Sentinel lymph node imaging guided IMRT for prostate cancer: Individualized pelvic radiation therapy versus RTOG guidelines

PURPOSE/OBJECTIVES Current Radiation Therapy Oncology Group (RTOG) guidelines for pelvic radiation therapy are based on general anatomic boundaries. Sentinel lymph node (SLN) imaging can identify potential sites of lymph node involvement. We sought to determine how tailored radiation therapy fields for prostate cancer would compare to standard RTOG-based fields. Such individualized radiation therapy could prioritize the most important areas to irradiate while potentially avoiding coverage in areas where critical structures would be overdosed. Individualized radiation therapy could therefore increase the therapeutic index of pelvic radiation therapy. METHODS AND MATERIALS Ten intermediate or high-risk prostate cancer patients received androgen deprivation therapy with definitive radiation therapy, including an SLN imaging-tailored elective nodal volume (ENV). For dosimetric analyses, the ENV was recontoured using RTOG guidelines (RTOG_ENV) and on SLNs alone (SLN_ENV). Separate intensity modulated radiation therapy (IMRT) plans were optimized using RTOG_ENV and SLN_ENV for each patient. Dosimetric comparisons for these IMRT plans were performed for each patient. Dose differences to targets and critical structures among the different IMRT plans were calculated. Distributions of dose parameters were analyzed using non-parametric methods. RESULTS Sixty percent of patients had SLNs outside of the RTOG_ENV. The larger volume IMRT plans covering SLN imaging-tailored elective nodal volume exhibited no significant dose differences versus plans covering RTOG_ENV. IMRT plans covering only the SLNs had significantly lower doses to bowel and femoral heads. CONCLUSIONS SLN-guided pelvic radiation therapy can be used to either treat the most critical nodes only or as an addition to RTOG guided pelvic radiation therapy to ensure that the most important nodes are included.