1 Scope
This Part of GBZ/T 201 specifies the dose control requirements, dose estimation and detection and evaluation methods for radiation shield of radiotherapy room of electron linear accelerators (hereinafter referred to as accelerators).
This part is applicable to radiotherapy room of accelerators with radiation energy below 30 MeV.
This part is not applicable to radiotherapy room of accelerator electron beam in surgery.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GBZ/T 201.1 Radiation shielding requirements for radiotherapy room - Part 1: General principle
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 201.1 and the following apply.
3.1
useful beam
radiation beam used for patient radiotherapy in radiotherapy device, also called as main radiation beam. The zone where may be radiated directly by the radiotherapy room useful beam is called as main shielding zone, and the others are called as second shielding zone
3.2
isocenter
intersection of the rack rotating axis of radiotherapy device for medical use and the radiation beam reference axis, which is also on the rotating axis of the treatment table
3.3
tenth-value layer, TVL
in the path whereby the radiation beams, like X, γ, n, etc. radiate into materials, the thickness of material on a path section reducing the radiation dose rate to 1/10 the initial value of certain place, also called as 1/10-value layer. For the radiation beam being in the material path, the first tenth-value layer from the entrance surface is usually different from the tenth-value layers thereafter, which is called as the first tenth-value layer and recorded as TVL1. In the case TVL1 is indicated, symbol “TVL” refers to a tenth-value layer after the first tenth-value layer; otherwise, “TVL” refers to a tenth-value layer of radiation beam at any depth in the material and is called as equalized tenth-value layer, recorded as TVLe.
3.4
intensity modulated radiation therapy, IMRT
to achieve three-dimensional radiation therapy based on optimized proper distribution of treatment field by modulating its shape, size and position using components like multi-leaf collimator, etc. in certain irradiation direction
3.5
intensity modulated radiation therapy factor
ratio of average irradiation time per patient treated by IMRT to that treated by conventional radiation therapy under the condition where the dose rates at the places on the radiotherapy device useful beam central axis 1m away from the target, generally expressed by the symbol N
4 Dose control requirements and shielding considerations for radiotherapy room
4.1 Principles for selecting focus points
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Dose control requirements and shielding considerations for radiotherapy room
5 Shielding estimation method
6 Detection and evaluation of radiation shielding protective dose
Annex A (Informative) Examples of weekly workload, weekly therapy irradiation time, and derived dose rate reference control level
Annex B (Informative) Data for radiation shielding estimation
Annex C (Informative) Neutron in the accelerator (>10 MV) radiotherapy room and neutron-capture gamma-ray as well as its shielding
Annex D (Informative) Examples for shielding estimation of different types of radiotherapy rooms
Bibliography
