Total body irradiation using helical tomotherapy: Set-up experience and in-vivo dosimetric evaluation.

PURPOSE: Helical Tomotherapy (HT) appears as a valuable technique for total body irradiation (TBI) to create highly homogeneous and conformal dose distributions with more precise repositioning than conventional TBI techniques. The aim of this work is to describe the technique implementation, including treatment preparation, planning and dosimetric monitoring of TBI delivered in our institution from October 2016 to March 2019. MATERIAL AND METHOD: Prior to patient care, irradiation protocol was set up using physical phantoms. Gafchromic films were used to assess dose distribution homogeneity and evaluate imprecise patient positioning impact. Sixteen patients' irradiations with a prescribed dose of 12Gy were delivered in 6 fractions of 2Gy over 3 days. Pre-treatment quality assurance (QA) was performed for the verification of dose distributions at selected positions. In addition, in-vivo dosimetry was carried out using optically stimulated luminescence dosimeters (OSLD). RESULTS: Planning evaluation, as well as results of pre-treatment verifications, are presented. In-vivo dosimetry showed the strong consistency of OSLD measured doses. OSLD mean relative dose differences between measurement and calculation were respectively +0,96% and -2% for armpit and hands locations, suggesting better reliability for armpit OSLD positioning. Repercussion of both longitudinal and transversal positioning inaccuracies on phantoms is depicted up to 2cm shifts. CONCLUSION: The full methodology to set up TBI protocol, as well as dosimetric evaluation and pre-treatment QA, were presented. Our investigations reveal strong correspondence between planned and delivered doses shedding light on the dose reliability of OSLD for HT based TBI in-vivo dosimetry.

Results of a cohort of 200 hormone-naïve consecutive patients with prostate cancer treated with iodine 125 permanent interstitial brachytherapy by the same multidisciplinary team.

PURPOSE: To report survival and morbidity of a cohort of 200 hormone-naïve consecutive patients with localized prostate cancer, treated by low-dose rate brachytherapy within the frame of multidisciplinary approach. PATIENTS AND METHODS: Between 2001 and 2011, 200 patients were treated by the same team with 125 iodine seeds: 167 low-risk and 33 intermediate risk according to the d'Amico classification; eligible patients had clinical stage T1/T2a-b, Gleason score 3+3 or 3+4, baseline prostate-specific antigen level below 15ng/mL, prostate volume less than 60cm(3). The median number of random biopsies was 12 (range 6-32) and the breakdown of positive cores was as follows: 1 (29%), 2 (35%), 3 or more (36%). Acute morbidity was assessed according to the Common Terminology Criteria for Adverse Events and late toxicity according to the EORTC/RTOG scale. Data were prospectively collected. RESULTS: The median follow-up was 69 months (range 16 to 135). The 5- and 10-year biochemical relapse free survivals were 95.6% (95% confidence interval [CI]: 91-98) and 89.7% (95% CI: 79.4-95.0). The 5-year and 10-year overall survival were respectively 96.4% (95% CI: 92-98.4) and 89.7% (95% CI: 80.8-94.6%) and the 10-year disease specific survival, 99.1% (95% CI: 93.0-99.9). The 5- and 10-year grade 3 acute toxicity cumulative rate were respectively 3.3% (95% CI: 1.4-6.6) and 4% (95% CI: 1.4-6.6) and the 5- and 10-year grades 3 cumulative late toxicity 2.5% (95% CI: 2.0-5.9) and 4% (95% CI: 2.0-5.9). CONCLUSION: Brachytherapy managed within the frame of a multidisciplinary approach - from diagnosis to evaluation - may offer optimized results with a reduced late toxicity rate, while remaining opened to dosimetry and technical improvements.

Fiber background rejection and crystal over-response compensation for GaN based in vivo dosimetry.

For dosimetric measurements using an implantable optical fiber probe with GaN (Gallium Nitride) scintillator as radioluminescence (RL) transducer, a bi-channel method is proposed to reject the background contribution of the irradiated fiber segment. It is based on spectral differences between the narrow-band light emission from GaN and the large-band background from the irradiated optical fiber. Experimental validation of this method using 6 MV photon beam has shown that the remaining background contribution after subtraction is below 1.2% for square field sizes ranging from 3 cm to 20 cm. Furthermore, a compensation method for the over-response of GaN is also proposed, since GaN is not tissue equivalent. The over-response factor of GaN exhibits a linear increase with square field aperture and depends on depth from phantom surface. This behaviour is modelled to allow compensation in specific conditions. The proposed method has been evaluated and has shown a maximum deviation of 3% for a 6 MV photon beam and 1% for an 18 MV photon beam at a depth beyond the build-up region.

