Erschienen in:
Journal of Applied Clinical Medical Physics, 19 (2018) 6, Seite 316-322
Sprache:
Englisch
DOI:
10.1002/acm2.12462
ISSN:
1526-9914
Entstehung:
Anmerkungen:
Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Modern three‐dimensional image‐guided intracavitary high dose rate (<jats:styled-content style="fixed-case">HDR</jats:styled-content>) brachytherapy is often used in combination with external beam radiotherapy (<jats:styled-content style="fixed-case">EBRT</jats:styled-content>) to manage cervical cancer. Intrafraction motion of critical organs relative to the <jats:styled-content style="fixed-case">HDR</jats:styled-content> applicator in the time between the planning <jats:styled-content style="fixed-case">CT</jats:styled-content> 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 <jats:styled-content style="fixed-case">CT</jats:styled-content> and treatment delivery. Eight patients who received <jats:styled-content style="fixed-case">EBRT</jats:styled-content> followed by <jats:styled-content style="fixed-case">HDR</jats:styled-content> boosts were retrospectively reviewed. A <jats:styled-content style="fixed-case">CT</jats:styled-content> scan was obtained for each insertion. Four strategies were simulated: (A) plans based on the current treatment day <jats:styled-content style="fixed-case">CT</jats:styled-content>; (B) plans based on the first fraction <jats:styled-content style="fixed-case">CT</jats:styled-content>; (C) plans based on the <jats:styled-content style="fixed-case">CT</jats:styled-content> from the immediately preceding fraction; (D) plans based on the closest anatomically matched previous <jats:styled-content style="fixed-case">CT</jats:styled-content>, 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 <jats:styled-content style="fixed-case">CT</jats:styled-content>. Equivalent doses in 2 Gy for combined <jats:styled-content style="fixed-case">EBRT</jats:styled-content> and <jats:styled-content style="fixed-case">HDR</jats:styled-content> were compared with online adaptive plans (strategy A) at <jats:italic>D</jats:italic><jats:sub>90</jats:sub> and <jats:italic>D</jats:italic><jats:sub>98</jats:sub> for the high‐risk <jats:styled-content style="fixed-case">CTV</jats:styled-content> (<jats:styled-content style="fixed-case">HR</jats:styled-content>‐<jats:styled-content style="fixed-case">CTV</jats:styled-content>), and <jats:italic>D</jats:italic><jats:sub>2 cc</jats:sub> for the bladder, rectum, sigmoid, and bowel. Compared to strategy A, <jats:italic>D</jats:italic><jats:sub>90</jats:sub> deviations for the <jats:styled-content style="fixed-case">HR</jats:styled-content>‐<jats:styled-content style="fixed-case">CTV</jats:styled-content> were −0.5 ± 2.8 Gy, −0.9 ± 1.0 Gy, and −0.7 ± 1.0 Gy for Strategies B, C, and D, respectively. <jats:italic>D</jats:italic><jats:sub>2 cc</jats:sub> 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 <jats:styled-content style="fixed-case">CT</jats:styled-content> and treatment delivery from hours to minutes, with minimal loss of dosimetric accuracy, greatly reducing the chance of intrafraction motion.</jats:p>