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Marko Laaksomaa
Participant

Hi

These are the results of ablation.

Purpose: The purpose of this study was to compare and investigate the AlignRT and laser setup accuracy of the free breathing breast mastectomy radiotherapy patients. The study answer to question: is it possible to treat the mastectomy patients in our unit without IGRT with the margin of 5 mm in the lymph node area with AlignRT?

Materials and methods: 17 + 17 laser (L) and AlignRT (A) patients and 380 (L), 224 (A) orthogonal image pairs and 169 (L), 231 (A) tangential images were retrospectively evaluated.  Patient setup was performed in group L with the four reference tattoos: middle tattoo on the sternum, one tattoo for the straightness 20 cm caudally and lateral tattoos on the rigid surface (below healthy breast and one on the opposite side). Delta couch shift was done after setup to reach the initial isocenter position before image guidance. In group A, area of interest was performed based on AlignRT ROI drawing guidelines, including the treated chest wall. Bolus was used in both groups and it was outside ROI in group A. The estimated issues in the images were isocenter shifts, the accuracy in the lymph node area with and without daily image guidance, tangential image accuracy and displacement of the structures near PTV in relation to each other to demonstrate the rotations.

Results: Systematic, random, margin (cm). AP=vertical, SI=longitudinal, LAT=Lateral (in this order). L=Laser setup, A=AlignRT setup. Daily IGRT=D, no IGRT = N#. Residual errors=R, errors from structure to structure=S. 1) Isocenter (N, R): L 0.09,0.16,0.18, 0.34,0.33,0.27,0.45,0.64,0.63; A 0.08,0.15,0.16, 0.16,0.22,0.21, 0.31,0.52,0.56. 2) TH1 SI,LAT (N, R): L 0.16,0.18,0.28, 0.38,0.35,0.31, 0.66,0.69,0.92; A 0.14,0.21,0.19,0.19,0.25,0.25,0.48,0.70,0.65. (D, R): L 0.16,0.09,0.14,0.18,0.16,0.16, 0.54, 0.35, 0.46; A 0.12,0.07,0.07,0.14,0.13,0.13,0.39,0.28,0.26. 3) Shoulder joint SI, LAT (N, R): L 0.25,0.25,0.31,0.30,0.84,0.83; A 0.27,0.28,0.26,0.27,0.86,0.88. (D, R): L 0.17,0.16,0.24,0.20,0.60,0.53 ; A 0.19,0.19,0.20,0.20,0.60,0.53. 4) Tangential image MID_PTV ribs VRT/LAT, SI (D pre orthogonal kV/kV!, R): L 0.07,0.09,0.08,0.11,0.23,0.3; A 0.08,0.06,0.07,0.11,0.24,0.21. 5) th1-th10 SI, LAT (S): L 0.11,0.06,0.15,0.14,0.11,0.17; A 0.05,0.04,0.19,0.09,0.09,0.16. 6) th6-sternum AP,SI (S): L 0.11,0.20,0.16,0.20; A 0.12,0.16,0.14,0.19. 7) th1-shoulder joint SI, LAT (S): L 0.28,0.16,0.28,0.19; A 0.21,0.19,0.23,0.19. #Isocenter error was corrected in both groups during the first three fractions with the action level of 4 mm and the data is collected beginning from the fourth fraction. Exceeding of 5 mm in th1 (L,N) AP 27%, SI 26%, LAT, 29% (A,N) 7%,19%,16 %. Exceeding of 7 mm in shoulder joint (L,A,N) SI 13%, LAT 10%. In the group A 49 tangential images were available from the fractions where only tangential image was acquired, none of those exceeded 2 mm in LAT/VRT and 3 mm in SI. Corresponding data was not available in group L.

Conclusions: Daily IGRT is recommended for the laser/tattoo- group to achieve adequate accuracy in the tangential image and lymph nodes due to large isocenter variation in the all investigated directions. In AlignRT group weekly IGRT with the thresholds is needed to verify/correct the combined effect of the isocenter- and displacement errors of the bony structures related to lymph nodes.  In the A group data 6/7 out of 10 patients could be treated completely without IGRT, in practice weekly IGRT is still demanded IGRT- protocoll in group A in our unit. The difference of the displacement errors demonstrating rotations and arm position was minor between the groups.