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Published on: June 7, 2015
Cone Beam CT-guided Online Adaptive Radiotherapy for Prostate Stereotactic Body Radiation Therapy
D M McClatchy1, J Pursley2, C Esposito3
1Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts, USA.
Purpose:
While CT-guided online adaptive radiotherapy (CTgART) is an emerging treatment modality for prostate stereotactic body radiotherapy (SBRT), the feasibility and dosimetric improvements have not yet been quantified in a large multi-center cohort.
Methods:
A cohort of 74 prostate cancer patients treated with a 5-fraction SBRT course of CTgART between 01/2023-06/2024 was collected from two centers and analyzed retrospectively. Timestamps of the adaptive process and the daily contoured volumes were collected in addition to the dose volume histogram (DVH) data for both the scheduled and adapted plans. The duration of the adaptive process and pre-treatment verification imaging shift magnitudes were compared. Differences in DVH metrics between the scheduled and adapted plans were analyzed.
Results:
The adapted plan was chosen in 95% of all fractions, with 81% of patients having all 5 fractions adapted. The mean adaptive planning time was 18.7 ± 4.8 minutes (mean ± standard deviation). The mean shift in each cardinal direction was <2 mm on the pretreatment verification image and was correlated with the adaptive planning time. For 90% and 68% of all fractions, the daily contoured clinical target volume (CTV) was within 5cc and 5% of the volume drawn at CT simulation, respectively. The two most common DVH improvements on the adapted plan were the planning target volume (PTV) V100% and the rectum V15Gy, with 52% and 37% of fractions exhibiting at least a 5% change, respectively. Overall, 85% of all fractions showed at least 1 clinically meaningful DVH metric improvement with adaptation. Body mass index, treated seminal vesicle length, and the number of DVH metrics improved on the first fraction were correlated with the number of DVH metric improvements during subsequent fractions.
Conclusions:
CTgART for SBRT treatment of prostate cancer can be done in a timely and reproducible manner while substantially improving the dosimetry of target coverage and OAR sparing.
