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Comparison of Radiation Necrosis in Adult Cranial Oligodendrogliomas and Astrocytomas Treated With Proton Versus Photon Therapy
Volume 99 Number 2S Supplement 2017 Purpose/Objective(s): This study investigate the effect of clinico-pathologic features, surgical approaches, and adjuvant radiotherapy on prognosis and to explore independent prognostic factors related to postoperative recurrence-free survival (RFS) in patients with breast phyllodes tumors (PTBs). Materials/Methods: A retrospective analysis was conducted in Fudan University Shanghai Cancer Center. The relationship of clinico-pathologic features, surgical treatment, and adjuvant radiotherapy with prognosis was analyzed. According to their histological type, benign PTBs were classified as a low-risk group while borderline and malignant PTBs were classified as a high-risk group. The Cox regression model was adopted to identify factors affecting postoperative RFS in the two groups and a nomogram was made to predict recurrence-free survival at 1, 3 and 5 years. Results: Of the 404 patients, 168 (41.6%) had benign PTB, 184 (45.5%) had borderline PTB, and 52 (12.9%) had malignant PTB. Fifty-five patients experienced postoperative local recurrence, including 6 benign cases, 26 borderline cases, and 22 malignant cases; the three histological types of PTB had local recurrence rates of 3.6%, 14.1%, and 42.3%, respectively. Stromal cell atypia was an independent prognostic factor for RFS in the low-risk group while surgical approach and tumor border were independent prognostic factors for RFS in the high-risk group, patients received simple excision and with infiltrative tumor border have a higher recurrence rate. A nomogram developed based on clinico-pathologic features and surgical approaches could predict recurrence-free survival at 1, 3 and 5 years. Conclusion: Histological grade and degree of stromal malignancy were closely associated with postoperative local recurrence of PTB. For high-risk patients, this predictive nomogram based on tumor border, tumor residue, mitotic activity, and degree of stromal cell hyperplasia and atypia can be applied for patient counselling and clinical management. The efficacy of adjuvant radiotherapy is still uncertain. Author Disclosure: Z. Zhou: None. C. Wang: None. X. Sun: None. Z. Yang: None. X. Chen: None. X. Yu: None. X. Guo: None.
2143 Evaluation of Single Fraction High-Gradient Partial Breast Irradiation as the Sole Method of Radiation Therapy for Low-Risk Stage 0 and I Breast CancerdEarly Results of a Single Institution Prospective Clinical Trial I. Zoberi, M.A. Thomas, and L.L. Ochoa; Washington University School of Medicine, Department of Radiation Oncology, St. Louis, MO Purpose/Objective(s): To test the hypothesis that a single fraction of external beam radiotherapy to breast tissue one centimeter around a partial mastectomy cavity will result in acceptable ipsilateral breast tumor recurrence rates, tolerance, and cosmesis in select women with low-risk early stage breast cancer. Materials/Methods: Postmenopausal women undergoing breast conserving surgery for breast cancers less than or equal to 2 cm in size were enrolled in a single institution prospective clinical trial. Patients had to be at least 50 years old and have estrogen receptor positive cancers without her2/neu gene amplification. Radiotherapy was administered with MR-guided teletherapy except in cases were MR was contraindicated in the outpatient setting within 8 weeks of surgery. Surgical margins were required to be negative by at least 2 mm. A dose of 20 Gy was prescribed to a planning target volume (PTV) defined as the surgical cavity truncated as least 5 mm from the skin surface while simultaneously prescribing a dose of 7 Gy to the surface of a PTV defined as a 1 cm expansion of the surgical cavity in breast tissue truncated 5 mm from the skin surface. The resulting high-gradient treatment was administered in a single fraction as the sole radiotherapy treatment.
