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Frameless Hypofractionated Stereotactic Radiosurgery for Acoustic Neuromas: A Single-Institution Experience
E62
International Journal of Radiation Oncology Biology Physics
from 2010-2015. We collected data on patient and disease characteristics, treatment details, and skin toxicity during radiation treatment. Chi-squared test was used to assess for differences in frequency of toxicity based on these factors. Results: The cohort included 139 patients with DCIS (n Z 30) and invasive breast cancer (n Z 109). Mean body mass index was 28.9, above the threshold for overweight. Among those with invasive breast cancer, 113 were T1, 25 T2, and 1 T3, and 30 were node positive. All underwent breast conserving surgery, and 136 (98%) had axillary nodal assessment (9 dissection, 97 sentinel node biopsy). 37 (26.6%) received adjuvant chemotherapy. All received whole breast radiation, 48 (34.5%) conventionally fractionated (fraction size 1.8-2 Gy) and 91 (65.5%) hypofractionated (fraction size 2.66-2.7 Gy). Total dose for all patients ranged from 4256-6700 cGy inclusive of boost. No patients with hypofractionation received regional nodal RT (RNI), and 52% with conventional fractionation had RNI. Within the whole cohort, the maximum RTOG skin toxicity grade during RT was 0 in 27 patients (19.4%), 1 in 68 (49%), and 2 in 44 (31.6%). Among those receiving conventional RT, mean BMI was 30.04 (range 19.4-44.8), and 20 (41.6%) had grade 0-1 skin toxicity and 25 (52%) grade 2. Among those with hypofractionated RT, mean BMI was 28.31, and grade 0-1 skin toxicity was seen in 74 patients (81.3%) and grade 2 in 16 (17.6%). On univariate analysis, conventional fractionation was associated with higher rates of grade 2 skin toxicity (<0.001), however, BMI, race, age, chemotherapy and menopausal status were not. BMI of > 25 was not associated with increased skin toxicity when analyzed within each fractionation cohort. Conclusion: Hypofractionated whole breast radiation therapy represents a reasonable means of delivering adjuvant radiation therapy for those patients with BMI of > 25, without increased skin toxicity. Higher BMI should not be a contraindication for offering this more convenient fractionation scheme to eligible patients. Author Disclosure: A. Parekh: None. A.D. Rao: None. F. Asrari: None. M. Camp: None. M. Habibi: None. J.L. Wright: None.
significant (P Z 0.113). Audiometric data were available in 41 affected ears. Among those ears, 17 had serviceable hearing, and the hearing preservation rate was 88.2% at a median follow-up of 30.8 months. Among the 57 treated patients, 6 developed complication including 2 with grade 3 to 4 hydrocephalus, 1 with perifocal edema, 1 with headache that needed medical or surgical intervention after treatment, 1 with facial pain, and 1 with facial spasm. Conclusion: Robotic radiosurgery is an effective therapy for AN. It can provide good results of tumor control, hearing preservation rate, and less complication in our cohort. However, patients with NF2 have a poor tumor control and hence further study for optimal dose and fraction might be needed. Author Disclosure: C. Huang: None. C. Yang: None. Y. Lin: None. T. Kuo: None. L. Lin: None.
