Radiation shield of therapeutic electron accelerator “CLINAC”
It is anticipated that a therapeutic electron accelerator “Clinac” (manufactured by Varian Co., USA) will be installed at NSC KIPT. It has been suggested that the available compartment having thick concrete walls might be used as a medical treatment room. In this connection, the analysis has been ma...
Gespeichert in:
| Datum: | 2017 |
|---|---|
| Hauptverfasser: | , , , , , |
| Format: | Artikel |
| Sprache: | English |
| Veröffentlicht: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2017
|
| Schriftenreihe: | Вопросы атомной науки и техники |
| Schlagworte: | |
| Online Zugang: | http://dspace.nbuv.gov.ua/handle/123456789/136196 |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Zitieren: | Radiation shield of therapeutic electron accelerator “CLINAC” / V.A. Voronko, A.N. Dovbnya, G.D. Pugachev, V.V. Sotnikov, V.L. Uvarov, V.S. Shestakova // Вопросы атомной науки и техники. — 2017. — № 6. — С. 181-184. — Бібліогр.: 5 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-136196 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-1361962018-06-17T03:06:54Z Radiation shield of therapeutic electron accelerator “CLINAC” Voronko, V.A. Dovbnya, A.N. Pugachev, G.D. Sotnikov, V.V. Uvarov, V.L. Shestakova, V.S. Применение ускорителей в радиационных технологиях It is anticipated that a therapeutic electron accelerator “Clinac” (manufactured by Varian Co., USA) will be installed at NSC KIPT. It has been suggested that the available compartment having thick concrete walls might be used as a medical treatment room. In this connection, the analysis has been made for correspondence of the com-partment protection characteristics to the accelerator safe operation requirements. The protection capability was estimated for a mode of the accelerator operation at electron energy of 18 MeV with a target made of tungsten. Equivalent dose rates behind the shield were calculated with due regard for the direct bremsstrahlung from the target, and also, for the scattered photon emission and neutron radiation. To reduce the scattered radiation level in the entrance area, the variant of shielding maze has been proposed. The estimated radiation dose of the accelerator staff does not exceed the values permissible by the radiation safety standards. According to the calculations made, the concentration of ozone produced in the treatment room will be also below the MPC level. У ННЦ ХФТІ передбачається встановити терапевтичний прискорювач електронів “Clinac” (фірма Varian, США). Як процедурний кабінет запропоновано використовувати наявне приміщення з товстими стінами із бетону. У зв'язку з цим проведено аналіз відповідності захисних характеристик приміщення вимогам безпечної експлуатації прискорювача. Оцінка захисту проводилася для режиму роботи прискорювача з енергією електронів 18 МеВ і мішенню із вольфраму. Розраховані значення потужності еквівалентної дози за захистом з урахуванням прямого гальмівного випромінювання від мішені, а також розсіяного фотонного випромінення і нейтронів. Для зниження рівня розсіяного випромінювання біля входу в приміщення запропонований варіант захисного лабіринту. Отримана оцінка дозового навантаження на обслуговуючий персонал прискорювача не перевищує значень, що допускаються нормами радіаційної безпеки. Проведений розрахунок напрацювання озону в процедурному кабінеті показав, що його концентрація також не перевищуватиме допустимий рівень. В ННЦ ХФТИ предполагается установить терапевтический ускоритель электронов “Clinac” (фирма Varian, США). В качестве процедурного кабинета предложено использовать имеющееся помещение с толстыми стенами из бетона. В связи с этим проведен анализ соответствия защитных характеристик помещения требованиям безопасной эксплуатации ускорителя. Оценка защиты проводилась для режима работы ускорителя с энергией электронов 18 МэВ и мишенью из вольфрама. Рассчитаны значения мощности эквивалентной дозы за защитой с учетом прямого тормозного излучения от мишени, а также рассеянного фотонного излучения и нейтронов. Для снижения уровня рассеянного излучения у входа в помещение предложен вариант защитного лабиринта. Полученная оценка дозовой нагрузки на обслуживающий персонал ускорителя не превышает значений, допускаемых нормами радиационной безопасности. Проведенный расчет наработки озона в процедурном кабинете показал, что его концентрация также не будет превышать допустимый уровень. 2017 Article Radiation shield of therapeutic electron accelerator “CLINAC” / V.A. Voronko, A.N. Dovbnya, G.D. Pugachev, V.V. Sotnikov, V.L. Uvarov, V.S. Shestakova // Вопросы атомной науки и техники. — 2017. — № 6. — С. 181-184. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS: 87.56.bd; 28.41.Qb http://dspace.nbuv.gov.ua/handle/123456789/136196 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Применение ускорителей в радиационных технологиях Применение ускорителей в радиационных технологиях |
