I’ve been using CK since 2018, now with an S7, and have had a very good experience. In an established practice with sufficient SRS/SBRT volume, I think it can be an excellent investment, but I would not buy one to replace a conventional linac. If I had one vault and needed to treat a general radiation oncology population, I would choose a conventional linac without much hesitation. CK makes the most sense as a complement: we use it when its tracking, motion management, and delivery capabilities are valuable, while conventional machines handle cases for which they are more efficient or better suited.
Its greatest strength for me is intrafraction motion management. We create highly conformal plans with steep gradients near critical structures, so knowing where the target is during treatment matters, particularly when delivering large doses per fraction. I especially value fiducial-based tracking for prostate SBRT, where the prostate may move after initial setup, and Synchrony for selected respiratory targets, including patients who cannot reliably perform breath hold. However, prospective buyers should understand the tracking workflow and its limitations; not every lung lesion is suitable for fiducial-less tracking.
The robotic geometry is also useful for complex spine, intracranial, and other stereotactic cases, although CK does not win every planning comparison. The MLC is important as well. Larger or irregular targets can be cumbersome with small circular fields, whereas an MLC plan may provide practical treatment times and good dosimetry. Collimator selection should be based on the intended case mix, delivery time, dosimetry, and patient-specific QA. Treatment time remains a legitimate criticism: compared with straightforward VMAT, CK will often take longer, so total room time—including setup, imaging, and interruptions—should be evaluated rather than relying on advertised minimum times. A dedicated stereotactic machine can nevertheless improve operations by keeping complex SBRT cases from disrupting a busy general-purpose linac schedule.
The financial case requires careful analysis. It depends on existing stereotactic volume, referral patterns, staffing, collections, service costs, and capital expenses. You must distinguish genuinely additional patients from cases simply transferred from another machine. The argument is stronger if you already have substantial volume, are referring appropriate patients elsewhere, or have a credible plan to grow the program, but installing CK alone will not create referrals. A committed team is also essential; planning, physics, therapist experience, fiducial placement, and imaging access all matter. I would visit a busy center with a similar patient population and speak with its therapists and physicists, not only its physicians.
I would not justify the purchase by claiming that CK produces superior outcomes to every well-equipped conventional linac. I value its specific capabilities and the flexibility of having a dedicated stereotactic platform, provided the volume supports the expense. For us, it has been an excellent addition, and I would consider buying it again in a practice with similar needs and resources. If the question is whether an S7 should replace an aging general-purpose linac, my answer is no; if you already have good conventional capacity and want to support a substantial SRS/SBRT program, it is well worth considering.