2149 Frameless Hypofractionated Stereotactic Radiosurgery for Acoustic Neuromas: A Single-Institution Experience C.I. Huang,1 C.C. Yang,2 Y.W. Lin,3 T.Y. Kuo,1 and L.C. Lin2; 1E-Da Cancer Hospital, Kaohsiung, Taiwan, 2Department of Radiation Oncology, Chi-Mei Medical Center, Tainan, Taiwan, 3Department of Radiation Oncology, Chi Mei Medical Center, Tainan, Taiwan Purpose/Objective(s): To retrospectively evaluate tumor control, hearing preservation, and complication rates after Robotic radiosurgery-based hypofractionated stereotactic radiosurgery (HFSRS) in patients with acoustic neuromas (ANs). Materials/Methods: Between 2009 and 2012, 57 patients with 63 ANs underwent FSRS. Among those patients, 6 were associated with neurofibromatosis type 2 (NF2). There were 25 males and 32 females with a median age of 50 years (range 18-80). The radiation dose ranged from 18 Gy to 30 Gy in 3 to 5 fractions. Tumor control rate was assessed using Response Evaluation Criteria In Solid Tumors (RECIST), and was calculated by Kaplan-Meier product-limit method. Hearing ability was assessed with Gardner-Robertson scale and hearing preservation was defined as maintenance of Gardner-Robertson grade 1-2 hearing after HFSRS. Results: With a median follow-up of 29.1 months (range 3.6-54.1), actuarial local control rate was 94.8% after 2 years and 89.3% after 3 years. In the subgroup analysis, there was a trend of worse 1-year tumor control rates for NF2eassociated tumors as compared with non-NF2-associated tumors (61.1% vs 95.6%, P Z 0.092). Using Koos stage as prognostic factor, our patients were divided in two groups. Group 1 included Koos stage I and II, and group 2 Koos stage III and IV. There was a trend that the disease with earlier stage had better local control. The PFS was 96.9% and 80.2% for group 1 and group 2, respectively, although statistically non-
2150 Mathematical Modeling and Diffusion Tensor Magnetic Resonance Imaging Estimates of the Invisibility Index of GBM as an Adjunct to Radiation Therapy Planning L. Hathout1 and V. Patel2; 1Harvard Medical School Boston, MA, 2David Geffen School of Medicine at UCLA, Los Angeles, CA Purpose/Objective(s): Glioblastoma (GBM) is a highly infiltrative and proliferative tumor. As most radiation fields for GBM incorporate a 1-3 cm margin to account for tumor below imaging thresholds, accurate characterization of subthreshold tumor is of clear import for the optimal design of radiation fields. Mathematical modeling and serial MR imaging can be used to calculate patient-specific rates of tumor diffusion (invasiveness), D, and proliferation, P, and can be combined to simulate GBM growth. Traditionally, such models simulate isotropic tumor growth in a single spatial dimension. The purpose of this work is to extend these models by using diffusion tensor (DTI) MR imaging to develop an anisotropic 3D model of GBM growth guided by the direction of adjacent white matter tracts. This model is then used to calculate the percent and extent of tumor cells which have infiltrated beyond the observable MRI T2 boundary of the tumor, and to show how this depends on the tumor’s D/P ratio. The findings of the 3-D anisotropic model are compared to the traditional 1-D isotropic model. Materials/Methods: A reaction-diffusion partial differential equation that accounts for tumor cell diffusion and proliferation is used to model tumor concentration as a function of time and space. This model can be stated as: c(t,x)/dt Z V∙(D(x)V c)+pc(1-c/K) where c, D, P, and K represent the concentration, diffusion, proliferation, and tissue carrying capacity of tumor cells respectively. In this work, D is the tumor cell diffusion tensor, calculated from scaled eigenvalues of the DTI MR water diffusion tensor. The growth of tumors with different D/P ratios is simulated under both isotropic and anisotropic conditions. Each tumor is grown to a T1 radius of 1.5 cm and the percent and extent of tumor cells beyond the T2 radius are calculated. Results: For both the isotropic and anisotropic growth models, higher D/P ratios correlated with a greater proportion and extent of MRI-invisible tumor cells. Furthermore, incorporating DTI imaging demonstrates an even higher proportion of subthreshold tumor and a farther extent of tumor cells beyond the T2 margin than isotropic modeling alone would suggest. For example, for D/P Z 0.4 and for D/P Z 2.0, 7.3% and 16.2% of tumor cells, respectively, are estimated to be beyond the visible MR tumor margins. Conclusion: Because the quantity and distribution of subthreshold tumor depend on the D/P ratio, this ratio should be considered when planning optimal radiation fields. Furthermore, the use of DTI data, which can account for anatomical boundaries and preferential diffusion in the direction of white matter tracts, represents a more refined approach to estimating the shape and extent of subthreshold tumor. Author Disclosure: L. Hathout: None. V. Patel: None.
