Liver Tumor Motion and Reconstructed Doses in a Clinical Trial of Respiratory-Gated Proton Therapy for Hepatocellular Carcinoma.
Saber Nankali, Esben Schjødt Worm, Jakob Borup Thomsen et al.
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In 30 seconds
This prospective phase II clinical trial evaluated tumor motion and reconstructed delivered doses during respiratory-gated pencil beam scanning proton therapy in 16 patients with hepatocellular carcinoma. Treatment was planned at exhale and delivered in 15 fractions. Mean tumor-position error during spot delivery was greatest in the cranio-caudal direction (2.9 ± 1.2 mm). Motion increased the clinical target volume homogeneity index by 4.1 ± 2.6 percentage points for individual fractions, but by 1.5 ± 2.1 percentage points when accumulated across analyzed fractions. Weekly control scans showed minimal dose variation from anatomic changes.
Key findings
- Mean tumor-position errors during spot delivery were 1.1 ± 0.8 mm left-right, 2.9 ± 1.2 mm cranio-caudal, and 1.6 ± 0.7 mm anterior-posterior.
- Motion increased the CTV homogeneity index by 4.1 ± 2.6 percentage points per fraction and 1.5 ± 2.1 percentage points across analyzed fractions.
- Weekly control 4DCTs showed minimal CTV dose variation from interfractional anatomic changes.
Why it matters
Respiratory motion can alter proton dose distribution within a treatment fraction, even with exhale gating and image-guided setup. The smaller accumulated homogeneity-index change suggests that fractionation may reduce the overall impact of these motion-related interplay effects. The findings also indicate that, in this trial, anatomic changes between fractions had little effect on reconstructed CTV dose.
What to keep in mind
The study included 16 patients, and motion was measured or estimated at only 3-8 fractions per patient; delivered doses were reconstructed rather than directly measured.