Titanium Implants for Field Verification in Proton Therapy – an Applicability Test

Positron emission tomography (PET) for off-line field verification has been found limited by the so-called wash-out of the produced activity distribution due to biological transport processes. The activation of implants has been proposed to overcome this limitation and the general potential of titanium implants has been demonstrated in the past. Compared to implanted markers, titanium implants are used during surgical resection especially in brain tumor patients which is often performed prior to the radiotherapy treatment. An applicability test for the use of titanium implants for field verification is demonstrated. The test includes a phantom study with simple geometric phantoms and an anthropomorphic phantom. Furthermore, Monte-Carlo (MC) simulations are performed to predict the expected activity in the implants. The visual analysis reveals the general applicability for clinical implantation, while the numerical analysis of the results demonstrates the current limitations given by PET imaging and the basic physical knowledge of the activation cross sections. With the results, requirements for future generations of PET scanners for field verification in proton therapy can be derived. Necessary physics research on activation cross section can be deduced from the results. With further development in PET imaging, the incorporation of implant activation may provide an additional means for the monitoring of treatment delivery. On a qualitative basis, PET imaging of titanium implants may already be used in clinical practice for patients which come with suitable implants. Furthermore, possibly suitable implant positions can be derived from the results.