Image guided particle therapy in CNAO room 2: implementation and clinical validation.

In this contribution we describe the implementation of a novel solution for image guided particle therapy, designed to ensure the maximal accuracy in patient setup. The presented system is installed in the central treatment room at Centro Nazionale di Adroterapia Oncologica (CNAO, Italy), featuring two fixed beam lines (horizontal and vertical) for proton and carbon ion therapy. Treatment geometry verification is based on robotic in-room imaging acquisitions, allowing for 2D/3D registration from double planar kV-images or 3D/3D alignment from cone beam image reconstruction. The calculated six degrees-of-freedom correction vector is transferred to the robotic patient positioning system, thus yielding automated setup error compensation. Sub-millimetre scale residual errors were measured in absolute positioning of rigid phantoms, in agreement with optical- and laser-based assessment. Sub-millimetre and sub-degree positioning accuracy was achieved when simulating setup errors with anthropomorphic head, thorax and pelvis phantoms. The in-house design and development allowed a high level of system customization, capable of replicating the clinical performance of commercially available products, as reported with preliminary clinical results in 10 patients.

Commissioning and quality assurance of an integrated system for patient positioning and setup verification in particle therapy.

In an increasing number of clinical indications, radiotherapy with accelerated particles shows relevant advantages when compared with high energy X-ray irradiation. However, due to the finite range of ions, particle therapy can be severely compromised by setup errors and geometric uncertainties. The purpose of this work is to describe the commissioning and the design of the quality assurance procedures for patient positioning and setup verification systems at the Italian National Center for Oncological Hadrontherapy (CNAO). The accuracy of systems installed in CNAO and devoted to patient positioning and setup verification have been assessed using a laser tracking device. The accuracy in calibration and image based setup verification relying on in room X-ray imaging system was also quantified. Quality assurance tests to check the integration among all patient setup systems were designed, and records of daily QA tests since the start of clinical operation (2011) are presented. The overall accuracy of the patient positioning system and the patient verification system motion was proved to be below 0.5 mm under all the examined conditions, with median values below the 0.3 mm threshold. Image based registration in phantom studies exhibited sub-millimetric accuracy in setup verification at both cranial and extra-cranial sites. The calibration residuals of the OTS were found consistent with the expectations, with peak values below 0.3 mm. Quality assurance tests, daily performed before clinical operation, confirm adequate integration and sub-millimetric setup accuracy. Robotic patient positioning was successfully integrated with optical tracking and stereoscopic X-ray verification for patient setup in particle therapy. Sub-millimetric setup accuracy was achieved and consistently verified in daily clinical operation.

Automated fiducial localization in CT images based on surface processing and geometrical prior knowledge for radiotherapy applications.

We propose a novel method for radio-opaque external marker localization in CT scans for infrared (IR) patient set-up in radiotherapy. Efforts were focused on the quantification of uncertainties in marker localization in the CT dataset as a function of algorithm performance. We implemented a 3-D approach to fiducial localization based on surface extraction and marker recognition according to geometrical prior knowledge. The algorithm parameters were optimized on a clinical CT dataset coming from 35 cranial and extra-cranial patients; the localization accuracy was benchmarked at variable image resolution versus laser tracker measurements. The applicability of conventional IR optical tracking systems for localizing external surrogates in daily patient set-up procedures was also investigated in 121 proton therapy treatment sessions. Our study shows that the implemented algorithm features surrogates localization with uncertainties lower than 0.3 mm and with a true positive rate of 90.1%, being this latter mainly influenced by fiducial homogeneity in the CT images. The reported clinical validation in proton therapy confirmed the submillimetric accuracy and the expected algorithm sensitivity. Geometrical prior knowledge allows judging the reliability of the extracted fiducial coordinates, ensuring the highest accuracy in patient set-up.