How would you alter your PTV margins for a lung SBRT target adjacent to the rib?
Overall, while I generally do not alter my margins substantially for an SBRT target adjacent to the rib, there are some circumstances in which I might make small/subtle changes. My driving thought process is that (in particular for stage I NSCLC) tumor control remains the most important factor, as c...
I agree with these previous answers. I have additionally applied these principles in treating many of these patients in 3 rather than 5 fractions, ensuring that they receive at least 45 Gy (BED10 of 112.5) to a larger PTV with my standard margins (5mm radial and 7mm sup-inf) without any cropping, wh...
I generally agree with Dr. @Dr. First Last, however, since the early days of SBRT, I have shaved the PTV out of the posterior chest wall. Remember that the PTV accounts for setup uncertainty (the IGTV from 4DCT accounts for motion). The setup uncertainty posteriorly, after a CBCT, is minimal. This m...
Recall that rib fractures and chest wall pain are temporary, while lung cancer recurrences are permanent. For this reason, the PTV shouldn't ever be reduced. Next, when pushing too hard on CW constraints, the intermediate dose ends up back in the lung which also leads to a permanent event: fibrosis....
As a non-thoracic radiation oncologist, I greatly appreciate the wisdom and experience represented above, and would just offer one theoretical consideration in addition. In a pure sense, as others have stated, a PTV represents setup uncertainty and therefore, should not be modified from an isotropic...
Retrospective data suggests that truncation of the PTV at the chest wall interface can be done with minimal CW toxicity, without affecting LC (3-year LC of 92%): Keane et al., PMID 33239160.
While I personally would not be enthusiastic to apply 0mm margin at the chest wall, I think shortening it (to ...
Strictly speaking, the PTV should represent your margin for uncertainty. There are circumstances where you can reasonably believe you have less setup uncertainty than normal. In addition to the examples listed above, I would add that there are times when the rib cage doesn’t really move with breathi...