Main Session
Sep
28
PQA 04 - Breast Cancer, Patient Reported Outcomes/QoL/Survivorship, Functional Radiation Medicine, Hematologic Malignancies, Palliative Care, and International/Global Oncology
Presenter(s)
John Hoyle, MD, MS - University of Alabama Birmingham School of Medicine, Birmingham, AL
J. Hoyle1, C. Stanley2, J. A. Pogue2, M. Soike1, K. S. Keene1, M. C. Dobelbower1, C. Cardenas2, D. N. Stanley2, and H. Boggs1; 1University of Alabama at Birmingham Department of Radiation Oncology, Birmingham, AL, 2University of Alabama at Birmingham, Birmingham, AL
Purpose/Objective(s):
This study investigates the feasibility and safety of reduced planning target volume (PTV) margin of 2mm in patients receiving accelerated partial breast irradiation (APBI) delivered using online adaptive radiation therapy (OART) with surface-guided RT (SGRT).Materials/Methods:
Ethos v2.0 (Varian Medical Systems) platform was used for daily adaption delivered on nonconsecutive days to a dose of 30 Gy in 5 fractions. A 10 mm clinical target volume (CTV) was added to the lumpectomy cavity with a reduced PTV margin of 2 mm per protocol. Real time surface tracking using Identify was employed to ensure that target drift did not exceed the PTV margin. Cone beam computed tomography (CBCT) was obtained at each fraction for planning, verification prior to treatment with positional correction, and post-treatment acquired immediately after beam-off (no correction applied). For each patient enrolled, 2 adaptive fractions were selected and all fractions requiring intrafraction shift based on surface tracking were analyzed. CTV target coverage was assessed for the planning CBCT, verification CBCT, and post-treatment CBCT. Fractions in which SGRT triggered repeat CBCT and re-alignment also had coverage on the triggered CBCT analyzed. All lumpectomy cavities with respective CTVs were recontoured by one physician and then coverage was compared on the adaptive plan and post treatment CBCT.Results:
At the time of data collection, 13 patients suitable for APBI according to ASTRO consensus guidelines were consented for participation and completed therapy which led to 30 total fractions for analysis: 26 per protocol and 4 due to intrafraction shift. CTV coverage on planning, verification, and post-treatment scans exceeded 95% agreement universally (V100% = 96.7% and D95% = 100.8%), while 3 of the 4 scans triggered by surface guidance showed unacceptable coverage (CTV V100% < 95%). These results are shown in Table 1.Conclusion:
Adaptive SBRT for APBI with 2 mm margin appears robust against target drift with utilization of real time surface tracking. Our results suggest that 2 mm PTV margin was feasible and may be an appropriate standard for APBI with online adaptive radiotherapy and surface guidance.| Mean CTV V100 (%) | Max CTV V100 (%) | Min CVT V100 (%) | Std Dev CTV V100 (%) | Mean CVT D95 (%) | Max CTV D95 (%) | Min CTV D95 (%) | Std Dev CTV D95 (%) | |
| Planning | 99.9 | 100.0 | 99.3 | 0.2 | 106.4 | 110.9 | 102.4 | 2.5 |
| Verification | 99.2 | 100.0 | 96.7 | 0.7 | 105.0 | 108.5 | 101.8 | 2.2 |
| Post | 99.2 | 100.0 | 97.3 | 0.8 | 105.0 | 109.3 | 100.8 | 2.3 |
| Triggered | 90.8 | 95.9 | 81.3 | 6.5 | 93.2 | 101.2 | 79.4 | 9.5 |