CBCT Dose Reduction to Lens of Eye Using Leaded Glasses

Objectives: The objective of this study was to measure the shielding effect of leaded glasses, tanning glasses with 1/16” Pb shielding and tanning glasses with lead foil in combination with thyroid collar compared with no shielding equipment to the lens of the eye to evaluate the percentage of dose reduction. Methods: A CIRS female phantom head was used to measure the patient radiation dose to the organs of the head and neck from a Morita X800 CBCT using nano Dot optically stimulated luminescent dosimeters (OSL’S) placed at 23 head and neck sites. Leaded glasses, tanning glasses with 1/16” Pb shielding, tanning glasses with lead foil were placed over the phantoms eyes in conjunction with a thyroid collar. No Protective Equipment was used as a control. Radiation was performed using manufacturers predetermined exposure settings. All dosimeters were exposed three times. Radiation dose fractions to various organ sites were determined using reference values from ICRP-89. Organ equivalent doses were based on ICRP-103 tissue weighting factors. Results: The per cent reduction to the lens of the eye for the leaded glasses compared to no Protective Equipment was 49.2%, 44.6% for the tanning glasses with 1/16” Pb shielding and 38.1% for the tanning glasses with lead foil. For all modes of eye wear the highest organ doses were seen in the salivary glands, extrathoracic airway, and the oral mucosa. The use of proper PPE is necessary to protect the eye from possible cataractogenesis. Conclusions: Research on the correlation between cataract formation and ionizing radiation has shown that the dosage and frequency of exposure play a role in damaging the DNA in the lens of the eye. Here we demonstrate that regular leaded glasses and the tanning glasses with 1/16”Pb shielding are about equal in reducing the dose to the lens of the eye. One caviat, the size of the regular lead glasses might interfere with anatomical landmarks while tanning glasses would allow more diagnostic information. Further studies should be performed.

Comparison of skin doses of treated and contralateral breasts during whole breast radiotherapy for different treatment techniques using optically stimulated luminescent dosimeters

Purpose: To measure and compare the skin doses received by treated left breast and contralateral breast (CB) during whole breast radiotherapy using five treatment techniques in an indigenously prepared wax breast phantom. Materials and methods: Computed tomography (CT) images of the breast phantom were used for treatment planning and comparison of skin dose calculated from treatment planning system (TPS) with measured dose. Planning target volume (PTV) and the CB were drawn arbitrarily on the CT images acquired for the breast phantom with 10 numbers of calibrated optically stimulated luminescent dosimeters (OSLDs) fixed on the surface of both breasts. The TPS calculated surface doses of PTV breast and CB for five treatment planning techniques, viz., conventional wedge (CW), irregular surface compensator-based (ISC), field-in-field (FiF), intensity-modulated radiotherapy (IMRT) and rapid arc (RA) techniques were obtained for comparison. The plans were executed in Clinac iX Linear Accelerator with the OSLDs fixed at the same locations on the phantom as in simulation. The TPS calculated mean dose at the surface of the treated left breast and CB was noted for the 10 OSLDs from dose-volume histogram (DVH) and compared with the measured dose. Also, the mean chamber dose at the centre of the left breast was noted from the DVH for comparing with ion chamber measured dose. Results: With reference to the results, it is seen that the dose to the CB is lowest in ISC technique and FiF technique and greatest in IMRT technique. The CW technique also delivered a dose comparable to IMRT to the CB of the phantom. The dose to the surface of PTV breast was highest and comparable in CW plans and FiF plans (68% and 67%) and lowest in IMRT and RA plans (50% each). Findings: Analysis of the results shows that the FiF and ISC techniques are preferred while planning breast radiotherapy due to the reduced dose to the CB.

CHARACTERISATION OF TLDS-200 AND OSLDS AT LOW X-RAY ENERGIES AND DETERMINATION OF EYE LENS DOSE, THYROID DOSE AND MEAN GLANDULAR DOSE DURING STANDARD MAMMOGRAPHY AND TOMOSYNTHESIS

The objective of this study was to characterise thermoluminescent (TLDs) and optically stimulated luminescent dosimeters (OSLDs) at low X-ray energies and estimate the eye lens (DL), thyroid (DT) and mean glandular (DG) doses received during Full-Field Digital Mammography (FFDM) and Digital Breast Tomosynthesis (DBT). The dosimeters were characterised in mammography energies. DL, DT and DG were estimated in FFDM and DBT mode taping dosimeters on the skin of the thyroid gland and on the left eye lens of an Alderson phantom. Dosimeters were also placed on the top of a NORMI PAS phantom simulating a compressed breast. The accuracy, precision and lower limit of detection (LLD) for TLDs and OSLDs were 5 and 8%, 6 and 3%, and 38 and 11 μSv, respectively. The linearity of the kerma response had an R2 > 0.99 and energy dependence was lower than 40%. DT ranged from 0.40 to 2.87 μGy for FFDM and 1.27 to 5.99 μGy for DBT. DG was between 0.50 and 1.27 mGy for FFDM and 1.07 and 1.60 mGy for DBT. DL was below the LLD. Dosimeters showed good performance. DG values were lower than those found in the literature, whereas DT value agreed with references. Differences between DG and DT determined with OSLDs and TLDs were lower than 10% and 200%.