Bootstrap Framework 3.3.6

[jose_carlos_pichardo]

We are having an issue with a left breast DIBH mono-isocentric setup patient. Patient is laying flat on the couch on a mat with a wingboard and small vac loc for the arms and head. We get an "insufficient surface overlap error" for one of the SCV fields with the gantry at 20 degrees and one of the tangent fields with the gantry at 310 degrees.  We are unable to monitor the breath hold (BH) at those two fields. We seldom do mono-isocentric left breast DIBH cases, so I am in the process of reviewing old cases and note the gantry angles used in each plan.

Has anyone experienced a similar issue with their left breast DIBH patients? Are the "bad" gantry angles patient-specific or is there a specific range that generally fails? How do you manage this from the treatment planning perspective?

Thank you,

Jose C Pichardo, Ph.D., DABR

21st Century Oncology, Boca Raton, FL

[jose_carlos_pichardo]

I looked through the VisionRT training documents and I found a troubleshooting document that indicated that my issue can be resolved by expanding the ROI to include both breasts and even expanding the SCV section of the ROI. My question now is, has anyone out there tried this and did it affect the breath hold level accuracy (e.g. determined from the kV LAT image)?

Thank you,

Jose C Pichardo, Ph.D., DABR

21st Century Oncology, Boca Raton, FL

[marko_laaksomaa]

Hi Jose

I can share your concern with the AlignRT version we have used couple years. Just a minute ago we had problematic DIBH patient for the first time in treatment, starting of the treatment thus. Entire chest wall was covered with ROI (because system asked us to increase the ROI) and still there was that error as you mentioned. This happened when we tried to acquire kV- tangential images (side pods were blocked). We had to remove kV- tangential image and add MV tangential image on the fly.

We have used ROI below and investigated its reproducibility with several IGRT studies. Based on the results, we have not seen any reasons to use breastROI as a primary setup-ROI. With that ROI below, sternum vertical reproducibility in the setup is very accurate, indicating for its part good accuracy in the BHL. We have been able to acquire daily tangential kV-images, when gantry and imagers are both blocking side cameras and typically this has no affect on image accuracy, if the deltas act as they should, without blinking. Rarely there is issues that you described, and if there is, it happens when the gantry is somewhere around 30°. Then the ROI needs to be adjusted, and if so, new orthogonal images and possibly new reference surfaces should be acquired, since we are now monitoring slightly different area.

With the larger sized breast and with the VMAT- treatments, we do a breastROI verification at the FB-setup process with the AlignRT, to see that also the soft tissue is inside thresholds after T-ROI setup. We have a data whether T -or BreastROI leads to better monitoring reproducibility with different gantry angles, but we have not investigated that.  Anyhow, setup accuracy comparison with the differently shaped ROIs based on offline image+AlignRT data evaluation is planned to be published this year. If you use ROI below and spread it laterally in a problematic cases, based on the results I can say that you are not loosing the accuracy concerning BHL in the LAT image in comparison to breastROI, which was your worry. As mentioned, you may anyway need new setup surfaces based on setup images if this corrective action is done only during the treatment course. 10° tilt in the breast board gives a better conditions for the cameras to monitor the patient chest wall.

It is much possible that these are ROI- related issues, but slight but in practice significant improvements also I have been waiting from VisionRT to optimize the camera system to better monitor different kind of  ROIs with all the gantry angles.

[jose_carlos_pichardo]

Marko. Thank you very much for your response. We will try your ROI design to monitor BHL in our problem case. The ROI makes sense since it is focused on the sternum. I measure the distance from the spine to midsternum to verify the accuracy of the BHL in the kV LAT image.