Digital breast tomosynthesis dosimetry using radiochromic film

DBT is being adopted more widely because it offers improved lesion detection and reduces the issue of tissue overlap compared to conventional 2D mammography. Digital breast tomosynthesis (DBT) is increasingly used, but oblique X-ray angles and scatter produce complex dose distributions not fully represented by mean glandular dose (MGD). This study aimed to quantify two-dimensional absorbed dose distributions in a breast-mimicking phantom using Gafchromic LD-V1 film under clinical DBT conditions.

A 40-mm-thick polymethyl methacrylate(PMMA) phantom embedded with LD-V1 films was irradiated on a clinical DBT unit (30 kVp, 300 mAs). Films were calibrated against an ionization chamber with doses from 0 to 75 mGy. Films placed at 0, 20, and 40 mm depths underwent ten repeated exposures. Scanned film images were analyzed to obtain two-dimensional dose maps.

Absorbed dose declined with depth: 8.3 mGy at the surface, 2.0 mGy at 20 mm, and 0.5 mGy at 40 mm (∼25 % and <10 % of surface dose). Lateral distributions were nonuniform, with higher peripheral doses and lower doses near the chest wall at depth, reflecting beam geometry and scatter. At 60 mm from the chest wall, dose was lower than the phantom mean, suggesting that single-point MGD may underestimate breast dose.

Film dosimetry was feasible and provided detailed DBT dose mapping. Findings confirmed strong depth-dependent attenuation and peripheral hotspots not captured by MGD, supporting film-based two-dimensional dosimetry as a complement to conventional methods.

Reliance on MGD may obscure dose heterogeneity. Incorporating film-based dose mapping could improve assessment accuracy and inform clinical risk-benefit evaluation.