Incorporation of SPECT bone marrow imaging into intensity modulated whole-pelvic radiation therapy treatment planning for gynecologic malignancies.

BACKGROUND AND PURPOSE To incorporate single-photon emission computed tomography (SPECT) bone marrow (BM) imaging into the treatment planning process to reduce the volume of BM irradiated in gynecologic patients receiving intensity-modulated whole-pelvic radiation therapy (IM-WPRT). MATERIALS AND METHODS A planning CT scan was obtained of a patient with early stage endometrial cancer. The same patient also underwent a Tc-99m sulfur colloid SPECT scan of the pelvis. Tc-99m sulfur colloid is sequestered by the macrophages in the BM thereby identifying areas of active (red) BM. Using image fusion software, the SPECT scan was aligned with the planning CT scan and used to delineate regions of active BM. An IMRT plan was then generated to provide coverage of the planning target volume (PTV) while sparing areas of active BM and other normal pelvic structures. RESULTS The areas of high active BM density were observed predominantly in the lumbar vertebrae, sacrum and medial iliac crests. IMRT planning reduced the dose to these areas by 50% for doses greater than 30Gy compared to conventional planning. Furthermore, the IMRT plan did not compromise coverage of the PTV or sparing of normal tissues. CONCLUSIONS Our results suggest that SPECT-BM imaging is a useful adjunct to IMRT planning in gynecologic patients undergoing IM-WPRT.