RADT-02. CLINICAL OUTCOMES OF BREAST BRAIN METASTASES BY SUBTYPE FOLLOWING LINAC BASED STEREOTACTIC RADIATION

BACKGROUND

Management of breast cancer brain metastases has become an increasing concern due to improved systemic control. Failure patterns in the brain may vary by breast cancer subtype.

OBJECTIVE

In this study, we sought to distinguish our institutional clinical outcomes following stereotactic radiation by breast cancer subtype.

METHODS

A total of 180 breast cancer patients treated over 279 stereotactic sessions to 646 brain metastases were identified from our LINAC based stereotactic radiation institutional registry. Patients were treated between August 2004 and May 2019. Outcomes including distant brain metastases control (DC) as well as overall survival (OS) following stereotactic radiation were assessed from review of the clinical chart and radiologic examinations.

RESULTS

The median age of patients was 55 (range: 28-86 years). Subtypes in order of decreasing frequency were hormone receptor (HR)+ (n=64; 36%), HR+/HER2+ (n=47; 26%), triple negative (TN) (n=43; 24%), and HR-/HER2+ (n=26; 14%). TN patients had the shortest interval from systemic metastases to brain metastases diagnosis; HR-/HER2 + 16 months, HR+ 13.3 months, HR+/HER2 + 11 months, and TN 1.4 months (p=0.02). Median follow-up from brain metastases diagnosis was 21.2 months (range: 0.9-135.4 months). Twenty-four month Kaplan-Meier (KM) DC rates varied by subtype and were 49% (HR+/HER2+), 38% (HR+), 33% (HR-/HER2+) and 21% (TN) (p=0.0004), respectively. Similar differences were noted in OS with 24 month KM rates of 58% (HR+/HER2+), 51% (HR-/HER2+), 27% (HR+), and 14% (TN), p< 0.0001. A total of 26 patients (14%) were noted to undergo leptomeningeal disease (LMD) progression. No differences were noted by subtype and LMD progression (p=0.88).

CONCLUSIONS

In our institutional series of breast cancer brain metastases treated with stereotactic radiation, significant differences were noted in clinical outcomes by breast cancer subtype. HR+/HER2+ patients had the best DC and OS rates while outcomes were poorest for TN patients.

Clinical outcomes of melanoma brain metastases treated with stereotactic radiosurgery and anti-PD-1 therapy, anti-CTLA-4 therapy, BRAF/MEK inhibitors, BRAF inhibitor, or conventional chemotherapy

BACKGROUND

The effect of immunologic and targeted agents on intracranial response rates in patients with melanoma brain metastases (MBMs) is not yet clearly understood. This report analyzes outcomes of intact MBMs treated with single-session stereotactic radiosurgery (SRS) and anti-PD-1 therapy, anti-CTLA-4 therapy, BRAF/MEK inhibitors(i), BRAFi, or conventional chemotherapy.

PATIENTS AND METHODS

Patients were included if MBMs were treated with single-session SRS within 3 months of receiving systemic therapy. The primary end point of this study was distant MBM control. Secondary end points were local MBM control defined as a >20% volume increase on follow-up MRI, systemic progression-free survival, overall survival (OS) from both SRS and cranial metastases diagnosis, and neurotoxicity. Images were reviewed alongside two neuro-radiologists at our institution.

RESULTS

Ninety-six patients were treated to 314 MBMs over 119 SRS treatment sessions between January 2007 and August 2015. No significant differences were noted in age (P = 0.27), gender (P = 0.85), treated gross tumor volume (P = 0.26), or the diagnosis-specific graded prognostic assessment (P = 0.51) between the treatment cohorts. Twelve-month Kaplan-Meier (KM) distant MBM control rates were 38%, 21%, 20%, 8%, and 5% (P = 0.008) for SRS with anti-PD-1 therapies, anti-CTLA-4 therapy, BRAF/MEKi, BRAFi, and conventional chemotherapy, respectively. No significant differences were noted in the KM local MBM control rates among treatment groups (P = 0.25). Treatment with anti-PD-1 therapy, anti-CTLA-4 therapy, or BRAF/MEKi significantly improved OS on both univariate and multivariate analyses when compared with conventional chemotherapy.

