Dosimetric Evaluation of Mean Glandular Dose for Mammography in Indian Women from North East Region

Introduction: The assessment of mean glandular dose is important to reduce and control the potential risk of radiation induced carcinogenesis during mammography procedure. The quantity which describes amount of risk for glandular tissue caused by application of radiation in mammography is called mean glandular dose (MGD). The purpose of the study was to estimate patient mean glandular doses in the two standard views, cranio-caudal and mediolateral oblique for mammography procedure. The study was also aimed to identify the various factors which influence the quantity MGD and Glandularity.

Study Objective: The objective of this study was to measure the MGD from CC and MLO views in each breast and total dose per woman (for both breasts and two views) from the exposure factors and CBT (compressed breast thickness) in the patients undergoing mammography procedure in the region of North East India.

Materials and Methods: The following clinical data were collected from 72 numbers of women, who were referred to Radiology department, in a designed format during diagnostic examination:

Patient demographic data like age, weight and height.
Applied clinical spectrum (Target/filter combination.)
Digital readout of CBT (compressed breast thickness) and type of projection (CC, MLO) for each breast.
Exposure factors: mAs and kVp.
The MGD per woman was calculated by summing the MGDs for all exposures and averaging it over both breasts. The MGD values are based on measurement of entrance surface air kerma (ESAK) and HVL. The measurements were done with Magic maxx mammography detector, IBA, using appropriate conversion coefficients as per IAEA protocol. For analysis of data Origin 2018b software was used for determining the descriptive and Pearson’s correlation.

Results: In this study, 72 women (18 to 78 years) were included. Mean age was (42.28±14.8) years. The mean CBT value of CC view is (4.04±1.13) c.m, which is lower than that of (4.75±1.19) c.m for MLO views. Significant difference was found between MGD from CC (1.10±0.02mGy) and MLO (1.26±0.13 mGy) views. (p=0.0386). Significant relationships were seen between MGD per patient with respect to CBT (R²=0.152, p=0.0007), mAs (R²=0.696, p=0.00001) and glandularity (R²=0.140, p=0.0011). It was also noted that there was a considerable significance between glandularity and CBT (R²=0.173, p=0.00028).

Discussion: The significant increase of doses in MLO in regard to CC projection can be explained with the fact that pectoral muscle is involved in MLO projection, which causes an increase of thickness of compressed tissue and require a greater dose for an image of a better quality. It is known that compressed breast thickness value shows a certain tendency of growth in younger patient and a tendency of decline in older patients, it was proved as true in our study and the similar symmetry was noted in other works (Suad Kunosic et al, 2012).

Conclusions: The total MGD value per woman is (2.36±0.22) mGy, which is between the limiting value of the Institute of Physical sciences in Medicine (2.0 mGy) and American College of Radiology (3.0 mGy) recommendation. These ensure that the mammography procedure performed in our centre is capable of achieving acceptable dose level for patient safety.