[Report of the mission commissioned by the Ministry of Health to the French Society of Radiation Oncology]. / Rapport de la mission confiée par le ministère de la Santé à la Société française de radiothérapie oncologique.

Further to the Epinal events, Health Ministers P. Bas then R. Bachelot-Narquin have launched a plan of work devoted to radiotherapy; they have also committed the SFRO President, within the framework of a mission, to make proposals taking into account the demography of professionals and their level of competence, valorization of careers, cooperation with medical oncologists, delegations of authorities, mutualisation of human and material resources. Due to the numerous actions of the roadmap managed by the tutelages, the aim of the mission was focused on the modalities of work of the professionals linked to radiotherapy: radiation oncologists, radiographers and physicists.

Radiotherapy quality assurance by individualized in vivo dosimetry: state of the art.

The quality insurance in radiotherapy in the frame of highly complex technical process as Intensity modulated radiotherapy (IMRT) needs independent control of the delivered dose to the patient. Actually, up to now, most of the radiotherapy treatments rely only on computed dosimetry through a rather complicated series of linked simulation tool. This dosimetry approach requires also qualified treatment means based on cautious quality insurance procedures. However, erroneous parameters could be difficult to detect and systematical errors could happen leading to radiotherapy accidents. In this context, in vivo dosimetry has a critical role of final control of the delivered dose. As many beam incidences and ports are used for any photontherapy treatment, external control could be very tedious and time consuming. Therefore, innovations are needed for in vivo dosimetry to provide ergonomic and efficient tools for these controls. This paper presents a review of technologies and products that can be used for in vivo dosimetry. It proposes also a reflection on the concepts to develop future devices suitable for this purpose. The technical means with their physical principles are reviewed, the clinical experiences demonstrating the feasibility of new techniques are then summarized and finally, the early clinical use and its impact on clinical practice is review.

MRI/TRUS data fusion for brachytherapy.

BACKGROUND: Prostate brachytherapy consists in placing radioactive seeds for tumour destruction under transrectal ultrasound imaging (TRUS) control. It requires prostate delineation from the images for dose planning. Because ultrasound imaging is patient- and operator-dependent, we have proposed to fuse MRI data to TRUS data to make image processing more reliable. The technical accuracy of this approach has already been evaluated. METHODS: We present work in progress concerning the evaluation of the approach from the dosimetry viewpoint. The objective is to determine what impact this system may have on the treatment of the patient. Dose planning is performed from initial TRUS prostate contours and evaluated on contours modified by data fusion. RESULTS: For the eight patients included, we demonstrate that TRUS prostate volume is most often underestimated and that dose is overestimated in a correlated way. However, dose constraints are still verified for those eight patients. CONCLUSIONS: This confirms our initial hypothesis.

Development of educational image databases and e-books for medical physics training.

Medical physics education and training requires the use of extensive imaging material and specific explanations. These requirements provide an excellent background for application of e-Learning. The EU projects Consortia EMERALD and EMIT developed five volumes of such materials, now used in 65 countries. EMERALD developed e-Learning materials in three areas of medical physics (X-ray diagnostic radiology, nuclear medicine and radiotherapy). EMIT developed e-Learning materials in two further areas: ultrasound and magnetic resonance imaging. This paper describes the development of these e-Learning materials (consisting of e-books and educational image databases). The e-books include tasks helping studying of various equipment and methods. The text of these PDF e-books is hyperlinked with respective images. The e-books are used through the readers' own Internet browser. Each Image Database (IDB) includes a browser, which displays hundreds of images of equipment, block diagrams and graphs, image quality examples, artefacts, etc. Both the e-books and IDB are engraved on five separate CD-ROMs. Demo of these materials can be taken from www.emerald2.net.

A dosimetric comparison of two multileaf collimator designs.

