Leak and Scattering Assessment by Optically Stimulated Luminescence Dosimetry in a Helical Linear Accelerator / Valoración de Fuga y Dispersión por medio de Dosimetría de Luminiscencia Estimulada Ópticamente (OSL) en un Acelerador Lineal Helicoidal

Radiation absorbed doses to organs outside the radiation therapy treatment beam can be significant and therefore of clinical interest. Two sets of out-of-beam measurements were performed measuring the leak dose and the scattered dose, at 5 points within the accelerator components (accelerator tube and collimator) and at 21 points on the equipment and surroundings based on a positioning scheme. For this purpose, 52 Optically Stimulated Luminescence (OSL) dosimeters were used in a latest generation helical linear accelerator. Of the 200 cGy fired at a cheese-like phantom, 0.332% of the out-of-beam dose contribution was found to come from the leak and 0.784% was transformed into scattering. For these dose values, estimates of the risk of second tumors in long-term survivors indicate a reduced probability of acquiring a second secondary radiation malignancy, based on information from the 1990 BEIR Committee report.

La dosis absorbida de radiación a órganos fuera del haz de tratamiento de radioterapia puede ser significativa y, por lo tanto, de interés clínico. Se realizaron dos sets de mediciones fuera del haz para determinar la dosis de fuga y la dosis dispersa, en 5 puntos dentro de los componentes del acelerador (tubo de aceleración y colimador) y 21 puntos en el equipo y alrededores basado en un esquema de posicionamiento. Para este fin se utilizaron 52 dosímetros de luminiscencia estimulada ópticamente (OSL, Optically Stimulated Luminescence), en un acelerador lineal helicoidal de última generación. De los 200 cGy disparados a un maniquí tipo queso, se encontró que el 0.332% de la contribución de dosis fuera del haz provenía de la fuga y 0.784% se transforma en dispersión. Para estos valores de dosis, las estimaciones del riesgo de segundos tumores en los supervivientes a largo plazo indican una reducida probabilidad de contraer una segunda malignidad por radiación secundaria, según la información del informe del Comité BEIR de 1990.

Comparación dosimétrica en radiocirugía intracraneal entre Cyberknife y un bisturí de rayos gamma y su puesta en marcha Centroamérica / Dosimetric comparison in intracranial radiosurgery between Cyberknife and a gamma knife and its implementation Central America

Introducción: La dupla Cyberknife y bisturí de rayos gamma (Infini) que se describe es la primera en Latinoamérica. Ambas máquinas han mostrado ser los mejores equipos para radiocirugía intracraneal. Se describe la experiencia inicial de Cyberknife en Centroamérica y su incorporación a un programa existente de bisturí de rayos gamma por vía de análisis comparativos dosimétricos. Material y método: En el año 2019 se realizaron planes comparativos y se trataron 180 pacientes con radiocirugía intracraneal con ambos sistemas tanto en patología tumoral, como vascular y funcional. Resultados: En el análisis dosimétrico comparativo en el gradiente de dosis de Infini mostró ser superior a Cyberknife en todos los casos. Para una esfera utilizando el colimador de 4 mm en Infini y de 5 mm en Cyberknife utilizando un plan isocéntrico con el -Trigeminal Path- el gradiente de dosis para Infini fue de 1.5 y para Cyberknife de 1.66. Para los casos de patología el gradiente de dosis media para Infini fue de 3 mm y para Cyberknife de 3.8 mm. Dando un puntaje de gradiente de dosis (Gradient Score Index) si Infini fuese de 100, Cyberknife obtuvo 87.3. Cyberknife mostró mejor conformalidad y cobertura (97% versus 96%) para todos los targets. Entre enero 2019 y enero 2020 se realizaron 180 radiocirugías, 60 con Cyberknife y 120 con Infini, 60 pacientes recibieron 146 sesiones con Cyberknife, radiocirugía fraccionada 39 (65%) y 21 (35%) en sesión única. Las dosis medias en tumores en dosis única fue 15 Gy (12.5 a 25 Gy) y en radiocirugía fraccionada 21 Gy (18 y 35). Ningún paciente ha experimentado toxicidad mayor a grado dos. Conclusiones: El bisturí de rayos gamma rotatorio reveló superioridad en gradiente de dosis con relación al Cyberknife. En su primer año Cyberknife ha mostrado ser una herramienta segura en el tratamiento de patología intracraneal. Más seguimiento clínico y radiológico es necesario para verificar su efectividad comparativa

