Geometric and dosimetric accuracy and imaging dose of the real-time tumour tracking system of a gimbal mounted linac.
OBJECTIVE
To suggest a comprehensive testing scheme to evaluate the geometric and dosimetric accuracy and the imaging dose of the VERO dynamic tumour tracking (DTT) for its clinical implementation.


METHODS
Geometric accuracy was evaluated for gantry 0° and 90° in terms of prediction (EP), mechanical (EM) and tracking (ET) errors for sinusoidal patterns with 10 and 20 mm amplitudes, 2-6 s periods and phase shift up to 1 s and for 3 patient patterns. The automatic 4D model update was investigated simulating changes in the breathing pattern during treatment. Dosimetric accuracy was evaluated with gafchromic films irradiated in static and moving phantom with and without DTT. The entrance skin dose (ESD) was assessed using a solid state detector and gafchromic films.


RESULTS
The RMS of EP, EM, and ET were up to 0.8, 0.5 and 0.9 mm for all non phased-shifted motion patterns while for the phased-shifted ones, EP and ET increased to 2.2 and 2.6 mm. Up to 4 updates are necessary to restore a good correlation model, according to type of change. For 100 kVp and 1 mA s X-ray beam, the ESD per portal due to 20 s fluoroscopy was 16.6 mGy, while treatment verification at a frequency of 1 Hz contributed with 4.2 mGy/min.


CONCLUSIONS
The proposed testing scheme highlighted that the VERO DTT system tracks a moving target with high accuracy. The automatic update of the 4D model is a powerful tool to guarantee the accuracy of tracking without increasing the imaging dose.
Unit of Medical Physics, European Institute of Oncology, Milano, Italy. Electronic address: cristina.garibaldi@ieo.it.
Cristina
C
Garibaldi
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Stefania
S
Russo
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Delia
D
Ciardo
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Stefania
S
Comi
Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milano, Italy.
Matteo
M
Seregni
Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milano, Italy.
Aurora
A
Fassi
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Gaia
G
Piperno
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Annamaria
A
Ferrari
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Floriana
F
Pansini
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Alessia
A
Bazani
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Rosalinda
R
Ricotti
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy; Department of Health Sciences, Università degli Studi di Milano, Milano, Italy.
Barbara Alicja
BA
Jereczek-Fossa
Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milano, Italy.
Guido
G
Baroni
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy; Department of Health Sciences, Università degli Studi di Milano, Milano, Italy.
Roberto
R
Orecchia
D016477:Artifacts; D005471:Fluoroscopy / Q000295:instrumentation*; D006801:Humans; D055595:Mechanical Phenomena; D009068:Movement; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000503:physiopathology; D010315:Particle Accelerators; D011829:Radiation Dosage; D011874:Radiometry; D013997:Time Factors
Gimbaled MV X-ray head; Imaging dose; Real-time dynamic tumour tracking; Tracking error