RESUMEN
PURPOSE: This study aims to evaluate different methods for calibrating EBT-XD films to develop a precise pre-treatment verification method for stereotactic radiotherapy (SRT) patients using the HyperArc (HA, Varian Medical System) technique. METHODS: Gafchromic EBT-XD films were calibrated using three different approaches: manual calibration, EDW calibration, and PDD calibration. Films were digitalized with an Epson V850 Pro scanner applying the local scanning protocol. Three clinical treatment plans were selected for evaluation. Patient-specific QA films were irradiated in the Mobius MVP phantom and the STEEV phantom. Scanned film images were converted into dose images using the calibration curves. Gamma analysis was performed to compare film dose and TPS calculated dose with various criteria. RESULTS: The scan-to-scan variation was evaluated to be ≤ 0.2%. The accuracy of the calibration curves was verified and the deviation from the converted dose deviates ≤ 3% from the known delivered dose. The gamma passing rate for all calibration methods was found to be over 94% with clinically relevant criteria. EDW calibration demonstrated higher average gamma passing rates compared to the manual method for single target plans, which is 99% ± 1.2% and 98.8% ± 1.5%, respectively. PDD method demonstrated improved agreement for multiple targets with the result of 99.3% ± 0.8%. CONCLUSIONS: The three calibration methods were validated, and they produced accurate calibration curves for EBT-XD films to enable pre-treatment patient-specific QA for stereotactic radiotherapy.
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Dosimetría por Película , Radiocirugia , Humanos , Calibración , Dosimetría por Película/métodos , Dosificación Radioterapéutica , Radiocirugia/métodos , Fantasmas de ImagenRESUMEN
BACKGROUND: Implementation of cone beam computed tomography (CBCT) in frameless stereotactic body radiotherapy (SBRT) of lung tumours enables setup correction based on tumour position. The aim of this study was to compare setup accuracy with daily soft tissue matching to bony anatomy matching and evaluate intra- and inter-fractional translational and rotational errors in patient and target positions. MATERIAL AND METHODS: Fifteen consecutive SBRT patients were included in the study. Vacuum cushions were used for immobilisation. SBRT plans were based on midventilation phase of four-dimensional (4D)-CT or three-dimensional (3D)-CT from PET/CT. Margins of 5 mm in the transversal plane and 10 mm in the cranio-caudal (CC) direction were applied. SBRT was delivered in three fractions within a week. At each fraction, CBCT was performed before and after the treatment. Setup accuracy comparison between soft tissue matching and bony anatomy matching was evaluated on pretreatment CBCTs. From differences in pre- and post-treatment CBCTs, we evaluated the extent of translational and rotational intra-fractional changes in patient position, tumour position and tumour baseline shift. All image registration was rigid with six degrees of freedom. RESULTS: The median 3D difference between patient position based on bony anatomy matching and soft tissue matching was 3.0 mm (0-8.3 mm). The median 3D intra-fractional change in patient position was 1.4 mm (0-12.2 mm) and 2.2 mm (0-13.2 mm) in tumour position. The median 3D intra-fractional baseline shift was 2.2 mm (0-4.7 mm). With correction of translational errors, the remaining systematic and random errors were approximately 1°. CONCLUSION: . Soft tissue tumour matching improved precision of treatment delivery in frameless SBRT of lung tumours compared to image guidance using bone matching. The intra-fractional displacement of the target position was affected by both translational and rotational changes in tumour baseline position relative to the bony anatomy and by changes in patient position.
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Carcinoma de Pulmón de Células no Pequeñas/cirugía , Neoplasias Pulmonares/cirugía , Melanoma/cirugía , Radiocirugia , Neoplasias del Recto/cirugía , Neoplasias Gástricas/cirugía , Adulto , Anciano , Anciano de 80 o más Años , Algoritmos , Carcinoma de Pulmón de Células no Pequeñas/patología , Tomografía Computarizada de Haz Cónico , Fraccionamiento de la Dosis de Radiación , Femenino , Estudios de Seguimiento , Humanos , Inmovilización , Neoplasias Pulmonares/patología , Masculino , Melanoma/patología , Persona de Mediana Edad , Movimiento , Imagen Multimodal , Posicionamiento del Paciente , Tomografía de Emisión de Positrones , Pronóstico , Planificación de la Radioterapia Asistida por Computador , Radioterapia Asistida por Computador , Neoplasias del Recto/patología , Neoplasias Gástricas/patología , Tasa de Supervivencia , Tomografía Computarizada por Rayos XRESUMEN
BACKGROUND AND PURPOSE: Positional uncertainties related to the set-up of the prostate, using internal markers and either 2D-2D or 3D images, were studied. Set-up using direct prostate localization on CBCT scans is compared to set-up using internal markers. MATERIAL AND METHODS: 20 patients with prostate cancer were enrolled in the study. After each daily session, a set of 2D-2D and 3D images were acquired. The images isocenter was compared to reference images isocenter. For the set-up error analysis the systematic error, µ, and the set-up uncertainties, Σ and σ, were determined for the translational shift in the three directions, lat, lng and vrt. The set-up errors and uncertainties were calculated in the same way for rotations around the three axes, lat, lng and vrt. RESULTS: Set-up uncertainties were evaluated for four different set-up methods. The systematic error uncertainties were found to be in the range 0.38-1.14 mm and for the random error 0.79-1.48 mm. For rotations the uncertainties ranges were 0.38-1.59° and 0.91-2.18° for systematic and random uncertainties, respectively. Set-up uncertainties, using internal markers or prostate itself to position the target in the isocenter, were comparable. The correlation between the two methods was better for translational shifts of the isocenter than for rotational shifts. CONCLUSIONS: The study shows that the precision of the 2D-2D set-up is equivalent to the precision of the 3D images. It also shows that the soft-tissue based set-up needs 1 mm larger set-up margins than the marker based set-up for the prostate patients, when CBCT is used for daily verification of the location of the prostate.
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Tomografía Computarizada de Haz Cónico , Imagenología Tridimensional , Próstata/diagnóstico por imagen , Neoplasias de la Próstata/diagnóstico por imagen , Humanos , MasculinoRESUMEN
BACKGROUND AND PURPOSE: Radiotherapy is the standard treatment in locally advanced prostate cancer. The latest technological improvement is modulated rotational radiotherapy, where one single rotation of the treatment machine is used to conform the dose delivery to the target and spare organs at risk, requiring less than 2 min of beam-on time per treatment fraction. MATERIALS AND METHODS: We report herein our experience from the first 46 patients treated for prostate cancer, clinical stage T1-3 with rotational therapy ("RapidArc®", Varian Medical systems) (RA). This patient group is compared to a group of 50 patients treated with a 5-field Intensity Modulated Radiation Therapy (IMRT) technique over the same period. The comparison parameters include target coverage, dose to OAR, treatment time and number of monitor units. Daily-IGRT using implanted gold markers is used before and after treatment to investigate intra-fractional prostate displacement. RESULTS: RA results in improved sparing of the rectum and achieves desired dose distributions with fewer monitor units and a shorter treatment time (<1.5 min versus up to 8.9 min with IMRT). This shorter treatment time also translates in a decreased risk of patient motion during treatment: daily-IGRT demonstrates reduced prostate motion (<3mm 3D vector) from 16.7% to 4.7% in RA patients. Only slight side-effects were seen in the two groups of patients. CONCLUSIONS: RA results in improved sparing of the rectum, however, at the expense of an increase in dose to the femoral heads in prostate patients. The treatment time is significantly reduced from 4.9 min on average with 5-field IMRT to 1.1 min with RA, which allows for a reduction of infractional prostate motion.