Purpose: According to the literature radiochromic film GafChromic EBT® (ISP Corp., USA) is an excellent detector to be used for small beam dosimetry. By using the fact that these films can be immersed in water for radiation measurements, this work investigates its performance in a water phantom for small beam measurements. Method and Materials: Tissue maximum ratios (TMR), total output factors (OF) and off axis ratios (OARs) were measured in a water phantom (MP3XS, PTW‐Freiburg, Germany) using GafChromic EBT® film and a shielded solid state detector (PFD3G, IBA‐dosimetry, Germany). Circular collimators (4 to 20 mm in diameter) coupled to a dedicated 6 MV linear accelerator (Novalis®, BrainLAB, Germany) were used. Films were calibrated against an ionization chamber at dmax covering a dose range from 0.01 to 450 cGy. Analysis was performed using a commercial flat bed scanner (Microtek 9600XL) in transmission mode at 100 dpi and 48 bit color depth (RGB format). The films were carefully handled and analyzed following the recommendations of the TG55 report and those proposed by others authors. The measurements using both detectors were compared to evaluate accuracy and reproducibility. Results: The reproducibility of the EBT film is reported to be within 1–2% using a commercial flat bed scanner. The highest differences between GafChromic EBT film and diode measurements for all circular collimators were 0.87%, 2.69% and 7.61% for OAR, OF and TMR, respectively. Conclusion: The use of GafChromic EBT immersed in a water phantom allowed reliable dose measurements. Although differences are present in the TMR values, the fact that the diode is not tissue equivalent as the film may explain these differences. The use of Monte Carlo simulations may be helpful to enlighten this issue.
Among all vascular malformations, the intracranial arteriovenous malformations (AVM's) have the most powerful impact from the clinical point of view. The manifestations include hemorrhage, seizures, headacheh, but sometimes they are incidentally found during the diagnostic approach of patients with head trauma or chronic headache. There are three different types of treatments: microsurgery, endovascular treatment and radiosurgery. The actual role of the endovascular treatment is as an adjuvant therapy before microsurgery or radiosurgery just to diminish the nidus size. The goal of all treatments is complete nidus obliteration without causing a new neurological deficit. The overall obliteration index with LINAC based radiosurgery is about 80% and the result is dose, volume and time dependent. The mean dose reported in the literature fluctuates between 15 and 25 Gy, and the isodose coverage curve for the AVM with LINAC is generally the one of the 80%. There can be a treatment failure defined as the necessity to retreat the patient after three years from the first radiosurgical treatment in about 26% of the patients. There is a lack of evidence, principally from randomized trials, to point out the role of each of the modalities in the treatment of the AVM.
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