GBZ/T 201.1-2007Radiation shielding requirements in room of radiotherapy installations - Part 1: General principle (English PDF)

2.1 controlled areas out of radiotherapy room

radiation staff working area directly connected with the radiotherapy room and

related to the treatment device in the room, such as treatment device control

room, treatment device auxiliary room, etc.

2.2 uncontrolled areas out of radiotherapy room

outside the radiotherapy room, other area except the controlled area out of

radiotherapy room, including radiation oncologist clinic, waiting room, etc.

2.3 T occupancy factor

within the start time of radiation source, the share of the average time spent

on the maximum exposure of the radiated person occupying the start time

within the area

2.4 U use factor

the share of the time at which the primary radiation beam (useful beam) is

irradiated in a direction of beam shielding occupying the total exposure time

<= 2.5 µSv/h (staff total occupancy place, T >1/2)

<= 10 µSv/h (staff partial and occasional occupancy place, T<=1/2)

3.2 Radiation dose rate reference control level of therapy room roof

shield

3.2.1 At the built, to-be-built two-storey building above therapy room or

when the height of neighboring building near therapy room exceeds the area

from radiation source point to the solid angle area of surface edge inside the

room roof, at the place 30 cm from therapy room roof external surface or at

the staff stay location in the high-rise building within this solid angle area, the

radiation dose rate reference control level shall be the same with 3.1.

3.2.2 In addition to 3.2.1 conditions, it shall consider the radiations of

skyshine radiation and side-scattered radiation to the public near the ground

and in the building outside the therapy room, as well as the illumination of the

radiation getting through the therapy room roof to the staff who occasionally

reach the top. Use equation (1) and take Hc=5 µSv/week, T=1/40. Use the

ambient dose equivalent rate determined at the place 30 cm from the therapy

room external surface as the radiation dose rate reference control level of

therapy room roof shielding.

3.3 Procedures for determination of ambient dose equivalent rate

reference control level

3.3.1 Ambient dose equivalent rate reference control level of therapy room

wall and at the place 30 cm from entrance door external surface

(1) select the assessment points and identify the partitions where the

assessment points are located (controlled areas out of radiotherapy

room and uncontrolled areas out of radiotherapy room);

(2) according to the radiotherapy workload given by the radiotherapy

organization, determine the week workload (W) of radiotherapy device

used, and refer to the method in Annex B to estimate the maximum

illumination time (h) of therapy device;

(3) estimate ; compare it with the dose rates in 3.1 and 3.1.2 and take

the smaller one as the ambient dose equivalent rate reference control

level.

3.3.2 Ambient dose equivalent rate reference control level of lager

occupancy factor (T >1/4) of neighboring therapy room

4.3.6 Secondary shielding radiation might contain the compound effect of

leakage radiation and scattered radiation. Usually, it shall respectively

estimate the leakage radiation and each scattered radiation. When the

difference between their shielding thicknesses is one layer (TVL) or more, it

shall use a thicker shielding. When the difference is less than one TVL, it shall

add half a layer (HVL) of thickness on the thicker shielding.

4.4 Considerations of therapy room shielding

4.4.1 In a choice of therapy conditions for radiotherapy device, it shall take

radiant matter of which the penetrating ability is relatively strong and

commonly used highest therapeutic output as radiation source parameters. It

shall also consider all the primary and secondary radiation factors of each

shielding locations.

4.4.2 Radiation dose rate reference control level of therapy room shielding

4.4.3 Week maximum workload and week therapy illumination time of

therapy device application

4.4.4 Use factor (U) of possible useful beam illumination direction during the

use of wide beam therapy device

4.4.5 See Annex A for personal area occupancy factor (T) in different places

at the peripherals of therapy room. The staff at the peripherals of therapy

room and at the neighboring places of therapy device are major consideration

objects. When some place that is directly connected with therapy room is

used for the place of smaller occupancy factor (T< 1/8), it shall also consider

the public members at the far place of larger occupancy factor.

4.5 Considerations of therapy room shielding with labyrinth

4.5.1 At the mouth of labyrinth, it shall prevent direct illumination of wide

beam useful beams on labyrinth external wall (see position k in Annex C).

And try to avoid the direct illumination of 4pi useful beam and leakage

radiation on labyrinth external wall.

4.5.2 When 4.5.1 is met, position k in Annex C shall consider the possible

scattered radiation illumination of useful beam and (or) leakage radiation.

When 4.5.1 is not met, position k in Annex C shall consider oblique

illumination of 4pi useful beam and (or) leakage radiation.

4.5.3 It shall consider the illumination from the radiation source in the

therapy room to corresponding wall of labyrinth mouth (see position k in

Annex C) and the scattered radiation dose from it to labyrinth mouth (see path

o-i-g in Annex C).

compensation to the place where partial shielding is weakened due to inlay

installation.

4.6.5 The pipeline holes (including ventilation, electrical appliances, water

pipes, etc.) that get through therapy room wall shall avoid the console and

other areas where staff often stay. And it shall use multi-fold road to efficiently

control the radiation leakage of pipeline hole.

4.7 Considerations of neutron shielding

4.7.1 While neutron shielding, it shall consider the shielding to neutron

capture gamma ray.

4.7.2 When accelerator therapy X ray is greater than 10 MV, because (gamma, n)

react to produce "spurious" neutron, it shall consider the neutron shielding in

the therapy room according to the indicators that are given by the therapy

device manufacturer and not exceed national standard.

4.7.3 For X ray therapy room greater than 10 MV, when it uses single

concrete shielding, the wall, roof shielding shall only consider the shielding to

X ray and neglect the shielding t...

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