Estimation of dose enhancement to soft tissue due to backscatter radiation near metal interfaces during head and neck radiothearpy - A phantom dosimetric study with radiochromic film

Assessment of the Absorbed Dose Variations in the Thyroid Gland Exposed to Orthopantomography (OPG) while Swallowing: A Novel Approach to Radiation Protection

Background

The reliance on specialized diagnostic techniques is on the rise across various medical fields, including dentistry. While orthopantomogram (OPG), offers many advantages in terms of dental diagnosis, it also poses potential risks to sensitive organs, notably the thyroid gland.

Objective

This study aimed to evaluate the fluctuations in the absorbed dose within the thyroid gland during swallowing while undergoing an OPG procedure.

Material and Methods

In this computational simulation study, the BEAMnrc Monte Carlo code was employed to model an OPG machine, using 700 million particles across the energy range of 60-75 keV, which is standard for OPG procedures. The Monte Carlo (MC) model was cross-verified by comparing the derived spectra with those in the IPEM Report 78. A head and neck phantom was constructed using CT scan images with a slice thickness of 5 mm. This phantom underwent simulated beam exposure under two conditions: pre-swallow and post-swallow. Subsequently, the percentage depth dose was measured and contrasted across different depths.

Results

After swallowing, there was an increase in the absorbed dose across all three regions of the thyroid (right, left, and center). Notably, regions near the hyoid bone exhibited a particularly significant increase in dose. In certain areas, the absorbed dose even tripled when compared to the pre-swallowing state.

Conclusion

The findings indicate that during OPG imaging, swallowing can lead to an increased radiation dose to the thyroid gland. Given the thyroid's heightened sensitivity to radiation, such an increase in dosage is noteworthy.

A dosimetric phantom study of thoracic radiotherapy based on three-dimensional modeling of mediastinal lymph nodes

The aim of the present study was to investigate the optimal strategy and dosimetric measurement of thoracic radiotherapy based on three-dimensional (3D) modeling of mediastinal lymph nodes (MLNs). A 3D model of MLNs was constructed from a Chinese Visible Human female dataset. Image registration and fusion between reconstructed MLNs and original chest computed tomography (CT) images was conducted in the Eclipse™ treatment planning system (TPS). There were three plans, including 3D conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), which were designed based on 10 cases of simulated lung lesions (SLLs) and MLNs. The quality of these plans was evaluated via examining indexes, including conformity index (CI), homogeneity index and clinical target volume (CTV) coverage. Dose-volume histogram analysis was performed on SLL, MLNs and organs at risk (OARs). A Chengdu Dosimetric Phantom (CDP) was then drilled at specific MLNs according to 20 patients with thoracic tumors and of a medium-build. These plans were repeated on fused MLNs and CDP CT images in the Eclipse™ TPS. Radiation doses at the SLLs and MLNs of the CDP were measured and compared with calculated doses. The established 3D MLN model demonstrated the spatial location of MLNs and adjacent structures. Precise image registration and fusion were conducted between reconstructed MLNs and the original chest CT or CDP CT images. IMRT demonstrated greater values in CI, CTV coverage and OAR (lungs and spinal cord) protection, compared with 3D-CRT and VMAT (P<0.05). The deviation between the measured and calculated doses was within ± 10% at SLL, and at the 2R and 7th MLN stations. In conclusion, the 3D MLN model can benefit plan optimization and dosimetric measurement of thoracic radiotherapy, and when combined with CDP, it may provide a tool for clinical dosimetric monitoring.