The role of adaptive planning in margin-reduced, MRI-guided stereotactic body radiotherapy to the prostate bed following radical prostatectomy: Post-hoc analysis of a phase II clinical trial

The role of adaptive planning in margin-reduced, MRI-guided stereotactic body radiotherapy to the prostate bed following radical prostatectomy: Post-hoc analysis of a phase II clinical trial

•CTV and PTV volume and shape were well-preserved. A 3 mm isotropic PTV margin allowed for adequate CTV coverage in more than 90% of patients.•There were significant changes in bladder volume, rectum volume, and rectal wall shape. Half of fractions failed to meet all bladder, rectum, and rectal wall...

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Bibliographic Details
Published in:Radiotherapy and oncology 2023-06, Vol.183, p.109631-109631, Article 109631
Main Authors: Nikitas, John, Smith, Lauren M., Gao, Yu, Ma, Ting Martin, Sachdeva, Ankush, Yoon, Stephanie M., Jiang, Tommy, Low, Daniel A., Ballas, Leslie K., Steinberg, Michael L., Cao, Minsong, Kishan, Amar U.
Format: Article
Language:eng
Subjects:
Adaptive radiotherapy
MR-guided radiotherapy
Post-prostatectomy
Prostate cancer
Stereotactic body radiotherapy
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Summary:•CTV and PTV volume and shape were well-preserved. A 3 mm isotropic PTV margin allowed for adequate CTV coverage in more than 90% of patients.•There were significant changes in bladder volume, rectum volume, and rectal wall shape. Half of fractions failed to meet all bladder, rectum, and rectal wall OAR dose constraints.•Adaptive planning allowed all fractions to meet adequate CTV and PTV coverage and more than three-quarters of fractions to meet all OAR dose constraints.•All fractions that continued to exceed at least one maximum dose constraints occurred in patients with simultaneous integrated boosts of 37.5 to 40 Gy to gross disease that was close to the bladder or rectum.•Adaptive planning appears to be feasible and effective in the post-prostatectomy setting. We examined the interfractional variations of clinical target volumes (CTVs), planning target volumes (PTVs), and organs-at-risk (OARs) in patients receiving MRI-guided stereotactic body radiotherapy (SBRT) to the prostate bed and evaluated the potential role of adaptive planning. 31 patients received 30–34 Gy in five fractions to the prostate bed on a phase II clinical trial. OARs, CTVs, and PTVs were retrospectively contoured on daily pretreatment MRIs (n = 155). Geometric comparisons were made between initial planning contours and daily pretreatment contours. Predicted treatment plans for each fraction were evaluated using the following constraints: CTV V95%>93%, PTV V95%>90%, bladder Dmax 
ISSN:0167-8140
1879-0887