Treatment plan quality during online adaptive re-planning.

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Online adaptive radiotherapy aims to mitigate treatment plan degradation from inter-fractional changes.
• Time constraints pose challenges for real-time online re-planning during radiotherapy.

Purpose of the Study:

• To compare the dosimetric quality of online-adapted radiotherapy plans against their reference treatment plans.
• To evaluate the impact of online adaptation on target volumes and organs at risk across various treatment sites.

Main Methods:

• Retrospective analysis of 238 online-adapted plans from 52 patients treated on a ViewRay MRIdian Linac.
• Plans were optimized via segment weight adjustment or full re-optimization across five treatment sites (prostate, abdomen, liver, lung, pelvis).
• Dosimetric parameters for GTV, PTV, surrounding ring, and OARs were analyzed using the Wilcoxon signed-rank test.

Main Results:

• Online adaptation averaged 24 ± 6 minutes, including contouring, optimization, and QA.
• Gross tumor volume (GTV) was slightly larger in adapted plans (1.9% ± 9.0%), with a significant increase in GTV-D2% (0.40% ± 1.5%).
• Rectal dose significantly decreased by 4.7% ± 16% for prostate plans, while ring Dmean increased by 1.0% ± 3.6% overall.

Conclusions:

• Online-adapted plans demonstrate comparable dosimetric quality to reference plans.
• Organ at risk (OAR) doses were comparable or reduced, varying by treatment site.
• A slight increase in dose spillage was noted with online adaptation.