Assessment of the effects of different dental restorative materials on radiotherapy dose distribution: A phantom study.

Background: One of the most specific effects of high-density dental restorative materials on head & neck cancer radiotherapy is generating variations on isodose distributions. These variations might have an impact on the accuracy and effectiveness of the radiation treatment. The aim of this study is investigating the possible dosimetric effect of six different restorative materials on isodose distributions in head & neck radiotherapy planning process. Materials and Methods: A special phantom was developed and twenty-one caries-free human third molars (a control group + six different restorative materials) were used for the measurements. After acquiring the computed tomography (CT) images, seven treatment plans were created. Hounsfield Unit (HU) numbers, horizontal line dose profile (HLDP) and vertical line dose profiles (VLDPs) were compared with the control group. Results: The amalgam sample deformed the HU numbers in CT images. The median HU value for the S4 material was considerably different than the other samples. The median values were quite close for the remaining samples. For the amalgam sample, the mean of the calculated median isodose values for HLDP and VLDP at 3.5 cm away from the isocenter line were lower than the mean of the control group 4.03% and 6.94%, respectively (for HLDP with tooth numbers of 36 and 38 P = 0.025 and P < 0.001, respectively; for VLDP P < 0.001). In C-S1 comparison results, the statistically significant differences were found for the measurement point at 1 cm away from the isocenter (P = 0.037, P = 0.002, and P = 0.018 for the tooth numbers 36, 37, and 38, respectively). In C-S2 and C-S6 comparisons, there was a statistically significant difference for tooth number 36 (P = 0.035 and P = 0.003, respectively). Conclusions: The findings of the present study showed that amalgam should not be used in head & neck cancer patients who are planned to have radiation therapy. A high viscosity glass ionomer cement (GIC) and a ceramic reinforced GIC sample can be used instead of amalgam to minimize the distorting effect on isodose distributions.

Evaluation of patient organ doses from kilovoltage cone-beam CT imaging in radiation therapy.

BACKGROUND: Currently, CBCT system is an indispensable component of radiation therapy units. Because of that, it is important in treatment planning and diagnosis. CBCT is also an crucial tool for patient positioning and verification in image-guided radiation therapy (IGRT). Therefore, it is critical to investigate the patient organ doses arising from CBCT imaging. The purpose of this study is to evaluate patient organ doses and effective dose to patients from three different protocols of Elekta Synergy XVI system for kV CBCT imaging examinations in image guided radiation therapy. MATERIALS AND METHODS: Organ dose measurements were done with thermoluminescent dosimeters in Alderson RA NDO male phantom for head & neck (H&N), chest and pelvis protocols of the Elekta Synergy XVI kV CBCT system. From the measured organ dose, effective dose to patients were calculated according to the International Commission on Radiological Protection 103 report recommendations. RESULTS: For H&N, chest and pelvis scans, the organ doses were in the range of 0.03-3.43 mGy, 6.04-22.94 mGy and 2.5-25.28 mGy, respectively. The calculated effective doses were 0.25 mSv, 5.56 mSv and 4.72 mSv, respectively. CONCLUSION: The obtained results were consistent with the most published studies in the literature. Although the doses to patient organs from the kV CBCT system were relatively low when compared with the prescribed treatment dose, the amount of delivered dose should be monitored and recorded carefully in order to avoid secondary cancer risk, especially in pediatric examinations.

The esophageal dose-volume parameters for predicting Grade I-II acute esophagitis correlated with weight loss and serum albumin decrease in lung cancer radiotherapy.

