Histosurgical mapping of endoscopic endonasal surgery of sinonasal tumours to improve radiotherapy guidance

PURPOSE

Endoscopic endonasal surgery (EES) is becoming a standard for most malignant sinonasal tumours. Margin analysis after piecemeal resection is complex and optimally relies on accurate histosurgical mapping. Postoperative radiotherapy may be adapted based on margin assessment mapping to reduce the dose to some sinonasal subvolumes. We assessed the use of histosurgical mapping by radiation oncologists (RO).

MATERIAL AND METHODS

A French practice survey was performed across 29 ENT expert RO (2 did not answer) regarding integration of information on EES, as well as quality of operative and pathology reportsto refine radiotherapy planning after EES. This was assessed through an electronic questionnaire.

RESULTS

EES was ubiquitously performed in France. Operative and pathology reports yielded accurate description of EES samples according to 66.7% of interviewed RO. Accuracy of margin assessment was however insufficient according to more than 40.0% of RO. Additional margins/biopsies of the operative bed were available in 55.2% (16/29) of the centres. In the absence of additional margins, quality of resection after EES was considered as microscopically incomplete in 48.3% or dubious in 48.3% of RO. As performed, histosurgical mapping allowed radiotherapy dose and volumes adaptation according to 26.3% of RO only.

CONCLUSIONS

Standardized histosurgical mapping with margin and additional margin analysis could be more systematic. Advantages of accurate EES reporting could be dose painting radiotherapy to further decrease morbidity in sinonasal tumours.

P14.78 Hypofractionated stereotactic radiotherapy as a salvage therapy for recurrent high-grade gliomas: Single-center experience

BACKGROUND

The standard of care for patients with recurrent glioblastoma or grade III glioma has not yet been clearly defined and many approaches are available for salvage strategies. These include surgery, re-irradiation or systemic agents. For the treatment of High-Grade (HGG) recurrence by radiation therapy, Hypofractionated Stereotactic Radiotherapy (HFSRT) is an interesting approach because it is minimally invasive, ambulatory, short-lasting and well tolerated. The aim of this study was to evaluate the efficacy of and safety to HFSRT as alvage treatment for patients suffering from HGG relapse in our cancer center and to compare these results with the literature.

MATERIAL AND METHODS

Between March 2012 and March 2017, 32 consecutive patients (12 women, 20 men) treated in a single-center were retrospectively included included in this study.Grade III gliomas were diagnosed in 14 patients and grade IV in 18 patients. Thirty-four lesions were treated with HFSRT on LINAC. HFSRT delivered a dose of 30 Gy in six fractions of 5Gy (27 Gy in three fractions for one patient) with two or three fractions per week. The treatment plans were normalized to 100% at the isocenter, and prescribed to the 80 % isodose line. Clinical outcomes and prognostic factors were analyzed.

RESULTS

HFSRT characteristics: The median tumor volume was of 6.1 (0.1–42.2) cm3 and the median PTV was 15 (0.6–67.5) cm3. The median maximum dose, median minimum dose and median mean dose were 38.7 (32.7–42.0) Gy, 29.1 (14.0–32.4) Gy and 35.1 (31.5–37.5) Gy, respectively. Median follow-up was 20.9 months.

Median overall survival (OS) following HFSRT was 15.6 months (Median OS for patients patients with GBM and grade III glioma were 8.2 and 19.5 months, respectively; p=0.0496).

Progression-free survival (PFS) was 3.7 months (Median PFS for patients with GBM and grade III glioma were 3.6 and 4.5months, respectively; p=0.2424).

In multivariate analysis, tumor grade III (p=0.0027), an ECOG status <2 at the time of reirradiation (p=0.0023) and a mean dose >35 Gy (p=0.0055) significantly improved OS. A maximum reirradiation dose above 38 Gy (p=0.0179) was significantly associated with longer PFS.

Treatment was well tolerated, no acute toxicity > grade 2 was observed.

During the follow-up, ten patients (31.25%) had suspected radionecrosis. In six patients, this suspicion corresponded to tumor progression. For the other patients, radionecrosis was suggested on multi-modal MRI.

CONCLUSION

HFSRT appears to be a feasible and effective salvage treatment option for recurrent high-grade gliomas, with OS of 15.6 months. Prognostic factors associated with longer OS were a good general state of health and grade III glioma. Dosimetric data suggested that the dose gradient had an impact on tumor control and indicate that a study with dose-escalation is warranted. These results need to be confirmed in a prospective study with a greater number of patients.