Tongue Displacement Device in Decreasing the Radiation Dose to Tongue and Preventing Proton Beam Overshoot in Proton Therapy for Unilateral Head and Neck Cancer

The aim of this study was to evaluate the dosimetric characteristics of a semi-customized tongue displacement device (SCTDD) fabricated using a 3D printer for patients receiving unilateral head and neck irradiation with intensity-modulated proton therapy (IMPT) and assess its feasibility as a proton beam stopper compared to a standard mouthpiece (SMP). Seven consecutive patients, three with tonsil cancer, and four with oral cavity cancer were included in this retrospective study. Planning computed tomography (CT) images of each patient were acquired for each device. Both the SCTDD and SMP plans were generated using a single-field optimized IMPT. The clinically relevant dose-volume parameters for the organs at risk (OARs), especially the tongue, were compared between the SCTDD and SMP plans. Additionally, to assess the feasibility of SCTDD as a proton beam stopper, the dose to the contralateral oral mucosa (COM) was compared with that from sMP use. The use of scTDD resulted in a statistically significant decrease in the radiation dose to the tongue and COM compared to sMP. The median mean dose to the tongue was significantly reduced with SCTDD (18.3 Gy(RBE)) compared to the SMP (22.9 Gy(RBE)) (p = 0.016). The percentages of tongue volume receiving doses between 15 and 60 Gy(RBE) were significantly lower with SCTDD. In the COM, SCTDD resulted in a significantly lower median mean (2.9 Gy(RBE) vs. 7.9 Gy(RBE), p = 0.018) and maximum dose (39.1 Gy(RBE) vs. 41.6 Gy(RBE), p = 0.018) doses compared to SMP. The SCTDD effectively decreased the radiation dose to the tongue compared to SMP in patients undergoing unilateral head and neck irradiation with IMPT and acted as a proton beam stopper to protect normal tissues located behind the target volume, such as the COM.

Particle Accelerator Focus Automation

The Laboratório de Aceleradores e Tecnologias de Radiação (LATR) at the Campus Tecnológico e Nuclear, of Instituto Superior Técnico (IST) has a horizontal electrostatic particle accelerator based on the Van de Graaff machine which is used for research in the area of material characterization. This machine produces alfa (He+) and proton (H+) beams of some μA currents up to 2 MeV/q energies. Beam focusing is obtained using a cylindrical lens of the Einzel type, assembled near the high voltage terminal. This paper describes the developed system that automatically focuses the ion beam, using a personal computer running the LabVIEW software, a multifunction input/output board and signal conditioning circuits. The focusing procedure consists of a scanning method to find the lens bias voltage which maximizes the beam current measured on a beam stopper target, which is used as feedback for the scanning cycle. This system, as part of a wider start up and shut down automation system built for this particle accelerator, brings great advantages to the operation of the accelerator by turning it faster and easier to operate, requiring less human presence, and adding the possibility of total remote control in safe conditions.

ANALISIS RANCANGAN DASAR SISTEM PGNAA MENGGUNAKAN SUMBER NEUTRON DARI BEAMPORT REAKTOR KARTINI

ABSTRAK ANALISIS RANCANGAN DASAR SISTEM PGNAA MENGGUNAKAN SUMBER NEUTRON DARI BEAMPORT REAKTOR KARTINI. Telah dilakukan perancangan dasar sistem PGNAA menggunakan salahsatu beamport reaktor Kartini sebagai sumber neutron. Moderator neutron ditempatkan pada ujung kolom berkas neutron untuk membuat berkas neutron menjadi termal. Berkas diarahkan menuju ruang sampel PGNAA dengan menggunakan kolimator yang berfungsi sebagai penyaring berkas neutron sejajar. Pada penggal kolimator yang berpotongan dengan jendela beamport dipasang neutron beam shutter untuk menutup berkas neutron apabila tidak digunakan untuk PGNAA. Beam stopper dipasang dibelakang ruang sampel PGNAA untuk menangkap berkas neutron yang lolos. Perhitungan sifat neutronik dilakukan untuk memilih bahan material yang memenuhi syarat fungsi sebagai sub-komponen PGNAA dan menentukan ukuran geometrinya. Dari hasil perhitungan diperoleh data bahan yang baik untuk moderator yaitu grafit, bahan kolimator adalah aluminium, bahan beam shutter dan beam stopper adalah komposit boraks-parafin. Panjang moderator 90 cm, panjang kolimator 173 cm dengan tetapan kolimasi D/L=0,015, tebal beam shutter dan beam stopper masing-masing 22 cm dan 30 cm. Dipasang perisai gamma dan perisai neutron untuk menutup berkas neutron keluar dari sela dinding dalam beamport dan didnding luar kolimator. Bahan perisai tersebut dibuat dari komposit boraks parafin 25% berat dan timbal yang masing-masing panjangnya 50 cm dan 30 cm. Hasil analisis menunjukkan bahwa dari fluks neutron awal pada beamport bagian dalam sebesar 1,5.1012 n/cm2s dapat menghasilkan fluks neutron termal di ruang sampel PGNAA 1,76.108 n/cm2s dengan arus neutron termal 9,29.108 n/s. Nilai fluks neutron termal tersebut memenuhi persyaratan untuk suatu sistem PGNAA yaitu berada pada orde 106 s/d 108 n/cm2s. Kata Kunci : PGNAA, rancangan dasar, prompt-gamma, analisis aktivasi, neutron-termal, beamport reaktor ABSTRACT BASIC DESIGN ANALYSIS OF PGNAA SYSTEM USING NEUTRON SOURCE FROM BEAMPORT OF KARTINI REACTOR. A basic design of PGNAA system using one of reactor beamports of Kartini reactor as a neutron source have been carried out. Neutron moderator is placed at the inner end of beamport column to make thermal neutron beam. A neutron beam directed to PGNAA counting chamber by using collimator as a filter to make parallel neutron beam. At the midle of collimator intersect with beamport window, neutron beam shutter is mounted to close when not in use for PGNAA. Beam stopper mounted behind the sample chamber of PGNAA to capture neutron beam that passes from the sample chamber. Calculation of neutronic properties of materials was done to choose the material that meet the functional requirements of PGNAA and to determine the geometry size. Based on the calculational results obtained that good material for moderator is graphite, aluminum as beam collimator, and beam shutter or stopper is made from borax-paraffin composite. The moderator length is 90 cm and collimator length is 173 cm with collimation constant D / L = 0,015. Beam shutter and beam stopper thickness are 22 cm and 30 cm respectively. Gamma and neutron shield are added surrounding beam colimator to shield the radiation out from the pitch between collimator and beamport wall. The shield material made from composite of parrafin 25 w % borax, and lead with the length of 50 cm and 30 cm respectively. The analysis result shows that from the neutron flux of 1,5.1012 n/cm2s at the inner side of beamport, can generate thermal neutron flux at the PGNAA sample chamber of 1,76.108 n/cm2s with the thermal neutron current of 9,29.108 n/s. This thermal neutron flux meet the requirement for a PGNAA system i.e. in the order of 106 to 108 n/cm2s. Keywords : PGNAA, basic design, prompt-gamma, activation analysis, thermal neutron, reactor beamport