| spellingShingle |
Применение ускорителей в радиационных технологиях Применение ускорителей в радиационных технологиях Voronko, V.A. Dovbnya, A.N. Pugachev, G.D. Sotnikov, V.V. Uvarov, V.L. Shestakova, V.S. Radiation shield of therapeutic electron accelerator “CLINAC” Вопросы атомной науки и техники |
| description |
It is anticipated that a therapeutic electron accelerator “Clinac” (manufactured by Varian Co., USA) will be installed at NSC KIPT. It has been suggested that the available compartment having thick concrete walls might be used as a medical treatment room. In this connection, the analysis has been made for correspondence of the com-partment protection characteristics to the accelerator safe operation requirements. The protection capability was estimated for a mode of the accelerator operation at electron energy of 18 MeV with a target made of tungsten. Equivalent dose rates behind the shield were calculated with due regard for the direct bremsstrahlung from the target, and also, for the scattered photon emission and neutron radiation. To reduce the scattered radiation level in the entrance area, the variant of shielding maze has been proposed. The estimated radiation dose of the accelerator staff does not exceed the values permissible by the radiation safety standards. According to the calculations made, the concentration of ozone produced in the treatment room will be also below the MPC level. |
| format |
Article |
| author |
Voronko, V.A. Dovbnya, A.N. Pugachev, G.D. Sotnikov, V.V. Uvarov, V.L. Shestakova, V.S. |
| author_facet |
Voronko, V.A. Dovbnya, A.N. Pugachev, G.D. Sotnikov, V.V. Uvarov, V.L. Shestakova, V.S. |
| author_sort |
Voronko, V.A. |
| title |
Radiation shield of therapeutic electron accelerator “CLINAC” |
| title_short |
Radiation shield of therapeutic electron accelerator “CLINAC” |
| title_full |
Radiation shield of therapeutic electron accelerator “CLINAC” |
| title_fullStr |
Radiation shield of therapeutic electron accelerator “CLINAC” |
| title_full_unstemmed |
Radiation shield of therapeutic electron accelerator “CLINAC” |
| title_sort |
radiation shield of therapeutic electron accelerator “clinac” |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2017 |
| topic_facet |
Применение ускорителей в радиационных технологиях |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/136196 |
| citation_txt |
Radiation shield of therapeutic electron accelerator “CLINAC” / V.A. Voronko, A.N. Dovbnya, G.D. Pugachev, V.V. Sotnikov, V.L. Uvarov, V.S. Shestakova // Вопросы атомной науки и техники. — 2017. — № 6. — С. 181-184. — Бібліогр.: 5 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
AT voronkova radiationshieldoftherapeuticelectronacceleratorclinac AT dovbnyaan radiationshieldoftherapeuticelectronacceleratorclinac AT pugachevgd radiationshieldoftherapeuticelectronacceleratorclinac AT sotnikovvv radiationshieldoftherapeuticelectronacceleratorclinac AT uvarovvl radiationshieldoftherapeuticelectronacceleratorclinac AT shestakovavs radiationshieldoftherapeuticelectronacceleratorclinac |
| first_indexed |
2025-07-10T00:50:20Z |
| last_indexed |
2025-07-10T00:50:20Z |
| _version_ |
1837219051677417472 |
| fulltext |
ISSN 1562-6016. ВАНТ. 2017. №6(112) 181
RADIATION SHIELD
OF THERAPEUTIC ELECTRON ACCELERATOR “CLINAC”
V.A. Voronko, A.N. Dovbnya, G.D. Pugachev, V.V. Sotnikov, V.L. Uvarov, V.S. Shestakova
National Science Center "Kharkov Institute of Physics and Technology", Kharkov, Ukraine
E-mail: uvarov@kipt.kharkov.ua
It is anticipated that a therapeutic electron accelerator “Clinac” (manufactured by Varian Co., USA) will be in-
stalled at NSC KIPT. It has been suggested that the available compartment having thick concrete walls might be
used as a medical treatment room. In this connection, the analysis has been made for correspondence of the com-
partment protection characteristics to the accelerator safe operation requirements. The protection capability was es-
timated for a mode of the accelerator operation at electron energy of 18 MeV with a target made of tungsten. Equiv-
alent dose rates behind the shield were calculated with due regard for the direct bremsstrahlung from the target, and
also, for the scattered photon emission and neutron radiation. To reduce the scattered radiation level in the entrance
area, the variant of shielding maze has been proposed. The estimated radiation dose of the accelerator staff does not
exceed the values permissible by the radiation safety standards. According to the calculations made, the concentra-
tion of ozone produced in the treatment room will be also below the MPC level.