Introduction: The match between Cyberknife and Infini here described in this article is the first in Latinamerica. Both machines have proven to be the best for intracranial radiosurgery, we describe our initial experience with Cyberknife in Central America and how it was incorporated in an existing gamma ray program by ways of dosimetry comparisons. Methods: During 2019 comparative plans were made and a total of 180 patients received intracranial radiosurgery with both technologies, patients were treated for tumors, vascular anomalies, and functional pathology. Results: Basic dosimetry analysis regarding dose gradient the Infini proved superior to Cyberknife in all plans. For a sphere using the 4 mm collimator in Infini and the 5 mm in Cyberknife along with an isocentric plan using the -Trigeminal Path- dose gradient was 1.5 for Infini and 1.66 for Cyberknife. For the pathology cases Infini was 3 mm and for Cyberknife 3.8 mm on mean. Giving a Gradient Score Index (GSI) if Infini would be 100, Cyberknife would be 87.3. Cyberknife showed better conformality and coverage for all pathology targets (97% versus 96%). From January 2019 to January 2020, 180 intracranial radiosurgeries were done, 60 with Cyberknife and 120 with Infini, 60 patients received 146 sessions with Cyberknife, fractionated scheme 39 (65%) and 21 (35%) single dose. The median dose for tumors was 15 Gy (12.5 a 25 Gy) for single session and 21 Gy (18 y 35) for fractionated scheme. No patient experienced a higher toxicity tan grade two. Conclusions: In its first year Cyberknife has shown to be safe in treating intracranial pathology. Infini had a better dose gradient than Cyberknife. Longer clinical and radiological follow-up is needed to verify its comparative effectiveness.

Radiocirugía cerebral estereotáctica en el tratamiento de tumores de base de cráneo / Stereotactic brain radiosurgery in the treatment of skull base tumors

La radiocirugía estereotáctica ha demostrado efectividad en el tratamiento multimodal de los tumores de base de cráneo, de todas maneras se sugiere que en áreas radiobioló;gicamente sensibles (ej. nervios ó;pticos y tronco cerebral) la dosis radiante debería reducirse por los efectos radiotó;xicos. Para evitar la ineficacia terapó;©utica, una alternativa recientemente implementada es la radiocirugía multisesió;n (RCH). Se analizó; en forma retrospectiva una serie de tumores de base de cráneo, con el fin de evaluar el tratamiento con RCH a travó;©s del control tumoral en las imágenes post-tratamiento. Se evaluó; tambín edad, sexo, histología tumoral, volumen tumoral, protocolo radiante, Karnofsky performance status (KPS) pre-tratamiento y neurocirugía y tratamiento radiante previos. Fueron tratados 84 pacientes entre enero 2009 y enero 2017. La mediana de edad fue 51.5 aó;±os; sexo femenino: 53.6%. Hubo un 92.7% de no-progresió;n luego del tratamiento, con una mediana de tiempo de seguimiento de 36 meses. Los tumores tratados fueron principalmente adenomas hipofisarios, neurinomas del acó;ºstico, y meningiomas de base de cráneo. La mayoría de los pacientes recibió; un esquema de tratamiento fraccionado de 5 días, con una dosis total de 25 Gy. No se observó; radiotoxicidad tardía clínicamente manifiesta. En el análisis multivariado, un KPS alto pre-tratamiento fue significativamente asociado a la no-progresió;n tumoral. En esta serie, la alta incidencia de no-progresió;n tumoral indicaría que el tratamiento con RCH podría ser una opció;n terapó;©utica en algunos casos de tumores de base de cráneo, principalmente recurrencias o remanencias tumorales de adenomas hipofisarios, neurinomas y meningiomas.

