Long-time clinical experience in patient setup for several particle therapy clinical indications: management of patient positioning and evaluation of setup reproducibility and stability

Abstract

Objective: Accurate patient positioning is crucial in particle therapy due to the geometrical selectivity of particles. We report and discuss the National Center for Oncological Hadrontherapy (CNAO) experience in positioning accuracy and stability achieved with solid thermoplastic masks fixed on index base plates and assessed by daily orthogonal X-ray imaging.

Methods: Positioning data were retrospectively collected (between 2012 and 2018) and grouped according to the treated anatomical site. 19696 fractions of 1325 patients were evaluated.The study was designed to assess:(i) the number of fractions in which a single correction vector was applied(SCV);(ii) the number of fractions in which further setup verification was performed (SV);(iii) the number of fractions in which SV lead to an additional correction within (MCV<5min) or after (MCV>5min) 5 minutes from the first setup correction;(iv) the systematic (Σ) and random (σ) error components of the correction vectors applied.

Results: A SCV was applied in 71.5% of fractions, otherwise SV was required. In 30.6% of fractions with SV, patient position was not further revised. In the remaining fractions, MCV<5min and MCV>5min were applied mainly in extracranial and cranial sites respectively.Interfraction Σ was ≤ 1.7 mm/0.7° and σ was ≤ 1.2 mm/0.6° in cranial sites while in extracranial sites Σ was ≤ 5.5 mm/0.9° and σ was ≤4.4 mm/0.9°. Setup residuals were submillimetric in all sites. In cranial patients, maximum intrafractional Σ was 0.8 mm/0.4°.

Conclusion: This report extensively quantifies inter- and intrafraction setup accuracy on an institutional basis and confirms the need of image guidance to fully benefit from the geometrical selectivity of particles.

Advances in knowledge: The reported analysis provides a board institutional data set on the evaluation of patient immobilization and bony anatomy alignment for several particle therapy clinical indications.

Figure 1.

Illustrative table summarizing some exemplary setups for each analyzed treated site. (*) bite block used to stabilize the mandible for the target in its close proximity.

Figure 2.

Schematic representation of the analyzed treatment workflow. MCV, multiple correctionvector; SCV, single correction vector; SV, setup verification.

Figure 3.

Distribution of setup correction vectors applied over the course of treatment fractions grouped by treated anatomical site. Boxplots report the distribution of the initial setup correction parameters (first CV), the distribution of the additional correction vectors applied within 5 min (MCV <5 min) and after 5 min (MCV >5 min) from the first setup correction. On each boxplot, the central mark indicates the median, and the bottom and top edges of the box indicate the 25th and 75th percentiles, respectively. The whiskers extend to the most extreme data points not considered outliers. Box whiskers contains approximately 99.3% of data. R-L, right left direction; I-S, inferosuperior direction; MCV, multiple correctionvector; P-A, posteroanterior direction.

Figure 4.

Distribution of the initial setup correction vectors (first CV) for prone and supine treatments grouped by treated anatomical site. Significant difference according to ANOVA test (p < 0.005) are marked with an asterisk (*). CV, correction vector; ANOVA, analysis of variance.