Radiation protection is a system for controlling radiation hazards by using radiation protection equipment and following radiation protection regulations that have been standardized1. Possible radiation hazards are caused by irradiation of the external body (external), if the radiation source is outside the body and maybe the radiation hazard is caused by irradiation of the inner body (internal), if the radiation source is in the body [1,2,3].

Biological Effects of Adverse Radiation are grouped into 3, namely the non-stockastic somatic effect which usually causes redness of the skin, the somatic stockastic effect which is for example cancer of leukemia and the genetic stochastic effect that can be inherited in the next generation. Non-stochastic effects occur when the dose received exceeds the prescribed threshold dose. The price of this threshold dose is not the same for everyone and depends on the conditions of irradiation [2,3].

If the reception of the dose above the threshold dose the effect will be even more severe if the dose received is higher. Usually it will arise immediately (less than 1 year after irradiation). The occurrence of a Stochastic effect follows a probabilitic relationship in the sense that if a group of people receives a higher dose there will be a greater likelihood of certain Stochastic effects. This effect (in somatic terms) will be experienced by several people in this group randomly. In this case the genetic frequency of an abnormality in the next generation is higher when the dose received by the group is higher [2,3].

For this reason, the Government issued regulations aimed at reducing these adverse factors, in the form of Government Regulation No. 11, 12, 13 of 1975, while the implementation provisions were issued through the Decree of the Director General of BATAN no. 24 / DJ / II / 1983. In it the scope is explained as follows: Provisions for occupational safety are intended as a guide for those who work with ionizing radiation sources in the fields of health, industry, education, research and so on. The provisions contained in this manual contain the basics of radiation protection, including regulating: Allowable radiation dose limit values, Work requirements with radiation sources and Work procedures that must be adhered to and carried out by everyone who works with radiation sources [4]. By using a dosage limitation system for body irradiation (both external and internal radiation) the possibility of radiation risk can be ignored. This is the job of a Radiation Protection Officer by following the Radiation Protection Regulations and using sophisticated protective equipment can save radiation workers and society in general.

The procedure commonly used to prevent and control radiation hazards is to eliminate radiation hazards, isolate radiation hazards from humans and isolate humans from radiation hazards. The application of the three radiation protection principles is carried out by the Radiation Protection Officer1, 4,5. The main principle is clear by obeying and implementing radiation protection regulations, secondly by designing the workplace and using radiation protection equipment and adequate radiation retention so that work and environment conditions are safe and secure and the third requires constant monitoring and supervision of radiation workers. environment using individual monitoring tools, environmental monitoring and surveymeter [5,6].

Given that besides the benefits of external and internal radiation which is ionizing radiation, it is potential to cause radiation hazards, while technically it is impossible to eliminate the source, the danger of radiation from external and internal radiation to the officer or the environment can be controlled with three basic rules of radiation protection, namely reducing radiation time. Seek distance from the radiation source as far as possible and use a radiation barrier [5,6].

A radiotherapy operator who has to work for a certain amount of time (according to the required dose calculation) which is relatively long and at a distance that is relatively close to the source of the only way to control radiation hazards is to install a radiation barrier between the source and the operator. There are two types of radiation retention to the source and barrier of radiation for the environment, namely the walls of the radiotherapy machine [4,5,8].

Calculation of barrier planning, anchoring is divided into two types, namely primary and secondary anchors. Primary deterrents provide protection against use rays, which are rays that come directly from the radiation source, while the secondary barrier provides protection against leaky radiation and scattered radiation7. As for the brachytherapy chamber, we consider all retaining walls as primary anchors, because the radiation source from brachytherapy is not collimated.

To improve radiotherapy services, Dr. Kariadi hospital Semarang plans to install a new Brakhiterapi machine using Co-60 sources. The radiotherapy room that was built was previously used for Brachytherapy using the Ir-192 source. In accordance with nuclear regulations in force in Indonesia, the Co-60 brachytherapy aircraft must be installed in a radiotherapy room that has obtained a new construction permit from the Nuclear Energy Supervisory Agency (Bapeten), considering that the radioactive source to be used is different from the previous radioactive source, activity and energy

In this study the calculation parameters we use are:

(According to PERKA BAPETEN No. 3 of 2013)

Fig 2. Room Br chytherapy Co-60 space roof plan

Assume the layout of the patient's bed during treatment so that the bed area is likely to position the source as shown in Figure 1.