Evaluation of conventional IMRT and VMAT strategies for postmastectomy radiation therapy after immediate implant-based reconstruction using the new ESTRO-ACROP contouring guidelines.

This study evaluated the usability of conventional templates based on the new contour guidelines of the European Society of Radiation and Oncology and Advisory Committee in Radiation Oncology Practice (ESTRO-ACROP) for treatment plans of postmastectomy radiotherapy after immediate implant-based reconstruction. Intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans generated with two different treatment planning systems (TPSs, Eclipse and Monaco) were examined. Six computed tomography scans of patients aged 35-54 years were retrospectively analysed who had undergone mastectomy and breast reconstruction using silicone implants after being diagnosed with left breast cancer. Six radiation oncologists participated in this study, and each of them contoured the target volume of one left breast using conventional contour (CTV-CONV) and new contour (CTV-ESTRO) methods. This study showed that compared with CTV-CONV, using CTV-ESTRO with objectives and cost functions similar to those of TPSs worsened the target volume coverage and increased the total number of monitor units. Considering the organs at risk, CTV-ESTRO tended to increase the mean dose delivered to the contralateral lung. It is concluded that the approach used for the new ESTRO-ACROP contour method cannot be applied in a manner similar to that for the conventional breast contour method, implying that the new ESTRO-ACROP contour method may require more time for improving plans for a given treatment.

Monte Carlo simulation of the Varian TrueBeam flattened-filtered beams using a surrogate geometry in PRIMO.

BACKGROUND: Monte Carlo simulation of radiation transport for medical linear accelerators (linacs) requires accurate knowledge of the geometrical description of the linac head. Since the geometry of Varian TrueBeam machines has not been disclosed, the manufacturer distributes phase-space files of the linac patient-independent part to allow researchers to compute absorbed dose distributions using the Monte Carlo method. This approach limits the possibility of achieving an arbitrarily small statistical uncertainty. This work investigates the use of the geometry of the Varian Clinac 2100, which is included in the Monte Carlo system PRIMO, as a surrogate. METHODS: Energy, radial and angular distributions extracted from the TrueBeam phase space files published by the manufacturer and from phase spaces tallied with PRIMO for the Clinac 2100 were compared for the 6, 8, 10 and 15 MV flattened-filtered beams. Dose distributions in water computed for the two sets of PSFs were compared with the Varian Representative Beam Data (RBD) for square fields with sides ranging from 3 to 30 cm. Output factors were calculated for square fields with sides ranging from 2 to 40 cm. RESULTS: Excellent agreement with the RBD was obtained for the simulations that employed the phase spaces distributed by Varian as well as for those that used the surrogate geometry, reaching in both cases Gamma ([Formula: see text], 2 mm) pass rates larger than [Formula: see text], except for the 15 MV surrogate. This result supports previous investigations that suggest a change in the material composition of the TrueBeam 15 MV flattening filter. In order to get the said agreement, PRIMO simulations were run using enlarged transport parameters to compensate the discrepancies between the actual and surrogate geometries. CONCLUSIONS: This work sustains the claim that the simulation of the 6, 8 and 10 MV flattening-filtered beams of the TrueBeam linac can be performed using the Clinac 2100 model of PRIMO without significant loss of accuracy.

Technological Improvements in Low- and Middle-Income Countries (LMICs): A Review of the Literature and the "Sociedad de Lucha Contra el Cáncer" (SOLCA) Institutional Experience in Neuro-Radiosurgery During the Coronavirus Disease 2019 (COVID-19) Pandemic.

OBJECTIVE: Neurosurgery is a medical field that requires specialized professionals and equipment, 2 important but scarce resources in low- and middle-income countries. Our goal was to report our experience with the replacement and implementation of linear accelerators with radiosurgery capabilities at "Sociedad de Lucha Contra el Cáncer" (SOLCA) Hospital in Quito, Ecuador, and give some recommendations for future technological replacements (TRs). METHODS: Two surveys were performed in SOLCA's radiosurgery department, one before the TR was finalized and one after, consisting of an open and multiple-choice questionnaire. Questions focused on the performance of the new equipment, perceptions regarding the training, and the influence of the pandemic on the whole process. In addition, we share our experience regarding the difficulties and benefits of TR at SOLCA. RESULTS: The most-reported limitation was lack of training (48%). By the time of the second survey, 95.2% of the staff had already treated patients or planned a radiosurgical procedure; 42.9% considered training to have been adequate, and 76.2% felt that the pandemic hindered the training process. Currently, 33 radiosurgeries have been done (26 for the central nervous system and 7 stereotactic radiation body therapies). CONCLUSIONS: The TR in SOLCA had similarities with other experiences in low- and middle-income countries, but the pandemic brought additional limitations, mainly complicating the staff training. Nevertheless, those limitations can be resolved with a structured training program and international collaboration. Overall, the benefits obtained from a TR result in exponentially better medical care and accessibility to novel treatments.

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.

