Use of genetic algorithm for PTV optimization in single isocenter multiple metastases radiosurgery treatments with Brainlab Elements™.

PURPOSE: To optimize PTV margins for single isocenter multiple metastases stereotactic radiosurgery through a genetic algorithm (GA) that determines the maximum effective displacement of each target (GTV) due to rotations. METHOD: 10 plans were optimized. The plans were created with Elements Multiple Mets™ (Brainlab AG, Munchen, Germany) from a predefined template. The mean number of metastases per plan was 5 ± 2 [3,9] and the mean volume of GTV was 1.1 ± 1.3 cc [0.02, 5.1]. PTV margin criterion was based on GTV-isocenter distance and target dimensions. The effective displacement to perform specific rotational combination (roll, pitch, yaw) was optimized by GA. The original plans were re-calculated using the PTV optimized margin and new dosimetric variations were obtained. The Dmean, D99, Paddick conformity index (PCI), gradient index (GI) and dose variations in healthy brain were studied. RESULTS: Regarding targets located shorter than 50 mm from the isocenter, the maximum calculated displacement was 2.5 mm. The differences between both PTV margin criteria were statistically significant for Dmean (p = 0.0163), D99 (p = 0.0439), PCI (p = 0.0242), GI (p = 0.0160) and for healthy brain V12 (p = 0.0218) and V10 (p = 0.0264). CONCLUSION: The GA allows to determine an optimized PTV margin based on the maximum displacement. Optimized PTV margins reduce the detriment of dosimetric parameters. Greater PTV margins are associated with an increase in healthy brain volume.

A method to enhance 2D ion chamber array patient specific quality assurance for IMRT.

Gamma index comparison has been established as a method for patient specific quality assurance in IMRT. Detector arrays can replace radiographic film systems to record 2D dose distributions and fulfill quality assurance requirements. These electronic devices present spatial resolution disadvantages with respect to films. This handicap can be partially overcome with a multiple acquisition sequence of adjacent 2D dose distributions. The detector spatial response influence can also be taken into account through the convolution of the calculated dose with the detector spatial response. A methodology that employs both approaches could allow for enhancements of the quality assurance procedure. 35 beams from different step and shoot IMRT plans were delivered on a phantom. 2D dose distributions were recorded with a PTW-729 ion chamber array for individual beams, following the multiple acquisition methodology. 2D dose distributions were also recorded on radiographic films. Measured dose distributions with films and with the PTW-729 array were processed with the software RITv5.2 for Gamma index comparison with calculated doses. Calculated dose was also convolved with the ion chamber 2D response and the Gamma index comparisons with the 2D dose distribution measured with the PTW-729 array was repeated. 3.7 ± 2.7% of points surpassed the accepted Gamma index when using radiographic films compared with calculated dose, with a minimum of 0.67 and a maximum of 13.27. With the PTW-729 multiple acquisition methodology compared with calculated dose, 4.1 ± 1.3% of points surpassed the accepted Gamma index, with a minimum of 1.44 and a maximum of 11.26. With the PTW- multiple acquisition methodology compared with convolved calculated dose, 2.7 ± 1.3% of points surpassed the accepted Gamma index, with a minimum of 0.42 and a maximum of 5.75. The results obtained in this work suggest that the comparison of merged adjacent dose distributions with convolved calculated dose represents an enhancement in the methodology for IMRT patient specific quality assurance with the PTW-729 ion chamber array.

Tratamiento multimodal e individualizado a pacientes con metástasis encefálica / Multimodal and individualized treatment for patients with brain metastases

Introduction: The treatment of Brain Metastases is palliative and it is ignored the ideal therapeutic combination, constituting this a controversial topic. Objective: To determine the results of the treatment to patient with Brain Metastases according to different modalities. Method: It was carried out a prospective cohort study between april 2010 to april 2013 in the National Institute of Oncology and Radiobiology. It was designated as universe the total of patient with diagnosis of Brain Metastases of primary tumor assisted in consultation of Neurosurgery. The Fischer exact test was used to correlate qualitative variables and the Kaplan Meier curvesto estimate the survival. Results: It was obtained a sample of 42 patients and 84 lesions. The age average was of 53,1 years. The primary lesions prevailed in lung and breast. The used modalities were: Surgery-Whole Brain Radiation Therapy (20 lesions), Whole Brain Radiation Therapy alone (29 lesions), Radiosurgery alone (21 lesions) and Surgery alone (9 lesions). Conclusions: The combinations of Radiosurgery-Whole Brain Radiation Therapy and Surgery-Radiosurgery associated to a better local control. The treatment with Whole Brain Radiation Therapy didn't associate to a better distance control. The overall survival to the 6 months was of 91 percent and to the 12 months of 57 percent. A bigger survival was observed in patient with controlled primary illness and absence of extracraneal metastases. The Surgery presents the biggest number of complications.

Introducción: El tratamiento de la Metástasis Encefálica es paliativo y se desconoce la modalidad o combinación terapéutica óptima, constituyendo éste un tema controvertido. Objetivo: Determinar los resultados del tratamiento a pacientes con Metástasis Encefálica según diferentes modalidades. Método: Se realizó un estudio de cohorte prospectivo durante el período abril de 2010 a abril de 2013 en el Instituto Nacional de Oncología y Radiobiología. Se designó como universo el total de pacientes con diagnóstico de Metástasis Encefálica de neoplasia primaria conocida atendidos en consulta de Neurocirugía. Se utilizó el test exacto de Fischer para correlacionar variables cualitativas y las curvas de Kaplan Meier para estimar la supervivencia. Resultados: Se obtuvo una muestra de 42 pacientes y 84 lesiones. El promedio de edad fue de 53,1 años. Predominaron las lesiones primarias en pulmón y mama. Las modalidades más utilizadas fueron: Cirugía-Radioterapia Holocraneal (20 lesiones), Radioterapia Holocraneal sola (29 lesiones), Radiocirugía sola (21 lesiones) y la Cirugía sola (9 lesiones). Conclusiones: Las combinaciones de Radiocirugía-Radioterapia Holocraneal y Cirugía-Radiocirugía se asociaron a un mejor control local. El tratamiento con Radioterapia Holocraneal no se asoció a un mejor control a distancia. La supervivencia global a los 6 meses fue del 91 por ciento y a los 12 meses del 57 por ciento. Se observó una mayor supervivencia en pacientes con enfermedad primaria controlada y ausencia de metástasis extra craneal. La Cirugía presentó el mayor número de complicaciones.