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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.

Purpose: To measure leakage and transmission factors using three different film detectors under the same conditions using a micro‐multileaf collimator coupled to a dedicated 6MV linear accelerator for head and neck treatments.Method and Materials:Measurements were performed using three different films: GafChromic EBT film, Kodak©‐XOMAT‐V2 (XV), and Kodak EDR2. Radiographic and Radiochromic films were handled according to protocol TG‐69 and TG‐55, respectively. Each film was calibrated following the same protocol and each film calibration curve relating dose and film response was acquired. Readout of all films was performed using a commercial flatbed scanner Microtek 9600XL. Images analysis was performed with ImageJ. Leakage and transmission measurements were done under the same conditions at Dmax. Open reference fields were irradiated for each film according to its particular dynamic range. Results: The transmission average percent values found were: 0.93% +− 0.09, 0.99% +−0.07, 0.95%+−0.08 and leakage average percent values found were 1.09%+−0.08, 1.14%+−0.09, 1.11%+−0.09 for EBT, XV and EDR2 respectively. When analyzing leakage and transmission profiles an over response in XV measurements is evident. Measurements between EBT and EDR2 present more similar values. Differences between films are more pronounced for transmission than for leakage and also are more pronounced for the peripheral region of the collimator than for the central region. Conclusion: Leakage and transmission measurements with film may present variations according to each detector.Radiographic films present an over response for low energy scatter photons, this was particularly present for XV film. This over response is more notorious for transmission than for leakage zones. Variations also are associated with the zone of the collimator. According to previous Monte Carlo simulations this may be due the over response from low energy electrons generated in the collimator.

Purpose: To establish a protocol for directly measuring spatial dose deposition and activity distribution of beta particles emitted by Re‐186 transported by liposomes in a HNSCC Xenografts in Nude Rats using HS GafChromic dosimetry media. Method and Materials: Nude rats (n=3) at 4–5 weeks age (75–100 g) bearing a tumor with an average volume of 1.73±0.37 cm3 were injected intratumorally with 0.29±0.05 ml of 18.5±2.7 MBq (0.50±0.09 mCi) 186Re‐liposomes, which contained 4.0±0.7 mg of DSPC and cholesterol. The 186Re‐liposome dose was equally divided and delivered to several separate locations of the tumor.SPECT and CTimages in vivo were acquired using a micro‐SPECT/CT scanner. The rats were sacrificed six hours after liposome injection, and tumor lobes were excised and sectioned in slices (3 mm thickness). HS films were placed between each slice and the tumor lobe was reassembled to its original shape. Film calibration was performed between 0–40 Gy using 60Co γ rays. Film response was measured using a flatbed scanner in 36 bits RGB transmission mode. Dose distributions were extracted from the red and green components. Results: The 2D spatial dose distributions are highly heterogeneous with dose regions above 40 Gy. Dose gradients up to 40 Gy in distances smaller than 2 mm in the center of the slice tumor were found. While comparing dose distributions between the 3 different tumors, significant differences in the volumes (larger than 30%) covered by the isodose curves of 1 Gy were observed. Conclusion: The method to measure direct dose distributions produced by Re‐186 transported by liposomes using GafChromic HS film has proved to be adequate for the large dose gradients produced. The use of the different components of the scanned image (red and green) allows us to extend the sensitivity range of the HS film without loss of precision.