Proceedings of the 49th Annual ASTRO Meeting S751

2978 3D Conformal Radiotherapy versus IMRT in the Adjuvant Treatment of Soft Tissue Sarcoma of the

Adductor Compartment of the Thigh

Y. K. Lee1, A. J. Stewart2, F. H. Saran2

1Joint Department of Physics, Royal Marsden NHS Foundation Trust, Sutton, United Kingdom, 2Radiotherapy Department,Royal Marsden NHS Foundation Trust, Sutton, United Kingdom

Purpose/Objective(s): Post-operative radiotherapy in patients with extremity sarcomas traditionally employs conventional or 3Dplanned fields to large volumes of the limb. Doses delivered in conventional fractionation potentially exceed tolerance doses ofsurrounding normal tissue. This study compares the ability of conformal radiotherapy plans versus IMRT plans to minimise theintegral dose to surrounding organs at risk (OAR).

Materials/Methods: A planning protocol was defined for target volume, OAR definition and dose/volume constraints. CTV wasdefined as tumor bed. A 5 cm margin was added superiorly and inferiorly and 3 cm circumferentially to form PTV1. PTV2 was 2 cmisotropic expansion of the CTV. The protocol defined modifications of the PTV for scar coverage, skin, femur and pelvic extension.OAR were defined as whole femur, neurovascular bundle, a tissue corridor and normal tissue outside the PTV. Pelvic organs werecontoured for 4 patients whose disease involved the insertion of the muscle group. Three types of treatment plan were created in 7patients designated for postoperative radiotherapy of primary adductor compartment sarcomas. The primary planning objectivewas to minimise the dose to femur and skin corridor. Volumetric dosimetry analysis was performed for all defined OAR to a con-ventional 3D conformal plan, which was forward-planned using wedges and MLCs, a 2/3 field inverse planned IMRT solutionusing the same gantry angles and an iteratively developed 4/5 field inverse planned IMRT for each patient. The mean dose (Dmean)and volume receiving greater than organ tolerance for each OAR were defined, eg V45 (%volume receiving 45 Gy or more). A doseequivalent to 66 Gy to PTV1 and 50 Gy to PTV2 in 2 Gy per fraction was modelled using a concomitant boost for the conformal anda simultaneous boost for the IMRT plans.

Results: The median volume of PTV1 was 1499 cc (range 597–3919 cc). The median volume of PTV2 was 902 cc (range 284–2629 cc). IMRT resulted in a greater decrease in dose to OAR than the conformal plans. 4/5 field IMRT resulted in a significantlylower V45 than conformal radiotherapy (p = 0.03). A greater decrease in dose was seen using IMRT in patients with large PTVs(volume of the central PTV slice greater than 50% of the central thigh slice) and/or whose PTV covered greater than 50% of thetransverse diameter of the femur.

Conclusions: For the first time a reproducible set of planning guidelines and dose volume constraints for 3D conformal planningand IMRT inverse planning for sarcomas of the extremity was devised. 4/5 field IMRT resulted in a decreased dose to OAR inpatients with large or wide PTVs but less so for smaller and superficially located PTVs.

OAR median dose/volume results from the three plans

3D Conformal 2/3 field IMRT 4/5 field IMRT

Femur V45

28.6% 22.7% 20.4%

Neurovascular bundle V45

27.6% 25.6% 26.9%

Tissue corridor Dmean

13.9 Gy 9.7 Gy 10.3 Gy

Normal tissue V55

8.7% 5.0% 1.1%

Author Disclosure: Y.K. Lee, None; A.J. Stewart, None; F.H. Saran, None.

2979 Intraoperative Radiotherapy in the Treatment of Extremity and Limb-Girdle Soft Tissue Sarcoma

S. Y. Tsuji, R. J. O’Donnell, D. Haas-Kogan, A. R. Gottschalk

University of California, San Francisco, San Francisco, CA

Purpose/Objective(s): Surgery continues to be the primary treatment modality for local control of extremity soft tissue sarcomas(STS), with the addition of radiotherapy allowing greater use of limb-sparing techniques. Despite the evidence of dose-dependencefor control of these tumors, the risk of radiation toxicity hampers the ability to deliver optimal dose. Intraoperative radiotherapy(IORT) can provide focused treatment to the area of highest risk, while avoiding critical structures, thereby reducing the necessarydose delivered by external beam radiotherapy (EBRT) and subsequently, the risk of treatment toxicity. This study reports theexperience of patients treated with surgery and IORT for primary or recurrent STS of the extremity and limb-girdle.

Materials/Methods: The IORT database at the University of California, San Francisco was searched for extremity and limb-girdleSTS treated using the Mobetron linear accelerator. This retrospective review identified fifty-six consecutive patients who under-went limb-sparing resection by a single orthopaedic oncologist followed by IORT between 1998 and 2007. Indications forIORT included: tumors whose proximity to critical structures resulted in the expectation of close or microscopically positive sur-gical margins, and recurrent tumors within previously irradiated fields. The median IORT dose was 12.5 Gy (range 10–17.9 Gy).

Results: The two most common tumor histologies were synovial sarcoma (21 patients) and malignant fibrous histiocytoma/mxyo-fibrosarcoma (10), with the remaining 25 patients scattered among 11 different histologies. Forty-five patients were treated for pri-mary disease, while 11 had locally recurrent disease; 6 had metastatic disease at time of resection with IORT. Thirty-five patientsreceived neoadjuvant and/or adjuvant chemotherapy. Thirty-five patients received adjuvant EBRT. With a median follow up of 22months (0–92) for living patients, the 2- and 5-year estimated rates of local control were 79% (95% CI 62–89%) and 76% (58–87%), respectively; rates of distant metastasis-free survival were 75% (59–86%) and 68% (50–81%), respectively; and rates ofoverall survival were 85% (69–93%) and 70% (50–83%), respectively. The two-year local control rate for tumors with positiveor close margins (#1 mm) was 76%, compared with 83% for margins .1 mm. The two-year local control rate for patientswho did not receive adjuvant EBRT was 65%, and 87% for those who did (median dose 56 Gy). The two-year local controlrate was 91% versus 47% for primary versus recurrent tumors (p = 0.01). Patients with primary tumors had a two-year local controlrate of 100% if the margin was .1 mm, and 83% for positive/close margins. Primary patients had a two-year local control rate of92% without EBRT, and a 90% rate if adjuvant EBRT was utilized. Eight patients (14%) developed grade 3 wound healing com-plications; 7 of these patients had received adjuvant EBRT.