[en] In vivo dosimetry of entrance dose was performed using thermoluminescent dosimeters (TLD) in order to evaluate the clinical application of the build up caps in patient dose measurements and for different treatment techniques. Peripheral dose (thyroid and skin) was measured for patients during breast radiotherapy to evaluate the probability of secondary cancer induction. TLD-100 chips were used with different Copper build up caps (for 6 MV and 15 MV photon beams from two linear accelerators. Entrance doses were measured for patients during radiotherapy course for breast, head and neck, abdomen and pelvis malignancies. The measured entrance dose for the different patients for 6 MV beams is found to be within the ±2.6% compared to the dose derived from theoretical estimation (normalized dose at D_max). The same measurements for 15 MV beams are found to be ±3 %. The perturbation value can reach up to 20% of the D_max, which acts as a limitation for entrance dose measurements. An average thyroid skin dose of 3.7% of the prescribed dose was measured per treatment session while the mean skin dose breast treatment session is estimated to be 42% of D_max, for both internal and external fields. These results are comparable in those of the in vivo of reported in literature. The risk of fatality due to thyroid cancer per treatment course is 3x10^-3