Tiny changes in tomographic system matrices can cause large changes in reconstruction quality.

This paper studies the impact of tiny changes in region-of-interest (ROI) tomography system matrices on the variance of the reconstructed ROI. In small-scale and medium-scale examples, the variance in the reconstructed ROI was estimated for different system matrices. The results revealed a striking and counterintuitive phenomenon: a tiny change in the system matrix can dramatically affect the variance of the ROI estimate. In one of our examples, a decrease of 0.1% in one element out of hundreds of thousands of the system matrix resulted in a systematic reduction of the variance inside the ROI, and by a factor of 5 to 10 for some pixels. Our results agree with a recently proven theorem about the ability of additional measurements to reduce the variance in ROI tomography.

SciFi detector and associated method for real-time determination of profile and output factor for small fields in stereotactic radiotherapy.

PURPOSE: For determining small-field profile and output factor during stereotactic radiotherapy quality assurance (QA) procedures, we propose a novel system based on the scintillating fiber (SciFi) detector with output image acquisition and processing to allow real-time monitoring of profile and output factor. MATERIALS AND METHODS: The employed detector is a SciFi detector made of tissue-equivalent scintillating plastic fibers arranged in 6-layer fiber ribbons with a fiber pitch of 275 µm in each layer. The scintillating signal at the detector output is acquired by a sCMOS (scientific complementary metal-oxide-semiconductor) camera and represents the projected field profile along the fibers axis. An iterative reconstruction method of the field from its projected profile based on a priori knowledge of some features of the radiation field defined by the stereotactic cones is suggested. The detector with implemented data processing has been tested in clinical conditions, for determining beam profiles and output factors, using cone collimators of different sizes from 4 to 15 mm diameter. The detector under test was placed at 1.4 cm depth and 98.6 cm source to surface distance (SSD) in a water-equivalent phantom and irradiated by a 6 MV photon beam. RESULTS: The reconstructed field profiles obtained from the detector are coherent with data from EBT3 radiochromic films, with differences within ±0.32 mm for both the FWHM and the penumbra region. For real-time determination of the field output factor, the measured data are also in good agreement with data independently determined by the French Institute for Radiological Protection and Nuclear Safety (IRSN) based on radiochromic films and thermoluminescent 1 × 1 mm2 micro-cubes dosimeters (TLD). The differences are within ±1.6% for all the tested cone sizes. CONCLUSIONS: We propose and have tested a SciFi plastic scintillating detector with an optimized signal processing method to characterize small fields defined by cone collimators. It allows the determination of key field parameters such as full width at half maximum (FWHM) and field output factors. The results are consistent with those independently measured using TLD and radiochromic films. As the SciFi detector does not require a correction factor, it is in line with the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) TRS-483 recommendations, and can be suitable for online QA of small radiation fields used in photon beam radiotherapy, and is compatible with MRI-LINAC.

Conformal external radiotherapy of prostatic carcinoma: requirements and experimental results.

The aim of conformal radiotherapy is to deliver, with high precision, a specific dose (which may be a high dose) to a planning target volume, concurrently with irradiating as little as possible healthy tissue and organs at risk. Radiation therapy may suffer from a number of problems that result in both over- or under-sizing the irradiation fields, making over-rough simplifications of the irradiation ballistics and delivering an insufficient tumoral dose (to spare critical organs and reduce toxicity). One of these problems lies in the accurate positioning of the planning target volume with respect to the irradiation system, thence in the correct execution of the ballistics. In this paper, we describe a system aiming at achieving a higher overall accuracy in the delivery of prostatic boost for carcinoma of the prostate. The system is based on the use of ultrasonic images for measuring the actual position of the prostate just before irradiation. Since these images are registered with pre-operative (CT or MR) images, the position and orientation of the planning target volume is computed with respect to the irradiation system, and can be corrected accordingly. First experiments have been performed on dummies, and the results are discussed.

Attenuation correction in SPECT using consistency conditions for the exponential ray transform.

Using data consistency conditions for the exponential ray transform, a method is derived to correct SPECT data for attenuation effects. No transmission measurements are required, and no operator-defined contours are needed. Furthermore, any 3D parallel-ray geometry can be considered for SPECT data acquisition, even unconventional geometries which do not lead to a set of 2D parallel-beam sinograms. The method is presented for both the 2D parallel-beam geometry and a particular 3D case, called the rotating slant hole geometry. Full details of the algorithms are given. Implementation has been carried out and results are presented in 2D and in 3D using simulated data.

[Feasibility of patient-injected anticoagulation therapy: the GRANTED experience]. / Faisabilité pratique de l'auto-injection des traitements anticoagulants: l'expérience du réseau GRANTED.

BACKGROUND: Injectable anticoagulation therapy is indicated for several months following diagnosis of venous thromboembolic disease (VTE) in a context of active neoplasia. Certain studies have shown an improvement in patient compliance using self-injections. PURPOSE: Allow patients to safely make their own injections of anticoagulants after checking their aptitude and motivation. METHODS: At the prescribing physician's request, the GRANTED network provided patients and/or the resource person with specific education and training. The educational program was proposed to patients with an indication for a treatment for at least 3 months. After becoming familiar with the injection material and its manipulation, the patient and/or resource person performed sham injections on test materials. Patients were then allowed to decide for themselves whether or not to participate in the self-injection protocol. The prescribing physician received a report from the training team. RESULTS: From November 2010 to July 2012, 39 patients participated in the educational program, generally in a context of vitamin K antagonist prescriptions. Sixteen of these patients had a neoplasia. The educational program corrected erroneous or imprecise points of information, particularly concerning syringe purging. DISCUSSION: The education program proved to be interesting for points other than those initially foreseen and allowed the team to rectify a certain number of erroneous messages unrecognized by the prescribing physicians. This result goes in line with the need for accompanying patients who have a prescription for self-injections and also emphasizes the need for careful follow-up.

Algebraic and analytic reconstruction methods for dynamic tomography.

In this work, we discuss algebraic and analytic approaches for dynamic tomography. We present a framework of dynamic tomography for both algebraic and analytic approaches. We finally present numerical experiments.