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Results: To date 19 of a planned total fifty women have been treated. The mean age was 64 years. Three patients had pTisN0, 10 pT1bN0, and 6 pT1cN0 disease. MR-guided teletherapy via Cobalt-60 was used in all but one patient who had a pacemaker. With a mean and median follow up time of 10.3 and 10 months from diagnosis there have been no breast cancer recurrences and no intercurrent deaths. No patient has been lost to follow up. All toxicities have been grade 1 with six patients having skin hyperpigmentation in the treatment region and three having transient breast pain. Cosmesis has remained excellent in all patients. Conclusion: Early results of our trial demonstrate that a single fraction of high-gradient radiotherapy is well tolerated. Continued enrollment and follow up is needed to determine cancer control outcomes. Author Disclosure: I. Zoberi: Employee; Washington University. M.A. Thomas: None. L.L. Ochoa: None.
2144 Comparison of Radiation Necrosis in Adult Cranial Oligodendrogliomas and Astrocytomas Treated With Proton Versus Photon Therapy S. Acharya,1 C.G. Robinson,2 J.M. Michalski,3 D. Mullen,4 C. Tsien,5 K. Rich,6 J.L. Campian,7 A. Chundury,8 S.M. Perkins,2 D.E. Hallahan,6 J.D. Bradley,2 and J. Huang2; 1Washington University in St. Louis, Department of Radiation Oncology, St. Louis, MO, 2Washington University School of Medicine, Department of Radiation Oncology, St. Louis, MO, 3 Washington University School of Medicine, St. Louis, MO, 4Washington University in St. Louis, Saint Louis, MO, 5Washington University St Louis, St Louis, MO, 6Washington University, St. Louis, MO, 7Washington University in St. Louis, Department of Medical Oncology, St. Louis, MO, 8 Department of Radiation Oncology, Siteman Cancer Center, Washington University School of Medicine, St. Louis, MO Purpose/Objective(s): Proton therapy is a promising treatment modality for gliomas; however, data on late effects remain limited. The purpose of this study is to compare the incidence of and risk factors for clinically significant radiation necrosis (cRN) in adult cranial oligodendrogliomas and astrocytomas treated with proton versus photon therapy. Materials/Methods: Between 2007 and 2015, 160 adult patients with grade II or III oligodendroglioma or astrocytoma were treated with proton (nZ37) or photon (nZ123) therapy with or without concurrent/ sequential chemotherapy at a single institution. Proton therapy was initiated in 2014. Tumor histology was defined using 2016 World Health Organization classification. cRN was defined as symptomatic RN or asymptomatic RN that resulted in surgery or bevacizumab administration. cRN was ascertained based on all available clinical data and confirmed by a panel of 3 radiation oncologists blinded from treatment modality and radiation dose. Cumulative incidence was calculated using competing risks. Risk factors were identified using Cox proportional hazards. Results: Median follow up was 28.5 months. Median prescription dose was 5940 cGy (range: 5040-6300 cGy). 53 patients (33%) had 1p19qcodeleted oligodendroglioma and 107 patients (67%) had non-codeleted astrocytoma. Eighteen patients developed cRN (protonZ6, photonZ12). Median time to cRN was 11 months (range: 2.8e34.2 months). There was no significant difference in two-year cumulative incidence of cRN between proton and photon therapy (18.7 vs. 9.7%; 95% Confidence Interval [CI]: 7.5-33.8% vs. 5.1-16%; pZ0.16). Proton was not a significant risk factor for cRN compared to photon (Hazard Ratio [HR]: 1.81, 95% CI: 0.67e4.9, pZ0.24). On multivariate analysis, risk factors for cRN included oligodendroglioma compared to astrocytoma (HR: 3.57, 95% CI: 1.38 e 9.25, pZ0.009) and prescription dose (Gy) (HR: 1.30, 95% CI: 1.05 e 1.61, pZ0.015). The two-year cumulative incidence of cRN in oligodendrogliomas was almost four-fold that of astrocytomas (23.4 vs. 6.2%, 95% CI: 12.4-
