Ponente
Descripción
ABSTRACT
Around 40$\%$ of people surviving cancer do so because of radiotherapy. However, to improve this statistic, treatments based on hadron radiotherapy (HT) are rapidly expanding worldwide [1]. HT achieves very high dose conformity around the tumor target, allowing better protection of the organs at risk. This is particularly critical for radioresistant tumors, for tumors localized near organs at risk, and for pediatric cancers. Nevertheless, some toxicities have recently been reported [2‒5]. It might be because ions deliver higher linear energy transfer (LET), which may generate collateral damages, e.g., acute and late effects, and even secondary cancer induction. However, there are no tools capable of measuring LET during treatments. In this context, the National Center of Microelectronics (IMB-CNM) has designed and manufactured new silicon 3D detectors [6‒8] based on a novel architecture of cylindrical electrodes with microscopic sizes as those from a cellular level (15-25 $\mu$m) [7]. This allows quantifying the LET at micrometer scale, namely lineal energy.\ Moving towards their clinical implementation requires designing large layouts covering several centimeters based on these successful prototypes and performing significant pre-clinical trials. The advanced detectors that we proposed could also be used for beam monitoring and dose evaluation during radiobiology trials in real-time. Quantifying LET with micrometer spatial resolution would allow us to optimize RBE-weighted treatments. RBE optimization can be carried out by removing high‒LET spots from critical structures, focalizing high‒LET regions into the target, and assessing the potential biological impact of the treatment plans on the target and surrounding normal tissue. It would allow guiding beam arrangements to enhance therapeutic ratios and minimize dose excesses due to physical uncertainties. This can be performed by using LET-painting [9], which has already demonstrated an increase of the tumor control probability in hypoxic tumors.
The present work shows the performance of the first multi-pad-type array of those 3D microdetectors containing 3 × 3 unit-cells with 200 $\mu$m of pitch between them. The 9 microdetectors in each array are connected to the same readout channel in the readout chip (ROC) [10]. The system has 8 pad-type arrays stacked laterally, each array contains 25 3 × 3 units, covering a total radiation-sensitive area of 0.4 mm × 12 cm.
The system has been tested at Centro Nacional de Aceleradores (Sevilla, Spain) under low-energy proton beam irradiations at different energies between 6.2 and 13.6 MeV with therapeutic-equivalent fluence rates ($10^7 p \cdot cm^{-2} \cdot s^{-1}$) to obtain the corresponding microdosimetry quantities along the Bragg peak and distal edge.The microdosimetry quantities were successfully obtained with spatial resolutions of 200 $\mu$m. Experimental results were compared to Monte Carlo simulations based on TOPAS [11] and an overall good agreement was found.
Microdosimetry spectra of lineal energy were recorded as well as the first microdosimetry 2D maps that show the number of particles detected in each case and the experimental $\bar{y}_f$ values, which cover from (7$\pm$1) to (17.4$\pm$0.5) keV$\mu m^{-1}$ in good agreement with the literature [10]. In addition, a double-check was performed to ensure the accuracy of the beam profile reaching the sensors using a radiochromic film. For this, we convoluted both the spectra from the detector map and the ones collected with the films to their cross-section profiles. A general good agreement between the plots of the detector and film data has been achieved.
This compelling consistency underscores the robustness of our microdosimeter arrays and the reliability of the data obtained. It demonstrates that the system can be clinically used as microdosimeters for measuring the lineal energy distributions in the context of proton therapy treatments. Additionally, they could be also used for beam monitoring.
REFERENCES
[1] Schardt, D. et al.,Reviews of Modern Physics, 82(1), 383–425
[2] Yock TI et al., Radiother Oncol. 2014 Oct; 113(1):89-94.
[3] McGovern et al., Int. J. Radiat. Oncol. Biol. Phys., Volume 90, Issue 5, 1143-1152
[4] Indelicato DJ, et al., Acta Oncol. 2014 Oct;53(10):1298-304.
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[6] Guardiola C. et al., Phys Med Biol. 2021;66(11):10.1088/1361-6560/abf811
[7] Guardiola C. et al., Appl. Phys. Lett. 107, 023505 (2015).
[8] Prieto-Pena J. et al., IEEE Transactions on Nuclear Science, Vol. 66, No. 7, July 2019
[9] Bassler, N., Jäkel, O., Søndergaard, C. S., Petersen, J. B. (2010). Dose-and LET-painting with particle therapy. Acta oncologica, 49(7), 1170-1176.
[10] Bachiller-Perea, D., Zhang, M., Fleta, C., Quirion, D., Bassignana, D.,Gómez, F., & Guardiola, C. (2022). Microdosimetry performance of the first multi-arrays of 3D-cylindrical microdetectors. Scientific Reports,12(1),12240.
[11] https://www.topasmc.org/
