Leonardo L. Amaral

A new transmission methodology for quality assurance in radiotherapy based on radiochromic film measurements

Despite individual quality assurance (QA) being recommended for complex techniques in radiotherapy (RT) treatment, the possibility of errors in dose delivery during therapeutic application has been verified. Therefore, it is fundamentally important to conduct in vivo QA during treatment. This work presents an in vivo transmission quality control methodology, using radiochromic film (RCF) coupled to the linear accelerator (linac) accessory holder. This QA methodology compares the dose distribution measured by the film in the linac accessory holder with the dose distribution expected by the treatment planning software. The calculated dose distribution is obtained in the coronal and central plane of a phantom with the same dimensions of the acrylic support used for positioning the film but in a source-to-detector distance (SDD) of 100 cm, as a result of transferring the IMRT plan in question with all the fields positioned with the gantry vertically, that is, perpendicular to the phantom. To validate this procedure, first of all a Monte Carlo simulation using PENELOPE code was done to evaluate the differences between the dose distributions measured by the film in a SDD of 56.8 cm and 100 cm. After that, several simple dose distribution tests were evaluated using the proposed methodology, and finally a study using IMRT treatments was done. In the Monte Carlo simulation, the mean percentage of points approved in the gamma function comparing the dose distribution acquired in the two SDDs were 99.92%±0.14%. In the simple dose distribution tests, the mean percentage of points approved in the gamma function were 99.85%±0.26% and the mean percentage differences in the normalization point doses were -1.41%. The transmission methodology was approved in 24 of 25 IMRT test irradiations. Based on these results, it can be concluded that the proposed methodology using RCFs can be applied for in vivo QA in RT treatments. PACS number: 87.55.Qr, 87.55.km, 87.55.N.Despite individual quality assurance (QA) being recommended for complex techniques in radiotherapy (RT) treatment, the possibility of errors in dose delivery during therapeutic application has been verified. Therefore, it is fundamentally important to conduct in vivo QA during treatment. This work presents an in vivo transmission quality control methodology, using radiochromic film (RCF) coupled to the linear accelerator (linac) accessory holder. This QA methodology compares the dose distribution measured by the film in the linac accessory holder with the dose distribution expected by the treatment planning software. The calculated dose distribution is obtained in the coronal and central plane of a phantom with the same dimensions of the acrylic support used for positioning the film but in a source‐to‐detector distance (SDD) of 100 cm, as a result of transferring the IMRT plan in question with all the fields positioned with the gantry vertically, that is, perpendicular to the phantom. To validate this procedure, first of all a Monte Carlo simulation using PENELOPE code was done to evaluate the differences between the dose distributions measured by the film in a SDD of 56.8 cm and 100 cm. After that, several simple dose distribution tests were evaluated using the proposed methodology, and finally a study using IMRT treatments was done. In the Monte Carlo simulation, the mean percentage of points approved in the gamma function comparing the dose distribution acquired in the two SDDs were 99.92%±0.14%. In the simple dose distribution tests, the mean percentage of points approved in the gamma function were 99.85%±0.26% and the mean percentage differences in the normalization point doses were −1.41%. The transmission methodology was approved in 24 of 25 IMRT test irradiations. Based on these results, it can be concluded that the proposed methodology using RCFs can be applied for in vivo QA in RT treatments. PACS number: 87.55.Qr, 87.55.km, 87.55.N‐

Accuracy of dose planning for prostate radiotherapy in the presence of metallic implants evaluated by electron spin resonance dosimetry

Radiotherapy is one of the main approaches to cure prostate cancer, and its success depends on the accuracy of dose planning. A complicating factor is the presence of a metallic prosthesis in the femur and pelvis, which is becoming more common in elderly populations. The goal of this work was to perform dose measurements to check the accuracy of radiotherapy treatment planning under these complicated conditions. To accomplish this, a scale phantom of an adult pelvic region was used with alanine dosimeters inserted in the prostate region. This phantom was irradiated according to the planned treatment under the following three conditions: with two metallic prostheses in the region of the femur head, with only one prosthesis, and without any prostheses. The combined relative standard uncertainty of dose measurement by electron spin resonance (ESR)/alanine was 5.05%, whereas the combined relative standard uncertainty of the applied dose was 3.35%, resulting in a combined relative standard uncertainty of the whole process of 6.06%. The ESR dosimetry indicated that there was no difference (P>0.05, ANOVA) in dosage between the planned dose and treatments. The results are in the range of the planned dose, within the combined relative uncertainty, demonstrating that the treatment-planning system compensates for the effects caused by the presence of femur and hip metal prostheses.

