms based on personal physiological data obtained by computed tomography. New procedures based on a new graphical user interface (GUI) for development of computational phantoms for Monte Carlo calculations and data analysis are being developed to take advantage of recent progress in image-processing codes. This paper presents the principal features of this new GUI. Results of calculations and comparison with experimental data are also presented and discussed in this work.

Determination of new European biometric equations for the calibration of in vivo lung counting systems using the Livermore phantom.

New biometric equations used for assessing the thickness of the overlay plate to be added to the physical phantom were determined based on the Computed Tomography (CT) chest images of 33 adult males in order to improve the calibration of in vivo lung counting systems using the Livermore phantom. These equations are specific to systems composed of four germanium detectors with the measured subject in supine position. A comparison with the biometric equations used to date as reference in France was carried out and proved the usefulness of equations directly applicable to the Livermore phantom.

Potential of modern technologies for improvement of in vivo calibration.

In the frame of IDEA project, a research programme has been carried out to study the potential of the reconstruction of numerical anthropomorphic phantoms based on personal physiological data obtained by computed tomography (CT) and Magnetic Resonance Imaging (MRI) for calibration in in vivo monitoring. As a result, new procedures have been developed taking advantage of recent progress in image processing codes that allow, after scanning and rapidly reconstructing a realistic voxel phantom, to convert the whole measurement geometry into computer file to be used on line for MCNP (Monte Carlo N-Particule code) calculations. The present paper overviews the major abilities of the OEDIPE software studies made in the frame of the IDEA project, on the examples of calibration for lung monitoring as well as whole body counting of a real patient.

Current developments at IRSN on computational tools dedicated to assessing doses for both internal and external exposure.

The paper presents the OEDIPE (French acronym that stands for tool for personalised internal dose assessment) and SESAME (for simulation of external source accident with medical images) computational tools, dedicated to internal and external dose assessment, respectively, and currently being developed at the Institute for Radiological Protection and Nuclear Safety. The originality of OEDIPE and SESAME, by using voxel phantoms in association with Monte Carlo codes, lies in their ability to construct personalised voxel phantoms from medical images and automatically generate the Monte Carlo input file and visualise the expected results. OEDIPE simulates in vivo measurements to improve their calibration, and calculates the dose distribution taking both internal contamination and internal radiotherapy cases into account. SESAME enables radiological overexposure doses to be reconstructed, as also victim, source and accident environment modelling. The paper presents the principles on which these tools function and an overview of specificities and results linked to their fields of application.

Application of Monte Carlo calculations to calibration of anthropomorphic phantoms used for activity assessment of actinides in lungs.

This paper reports on a new utility for development of computational phantoms for Monte Carlo calculations and data analysis for in vivo measurements of radionuclides deposited in tissues. The individual parameters of each worker can be acquired for an exact geometric representation of his or her anatomy, which is particularly important for low-energy gamma ray emitting sources such as thorium, uranium, plutonium and other actinides. The software discussed here enables automatic creation of an MCNP input data file based on computed tomography (CT) scanning data. The utility was first tested for low- and medium-energy actinide emitters on Livermore phantoms, the mannequins generally used for lung counting, in order to compare the results of simulation and measurement. From these results, the utility's ability to study uncertainties in in vivo calibration were investigated. Calculations and comparison with the experimental data are presented and discussed in this paper.