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Stereotactic Radiosurgery with or without Whole Brain Radiotherapy for Patients with a Single Radioresistant Brain Metastasis
Proceedings of the 50th Annual ASTRO Meeting
2146
A Comparison of Helical Tomotherapy (HT), Fixed-field Intensity-modulated Radiotherapy (IMRT) and 3D Conformal Radiotherapy (3DCRT) Plans in Stereotactic Radiation Therapy of Skull Base Meningioma
H. S. Elhateer, R. Ruo, T. Muanza, D. Roberge, C. Lambert, L. Souhami, G. Shenouda McGill University, Montreal, QC, Canada Purpose/Objective(s): To assess the potential benefits and limitations of IMRT in the treatment of skull base meningioma. Materials/Methods: We undertook a retrospective treatment planning study using the CT simulation data for 8 patients with meningiomas of the skull base originally treated with fractionated stereotactic radiotherapy. Target volumes and organs at risk were delineated with the help of co-registered MRI images. A 3 mm margin was added to the gross tumor volume to create the planning target volume (PTV). Treatment plans were generated for non-coplanar 3DCRT, coplanar fixed-field IMRT (7-9 fields) and Helical Tomotherapy (HT) to deliver a total dose of 52.2 Gy in 1.8 Gy fractions. The treatment goals were to cover $95% and 99% of the PTV with 100% and $95% of the prescribed dose , respectively, whilst keeping the maximum point dose to optic nerves, chiasm and brain stem #54 Gy. Based on review by experienced radiation oncologist, a clinically accepted plan from each modality was selected for comparison. The parameters used for comparison were the ability of each plan to achieve the predetermined treatment goals along with the conformity index (CI), homogeneity index (HI), and target coverage index (Cov. I). Direct comparison of the DVH data for the PTV coverage and OAR sparing was done along with the repeated measures ANOVA with Tukey’s multiple comparison post hoc tests for CI, HI, and Cov. I comparison. Results: The eight meningiomas of the skull base (6 cavernous sinus, 1 suprasellar, and 1 olfactory groove tumors) had a median PTV of 20.3 cc (range, 7.4-50.7 cc). The PTV coverage goals has been achieved in all HT plans, compared to 7 and 6 plans for fixed-field IMRT and 3DCRT , respectively, with 1-1.5% of the PTV missing the goals by 1-3% of the prescribed dose. The PTV coverage index for HT plans was significantly higher compared to fixed-field IMRT (p = 0.004), with no significant difference between either HT and 3DCRT or fixed-field IMRT and 3DCRT. The HT plans achieved the highest HI followed by fixed-field IMRT then 3DCRT (p = 0.002). In contrast, 3DCRT plans had higher CI than both IMRT modalities (p \ 0.001). The treatment goals for the optic chiasm and optic nerves were achieved in all IMRT plans while it has been violated in 5 3DCRT (by 0.8-1.2 Gy). The treatment goal for the brainstem was achieved in all plans with no significant differences. Conclusions: When treating base of skull meningiomas, HT resulted in the best target coverage and dose homogeneity. When compared to 3DCRT, sparing of organs at risk was improved with either HT or fixed-field IMRT at the expense of a lower CI. Author Disclosure: H.S. Elhateer, None; R. Ruo, None; T. Muanza, None; D. Roberge, None; C. Lambert, None; L. Souhami, None; G. Shenouda, None.
