Today I finished a course of radiation with CyberKnife. The target was a tumor at the front of my pubic bone. The tumor showed up on PET/CT scans in May. It was a bit of a surprise since it wasn't noticed on previous scans or during my big surgery last December. Unlike the tumor near my tailbone it wasn't painful either and wasn't causing any notable symptoms, but we wanted to zap it before it did become a problem.
After getting CyberKnife to my tailbone and conventional radiation to the rest of my pelvis, I went to an interventional radiologist to have fiducial markers implanted. CyberKnife uses live X-ray imaging during treatment to aim precisely at the tumor, even if it moves day to day or with breathing and digestion (unlike conventional radiation which aims at a wider area based on landmarks on the surface of the body). For my tailbone, the bone itself and metal staples left from surgeries acted as beacons for aiming. But this tumor was in soft tissue so I needed tiny gold springs implanted with a long needle while I was sedated. Then, after waiting a week for the wounds to heal and the markers to settle, another CT scan located the markers relative to the tumor so that the CyberKnife could be programmed.
Two advantages of CyberKnife are that it is targeted more precisely and the targeting responds to internal movement. Another advantage is that the therapeutic X-rays hit the tumor from thousands of angles through the body, rather than just three angles like my conventional radiation treatment. That spreads the incoming X-rays more thinly across healthy tissue, causing less collateral damage.
The CyberKnife machine is set up in an isolated room next to the control station. There's a table to lay on that can lift, slide, and tilt. Detectors near the ceiling look at imaging X-rays cast through the body. And the treatment beam comes from a big box mounted at the end of a massive robot arm – the same kind used in automotive manufacturing plants.
Each day I laid down on the table, got positioned by the technician, and then kept still while the CyberKnife came to life. Despite its mass, the robot moved quickly and precisely. It looked like a giant bird, examining me from different angles to decide if I was edible. It almost tickled to see it moving over me, but it stayed at least several inches away and never actually touched me. If I moved more than a breath – to shift my weight or scratch an itch – the machine detected the movement and stopped. Then the technician checked on me, got me back in alignment, and resumed the treatment.
The actual radiation didn't hurt at all. The only way I knew anything was happening was from the mechanical and electronic noises of the machine. Most of the time I just closed my eyes, listened to my iPod, and tried to nap without moving. That's actually harder than it sounds, since my body prefers to fidget rather than lie perfectly still for a whole hour. During the treatment of my tailbone, it actually got very painful to stay so still because of how that tumor was deforming my muscles and nerves. But by the time of this treatment those problems were gone and the greatest hardship was mere boredom.
The whole course of treatment was five days of one-hour sessions. That's another advantage over conventional radiation which was a less convenient six weeks of ten-minute sessions. I haven't noticed any effects from the radiation yet, but I expect some fatigue, reddened skin, and local hair loss if it's anything like my previous doses.
Hopefully my blood tests and next set of scans will show that this summer of radiation has finally finished the job of last December's surgery and five years of chemotherapy.