ESTRO 2024 - Abstract Book

S1948

Clinical - Mixed sites, palliation

ESTRO 2024

metastases, is also applied. Smaller target volumes might lead to reduced treatment toxicity, and sparing bone marrow is crucial when chemotherapy follows pRT. It is however unclear if target volume reduction compromises local tumor control (LC). With this analysis, we seek to assess whether the TVD strategy in pRT after stabilization surgery for spinal metastases impacts LC.

Material/Methods:

The institute’s own database was screened for patients having received pRT to spinal metastases after stabilization surgery between 01/2010 and 12/2021 with local follow-up imaging of at least 12 months after pRT available (n=65). Since metastatically affected vertebrae were generally included in the target volume, patients with metastases in all vertebral heights over which the instrumentation extended (n=16) were excluded from this retrospective analysis. Patients were stratified by TVD i.e., inclusion of all (extended) vs. less than all (reduced) vertebral heights over which the surgical instrumentation extended. LC was assessed with Kaplan-Meier estimator, and TVD and possible other influencing factors were tested for significance with Log-rank test.

Results:

The study population comprised 31 patients (63.27%) who received extended volume pRT and 18 patients (36.73%) treated with reduced volume pRT. Gender was equally distributed (25 female and 24 male patients), and breast (n=12, 24.49%), renal cell (n=9, 18.37%), lung (n=8, 16.33%) and prostate cancer (n=7, 14.29%) were the most frequent tumor entities. Other primary tumors were melanoma, sigmoid and urothelial cancer in two cases each and CUP, GIST, SFT, leiomyosarcoma and anal, larynx and follicular thyroid carcinoma in one case each. At the timepoint of pRT, median age was 63 years (R 38-87). Median time from surgery to pRT was 33 days (R 12-132) and median cumulative pRT dose (BED 10 ) was 45.25 Gy (R 28-50.7). Median time from pRT to last imaging follow-up was 30 months (R 12-80). Six cases of screw loosening were detected in imaging follow-up, all of which occurred after extended volume pRT. Local recurrence after pRT was observed in 11 patients (22.25%). Estimated LC rates at one, two and three years after pRT were 89.80% (SE 0.04), 81.60% (SE 0.06) and 76.50% (SE 0.07), respectively. There was no significant association between TVD (extended vs. reduced) and LC (p=0.989, see figure 1). pRT dose (p=0.58) and time from surgery to pRT (p=0.073) did not significantly impact LC. Histology however had a significant impact on LC (p<0.001), with especially high local failure rates in patients with renal cell cancer metastases (44.44%). Patients who did not receive systemic therapy after pRT had significantly higher local failure rates as well (p<0.001).

Figure 1: Kaplan-Meier curve for local tumor control after pRT by target volume definition strategy (reduced vs. extended), n=49