Hao-Yun Hsu*, Yulin Song, Boris A Mueller, Paul Tamas, Lior Z Braunstein, Memorial Sloan-Kettering Cancer Center, New York, NY

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  H Hsu

PO-BPC-Virtual-19 (Saturday, 4/17/2021)   [Eastern Time (GMT-4)]

Purpose: Skin tattoos represent the long-held standard for surface alignment and setup of breast cancer radiotherapy yet contribute to adverse cosmesis and patient dissatisfaction. With the advent of contemporary surface imaging technology, we evaluated setup accuracy, setup time, total in-room time, and dosimetry between “tattoo-less” and traditional tattoo-based setup techniques.

Methods: Patients receiving accelerated partial breast irradiation (APBI) underwent traditional tattoo-based setup, alternating daily with setup by AlignRTv5.1 (tattooless). Following initial setup, the position was verified by daily kV imaging, with matching on surgical clips to represent ground truth. Translational shifts prompted by kV imaging were ascertained as were setup time and total in-room time. Delivered dosimetry was calculated using the reverse isocenter shift technique. Statistical analysis was performed using Paired Samples t-test.

Results: For the first ten patients analyzed, the mean shifts were -0.215±0.146 cm, 0.111±0.138 cm, and -0.148±0.174 cm for the AlignRT-based setup in vertical, lateral, and longitudinal direction respectively. The mean shifts using tattoo-based setup were 0.095±0.181 cm, -0.06±0.326 cm, and 0.075±0.105 cm in vertical, lateral and longitudinal direction respectively. AlignRT-based setup was not significantly different from tattoo-based setup in terms of translational shifts. No statistically significant difference was found in patient setup time and total in-room time between the two techniques. However, AlignRT-based setup showed a narrower distribution in setup time with fewer lengthy outliers as in the tattoo-based approach. The setup time range for tattoos was 157-2481 seconds versus for AlignRT: 215-1323 seconds.

Conclusion: These results suggest that a tattooless setup approach to breast radiotherapy with AlignRT may be sufficiently accurate to obviate the need for surface tattoos. Further analyses among large cohorts and including all six degrees of freedom (three translational dimensions along with pitch, roll, and yaw) will determine whether tattoo-based approaches can be replaced by surface imaging.

Keywords

Not Applicable / None Entered.

Taxonomy

TH- RT Interfraction Motion Management: setup errors, immobilization, localization

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