Entrance and peripheral doses measurements during radiotherapy

Abstract EN

The aim of in-vivo dosimetry of entrance dose was performed using thermoluminescent dosimeters (TLD) in order to evaluate patient dose and different treatment techniques in use.

Peripheral dose (thyroid and skin) was measured for patients during breast radiotherapy to evaluate the probability of radiation induced cancer.

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 on 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 was found to be within the 2.6% compared to the dose derived from theoretical estimation (normalized dose at Dmax).

The same measurements for 15 MV beams were found to be 3 %.

The perturbation value can reach up to 20% of the Dmax, which acts as a limitation for entrance dose measurements.

An average thyroid skin dose of 3.7% of the prescribed dose measured per treatment session while the mean skin dose breast treatment session estimated to be 42% of Dmax, for both internal and external fields.

The risk of fatality due to thyroid cancer per treatment course was 3x10–3.

Copper build up caps are reliable enough and feasible.

The risk of thyroid dose due to breast cancer was considerable.

It is important for a suitable protection of the thyroid gland to be provided especially for patients receiving radical radiotherapy if they are young.

KEYWORDS: Entrance Doses, Exit dose, TLD,Radiotherapy