ESTRO 2022 - Abstract Book

S653

Abstract book

ESTRO 2022

Conclusion TPRs displayed considerable variation across institutions and time and were vulnerable to COVID 19 related restrictions. Even with a straight-forward trial design and the prospect of a shortened LR-RT course, only one institution succeeded in accruing more than half of the patients likely to be trial candidates. The results indicate, that a TPR around 50% was feasible for the best performing department, thus implying a large potential for better trial accrual in most centres. In future trials, systematic monitoring of TPRs and reasons for not participating should be undertaken to optimize trial designs and accrual procedures.

PD-0741 Tattoo-less Accelerated Partial Breast Irradiation (APBI) using Surface Imaging

B. Mueller 1 , Y. Song 2 , W. Chia-Ko 2 , H. Hsu 3 , X. Zhai 2 , P. Tamas 1 , S. Powell 1 , O. Cahlon 1 , B. McCormick 1 , A. Khan 1 , E. Gillespie 1 , L. Hong 2 , L. Cervino-Arriba 2 , B. Zhao 2 , L. Braunstein 1 1 MSKCC, Radiation Oncology, New York, USA; 2 MSKCC, Medical Physics, New York, USA; 3 Columbia University, Radiology, New York, USA Purpose or Objective Skin tattoos represent the 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, time, and dosimetry between “tattoo-less” and traditional tattoo-based setup techniques. Materials and Methods Patients receiving accelerated partial breast irradiation (APBI) underwent traditional tattoo-based setup (TTB), alternating daily with a tattoo-less setup via surface imaging using AlignRT (ART). Following initial setup, position was verified by daily kV imaging, with matching on surgical clips representing ground truth. Translational shifts (TS) and rotational shifts (RS) were ascertained as were setup time and total in-room time. Delivered dosimetry was calculated using the reverse isocenter shift technique. Statistical analyses used the Wilcoxon Signed Rank test and Pitman-Morgan variance test. Results A total of 43 APBI patients were analyzed for this study. For tattoo-less setup via ART, the median absolute TS were 0.31cm vertical (range: 0.08-0.82), 0.23cm lateral (0.05-0.86), and 0.26cm longitudinal (0.02-0.72). For TTB setup, the corresponding median TS were 0.34cm (0.05-1.98), 0.31cm (0.09-1.84), and 0.34cm (0.08-1.25). The median magnitude shifts were 0.59 (0.30-1.31) for ART and 0.80 (0.27-2.13) for TTB. ART was not statistically distinguishable from TTB in terms of TS (p=0.154, 0.059, 0.021, respectively) and was superior to TTB for magnitude shift (p<0.001). Variance testing of each TS variable also showed an advantage of ART over TTB (p ≤ 0.001, 0.001, 0.005, respectively). The median absolute RS for ART was 0.64° rotation (range:0.00-1.90), 0.65° roll (0.05-2.90), 0.30° pitch (0.00-1.50). The corresponding median RS for TTB were 0.80° (0.00-2.50), 0.64° (0.00-3.00), and 0.46° (0.00-2.90). ART setup was not statistically different from TTB in terms of RS (p=0.868, 0.236, 0.079, respectively). ART showed lower variance than TTB in terms of pitch (p=0.009). The median total in-room time was 15.42 minutes (range: 9.80-37.00) for ART and 17.25 minutes (9.50-46.00) for TTB (p=0.008). The median setup time was 11.12 minutes (5.58-31.54) for ART and 13.00 minutes (5.66-42.90) for TTB (p=0.001). Moreover, ART had a narrower distribution of setup time with fewer lengthy outliers vs TTB.