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36.4% vs. 2.5-11%, pZ0.01). On subgroup analysis, there was no difference in two-year cumulative incidence of cRN between proton and photon therapy within oligodendrogliomas (28 vs. 21%, pZ0.68) and within astrocytomas (10 vs. 5.2%, pZ0.28). Although prescription dose did not differ between the two histologies, the relative volume (%) of brain receiving 55 Gy (V55Gy) and V60Gy was significantly associated with cRN in oligodendrogliomas (V55Gy HR: 1.07, 95% CI: 1.01 e 1.14, pZ0.03; V60Gy HR: 1.11, 95% CI: 1.03 e 1.20, pZ0.005) but not in astrocytomas. Conclusion: At two years, proton therapy is not associated with increased risk of cRN compared to photon therapy. 1p19q-codeleted oligodendroglioma is associated with increased risk of cRN and may have a different dose-toxicity threshold for cRN compared to non-codeleted astrocytoma. Author Disclosure: S. Acharya: None. C.G. Robinson: Research Grant; Elekta, Varian Medical Systems. Speaker’s Bureau; DFINE, Varian Medical Systems. Advisory Board; Radialogica. Travel Expenses; DFINE, Varian Medical Systems. Stock Options; Radialogica. J.M. Michalski: Independent Contractor; Sheila Michalski and Associates. Research Grant; NCI. Co-Principal Investigator; Veterans Affairs. ; NRG Oncology. oversight of clinical trial proposals related to GU cancers.; NCI. Board member; National Children’s Cancer Society. D. Mullen: None. C. Tsien: None. K. Rich: None. J.L. Campian: None. A. Chundury: None. S.M. Perkins: None. D.E. Hallahan: Research Grant; MGS,LLC. Stock; MGS,LLC, GenVec. ; BJH Medical Center. J.D. Bradley: Research Grant; Mevion Medical Systems, ViewRay, Inc. Travel Expenses; Mevion Medical Systems. Organize NRG Oncology research agenda on lung cancer; American College of Radiology. Organize oral board examinations; American Board of Radiology. J. Huang: Honoraria; Viewray Inc.. Speaker’s Bureau; Viewray Inc.. Travel Expenses; Viewray Inc..
Overall survival (OS) and progression-free survival (PFS) from time of RT were estimated using the Kaplan Meier method and compared using the log-rank test. Patients were also stratified by 1p/19q co-deletion status and the effect of TMZ on OS and PFS were compared using the same technique. Results: The median age at diagnosis for the TMZ and non-TMZ group was 52 and 50 years respectively. The median Karnofsky Performance Status (KPS) was 80 for both groups. Intensity modulated RT was used in approximately 25% of patients in both groups, with the remainder treated with forward-planned 3D-conformal technique. The majority of patients in the TMZ group subsequently received adjuvant TMZ, typically for a 6 month course at a dose of 150-200 mg/m2. Median PFS was 35 months for the TMZ group and 33 months for the non-TMZ group. This difference was not statistically significant with a p-value of 0.7. Median OS was 50 months for the TMZ group and 48 months for the non-TMZ group. This difference was not statistically significant with a p-value of 0.85. Of the patients with 1p/19q co-deletion (nZ11 out of 46 with co-deletion status reported), no difference was observed in PFS when comparing those treated with or without concurrent TMZ (pZ0.75). Conclusion: In our institutional experience of 152 patients with WHO grade III AA, we did not observe a difference in OS or PFS with the concurrent use of TMZ with RT after maximal safe resection. There was similarly no difference observed in PFS for patients with 1p/19q codeletion present, although the sample size for this subset is small. Current ongoing clinical trials will be useful to investigate this question further in a prospective manner. Author Disclosure: A. Ali: None. S. Garg: None. L. Kim: None. J. Glass: None. B.E. Leiby: None. N. Dabbish: None. M. Werner-Wasik: Stock; Illumina. W. Shi: None.