2147
Radiotherapy with Concomitant Temozolomide in WHO Grade III Glial Tumors
F. Zorlu1, M. Gurkaynak1, U. Selek1, S. Ulger1, A. Turker2, A. Kars2 1 Hacettepe University Oncology Hospital, Radiation Oncology Department, Ankara, Turkey, 2Hacettepe University Oncology Hospital, Medical Oncology Division, Ankara, Turkey
Purpose/Objective(s): Concomitant chemoradiotherapy with Temozolomide (CRT) is the current standard for glioblastoma multiforme. As CRT literature is evolving for Grade III glial tumors, here we present our experience in Grade III glial tumors. Materials/Methods: Twenty-five patients with Grade III glial tumors treated between November 2003 and March 2007 in our center were evaluated. Inclusion criteria required histopathologic diagnosis, normal creatinine clearance, liver enzymes, and blood count. Exclusion criteria were age over 60-years-old and KPS less than 70. The 3DCRT was a total of 60 Gy (2 Gy/fractions/day) and initial CTV was based on a 2-cm margin on GTV in T1 postcontrast MRI images rather than on peritumoral edema to 40 Gy and 20 Gy boost was applied with CTV of 1 cm. Concomitant Temozolomide was prescribed with two schedules: 150 mg/m2 /day in 5 days in each cycle in the first and fifth weeks of radiotherapy (protocol week 1 and 5) and 75 mg/m2 /day given 7 days per week from the first to last day of RT (protocol daily). Ten patients in protocol week 1 and 5 and 15 in protocol daily were treated. Results: Grade III histopathology was as follows; astrocytoma, 15; mixed-oligoastrocytoma, 5; and oligodendroglioma 5. Median age was 40 (range, 19-56 years) and median KPS were 90 (range, 80-100). Surgical excision was gross total in 24 patients, and only biopsy in 1 patient. Median follow-up period was 15.4 months (range, 3 -42 months) after CRT. No acute Grade 3-4 toxicity was recorded for radiotherapy and chemotherapy. Eleven patients had local progression/recurrence and successful salvage was only possible in 3 (2 resection, 1 reirradiation with CyberKnife) while other 8 died following second-line chemotherapy. Fourteen patients are radiological and clinical progression-free on last follow-up (astrocytoma, 7 alive/15; oligodendrogliomas, 3 alive/5; mixed- oligoastrocytoma, 4 alive/ 5 patients). Progression-free survival (PFS) was 62.4% (SE 10.6%) and 42.8% (SE 11.9%) at 1 and 2 year, respectively. Median progression-free survival was 19.6 months. Overall survival (OS) was 86.1% (SE 7.6%) and 61.8% (SE 11.7%) at 1 and 2 year, respectively. Concomitant chemotherapy protocol did not significantly affect PFS or OS. Two-year overall survival for Grade III astrocytoma, Grade III oligodendroglioma, Grade III oligoastrocytoma were as follows: 51.3% (SE 16.6%), 66.7% (SE 27.2%), and 80% (SE 17.9%), respectively. No prognostic factor was found significant in univariate and multivariate analysis for survival. Conclusions: Radiotherapy with concomitant Temozolomide was well-tolerated in our limited number cohort with no apparent superior outcome in comparison to literature with radiotherapy alone series. Long-term follow-up will highlight the final outcome. Author Disclosure: F. Zorlu, None; M. Gurkaynak, None; U. Selek, None; S. Ulger, None; A. Turker, None; A. Kars, None.
2148
Stereotactic Radiosurgery with or without Whole Brain Radiotherapy for Patients with a Single Radioresistant Brain Metastasis
J. W. Clarke, J. McGregor, J. C. Grecula, N. A. Mayr, J. Z. Wang, K. Li, N. Gupta, R. Cavaliere, S. Register, S. S. Lo Arthur G. James Cancer Hospital, The Ohio State University Medical Center, Columbus, OH Purpose/Objective(s): To examine the outcomes of patients with a single brain metastasis from radioresistant histologies (renal cell carcinoma and melanoma) treated with stereotactic radiosurgery (SRS) with or without whole-brain radiotherapy (WBRT).
