What if: A retrospective reconstruction of resection cavity stereotactic radiosurgery to mimic neoadjuvant stereotactic radiosurgery

Abstract

IntroductionNeoadjuvant stereotactic radiosurgery (NaSRS) of brain metastases has gained importance, but it is not routinely performed. While awaiting the results of prospective studies, we aimed to analyze the changes in the volume of brain metastases irradiated pre- and postoperatively and the resulting dosimetric effects on normal brain tissue (NBT).MethodsWe identified patients treated with SRS at our institution to compare hypothetical preoperative gross tumor and planning target volumes (pre-GTV and pre-PTV) with original postoperative resection cavity volumes (post-GTV and post-PTV) as well as with a standardized-hypothetical PTV with 2.0 mm margin. We used Pearson correlation to assess the association between the GTV and PTV changes with the pre-GTV. A multiple linear regression analysis was established to predict the GTV change. Hypothetical planning for the selected cases was created to assess the volume effect on the NBT exposure. We performed a literature review on NaSRS and searched for ongoing prospective trials.ResultsWe included 30 patients in the analysis. The pre-/post-GTV and pre-/post-PTV did not differ significantly. We observed a negative correlation between pre-GTV and GTV-change, which was also a predictor of volume change in the regression analysis, in terms of a larger volume change for a smaller pre-GTV. In total, 62.5% of cases with an enlargement greater than 5.0 cm3 were smaller tumors (pre-GTV < 15.0 cm3), whereas larger tumors greater than 25.0 cm3 showed only a decrease in post-GTV. Hypothetical planning for the selected cases to evaluate the volume effect resulted in a median NBT exposure of only 67.6% (range: 33.2–84.5%) relative to the dose received by the NBT in the postoperative SRS setting. Nine published studies and twenty ongoing studies are listed as an overview.ConclusionPatients with smaller brain metastases may have a higher risk of volume increase when irradiated postoperatively. Target volume delineation is of great importance because the PTV directly affects the exposure of NBT, but it is a challenge when contouring resection cavities. Further studies should identify patients at risk of relevant volume increase to be preferably treated with NaSRS in routine practice. Ongoing clinical trials will evaluate additional benefits of NaSRS.

Preoperative radiosurgery for brain metastases (PREOP-1): A feasibility trial

“…Several groups have compared the preoperative metastasis volume and hypothetical preoperative SRS plan with the corresponding postoperative cavity volume to try to refine the patient selection criteria. Using this approach, a recent publication recommended smaller metastases (<15 cm 3 ) for preoperative SRS as these tend to be associated with larger postoperative cavities [28] . SRS to a smaller target would certainly be preferable than to a larger target, however fractionation could be used to offset the potential toxicity of irradiating a larger cavity.…”

Robotic stereotactic radiosurgery for intracranial meningiomas in elderly patients: assessment of treatment efficacy and safety

“…In cases where the meningioma was situated close to an eloquent area (e.g., the brainstem or along the optic pathway), either a reduction in the dose per fraction or hypofractionation was implemented, depending on the fulfillment of dose constraints. The isodose volume of the normal brain tissue (NTB, excluding the PTV) for a single fraction (V10 Gy < 10cm 3 ), three fractions (V18 < 10 cm 3 ), and five fractions (V28.8 < 7 cm 3 ) was calculated and noted in each patient as a standard clinical practice to ascertain the potential risk of adverse effects on the adjacent healthy brain tissue, as described previously (27). To protect other organs at risk, we applied the recommended threshold doses for SRS/HF-SRS published by Benedict et al (28).…”