2145 Comparing Outcomes of Patients Treated With Radiation Therapy With or Without Concurrent and Adjuvant Temozolomide After Surgical Resection for Newly Diagnosed WHO Grade 3 Anaplastic Astrocytoma A. Ali,1 S. Garg,2 L. Kim,2 J. Glass,2 B.E. Leiby,3 N. Dabbish,2 M. Werner-Wasik,2 and W. Shi2; 1Penn State University, Hershey, PA, 2 Sidney Kimmel Medical College at Thomas Jefferson University, Sidney Kimmel Cancer Center, Philadelphia, PA, 3Thomas Jefferson University, Philadelphia, PA Purpose/Objective(s): Treatment of patients (pts) with WHO grade III anaplastic astrocytomas (AA) includes maximal safe tumor resection and adjuvant radiation therapy (RT). The role of chemotherapy in this patient population has become of increasing interest in recent years, and has been the subject of multiple ongoing randomized clinical trials. The utility of temozolomide (TMZ) has been of particular interest given its established survival benefit in patients with WHO grade IV glioblastoma. This study investigates outcomes from our institutional experience treating patients with WHO grade III AA with surgery and RT, with or without concurrent TMZ. Materials/Methods: 152 patients with WHO grade III AA treated with surgical resection and adjuvant RT from 2004-2014 were analyzed retrospectively. Patients were divided into 2 groups, surgery followed by RT alone (nZ 51 pts) and surgery followed by RT + concurrent TMZ (nZ 101 pts). The decision to use TMZ was made based on the preference of the patient’s treating medical oncologist. When used, TMZ was administered at a dose of 75 mg/m2 daily concurrent with RT and at 150-200 mg/m2 during the maintenance phase for 6 cycles or as tolerated. Median RT dose was 59.4 Gy delivered in 1.8 Gy daily fractions.
2146 Initial Volumetric Response and Local Control Following Stereotactic Radiosurgery for Melanoma Brain Metastases S. All,1 H. Patel,2 A. Keller,1 and N.R. Ramakrishna3; 1University of Central Florida College of Medicine, Orlando, FL, 2UCF College of Medicine, Orlando, FL, 3UF Health Cancer Center - Orlando Health, Orlando, FL Purpose/Objective(s): The factors determining local control and the initial volumetric response of brain metastases following stereotactic radiosurgery are not well characterized. We examined the impact of multiple tumor-specific characteristics and SRS treatment parameters on local control and initial volumetric response following SRS for brain metastases from melanoma. Materials/Methods: 58 melanoma patients treated between November 2008 and July 2016 with linear-accelerator based SRS for brain metastases were selected for study inclusion. Tumor volumes were measured prior to SRS session and on initial follow-up MRI at mean of 2.2 months post-SRS to evaluate initial volumetric response. Local control failure was defined as the time at which a brain metastasis increased to greater than 1.20 times its original size at initial SRS treatment and maintained this increase in size on subsequent imaging. The ratio of volume at initial post-treatment imaging to pre-treatment volume was used to determine initial volumetric response. Kaplan-Meier analysis and log rank tests were used to evaluate local control. Independent T-tests were used to analyze effects of tumor and treatment parameters on initial volumetric response. Results: The median radiographic follow-up was 3 months (range 1-68 months). Kaplan-Meier local control estimates at 6 and 12 months were 75.7% and 70.9%, respectively. A statistically significant positive
2143 Evaluation of Single Fraction High-Gradient Partial Breast Irradiation as the Sole Method of Radiation Therapy for Low-Risk Stage 0 and I Breast CancerdEarly Results of a Single Institution Prospective Clinical Trial I. Zoberi, M.A. Thomas, and L.L. Ochoa; Washington University School of Medicine, Department of Radiation Oncology, St. Louis, MO Purpose/Objective(s): To test the hypothesis that a single fraction of external beam radiotherapy to breast tissue one centimeter around a partial mastectomy cavity will result in acceptable ipsilateral breast tumor recurrence rates, tolerance, and cosmesis in select women with low-risk early stage breast cancer. Materials/Methods: Postmenopausal women undergoing breast conserving surgery for breast cancers less than or equal to 2 cm in size were enrolled in a single institution prospective clinical trial. Patients had to be at least 50 years old and have estrogen receptor positive cancers without her2/neu gene amplification. Radiotherapy was administered with MR-guided teletherapy except in cases were MR was contraindicated in the outpatient setting within 8 weeks of surgery. Surgical margins were required to be negative by at least 2 mm. A dose of 20 Gy was prescribed to a planning target volume (PTV) defined as the surgical cavity truncated as least 5 mm from the skin surface while simultaneously prescribing a dose of 7 Gy to the surface of a PTV defined as a 1 cm expansion of the surgical cavity in breast tissue truncated 5 mm from the skin surface. The resulting high-gradient treatment was administered in a single fraction as the sole radiotherapy treatment.
