Marcin Dybek

Correlation between radioactivity induced inside the treatment room and the undesirable thermal/ resonance neutron radiation produced by linac

High-energy therapeutic beams used in the radiotherapy induce photonuclear and electronuclear reactions which are accompanied by generation of undesirable radioisotopes and neutrons inside the treatment room. These neutrons at thermal and resonance energies induce nuclear reactions through the whole accelerator bunker. In consequence various radioisotopes emitting high-energy photons appear. In this paper the correlation between radioactivity induced inside the treatment room and the undesirable thermal and resonance neutron radiation generated by the therapeutic accelerator X-rays was studied. The thermal and resonance neutron fluence determined in chosen places inside the bunkers was 1.0x10(5)-3.4x10(5)cm(-2)Gy(-1) and 1.0x10(5)-1.6x10(6)cm(-2)Gy(-1) at thermal energies (<0.1eV) and 3.9x10(4)-1.3x10(5)cm(-2)Gy(-1) and 1.0x10(5)-1.1x10(6)cm(-2)Gy(-1) at epithermal energies (0.1eV-10keV), for the 15MV and 20MV beams, respectively. The gamma energy spectra measured inside the accelerator bunker depended on the neutron radiation level. The net count rates of the gamma peaks from the decays of the excited state (56)Fe* and (28)Si*, the result of the simple capture of the neutron, for the 20MV beam were almost one order of magnitude greater than those for the 15MV beam. Moreover, it turned out that the activation of the wedge - the main accelerator accessory was caused by neutrons.

Linear accelerator therapeutic dose-induced radioactivity dependence.

Dependence between therapeutic dose and activity induced in mammal bones is discussed. This activity leads to gamma ray emission registered by HPGe detector and scintilation probe. Presented results are focused on activation which occurs during emission of 15 and 20 MV photon beams. The purpose is to describe how therapeutic conditions (dose, time of irradiation) influence the induced radioactivity. Preliminary studies of decay rate, calculation of half-life and identification of isotopes involved in this dynamic process are given.

The technique of total body irradiation applied at the leszczyński memorial hospital

Abstract Purpose To improve the reproducibility of patient positioning in fractionated irradiation and to achieve uniform irradiation of the patient, within 12–15Gy, excluding the lungs. Method Two special body frames were manufactured, one for treatment planning and the other for the treatment itself. Special tin markers were inserted in the walls to make it possible for a patient to maintain the same position during each fraction of irradiation. Patient treatment was carried out in six fractions (four lateral and two AP/PA fields), twice a day, over three consecutive days. The lungs were shielded during AP/PA fractions and during one lateral fraction. The shape of the shields for AP/PA fields was determined with the use of computer tomography scans, and for lateral fields on the basis of radiographic pictures taken by a simulator. The doses calculated at some selected anatomical points for every patient were checked by in vivo measurements which were carried out by means of MOSFET detectors. Results and conclusions Reproducibility of patient positioning during consecutive treatments and a uniform total dose distribution over the range of 12 – 15 Gy (except in the lungs) have been achieved. This has been confirmed by in vivo measurements.

MOSFET detectors as a tool for the verification of therapeutic doses of electron beams in radiotherapy

Summary Aim To examine the characteristics of MOSFET (Metal – Oxide Semiconductor Field Effect Transistor) detectors for the purpose of electron beam dose determination in in vivo radiotherapy. Materials/Methods Indications of MOSFET detectors were recorded from phantom measurements, including: dose values of electron beams, the environmental temperature of the detectors, the incidence direction of an electron beam on the detector, the size of the irradiated field. The change in sensitivity of the detectors when under the effects of accumulated doses was also tested. Because of the very small dimensions of the detectors, they were placed in specially designed aluminium capsules – to ensure electron equilibrium (δ electrons) during the dose measurement. The detector indications were compared to those seen in a Markus type ionization chamber with a calibration certificate. The measurements were made for electron beams with energies of 6, 9, 12, 15, 18 and 21 MeV. Results The following were established experimentally: There is a linear relationship between detector indications and the dose value. A drop in detector sensitivity is associated with increased environmental temperature (as much as 6% as temperatures rise from 22°C to 42°C). There is a non-linear drop in detector sensitivity with accumulated dose. Detector indications are not affected by changes in incident beam angles within the range of –70° to +70°. The dependency of detector indications on the size of the irradiated field conform with those recorded in the ionization chamber, with variations of up to 1.5%. The dependencies and correction coefficients determined in this study allow measurement of electron beam doses with an accuracy of 2.2%. Conclusions MOSFET detectors are a useful tool for verification of the entrance doses in electron beam radiotherapy.

