Combined treatment planning and therapy using 153Sm-EDTMP RPT with XRT in pediatric metastatic osteosarcoma patients

341 Objectives Metastatic osteosarcoma is a cancer of adolescents and young adults which has a low survival rate. We present results and describe a methodology related to an ongoing trial designed to boost the radiation dose to lesions in cases where XRT is limited by normal organ toxicity. We combine RPT using 153Sm-EDTMP a FDA approved bone seeking calcium mimetic with XRT, and provide a treatment plan that incorporates the dose from both modalities. Methods We illustrate the methodology using data from the last patient treated. The treatment protocol is myeloablative and patients first undergo stem cell harvesting. The last patient treated was injected with a 58 mCi pre-dose of 153Sm-EDTMP and imaged at 4, 24 and 48 h p.i. The RPT treatment planning system, 3D-RD, was used to establish the maximum safe administered activity based on normal tissues absorbed dose (AD) constraints derived from RPT and the projected XRT treatment plan. One week after the pre-dose, a therapeutic dose of 600 mCi 153Sm-EDTMP was administered, and the patient was imaged at 4, 24 and 48 h p.i. The images were reconstructed including a count-rate saturation correction. AD-maps and DVHs were generated using 3D-RD for the RPT part of the treatment. These were entered into the XRT treatment planning system, which was used to create a combined RPT/XRT treatment plan. Results The AD delivered to the tumor by RPT was 25.5 Gy. The XRT plan was created based on the RPT plan and 51.3 Gy was delivered to the tumor by XRT, resulting in a total AD of 76.8 Gy. The AD to adjacent spinal cord from the combined treatments was 30.9 Gy. Conclusions The created treatment planning protocol combining RPT and XRT for metastatic osteosarcoma in pediatric patients showed great promise reducing the AD to the adjacent spinal cord with 13.6 Gy compared with using only XRT.