BackgroundRadiotherapy (RT) is frequently used in the treatment of head and neck cancer, but different side-effects are frequently reported, including a higher frequency of radiation-related caries, what may be consequence of direct radiation to dental tissue. The intensity-modulated radiotherapy (IMRT) was developed to improve tumor control and decrease patient’s morbidity by delivering radiation beams only to tumor shapes and sparing normal tissue. However, teeth are usually not included in IMRT plannings and the real efficacy of IMRT in the dental context has not been addressed. Therefore, the aim of this study is to assess whether IMRT delivers lower radiation doses to dental structures than conformal 3D radiotherapy (3DRT).Material and methodsRadiation dose delivery to dental structures of 80 patients treated for head and neck cancers (oral cavity, tongue, nasopharynx and oropharynx) with IMRT (40 patients) and 3DRT (40 patients) were assessed by individually contouring tooth crowns on patients’ treatment plans. Clinicopathological data were retrieved from patients’ medical files.ResultsThe average dose of radiation to teeth delivered by IMRT was significantly lower than with 3DRT (p = 0.007); however, only patients affected by nasopharynx and oral cavity cancers demonstrated significantly lower doses with IMRT (p = 0.012 and p = 0.011, respectively). Molars received more radiation with both 3DRT and IMRT, but the latter delivered significantly lower radiation in this group of teeth (p < 0.001), whereas no significant difference was found for the other dental groups. Maxillary teeth received lower doses than mandibular teeth, but only IMRT delivered significantly lower doses (p = 0.011 and p = 0.003). Ipsilateral teeth received higher doses than contralateral teeth with both techniques and IMRT delivered significantly lower radiation than 3DRT for contralateral dental structures (p < 0.001).ConclusionIMRT delivered lower radiation doses to teeth than 3DRT, but only for some groups of patients and teeth, suggesting that this decrease was more likely due to the protection of other high risk organs, and was not enough to remove teeth from the zone of high risk for radiogenic disturbance (>30Gy).
The lack of well established dosimetry protocols for HDR sources is a point of great concern regarding the uniformity of procedures within a particular country and worldwide. The main objective of this paper is to report the results from ten institutions of an intercomparison of calibration procedures for 192Ir HDR sources currently in use in Brazil. The treatment irradiator of one institution was calibrated by a reference system and used by all participants with their own measuring electrometers and ionization chambers under the same experimental conditions. Two methods were used: the calibration jig and the well-type ionization chamber. Each participant was allowed to use their own method and formalism. The results of this exercise were very positive since this was the first time in Brazil that a group of users gathered to share their experience and openly discuss the physical concepts behind the calibration procedures. The results were all within +/-3.0%, except one case where -4.6% was observed and later identified as a problem with the Nk value for x-rays. Though the magnitude of the deviations found was generally acceptable considering the diversity of formalisms currently in use, a proposal is now being prepared to be adopted as a national protocol. The identification of the institutions was left out for the sake of confidentiality.
Ionization chambers are special detectors for radiation beam dosimetry in hospitals. In this work, a PMMA parallel-plate ionization chamber with air sensitive volume was designed and built for use in electron beams of linear accelerators. This ionization chamber has a PMMA collecting electrode covered with silver paint. Several characterization tests were undertaken following international recommendations. The ionization chamber showed good performance in the characterization tests of its electrical properties and in most of the tests performed in the linear accelerator beams.
The formalism used for barriers calculations is based on a conservative estimation of workload, use factor, and occupancy factor. IMRT techniques (Intensity Modulated Radiation Therapy) and VMAT (Volumetric Modulated Arc Therapy) are known for being superior to conventional techniques, but costly from the shielding standpoint, as they increase the number of monitor units used to deliver the same dose to the patient, increasing the leakage radiation produced and, consequently, the thickness of the secondary barriers. At InRad (Radiology Institute of HC-FMUSP) a 2100CD LINAC already installed was upgraded to perform IMRT/VMAT techniques, and the existing barrier was reassessed. The present study proposes a methodology for acquiring real workload data from the institution's management software (MOSAIQ®) to replace the initially estimated data and recalculate the thickness of the barriers, assessing the impact of the introduction of these techniques and understanding the profile of the treatments carried out at the institution over the years of 2010 to 2020. Through this methodology, a decrease in the workload of 15 MV was observed as the technique of modulated intensity with 6 MV was introduced, reducing the thicknesses calculated for primary barriers. However, no significant changes were observed in the thicknesses calculated for the secondary barriers, because despite the increase in the leakage workload of 6 MV, the total workload of 15 MV decreased. There was also a trend towards an increase in the number of patients treated with modulated intensity year after year, which went from 5% in 2016 to 67% in 2020.
OBJETIVO: Este trabalho foi realizado com o objetivo de caracterizar o detector de diamante, bem como observar seu comportamento. MATERIAIS E MÉTODOS: As características dosimétricas de feixes de fótons de 6 MV de energia foram medidas utilizando o sistema automático de varredura MP3 da PTW com um detector de diamante e foram comparadas com medidas usando uma câmara de ionização 31010 da PTW. RESULTADOS: As características dosimétricas do detector de diamante foram observadas por meio de medidas de linearidade com a dose, dependência com a taxa de dose e distribuições de dose em profundidade, bem como perfis. CONCLUSÃO: Algumas medidas com diamante e câmara de ionização foram validadas com resultados publicados na literatura, o que demonstrou um bom comportamento do detector de diamante na comparação com a câmara de ionização, muito utilizada para dosimetria em radioterapia, evidenciando que o diamante é uma boa escolha de detector para dosimetria de campos pequenos.
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