CONCLUSION

In our institutional analysis of patients treated with SRS and various systemic immunologic and targeted melanoma agents, significant differences in distant MBM control and OS are noted. Prospective evaluation of the potential synergistic effect between these agents and SRS is warranted.

Potential role for LINAC-based stereotactic radiosurgery for the treatment of 5 or more radioresistant melanoma brain metastases

OBJECT

Linear accelerator (LINAC)-based stereotactic radiosurgery (SRS) is a treatment option for patients with melanoma in whom brain metastases have developed. Very limited data are available on treating patients with ≥5 lesions. The authors sought to determine the effectiveness of SRS in patients with ≥5 melanoma brain metastases.

METHODS

A retrospective analysis of metastatic melanoma treated with SRS in a single treatment session for ≥5 lesions was performed. Magnetic resonance imaging studies were reviewed post-SRS to evaluate local control (LC). Disease progression on imaging was defined using the 2009 Response Evaluation Criteria in Solid Tumors (RECIST). Survival curves were calculated from the date of brain metastases diagnosis or the date of SRS by using the Kaplan-Meier (KM) method. Univariate and multivariate analysis (UVA and MVA, respectively) were performed using the Cox proportional-hazards model.

RESULTS

The authors identified 149 metastatic brain lesions treated in 28 patients. The median patient age was 60.5 years (range 38-83 years), and the majority of patients (24 [85.7%]) had extracranial metastases. Four patients (14.3%) had received previous whole-brain radiotherapy (WBRT), and 11 (39.3%) had undergone previous SRS. The median planning target volume (PTV) was 0.34 cm3 (range 0.01-12.5 cm3). Median follow-up was 6.3 months (range 1-46 months). At the time of treatment, 7% of patients were categorized as recursive partitioning analysis (RPA) Class I, 89% as RPA Class II, and 4% as RPA Class III. The rate of local failure was 11.4%. Kaplan-Meier LC estimates at 6 and 12 months were 91.3% and 82.2%, respectively. A PTV volume≥0.34 cm3 was a significant predictor of local failure on UVA (HR 16.1, 95% CI 3.2-292.6, p<0.0001) and MVA (HR 14.8, 95% CI 3.0-268.5, p=0.0002). Sixteen patients (57.1%) were noted to have distant failure in the brain with a median time to failure of 3 months (range 1-15 months). Nine patients with distant failures received WBRT, and 7 received additional SRS. Median overall survival (OS) was 9.4 and 7.6 months from the date of brain metastases diagnosis and the date of SRS, respectively. The KM OS estimates at 6 and 12 months were 57.8% and 28.2%, respectively, from the time of SRS treatment. The RPA class was a significant predictor of KM OS estimates from the date of treatment (p=0.02). Patients who did not receive WBRT after SRS treatment had decreased OS on MVA (HR 3.5, 95% CI 1.1-12.0, p=0.03), and patients who did not receive WBRT prior to SRS had improved OS (HR 0.11, 95% CI 0.02-0.53, p=0.007).

CONCLUSIONS

Stereotactic radiosurgery for ≥5 lesions appears to be effective for selected patients with metastatic melanoma, offering excellent LC. This is particularly important for patients as new targeted systemic agents are improving outcomes but still have limited efficacy within the central nervous system.

Clinical and dosimetric predictors of radiation pneumonitis in a large series of patients treated with stereotactic body radiation therapy to the lung

PURPOSE

To report clinical and dosimetric factors predictive of radiation pneumonitis (RP) in patients receiving lung stereotactic body radiation therapy (SBRT) from a series of 240 patients.

METHODS AND MATERIALS

Of the 297 isocenters treating 263 patients, 240 patients (n=263 isocenters) had evaluable information regarding RP. Age, gender, current smoking status and pack-years, O2 use, Charlson Comorbidity Index, prior lung radiation therapy (yes/no), dose/fractionation, V5, V13, V20, Vprescription, mean lung dose, planning target volume (PTV), total lung volume, and PTV/lung volume ratio were recorded.