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Results: To date 19 of a planned total fifty women have been treated. The mean age was 64 years. Three patients had pTisN0, 10 pT1bN0, and 6 pT1cN0 disease. MR-guided teletherapy via Cobalt-60 was used in all but one patient who had a pacemaker. With a mean and median follow up time of 10.3 and 10 months from diagnosis there have been no breast cancer recurrences and no intercurrent deaths. No patient has been lost to follow up. All toxicities have been grade 1 with six patients having skin hyperpigmentation in the treatment region and three having transient breast pain. Cosmesis has remained excellent in all patients. Conclusion: Early results of our trial demonstrate that a single fraction of high-gradient radiotherapy is well tolerated. Continued enrollment and follow up is needed to determine cancer control outcomes. Author Disclosure: I. Zoberi: Employee; Washington University. M.A. Thomas: None. L.L. Ochoa: None.
2144 Comparison of Radiation Necrosis in Adult Cranial Oligodendrogliomas and Astrocytomas Treated With Proton Versus Photon Therapy S. Acharya,1 C.G. Robinson,2 J.M. Michalski,3 D. Mullen,4 C. Tsien,5 K. Rich,6 J.L. Campian,7 A. Chundury,8 S.M. Perkins,2 D.E. Hallahan,6 J.D. Bradley,2 and J. Huang2; 1Washington University in St. Louis, Department of Radiation Oncology, St. Louis, MO, 2Washington University School of Medicine, Department of Radiation Oncology, St. Louis, MO, 3 Washington University School of Medicine, St. Louis, MO, 4Washington University in St. Louis, Saint Louis, MO, 5Washington University St Louis, St Louis, MO, 6Washington University, St. Louis, MO, 7Washington University in St. Louis, Department of Medical Oncology, St. Louis, MO, 8 Department of Radiation Oncology, Siteman Cancer Center, Washington University School of Medicine, St. Louis, MO Purpose/Objective(s): Proton therapy is a promising treatment modality for gliomas; however, data on late effects remain limited. The purpose of this study is to compare the incidence of and risk factors for clinically significant radiation necrosis (cRN) in adult cranial oligodendrogliomas and astrocytomas treated with proton versus photon therapy. Materials/Methods: Between 2007 and 2015, 160 adult patients with grade II or III oligodendroglioma or astrocytoma were treated with proton (nZ37) or photon (nZ123) therapy with or without concurrent/ sequential chemotherapy at a single institution. Proton therapy was initiated in 2014. Tumor histology was defined using 2016 World Health Organization classification. cRN was defined as symptomatic RN or asymptomatic RN that resulted in surgery or bevacizumab administration. cRN was ascertained based on all available clinical data and confirmed by a panel of 3 radiation oncologists blinded from treatment modality and radiation dose. Cumulative incidence was calculated using competing risks. Risk factors were identified using Cox proportional hazards. Results: Median follow up was 28.5 months. Median prescription dose was 5940 cGy (range: 5040-6300 cGy). 53 patients (33%) had 1p19qcodeleted oligodendroglioma and 107 patients (67%) had non-codeleted astrocytoma. Eighteen patients developed cRN (protonZ6, photonZ12). Median time to cRN was 11 months (range: 2.8e34.2 months). There was no significant difference in two-year cumulative incidence of cRN between proton and photon therapy (18.7 vs. 9.7%; 95% Confidence Interval [CI]: 7.5-33.8% vs. 5.1-16%; pZ0.16). Proton was not a significant risk factor for cRN compared to photon (Hazard Ratio [HR]: 1.81, 95% CI: 0.67e4.9, pZ0.24). On multivariate analysis, risk factors for cRN included oligodendroglioma compared to astrocytoma (HR: 3.57, 95% CI: 1.38 e 9.25, pZ0.009) and prescription dose (Gy) (HR: 1.30, 95% CI: 1.05 e 1.61, pZ0.015). The two-year cumulative incidence of cRN in oligodendrogliomas was almost four-fold that of astrocytomas (23.4 vs. 6.2%, 95% CI: 12.4-