PACS: 87.56.bd; 28.41.Qb
INTRODUCTION
The National Science Center “Kharkiv Institute of
Physics and Technology (NSC KIPT) is going to install
an electron accelerator manufactured by Varian Co.
(model Clinac 2300 C/D). On delivery, the Company
provides only tabular standard protection data for the
treatment room, which are intended for the use at the
early stages of the therapeutic complex design. There-
fore it was necessary to confirm its compliance with the
regulatory requirements of a country where the accel-
erator is to be installed. In this connection, an analysis
was performed to assess both the radiation protection of
the intended accelerator chamber, as well as the ozone
production during accelerator operation. The analysis
was carried out with regard to the “Radiation safety
rules for electron accelerators under No. 1442/23971 d/d
21 August, 2013”, to the recommendations on radiation
shield calculations for electron accelerators, and also,
other regulatory documents.
Fig. 1 shows the schematic of the intended Clinac
working chamber at the level -4.800 is 6.9 m wide, 9 m
long, the floor-ceiling height being 3.4 m. The side
shielding of the facility will be provided by the existing
2 m thick concrete walls, and by the earth. At the top,
the chamber is shielding by 1.2 m thick concrete con-
structions.
The installation control is assumed to be arranged in
the adjacent premise at the level -4.800 separated from
the accelerator chamber by the maze shielding against
scattered radiation. The auxiliary operational areas are
supposed to be located in the adjacent premises.
1. BREMSSTRAHLUNG SHIELDING
CALCULATIONS
The analysis has been performed for the radiation
shielding of the Clinac accelerator and its production of
ozone at an electron energy of 18 MeV and a working
load of 2000 Sv/week. For calculations, we have chosen
the points A1 – A8 at mark -4.800, which are at service
personnel location sites expected to have the highest
radiation level (see Fig. 1), and also outside the building
in the fill-up ground.
Longitudinal section of the accelerator working chamber, passing through the isocenter:
1 – accelerator CLINAC; 2 – therapeutic couch; 3 – modulator casing; 4 – stand and gantry; 5 – concrete shield;
6 – shielding maze; O’ – isocenter
mailto:uvarov@kipt.kharkov.ua
ISSN 1562-6016. ВАНТ. 2017. №6(112) 182
Referring to Figure, we use the following notation:
O and O
1
are the radiation source (accelerator head) and
the isocenter, respectively; A1 – is the point at the angle
of radiation θ = 0 outside the maze shield; A2 – is the
point at the maze entrance, θ = 34°; A3 – is the point
behind the side shield of the vault; A4 – is the point out-
side the building in the ground; A5 – is the point at mark
– 3.800 in an adjacent hall; A6 – is the point outside the
maze’s entry; A7 – is the point at θ = 20° in the hall,
before the maze’s entrance; A8 – is the point on the
ground floor, above the isocenter (at mark 1.000). The
Clinac radiation characteristics used in the calculations
are as follows.
