SGRT Forum

Hi all

I created a small poster kind of letter to this forum about what I have find out from the RTTs view.

Purpose: FB n0- breast patients setup errors were compared between AlignRT (A) n=17 and laser setup (L) n=17, number of orthogonal image pairs 400 (179+221) in total. Methods: The estimated errors were pitch (errors between MID_PTV vertebra and sternum, errors between th1-4 - th10 in vertical), rotation (errors between th1 and th10 in LAT) and arm position (errors between th1 and shoulder joint in LNG and LAT), residual errors for the named structures with A setup only and with daily IGRT, isocenter corrections after A/L- setup and tangential image accuracy (chest wall, breast). For the setup 1 mm and 1 degree accuracy was demanded with A. In group L four tattoos were used for the setup: mid- line tattoos on the sternum and 20 cm caudally, lateral tattoos below breasts on the rigid surface. In total 86 errors were compared in VRT,LNG and LAT directions (43 systematic and 43 random). Opposite T-Roi was used in A including small medial portion of both breast and excluding the diapraghm. Position of the arm was checked and when needed corrected with the aid of treatment capture at the setup process. Results: 23% (20/86) of the estimated errors were better (p<0.05) with A than with L, none of the errors were better with L. From those 20 improved errors, the type of the errors were in 80% of the cases random and in 20% systematic. Random errors for the isocenter corrections in online match were in LNG and LAT directions with A 0.22 cm,0.21 cm and with L setup 0.39 cm,0.34 cm. Residual errors with only A setup, without IGRT, exceeded 5mm in 14% of the fractions in th1 area, 7 mm in shoulder joint area was exceeded in 13% of the fractions. 1% of the MID_PTV ribs in tangential images were out of tolerance 5mm in LNG and 4 mm in LAT/VRT. Conclusions: Possibility that only tangential image (without the aid of orthogonal image match) is daily in tolerances is much better with A setup than with L setup due to smaller isocenter variation. Also random errors in the patient posture changes were found partly lower with A in the investigated groups. To minimize systematic posture errors with A, offline review is recommended and permanent reference surface for the setup should not be taken at the fraction there is displacement errors of the structures in the images. AlignRT is more reproducible method to setup FB n0 patients than conventional tattoo based setup. For the A breast patients treated with lymph nodes at our unit, 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.

Sometimes earlier we discussed about pitch, which causes residual errors for the spine in LNG direction. As a free discussion I could say that I have noticed three different kind of pitch in the images with and without AlignRT. First one is seen in the vertebra. There is displacement error between cranial and caudal part of spine in LAT- image in vertical. This seems to be possible to correct with AlignRT- setup such that patient moves in CC direction and mostly AlignRT notices this kind of pitch in the sternum, as someone here mentioned earlier. The other case is such that there is not displacement error in the vertebra in LAT kV- image, but there is pitch in the sternum which is seen also in AlignRT. This has something to do with the different relaxation between CT and setup and correction may be difficult. The third case is that entire chest wall and the arm is shifted in CC without numerical or visual pitch in the AlignRT. Fixation seems important in this as mentioned here. The correction strategy usually needs offline review evaluation during the first fractions. If in theory 2 out of 3 error types in pitch is visible with AlignRT, I agree that also this is as an advantage for SGRT. The realized spine accuracy in LNG is what I am interested in other units results with AlignRT setup. In n0 breast this knowledge may have negligible significance, but in n+ treatments we consider this important as spine and arm position correlates with the lymph nodes. For comparison with us, I challenge you to offline match the th1-4 (and shoulder joint) from about 20 patients and add those results in Excell to existing isocenter correction-results to find out the local accuracy of the structure with AlignRT setup (without IGRT). It is all done in one day.

