Proceedings of the 50th Annual ASTRO Meeting S507

Conclusions: Low- and high-grade soft-tissue sarcomas show significant pathological treatment responses in the form of hyalinefibrosis, necrosis and granulation tissue. Despite this, there is minimal early volumetric response to radiation, especially for high-grade tumors. Although radiological partial response, seen in 18% of patients, was predictive of pathological response, the signif-icance of radiological progression was unclear. Myxoid liposarcoma subtype was predictive of response.

Author Disclosure: D. Roberge, None; T. Skamene, None; A. Nahal, None; R. Turcotte, None; C. Freeman, None.

2756 Proton Beam Radiation Therapy for Soft Tissue Sarcomas of the Paranasal Sinus and Nasal Cavity

M. Truong1,2, U. R. Kamat1,2, T. F. DeLaney1,2, A. W. Chan1,2

1Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, 2Harvard Medical School, Boston, MA

Purpose/Objective(s): To evaluate the treatment outcome in patients with soft tissue sarcomas of the paranasal sinus and nasalcavity soft tissue sarcoma with highly conformal proton radiotherapy (RT).

Materials/Methods: Between 1991 and 2006, 19 patients with non-metastatic paranasal and nasal cavity soft tissue sarcomasreceived 3-D conformal proton at the Massachusetts General Hospital. The median age was 43 years (range, 21-89). The me-dian KPS was 90. The primary tumor location included the maxillary sinus in 11, ethmoid sinus in 4, nasal cavity in 4. Histo-pathology included 5 patients with malignant fibrous histiocytoma, 4 rhabdomyosarcoma (alveolar type), 4 fibrosarcoma, 2synovial, 1 primitive neuroectodermal tumor (PNET), 1 leiomyosarcoma, 1 myxoid spindle cell sarcoma and 1 angiosarcoma.Four patients with rhabdomyosarcoma histology presented with nodal disease at diagnosis. Except for 5 patients with rhabdo-myosarcoma and PNET, all underwent attempted resection of which 6 had a gross total resection, 8 underwent partial tumorresection prior to RT. Patients with rhabdomyosarcoma and PNET underwent neoadjuvant, adjuvant chemotherapy and concur-rent chemoradiation therapy (Vincristine, Adriamycin, Cyclophosphamide, Ifosfamide and Etoposide). The median total radia-tion dose to the primary tumor volume was 70 Gray-Equivalent (range, 55-82) over 50 days. The median follow-up for allpatients was 35 months.

Results: As the first site of failure, 3, 2, and 4 patients developed local, regional, and distant metastasis, respectively. Of the dis-tant recurrences, 1 was leptomeningeal and 3 were systemic (bone and lungs). The 3-year actuarial rates of local, regional, andfreedom from distant metastasis were 85%, 89%, and 79%, respectively. The disease-free and overall survival rates at 3 yearswere 47% and 68%, respectively. Complications from combined therapy included 1 patient treated with a craniofacial resectionwith Common Toxicity Criteria grade 4 osteomyelitis and recurrent infections requiring revision surgery, 1 patient with nasola-crimal duct obstruction requiring endoscopic dacryocystorhinostomy and 1 patient with a second malignancy in the brain 6 yearsafter RT.

Conclusions: Proton RT results in a promising local control and survival for patients with locally advanced paranasal sinus andnasal cavity soft tissue sarcoma with acceptable toxicity.

Author Disclosure: M. Truong, None; U.R. Kamat, None; T.F. DeLaney, None; A.W. Chan, None.

2757 The Feasibility of Hypofractionated Preoperative Intensity Modulated Radiation Therapy to a Partial

Tumor Volume in Retroperitoneal Sarcoma: Dosimetric Analysis

S. L. Berry, M. Hunt, S. Singer, K. M. Alektiar

Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s): Retroperitoneal sarcomas (RSTS) tend to be large, making adjuvant radiation therapy (RT) somewhat chal-lenging. There is growing interest in limiting RT to the portion of the tumor that is at the highest risk for recurrence, namely theinterface between the tumor and posterior abdominal wall structures. For RT to this smaller region, one asks if it is possible tohypofractionate (HF) without exceeding normal tissue tolerance. We report the dosimetric feasibility of using HF preoperative in-tensity modulated radiation therapy (IMRT) in RSTS as a potential clinical application of image guided radiation therapy (IGRT) inthis disease.

Materials/Methods: Two separate treatment plans were created for each of 10 patients with RSTS using IMRT. The first (Plan2.15

Gy) was designed to deliver 60.2 Gy at 2.15 Gy per fraction, consistent with the target dose that RSTS patients at our institutioncurrently receive using a dose painting approach. The second (Plan6 Gy) was designed to deliver 30 Gy at 6 Gy per fraction, a typ-ical HF scheme used at our institution for paraspinal IGRT. Critical organs were constrained in each plan to tolerance levels typ-ically used in our clinic for conventionally fractionated and HF deliveries, respectively. The planning target volume (PTV) wascreated by adding a margin of 1.5 - 3 cm posteriorly and 1 cm elsewhere around the interface of the GTV with the posterior ab-dominal wall, defined as such to provide adequate coverage of this region but to spare normal tissue nearby. For comparison to thePlan2.15 Gy, biologically equivalent dose-volume histograms (DVH) were generated for the HF Plan6 Gy using alpha/beta ratios tocalculate the equivalent dose in fraction sizes of 2.15 Gy. The alpha/beta ratios used were 2 for the cord, 3 for the sarcoma, liver,kidneys, and cauda, and 4 for the bowel.

Results: PTV coverage, in terms of D95, was comparable between Plan2.15 Gy and Plan6 Gy (99.5 ± 1.1% vs. 99.0 ± 1.7% p =0.34). There was a significant decrease in critical organ dose between Plan2.15 Gy and Plan6 Gy in the bowel mean (13.4 ± 4.8Gy vs. 4.3 ± 1.6 Gy), the bowel D5cc (51.2 ± 6.9 Gy vs. 36.5 ± 6.1 Gy), the ipsilateral kidney mean (18.4 ± 14.6 Gy vs. 5.4 ±4.3 Gy), the cord D1cc (41.1 ± 3.1 Gy vs. 30.7 ± 4.8 Gy), the cauda D1cc (42.3 ± 8.2 Gy vs. 29.8 ± 7.0 Gy), the contralateralkidney mean (4.3 ± 2.1 Gy vs. 1.3 ± 0.6 Gy) and the liver mean (6.9 ± 4.9 Gy vs. 2.0 ± 1.4 Gy). All critical organ comparisonshad p \ 0.01.

Conclusions: HF preoperative IMRT to a partial tumor volume is a feasible option in RSTS, without exceeding normal tissue tol-erance and while maintaining PTV coverage similar to current techniques. More investigations are needed to determine if thesedosimetric improvements translate into a lower complication rate and improved local control.

Author Disclosure: S.L. Berry, None; M. Hunt, None; S. Singer, None; K.M. Alektiar, None.