S235
I. J. Radiation Oncology d Biology d Physics
S236
Volume 72, Number 1, Supplement, 2008
Materials/Methods: Exempt review was granted by our cancer hospital institutional review board for the collection of data of patients with radioresistant brain metastases treated with gamma knife (GK)-based SRS in our department. In the period of 2000 to 2007, a total of 97 patients with radioresistant brain metastases were treated with SRS. Out of the 97 patients, 27 (15 male and 12 female) had single metastasis. Five patients received WBRT in addition to SRS. The median age was 58 years (range, 39-81 years). Nine and 18 patients had renal cell carcinoma (RCC) and melanoma brain metastases, respectively. Twenty-four patients who had metastases were located in the supratentorial areas. Distribution of RTOG recursive partitioning analysis (RPA) classes was as follows: I, 1 patient; II, 25 patients; and III, 1 patient. Out of 27 patients, 4 had stable extracranial disease. Results: The median marginal dose was 20 Gy (range, 15-22 Gy). The target volume ranged from 0.054 to 17.3 cm3. At follow-up intervals ranging from 1.8 to 23.2 months, the radiographic responses were as follows: progression in 7 patients; stable in 5 patients; and shrinkage in 15 patients. Fifteen patients (56%) developed distant brain failure. Seven of the 27 patients were alive at last follow-up. The 3-, 6-, 9-, 12-, and 18-month local control (LC) rates were 82.8%, 77.9%, 69.3%, 69.3%, and 55.4%, respectively. The corresponding distant brain control (DBC) rates were 74.4%, 60.2%, 54.1%, 40.6%, and 22.6%. The corresponding progressionfree survival (PFS) rates were 63%, 42.5%, 38%, 28.5%, and 12.7%. The corresponding overall survival (OS) rates were 85.25, 53.6%, 48.7%, 43.8%, and 26.3%. Conclusions: Approximately 30% of the patients failed locally and 60% had distant brain failure within 1 year. Stable extracranial disease was associated with better DBC, PFS, and OS although the difference did not reach statistical significance (p = 0.21, 0.12, 0.24). None of the 5 patients who received WBRT developed distant brain failure although the follow-up intervals were short (range, 0.6-13.7 months; median, 5.1 months). The WBRT did not appear to affect LC, PFS, and OS (p = 0.32, 0.87, 0.69). Author Disclosure: J.W. Clarke, None; J. McGregor, None; J.C. Grecula, None; N.A. Mayr, None; J.Z. Wang, None; K. Li, None; N. Gupta, None; R. Cavaliere, None; S. Register, None; S.S. Lo, None.
2149
Decreased Temporal Lobe Dose with 5-Field IMRT for Pituitary Macroadenoma Treatment
T. Duckworth, P. Parhar, P. Shah, K. DeWyngaert, A. Narayana, S. C. Formenti, J. N. Shah New York University School of Medicine, New York, NY Purpose/Objective(s): Pituitary macroadenomas ($1 cm) are often treated with external beam radiotherapy (EBRT). Cognitive decline is associated with temporal lobe irradiation, which is especially relevant for pituitary macroadenoma patients due to often long post-EBRT life expectancy. In this dosimetric study, we compared temporal lobe dose delivered by two commonly used EBRT techniques, 3-field three-dimensional conformal radiotherapy (3DCRT) and 3-field intensity modulated radiotherapy (3F IMRT), and one proposed alternative approach, 5-field IMRT (5F IMRT). Materials/Methods: A CT-based planning was performed for 15 pituitary macroadenoma patients using three techniques: 3-field 3DCRT (one midline superior anterior oblique, two lateral beams); 3-field IMRT (same beam angles as 3DCRT); 5-field IMRT (same beam angles as the other two approaches, but additional right superior anterior oblique and left superior anterior oblique beams). Prescription dose (PD) was 45 Gy. Tumor volumes were: GTV = macroadenoma (mean 10.2 cc), CTV = GTV, PTV = CTV + 0.5 cm (mean 27.6 cc). Results: Mean right temporal lobe dose (Gy) and integral dose (kg-Gy) were significantly lower with 5F IMRT vs. 3DCRT (9.83 vs. 11.15, p\10-4; 0.93 vs. 1.07, p\10-3) and 5F IMRT vs. 3F IMRT (9.83 vs. 12.14, p\10-6; 0.93 vs. 1.16, p\10-6). Mean left temporal lobe dose (Gy) and integral dose (kg-Gy) were also significantly lower with 5F IMRT vs. 3DCRT (10.24 vs. 11.49, p \ 10-4; 0.97 vs. 1.10, p\10-4) and 5F IMRT vs. 3F IMRT (10.24 vs. 12.44, p\10-9; 0.97 vs. 1.19, p\10-8). Temporal lobe sparing with 5F IMRT was most pronounced at intermediate doses: right temporal lobe V20 Gy (% right temporal lobe volume receiving $20 Gy) of 25% for 5F IMRT vs. 33% for 3DCRT (p \ 10-6) and 32% for 3F IMRT (p \ 10-6); left temporal lobe V20 Gy of 27% for 5F IMRT vs. 34% for 3DCRT (p \ 10-6) and 33% for 3F IMRT (p \ 10-6). Notably, V30 Gy was markedly higher with 3F IMRT vs. 5F IMRT: right temporal lobe, 25% vs. 7% (p \ 10-7); left temporal lobe, 25% vs. 8% (p \ 10-9). Improved temporal lobe sparing with 5F IMRT did not compromise target coverage: GTV V100 (% GTV receiving $100% PD) of 99.98, 100.00, 100.00 for 5F IMRT, 3DCRT, 3F IMRT (p . 