INTRODUCTION: Acute esophagitis (AE) is a commonly encountered side effect of curative thoracic radiotherapy (CTRT) for lung cancer patients. Nevertheless, its identification for widely used scoring systems depends on patients' statements. It is aimed to evaluate the correlation between the esophagus doses during CTRT and Grade 1-2 AE, weight change, and change in serum albumin (Alb) levels. SUBJECTS AND METHODS: The data collected from 124 lung cancer patients treated with ≥60 Gy CTRT were evaluated retrospectively. Weight and serum Alb level difference of each patient, throughout CTRT, were calculated. The percentage of the esophagus volume receiving ≥5 Gy (V5), V10, V35, V50, and V60; the absolute esophagus volume receiving ≥60 Gy (V60(cc)); the length of esophagus receiving ≥60 Gy (L60); the average esophagus dose (Dmean); and the maximum esophagus dose (Dmax) were the dose parameters calculated. The correlations were performed by Spearman's rank correlation coefficient. RESULTS: Grade 1 and Grade 2 AE were reported in 62 and 25 patients, respectively. All of the dose parameters were correlated with Grade 1-2 AE (P < 0.001) and weight loss (P < 0.001 for all, except Dmax P = 0.018). Decrease in serum Alb level was significantly correlated with all the parameters, but V5 and V10. Receiver operating characteristic curve analysis was performed for five parameters with the highest correlation coefficient (V35, V50, V60(%), V60(cc), and Dmean), and the cutoff values were 39.5%, 28.17%, 2.21%, 0.5cc, and 26.04 Gy, respectively. CONCLUSIONS: The correlation of the dose parameters that might be effective on Grade 1-2 AE with the weight loss and Alb loss was investigated, and the cutoff values corresponding to the best sensitivity and specificity were identified.

Detection of radiotherapy-related damage in head and neck cancer patients by evaluating volumetric changes in lacrimal gland, nasolacrimal duct and computed tomography attenuation changes in lens.

PURPOSE: In our study, we aimed to evaluate the change in attenuation of lens in CT images, volumetric changes, in lacrimal gland (LG) and nasolacrimal duct (NLD) of the patients receiving radiotherapy for brain or head & neck tumor. Additionally, the correlation between these changes and radiation dose data were investigated. METHODS: Patient simulation CT images and control CT images were used to evaluate the volume and attenuation changes. Pre- and post-treatment MR and CT images were used to evaluate radiation-induced volumetric alterations in NLD and LG, respectively. Radiation therapy was given to a total dose of 54-70 Gy with conventional fractionated scheme using intensity-modulated radiotherapy technique (IMRT). Dose volume parameters were evaluated via dose volume histograms (DVHs). RESULTS: Dose volume parameters, volume and densities of 59 lenses (L), 60 LG and 60 NLD of 30 patients were retrospectively assessed. The median LG volume was significantly lower in the post-treatment images (p < 0.001), whereas the median volumes of NLD in pre- and post-RT images were similar. The Hounsfield unit (HU) numbers of lenses were significantly lower on post-RT CT images (p < 0.001). No statistically significant correlation was found between dose parameters and volume or HU changes (p = 0.054-0.817). CONCLUSION: It was observed that the attenuation of lenses and lacrimal gland volume significantly lowers following radiation. However, these alterations were not found to be correlated with dose.

The effect of ionizing radiation on properties of fluoride-releasing restorative materials.

The purpose of this study was to evaluate the effect of ionizing radiation from high energy X-ray on fluoride release, surface roughness, flexural strength, and surface chemical composition of the materials. The study groups comprised five different restorative materials: Beautifil II, GCP Glass Fill, Amalgomer CR, Zirconomer, and Fuji IX GP. Twenty disk-shaped specimens (8x2 mm) for fluoride release and 20 bar-shaped specimens (25 x 2x 2 mm) for flexural strength were prepared from each material. Each material group was divided into two subgroups: irradiated (IR) and non-irradiated (Non-IR). The specimens from IR groups were irradiated with 1.8 Gy/day for 39 days (total IR = 70.2 Gy). The amount of fluoride released into deionized water was measured using a fluoride ion-selective electrode and ion analyzer after 24 hours and on days 2, 3, 7, 15, 21, 28, 35, and 39 (n = 10). The flexural strength was evaluated using the three-point bending test (n = 10). After the period of measurement of fluoride release, seven specimens (n = 7) from each group were randomly selected to evaluate surface roughness using AFM and one specimen was randomly selected for the SEM and EDS analyses. Data were analyzed with two-way ANOVA and Tukey tests (p = 0.05). The irradiation significantly increased fluoride release and surface roughness for Amalgomer CR and Zirconomer groups (p < 0.05). No significant change in flexural strength of the materials was observed after irradiation (p > 0.05). The ionizing radiation altered the amount of fluoride release and surface roughness of only Amalgomer CR and Zirconomer. The effect could be related to the chemical compositions of materials.

