Calibration method and performance of a time-of-flight detector to measure absolute beam energy in proton therapy

Background: The beam energy is one of the most significant parameters in particle therapy since it is directly correlated to the particles' penetration depth inside the patient. Nowadays, the range accuracy is guaranteed by offline routine quality control checks mainly performed with water phantoms, 2D detectors with PMMA wedges, or multi-layer ionization chambers. The latter feature low sensitivity, slow collection time, and response dependent on external parameters, which represent limiting factors for the quality controls of beams delivered with fast energy switching modalities, as foreseen in future treatments. In this context, a device based on solid-state detectors technology, able to perform a direct and absolute beam energy measurement, is proposed as a viable alternative for quality assurance measurements and beam commissioning, paving the way for online range monitoring and treatment verification. Purpose: This work follows the proof of concept of an energy monitoring system for clinical proton beams, based on Ultra Fast Silicon Detectors (featuring tenths of ps time resolution in 50 μm active thickness, and single particle detection capability) and time-of-flight techniques. An upgrade of such a system is presented here, together with the description of a dedicated self-calibration method, proving that this second prototype is able to assess the mean particles energy of a monoenergetic beam without any constraint on the beam temporal structure, neither any a priori knowledge of the beam energy for the calibration of the system. Methods: A new detector geometry, consisting of sensors segmented in strips, has been designed and implemented in order to enhance the statistics of coincident protons, thus improving the accuracy of the measured time differences. The prototype was tested on the cyclotron proton beam of the Trento Protontherapy Center (TPC). In addition, a dedicated self-calibration method, exploiting the measurement of monoenergetic beams crossing the two telescope sensors for different flight distances, was introduced to remove the systematic uncertainties independently from any external reference. Results: The novel calibration strategy was applied to the experimental data collected at TPC (Trento) and CNAO (Pavia). Deviations between measured and reference beam energies in the order of a few hundreds of keV with a maximum uncertainty of 0.5 MeV were found, in compliance with the clinically required water range accuracy of 1 mm. Conclusions: The presented version of the telescope system, minimally perturbative of the beam, relies on a few seconds of acquisition time to achieve the required clinical accuracy and therefore represents a feasible solution for beam commission, quality assurance checks, and online beam energy monitoring

تاثير اشعاع الموجات الكهرومغناطيسية على الغدة الدرقية للانسان

This study aims to investigate the effects of non-ionizing radiation emitted from mobile phone base station on some target group of children. Their thyroid-stimulating hormone (TSH) has been investigated taking into account the children were provided with possible protective olive oil supplement. The target group was composed of 120 children (6–12 years) and it was divided into three sets. The first group served as control group. The second group was exposed to electromagnetic field (EMF) alone, the third group was exposed to EMF and given 2.5 mL/day olive oil supplementation for 5 weeks. The second and the third groups lived nearby mobile phone base station (100–150 m) for more than 5 years. The thyroid-stimulating hormone (TSH) was assumed. EMF exposure caused decrease in TSH. Furthermore, this work presents a simulation study of electric fields, magnetic fields, power density and specific absorption rate (SAR) distribution in human thyroid tissue. Concerning numerical modeling, the power absorption and specific absorption rate in a thyroid tissue are generally computed using FDTD methods. Results show that electromagnetic radiation (EMR) from mobile phone penetrates the thyroid tissues and attenuates rapidly to reach zero at the inner of the tissue. The absorbent power and SAR show a maximum at the interface.تهدف هذه الدراسة إلى دراسة آثار الإشعاعات غير المؤينة المنبعثة منها محطة قاعدة الهاتف المحمول على بعض المجموعة المستهدفة من الأطفال. هرمون منشط للغدة الدرقية (TSH) وقد تم التحقيق مع الأخذ في الاعتبار تم تزويد الأطفال مع واقية ممكن ملحق زيت الزيتون. كانت المجموعة المستهدفة تتألف من 120 طفلاً (6-12 سنة) وتم تقسيمها إلى ثلاث مجموعات. خدمت المجموعة الأولى كمجموعة تحكم. المجموعة الثانية تعرضت ل المجال الكهرومغناطيسي (EMF) وحده ، المجموعة الثالثة تعرضت ل EMF وأعطيت 2.5 مل / يوم زيتون مكملات النفط لمدة 5 أسابيع. المجموعتان الثانية والثالثة عاشتا بالقرب من قاعدة للهاتف المحمول محطة (100-150 م) لأكثر من 5 سنوات. كان من المفترض هرمون محفز الغدة الدرقية (TSH). تسبب التعرض EMF انخفاض في TSH. علاوة على ذلك ، يقدم هذا العمل دراسة محاكاة للكهرباء الحقول ، الحقول المغناطيسية ، كثافة الطاقة وتوزيع معدل الامتصاص النوعي (SAR) في الغدة الدرقية البشرية الانسجة. فيما يتعلق بالنمذجة العددية ، امتصاص الطاقة ومعدل الامتصاص المحدد في الغدة الدرقية يتم حساب الأنسجة عموما باستخدام أساليب FDTD. أظهرت النتائج أن الإشعاع الكهرومغناطيسي (EMR) من الهاتف المحمول يخترق أنسجة الغدة الدرقية ويخفف بسرعة للوصول إلى الصفر في داخل الأنسجة. تظهر القوة الماصة و SAR كحد أقصى في الواجهة

Two-channel combination methods for count-loss correction in radiation measurements at high rates and with pulsed sources

Pile-up effects due to the overlap of signals within the system dead-time () influence the counting capability of radiation detection devices, necessitating the use of correction algorithms to compensate for the count-losses at high radiation rates. Count-rate linearity is especially critical for clinical applications like X-ray imaging or beam monitoring in particle therapy. In particular, in proton therapy the number of delivered particles must be measured online during the treatment session with a maximum error of 1 % up to an average input beam flux of about . For a segmented detector used to identify and count the single beam particles, assuming a channel area of 1 mm2 and a dead-time a maximum counting inefficiency of 1 % is required up to for each detector channel, where represents the input rate. Moreover, the beam is often delivered in bunches with higher instantaneous particle rates, and the saturation model of the detector and electronic chain could not be easily determined. Similar considerations are applicable for pixelated detectors used for photon counting. Two methods are proposed to mitigate counting inefficiencies with radiation sources of variable time-structures. Both methods are based on the collection of logic signals provided by two independent detector channels exposed to the same radiation field after discriminating the detector analog outputs with a fixed threshold, assuming that the duration of the discriminator output signal corresponds to the system dead-time. The correction algorithms employ the measurements of the time durations, the number of signals from the two channels and of their AND/OR combinations. The methods provide count-loss corrections without the need to know the dead-time model. The performances of the proposed algorithms are evaluated by using simulations of ideal boxcar signals of fixed duration , distributed randomly in time to emulate the dead-time behavior of the system. Both methods provide an effective count-loss correction with a maximum deviation of 1% for different input rates up to , assuming a uniform random time distribution of input events for both paralyzable and non-paralyzable systems. The simulations of pulsed radiation fluxes provide the same results as a function of the instantaneous input rates. These results are similar to those obtainable by the standard live-time correction algorithm. However, the latter algorithm can only be applied to continuous particle fluxes, while the proposed algorithms work also for pulsed beams, without any hypothesis on the bunch duration or frequency. The robustness of the algorithms with respect to the resolution of the time measurement is studied and the potential limitations in more realistic systems are discussed. The algorithms can be easily implemented in standard logical circuits with multiple input signals provided by segmented detectors. Even if the methods are intended for real-time correction in beam particle counting, they could be applied in a wider range of applications of radiation measurements