Purpose: When comparing different scans of the same radiochromic film, several patterns can be observed. These patterns are caused by different sources of uncertainty, which affect the repeatability of the scanner. The purpose of this work was to study these uncertainties. Methods:The variance of the scanner noise, as a function of the pixel position, was studied for different resolutions. The inter-scan variability of the scanner response was analyzed taking into account spatial discrepancies. Finally, the distance between the position of the same point in different scans was examined.Results: The variance of noise follows periodical patterns in both axes, causing the grid patterns. These patterns were identified for resolutions of 50, 72 and 96 dpi, but not for 150 dpi. Specially recognizable is the sinusoidal shape with a period of 8.5 mm that is produced with 72 dpi. Inter-scan variations of the response caused systematic relative dose deviations larger than 1% in 5% of the red channel images, 9% of the green and 51% of the blue. No systematic deviation larger than 1% was found after applying response corrections. The initial positioning and the speed of the scanner lamp vary between scans.Conclusions: Three new sources of uncertainty, which influence radiochromic film dosimetry with flatbed scanners, have been identified and analyzed in this work: grid patterns, spatial inter-scan variations and scanning reading repeatability. A novel correction method is proposed, which mitigates spatial inter-scan variations caused by deviations in the autocalibration of the individual Charge Coupled Device detectors.

BackgroundThe aim of the study was to quantify planned doses to the heart and specific cardiac substructures in free-breathing adjuvant three-dimensional radiation therapy (3D-CRT) and tangential intensity modulated radiotherapy (t-IMRT) for left-sided node-negative breast cancer, and to assess the differences in planned doses to organs at risk according to patients’ individual anatomy, including breast volume.Patients and methodsIn the study, the whole heart and cardiac substructures were delineated for 60 patients using cardiac atlas. For each patient, 3D-CRT and t-IMRT plans were generated. The prescribed dose was 42.72 Gy in 16 fractions. Patients were divided into groups with small, medium, and large clinical target volume (CTV). Calculated dose distributions were compared amongst the two techniques and the three different groups of CTV.ResultsMean absorbed dose to the whole heart (MWHD) (1.9 vs. 2.1 Gy, P < 0.005), left anterior descending coronary artery mean dose (8.2 vs. 8.4 Gy, P < 0.005) and left ventricle (LV) mean dose (3.0 vs. 3.2, P < 0.005) were all significantly lower with 3D-CRT technique compared to t-IMRT. Apical (8.5 vs. 9.0, P < 0.005) and anterior LV walls (5.0 vs. 5.4 Gy, P < 0.005) received the highest mean dose (Dmean). MWHD and LV-Dmean increased with increasing CTV size regardless of the technique. Low MWHD values (< 2.5 Gy) were achieved in 44 (73.3%) and 41 (68.3%) patients for 3D-CRT and t-IMRT techniques, correspondingly.ConclusionsOur study confirms a considerable range of the planned doses within the heart for adjuvant 3D-CRT or t-IMRT in node-negative breast cancer. We observed differences in heart dosimetric metrics between the three groups of CTV size, regardless of the radiotherapy planning technique.

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