Frameless radiosurgical third ventriculostomy: Technical report.

BACKGROUND: We describe the technical report and results of the first image-guided, linear accelerator, frameless radiosurgical third ventriculostomy. METHODS: We report a 20 years old man, with diplopia, balance disturbances, and limitation for gaze supraversion. Magnetic resonance imaging resonance imaging of the brain and cranial computed tomography showed showed a left thalamic-midbrain lesion that caused partial compression of the Silvio aqueduct and mild ventricular dilatation. The biopsy revealed the diagnosis of pleomorphic xanthoastrocytoma. Before radical treatment of the tumor with fractionated stereotactic radiotherapy, the patient underwent to frameless radiosurgical third ventriculostomy, on the TrueBeam STX® platform with the ExacTrac localization system. The target used was the one defined on the floor of the third ventricle, at the midpoint between the mammillary bodies and the infundibular recess. The prescription dose was 120 Gy, given using a monoisocentric technique of multiple noncoplanar circular arches. The geometric arrangement of the plan consisted of 15 arches, with a 4 mm cone, distributed over a 110° table. RESULTS: There was symptomatic and image improvement two days after radiosurgery. On CT, a reduction in ventricular dilation was observed with a reduction in the Evans index from 0.39 (initial CT) to 0.29 (CT at 15 days). In 3.0T magnetic resonance image at 3 months, we showed the third ventriculostomy. There have been no treatment failures or complications. CONCLUSION: It is possible to effectively perform the frameless radiosurgical third ventriculostomy without associated morbidity in the short term.

Linear Accelerator-Based Radiosurgery of Grade I Intracranial Meningiomas.

OBJECTIVE: To determine the local control rate and complication rate in the treatment of grade I intracranial meningiomas. METHODS: A retrospective study was performed of patients with grade I meningioma who received radiosurgery with a dedicated linear accelerator from January 2002 to August 2012 with a minimum follow-up of 2 years. We performed descriptive statistics, logistic regression, and progression-free survival analysis through a Kaplan-Meier curve. RESULTS: Seventy-five patients with 78 grade I meningiomas received radiosurgery, 39 underwent surgery plus adjuvant radiosurgery, and 36 only radiosurgery. The follow-up median time was 68 months (range, 35-120 months). The tumor control rate was 93%, the 5-year progression-free survival was 92% (95% confidence interval, 77%-98%). Acute toxicity was 2.6%, and grade 1-2 late toxicity was 26.6%. Postradiosurgery edema was the main late morbidity. Age >55 years was the only significant factor for attaining a response >75%. The background of surgery before radiosurgery was the only significant prognostic factor for showing edema (odds ratio 5.78 [95% confidence interval, 2.14-15.64]). CONCLUSIONS: The local control rate attained in our series is similar to that reported in other series worldwide; the acute toxicity rate was low and late toxicity was moderate.

DPM as a radiation transport engine for PRIMO.

BACKGROUND: PRIMO is a dose verification system based on the general-purpose Monte Carlo radiation transport code PENELOPE, which implements an accurate physics model of the interaction cross sections and the radiation transport process but with low computational efficiency as compared with fast Monte Carlo codes. One of these fast Monte Carlo codes is the Dose Planning Method (DPM). The purpose of this work is to describe the adaptation of DPM as an alternative PRIMO computation engine, to validate its performance against PENELOPE and to validate it for some specific cases. METHODS: DPM was parallelized and modified to perform radiation transport in quadric geometries, which are used to describe linacs, thus allowing the simulation of dynamic treatments. To benchmark the new code versus PENELOPE, both in terms of accuracy of results and simulation time, several tests were performed, namely, irradiation of a multi-layer phantom, irradiation of a water phantom using a collimating pattern defined by the multileaf collimator (MLC), and four clinical cases. The gamma index, with passing criteria of 1 mm/1%, was used to compare the absorbed dose distributions. Clinical cases were compared using a 3-D gamma analysis. RESULTS: The percentage of voxels passing the gamma criteria always exceeded 99% for the phantom cases, with the exception of the transport through air, for which dose differences between DPM and PENELOPE were as large as 24%. The corresponding percentage for the clinical cases was larger than 99%. The speedup factor between DPM and PENELOPE ranged from 2.5 ×, for the simulation of the radiation transport through a MLC and the subsequent dose estimation in a water phantom, up to 11.8 × for a lung treatment. A further increase of the computational speed, up to 25 ×, can be obtained in the clinical cases when a voxel size of (2.5 mm)3 is used. CONCLUSIONS: DPM has been incorporated as an efficient and accurate Monte Carlo engine for dose estimation in PRIMO. It allows the concatenated simulation of the patient-dependent part of the linac and the patient geometry in static and dynamic treatments. The discrepancy observed between DPM and PENELOPE, which is due to an artifact of the cross section interpolation algorithm for low energy electrons in air, does not affect the results in other materials.

