65/Detektory MOSFET jako narzędzie do weryfikowania dawek terapeutycznych wiązek elektronów w radioterapii

CelZastosowanie detektorów MOSFET (Metal – Oxide Semiconductor Field Effect Transistor) do pomiaru dawki in vivo wiązek elektronów w radioterapii.Metody i materiałyWykonano pomiary fantomowe polegające na zbadaniu zależności wskazań detektorów MOSFET od: – wartości dawki wiązek elektronów, – temperatury otoczenia detektorów, – kierunku padania wiązki elektronów na detektor, – wielkości napromienianego pola.Zbadano także zmianę czułości detektorów w zależności od skumulowanej dawki. Detektory, ze względu na bardzo małe wymiary, umieszczano w odpowiednio zaprojektowanych nakładkach aluminiowych – w celu zapewnienia równowagi elektronowej podczas pomiaru dawki. Wskazania detektorów porównywano do wskazańkomory jonizacyjnej typu Markus, posiadającej świadectwowzorcowania. Pomiary wykonano z użyciem wiązek elektronów o energii 6, 9, 12, 15, 18,21 MeV.WynikiZbadane zależności i określone na ich podstawie współczynniki korekcyjne umożliwiają zmierzyć dawkę wiązki elektronów z dokładnością ±2.5%.WniosekDetektory MOSFET są dobrym narzędziemdo weryfikowania dawki wejściowej w radioterapii wiązkami elektronów

Verification of doses in electron beam radiotherapy

Entrance doses measured in 50 patients treated by electron beams were compared with planned values as the percentage difference between the given dose and its planned value. Electron beams of energy 6, 9, 12, 15, 18 and 22 MeV were generated by the Clinac 2300 C/D linear accelerator (Varian). Semiconductor EDE-5 diodes connected to a DPD-510 (Scanditronix) electrometer were applied for entrance dose measurements. In our investigations, the mean values of doses administered agreed well with the values of planned doses. The observed relatively large discrepancies in a few patients (up to 12%) should be carefully investigated

6. The technique of total body irradiation applied in the St. Leszczyński Memorial Hospital in Katowice

At the St. Leszczyński Memorial Hospital in Katowice a modification of TBI technique was prepared. For this a special two variant of body frame – one for treatment planning and an another one for treatment delivery – was made. The total dose of 12 – 15 Gy (in lung not more than 9 Gy) was delivered in six fraction of 15 MV photons, produced in Primus linear accelerator, for 3 consecutive days. Patient was treated by a combination of fields: lateral – set at SSD of 330 cm and AP/PA – set at 135 cm. The dose-rate measured at 10 cm in a water phantom for lateral fields was 4,3 cGy/min., and for AP/PA fields 23,6 cGy/min. Lung shields were made from wood alloy and their shape was carried out from computerized tomograph scans (CT). For each patient a set of computerized tomograph scans was prepared. Patient during the CT was laying in supine position in the body frame made of 1 cm thick plexi plates. On the walls of that body frame a special marks of tin material were inserted. These marks allow to reproduce both – the same patient position during the irradiation and also in the treatment planning system HELAX. Position of shields before AP/PA fraction was determined by means of HELAX, and then shields were fastened to plexi trays inserted in the head of Primus. Lung was also shielded during one lateral fraction and the shape of the shield was carried out on a simulator. The volume between the patient and walls of the body frame was fulfilled by bolus (bags with rice) to get a homogenous dose distribution. The electron boost to the thorax wall (shielded for 15 MV photons) was delivered with a 6 or 9 MeV electron beam.The percentage deviation of dose, for all 9 irradiated patients, calculated at ten anatomical points representative of the body anatomy, was in the limit −0,4% to +13% (excluded in lung) from the dose delivered to PC (reference point: 1/2 AP and 1/2 lateral dimension at 1/2 of patient length in irradiation position). The in vivo measurements carried out by means of MOSFET detectors confirmed that accuracy

Thermal and epithermal neutrons in the vicinity of the Primus Siemens biomedical accelerator

In this paper, the thermal and epithermal neutron fluence distributions in the vicinity of the Primus Siemens accelerator are presented. The measurements were carried out by the use of the neutron activation method for 15 MV X-rays and electron beams of 18 MeV and 21 MeV. From the radiation safety point of view for the hospital personnel, it is important to know the thermal and epithermal neutron fluence distribution in the vicinity of the accelerator because the neutrons interacting with atoms of a medium by various processes induce the activity of objects (accelerator, other apparatus etc.) and walls in the treatment room. The thermal and epithermal neutron capture, particularly, in high atomic number materials of the accelerator head can be a significant source of gamma radiation and it has to be taken into account for estimation of the work safety of the personnel. Values of the neutron fluence were normalized to the maximum photon (or electron) dose Dmax,gamma (e) measured at the central axis of therapeutic X-ray (or electron) beam in a water phantom. The thermal neutron fluences measured during the 15 MV X-ray emission varied between 1.1 × 10 5 n ź cm 2ź Gy -1 and 4.4 × 10 5 n ź cm -2ź Gy 1 whereas the epithermal neutron fluences ranged from 0.2 × 10 5 n ź cm 2ź Gy- 1 to 1.8 × 105 n ź cm -2ź Gy -1. In the case of electron beams, the neutron fluence measurements were performed only at the isocentre. The obtained thermal and epithermal neutron fluences were 1.2 × 10 4 n ź cm -2ź Gy -1 and 0.6 × 10 4 n ź cm -2ź Gy -1, respectively, for the 18 MeV electrons. In the the case of the 21 MeV electron beams the thermal neutron fluence was -2.0 × 10 4 n ź cm -2ź Gy -1 whereas the epithermal neutron fluence was 0.8 × 10 4 n ź cm -2ź Gy-1