Investigation of 3D-Conformal and Intensity-Modulated Therapy Techniques to Determine the Absorbed Fetal Dose in Patients With Nasopharyngeal Cancer During Pregnancy

Abstract

The aim of this research was to investigate the fetal doses of pregnant patients undergoing conformal radiotherapy or intensity-modulated radiation therapy (IMRT) for nasopharyngeal cancers at various times during pregnancy. In this work, the head and neck cancer treatment of a pregnant patient was experimentally simulated. Two treatment plans were calculated using a female RANDO anthropomorphic phantom. This phantom was irradiated using the Clinac DHX linear accelerator, according to the Standard treatment plans of both three-dimensional conformal radiation therapy (3-DCRT) and IMRT techniques. During pregnancy, the height of the fundus at different weeks was determined and a sign was placed on the phantom. OSLD (optically stimulated luminescence dosimeter) and MOSFET (Metal oxide semiconductor field effect transistor) dosimeters were used to measure the dose of virtually designated uterus area at various times during pregnancy. The data carried out by TPS were compared with measured data. PBC calculation method in the treatment planning system (TPS) was unable to estimate the peripheral doses in uterus area. TPS showed a dose of 0 cGy at many points. On the contrary, OSLD measurement results revealed that the uterus (fetus) doses were ranging from 14.46–43.05 cGy (mean 27.9 ± 10.1 cGy) for 7-field IMRT treatment plan and 6,12–27,3 cGy (mean 14,7 ± 7,97 cGy) for 3-DCRT in Alderson anthropomorphic female RANDO phantom. MOSFET measurements showed that the uterus (fetus) doses were ranging from 15–50.1 cGy (mean 36.25 ± 11.7 cGy) for 7-field IMRT treatment plan and 10–36.3 cGy (mean 21.3 ± 9.54 cGy) for 3-DCRT treatment plan. All the observed fetal dose for the measurements and TPS data for two techniques are given in the Table below. In summary, comparing two techniques, it is clear that IMRT causes higher fetal radiation dose than 3-D CRT due to its higher MU value. Considering that fetal radiogenic effects are seen at 5-10 cGy (American Association of Physicists in Medicine Radiation Therapy Committee Task Group 36), 3-D CRT is a more reliable method. The TPS is unable to estimate peripheral doses accurately. Since the TPS underestimates the fetal dose, relying on the dose calculated by TPS does not seem possible under the current circumstances. The fetal dose from radiotherapy may vary depending on the gestational age at the time of treatment. The use of special shielding devices can considerably reduce the fetal dose from radiation therapy.Tabled 1Abstract 2597; TableIMRT3DMOSFETOSLDTPSMOSFETOSLDTPS12weeks15 cGy14.46cGy0.0cGy12weeks10cGy6.12cGy0.0cGy16 weeks32.2cGy22cGy0.0cGy16 weeks12.3cGy8.68cGy0.0cGy20-22 weeks32.55cGy23.1 cGy0.7cGy20-22 weeks15.6cGy10.5cGy0.0cGy24-26 weeks36.5 cGy25.69 cGy0.7cGy24-26 weeks21.5cGy12.25cGy0.0cGy28 weeks39.6 cGy27.09 cGy11cGy28 weeks23.4cGy14.03cGy0.0cGy36 weeks50.1 cGy43.05 cGy15cGy36 weeks36.3cGy27.3cGy9.7cGy40 weeks47.8 cGy40.01cGy11.6cGy40 weeks30cGy24.1cGy9.7cGy Open table in a new tab