Improving Patient-Specific QA Effectiveness through Multi-Point Plastic Scintillation Detectors
Abstract
Purpose
The high modulation and spatial complexity of IMRT/VMAT treatment plans motivates the use of patient-specific quality assurance (QA) to verify accurate dose delivery. This study aims to enhance the interpretability of patient-specific QA by adding spatially and temporally resolved dose information using multiple plastic scintillation detectors (PSDs).
Methods
Ten clinical patient plans were delivered to an ArcCHECK (Sun Nuclear) with an ionization chamber (IC) (Exradin A12, Standard Imaging) and two PSDs (PRO-Series, Medscint) inserted into the phantom. The IC was positioned in a high-dose, low-gradient region according to clinical practice. PSDs were optimally placed at clinically relevant locations regardless of gradient or dose level, including different clinical target volumes (CTVs) and organs at risk (OARs). Local dose gradients were extracted from the TPS within a region of interest of 0.64 cm³ centered at each detector position, matching the sensitive volume of the ionization chamber.
Results
Measured doses agreed with TPS within 1 ± 1 cGy and 5 ± 8 cGy (mean ± standard deviation) for IC and PSDs, respectively. Larger PSD discrepancies were associated with placement in higher local dose gradients (on average 27% for PSDs versus 17% for IC). PSDs enabled multi-point dose sampling beyond the IC location; for example, in a prostate plan with nodal involvement, IC verified the nodal region while PSDs sampled the prostate CTV and an OAR. The air cavity introduced by the IC perturbed local dose deposition (up to −1.72% for a static field, measured 2 cm away), potentially affecting nearby detector measurements. In contrast, PSDs water-equivalence allowed multi-point measurements without perturbing the dose distribution.
Conclusion
Multi-point PSD measurements were evaluated for patient-specific QA, improving interpretability through sampling of targets and organs at risk. Future studies will investigate leveraging PSD temporal information to further enhance QA and insights into dose delivery.