Michael Tallhamer, MSC, DABR
We have Vision RT’s AlignRT and GateCT at 4 of our hospitals and use the AlignRT product as our SGRT solution for SBRT and SRS.
We use a number of techniques for SBRT including DIBH for lung and liver in addition to the more common 4DCT GTV-ITV-PTV expansion using either all 10 phases or the MIP/MinIP/AveIP composite scans. We find AlignRT excellent for the previous and GateCT works well for acquiring the latter on our Philips CTs. The nice thing is we do lots of DIBH Lt Breast so the DIBH workflow is well understood in our clinics with AlignRT so transitioning it to DIBH for SBRT required only minor tweaking to the process with the operation of the software being identical.
SGRT is great for monitoring during CBCT and physician alignment as Serpil mentioned above. We have differing skill sets with some of our doctors and the ability to monitor the patient while the process takes place has been great.
Some things to think about going to DIBH for SBRT of lung an liver
- Many times the target is off axis enough to require couch centering (on a Varian linac) so care must be taken in getting a good reference capture at the CBCT position with the DIBH for monitoring during imaging.
- The workflow from couch center monitoring back to original position monitoring to applying the shifts must be done carefully as not to reference out a misalignment.
Some “good-catch” or “near-miss” scenarios we have seen are below
- DIBH Liver SBRT – Patient was setup with AlignRT, positioned for CBCT, monitored during and post imaging and then shifts applied. After first arc was delivered pt was instructed to take in a deep breath and hold it in preparation for second arc when AlignRT indicated that the patient had moved suddenly in the vertical and lateral directions while holding his breath (both directions >1.0cm on a 1.5cm target). Physics went into the room to find two of the three body mask pins on the patients left side (away from linac camera) had sheared off when the patient had taken his deep breath leaving the body mask still visually secured on the patient but without the ability to maintain the mobilization. Pins were replaced and patient re-setup for final 2 arcs without issue. Had we not had Align RT we could have potentially missed the issue until entering the room to get the patient up post treatment since the mask failure was not visually noticeable from the linac cameras.
- Failing VacLoc bag during SBRT delivery. Patient in vacloc bag and body mask for lung SBRT. Patient exhibits strange vertical offset under body mask post CBCT shifts being applied and new reference being taken. Therapists enter room to find bag has taken on air due to small rip in bag caused by another immobilization device. Offset was <1.0cm but outside of 0.3cm tolerance.
Hope that helps