Abstract:
:Modern three-dimensional image-guided intracavitary high dose rate (HDR) brachytherapy is often used in combination with external beam radiotherapy (EBRT) to manage cervical cancer. Intrafraction motion of critical organs relative to the HDR applicator in the time between the planning CT and treatment delivery can cause marked deviations between the planned and delivered doses. This study examines offline adaptive planning techniques that may reduce intrafraction uncertainties by shortening the time between the planning CT and treatment delivery. Eight patients who received EBRT followed by HDR boosts were retrospectively reviewed. A CT scan was obtained for each insertion. Four strategies were simulated: (A) plans based on the current treatment day CT; (B) plans based on the first fraction CT; (C) plans based on the CT from the immediately preceding fraction; (D) plans based on the closest anatomically matched previous CT, using all prior plans as a library. Strategies B, C, and D allow plans to be created prior to the treatment day insertion, and then rapidly compared with the new CT. Equivalent doses in 2 Gy for combined EBRT and HDR were compared with online adaptive plans (strategy A) at D90 and D98 for the high-risk CTV (HR-CTV), and D2 cc for the bladder, rectum, sigmoid, and bowel. Compared to strategy A, D90 deviations for the HR-CTV were -0.5 ± 2.8 Gy, -0.9 ± 1.0 Gy, and -0.7 ± 1.0 Gy for Strategies B, C, and D, respectively. D2 cc changes for rectum were 2.7 ± 5.6 Gy, 0.6 ± 1.7 Gy, and 1.1 ± 2.4 Gy for Strategies B, C, and D. With the exception of one patient using strategy B, no notable variations for bladder, sigmoid, and bowel were found. Offline adaptive planning techniques can shorten time between CT and treatment delivery from hours to minutes, with minimal loss of dosimetric accuracy, greatly reducing the chance of intrafraction motion.
journal_name
J Appl Clin Med Physjournal_title
Journal of applied clinical medical physicsauthors
Liu H,Kinard J,Maurer J,Shang Q,Vanderstraeten C,Hayes L,Sintay B,Wiant Ddoi
10.1002/acm2.12462subject
Has Abstractpub_date
2018-11-01 00:00:00pages
316-322issue
6issn
1526-9914journal_volume
19pub_type
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