Evaluating the predictive value of quantec rectum tolerance dose suggestions on acute rectal toxicity in prostate carcinoma patients treated with IMRT.

AIM: To investigate the predictive value of convenience of rectum dosimetry with Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) dose limits, maximum rectum dose (Dmax), total rectal volume (TVrectum), rectal volume included in PTV (VrectumPTV) on Grade 2-3 acute rectal toxicity for utilization in clinical practice. BACKGROUND: Numerous previous data have reported frequent acute proctitis after external-beam RT of prostate cancer. Predicting toxicity limited with dose information is inadequate in clinical practice due to comorbidities and medications used. MATERIALS AND METHOD: Sixty-four non-metastatic prostate cancer patients treated with IMRT were enrolled. Patients were treated to a total dose of 70-76 Gy. Rectal dose volume histograms (DVH) of all patients were evaluated retrospectively, and a QUANTEC Score between 0 and 5 was calculated for each patient. The correlation between the rectal DVH data, QUANTEC score, TVrectum, VrectumPTV, rectum Dmax and Grade 2-3 rectal toxicity was investigated. RESULTS: In the whole group grade 1, 2 and 3 acute rectal toxicities were 25%, 18.8% and 3.1%, respectively. In the DVH data, rectum doses of all patients were under RTOG dose limits. Statistically significant correlation was found between grade 2-3 rectal toxicity and TVrectum (p = 0,043); however. It was not correlated with QUANTEC score, VrectumPTV and Dmax. CONCLUSION: Our results were not able to show any significant correlation between increasing convenience with QUANTEC limits and lower rectal toxicity. Conclusively, new dosimetric definitions are warranted to predict acute rectal toxicity more accurately in prostate cancer patients during IMRT treatment.

The effect of ionizing radiation on properties of fluoride-releasing restorative materials

Abstract The purpose of this study was to evaluate the effect of ionizing radiation from high energy X-ray on fluoride release, surface roughness, flexural strength, and surface chemical composition of the materials. The study groups comprised five different restorative materials: Beautifil II, GCP Glass Fill, Amalgomer CR, Zirconomer, and Fuji IX GP. Twenty disk-shaped specimens (8x2 mm) for fluoride release and 20 bar-shaped specimens (25 x 2x 2 mm) for flexural strength were prepared from each material. Each material group was divided into two subgroups: irradiated (IR) and non-irradiated (Non-IR). The specimens from IR groups were irradiated with 1.8 Gy/day for 39 days (total IR = 70.2 Gy). The amount of fluoride released into deionized water was measured using a fluoride ion-selective electrode and ion analyzer after 24 hours and on days 2, 3, 7, 15, 21, 28, 35, and 39 (n = 10). The flexural strength was evaluated using the three-point bending test (n = 10). After the period of measurement of fluoride release, seven specimens (n = 7) from each group were randomly selected to evaluate surface roughness using AFM and one specimen was randomly selected for the SEM and EDS analyses. Data were analyzed with two-way ANOVA and Tukey tests (p = 0.05). The irradiation significantly increased fluoride release and surface roughness for Amalgomer CR and Zirconomer groups (p < 0.05). No significant change in flexural strength of the materials was observed after irradiation (p > 0.05). The ionizing radiation altered the amount of fluoride release and surface roughness of only Amalgomer CR and Zirconomer. The effect could be related to the chemical compositions of materials.