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36.4% vs. 2.5-11%, pZ0.01). On subgroup analysis, there was no difference in two-year cumulative incidence of cRN between proton and photon therapy within oligodendrogliomas (28 vs. 21%, pZ0.68) and within astrocytomas (10 vs. 5.2%, pZ0.28). Although prescription dose did not differ between the two histologies, the relative volume (%) of brain receiving 55 Gy (V55Gy) and V60Gy was significantly associated with cRN in oligodendrogliomas (V55Gy HR: 1.07, 95% CI: 1.01 e 1.14, pZ0.03; V60Gy HR: 1.11, 95% CI: 1.03 e 1.20, pZ0.005) but not in astrocytomas. Conclusion: At two years, proton therapy is not associated with increased risk of cRN compared to photon therapy. 1p19q-codeleted oligodendroglioma is associated with increased risk of cRN and may have a different dose-toxicity threshold for cRN compared to non-codeleted astrocytoma. Author Disclosure: S. Acharya: None. C.G. Robinson: Research Grant; Elekta, Varian Medical Systems. Speaker’s Bureau; DFINE, Varian Medical Systems. Advisory Board; Radialogica. Travel Expenses; DFINE, Varian Medical Systems. Stock Options; Radialogica. J.M. Michalski: Independent Contractor; Sheila Michalski and Associates. Research Grant; NCI. Co-Principal Investigator; Veterans Affairs. ; NRG Oncology. oversight of clinical trial proposals related to GU cancers.; NCI. Board member; National Children’s Cancer Society. D. Mullen: None. C. Tsien: None. K. Rich: None. J.L. Campian: None. A. Chundury: None. S.M. Perkins: None. D.E. Hallahan: Research Grant; MGS,LLC. Stock; MGS,LLC, GenVec. ; BJH Medical Center. J.D. Bradley: Research Grant; Mevion Medical Systems, ViewRay, Inc. Travel Expenses; Mevion Medical Systems. Organize NRG Oncology research agenda on lung cancer; American College of Radiology. Organize oral board examinations; American Board of Radiology. J. Huang: Honoraria; Viewray Inc.. Speaker’s Bureau; Viewray Inc.. Travel Expenses; Viewray Inc..
Overall survival (OS) and progression-free survival (PFS) from time of RT were estimated using the Kaplan Meier method and compared using the log-rank test. Patients were also stratified by 1p/19q co-deletion status and the effect of TMZ on OS and PFS were compared using the same technique. Results: The median age at diagnosis for the TMZ and non-TMZ group was 52 and 50 years respectively. The median Karnofsky Performance Status (KPS) was 80 for both groups. Intensity modulated RT was used in approximately 25% of patients in both groups, with the remainder treated with forward-planned 3D-conformal technique. The majority of patients in the TMZ group subsequently received adjuvant TMZ, typically for a 6 month course at a dose of 150-200 mg/m2. Median PFS was 35 months for the TMZ group and 33 months for the non-TMZ group. This difference was not statistically significant with a p-value of 0.7. Median OS was 50 months for the TMZ group and 48 months for the non-TMZ group. This difference was not statistically significant with a p-value of 0.85. Of the patients with 1p/19q co-deletion (nZ11 out of 46 with co-deletion status reported), no difference was observed in PFS when comparing those treated with or without concurrent TMZ (pZ0.75). Conclusion: In our institutional experience of 152 patients with WHO grade III AA, we did not observe a difference in OS or PFS with the concurrent use of TMZ with RT after maximal safe resection. There was similarly no difference observed in PFS for patients with 1p/19q codeletion present, although the sample size for this subset is small. Current ongoing clinical trials will be useful to investigate this question further in a prospective manner. Author Disclosure: A. Ali: None. S. Garg: None. L. Kim: None. J. Glass: None. B.E. Leiby: None. N. Dabbish: None. M. Werner-Wasik: Stock; Illumina. W. Shi: None.
