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1.
Technol Cancer Res Treat ; 15(4): 632-8, 2016 08.
Artigo em Inglês | MEDLINE | ID: mdl-26048909

RESUMO

Intramodality ultrasound image-guided radiotherapy systems compare daily ultrasound to reference ultrasound images. Nevertheless, because the actual treatment planning is based on a reference computed tomography image, and not on a reference ultrasound image, their accuracy depends partially on the correct intermodality registration of the reference ultrasound and computed tomography images for treatment planning. The error propagation in daily patient positioning due to potential registration errors at the planning stage was assessed in this work. Five different scenarios were simulated involving shifts or rotations of ultrasound or computed tomography images. The consequences of several workflow procedures were tested with a phantom setup. As long as the reference ultrasound and computed tomography images are made to match, the patient will be in the correct treatment position. In an example with a phantom measurement, the accuracy of the performed manual fusion was found to be ≤2 mm. In clinical practice, manual registration of patient images is expected to be more difficult. Uncorrected mismatches will lead to a systematically incorrect final patient position because there will be no indication that there was a misregistration between the computed tomography and reference ultrasound images. In the treatment room, the fusion with the computed tomography image will not be visible and based on the ultrasound images the patient position seems correct.


Assuntos
Imageamento Tridimensional , Radioterapia Guiada por Imagem , Ultrassonografia , Humanos , Posicionamento do Paciente , Imagens de Fantasmas , Planejamento da Radioterapia Assistida por Computador , Radioterapia Guiada por Imagem/instrumentação , Radioterapia Guiada por Imagem/métodos , Radioterapia Guiada por Imagem/normas , Tomografia Computadorizada por Raios X , Ultrassonografia/métodos , Fluxo de Trabalho
2.
Int J Radiat Oncol Biol Phys ; 75(4): 1266-72, 2009 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-19665317

RESUMO

PURPOSE: To develop a technique to monitor the dose rate in the urethra during permanent implant brachytherapy using a linear MOSFET array, with sufficient accuracy and without significantly extending the implantation time. METHODS AND MATERIALS: Phantom measurements were performed to determine the optimal conditions for clinical measurements. In vivo measurements were performed in 5 patients during the (125)I brachytherapy implant procedure. To evaluate if the urethra dose obtained in the operating room with the ultrasound transducer in the rectum and the patient in treatment position is a reference for the total accumulated dose; additional measurements were performed after the implantation procedure, in the recovery room. RESULTS: In vivo measurements during and after the implantation procedure agree very well, illustrating that the ultrasound transducer in the rectum and patient positioning do not influence the measured dose in the urethra. In vivo dose values obtained during the implantation are therefore representative for the total accumulated dose in the urethra. In 5 patients, the dose rates during and after the implantation were below the maximum dose rate of the urethra, using the planned seed distribution. CONCLUSION: In vivo dosimetry during the implantation, using a MOSFET array, is a feasible technique to evaluate the dose in the urethra during the implantation of (125)I seeds for prostate brachytherapy.


Assuntos
Braquiterapia/métodos , Radioisótopos do Iodo/uso terapêutico , Neoplasias da Próstata/radioterapia , Uretra/efeitos da radiação , Calibragem , Desenho de Equipamento , Estudos de Viabilidade , Humanos , Masculino , Dose Máxima Tolerável , Imagens de Fantasmas , Radiometria/instrumentação , Radiometria/métodos , Reto
3.
Int J Radiat Oncol Biol Phys ; 73(1): 314-21, 2009 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-19100925

RESUMO

PURPOSE: In vivo dosimetry during brachytherapy of the prostate with (125)I seeds is challenging because of the high dose gradients and low photon energies involved. We present the results of a study using metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters to evaluate the dose in the urethra after a permanent prostate implantation procedure. METHODS AND MATERIALS: Phantom measurements were made to validate the measurement technique, determine the measurement accuracy, and define action levels for clinical measurements. Patient measurements were performed with a MOSFET array in the urinary catheter immediately after the implantation procedure. A CT scan was performed, and dose values, calculated by the treatment planning system, were compared to in vivo dose values measured with MOSFET dosimeters. RESULTS: Corrections for temperature dependence of the MOSFET array response and photon attenuation in the catheter on the in vivo dose values are necessary. The overall uncertainty in the measurement procedure, determined in a simulation experiment, is 8.0% (1 SD). In vivo dose values were obtained for 17 patients. In the high-dose region (> 100 Gy), calculated and measured dose values agreed within 1.7% +/- 10.7% (1 SD). In the low-dose region outside the prostate (< 100 Gy), larger deviations occurred. CONCLUSIONS: MOSFET detectors are suitable for in vivo dosimetry during (125)I brachytherapy of prostate cancer. An action level of +/- 16% (2 SD) for detection of errors in the implantation procedure is achievable after validation of the detector system and measurement conditions.