Radioterapia de intensidade modulada (IMRT) para pacientes do SUS: análise de 508 tratamentos em dois anos de instalação da técnica

The Bosniak classification for renal cysts was developed in the late 1980s in an attempt to standardize the description and management of complex cystic renal lesions. Alterations were made to such a classification in the 1990s and, the last one, in 2005. Currently, five categories of cystic renal lesions are defined - namely, I, II, II-F, III and IV –, according to their degree of complexity and likelihood of malignancy. Despite being initially described for computed tomography, this classification has been also utilized with some advantages also for magnetic resonance imaging. The present article reviews the different phases of this classification, its diagnostic efficacy and the most controversial features of its use.The Bosniak classification for renal cysts was developed in the late 1980s in an attempt to standardize the description and management of complex cystic renal lesions. Alterations were made to such a classification in the 1990s and, the last one, in 2005. Currently, five categories of cystic renal lesions are defined - namely, I, II, II-F, III and IV –, according to their degree of complexity and likelihood of malignancy. Despite being initially described for computed tomography, this classification has been also utilized with some advantages also for magnetic resonance imaging. The present article reviews the different phases of this classification, its diagnostic efficacy and the most controversial features of its use.

Calibração de diodos semicondutores para dosimetria in vivo em tratamentos de irradiação de corpo inteiro

Este trabalho apresenta os resultados de dosimetria in vivo com diodos semicondutores tipo-p, EDP-15 (Scanditronix Wellhofer), em tratamentos de irradiacao de corpo inteiro de dois pacientes, do Hospital das Clinicas da Faculdade de Medicina de Ribeirao Preto da Universidade de Sao Paulo (HCFMRP-USP). Os diodos foram previamente calibrados e os fatores de calibracao foram determinados com o auxilio de uma câmara de ionizacao de referencia (FC065, IBA Dosimetry, volume sensivel de 0,65 cm3 ). A calibracao foi realizada em um setup de Irradiacao de Corpo Inteiro (TBI), utilizando objetos simuladores de agua solida. Diferentes espessuras do diâmetro latero-lateral (DLL) de um paciente foram simuladas e, posteriormente, determinados os fatores de calibracao com base nas leituras de dose na profundidade de maxima dose (metade da espessura do DLL). A diferenca na resposta do diodo para a dose prescrita nos dois tratamentos foi inferior a 4%. Assim, ficou demonstrado que essa diferenca esta dentro do recomendado pelo International Comission on Radiation Units (ICRU), que e igual a ±5%

Validação dos algoritmos de cálculo de dose do sistema de planejamento XiO® considerando as correções para heterogeneidade dos tecidos

Uma vez que a secao de choque para diferentes tipos de interacao da radiacao com a materia tem dependencia com o tipo de material ou tecido, a presenca de heterogeneidade nos mesmos influencia a dose total administrada. O objetivo deste trabalho e analisar o calculo da distribuicao de dose dos algoritmos do sistema de planejamento XiO® (Fast FourierTransform, Convolution, Superposition, Fast Superposition e Clarkson) quando se utiliza correcao de heterogeneidade entre tecidos de diferentes densidades. Foram utilizados objetos simuladores com placas de aluminio, osso, agua solida e cortica e uma câmara de ionizacao tipo Farmer da Iba modelo FC65-G, posicionados sobre as mesmas condicoes no acelerador linear ONCOR® e no CT Simulador Brilliance, para comparar a dose medida com a dose calculada pelos algoritmos do sistema de planejamento. A diferenca percentual entre os valores medidos e calculados pelos algoritmos foram menores que 5%. O metodo com calculo mais preciso para materiais de maior densidade foi o Convolution, em que esta diferenca percentual foi de aproximadamente 1%. Ja para materiais de menor densidade o Superposition foi mais preciso, com diferenca percentual de 1,1%.