Stereotactic radiosurgery has shown effectiveness in the multimodal treatment of skull base tumors, however it is suggested that in radiobiologically sensitive areas (eg. optic nerves and brainstem) the radiation dose should be reduced due to radiotoxic effects. To avoid the consequent therapeutic ineffectiveness, a recently implemented alternative is multisession radiosurgery (RCH). We retrospectively analyzed a series of patients with skull base tumors, in order to evaluate the treatment with RCH through tumor control in the post-treatment images. Age, sex, tumor histology, tumor volume, radiation protocol, pre-treatment Karnofsky performance status (KPS) previous neurosurgery and radiant treatment were also evaluated. Eighty-four patients were treated between January 2009 and January 2017. The median age was 51.5 years; females: 53.6%. There was a 92.7% non-progression after treatment, with a median follow-up time of 36 months. Treated tumors were mainly pituitary adenomas, acoustic schwannomas, and skull base meningiomas. Most of the patients received a 5-day fractionated treatment scheme, with a total dose of 25 Gy. No clinically manifest late radiotoxicity was observed. In the multivariate analysis, a high pre-treatment KPS was significantly associated with tumor non-progression. In our series, the high incidence of tumor non-progression would indicate that treatment with RCH could be a therapeutic option in some cases of skull-base tumors, mainly recurrences or tumor residuals of pituitary adenomas, neurinomas and meningiomas.

LINAC radiosurgery treatment for vestibular schwannoma.

OBJECTIVE: The aims of our study were to evaluate tumour response in a series of patients with vestibular schwannoma (VS) treated with linear accelerator stereotactic radiosurgery (LINAC-RS), to describe the complications and to analyze the variables associated with the response to treatment. MATERIAL AND METHODS: This retrospective descriptive study included 64 patients treated from 2010 to 2016 with a minimum follow-up of one year, excluding patients with neurofibromatosis. Clinical-radiological parameters were evaluated. The treatment was performed using LINAC-RS. The prescribed dose was 12Gy at 90% isodose. RESULTS: The mean age at treatment was 53 years, 56% were women. Ninety-eight percent of the patients had hearing loss, 71% with grade III according to the Gardner-Robertson Classification. The mean volume at treatment was 2.92cc and the mean follow-up, 40.95 months. The overall therapeutic success was 90%, reaching 100% at 12 and 24 months, and 86% after 36 months of follow-up. The radiological result was significantly related to the initial tumour volume (p<0.037). In 20 patients there was evidence of transient tumour growth compatible with pseudoprogression. Acute complications were present in 37.5%, and transitory complications in 50%. Chronic complications were found in 20%, with 84% being permanent. The rate of acute complications was lower in patients with regression (p<0.016). Chronic complications were more frequent in the 41-60 year old age group (p<0.040). CONCLUSIONS: In our study, the overall tumour control was in accordance with other published series. The radiological result significantly related to the tumour volume at the commencement of treatment. The rate of acute complications was lower in patients with regression.

[Experience with the radiosurgical treatment of brain metastases]. / Experiencia en el manejo de metástasis cerebrales tratadas con radiocirugía estereotáctica.