- Maximum energy of accelerated electrons for the
modes of exposure to electrons and bremsstrah-
lung 18 MeV;
- bremsstrahlung dose rate at the isocenter 720 Gy/h;
- bremsstrahlung dose rate external to the isocenter
0.72 Gy/h;
- neutron -to-bremsstrahlung dose ratio at the isocen-
ter < 0.2%;
- shield materials concrete, lead;
- beam size and possible beam directions are provid-
ed by Varian Co. on delivery of Clinac with a set
of electronic applicators enabling the formation of
six different fields measuring 66 cm,
1010 cm, 1515 cm, 2020 cm, 2525 cm;
- feasible directions of the accelerator head: straight
down – θ= 0°, and sideways – θ = 90°;
- radiation source- to- isocenter distance 1.05 m;
- accelerator operational mode (workload per week,
equal to the product of the mean dose received by
a single patient for the time of exposure by the
number of patients) 2000 Sv/week.
The given below equivalent dose H
rates at the
points of interest correspond to the mode of facility op-
eration with a tungsten target and a tantalum smoothing
filter. Under these conditions, the bremsstrahlung is the
dominant factor of radiation hazard, which governs the
accelerator shield thickness. Noteworthy also is the pro-
duction of harmful chemical substances (ozone and ni-
trogen oxides) in the air.
For a soft biological tissue, the relation between the
absorbed and equivalent doses of bremsstrahlung is de-
termined by the formula H(Sv)= 1.09 D(Gy). For sim-
plicity, in our calculations, H was assumed to equal D.
For a soft biological tissue, the relation between the
absorbed and equivalent doses of bremsstrahlung is de-
termined by the formula H(Sv)= 1.09 D(Gy). For sim-
plicity, in our calculations, H was assumed to equal D.
At the NSC KIPT, the design value of the standard
reference dose rate RDRA with the safety factor 2 at the
workplaces of category “A” staff amounts to 4.1 μSv/h.
The maximum workload W for the procedures without
the smoothing filter (Field Flow Fractionation, FFF) has
been determined by the Clinac supplier to be
2000 Sv/week at a 50-hour work week. The permissible
bremsstrahlung dose rate P at a distance R is given by
the expression
6 2
2
1.0 10 ( )
( )
Wr b
P
T R
, (1)
where W is the workload (Sv/week), r is the radiation
source-to-isocenter distance (m); Tx is the operational
period of all the category “A” personnel shifts per week;
b(θ) is the radiation yield factor in the (θ )-direction. In
accordance to the data of refs. [2], [5], we put the solid
angle value in the range from 0° to 14° to be b()=1;
and in the angular ranges from 14° to 20°
and from 20°
to 40° we put b()=0.26 and b()=0.1, respectively. For
solid angles greater than 40°, b(θ) is taken to be 0.01.
The angular coordinates and the distances to the
points of interest with respect to the point O, at which
the electron accelerator target is located, are given in
Table 1.
Table 1
Distances to the points of interest, angular coordinates
and yield factors
Points А1 А2 А3 А4 А5 А6 А7 А8
R (m) 8 10 6 8 8 10 8.5 3.5
0
0
0
34 90 0 90 40 20 180
b() 1 0.1 0.01 1 0.01 0.1 0.2
6
0.01
Table 2 gives the calculated values for the equiva-
lent dose rates (EDR) at unshielded control points, the
necessary dose attenuation K(X), the concrete shield
thickness Xcalc., and also the thickness of the existing
shield Xactual. Here and below, we use the attenuation of
the bremsstrahlung dose rate for the concrete shield of
density 2.3 g/cm
3
.
Table 2
EDR at points of interest (μSv/h), the necessary attenuation К(х), shield thickness (required and existing)
Points А1 А2 А3 А4 А5 А6 А7 А8
H , μSv/h 6.910
5
4.410
4
1.210
4
6.910
5
6.910
3
4.410
3
1.610
5
3.610
4
К(Х) 1.710
5
1.110
4
310
3
1.710
5
1.710
3
1.110
3
410
4
8.810
3
Хcalcul., cm 240 190 160 240 152 145 207 185
Хactual, cm 300 270 200 300 200 200 250 120
The obtained shield thickness data for primary
screening at points A1 and A4, X=240 cm, are in good
agreement with the data of Table 2-1 for typical shield
of the Clinac accelerator under standard procedures
(X= 236.2 cm) at the concrete density ρ=2.355 g/cm
3
.
