Abstract
Purpose: Radiation therapy for retroperitoneal sarcoma remains challenging because of proximity to surrounding organs at risk (OAR). We report the use of intensity modulated radiation therapy (IMRT) in the treatment of retroperitoneal sarcomas to minimize dose to OAR while concurrently optimizing tumor dose coverage. Patients and methods: From January 2000 to October 2002, 10 patients (average age 56 years) with retroperitoneal sarcoma and one with inguinal sarcoma were treated with radiation at Emory University. Prescription dose to the planning treatment volume (PTV) was commonly 50.4 at 1.8 Gy/fraction. CT simulation was used in each patient, three patients were treated with 3D-conformal treatment (3D-CRT), and the remaining eight received multi-leaf collimator-based (MLC) IMRT. IMRT treatment fields ranged from eight to 11 and average volume treated was 3498 cc. Optimal 3D-CRT plans were generated and compared with IMRT with respect to tumor coverage and OAR dose toxicity. Dose volume histograms were compared for both the 3D-CRT and IMRT plans. Results: Mean dose to small bowel decreased from 36 Gy with 3D-CRT to 27 Gy using IMRT, and tumor coverage (V95) increased from 95.3% with 3D-CRT to 98.6% using IMRT. Maximum and minimum doses delivered to the PTV were significantly increased by 6 and 22%, respectively (P = 0.011, P = 0.055). Volume of small bowel receiving > 30Gy was significantly decreased from 63.5 to 43.1% with IMRT compared with conventional treatment (P = 0.043). Seven patients developed grade 2 nausea, three developed grade 2 diarrhea, one had grade 2 skin toxicity, and one patient developed grade 3 liver toxicity (RTOG toxicity scale). No other delayed toxicities related to radiation were observed. At a median follow-up of 58 weeks, there were no local recurrences and only one patient developed disease progression with distant metastasis in the liver. Conclusions: IMRT for retroperitoneal sarcoma allowed enhanced tumor coverage and better sparing of dose to critical normal structures such as small bowel, liver, and kidney. Escalation of dose has a positive impact on local control for retroperitoneal sarcoma; IMRT may be an effective method to achieve this goal. We are evaluating preoperative dose escalation to 59.4 Gy.
Highlights
Intensity-modulated radiation therapy (IMRT) is a new and revolutionary method of radiation delivery based on the use of optimized non-uniform radiation beam intensities incident on the patient.[1]
We report the use of IMRT as a means to minimize dose to organs at risk (OAR) and concurrently maximize tumor dose coverage
We reported on the use of preoperative IMRT in pancreatic cancer in which IMRT allowed for dose escalation to 61.2 Gy and resulted in reduced average dose to small bowel and a 10% reduction in volume of small bowel receiving > 50 Gy.[9]
Summary
Intensity-modulated radiation therapy (IMRT) is a new and revolutionary method of radiation delivery based on the use of optimized non-uniform radiation beam intensities incident on the patient.[1] IMRT used in our department relies on an inverse planning system that employs computer-assisted optimization methods to determine the fluence intensities given to a specific tumor volume. By setting dose constraints to critical organs at risk (OAR) and tumor volume, dose conformality and OAR toxicity has been optimized. Local recurrence in retroperitoneal sarcoma is the primary cause of mortality in patients with this disease.[2,3,4] Retroperitoneal sarcoma has been responsive to radiation dose escalation,[5,6,7] yet efforts to achieve this with external beam radiation alone (EBRT) have been hampered by OAR toxicity. We report the use of IMRT as a means to minimize dose to OAR and concurrently maximize tumor dose coverage
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