OBJECTIVE: To analyse the survival rate of a cohort of patients with intracranial metastases treated with radiosurgery, and to determine the factors that influence the results. PATIENTS AND METHOD: Retrospective analysis performed on a cohort of 126 patients undergoing radiosurgery for brain metastases. Patients treated with surgery before or after radiosurgery were excluded. Survival is analysed based on clinical (age, sex, primary tumour), radiological (number, location and volume of lesions), and radiotherapy factors (treatment dose, holocraneal radiation). Univariate and multivariate analyses were performed to determine significant prognostic factors. RESULTS: A total of 225 brain metastases in 126 patients, with a mean age of 59.8±11.6years, were treated between February 2008 and April 2015. The mean survival was 8.2 months. The overall survival rates at 6months, 1year, and 2years were 60.3%, 31.5%, and 12.8%, respectively. Lung (59.5%) and breast (14.3) were the most common primary tumours, and the most common site for metastases was the cerebral hemisphere (77%) and the average volume was 10.35 cc (0.2-43.5). Significant survival factors were: age under 60 (P=.046), female (P<.001), breast cancer (P<.001), KPS >80 (P=.001), SIR6 >5 (P=.031), and GPA ≥2.5 (P=.003). CONCLUSIONS: Radiosurgery is an appropriate technique for the treatment of brain metastases, and the main prognostic factors include being age under 65, female, breast cancer, and good scores on Karnofsky, SIR, and GPA scales.

Outcome of radiosurgery treatment with a linear accelerator in patients with trigeminal neuralgia. / Resultados de la aplicación de radiocirugía con acelerador lineal en pacientes con neuralgia del trigémino.

INTRODUCTION: An overview of the effectiveness of radiosurgery in patients diagnosed with trigeminal neuralgia with an analysis of potential predictors of good outcome. METHODS: All patients treated with linear accelerator radiosurgery between 2004 and 2011 were analysed. A dose of 60Gy dose was administered 1 to 2mm from the root entry zone with a maximum isodose of 20% delivered to the brainstem. Clinical results for pain control and any side effects were analysed at 12 and 36 months (BNI score). RESULTS: The study included 71 patients (mean follow-up 50.5 months). Pain improvement at 12 months was observed in 68.11% of the total (28.98% with BNI score i-ii; 39.12% with BNI score iii) and at 36 months in 58.21% (23.88% BNI score i-ii; 34.32% BNI score iii). Average recovery time was 3.69 months and the relapse rate was 44.68%. Patients with typical pain displayed statistically significant differences in improvement rates at 12 and at 36 months (P<047 and P<.002). Onset of improvement was analysed using Kaplan-Meyer plots. Statistically significant differences were observed between patients with typical and atypical pain at 36 months (P<.012) in Kaplan-Meyer plots. Side effects were recorded in 15 patients (20.89%), including 9 cases of facial numbness (13.43%); only 2 cases were clinically relevant (2.98%). CONCLUSION: According to our results, radiosurgery is an effective treatment for trigeminal neuralgia, with few side effects. Typical pain seems to be a good predictor of pain relief.

Kinetic Energy of Emerging Neutrons Produced by Photodisintegration in a Medical Linear Accelerator / Energía cinética de neutrones emergentes producidos por fotodesintegración en un acelerador médico lineal

When a gamma photon interacts with a target nucleus a nuclear reaction can be generated, producing as a consequence the expulsion of particles from the atomic nucleus, this process is called photodisintegration. For this work, are of interest nuclear reactions of photodisintegration in which neutrons are ejected due to the interaction of photons with atomic nuclei of different materials in a linear accelerator for medical use. In this paper, the kinetic energy of photoneutrons produced by interactions with atomic nuclei of 184W, 63Cu, 27Al and 12C, which are some of the materials that constitute the head of a medical linear accelerator, is calculated. Also, the nuclei present in the construction materials of the room and the maze of the accelerator, such as, 23Na, 40Ca and 28Si, as also in the human body, ²H, 14N and 16O, are considered. It derives an exact theoretical expression, which has a linear dependence of the energy of the produced neutrons relative to the incident photon energy. It is found that, in the majority of cases, just photons with energies above 10 MV contribute to the production of neutrons. The values calculated from the expression obtained in this work are in good agreement with those reported in the literature, that are obtained by other approaches.

