You’re in luck - published this week
To interrogate inter-observer variability in gross tumour volume (GTV) and clinical target volume (CTV) delineation specific to the treatment of sacra…
www.sciencedirect.com
Recently had a discussion with a colleague regarding sacral plexus dose constraints. It was a 32Gy Dmax vs 35Gy Dmax discussion for 5 fraction SBRT (600 X 5) in pt with encasement of sacral plexus/neural foramina by tumor.
Found this paper useful. Gotta read the supplement for the goodies.
From the supplement:
"The median nBED dose to the TS (thecal sac) was 72 Gy2/2 (range, 72 – 111.3 Gy2/2) for cases treated with 16 – 24 Gy in a single fraction,
44.6 Gy2/2 (range, 44.6 – 71.5 Gy2/2), 69.3 Gy2/2 (range, 36 – 76.8 Gy2/2) and 71.3 Gy2/2 (range, 52.7 – 71.3 Gy2/2) and 67.2 Gy2/2 for 24Gy in 2 fractions,
24 – 30 Gy in 3 fractions,
30 – 40 Gy in 4 fractions and
35 Gy in 5 fractions respectively."
"There was no different in the dose constrains stated whether the TS was contoured as an individual structure or combined with the SP and/or NR. Seven of the nine experts specifically contoured the nerve roots, however, each of these experts
wouldn’t underdoes the PTV to spare the nerve roots if disease involved the neural foramen."
“For spine SBRT, that intent is local control.”
“Sacral metastases are rare accounting for fewer than 5% of all cases of metastatic disease to the spine”
“no pattern of failure analyses specific to the sacrum have been published.”
“Notably, there was the tendency amongst the majority of the experts to apply an anatomic approach when contouring the CTV which typically involved contouring the entirety of the compartment the disease was located, in addition to contouring the next adjacent marrow space at risk of microscopic disease spread.”
“Outcomes for sacrum SBRT are limited.”
“The most common pattern of sacral failure was progression within the vertebral body in conjunction with paraspinal tissue followed by isolated epidural progression.”
“Without consistent recommendations for delineating the sacrum, it is
almost impossible to draw firm conclusions regarding dose distribution with respect to toxicity or outcome across centres”
FROM THE SUPPLEMENT:
***** “Six experts contoured the TS, two the sacral canal and one the nerves in cauda equina as a surrogate for the TS. It was the practice of five experts to contour the TS (or surrogate) as an independent structure to the SP and NR structures.
Two experts didn’t contour the sacral plexus stating the lack of guidelines to accurately delineate this structure and the low rate of plexopathy observed in individual institutional databases.“
***** “The median nBED dose to the TS was… 35 Gy in 5 fractions respectively.
***** “Seven of the nine experts specifically contoured the nerve roots, however, each of these experts wouldn’t underdoes the PTV to spare the nerve roots if disease involved the neural foramen. “
