Commissioning a small-field biological irradiator using point, 2D, and 3D dosimetry techniques

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate dosimetry is critical for small-field radiation therapy.
• Commissioning new irradiator systems requires thorough characterization.
• Evaluating dosimetry systems for small fields presents unique challenges.

Purpose of the Study:

• To commission the XRad225Cx small-field biological irradiator.
• To determine output factors (OF), percent-depth-dose (PDD), and dose profiles using multiple dosimetry systems.
• To compare the performance of ion-chambers, radiochromic film (EBT2), and a 3D dosimetry system (DLOS/PRESAGE®).

Main Methods:

• Utilized three independent dosimetry systems: ion-chambers, 2D EBT2 film, and 3D DLOS/PRESAGE®.
• Performed in-air ionization chamber measurements for reference dose rates and OFs (TG61 formalism).
• Acquired PDD, profiles, and OFs at multiple depths using EBT2 film and PRESAGE® in solid water.

Main Results:

• Output factors decreased with smaller field sizes, with dramatic drops observed below 13 mm.
• PRESAGE® and EBT2 film showed good agreement for OFs (<20 mm) and PDDs (1-4 cm depth).
• Ion-chamber, EBT2 film, and PRESAGE® demonstrated overall consistency in measured OFs, PDDs, and profiles.

Conclusions:

• Combining 2D and 3D measurements is valuable for comprehensive irradiator commissioning.
• PRESAGE® 3D dosimetry offers efficient and accurate measurements for small fields, minimizing alignment errors.
• Film measurements are time-consuming and challenging for small fields; PRESAGE® has limitations for superficial data accuracy.