INVESTIGATION OF TESTICULAR DOSE BY TLD IN RADIOTHERAPY FOR RECTAL CANCER

INTERNATIONAL CONFERENCE ON LUMİNESCENCE AND ESR Dosimetry (LumiDoz 11), Gaziantep, Türkiye, 5 - 07 Eylül 2018, ss.13-14

Objective: This study is aimed to examine the doses of testes which are outside of the

treatment field with TLD in the radiotherapy for rectal cancer.

Materials and Methods: In the study, human-like phantom was used. The testicular

structure was formed by mixture of wax and paraffin (Figure 1) then fixed on phantom.

The cross-sectional images were obtained with the GE-Light speed RT computerized

tomography device for dose calculations in the Precise treatment planning system. A

three-dimensional conformal radiotherapy plan of 28 fractions with 180 cGy doses per

day was designed by using 18MV photon energy in the treatment planning system and

then the dose of the defined points in the testis was calculated. According to the treatment

plan, the phantom was irradiated in the linear accelerator by placing the TLDs in the

testicle structure at the defined points and also in the two points 1.5 cm away from isocenter

of plan. The TLD100 (LiF: Mg, Ti) solid pellets of 4.5 mm diameter and 0.9 mm

thickness was used MTS (MTS-N Poland). Two TLD chips were placed in every selected

position. After the exposure of TLDs, the pre-read heating processes was per-formed

(100 ̊C for 1h). The luminescent signals were counted by an automated TLD reader

RADOS RE-2000RT (RadRro Int. GmbH Germany). Before exposure, the TLDs were

annealed at 400 ̊C for 1 h and 100 ̊C for 1 h using a PTW high temperature oven (PTW

Freiburg GmbH). TLD measurements were done two times for each examination. TLcount

conversion to MU was done for 18 MV photon beam at 10 cm depth in slap

phantom with 100 cm source surface distance and 10x10 cm2 field size. The applied

monitor units were 260,130, 60, 30 and 15 MU for obtained doses of 202, 101, 47, 23,

and 12 cGy respectively.

Results: The calculated and measured point doses that, reflect treatment dose for

isocenter were in good agreement with difference lower than 1% (Table 1). The testis

point dose that was placed at the closest and the farthest to the edge of the field were 206

cGy and 82 cGy, respectively for a total treatment of rectum cancer (Table 2).

Conclusion: The calculated dose by treatment planning for organs that placed in

treatment field generally was good correlated with dose measurements but, the dose

difference was occurred when the organs placed on the out-side of treatment field. The

result of our study showed that, TLDs could be confidently used for in-field and out of

field dose measurements in radiotherapy.