It is evident from Table 2 that the existing shield
thickness at the at mark -4.800 is sufficient for the pri-
mary and secondary screening of the personnel against
the accelerator radiation. Point A8 is found in the attic-
floor room, where the coefficient of occasional presence
of the personnel is equal to T=0.06, and the existing
shield will suffice for the protection.
ISSN 1562-6016. ВАНТ. 2017. №6(112) 183
2. CONSIDERATION OF THE SCATTERED
RADIATION
To calculate the scattered radiation contribution to
the EDR at the entry to the treatment room (working
chamber of the accelerator), the principal reflecting sur-
face S1 was chosen in accordance with the recommenda-
tions given in ref. [3]. In the calculations, the brems-
strahlung was assumed to be produced at the point O
resulting from interaction of electron beam with the
tungsten target, the primary collimator, the smoothing
filter, the secondary collimator, and thereupon incidents
on the scattering surface S1.
The EDR of the scattered radiation at point B1, scat-
tered by the surface S1, is determined according to ref.
[3] by the formula
1 2
6 2
1 1, 0 1 1
2
1
( )1.0 10 ( )
b
E S CosWr b
H
RT R
, (2)
where 1(1,E0) is the differential dose albedo for the
bremsstrahlung with end-point energy E0, incident on
the scattering surface S1 at an angle 1 relative to the
normal to this surface. rad. is the radiation angle, R is
the distance from the radiation source to the scattering
surface S1 (m) in the maze of the treatment room, R1 is
the distance from the surface S1 to the maze entry (point
В1). Using the parameters of the accelerator and the
geometrical dimensions of the accelerator chamber, we
obtain the initial data for calculating the EDR of the
scattered radiation: R=7.2 m; R1=11.2 m; rad.=30;
1=60
°
; (,Е)=310
-3
; S1=2.1 m
2
; b()=0.01; r=1.05.
Based on these data and formula (2), one can estimate
the scattered radiation contribution to the EDR at point
B (Нв = 0.21 μSv/h). With account of the direct radia-
tion contribution from point O at point B (Нв =
0.34 μSv/h), the total dose rate at point B1 is estimated
to be НΣ=0.55 μSv/h. Thus, the steel layer 6 mm thick
will be sufficient for screening the door of the Clinac
treatment room.
3. NEUTRON SHIELDING CALCULATION
In a working shift time, at an operating load of
2000 Sv/week and a 50-hour workweek, the mean EDR
value of photoneutrons produced during accelerator
operation, at a distance of 2 m from the target at the
isocenter, will amount to
6 2
71.0 10
4,41 10n
n
W r c
H c
T
, (3)
where c is the ratio of the neutron EDR at the isocenter
to the bremsstrahlung dose rate (c=0.2%); α is the neu-
tron flux density-to-EDR conversion factor
(α=1.7 μSv·cm
2
·s/h).
So, the neutron flux density at the distance R=1 m
(at the isocenter) will be Hn=5.2·10
4
n/cm
2
·s.
The attenuation of photoneutron EDR in the con-
crete shielding can be estimated using the relation
Кн=ехр(d/λ), (4)
where d is the concrete shielding thickness (cm); λ is the
photoneutron relaxation length in the concrete (equal to
16 cm).
Table 3 lists the values of neutron flux density at the
calculation points without radiation shielding Nn, the
neutron-induced dose rate H
, and also, the necessary
dose rate attenuation Kn.
The data on the existing practical shield thickness
Xactual, the required neutron shield thickness Dmarg., and
the margin of neutron EDR attenuation Kmarg. are given
in Table 4.
