Abstract
The present overview describes the evolution of new microdosimeters developed in the National Microelectronics Center in Spain (IMB-CNM, CSIC), ranging from the first ultra-thin 3D diodes (U3DTHINs) to the advanced 3D-cylindrical microdetectors, which have been developed over the last 10 years. In this work, we summarize the design, main manufacture processes, and electrical characterization of these devices. These sensors were specifically customized for use in particle therapy and overcame some of the technological challenges in this domain, namely the low noise capability, well-defined sensitive volume, high spatial resolution, and pile-up robustness. Likewise, both architectures reduce the loss of charge carriers due to trapping effects, the charge collection time, and the voltage required for full depletion compared to planar silicon detectors. In particular, a 3D‒cylindrical architecture with electrodes inserted into the silicon bulk and with a very well‒delimited sensitive volume (SV) mimicked a cell array with shapes and sizes similar to those of mammalian cells for the first time. Experimental tests of the carbon beamlines at the Grand Accélérateur National d’Lourds (GANIL, France) and Centro Nazionale Adroterapia Oncologica (CNAO, Italy) showed the feasibility of the U3DTHINs in hadron therapy beams and the good performance of the 3D‒cylindrical microdetectors for assessing linear energy distributions of clinical beams, with clinical fluence rates of 5 × 107 s−1cm−2 without saturation. The dose-averaged lineal energies showed a generally good agreement with Monte Carlo simulations. The results indicated that these devices can be used to characterize the microdosimetric properties in hadron therapy, even though the charge collection efficiency (CCE) and electronic noise may pose limitations on their performance, which is studied and discussed herein. In the last 3D‒cylindrical microdetector generation, we considerably improved the CCE due to the microfabrication enhancements, which have led to shallower and steeper dopant profiles. We also summarize the successive microdosimetric characterizations performed with both devices in proton and carbon beamlines.
Highlights
Exposure to radiation produces a great diversity of biochemical effects in tissues
New techniques for external-beam Radiation therapy (RT) that provide treatment noninvasively have been introduced in recent years to reduce the side-effects, such as intensity-modulated radiation therapy (IMRT) and particle therapy (PT), known as hadron therapy
This is characterized by the photon absorption curve, where there is an initial growth in the deposited dose followed by an exponential decrease
Summary
Exposure to radiation produces a great diversity of biochemical effects in tissues. The cellular responses depend on the amount of energy deposited by the radiation as well as the pattern of energy deposition distribution in the track structures. Since the Bragg peak is too narrow to treat extended tumor volumes, beams of different energies are superimposed to generate a spread-out Bragg peak (SOBP) to cover uniform dose distributions; (ii) it may reduce the radiation dose to nearby healthy tissue and critical organs; (iii) there is a smaller angular scattering area and penumbra, and (iv) lastly, it may deliver a more radiobiologically effective dose [3] This last property is due to the fact that the charged particles exhibit a high ionization pattern along their tracks, and the energy transferred locally into cells is higher than in conventional RT, inducing complex cellular damage. These sensors allow for further RBE calculations in hadron therapy beams under clinical conditions
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