marko.laaksomaa@pshp.fi

Best regards Marko

I add here part of those AlignRT/Laser FB n0 setup 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 0.09,0.17,0.17, 0.22,0.39,0.34, 0.39,0.70,0.67; A 0.09,0.15,0.13, 0.18,0.22,0.21, 0.35,0.52,0.48. 2) TH1 (N, R): L 0.12,0.26,0.21, 0.25,0.42,0.39, 0.48,0.95,0.8; A 0.16,0.21,0.21,0.18,0.25,0.27,0.53,0.71,0.71. (D, R): L 0.16,0.14,0.08,0.19,0.22,0.17, 0.54, 0.51, 0.32; A 0.13,0.07,0.10,0.15,0.13,0.15,0.43,0.28,0.34. 3) Shoulder joint SI, LAT (N, R): L 0.35,0.20,0.36,0.36,1.13,0.75; A 0.31,0.24,0.33,0.27,1.00,0.79. (D, R): L 0.28,0.16,0.31,0.19,0.92,0.53 ; A 0.25,0.23,0.28,0.21,0.82,0.72. 4) Tangential image MID_PTV ribs VRT/LAT, SI (D pre orthogonal kV/kV!, R): L 0.06,0.08,0.05,0.08,0.18,0.25; A 0.06,0.08,0.08,0.12,0.22,0.29. 5) th1-th10 (S): L 0.17,0.06,0.13,0.15,0.11,0.21; A 0.09,0.04,0.12,0.15,0.08,0.17. 6) th6-sternum (S): L 0.22,0.26,0.21,0.27; A 0.15,0.26,0.16,0.18. 7) th1-shoulder joint (S): L 0.40,0.16,0.36,0.23; A 0.28,0.28,0.29,0.21.

#Isocenter error is corrected in both groups during the first three fractions and the data is collected beginning from the fourth fraction.

As seen, in laser group with the daily AP+LAT IGRT residual margins are adequate and near daily SGRT+IGRT margins. Main conclusion is that with AlignRT isocenter and patient posture variation is small  enough in n0 group in most cases to go on with the tangential images only, which is not possible in laser group mostly due to larger isocenter variation.

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.

Hello

Introduction: During this week I did some different additional calculations to presented FB mastectomy (M) and resection (n0) setup results, mostly regarding tangential image accuracy without IGRT. I added isocenter couch correction values (based on the online match and which include observer variation) in SI direction to offline matched tangential image MID_PTV ribs residual error values in SI. In that way we get isocenter errors in tangential images in SI direction without IGRT. All the fractions where only tangential image was acquired were also taken into account. Also residual errors without IGRT, to the most commonly used matching compromise point in between of MID_PTV ribs (lateral border) in AP image and MID_PTV sternum in LAT image in orthogonal images was calculated similarly in AP, SI and LAT directions (=online couch shift + error to the structure) in M group.

Results: Tangential image MID_PTV ribs (N, R) SI, M, L 0.16, 0.33, 0.65.M, A 0.1, 0.19, 0.38. n0, L 0.22, 0.35, 0.79. n0, A 0.11, 0.20, 0.41. and residual errors larger than 4.5 mm M, L 20%, A 4.5%, n0, L 24%, A 4%. Compromise MID_PTV ribs  (AP- image) + sternum (LAT- image) (N, R)  AP, SI, LAT, M, L 0.14, 0.16, 0.18, 0.37, 0.29, 0.26, 0.60, 0.63, 0.69. M, A 0.13, 0.15, 0.15, 0.19, 0.22, 0.23, 0.45, 0.53, 0.54, residual errors larger than 4.5 mm M, L 27, 20, 13%, A 7, 10, 9%. AP- image MID_PTV ribs- th6 (roll) (S) M, LAT L 0.11, 0.15. A 0.11, 0.10.

Conclusion: With AlignRT setup in group M, residual errors to the most commonly used compromised matching location in orthogonal images (MID_ribs + sternum) were in 90% of the fractions inside 4.5 mm accuracy after systematic isocenter error was corrected with 4 mm AL in the first three fractions. The possibility that more than 4.5mm errors exists without IGRT with mastectomy patients is approximately two times more possible 1) in total in group L than in group A in MID_ribs + sternum location and 2) in SI direction in location th1 (demonstrating lymph node area) than in location MID_ribs+sternum (demonstrating general matching point for tangential images ribs) in group A . Realized tangential image accuracy in MID_ribs without IGRT in SI direction was noticed adequate with the margins of 4mm in group A in both n0 and mastectomy groups.

Without IGRT (N)= systematic isocenter error was corrected with 4 mm AL during the first three fractions based on IGRT

R= residual error

S= error from structure to structure

systematic, random, margin with the margin formula 2.5Σ+0.7σ (cm)

I think this clinical study that I wanted to share at this point is finished now. It is free to comment and discuss. Do you feel any similarities with your findings?

Have a good weekend.

Marko