Table 3
Neutron flux density (n/cm
2
s·), neutron-induced dose rateH
(μSv/h) and the necessary neutron dose rate attenuation Kn
Points А1 А2 А3 А4 А5 А6 А7 А8
R(m) 8 10 6 8 8 10 8.5 3.5
Nn 8.1·10
2
5.2·10
2
1.44·10
3
8.1·10
2
8.1·10
2
5.2·10
2
7.2·10
2
4.2·10
3
H n
1.38·10
3
8.84·10
2
2,45·10
3
1.38·10
3
1.38·10
3
8.84·10
2
1.22·10
3
7.14·10
3
Kn 3.37·10
2
2.16·10
2
6·10
2
3.37·10
2
3.37·10
2
2.16·10
2
3·10
2
1.74·10
2
Table 4
Neutron shielding characteristics
Points А1 А2 А3 А4 А5 А6 А7 А8
d(Х)actual(cm) 300 270 200 300 200 200 250 120
Dconcrete(cm) 94 86 103 94 94 86 92 120
Кmargin 3.9·10
5
6.4·10
5
4.3·10
2
3.9·10
5
7.5·10
2
1.2·10
3
1.9·10
4
1
It is evident from the table that neutrons make prac-
tically no contribution to the EDR behind the shield, and
their impact may be neglected.
4. CALCULATION OF OZONE CONCENT-
RATION AND FORBIDDEN PERIOD
Considering that at operation of an accelerator with
energy up to 30 MeV the toxicity of air radiolysis prod-
ucts (ozone and nitrogen oxides) is mainly determined
by ozone (ozone MPC is by a factor of 50 lower than
the MPC of nitrogen oxides), the ventilation calculation
is based on the provision of the desired ozone concen-
tration reduction. In the “Radiation safety regulations
for electron accelerators”, there are no instructions for
calculating the ozone production by medical accelera-
tors. There is a belief that when interacting with air, the
bremsstrahlung of the accelerator produces far less radi-
olysis products than the electron beam does. It is as-
sumed also that with the operating exhaust ventilation,
the reduction in ozone concentration down to the per-
missible value occurs practically for a few seconds after
the accelerator is turned off; and in this case, the forbid-
den period concept loses its practical meaning for the
operating staff. For all that the patient stays all the time
ISSN 1562-6016. ВАНТ. 2017. №6(112) 184
in the accelerator chamber (treatment room) with the
accelerator being in operation. In view of this, the anal-
ysis has been performed to estimate the ozone produc-
tion in the accelerator working chamber with the use of
the data of practice guidelines [2, 3] and the available
literary sources. In accordance with Supplement 2 to the
“Radiation safety regulations for electron accelerators”
(i. 2.16), the forbidden period of staff entrance to the
working chamber is determined by the formula
ln / ( ) ,oz
FORB chamb chem
oz
C
T K
MPC
(5)
where Coz is the ozone concentration in the working
chamber at the instant of radiation exposure, mg/m
3
;
MPCoz is the maximum permissible ozone concentra-
tion, 0.1 mg/mm
3
; Кchamb. is the air change per hour in
the accelerator working chamber, hour
-1
; λchem. is the
coefficient characterizing the chemical instability of
ozone, hour
-1
, (chem=1.2 h
-1
)
For determining the ozone concentration in the
working chamber with the point radiator at its center,
the chamber was assumed to be spherical with radius R.
The ozone concentration was calculated by the formula
22.4 10
1 exp ( ) ,oz chamb
chamb
Ð
C K t
K
(6)
where P is the average absorbed dose rate in air, Gy/s;
Кchamb. is the air change in the irradiated volume, h
-1
; t is
the time of air irradiation, h; =rad+chem. characterizes
the radiation and chemical instabilities of ozone, h
-1
.
rad is calculated by the formula
rad=34P 0,6
, h
-
. (7)
The average absorbed dose rate in air for the cham-
ber with the point radiator was determined through nu-
merical integration of expression (1) over 4π. The angu-
lar distribution data are given in Section 1.
On exposure of a patient to radiation having the
EDR equal to 12.1 Gy/min. (0.2 Gy/s) in the angular
range from 0 to 14°, the maximum average EDR value
in the treatment room of 211 m
3
in volume will make
0.0065P Gy/s; and λ=1.66 h
-1
; Coz=0.042 mg/m3.
Thus, even in the mode of operation without the
smoothing filter at the patient dose of 20 Gy per run, the
ozone concentration will not exceed the MPC value.
Therefore, the forbidden period of entrance to the work-
ing chamber after the accelerator is turned off, loses its
meaning. During the whole session of patient exposure,
the ozone concentration in the chamber also will not
exceed the MPC value.
