Aims: The aim of this graduation thesis is to present the results of in vivo dosiometry in the rectum radiation treatment of prostate cancer and to compare them with the calculated radiation dose at the same point of radiation treatment plan. A comparison of the measured readings with the calculated dose is to enable us to evaluate the risk of rectal lining damage as well as to improve the protection of the rectum in general Patients and methods: The measurements on both types of dosimeters were performed in 10 patients treated with radiotherapy for prostate cancer. For measurements are used TLD and semiconductor detector about 6 centimeters from the asus border, with patients treated at the University Hospital for Tumors in Zagreb in August 2016. Results: The readings of TLD doses show certain deviation from the readings of XiO programme but at the same time there is a visible tendency of growth and fall of readings when they are presented in a linear graph. Measurements semiconductor detector PFD 39 also show discrepancies between measured and calculated dose as soon as possible to explain the position of the detector or due to the low volume measurement results are not reliable, especially as they cannot be compared with the results of the measurements with TLD. Conclusion: The value of this research resides with the fact that an acceptable procedure of placing the detector intracavitarily has been created. This procedure does not cause great discomfort and pain for the patient which makes him/her more cooperative during the procedure and leads to a more positive attitude towards the medical staff as well as the radiation therapy itself.