Abstract
The purpose of this study was to evaluate the use of the pre-treatment daily imaging system with the Brainlab ExacTrac X-Ray 6D for patients in hypofractionated intracranial treatments and radiosurgery procedures in order to quantify setups errors and review margins used by the institution in the current planning protocol. The deviations generated in the translational and rotational coordinates were given in terms of the mean values and their respective standard deviations. The random and systematic errors were determined through the Stroom and Wang relation and 36 patients treated with intracranial hypofractionated radiosurgery from August 2015 to October 2016 were evaluated. The prescribed dose was 25-30 Gy in 5 fractions for 30 patients and 12-18 Gy in a single fraction for 6 patients. The calculated margin for the planning target volume (PTV) from the deviations analyzed was 1.3mm, consistent with that adopted by the institution. When the correlation between the volume of the PTV, vector and its respective loss of coverage is evaluated and a tendency can be observed for smaller volumes to suffer greater losses in coverage when the isocenters were displaced with the resulting margins. We can suggest that for volumes smaller than 2.6 cm3, margins greater than 1 mm are required in order to guarantee the expected coverage of the PTV.
Highlights
The International Commission on Radiation Units and Measurements (ICRU) considers three sources of uncertainties in the delivery of the planned dose to the patient: variations in patient positioning, internal organ movement, and equipment-related failures
The objective of this study is to evaluate the use of the pre-treatment daily imaging system with the Brainlab ExacTrac X-Ray 6D for patients in hypofractionated intracranial and radiosurgery treatments in order to quantify the setups errors, review margins used by the institution for the current planning protocol and create a model between the volume of the planning target volume (PTV), shift vector and its respective loss of coverage
It was found that set up uncertainties for patients treated with hypofractionated intracranial radiosurgery using Image-guided radiation therapy (IGRT) with ExacTrac at this institution are in agreement with the radiosurgery protocols as presented in a preliminary research[15]
Summary
The International Commission on Radiation Units and Measurements (ICRU) considers three sources of uncertainties in the delivery of the planned dose to the patient: variations in patient positioning, internal organ movement, and equipment-related failures. With increasing technology in radiotherapy, the complexity of treatment planning has increased and higher doses have been delivered to the tumor, so it is necessary to accurately assess the intrinsic deviations associated with the treatment in order to ensure better compliance of the tumor with greater protection of healthy tissues. To achieve this goal, high-accurate positioning plays a mandatory role, especially for hypofractionated treatments, as well as cranial radiosurgery evaluated in this study[2]. The acquired images during treatment can be used for monitoring patient and target geometry changes, potential adaptive planning or margin reduction[4,5]
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