Abstract # 2215 Seed Marker-based IGRT for Prostate Cancer: Excellent Preliminary Toxicity Outcomes

Presenter: Scarbrough, Todd

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Only pts followed a minimum of 6 months post-treatment were included in this retrospective analysis; a continuous cohort of 231 pts meet this criteria and have a median followup of 1.4 years. The seed marker insertion and setup method is previously described (Scarbrough et al., IJROBP 2006;65:378-87). All pts received a minimum prostate dose of 81 Gy/45 fx. For pts receiving pelvic nodal plus seminal vesicle (21/231 pts) or seminal vesicle (151/231) elective irradiation, the combined CTV (elective structures plus prostate) was expanded 1.0 cm circumferentially/0.5 cm posteriorly to create PTV1. PTV1 received 45 Gy/25 fx. The prostate was expanded 4 mm circumferentially to create PTV2 which received 27 Gy/15 fx. The prostate was expanded 4 mm circumferentially/0 mm posteriorly to create PTV3 which received 9 Gy/5 fx. In low-risk pts, the prostate was expanded circumferentially by 4 mm to create PTV1 which received 72 Gy/40 fx, and by 4 mm/0 mm posteriorly to create PTV2 which received 9 Gy/5 fx. This yielded an "average rectal margin" of ~3-4 mm for all plans. PTVs were normalized so >=95% of the volume received 100% of the Rx dose (keeping the prostate minimum dose always 81 Gy); this yielded a mean dose maximum of 85.7 Gy for all pts. Most pts' (75%) prostates were contoured using thin-slice (2.5 mm) MRI with marker-to-marker/MRI-to-CT fusion. All pts were treated using sliding-window IMRT (600 MU/min dose rate), 6MV energy, 7-11 discrete beams, and kV X-ray seed marker-based IGRT; 132/231 pts received anti-androgen therapy of 4-8 months duration. Toxicities were assessed in followup according to CTCAE v.3.0 for rectal morbidity and International Prostate Symptom Score (IPSS) for GU morbidity. Pts (220/231) also completed sexual satisfaction questionnaires in followup.