Thyroid and gonads are radiosensitive organs which requires radiation shield to reduce the dose received. However,
radiation shielding is not widely used in radionuclide imaging because it is heavy, uncomfortable and can cause pain
in the spine. Therefore, a research was carried out to determine the ability of thyroid and gonad radiation shield
which is thinner and lighter in reducing radiation dose. A study was conducted in Hospital Putrajaya to determine
the radiation dose received by the thyroid and gonads during a complete Positron Emission Tomography-Computed
Tomography (PET-CT) procedure with and without radiation shield. A total of six male staffs have been chosen as subject
and data from 33 complete PET-CT procedures have been collected. For every PET-CT procedure, the subject’s thyroid
and gonad were shielded using 0.5-mm thick radiation shielded, model Mavig 615 (USA) and Shielding International
(USA) respectively. Thermal luminescent dosimeter (TLD) chips were used as radiation dose detector. The average 18FFDG radioactivity administered to the patient was 387 MBq and the average scan time is 9.224 ± 1.797 minutes. The
results showed that the mean equivalent dose received by the thyroid with and without shielding were 0.080 ± 0.033
mSv and 0.078 ± 0.039 mSv respectively. The mean equivalent dose received by gonad with and without shielding
were 0.059 ± 0.040 mSv and 0.061 ± 0.030 mSv respectively. Radiation shield with 0.5 mm thickness is unable to
reduce radiation dose received by the thyroid (p = 0.76) and gonads (p = 0.79) because it is too thin to resist the
high-energy radiation during PET-CT procedures. Thyroid receive higher radiation dose of 0.016 m Sv compared to
the gonads (p < 0.05) because the thyroid’s position is more exposed to radiation sources which are 18F-FDG during
radiopharmaceutical preparation and patients after administered with 18F-FDG during PET-CT procedure.
Keywords: equivalent dose, radiation shield, TLD
Excellent treatment setup accuracy with highly conformal radiation technique will improve oral mucosal sparing by
limiting uninvolved mucosal structures from receiving high dose radiation. Therefore, a study was conducted to identify
the ideal immobilization device for interfraction treatment setup accuracy improvement. A total of twelve oral cancer
patients underwent volumetric modulated arc therapy (VMAT) was categorized into three different group depending on
immobilization device they used for treatment. HFW: headFIX® mouthpiece molded with wax, SYR: 10 cc/ml syringe and
TDW: wooden tongue depressor molded by wax. Each patient underwent image-guided radiotherapy with a total of 292
cone beam computed tomography (CBCT) data sets for position treatment setup errors measurement. The variations in
translational (lateral, longitudinal, vertical) and rotational (pitch, yaw, roll) in each CBCT image were calculated. Patient
positioning errors were analyzed for time trends over the course of radiotherapy. CTV-PTV margins were calculated from
the systematic (Σ) and random (σ) errors. Mean ± SD for absolute treatment setup error was statistically significant
(p < 0.001) lower for all translational errors and yaw direction in HFW. The interfraction 3D vector errors were 1.93 ±
0.66, 3.84 ± 1.34 and 2.79 ± 1.17 mm for the HFW, SYR and TDW respectively. There are positive increments between 3D
vector errors over the treatment fraction for all devices. The calculated CTV-PTV margins were 3.08, 2.22 and 0.81 mm,
3.76, 6.24 and 5.06 mm and 3.06, 3.45 and 4.84 mm in R-L, S-I and A-P directions, respectively. HFW shows smaller errors
in almost all comparison indicating higher accuracy and reproducibility of the immobilization device in maintaining
patient’s position. All margins calculated did not exceed hospital protocol (5 mm) except S-I and A-P directions using
SYR. However, in some special situations, such as re-irradiation or the close proximity of organs at risk and high-dose
regions or lower (i.e., 3 mm) margins could benefit from daily image guidance.