0.05 all comparisons); PTV V100 of 98.06, 99.02, 98.68 (p . 0.05 all comparisons). The 5F IMRT also did not result in exceeding of 54 Gy optic chiasm tolerance (mean max dose, 49.08 Gy), 50 Gy optic nerve tolerance (mean max right and left doses, 46.98 Gy and 46.66 Gy), 45 Gy retina tolerance (mean max right and left doses, 8.66 Gy and 8.18 Gy), or 54 Gy brainstem tolerance (mean max dose, 43.84 Gy). Conclusions: The 5-field IMRT decreased temporal lobe dosing vs. 3DCRT and 3-field IMRT for pituitary macroadenoma EBRT without compromising target coverage or exceeding normal tissue constraints. Use of 5-field IMRT may thus minimize cognitive decline in irradiated pituitary macroadenoma patients. Author Disclosure: T. Duckworth, None; P. Parhar, None; P. Shah, None; K. DeWyngaert, None; A. Narayana, None; S.C. Formenti, None; J.N. Shah, None.
2150
A Novel Approach for Highly Conformal Irradiation of Vestibular Schwannoma using a Single Volumetric Aperture Based Intensity Modulated Arc
B. J. Slotman, F. J. Lagerwaard, W. F. Verbakel, E. van der Hoorn, S. Senan VU University Medical Center, Amsterdam HV, Netherlands Purpose/Objective(s): Radiosurgery (RS) is the mainstay of treatment for patients with vestibular schwannomas (VS) with reported local control rates of $95%. To minimize toxicity to the ipsilateral cochlea and brainstem, high conformity of treatment plans is essential. In addition, avoiding low dose irradiation to the normal brain is preferential. A novel approach using volumetric aparture-based intensity modulated arc therapy (RapidArc, Varian Medical Systems) for VS was evaluated. RapidArc treatment, using one single modulated arc can be delivered in only a few minutes per fraction, benefiting both patients and radiotherapy departments.
2146
A Comparison of Helical Tomotherapy (HT), Fixed-field Intensity-modulated Radiotherapy (IMRT) and 3D Conformal Radiotherapy (3DCRT) Plans in Stereotactic Radiation Therapy of Skull Base Meningioma
H. S. Elhateer, R. Ruo, T. Muanza, D. Roberge, C. Lambert, L. Souhami, G. Shenouda McGill University, Montreal, QC, Canada Purpose/Objective(s): To assess the potential benefits and limitations of IMRT in the treatment of skull base meningioma. Materials/Methods: We undertook a retrospective treatment planning study using the CT simulation data for 8 patients with meningiomas of the skull base originally treated with fractionated stereotactic radiotherapy. Target volumes and organs at risk were delineated with the help of co-registered MRI images. A 3 mm margin was added to the gross tumor volume to create the planning target volume (PTV). Treatment plans were generated for non-coplanar 3DCRT, coplanar fixed-field IMRT (7-9 fields) and Helical Tomotherapy (HT) to deliver a total dose of 52.2 Gy in 1.8 Gy fractions. The treatment goals were to cover $95% and 99% of the PTV with 100% and $95% of the prescribed dose , respectively, whilst keeping the maximum point dose to optic nerves, chiasm and brain stem #54 Gy. Based on review by experienced radiation oncologist, a clinically accepted plan from each modality was selected for comparison. The parameters used for comparison were the ability of each plan to achieve the predetermined treatment goals along with the conformity index (CI), homogeneity index (HI), and target coverage index (Cov. I). Direct comparison of the DVH data for the PTV coverage and OAR sparing was done along with the repeated measures ANOVA with Tukey’s multiple comparison post hoc tests for CI, HI, and Cov. I comparison. Results: The eight meningiomas of the skull base (6 cavernous sinus, 1 suprasellar, and 1 olfactory groove tumors) had a median PTV of 20.3 cc (range, 7.4-50.7 cc). The PTV coverage goals has been achieved in all HT plans, compared to 7 and 6 plans for fixed-field IMRT and 3DCRT , respectively, with 1-1.5% of the PTV missing the goals by 1-3% of the prescribed dose. The PTV coverage index for HT plans was significantly higher compared to fixed-field IMRT (p = 0.004), with no significant difference between either HT and 3DCRT or fixed-field IMRT and 3DCRT. The HT plans achieved the highest HI followed by fixed-field IMRT then 3DCRT (p = 0.002). In contrast, 3DCRT plans had higher CI than both IMRT modalities (p \ 0.001). The treatment goals for the optic chiasm and optic nerves were achieved in all IMRT plans while it has been violated in 5 3DCRT (by 0.8-1.2 Gy). The treatment goal for the brainstem was achieved in all plans with no significant differences. Conclusions: When treating base of skull meningiomas, HT resulted in the best target coverage and dose homogeneity. When compared to 3DCRT, sparing of organs at risk was improved with either HT or fixed-field IMRT at the expense of a lower CI. Author Disclosure: H.S. Elhateer, None; R. Ruo, None; T. Muanza, None; D. Roberge, None; C. Lambert, None; L. Souhami, None; G. Shenouda, None.
