Ion chamber and film‐based quality assurance of mixed electron‐photon radiation therapy

Purpose In previous work, we demonstrated that mixed electron-photon radiation therapy (MBRT) produces treatment plans with improved normal tissue sparing and similar target coverage, when compared to photon-only plans. The purpose of this work was validate the MBRT delivery process on a Varian TrueBeam accelerator laying groundwork for patient-specific quality assurance (QA) protocol based ion chamber point measurements 2D film measurements. Methods MC beam models used calculate dose distributions each modality (photons/electrons) were validated single-angle plan delivered slab Solid Water phantom positioned at depth 2 cm. measured absorbed calculated dose. To clinical deliveries, polymethyl methacrylate (PMMA) cylinder machined holes made fit an ionization chamber. A complex involving photon arc three electron angles created aim reproducing clinically realistic distribution in typical soft sarcoma tumours extremities. PMMA cylinder. Point taken Exradin A1SL two nominal depths: 1.4 cm 2.1 also second identical insert depth, where placed. An existing EGSnrc user-code, SPRRZnrc, modified stopping power ratios between any materials same voxelized geometry calculation purposes. This code, called SPRXYZnrc, correction factor, , accounting differences fluence spectrum measurement reference conditions. uncertainty associated neglecting potential perturbation factors using approach estimated. Results from good agreement simulated distribution, gamma pass rate 96.1% 3%/2 mm criteria. For delivery, criteria, 97.3%. total agreed MC-simulated within 2.1%. amounted to, most, 4% measurement. However, individual contribution low energies proved difficult precisely measure due their steep gradients, disagreements up 28% ± 15% (6 MeV). Ion procedure beams achieved less than 5 min, entire validation including setup performed 30 min. Conclusion doses indicates obtained planning algorithm are realistically achievable. SPRXYZnrc code allowed convenient calculations simultaneously distributions, QA practical use. Further investigation is needed establish accuracy our energies.