3076 - Prostate Stereotactic Body Radiation Therapy Utilizing Cone Beam CT-Guided Online Adaptive Radiotherapy: Clinical Efficiency, Dosimetric Benefits and Clinical Characteristics Associated with Benefit
Presenter(s)
D. M. McClatchy III1, J. Pursley2, C. Esposito3, L. L. Zhu4, K. Kim5, C. Foote6, C. Hancox7, Y. H. Hu8, P. L. Nguyen9, D. T. Miyamoto10, N. E. Martin11, J. A. Efstathiou6, J. E. Leeman12, J. S. Bredfeldt8, and S. C. Kamran6; 1Department of Radiation Oncology, Massachusetts General Hospital/Mass General Brigham and Harvard Medical School, Boston, MA, 2Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 3National Cancer Intitute, Bethesda, MD, 4Harvard Radiation Oncology Program, Boston, MA, 5Massachusetts General Hospital Cancer Center, Boston, MA, 6Massachusetts General Hospital, Boston, MA, 7Department of Radiation Oncology, Brigham and Women’s Hospital/Dana-Farber Cancer Institute, Boston, MA, 8Department of Radiation Oncology, Brigham and Women’s Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, 9Mass General Brigham Cancer Institute, Boston, MA, 10Massachusetts General Hospital and Harvard Medical School, Boston, MA, 11Brigham and Women's Hospital, Boston, MA, 12Department of Radiation Oncology, Mass General Brigham, Harvard Medical School, Boston, MA
Purpose/Objective(s):
CT-guided online adaptive radiotherapy (CTgART) can be used to adjust for daily anatomic variations during prostate stereotactic body radiotherapy (SBRT), but often at a cost of increased personnel resources. The treatment efficiency, dosimetric improvements, and patient characteristics associated with CTgART benefit have yet to be demonstrated in a large multi-center cohort for this indication.Materials/Methods:
From 01/2023-06/2024, a sequential cohort of 74 prostate cancer patients treated at two centers with unique coverage models was collected and analyzed retrospectively. All patients received a 5-fraction CTgART SBRT course. Treatment metadata, including timestamps of the adaptive process, pre-treatment alignment shifts, and daily contoured volumes, were collected along with the dose volume histogram (DVH) data for both the scheduled and adapted plans. The elapsed time of the adaptive process was analyzed and compared to the pre-treatment verification imaging shift magnitudes. Differences in DVH metrics between the scheduled and adapted plans were identified and analyzed. Associations between patient characteristics and the frequency of DVH metric improvements in the adaptive versus scheduled plans were explored.Results:
Overall, 81% of patients had all 5 fractions adapted, and the adapted plan was chosen in 95% of all fractions. The elapsed time between initial and pre-treatment verification imaging was 18.7 ± 4.8 minutes, quantifying the time for adaptation. The mean shift in each cardinal direction was <2 mm on the pretreatment verification image, while the mean shift magnitude was correlated with the elapsed adaptive planning time (r=0.31, p<0.00001). The daily contoured clinical target volume (CTV) was within 5cc of the volume drawn at CT simulation for 90% of all fractions. On 85% of all fractions, at least 1 DVH metric improved significantly with the adaptation. The most frequently improved target metric was planning target volume (PTV) V100%, with increases of 5%, 10%, and 15% occurring in 52%, 28%, and 15% of all fractions. The most common OAR DVH metric improvement was the rectum V15Gy with 37% of fractions improving by 5% or more. Both body mass index (r=0.21, p=0.0001) and treated seminal vesicle length (r=0.2, p=0.0001) were weakly but significantly correlated with frequency of DVH metric improvement. In addition, the number of DVH metric improvements observed during the first fraction were correlated (r=0.48, p<0.00001) with DVH improvements during subsequent fractions.Conclusion:
Despite additional personnel resources needed, CTgART for prostate SBRT can be done efficiently and lead to dosimetric improvements of target coverage and OAR sparing. Potential patient characteristics associated with adaptive benefit have been identified.