Degree

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

Document Type

Dissertation

Abstract

Purpose: Daily anatomical changes can invalidate the geometric, dosimetric, and biological assumptions of reference radiotherapy plans, yet quantitative evidence describing fraction-level deviations across disease sites remains limited. This work developed and evaluated a metric-based framework for daily dose assessment to characterize temporal treatment behavior and inform adaptive decision-making in Head and Neck (H&N) radiotherapy and Prostate stereotactic body radiotherapy (SBRT). Methods: A web-based Dashboard was created to compute geometric, dosimetric, and radiobiological metrics from daily dose recalculations. Calculations were first verified against a commercial treatment-planning analysis platform. Daily dose on anatomy-of-the-day was reconstructed using CBCT-based pseudo-CTs for H&N and daily MR images for Prostate. Seventy-two patients were analyzed (H&N: n=18, 28–35 fractions; Prostate SBRT: n=54, 5 fractions). Five metrics were evaluated per fraction: displacement, intrafraction Dice, interfraction Dice, objective scores for targets and organs at risk (OARs), and a radiobiology score, with a composite radar area summarizing overall deviation. Results: Verification demonstrated strong agreement between the Dashboard and reference calculations across all metric classes within predefined tolerances. In H&N treatments, averaged dose–volume histograms and objective pass rates revealed cumulative dose changes, particularly increasing OAR dose and hotspot-sensitive target deviations over time. Longitudinal metrics showed coordinated upward shifts in interfraction Dice, OAR objective scores, radiobiology, and radar area, with notable escalation phases around fractions 10–13 and 18–22. In contrast, Prostate SBRT exhibited substantial fraction-to-fraction variability without sustained temporal drift. OAR metrics fluctuated daily, while target coverage metrics were frequently degraded from the first fraction and remained persistently variable. Radar area increased over time for H&N but remained elevated and stable for Prostate, reflecting progressive versus fraction-specific deviation patterns. Conclusions: H&N radiotherapy behaves as a time-dependent system with cumulative anatomical change, supporting threshold-based reassessment during treatment. Prostate SBRT demonstrates predominantly day-specific variability, supporting fraction-level evaluation rather than fixed replanning schedules. Metric-based daily dose assessment provides objective, site-specific insight that may enable more efficient and clinically responsive adaptive radiotherapy strategies.

Date

3-26-2026

Committee Chair

Stathakis, Sotiri

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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