We present the results of measurements designed to compare two different multileaf collimator (MLC) designs using a novel evaluation technique. The MLC designs evaluated were: a "single-focused" MLC (SF-MLC) mounted below the jaws, and a "double-focused" MLC, which is a complete replacement for the lower jaws. The ability of each MLC to conform isodose lines to a prescribed field edge (PFE) was evaluated using film dosimetry. Circular fields, centered on axis and off axis, were used because they produce a range of "angles of approach" between the MLC leaves and the PFE. They also have the advantage that for an ideal field shaping system the resulting isodoses are concentric perfect circles, a well-defined basis for evaluation. The amplitude of the oscillations of the 50% isodose line about the PFE and the penumbra width as determined by the 20%, 80%, and 90% isodose lines was examined. We observe that the 50% isodose line oscillates around the PFE with greater amplitude for SF-MLC. We attribute this, at least in part, to the rounded ends of the SF-MLC leaves. However, the SF-MLC has a noticeably sharper penumbra, which we attribute to its position further from the source. We conclude that these results are relevant for accurate dosimetric modeling of these devices.

[Absorbed dose during helical acquisition CT. Effect of acquisition parameters]. / Dose délivrée lors d'un examen scanner en acquisition hélicoïdale. Influence des paramètres d'acquisition.

PURPOSE: European directive 97/43 specifies that the dose delivered to the patient during a radiological procedure should be estimated. In order to prepare for implementation of this new regulation, we have studied the dose delivered during spiral CT acquisition. MATERIALS AND METHODS: We have studied the influence of slice thickness, pitch, tube voltage and intensity, and acquisition volume length. We present measurements for single and dual detector CT scanners. We used a pencil ionization chamber to measure air kerma. We measured absorbed dose in water with a waterproof ionization chamber set in a semi-customized phantom filled with water. Chambers were set on the rotation axis of the CT scanners. We studied the dose outside the acquisition volume. RESULTS: We quantified the influence of each parameter on the absorbed dose. We used our measurements to calculate the dose for different acquisition protocols. Also we evaluated the dose to organs distant from the acquisition area. CONCLUSION: This study is one step toward a systematic estimation of the dose delivered to patient during helical CT exams. To use these results in daily practice, we have to develop software using our measurements.

Patient set-up using portal images: 2D/2D image registration using mutual information.

OBJECTIVE: Conformal radiation therapy requires accurate patient set-up for each fraction delivery. Electronic portal imaging devices allow the acquisition of portal images just before and even during dose delivery. However, the quantitative interpretation of these images in determining and correcting the patient's position remains uncertain, and automated methods are therefore being developed. Such methods must be usable for the different radiation therapy techniques. They must be robust and as automated as possible for use in clinical routines. This work was undertaken to establish the feasibility of 2D/2D registration for portal/portal and portal/simulator images in radiotherapy. MATERIALS AND METHODS: This paper describes an automated method based on the combination of calibration algorithms and pixel-based registration algorithms. We present experiments with the different imaging techniques, some of which use a phantom with and without a gold standard. Preliminary results obtained using patient data are also presented and discussed. RESULTS: The results obtained with a phantom demonstrated that this automated method for 2D/2D registration is fast, accurate, and robust, even in the case of blurred images for small treatment fields. CONCLUSIONS: Mutual information is a feasible method for 2D/2D portal/portal and portal/simulator image registration in radiotherapy.

[Patient positioning and its verification: justification, state of the art of the classical practices]. / Positionnement du patient et sa vérification: justifications, état de l'art des moyens classiques.

Patient immobilization is considered an important part of the quality control program in radiation therapy. The need for patient immobilization according to the symptoms, ensuring both reproducibility and comfort, is described in the recommendations for level 1 published by the SFPM (Société française de physique médicale) and the SFRO (Société française de radiothérapie oncologique). A customized device, associated with regular controls, is required for level 2. Customized procedures are mandatory in clinical practice for head and neck and brain treatments. Internal margins and movements of patients must be analyzed and controlled as deviations of CTV placement relative to the isocenter of linacs. They could be reduced with efficient positioning devices and accurate customized immobilization systems. Different devices could be used according to tumor locations. Except for subclavicular tumors, their efficacy remains controversial.

[Image fusion methods for the repositioning of the patient in radiotherapy]. / Méthodes de recalage d'images pour le repositionnement de patients en radiothérapie.

Conformal radiotherapy requires the accurate and reproducible setup of the patient for each fraction delivery. Megavoltage imaging could enable this. This requires the development of image processing and data fusion algorithms. We describe an automated method based on the use of mutual information for registration. Such a method does not require any preliminary segmentation of the images. This method has been extensively tested on phantom as well as on some patient data. The obtained results demonstrated that this automated method for 2D/2D registration is rapid, accurate and robust even in the case of blurred images for small treatment fields.