2147
Radiotherapy with Concomitant Temozolomide in WHO Grade III Glial Tumors
F. Zorlu1, M. Gurkaynak1, U. Selek1, S. Ulger1, A. Turker2, A. Kars2 1 Hacettepe University Oncology Hospital, Radiation Oncology Department, Ankara, Turkey, 2Hacettepe University Oncology Hospital, Medical Oncology Division, Ankara, Turkey
Purpose/Objective(s): Concomitant chemoradiotherapy with Temozolomide (CRT) is the current standard for glioblastoma multiforme. As CRT literature is evolving for Grade III glial tumors, here we present our experience in Grade III glial tumors. Materials/Methods: Twenty-five patients with Grade III glial tumors treated between November 2003 and March 2007 in our center were evaluated. Inclusion criteria required histopathologic diagnosis, normal creatinine clearance, liver enzymes, and blood count. Exclusion criteria were age over 60-years-old and KPS less than 70. The 3DCRT was a total of 60 Gy (2 Gy/fractions/day) and initial CTV was based on a 2-cm margin on GTV in T1 postcontrast MRI images rather than on peritumoral edema to 40 Gy and 20 Gy boost was applied with CTV of 1 cm. Concomitant Temozolomide was prescribed with two schedules: 150 mg/m2 /day in 5 days in each cycle in the first and fifth weeks of radiotherapy (protocol week 1 and 5) and 75 mg/m2 /day given 7 days per week from the first to last day of RT (protocol daily). Ten patients in protocol week 1 and 5 and 15 in protocol daily were treated. Results: Grade III histopathology was as follows; astrocytoma, 15; mixed-oligoastrocytoma, 5; and oligodendroglioma 5. Median age was 40 (range, 19-56 years) and median KPS were 90 (range, 80-100). Surgical excision was gross total in 24 patients, and only biopsy in 1 patient. Median follow-up period was 15.4 months (range, 3 -42 months) after CRT. No acute Grade 3-4 toxicity was recorded for radiotherapy and chemotherapy. Eleven patients had local progression/recurrence and successful salvage was only possible in 3 (2 resection, 1 reirradiation with CyberKnife) while other 8 died following second-line chemotherapy. Fourteen patients are radiological and clinical progression-free on last follow-up (astrocytoma, 7 alive/15; oligodendrogliomas, 3 alive/5; mixed- oligoastrocytoma, 4 alive/ 5 patients). Progression-free survival (PFS) was 62.4% (SE 10.6%) and 42.8% (SE 11.9%) at 1 and 2 year, respectively. Median progression-free survival was 19.6 months. Overall survival (OS) was 86.1% (SE 7.6%) and 61.8% (SE 11.7%) at 1 and 2 year, respectively. Concomitant chemotherapy protocol did not significantly affect PFS or OS. Two-year overall survival for Grade III astrocytoma, Grade III oligodendroglioma, Grade III oligoastrocytoma were as follows: 51.3% (SE 16.6%), 66.7% (SE 27.2%), and 80% (SE 17.9%), respectively. No prognostic factor was found significant in univariate and multivariate analysis for survival. Conclusions: Radiotherapy with concomitant Temozolomide was well-tolerated in our limited number cohort with no apparent superior outcome in comparison to literature with radiotherapy alone series. Long-term follow-up will highlight the final outcome. Author Disclosure: F. Zorlu, None; M. Gurkaynak, None; U. Selek, None; S. Ulger, None; A. Turker, None; A. Kars, None.