CONCLUSIONS
The necessary design values for concrete shield
thickness have been tabulated to provide safe operation
of the installation with electron energy of up to 18 MeV.
It follows from the present data that the existing radia-
tion shield is sufficient to prevent the excess of the tol-
erable dose rate (TDRA). For the treatment room protec-
tion, a 6 mm thick steel door must be installed in the
shielding maze. During the irradiation session, the
ozone concentration in the treatment room will not ex-
ceed the MPC value. Therefore, there is no need for
setting a forbidden period for the staff to enter the
treatment room.
REFERENCES
1. Radiation safety standards in Ukraine (NRBU-97),
Kiev, 1997; “Main sanitary regulations for radiation
safety of Ukraine”, National sanitary rules 6.177-
2005-09-02. Kiev, 2005.
2. Radiation safety regulations for electron accelerators
under No. 1442/23974, d/d 21 August, 2013.
3. Uniform rules for design and safe service of radia-
tion-process installations. (Unified rules for gamma-
electron). Moscow, 1988.
4. Health Physics. Two-volume book / Edited by
N.G. Gusev. 3
rd
edition, revised and enlarged. Mos-
cow: “Ehnergoatomizdat”, 1989.
5. K. Nurlybaev, Yu.N. Martynyuk, A.I. Karakash, et
al. Radiation safety in beam therapy using electron
accelerators // ANRI. 2014, № 1, p. 15.
Article received 09.10.2017
РАДИАЦИОННАЯ ЗАЩИТА ТЕРАПЕВТИЧЕСКОГО УСКОРИТЕЛЯ ЭЛЕКТРОНОВ “CLINAC”
В.А. Воронко, А.Н. Довбня, Г.Д. Пугачeв, В.В. Сотников, В.Л. Уваров, В.С. Шестакова
В ННЦ ХФТИ предполагается установить терапевтический ускоритель электронов “Clinac” (фирма Varian, США). В
качестве процедурного кабинета предложено использовать имеющееся помещение с толстыми стенами из бетона. В
связи с этим проведен анализ соответствия защитных характеристик помещения требованиям безопасной эксплуатации
ускорителя. Оценка защиты проводилась для режима работы ускорителя с энергией электронов 18 МэВ и мишенью из
вольфрама. Рассчитаны значения мощности эквивалентной дозы за защитой с учетом прямого тормозного излучения от
мишени, а также рассеянного фотонного излучения и нейтронов. Для снижения уровня рассеянного излучения у входа в
помещение предложен вариант защитного лабиринта. Полученная оценка дозовой нагрузки на обслуживающий персо-
нал ускорителя не превышает значений, допускаемых нормами радиационной безопасности. Проведенный расчет нара-
ботки озона в процедурном кабинете показал, что его концентрация также не будет превышать допустимый уровень.
РАДІАЦІЙНИЙ ЗАХИСТ ТЕРАПЕВТИЧНОГО ПРИСКОРЮВАЧА ЕЛЕКТРОНІВ “CLINAC”
В.О. Воронко, А.М. Довбня, Г.Д. Пугачов, В.В. Сотников, В.Л. Уваров, В.С. Шестакова
У ННЦ ХФТІ передбачається встановити терапевтичний прискорювач електронів “Clinac” (фірма Varian, США). Як
процедурний кабінет запропоновано використовувати наявне приміщення з товстими стінами із бетону. У зв'язку з цим
проведено аналіз відповідності захисних характеристик приміщення вимогам безпечної експлуатації прискорювача.
Оцінка захисту проводилася для режиму роботи прискорювача з енергією електронів 18 МеВ і мішенню із вольфраму.
Розраховані значення потужності еквівалентної дози за захистом з урахуванням прямого гальмівного випромінювання
від мішені, а також розсіяного фотонного випромінення і нейтронів. Для зниження рівня розсіяного випромінювання
біля входу в приміщення запропонований варіант захисного лабіринту. Отримана оцінка дозового навантаження на об-
слуговуючий персонал прискорювача не перевищує значень, що допускаються нормами радіаційної безпеки. Проведе-
ний розрахунок напрацювання озону в процедурному кабінеті показав, що його концентрація також не перевищуватиме
допустимий рівень.
|