The purpose of this study was to evaluate the triple channel correction acquisition (TCCA) method for radiochromic film dosimetry performed with a flatbed scanner. The study had two parts: a fundamental and a clinical examination. In the fundamental examination, we evaluated the accuracy of calibration curves for Gafchromic EBT2 (EBT2). The films were calibrated using a field-by-field method with 13 dose steps. Seven calibration curves obtained by TCCA were compared with those produced by a single channel acquisition (SCA) method. For the clinical examination, we compared relative dose distributions obtained by TCCA and SCA for four cases of intensity-modulated radiation therapy (IMRT) and intensity-modulated arc therapy (IMAT). The fundamental examination showed that the consistency of the calibration curves was better for TCCA than for SCA, particularly for the dose range between 0.25 Gy and 1.00 Gy. The clinical examination showed that the dose differences between the measured and calculated doses in high-gradient regions were smaller with TCCA than with SCA. The average pass rates in gamma analysis for the TCCA and SCA methods were 97.2 ± 0.8% (n = 20) and 93.0 ± 1.2% (n = 20), respectively. In conclusion, TCCA can acquire accurate average dose values when creating the calibration curve. The potential advantage of TCCA for EBT2 film dosimetry was seen in high-gradient regions in clinically relevant IMRT and IMAT cases. TCCA is useful to verify dose distribution.

Several tools are used for the dosimetric verification of intensity-modulated arc therapy (IMAT) treatment delivery. However, limited information is available for composite on-line evaluation of these tools. The purpose of this study was to evaluate the dosimetric verification of IMAT treatment plans using a 2D diode array detector (2D array), radiochromic film (RCF) and radiosensitive polymer gel dosimeter (RPGD). The specific verification plans were created for IMAT for two prostate cancer patients by use of the clinical treatment plans. Accordingly, the IMAT deliveries were performed with the 2D array on a gantry-mounting device, RCF in a cylindrical acrylic phantom, and the RPGD in two cylindrical phantoms. After the irradiation, the planar dose distributions from the 2D array and the RCFs, and the 3D dose distributions from the RPGD measurements were compared with the calculated dose distributions using the gamma analysis method (3% dose difference and 3-mm distance-to-agreement criterion), dose-dependent dose difference diagrams, dose difference histograms, and isodose distributions. The gamma passing rates of 2D array, RCFs and RPGD for one patient were 99.5%, 96.5% and 93.7%, respectively; the corresponding values for the second patient were 97.5%, 92.6% and 92.9%. Mean percentage differences between the RPGD measured and calculated doses in 3D volumes containing PTVs were –0.29 ± 7.1% and 0.97 ± 7.6% for the two patients, respectively. In conclusion, IMAT prostate plans can be delivered with high accuracy, although the 3D measurements indicated less satisfactory agreement with the treatment plans, mainly due to the dosimetric inaccuracy in low-dose regions of the RPGD measurements.

Purpose: To verify 3D dose distributions predicted by Eclipse treatment planning software (with AAA version 8.2.23) with those measured by polymer gel dosimeters for RapidArc intensity modulated arc radiation therapy. Methods: Treatment plans were created for RapidArc therapy of two prostate cancer patients. The daily fraction size was 180 cGy for both plans (R and E). The treatments used 10MV photon beams from a Varian iX linear accelerator. Two cylindrical phantoms (15 cm diameter and 15 cm long) containing BANG3‐PRO polymer gel were used. For dosimetric verification, QA plans were created using the CT images of the polymer gel phantom, which were obtained using 3‐mm thick slices. The phantoms were irradiated using the dose delivery techniques identical to those used for the patient treatments. After irradiation, the phantoms were scanned using a 32 spin‐echo technique with a 3T MRI scanner. The major imaging parameters were as follows: 1 mm × 1mm pixels, 45 2‐mm thick slices, and the echo spacing of 13.6 ms. The MRI images were processed to obtain 3D dose distributions using in‐house MATLAB programs. 3D dose distributions of measurements and calculations were compared using gamma index (3 % and 3 mm criteria), dose volume and dose difference diagrams, line dose profiles, and planer dose distributions. Results: Mean percentage differences between the measured and calculated doses in the 3D volumes containing PTVs were −3.1±11.9 % and 1.6±9.8 % for Plans R and E, respectively. The passing rates of the gamma index analyses were 90% and 84% for doses greater than 80% of the maximum doses of those plans. Conclusions: The current study has demonstrated a potential usefulness of polymer gel dosimetry for 3D dose verification of RapidArc plans. However, the agreement of measured and calculated doses was not satisfactory. The causes of the disagreements need to be investigated. Japanese Society of Radiological Technology