International Journal of Radiation Oncology Biology Physics
from 2010-2015. We collected data on patient and disease characteristics, treatment details, and skin toxicity during radiation treatment. Chi-squared test was used to assess for differences in frequency of toxicity based on these factors. Results: The cohort included 139 patients with DCIS (n Z 30) and invasive breast cancer (n Z 109). Mean body mass index was 28.9, above the threshold for overweight. Among those with invasive breast cancer, 113 were T1, 25 T2, and 1 T3, and 30 were node positive. All underwent breast conserving surgery, and 136 (98%) had axillary nodal assessment (9 dissection, 97 sentinel node biopsy). 37 (26.6%) received adjuvant chemotherapy. All received whole breast radiation, 48 (34.5%) conventionally fractionated (fraction size 1.8-2 Gy) and 91 (65.5%) hypofractionated (fraction size 2.66-2.7 Gy). Total dose for all patients ranged from 4256-6700 cGy inclusive of boost. No patients with hypofractionation received regional nodal RT (RNI), and 52% with conventional fractionation had RNI. Within the whole cohort, the maximum RTOG skin toxicity grade during RT was 0 in 27 patients (19.4%), 1 in 68 (49%), and 2 in 44 (31.6%). Among those receiving conventional RT, mean BMI was 30.04 (range 19.4-44.8), and 20 (41.6%) had grade 0-1 skin toxicity and 25 (52%) grade 2. Among those with hypofractionated RT, mean BMI was 28.31, and grade 0-1 skin toxicity was seen in 74 patients (81.3%) and grade 2 in 16 (17.6%). On univariate analysis, conventional fractionation was associated with higher rates of grade 2 skin toxicity (<0.001), however, BMI, race, age, chemotherapy and menopausal status were not. BMI of > 25 was not associated with increased skin toxicity when analyzed within each fractionation cohort. Conclusion: Hypofractionated whole breast radiation therapy represents a reasonable means of delivering adjuvant radiation therapy for those patients with BMI of > 25, without increased skin toxicity. Higher BMI should not be a contraindication for offering this more convenient fractionation scheme to eligible patients. Author Disclosure: A. Parekh: None. A.D. Rao: None. F. Asrari: None. M. Camp: None. M. Habibi: None. J.L. Wright: None.
significant (P Z 0.113). Audiometric data were available in 41 affected ears. Among those ears, 17 had serviceable hearing, and the hearing preservation rate was 88.2% at a median follow-up of 30.8 months. Among the 57 treated patients, 6 developed complication including 2 with grade 3 to 4 hydrocephalus, 1 with perifocal edema, 1 with headache that needed medical or surgical intervention after treatment, 1 with facial pain, and 1 with facial spasm. Conclusion: Robotic radiosurgery is an effective therapy for AN. It can provide good results of tumor control, hearing preservation rate, and less complication in our cohort. However, patients with NF2 have a poor tumor control and hence further study for optimal dose and fraction might be needed. Author Disclosure: C. Huang: None. C. Yang: None. Y. Lin: None. T. Kuo: None. L. Lin: None.