2145 Comparing Outcomes of Patients Treated With Radiation Therapy With or Without Concurrent and Adjuvant Temozolomide After Surgical Resection for Newly Diagnosed WHO Grade 3 Anaplastic Astrocytoma A. Ali,1 S. Garg,2 L. Kim,2 J. Glass,2 B.E. Leiby,3 N. Dabbish,2 M. Werner-Wasik,2 and W. Shi2; 1Penn State University, Hershey, PA, 2 Sidney Kimmel Medical College at Thomas Jefferson University, Sidney Kimmel Cancer Center, Philadelphia, PA, 3Thomas Jefferson University, Philadelphia, PA Purpose/Objective(s): Treatment of patients (pts) with WHO grade III anaplastic astrocytomas (AA) includes maximal safe tumor resection and adjuvant radiation therapy (RT). The role of chemotherapy in this patient population has become of increasing interest in recent years, and has been the subject of multiple ongoing randomized clinical trials. The utility of temozolomide (TMZ) has been of particular interest given its established survival benefit in patients with WHO grade IV glioblastoma. This study investigates outcomes from our institutional experience treating patients with WHO grade III AA with surgery and RT, with or without concurrent TMZ. Materials/Methods: 152 patients with WHO grade III AA treated with surgical resection and adjuvant RT from 2004-2014 were analyzed retrospectively. Patients were divided into 2 groups, surgery followed by RT alone (nZ 51 pts) and surgery followed by RT + concurrent TMZ (nZ 101 pts). The decision to use TMZ was made based on the preference of the patient’s treating medical oncologist. When used, TMZ was administered at a dose of 75 mg/m2 daily concurrent with RT and at 150-200 mg/m2 during the maintenance phase for 6 cycles or as tolerated. Median RT dose was 59.4 Gy delivered in 1.8 Gy daily fractions.
2146 Initial Volumetric Response and Local Control Following Stereotactic Radiosurgery for Melanoma Brain Metastases S. All,1 H. Patel,2 A. Keller,1 and N.R. Ramakrishna3; 1University of Central Florida College of Medicine, Orlando, FL, 2UCF College of Medicine, Orlando, FL, 3UF Health Cancer Center - Orlando Health, Orlando, FL Purpose/Objective(s): The factors determining local control and the initial volumetric response of brain metastases following stereotactic radiosurgery are not well characterized. We examined the impact of multiple tumor-specific characteristics and SRS treatment parameters on local control and initial volumetric response following SRS for brain metastases from melanoma. Materials/Methods: 58 melanoma patients treated between November 2008 and July 2016 with linear-accelerator based SRS for brain metastases were selected for study inclusion. Tumor volumes were measured prior to SRS session and on initial follow-up MRI at mean of 2.2 months post-SRS to evaluate initial volumetric response. Local control failure was defined as the time at which a brain metastasis increased to greater than 1.20 times its original size at initial SRS treatment and maintained this increase in size on subsequent imaging. The ratio of volume at initial post-treatment imaging to pre-treatment volume was used to determine initial volumetric response. Kaplan-Meier analysis and log rank tests were used to evaluate local control. Independent T-tests were used to analyze effects of tumor and treatment parameters on initial volumetric response. Results: The median radiographic follow-up was 3 months (range 1-68 months). Kaplan-Meier local control estimates at 6 and 12 months were 75.7% and 70.9%, respectively. A statistically significant positive