Multi-institutional experimental validation of online adaptive proton therapy workflows

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Online adaptive proton therapy (APT) aims to improve treatment accuracy by adjusting plans based on daily anatomical changes.
• Non-adaptive workflows may struggle to account for significant interfractional variations, potentially compromising dose delivery.
• Experimental validation of different online APT strategies is crucial for clinical implementation.

Purpose of the Study:

• To experimentally validate two distinct online adaptive proton therapy (APT) workflows: daily APT (DAPT_PSI) and online adaptation (OA_MGH).
• To compare the dosimetric performance of these adaptive workflows against a non-adaptive (NA) approach using Gafchromic films and OSLDs.
• To assess the ability of APT to manage interfractional anatomical variations in an anthropomorphic head-and-neck phantom.

Main Methods:

• Proton therapy plans were optimized for a head-and-neck phantom with a prescription of 2.0 Gy(RBE) per fraction.
• Four fractions were simulated with varying internal anatomy.
• Three workflows were tested: DAPT_PSI (full online replanning), OA_MGH (online adaptation of beamlet fluences), and NA (couch-shift correction).
• Dosimetric measurements were performed using Gafchromic EBT3 films and optically stimulated luminescent dosimeters (OSLDs).

Main Results:

• Both DAPT_PSI and OA_MGH demonstrated significantly higher gamma pass rates (3%/3 mm) compared to the NA workflow (91.5%-96.1% and 94.0%-95.8% vs. 67.2%-93.1%, respectively).
• OSLDs confirmed the accuracy of absolute dose calculations for all tested methods.
• OA_MGH provided improved target coverage, while DAPT_PSI offered better normal tissue sparing, particularly for the brainstem.

Conclusions:

• This multi-institutional study provides the first experimental validation of two online APT workflow concepts.
• Both adaptive strategies offer significant dosimetric advantages over non-adaptive methods in managing interfractional anatomical variations.
• Online adaptive proton therapy is essential for optimizing dose delivery in scenarios with significant patient anatomy changes.