Cuando un fotón gamma interactúa con un núcleo blanco una reacción nuclear puede ser generada, produciendo como consecuencia la expulsión de partículas del núcleo atómico, este proceso se denomina fotodesintegración. Para este trabajo, son de interés las reacciones nucleares de fotodesintegración en las que los neutrones son expulsados debido a la interacción de los fotones con los núcleos atómicos de diferentes materiales en un acelerador lineal para uso médico. En este trabajo, la energía cinética de fotoneutrones producidos por la interacción con los núcleos atómicos de 184 W, 63 Cu, 27 Al y 12 C, que son algunos de los materiales que constituyen el cabezal de un acelerador lineal médico, es calculada. Además, los núcleos presentes en los materiales de construcción de la sala y el laberinto del acelerador, como por ejemplo, 23Na, 40Ca y 28Si, como también en el cuerpo humano, ²H, 14N y 16O, son considerados. Se obtiene una expresión exacta teórica, la cual tiene una dependencia lineal de la energía de los neutrones producidos en relación a la energía del fotón incidente. Se ha encontrado que, en la mayoría de los casos, sólo los fotones con energías por encima de 10 MV contribuyen a la producción de neutrones. Los valores calculados a partir de la expresión obtenida en este trabajo están en buen acuerdo con los reportados en la literatura, los cuales se obtienen mediante otros métodos.

Radiocirugía estereotáxica con acelerador lineal (LINAC): Informe de la experiencia técnica en el manejo de 100 casos en el Hospital General de México / Stereotactic radiosurgery with linear accelerator (LINAC): Report of the technical experience in 100 cases treated at the Mexico General Hospital

La radiocirugía estereotáxica consiste en la liberación de una dosis única y grande de radiación a una lesión intracraneal, pequeña, bien definida y localizada estereotáxicamente. Objetivo: El objetivo de este estudio es detallar las consideraciones técnicas y correlacionarlas con los resultados clínicos, así como reportar los márgenes de dosis utilizados. Métodos: Fueron tratados 100 pacientes mediante radiocirugía estereotáxica con LINAC. Treinta y cuatro casos de malformaciones arteriovenosas, 22 meningiomas, 18 astrocitomas, 11 adenomas hipofisiarios, 5 angiomas cavernosos, 3 neurinomas del acústico, 3 craneofaringiomas, 2 casos de epilepsia, una metástasis cerebral y un ependimoma. Las dosis de radiación utilizadas variaron en cada caso. Variables estudiadas: respuesta de la lesión, toxicidad, dosis al volumen blanco, número de isocentros, número de arcos de tratamiento, número de colimadores, dosis a órganos riesgo, homogeneidad volumen blanco, margen de error, volumen blanco, diámetro de colimadores y localización del volumen blanco. Se realizó la prueba x² con significancia estadística p <0.05. La media seguimiento fue de 17.7 meses. Resultados: Se presentaron tres casos de toxicidad menor. Se confirmó que a mayor volumen blanco tratado será necesario mayor número de arcos de tratamiento, con amplio margen de error y mayor número de isocentros. Conclusión: La radiocirugía es un método seguro y confiable para el manejo de entidades patológicas benignas y malignas intracraneales.

Stereotactic radiosurgery consists of the release and high dose radiation inside the intracraneal, small, well defined and stereotactic localized injury. Objective: In this study we describe the technical aspects, clinical results and dose radiation levels used in 100 patients treated with LINAC. Methods: One hundred patients received treatment withe LINAC stereotactic radiosurgery, 34 AVM, 22 meningiomas, 18 astrocytomas, 11 pituitary adenomas, 5 cavernous malformations, 3 acoustic neuromas, 3 craniopharyngiomas, 2 cases of epilepsy, one brain metastases and one ependymoma. The radiation dose changed in each case. Studied variables: response of the injury, toxicity, in target dose, number of isocenters, number of treatment arcs, number of collimators, dose of risk organ, homogeneity of target, margin of error, target, diameter of collimator and location of target. We applied the %2 test with statistical significance of p < 0.05. Results: The median follow up was 17.7 months. We had 3 cases of minor toxicity. We confirmed that for a greater target volume, greater number oftreatment arcs were necessary, with greater margins of errors and greater number of isocenters. Conclusions: Radiosurgery is a safe and reliable technique to treat benign and malignant intracranial lesions.