RESUMEN
PURPOSE: 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.
Asunto(s)
Fluoroscopía/instrumentación , Neoplasias/diagnóstico por imagen , Aceleradores de Partículas , Dosis de Radiación , Artefactos , Humanos , Fenómenos Mecánicos , Movimiento , Neoplasias/fisiopatología , Radiometría , Factores de TiempoRESUMEN
PURPOSE: This study aimed to compare procedures for dynamic tumour tracking (DTT) using a gimbal-mounted linac between centres in Japan (KU-IBRI) and Belgium (UZB), to quantify tracking error (TE), and to estimate tumour-fiducial uncertainties and PTV margins. METHODS: Twenty-two patients were evaluated. TE was divided into components originating from the patient, fraction, segment, and residuals. RESULTS: KU-IBRI applied DTT to lung cancer, while UZB treated both the lung and liver. Patients from UZB were younger and had a higher body mass index. DTT procedures differed in the use of body fixation, correction for set-up error, type of fiducial markers, and goodness of fit of correlation model. TE was larger at UZB in the intra-fraction components, whereas the tumour-fiducial uncertainties were estimated to be larger at KU-IBRI. These results ultimately led to similar PTV margins at both centres (2.1, 4.2, and 2.6 mm for KU-IBRI; 2.4, 3.6, and 2.0 mm for UZB in LR, AP, and SI, respectively, for 99% coverage of patients). CONCLUSION: Several differences in procedures and patient characteristics were observed that affected TE and tumour-fiducial uncertainties. This analysis confirmed similar accuracy in DTT delivery and adequate PTV margins in the different centres based on their local specific workflows.
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Neoplasias/radioterapia , Planificación de la Radioterapia Asistida por Computador/métodos , Bélgica , Marcadores Fiduciales , Humanos , Japón , IncertidumbreRESUMEN
PURPOSE: To evaluate feasibility and acute toxicities after dynamic tumour tracking (DTT) irradiation with real-time monitoring for lung tumours using a gimbal mounted linac. MATERIALS AND METHODS: Spherical gold markers were placed around the tumour using a bronchoscope prior to treatment planning. Prescription dose at the isocentre was 56 Gy in 4 fractions for T2a lung cancer and metastatic tumour, and 48 Gy in 4 fractions for the others. Dose-volume metrics were compared between DTT and conventional static irradiation using in-house developed software. RESULTS: Of twenty-two patients enrolled, DTT radiotherapy was successfully performed for 16 patients, except 4 patients who coughed out the gold markers, one who showed spontaneous tumour regression, and one where the abdominal wall motion did not correlate with the tumour motion. Dose covering 95% volume of GTV was not different between the two techniques, while normal lung volume receiving 20 Gy or more was reduced by 20%. A mean treatment time per fraction was 36 min using DTT. With a median follow-up period of 13.2 months, no severe toxicity grade 3 or worse was observed. CONCLUSIONS: DTT radiotherapy using a gimbal mounted linac was clinically feasible for lung treatment without any severe acute toxicity.
Asunto(s)
Neoplasias Pulmonares/cirugía , Radiocirugia/métodos , Planificación de la Radioterapia Asistida por Computador/instrumentación , Planificación de la Radioterapia Asistida por Computador/métodos , Anciano , Anciano de 80 o más Años , Estudios de Factibilidad , Femenino , Marcadores Fiduciales , Estudios de Seguimiento , Humanos , Pulmón/diagnóstico por imagen , Pulmón/cirugía , Neoplasias Pulmonares/diagnóstico por imagen , Masculino , Persona de Mediana Edad , Movimiento (Física) , Tomografía Computarizada por Rayos X/métodosRESUMEN
PURPOSE: To verify the intrafractional tracking accuracy in infrared (IR) marker-based hybrid dynamic tumour tracking irradiation ("IR Tracking") with the Vero4DRT. MATERIALS AND METHODS: The gimballed X-ray head tracks a moving target by predicting its future position from displacements of IR markers in real-time. Ten lung cancer patients who underwent IR Tracking were enrolled. The 95th percentiles of intrafractional mechanical (iEM(95)), prediction (iEP(95)), and overall targeting errors (iET(95)) were calculated from orthogonal fluoroscopy images acquired during tracking irradiation and from the synchronously acquired log files. RESULTS: Averaged intrafractional errors were (left-right, cranio-caudal [CC], anterior-posterior [AP])=(0.1mm, 0.4mm, 0.1mm) for iEM(95), (1.2mm, 2.7mm, 2.1mm) for iEP(95), and (1.3mm, 2.4mm, 1.4mm) for iET(95). By correcting systematic prediction errors in the previous field, the iEP(95) was reduced significantly, by an average of 0.4mm in the CC (p<0.05) and by 0.3mm in the AP (p<0.01) directions. CONCLUSIONS: Prediction errors were the primary cause of overall targeting errors, whereas mechanical errors were negligible. Furthermore, improvement of the prediction accuracy could be achieved by correcting systematic prediction errors in the previous field.