Detektory MOSFET jako narzędzie do weryfikowania dawek promieniowania X w radioterapii

Streszczenie Cel Zastosowanie detektorow typu MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) do pomiaru dawki in vivo w radioterapii. Metody i materialy Wykonano pomiary polegające na zbadaniu zalezności wskazan detektorow MOSFET od podanej dawki promieniowania, temperatury ich otoczenia, kierunku padania wiązki promieniowania na detektor oraz od wielkości napromienianego pola – dla wiązek fotonow 6MV i 16 MV. Pomiary zalezności wskazan detektorow zostaly wykonane w fantomie oraz w powietrzu, w warunkach rownowagi elektronowej. W tym celu, ze wzgledu na bardzo male wymiary detektorow, zaprojektowano nakladki z aluminium, ktore zapewnialy warunki rownowagi elektronowej podczas pomiaru dawki. Detektory zostaly wykalibrowane z pomocą komory jonizacyjnej typu Farmer 0,6 cm 3 . Wyniki Wyniki badan wymienionych wyzej zalezności przedstawiono na wykresach. Wykonane, wykalibrowanymi detektorami, pomiary in vivo dawki wejściowej (na glebokości maksymalnej dawki) wykazaly zgodnośc miedzy zaplanowaną i zmierzoną dawką – w granicach tolerancji ±5% – u 86% pacjentow poddanych radioterapii z uzyciem wiązki fotonow 6MV i u 91% pacjentow z uzyciem wiązki fotonow 15MV (SD=3.5%). Wniosek Detektory MOSFET stanowią dobre narzedzie pomiarowe w radioterapii do weryfikowania zaplanowanej dawki promieniowania X wytwarzanego w liniowych przyspieszaczach.

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

At the St. Leszczynski 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.

Assessment of radiation exposure outside the radiotherapeutic room during medical accelerator beam emission with the use of TL detectors (radiation exposure outside a LINAC room).

Photon and neutron soft tissue absorbed doses near the entrance door to the medical LINAC treatment room were measured with the use of thermoluminescent detectors LiF:Mg,Cu,P in the anthropomorphic phantom. Two different therapeutic beams (6 and 15 MV) and four treatment techniques were involved in the present study. This allowed one to investigate the contribution of scattered X rays, secondary neutrons and gamma rays to the radiation field. Photon absorbed dose rates 50 cm away from the LINAC room door during emission of 15-MV X rays varied between 4.1×10(-4) and 5.6×10(-4) Gy h(-1), depending on the gantry position and the irradiation field size, whereas in the case of 6-MV therapeutic irradiation these doses are ∼1.5 times lower. In the case of 15-MV beam emission, a mixed radiation field near the bunker door is observed with the photon radiation as the main component, which includes a 33.1 % contribution of the induced gamma radioactivity and ∼2.1 % contribution of the neutron radiation.

Kontrola Systemów Planowania Leczenia 3D W Radioterapii Wiązkami Zewnętrznymi Fotonów I Elektronów