The use of a semi-customized phantom for verification of conformal plans.

We have developed a technique for inverse treatment planning of prostate therapy designed to improve the degree of conformation between the dose distribution and the target volume. We compared the inverse plan with a "standard" four-field box technique as well as a four-field technique using oblique fields ("cross technique"). We validated the dosimetry of the inverse plan using Fricke gel solution in phantom specifically designed for this purpose. The phantom is a Plexiglas tank with a cross section, which approximates the dimensions of the pelvis. Anatomical data from computed tomography (CT) images of a patient were used to simulate organs in our phantom. This allows us to calculate dose distributions with the external geometry of the phantom and internal anatomy of the patient. Dose-volume histograms (DVHs) for the three different plans were calculated. The phantom containing the Fricke gel was irradiated according to the inverse plan. Magnetic resonance (MR) images was used to determine the dose distribution delivered to the phantom. We observe, on DVHs, that the inverse plan significantly reduces the dose to the rectum and the bladder but slightly increases the inhomogeneity inside the target volume. Correlation is good between isodoses on MR images and calculated isodoses. We conclude that inverse planning software can greatly improve the conformal degree of treatment to the prostate. This technique could be applied to other complex anatomic sites at which dose to organs at risk is a limiting factor and increased dose to the target volume is indicated. Our phantom and the Fricke gel solution are convenient to carry out validation of conformal treatments.

[Survey of the use of contention shells in Centre-Rhône-Alpes area]. / Enquête sur l'utilisation des moules de contention dans la région Centre-Rhône-Alpes.

Contention shells are frequently used in radiotherapy. They allow improvements in the reproducibility of treatments and take part in quality assurance. The aim of our survey is to establish how centers use contention masks. Ninety-five percent of the centers questioned use contention masks. The fixation device is in most cases made of Plexiglas. The masks are always made of thermoplastics materials with low modeling temperature. They are made just before simulation or scanner by a radiographer. The surface dose problem can be overcome by two different techniques. One consists in the stretching of the material to reduce the density. The other consists of cutting out the mask where the irradiation fields are projected. Whatever the technique, there is a loss of rigidity of the mask, which means the immobilization is not so effective. Despite drawbacks, contention masks have an important role in the quality insurance in radiotherapy.

[3-D conformal radiotherapy procedure and registration of pre- and intra-radiotherapeutic data]. / Procédure de la radiothérapie conformative tridimensionnelle et mise en correspondance des données pré- et per-radiothérapiques.

The authors describe the different steps of 3-D conformal external irradiation. They mention as well two procedures of isocentric repositioning which are mandatory for the matching of anatomical data: the first one is acquired before the simulation and the second one just before the radiotherapy session.

Quality assurance of the EORTC radiotherapy trial 22863 for prostatic cancer: the dummy run.

The results of a dummy run involving nine centers participating in a study comparing radiotherapy alone with radiotherapy plus hormone therapy in patients with high metastatic risk prostatic cancer (EORTC protocol 22863) show that, in all centers but one, patients are treated in the same way. However, they have also indicated that protocol compliance could be improved by a better assessment of the target volume, by taking into account of the use of protective shields and of variations in radiological density, by determining beam position on a large number of slices, and by the use of CT scan images for treatment planning.

Patient setup optimization for external conformal radiotherapy.

The aim of conformal radiotherapy is to deliver precisely a specific dose of radiation to a planning target volume, concurrently radiating as little healthy tissue and organs as possible. This can be accomplished only with the accurate positioning of the patient with respect to the radiotherapy system. In this paper, we describe a system to achieve a higher overall accuracy in the delivery of a prostatic radiation boost for treatment of carcinoma of the prostate. The system is based on the use of ultrasound images for measuring the actual position of the patient's prostate just before the radiation. Since these images are registered with pretreatment computed tomography or magnetic resonance imaging, the position and orientation of the planning target volume are computed with respect to the radiotherapy system and can be corrected as needed. This system is under clinical evaluation.

Bone cutting.

Bone cutting has always been a problem for surgeons because bone is a hard living material, and many osteotomes are still very crude tools. Technical improvement of these surgical tools has first been their motorization. Studies of the bone cutting process have indicated better features for conventional tools. Several non-conventional osteotomes, particularly ultrasonic osteotomes are described. Some studies on the possible use of lasers for bone cutting are also reported. Use of a pressurised water jet is also briefly examined. Despite their advantages, non-conventional tools still require improvement if they are to be used by surgeons.