**Acknowledgements**

*Use of Gamma Radiation Techniques in Peaceful Applications*

accompanying the neutron capture process.

Effective doses in studied location depend on the neutron source strength Q of particular linac as well as on the construction of the treatment room door. For 18-MV photon beam, more important is the first factor (linac construction), ranging the doses from 30.6 ± 7.7 to 56.2 ± 14.1 μSv/h. The second factor plays the crucial role for 10 MV photon beams, for which neutron generation is of the lowest intensity, ranging the doses from 1.8 ± 0.4 μSv/h (for flattening filterfree (FFF) beam), through 3.4 ± 0.8 μSv/h (for thick door construction) up to 10.5 ± 2.6 μSv/h (for thin door construction). However, also in this case, neutron production intensity in linac head plays significant role, what is concluded from the differences between FFF beam and conventional linac, since flattening filter takes part in neutron production [29, 30]. Effective dose rates measured during 15-MV beam emission using Geiger-Mueller radiometer (calibrated on 60Co source) and the result obtained using spectrometry analysis presented here are 13.5 ± 3.0 μSv/h and 22.2 ± 5.5 μSv/h, respectively. This comparison shows that even 60% of dose could be omitted in the first case when excluding high-energy component of radiation leakage through the door due to prompt gamma rays

Production of neutron secondary radiation during emission of high-energy photon therapeutic beams is generally known and widely studied issue [29–46, 48]. Also, the phenomenon of high-energy X-rays and secondary neutron-induced radioactivity is well recognized [57]. However, the impact of photon radiation connected with neutron interaction in treatment room shielding materials on occupational safety is still difficult to assess experimentally in clinical conditions due to limited availability of high-resolution extended-energy range spectrometry systems, which often require special operating conditions (e.g., nitrogen cooling) and time-/labor-consuming data analysis. Nevertheless, recommendations concerning design of linac rooms [17] refer to publications devoted to this issue [58]. The use of a spectrometer (the usefulness of which has been demonstrated in presented study) is advised by IAEA [59] as a supplementary method for workplace monitoring, and its usage to characterize the energy spectrum of a given radiation type is recommended to support the performance of routinely used monitoring

The qualitative analysis performed by us has shown that the major component

7 Li and

of gamma radiation field near the treatment room door comes from prompt photons emitted during neutron capture reaction and is common in door construction as well as in concrete materials. Comprehensive study of this issue requires extended energy range of spectrometric system, as demonstrated in presented investigations. High-energy gamma rays above 3 MeV (omitted in standard spectrometric measurements) contribute to the effective dose values from 26 to 58%, for low (10 MV FFF beam) and for high (18 MV beam) neutron source strength

Reactions intended for neutron capture in door construction: 10B(n,α)

Presented study proves the correctness of radiation protection guidelines to avoid the vicinity of treatment door during therapeutic beam emission and additionally provides the justification in terms of dose values and mechanisms of

H contribute to the effective dose of 0–17% and 4–19%, respectively. Borated inner layer of the door is not always used, whereas hydrogen-rich material

**168**

1 H(n,γ) 2

instruments.

**4. Conclusion**

linacs, respectively.

gamma ray production.

is the commonly used neutron absorber.

This work was possible due to one of the authors (KPG) involvement in scientific activity in University of Silesia in Katowice, Poland. Therefore, the authors express their gratitude for the opportunity to use in situ gamma spectrometric system.
