Two-dimensional (2D) arrays of thick segmented scintillators are of interest as X-ray detectors for both 2D and 3D image-guided radiotherapy (IGRT). Their detection process involves ionizing radiation energy deposition followed by production and transport of optical photons. Only a very limited number of optical Monte Carlo simulation models exist, which has limited the number of modeling studies that have considered both stages of the detection process. We present ScintSim1, an in-house optical Monte Carlo simulation code for 2D arrays of scintillation crystals, developed in the MATLAB programming environment. The code was rewritten and revised based on an existing program for single-element detectors, with the additional capability to model 2D arrays of elements with configurable dimensions, material, etc., The code generates and follows each optical photon history through the detector element (and, in case of cross-talk, the surrounding ones) until it reaches a configurable receptor, or is attenuated. The new model was verified by testing against relevant theoretically known behaviors or quantities and the results of a validated single-element model. For both sets of comparisons, the discrepancies in the calculated quantities were all <1%. The results validate the accuracy of the new code, which is a useful tool in scintillation detector optimization.

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Thyroid carcinoma is the most common cancer of the endocrine system, accounting for 12% of all cancer cases in adolescents in the United States. Radioiodine therapy plays a key role in differentiated thyroid cancer (DTC) treatment. This double-blind, randomized, placebo-controlled clinical trial was aimed at evaluating the effect of probiotics supplementation in reducing the acute side-effects of radioiodine therapy in PTC patients. Fifty-six patients were randomly divided into four groups: one placebo and three intervention groups. The probiotics product used in this study was LactoCare (ZistTakhmir Co., Iran), a multi-strain commercially available symbiotic containing 12 strains of probiotic species including Lactobacillus strains, Bifidobacteria strains, and Streptococcus thermophilus, plus Fructo-oligosaccharides as the prebiotic. Group 0 was our placebo group (no probiotics), while the other three groups received probiotics capsules for 2/4 days, starting only 2 days prior to radioiodine therapy, only 4 days after radioiodine therapy or 2 days prior and 4 days after radioiodine therapy. Six patients were withdrawn during the study because of poor compliance or at their own request. The symptoms reported by patients including data about the incidence and duration of each complication were recorded. The probiotics' effectiveness was confirmed for dry mouth and taste loss or change when it was administered prior to the radioiodine treatment. The benefit was not confirmed for other radiation-induced complications such as pain and swelling in the neck, nausea and vomiting, salivary gland swelling, and diarrhea. Further large-scale clinical trials are warranted to improve our knowledge in this quickly evolving field.

Background Arrays of thick segmented crystalline scintillators are useful x‐ray converters for image‐guided radiation therapy using electronic portal imaging (EPI) and megavoltage cone‐beam computed tomography (MV‐CBCT). Ionizing‐radiation‐only simulations previously showed relatively low modulation transfer function (MTF) in parallel‐element arrays because of beam divergence. Hence, a focused‐element geometry (matching the beam divergence) has been proposed. The “full” (ionizing and optical) MTF performance of such a focused geometry compared to its radiation‐only MTF has, however, not been fully investigated. Purpose To study the full MTF performance of such arrays in a more realistic situation in which optical characteristics are also included using an in‐house detector model that supports light transport, and quantify the errors in MTF estimation when the optical stage is ignored. Methods First, radiation (x‐ray and electron) transport was simulated. Then, transport of the generated optical photons was modeled using ScintSim2, an optical Monte Carlo (MC) code developed in MATLAB for simulation of two‐dimensional (2D) parallel‐ and focused‐element scintillator arrays. The full‐MTF responses of focused‐ and parallel‐element geometries, for a large array of 3 × 3 mm2 CsI:Tl detector elements of 10, 40, and 60 mm thicknesses, were examined. For each configuration, a composite line spread function (LSF) was calculated to obtain the MTF. Results At the Nyquist frequency, for 10 mm‐thick central elements and 60 mm‐thick peripheral parallel elements, full‐MTF exhibited a drop of up to 15 and 79 times, respectively, compared with radiation‐only MTF. This was found to be partly attributable to the angular distribution of the light emerging from the detector‐element exit face and the dependence on its aspect ratio, since the light exiting thicker scintillators exhibited a more forward‐directed distribution. Focused elements provided an increase of up to nine times in peripheral‐area full MTF values. Conclusions Full MTF was up to 79 times lower than radiation‐only MTF. Focused arrays preserved full MTF by up to nine times compared to parallel elements. The differences in the results obtained with and without inclusion of optical photons emphasize the need to include light transport when optimizing thick segmented scintillation detectors. Besides their application in detector optimization for radiotherapy megavoltage photon imaging, these findings can also be useful for other segmented‐scintillator‐based imaging systems, for example, in nuclear medicine, or in 2D detection systems for quality assurance of MR‐linacs.