RESULTS

Twenty-nine patients (11.0%) developed symptomatic pneumonitis (26 grade 2, 3 grade 3). The mean V20 was 6.5% (range, 0.4%-20.2%), and the average mean lung dose was 5.03 Gy (0.547-12.2 Gy). In univariable analysis female gender (P=.0257) and Charlson Comorbidity index (P=.0366) were significantly predictive of RP. Among dosimetric parameters, V5 (P=.0186), V13 (P=.0438), and Vprescription (where dose=60 Gy) (P=.0128) were significant. There was only a trend toward significance for V20 (P=.0610). Planning target volume/normal lung volume ratio was highly significant (P=.0024). In multivariable analysis the clinical factors of female gender, pack-years smoking, and larger gross internal tumor volume and PTV were predictive (P=.0094, .0312, .0364, and .052, respectively), but no dosimetric factors were significant.

CONCLUSIONS

Rate of symptomatic RP was 11%. Our mean lung dose was <600 cGy in most cases and V20<10%. In univariable analysis, dosimetric factors were predictive, while tumor size (or tumor/lung volume ratio) played a role in multivariable and univariable and analysis, respectively.

Dosimetric analysis of modulated and hybrid arcs in stereotactic radiosurgery

PURPOSE

Forward-planned conformal arcs (termed dynamic arcs in the BrainLab iPlan system) have been routinely used in cranial stereotactic radiosurgery (SRS) for many yeras. This study compares dosimetric parameters of the newer, inversely-planned volumetric modulated arc therapy (VMAT) and VMAT-conformal hybrid plans with conformal arc plans. In the hybrid plans, various numbers of conformal arcs in a conformal plan are replaced with VMAT arcs.

METHODS

Ten brain cancer cases previously treated on a Novalis accelerator for frameless cranial stereotactic radiosurgery using conformal arcs generated by BrainLab iPlan treatment planning system were retrospectively studied with various numbers of VMAT arcs replacing the conformal arcs. Pure VMAT plans of different numbers of arcs were also generated using the same angle and arc length setup for all or part of the conformal arcs and compared with both the original and hybrid plans. Pinnacle version 9.0 was used for treatment plan generation. SmartArc was used for the VMAT planning for a Novalis accelerator. The conformity index (CI), defined as the ratio of the isodose volume to the isodose covered target volume, gradient index (GI), defined as the ratio of the 50% isodose volume (V₅₀) to the 100% isodose volume, volume covered by 12 Gy isodose (V₁₂), mean dose and standard deviation of dose in target were studied.

RESULTS

With one of the conformal arcs replaced with a VMAT arc of the same weighting and geometric setup, the average CI with one standard deviation was improved from 1.35 ± 0.18 to 1.29 ± 0.15 (p-value 0.03), while the average GI degraded from 3.8 ± 1.0 to 4.9 ± 1.5 (p-value < 0.01). The degraded GI in the VMAT plans is due to the absence of beam margin limit in SmartArc planning. Pure VMAT plans usually demonstrated better CI values than the hybrid and conformal arc plans when the number of arcs was greater than 2. The GI value was improved with increasing number of arcs in VMAT plans. For target volumes greater than 1 cc, VMAT plans demonstrated improved CI and smaller V₅₀ and V₁₂ than that in conformal arc plans. Better dose fall-off in normal tissue in VMAT plans is accompanied with higher dose heterogeneity in the target volume.

CONCLUSION

VMAT and conformal-VMAT hybrid plans usually offer better target conformity. The dose fall-off in normal tissue is also better in VMAT plans when the number of arcs is greater than 3 and target volume is greater than 1 cc, but compromise the dose homogeneity in target volumes. VMAT plans are the best option for targets that are greater than 1 cc for cranial radiosurgery treatments, while for very small targets, conformal arc technique may still be the better choice based on data of dose fall-off in normal tissues.