A dose-response curve for biodosimetry from a 6 MV electron linear accelerator

Biological dosimetry (biodosimetry) is based on the investigation of radiation-induced biological effects (biomarkers), mainly dicentric chromosomes, in order to correlate them with radiation dose. To interpret the dicentric score in terms of absorbed dose, a calibration curve is needed. Each curve should be constructed with respect to basic physical parameters, such as the type of ionizing radiation characterized by low or high linear energy transfer (LET) and dose rate. This study was designed to obtain dose calibration curves by scoring of dicentric chromosomes in peripheral blood lymphocytes irradiated in vitro with a 6 MV electron linear accelerator (Mevatron M, Siemens, USA). Two software programs, CABAS (Chromosomal Aberration Calculation Software) and Dose Estimate, were used to generate the curve. The two software programs are discussed; the results obtained were compared with each other and with other published low LET radiation curves. Both software programs resulted in identical linear and quadratic terms for the curve presented here, which was in good agreement with published curves for similar radiation quality and dose rates.

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.

Radiosurgery with a linear accelerator in cerebral arteriovenous malformations / Radiocirurgia com acelerador linear em malformações arteriovenosas cerebrais

OBJECTIVE: To evaluate results achieved with radiosurgery and complications of the procedure when treating arteriovenous malformations with linear accelerator. METHODS: This retrospective study was conducted between October 1993 and December 1996. Sixty-one patients with arteriovenous malformations were treated with radiosurgery utilizing a 6MV energy linear accelerator. Ages of the 32 female and 29 male patients ranged from 6 to 54 years (mean: 28.3 years). The most frequent initial symptom was cephalea (45.9 percent), followed by neurological deficit (36.1 percent). Cerebral hemorrhage diagnosed by image was observed in 35 patients (57.3 percent). Most arteriovenous malformations (67.2 percent) were graded Spetzler III and IV. Venous stenosis (21.3 percent) and aneurysm (13.1 percent) were the most frequent angioarchitecture changes. The dose administered varied from 12 to 27.5Gy in the periphery of the lesion. RESULTS: Out of twenty-eight patients that underwent conclusive angiography control, complete obliteration was achieved in 18 (72 percent) and treatment failed in 7 (absence of occlusion with more than 3 years of follow-up). Four were submitted to a second radiosurgery, and one of these has shown obliteration after 18 months of follow-up. DISCUSSION: Several factors were analyzed regarding the occlusion rate (gender, age, volume, localization, Spetzler, flow, embolization, total of isocenters, prescribed dose and chosen isodose) and complications (total of isocenters, localization, volume, maximum dose, prescribed dose and chosen isodose). Analyzed variables showed no statistical significance for obliteration of the vessel, as well as for treatment complications. The largest diameter of the arteriovenous malformation, its volume and the dose administered did not influence time of obliteration. CONCLUSION: Radiosurgery is effective in the treatment of arteriovenous malformations and can be an alternative for patients with clinical...

OBJETIVO: Analisar os resultados obtidos com radiocirurgia e as suas complicações do procedimento, no tratamento das malformações arteriovenosas com acelerador linear. MÉTODOS: Este é um estudo retrospectivo. Entre Outubro de 93 e Dezembro de 96, sessenta e um pacientes com malformações arteriovenosas foram tratados, utilizando um acelerador linear com 6MV de energia. As idades variaram de 6 a 54 anos (média: 28,3 anos), 32 pacientes mulheres e 29 pacientes homens. O sintoma inicial mais freqüente foi cefaléia (45,9 por cento), seguido de déficit neurológico (36,1 por cento). Hemorragia cerebral diagnostica por exame de imagem foi observada em 35 pacientes (57,3 por cento). A maioria das malformações arteriovenosas (67,2 por cento) eram graus III e IV de Spetzler. Estenose venosa (21,3 por cento) e aneurisma (13,1 por cento) foram as mais freqüentes alterações da arquitetura vascular. A dose administrada variou de 12 a 27,5Gy na periferia da lesão. RESULTADOS: Dos vinte e oito pacientes que se submeteram a controle angiográfico conclusivo, 18 tiveram obliteração completa (72 por cento) e 7 falharam ao tratamento (ausência de oclusão com mais de três anos de seguimento). Quatro pacientes foram submetidos a uma segunda radiocirurgia, e um paciente deste grupo apresentou obliteração em 18 meses de seguimento. DISCUSSÃO: Vários fatores foram analisados em relação ao grau de oclusão (sexo, idade, volume, localização, Spetzler, fluxo, embolização, total de isocentros, dose prescrita e isodose escolhida) e complicações (total de isocentros, localização, volume, dose máxima, dose prescrita e isodose escolhida). As variáveis analisadas não mostraram significância estatística para a obliteração do vaso, bem como para as complicações de tratamento. O maior diâmetro da malformação arteriovenosa, seu volume e a dose administrada não influenciaram no tempo de obliteração. CONCLUSÃO: Radiocirurgia é eficiente no tratamento das malformações arteriovenosas...

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.