Dosimetric Comparison of Different Radiotherapy Techniques to Determine the Absorbed Fetal Dose in Pregnant Patients with Left-Sided Breast Cancer

This study aimed to measure the dose exposed by the fetus during three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) treatment techniques in pregnant patients who had to undergo radiotherapy due to breast cancer with thermoluminescence dosimetry (TLD) and compare these measurements with treatment planning system (TPS). 2.5 mm- thick computed tomography (CT) images of Alderson Rando phantom device were taken for measurements. Heart, ipsilateral lung, contralateral lung and contralateral breast were defined as critical organs at risk (OARs) and planned tumor volume (PTV) as target volume. In TPS (Eclipse, version 15.1), using 3D-CRT and INERT treatment methods, the criterion that 95% of the PTV volume should receive more than 95% of the predicted dose was taken into consideration. OAR has been preserved as much as possible in the used techniques. In order to compare the TPS and TLD readings in PTV, 60 TLDs were placed in the target volume in the Rando phantom. Twenty-four TLDs were placed in the 30th and 31st sections of the phantom, which is likely to be in the volumetric size of the first trimester of pregnancy which is also located 25.84 cm from the lower limit of the PTV. Six MV were used in seven different treatment techniques and the measurements were repeated 5 times for each technique and averaged. The differences between the average TPS and TLD readings for PTV were 1.34% 0.86% 1.04%, 0.64% 0.48% 0.84% and 0.73% for 3D-CRT, 5 MSS-IMRT, 5 SW-IMRT, 7 MSS-IMRT, 7 SW-IMRT, 9 MSS-IMRT and 9 SW-IMRT, respectively. Fetal doses for all treatment techniques in TPS were found as 0.00 cGy. However, in TLD measurements fetal doses were found as, 3.36 +/- 0.19 cGy, 9.32 +/- 0.91 cGy 10.29 +/- 1.19 cGy, 12.35 +/- 1.42 cGy, 12.99 +/- 1.46 cGy, 13.18 +/- 1.53 cGy and 16.10 +/- 2.04 cGy for 3D-CRT, 5 MSS-IMRT, 5 SW-IMRT, 7 MSS-IMRT, 7 SW-INERT, 9 MSS-IMRT and 9 SW-IMRT, respectively. In 3D-CRT treatment technique the fetus received the lowest dose. In addition, for plans made using the INERT method, it is seen that the MSS-INERT technique provides better fetal protection compared to the SW-IMRT technique. The 3D-CRT should be the first priority for a pregnant patient who has to undergo left breast RT, but if the desired dose-volume histogram (DVH) cannot be obtained with 3D-CRT, 5 MSS-INERT technique may be preferred.