2149 Frameless Hypofractionated Stereotactic Radiosurgery for Acoustic Neuromas: A Single-Institution Experience C.I. Huang,1 C.C. Yang,2 Y.W. Lin,3 T.Y. Kuo,1 and L.C. Lin2; 1E-Da Cancer Hospital, Kaohsiung, Taiwan, 2Department of Radiation Oncology, Chi-Mei Medical Center, Tainan, Taiwan, 3Department of Radiation Oncology, Chi Mei Medical Center, Tainan, Taiwan Purpose/Objective(s): To retrospectively evaluate tumor control, hearing preservation, and complication rates after Robotic radiosurgery-based hypofractionated stereotactic radiosurgery (HFSRS) in patients with acoustic neuromas (ANs). Materials/Methods: Between 2009 and 2012, 57 patients with 63 ANs underwent FSRS. Among those patients, 6 were associated with neurofibromatosis type 2 (NF2). There were 25 males and 32 females with a median age of 50 years (range 18-80). The radiation dose ranged from 18 Gy to 30 Gy in 3 to 5 fractions. Tumor control rate was assessed using Response Evaluation Criteria In Solid Tumors (RECIST), and was calculated by Kaplan-Meier product-limit method. Hearing ability was assessed with Gardner-Robertson scale and hearing preservation was defined as maintenance of Gardner-Robertson grade 1-2 hearing after HFSRS. Results: With a median follow-up of 29.1 months (range 3.6-54.1), actuarial local control rate was 94.8% after 2 years and 89.3% after 3 years. In the subgroup analysis, there was a trend of worse 1-year tumor control rates for NF2eassociated tumors as compared with non-NF2-associated tumors (61.1% vs 95.6%, P Z 0.092). Using Koos stage as prognostic factor, our patients were divided in two groups. Group 1 included Koos stage I and II, and group 2 Koos stage III and IV. There was a trend that the disease with earlier stage had better local control. The PFS was 96.9% and 80.2% for group 1 and group 2, respectively, although statistically non-
2150 Mathematical Modeling and Diffusion Tensor Magnetic Resonance Imaging Estimates of the Invisibility Index of GBM as an Adjunct to Radiation Therapy Planning L. Hathout1 and V. Patel2; 1Harvard Medical School Boston, MA, 2David Geffen School of Medicine at UCLA, Los Angeles, CA Purpose/Objective(s): Glioblastoma (GBM) is a highly infiltrative and proliferative tumor. As most radiation fields for GBM incorporate a 1-3 cm margin to account for tumor below imaging thresholds, accurate characterization of subthreshold tumor is of clear import for the optimal design of radiation fields. Mathematical modeling and serial MR imaging can be used to calculate patient-specific rates of tumor diffusion (invasiveness), D, and proliferation, P, and can be combined to simulate GBM growth. Traditionally, such models simulate isotropic tumor growth in a single spatial dimension. The purpose of this work is to extend these models by using diffusion tensor (DTI) MR imaging to develop an anisotropic 3D model of GBM growth guided by the direction of adjacent white matter tracts. This model is then used to calculate the percent and extent of tumor cells which have infiltrated beyond the observable MRI T2 boundary of the tumor, and to show how this depends on the tumor’s D/P ratio. The findings of the 3-D anisotropic model are compared to the traditional 1-D isotropic model. Materials/Methods: A reaction-diffusion partial differential equation that accounts for tumor cell diffusion and proliferation is used to model tumor concentration as a function of time and space. This model can be stated as: c(t,x)/dt Z V∙(D(x)V c)+pc(1-c/K) where c, D, P, and K represent the concentration, diffusion, proliferation, and tissue carrying capacity of tumor cells respectively. In this work, D is the tumor cell diffusion tensor, calculated from scaled eigenvalues of the DTI MR water diffusion tensor. The growth of tumors with different D/P ratios is simulated under both isotropic and anisotropic conditions. Each tumor is grown to a T1 radius of 1.5 cm and the percent and extent of tumor cells beyond the T2 radius are calculated. Results: For both the isotropic and anisotropic growth models, higher D/P ratios correlated with a greater proportion and extent of MRI-invisible tumor cells. Furthermore, incorporating DTI imaging demonstrates an even higher proportion of subthreshold tumor and a farther extent of tumor cells beyond the T2 margin than isotropic modeling alone would suggest. For example, for D/P Z 0.4 and for D/P Z 2.0, 7.3% and 16.2% of tumor cells, respectively, are estimated to be beyond the visible MR tumor margins. Conclusion: Because the quantity and distribution of subthreshold tumor depend on the D/P ratio, this ratio should be considered when planning optimal radiation fields. Furthermore, the use of DTI data, which can account for anatomical boundaries and preferential diffusion in the direction of white matter tracts, represents a more refined approach to estimating the shape and extent of subthreshold tumor. Author Disclosure: L. Hathout: None. V. Patel: None.