Assuntos
Braquiterapia/métodos , Radioisótopos do Iodo/análise , Radioisótopos do Iodo/uso terapêutico , Radiometria/instrumentação , Radiometria/métodos , Eficiência Biológica Relativa , Uretra , Humanos , Masculino , Especificidade de Órgãos , Dosagem Radioterapêutica , Espalhamento de Radiação , Semicondutores
4.
Int J Radiat Oncol Biol Phys ; 69(4): 1297-304, 2007 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-17881143

RESUMO

PURPOSE: To predict the three-dimensional dose distribution of our total body irradiation technique, using a commercial treatment planning system (TPS). In vivo dosimetry, using metal oxide field effect transistors (MOSFETs) and thermoluminescence detectors (TLDs), was used to verify the calculated dose distributions. METHODS AND MATERIALS: A total body computed tomography scan was performed and loaded into our TPS, and a three-dimensional-dose distribution was generated. In vivo dosimetry was performed at five locations on the patient. Entrance and exit dose values were converted to midline doses using conversion factors, previously determined with phantom measurements. The TPS-predicted dose values were compared with the MOSFET and TLD in vivo dose values. RESULTS: The MOSFET and TLD dose values agreed within 3.0% and the MOSFET and TPS data within 0.5%. The convolution algorithm of the TPS, which is routinely applied in the clinic, overestimated the dose in the lung region. Using a superposition algorithm reduced the calculated lung dose by approximately 3%. The dose inhomogeneity, as predicted by the TPS, can be reduced using a simple intensity-modulated radiotherapy technique. CONCLUSIONS: The use of a TPS to calculate the dose distributions in individual patients during total body irradiation is strongly recommended. Using a TPS gives good insight of the over- and underdosage in a patient and the influence of patient positioning on dose homogeneity. MOSFETs are suitable for in vivo dosimetry purposes during total body irradiation, when using appropriate conversion factors. The MOSFET, TLD, and TPS results agreed within acceptable margins.


Assuntos
Imageamento Tridimensional/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Dosimetria Termoluminescente/instrumentação , Tomografia Computadorizada por Raios X/métodos , Irradiação Corporal Total/métodos , Algoritmos , Humanos , Óxidos , Imagens de Fantasmas , Radiometria/instrumentação , Dosagem Radioterapêutica , Dosimetria Termoluminescente/métodos , Transistores Eletrônicos
5.
Radiother Oncol ; 80(3): 288-95, 2006 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-16916563

RESUMO

BACKGROUND AND PURPOSE: To determine the factors converting the reading of a MOSFET detector placed on the patient's skin without additional build-up to the dose at the depth of dose maximum (D(max)) and investigate their feasibility for in vivo dose measurements in electron beams. MATERIALS AND METHODS: Factors were determined to relate the reading of a MOSFET detector to D(max) for 4 - 15 MeV electron beams in reference conditions. The influence of variation in field size, SSD, angle and field shape on the MOSFET reading, obtained without additional build-up, was evaluated using 4, 8 and 15 MeV beams and compared to ionisation chamber data at the depth of dose maximum (z(max)). Patient entrance in vivo measurements included 40 patients, mostly treated for breast tumours. The MOSFET reading, converted to D(max), was compared to the dose prescribed at this depth. RESULTS: The factors to convert MOSFET reading to D(max) vary between 1.33 and 1.20 for the 4 and 15 MeV beams, respectively. The SSD correction factor is approximately 8% for a change in SSD from 95 to 100 cm, and 2% for each 5-cm increment above 100 cm SSD. A correction for fields having sides smaller than 6 cm and for irregular field shape is also recommended. For fields up to 20 x 20 cm(2) and for oblique incidence up to 45 degrees, a correction is not necessary. Patient measurements demonstrated deviations from the prescribed dose with a mean difference of -0.7% and a standard deviation of 2.9%. CONCLUSION: Performing dose measurements with MOSFET detectors placed on the patient's skin without additional build-up is a well suited technique for routine dose verification in electron beams, when applying the appropriate conversion and correction factors.


Assuntos
Neoplasias da Mama/radioterapia , Elétrons/uso terapêutico , Garantia da Qualidade dos Cuidados de Saúde , Radiometria/instrumentação , Planejamento da Radioterapia Assistida por Computador/instrumentação , Pele/efeitos da radiação , Calibragem , Estudos de Viabilidade , Humanos , Radiometria/normas , Dosagem Radioterapêutica , Semicondutores , Sensibilidade e Especificidade , Transistores Eletrônicos
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