Zalecenia pt. „Kontrola systemów planowania leczenia 3D stosowanych w radioterapii wiązkami zewnętrznymi dla wiązek fotonów i elektronów” powstały dzięki wysiłkowi wielu osób. Szczególnie dużo pracy włożyli wymienieni z imienia i nazwiska autorzy tego dokumentu. Ze względu na to, że dość trudno określić precyzyjnie wkład poszczególnych osób, autorzy zostali wymienieni w kolejności alfabetycznej z jednym wyjątkiem. Na drugim miejscu został wymieniony Janusz Winiecki, którego wkład w ostateczny kształt zaleceń jest ogromny. Ostateczna wersja dokumentu została przedyskutowana na V Spotkaniu Kierowników Zakładów Fizyki Medycznej. Bardzo dziękuję wszystkim za zaangażowanie. Dokument został uzupełniony o Dodatek przygotowany merytorycznie i napisany przez fizyków medycznych z Opola. Bardzo dziękuję za ich cenną propozycję. Słowo „zalecenia” należy traktować tak, jak jest ono rozumiane w podobnych dokumentach przygotowywanych przez inne towarzystwa fizyki medycznej, np. American Association of Phyicists In Medicine. Niniejszy dokument określa minimalny zakres testów, jaki zdaniem Polskiego Towarzystwa Fizyki Medycznej, powinien zostać wykonany przed oddaniem do użytku systemu planowania leczenia (SPL). Sformułowanie „oddanie do użytku SPL” należy rozumieć szeroko, o czym mówi ten dokument we wstępie. Chcemy podkreślić, że zalecenia nie stanowią prawa. Testowanie oprogramowania jest procesem niezwykle złożonym i bardzo żmudnym. Przeprowadzenie nawet bardzo szerokich testów nie pozwala na wykrycie wszystkich mankamentów konkretnego systemu. Dlatego warto podkreślić, że wykonanie wszystkich testów i uzyskanie pozytywnych wyników nie zwalnia użytkownika z czujności w trakcie użytkowania SPL. Mam nadzieję, że niniejszy dokument ułatwi wykonywanie testów systemów planowania leczenia. Jakkolwiek autorzy starali się uniknąć błędów redakcyjnych, tym niemniej pomimo włożonej ogromnej pracy nie wszystkie usterki zostały zapewne usunięte. Wszelkiego rodzaju uwagi do dokumentu proszę kierować do mnie na adres p.kukolowicz@zfm.coi.pl.

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

Cel Zastosowanie detektorow MOSFET (Metal – Oxide Semiconductor Field Effect Transistor) do pomiaru dawki in vivo wiązek elektronow w radioterapii. Metody i materialy Wykonano pomiary fantomowe polegające na zbadaniu zalezności wskazan detektorow MOSFET od: – wartości dawki wiązek elektronow, – temperatury otoczenia detektorow, – kierunku padania wiązki elektronow na detektor, – wielkości napromienianego pola. Zbadano takze zmiane czulości detektorow w zalezności od skumulowanej dawki. Detektory, ze wzgledu na bardzo male wymiary, umieszczano w odpowiednio zaprojektowanych nakladkach aluminiowych – w celu zapewnienia rownowagi elektronowej podczas pomiaru dawki. Wskazania detektorow porownywano do wskazankomory jonizacyjnej typu Markus, posiadającej świadectwowzorcowania. Pomiary wykonano z uzyciem wiązek elektronow o energii 6, 9, 12, 15, 18,21 MeV. Wyniki Zbadane zalezności i określone na ich podstawie wspolczynniki korekcyjne umozliwiają zmierzyc dawke wiązki elektronow z dokladnością ±2.5%. Wniosek Detektory MOSFET są dobrym narzedziemdo weryfikowania dawki wejściowej w radioterapii wiązkami elektronow.

82. Mosfet detectors as a tool to verify the doses in photon beam radiotherapy

Purpose We report on the accuracy of metal oxide – silicon semiconductor field effect transistor (MOSFET) detectors to measure the entrance dose during the patient treatment using the photon beam. Such measurements make possible to examine the conformity between the planned and given dose to a treated patient – which is one of the main procedures in quality assurance of external radiotherapy. Methods and materials Phantom measurements were carried out to investigate the MOSFET detectors accuracy for measuring the entrance dose of 6 MV and 15 MV photon beams. Before that the following parameters had been examined: the linear variation of the dosimeters response to the dose absorption, the variation in detector response with temperature, gantry angles and field sides changes. Calibration of the detectors was performed under full build up, with the 6 MV and 15 MV photon beams and a cylindrical ionization chamber (type 0.6 cm 3 Farmer). The entrance dose calculated by means of the HELAX planning system was verified using the calibrated MOSFET detectors. 605 patients were put to the test of the conformity of the planned and the measured entrance dosa, According to our procedure the deviation of the measured entrance dose and the dose calculated by Helax system could not exceeds ±5% – otherwise the measurement has to be revised and eventually another simulation should be done. Results The conformity of the planned and measured dose within ±5% was observed at 86% treated by the 6 MV and at 91% patients treated by 15 MV photon beams. The deviation at remaining 12% and 8% of patients treated respectively by 6 MV and 15 MV photon beams ranged from 6% to 8%. In these cases the detectors were improper by located. At about 1.5% of patients the simulation had to be repeated. The percetage standart deviation was 1.6 and −1.7 respectively by 6 MV and 15 MV. Conclusion The MOSFET detectors are an useful tool for verifying the planned dose in external radiotherapy.