Abstract
Large fraction radiation therapy offers a shorter course of treatment and radiobiological advantages for prostate cancer treatment. The CyberKnife is an attractive technology for delivering large fraction doses based on the ability to deliver highly conformal radiation therapy to moving targets. In addition to intra-fractional translational motion (left–right, superior–inferior, and anterior–posterior), prostate rotation (pitch, roll, and yaw) can increase geographical miss risk. We describe our experience with six-dimensional (6D) intra-fraction prostate motion correction using CyberKnife stereotactic body radiation therapy (SBRT). Eighty-eight patients were treated by SBRT alone or with supplemental external radiation therapy. Trans-perineal placement of four gold fiducials within the prostate accommodated X-ray guided prostate localization and beam adjustment. Fiducial separation and non-overlapping positioning permitted the orthogonal imaging required for 6D tracking. Fiducial placement accuracy was assessed using the CyberKnife fiducial extraction algorithm. Acute toxicities were assessed using Common Toxicity Criteria v3. There were no Grade 3, or higher, complications and acute morbidity was minimal. Ninety-eight percent of patients completed treatment employing 6D prostate motion tracking with intra-fractional beam correction. Suboptimal fiducial placement limited treatment to 3D tracking in two patients. Our experience may guide others in performing 6D correction of prostate motion with CyberKnife SBRT.
Highlights
Current radiation therapy options for treating clinically localized prostate cancers include intensity-modulated radiation therapy (IMRT), low-dose-rate (LDR) brachytherapy, high-dose-rate (HDR) brachytherapy, proton beam therapy, and stereotactic body radiation therapy (SBRT; Collins et al, 2011)
Sixty-nine patients received CyberKnife SBRT alone and 19 patients received CyberKnife SBRT followed by IMRT
Each CyberKnife SBRT treatment was typically completed in 40–60 min
Summary
Current radiation therapy options for treating clinically localized prostate cancers include intensity-modulated radiation therapy (IMRT), low-dose-rate (LDR) brachytherapy, high-dose-rate (HDR) brachytherapy, proton beam therapy, and stereotactic body radiation therapy (SBRT; Collins et al, 2011). Recent trends for improving local control and patient quality of life, have focused on dose escalation (Pollack et al, 2002; Zelefsky et al, 2002) and on hypo-fractionation (Fowler, 2005; Miles and Lee, 2008) Such treatment requires smaller treatment margins and greater precision to limit geographic misses. Due to rectal and bladder filling, prostate gland position has been shown to vary on a day-to-day basis (inter-fraction motion) and within a treatment session (intra-fraction motion; Kupelian et al, 2008) This motion is commonly largest in the anterior–posterior and inferior–superior directions (Crook et al, 1995; Dawson et al, 1998; Langen et al, 2008).
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