A randomized control trial evaluating fluorescent ink versus dark ink tattoos for breast radiotherapy

Abstract

Objective: The purpose of this UK study was to evaluate interfraction reproducibility and body image score when using ultraviolet (UV) tattoos (not visible in ambient lighting) for external references during breast/chest wall radiotherapy and compare with conventional dark ink.

Methods: In this non-blinded, single-centre, parallel group, randomized control trial, patients were allocated to receive either conventional dark ink or UV ink tattoos using computer-generated random blocks. Participant assignment was not masked. Systematic (∑) and random (σ) setup errors were determined using electronic portal images. Body image questionnaires were completed at pre-treatment, 1 month and 6 months to determine the impact of tattoo type on body image. The primary end point was to determine that UV tattoo random error (σ_setup) was no less accurate than with conventional dark ink tattoos, i.e. <2.8 mm.

Results: 46 patients were randomized to receive conventional dark or UV ink tattoos. 45 patients completed treatment (UV: n = 23, dark: n = 22). σ_setup for the UV tattoo group was <2.8 mm in the u and v directions (p = 0.001 and p = 0.009, respectively). A larger proportion of patients reported improvement in body image score in the UV tattoo group compared with the dark ink group at 1 month [56% (13/23) vs 14% (3/22), respectively] and 6 months [52% (11/21) vs 38% (8/21), respectively].

Conclusion: UV tattoos were associated with interfraction setup reproducibility comparable with conventional dark ink. Patients reported a more favourable change in body image score up to 6 months following treatment. Advances in knowledge: This study is the first to evaluate UV tattoo external references in a randomized control trial.

Figure 1.

Principle of invisible tattoos: (a) a wide-field fluorescence micrograph of a 10⁶ dilution of tattoo ink in Phosphate-buffered saline (PBS) (excited with 405 nm light) is demonstrating a dye molecule dispersed in the polymer; scale bar is 3 µm. (b) Spectral properties of ultraviolet (UV) tattoo ink: excitation (Exc.) (dashed red) and emission (Em.) (solid red) spectra of the UV ink and the emission spectrum of the handheld torch are used to visualize the dye (blue). (c) Manufactured sample skin tattooed with standard dark (left) and UV ink (right) under ambient (top) and UV light (bottom): UV is invisible under ambient light and clearly visible under UV illumination with a handheld UV torch; scale bar is 25 mm.

Figure 2.

The right anterior oblique tangential field digitally reconstructed radiograph to illustrate the u and v directions (arrows) in the imaging plane.

Figure 3.

Radiographer satisfaction scores for ultraviolet (UV) (left) and dark (right) ink tattoos at CT simulation and each week of treatment.