neck tumors

The presence of a dental implant across the irradiation beam has the potential to perturb the dose distribution. In this study, the effect of different commercial dental implants on dose distribution was investigated in electron beam therapy.

The Varian 2100 C/D linear accelerator (Linac) head was modeled precisely with proper components for electron mode (6 and 9 MeV) by MCNPX 2.6.1 and was benchmarked according to the International Atomic Energy Agency (IAEA) protocol, TRS -398. Dose distribution was calculated for Six different implant materials, including Titanium, Titanium alloy, Zirconia (Y-TZP), Zirconium oxide, Alumina, and PolyetherEtherKetone (PEEK), and for Four different scenarios.

The highest and lowest increasing doses occurred for Y-TZP (114.44% and 108.69% for 6 and 9 MeV, respectively) and PEEK (104.85% and 98.84% for 6 and 9 MeV, respectively) directly in front of the implant, respectively. By removing an implant from the jaw, an increasing dose was not seen, but an increasing dose occurred behind its depths in the bone region (31.81 %).

The amount of dose perturbation due to the dental implant's presence depends on the beam energy, mass density, and atomic numbers of implants. Maximum and minimum increased doses were estimated for Y-TZP and PEEK implants, respectively. Considering the correction factors due to the presence of high density and atomic number dental implants are essential to estimate the accurate dose delivery in radiotherapy with electron beams.

Metal artifacts cause to increase in the uncorrected dose evaluation during radiotherapy planning. This study aimed to evaluate the probable difference of the dose parameters calculated by the Treatment Planning System (TPS) in radiotherapy of head and neck cancer before and after metal artifact correction in Neusoft-Philips Corporation Computed Tomography (CT) images.

In the present study, the radiotherapy planning of the head and neck cancer from thirty patients was first performed on the CT default images with dental implants. The same processes were applied after performing a body standard metal kernel on the CT images to reduce the metal artifacts. The Gross Tumor Volume (GTV) and Organ At Risks (OARs) were contoured on the CT slices. The dosimetric parameters (mean, minimum, and maximum) for the GTV and OARs (eyes and spinal cord) were obtained for both sets of CT images (defaults and filtered). Wilcoxon signed-rank test was used to calculate the probability dose variations between the two sets.

There are significant differences in several dose parameters between the default and filtered CT images (P-value < 0.05). These dosimetric parameters are related to the GTV (mean dose), spinal cord (minimum and mean doses), right eye (maximum dose), as well as left eye (mean dose). The average range of dose differences between the default and filtered images was obtained; 1.12%-3.11% for the GTV as well as 0.22%-12.05% for the OARs.

Based on the results, the body standard metal kernel can cause a significant difference in several dosimetric parameters of GTV and OARs during the radiotherapy of head and neck cancer. Therefore, it is recommended to make a metal artifact correction on CT images for accurate dose calculation before designing a treatment plan.

The study aims to compare target coverage and critical structure dose difference between various dose computing algorithms with small segment dose calculation in Intensity Modulated Radiation Therapy (IMRT) and large segment dose calculation in 3-Dimensional Conformal Radiation Therapy (3DCRT) treatment plan for Head and Neck (H&N) tumor. For the present study, thirty-eight H&N cancer patients were selected retrospectively. Twenty-seven patients were planned with IMRT plan using Monte Carlo (MC) algorithm and eleven patients with 3DCRT plan using Collapsed Cone/Superposition (CCS) algorithm. IMRT plan was recalculated with Pencil Beam (PB) and the 3DCRT plan was recalculated with MC and PB algorithms. An Independent student t-test was performed as a part of statistical analysis for dosimetric comparison of the p-value. In the IMRT plan, mean dose, Conformity Index (CI), D2%, D98%, and D50% showed a significant difference in p-values (p<0.05), but the critical structure did not have a significant difference in p-value between the MC and PB algorithms, except Planning Risk Volume (PRV) spine. In the 3DCRT plan, mean dose, CI, Homogeneity Index (HI), D98%, D50%,and all the critical structures showed no statistically significant p-values (p<0.05) between the CCS with MC and CCS with PB algorithms. The study concludes that in the IMRT treatment technique, PB algorithms overestimate the dose compared to the MC algorithm, even in the head and neck treatment area. For 3DCRT treatment plans, CCS, MC, and PB algorithms showed no statistically significant differences between them. Moreover, this study ensured the accuracy of various dose calculation algorithms in H&N radiotherapy.

Radiation Therapy has a fundamental role in the treatment of cancer. Achieving Tumor Control Probability (TCP), while avoiding normal tissue complication is the goal of this treatment modality. The sensitivity of the thyroid gland to radiation increases the risk of developing secondary thyroid cancer and hypothyroidism.

The average dose to the thyroid from head and neck irradiation was measured using in vivo dosimetry (Thermolumincsence Dosimetry). The Radiotherapy technique was given using 6 MV x-rays from an Elekta compact linear accelerator and conformal technique delivered 1.8 to 2.0 Gy over 5 sequential days per week.

The average absorbed dose to the thyroid from head and neck radiotherapy was 4.4% of the prescription dose and from whole brain radiotherapy was 0.7% of the prescription dose. Thyroid Stimulating Hormone (TSH) levels were determined in 30 patients before and after completion of radiation therapy. The average concentration of TSH increased from 0.88 +/- 0.55 (pre-radiotherapy) to 1.7 +/- 0.66 (post-radiotherapy), (p < 0.05).

Thyroid absorbed dose was less than the threshold dose for patients who received radiotherapy to the head and neck based on thyroid function tests.