2148
Stereotactic Radiosurgery with or without Whole Brain Radiotherapy for Patients with a Single Radioresistant Brain Metastasis
J. W. Clarke, J. McGregor, J. C. Grecula, N. A. Mayr, J. Z. Wang, K. Li, N. Gupta, R. Cavaliere, S. Register, S. S. Lo Arthur G. James Cancer Hospital, The Ohio State University Medical Center, Columbus, OH Purpose/Objective(s): To examine the outcomes of patients with a single brain metastasis from radioresistant histologies (renal cell carcinoma and melanoma) treated with stereotactic radiosurgery (SRS) with or without whole-brain radiotherapy (WBRT).
S235
I. J. Radiation Oncology d Biology d Physics
S236
Volume 72, Number 1, Supplement, 2008
Materials/Methods: Exempt review was granted by our cancer hospital institutional review board for the collection of data of patients with radioresistant brain metastases treated with gamma knife (GK)-based SRS in our department. In the period of 2000 to 2007, a total of 97 patients with radioresistant brain metastases were treated with SRS. Out of the 97 patients, 27 (15 male and 12 female) had single metastasis. Five patients received WBRT in addition to SRS. The median age was 58 years (range, 39-81 years). Nine and 18 patients had renal cell carcinoma (RCC) and melanoma brain metastases, respectively. Twenty-four patients who had metastases were located in the supratentorial areas. Distribution of RTOG recursive partitioning analysis (RPA) classes was as follows: I, 1 patient; II, 25 patients; and III, 1 patient. Out of 27 patients, 4 had stable extracranial disease. Results: The median marginal dose was 20 Gy (range, 15-22 Gy). The target volume ranged from 0.054 to 17.3 cm3. At follow-up intervals ranging from 1.8 to 23.2 months, the radiographic responses were as follows: progression in 7 patients; stable in 5 patients; and shrinkage in 15 patients. Fifteen patients (56%) developed distant brain failure. Seven of the 27 patients were alive at last follow-up. The 3-, 6-, 9-, 12-, and 18-month local control (LC) rates were 82.8%, 77.9%, 69.3%, 69.3%, and 55.4%, respectively. The corresponding distant brain control (DBC) rates were 74.4%, 60.2%, 54.1%, 40.6%, and 22.6%. The corresponding progressionfree survival (PFS) rates were 63%, 42.5%, 38%, 28.5%, and 12.7%. The corresponding overall survival (OS) rates were 85.25, 53.6%, 48.7%, 43.8%, and 26.3%. Conclusions: Approximately 30% of the patients failed locally and 60% had distant brain failure within 1 year. Stable extracranial disease was associated with better DBC, PFS, and OS although the difference did not reach statistical significance (p = 0.21, 0.12, 0.24). None of the 5 patients who received WBRT developed distant brain failure although the follow-up intervals were short (range, 0.6-13.7 months; median, 5.1 months). The WBRT did not appear to affect LC, PFS, and OS (p = 0.32, 0.87, 0.69). Author Disclosure: J.W. Clarke, None; J. McGregor, None; J.C. Grecula, None; N.A. Mayr, None; J.Z. Wang, None; K. Li, None; N. Gupta, None; R. Cavaliere, None; S. Register, None; S.S. Lo, None.
2149
Decreased Temporal Lobe Dose with 5-Field IMRT for Pituitary Macroadenoma Treatment
T. Duckworth, P. Parhar, P. Shah, K. DeWyngaert, A. Narayana, S. C. Formenti, J. N. Shah New York University School of Medicine, New York, NY Purpose/Objective(s): Pituitary macroadenomas ($1 cm) are often treated with external beam radiotherapy (EBRT). Cognitive decline is associated with temporal lobe irradiation, which is especially relevant for pituitary macroadenoma patients due to often long post-EBRT life expectancy. In this dosimetric study, we compared temporal lobe dose delivered by two commonly used EBRT techniques, 3-field three-dimensional conformal radiotherapy (3DCRT) and 3-field intensity modulated radiotherapy (3F IMRT), and one proposed alternative approach, 5-field IMRT (5F IMRT). Materials/Methods: A CT-based planning was performed for 15 pituitary macroadenoma patients using three techniques: 3-field 3DCRT (one midline superior anterior oblique, two lateral beams); 3-field IMRT (same beam angles as 3DCRT); 5-field IMRT (same beam angles as the other two approaches, but additional right superior anterior oblique and left superior anterior oblique beams). Prescription dose (PD) was 45 Gy. Tumor volumes were: GTV = macroadenoma (mean 10.2 cc), CTV = GTV, PTV = CTV + 0.5 cm (mean 27.6 cc). Results: Mean right temporal lobe dose (Gy) and integral dose (kg-Gy) were significantly lower with 5F IMRT vs. 3DCRT (9.83 vs. 11.15, p\10-4; 0.93 vs. 1.07, p\10-3) and 5F IMRT vs. 3F IMRT (9.83 vs. 12.14, p\10-6; 0.93 vs. 1.16, p\10-6). Mean left temporal lobe dose (Gy) and integral dose (kg-Gy) were also significantly lower with 5F IMRT vs. 3DCRT (10.24 vs. 11.49, p \ 10-4; 0.97 vs. 1.10, p\10-4) and 5F IMRT vs. 3F IMRT (10.24 vs. 12.44, p\10-9; 0.97 vs. 1.19, p\10-8). Temporal lobe sparing with 5F IMRT was most pronounced at intermediate doses: right temporal lobe V20 Gy (% right temporal lobe volume receiving $20 Gy) of 25% for 5F IMRT vs. 33% for 3DCRT (p \ 10-6) and 32% for 3F IMRT (p \ 10-6); left temporal lobe V20 Gy of 27% for 5F IMRT vs. 34% for 3DCRT (p \ 10-6) and 33% for 3F IMRT (p \ 10-6). Notably, V30 Gy was markedly higher with 3F IMRT vs. 5F IMRT: right temporal lobe, 25% vs. 7% (p \ 10-7); left temporal lobe, 25% vs. 8% (p \ 10-9). Improved temporal lobe sparing with 5F IMRT did not compromise target coverage: GTV V100 (% GTV receiving $100% PD) of 99.98, 100.00, 100.00 for 5F IMRT, 3DCRT, 3F IMRT (p . 0.05 all comparisons); PTV V100 of 98.06, 99.02, 98.68 (p . 0.05 all comparisons). The 5F IMRT also did not result in exceeding of 54 Gy optic chiasm tolerance (mean max dose, 49.08 Gy), 50 Gy optic nerve tolerance (mean max right and left doses, 46.98 Gy and 46.66 Gy), 45 Gy retina tolerance (mean max right and left doses, 8.66 Gy and 8.18 Gy), or 54 Gy brainstem tolerance (mean max dose, 43.84 Gy). Conclusions: The 5-field IMRT decreased temporal lobe dosing vs. 3DCRT and 3-field IMRT for pituitary macroadenoma EBRT without compromising target coverage or exceeding normal tissue constraints. Use of 5-field IMRT may thus minimize cognitive decline in irradiated pituitary macroadenoma patients. Author Disclosure: T. Duckworth, None; P. Parhar, None; P. Shah, None; K. DeWyngaert, None; A. Narayana, None; S.C. Formenti, None; J.N. Shah, None.
2150
A Novel Approach for Highly Conformal Irradiation of Vestibular Schwannoma using a Single Volumetric Aperture Based Intensity Modulated Arc
B. J. Slotman, F. J. Lagerwaard, W. F. Verbakel, E. van der Hoorn, S. Senan VU University Medical Center, Amsterdam HV, Netherlands Purpose/Objective(s): Radiosurgery (RS) is the mainstay of treatment for patients with vestibular schwannomas (VS) with reported local control rates of $95%. To minimize toxicity to the ipsilateral cochlea and brainstem, high conformity of treatment plans is essential. In addition, avoiding low dose irradiation to the normal brain is preferential. A novel approach using volumetric aparture-based intensity modulated arc therapy (RapidArc, Varian Medical Systems) for VS was evaluated. RapidArc treatment, using one single modulated arc can be delivered in only a few minutes per fraction, benefiting both patients and radiotherapy departments.