The purpose of this clinical study is to investigate the clinical feasibility and effectiveness of off-line Positron-Emission-Tomography (PET) quality assurance for promoting the accuracy of proton and carbon ion beam therapy. One main clinical advantage of ion therapy over conventional radiation therapy is the excellent conformation of the delivered dose to the tumour volume while well sparing the surrounding healthy tissue. However, clinical exploitation of this potential to the maximum extent requires in-vivo validation of the actual treatment delivery and, in particular, of the ion beam range within the patient. Since the primary ions are completely stopped in the target volume as opposed to photon radiation, no conventional quality assurance techniques like transmission electronic portal imaging can be applied to monitor ion beam therapy. Hence, ion treatment planning currently relies on models and experimental data accurately validated in tissue-equivalent targets, but no direct verification of the actual treatment delivery and of the ion beam range within the patient is possible in standard clinical practice.
At present, PET offers the unique possibility to monitor the precision of ion irradiation in-vivo and non-invasively. The method is based on the detection of the b+-activity which is formed as a by-product of the irradiation, i.e. without administration of radio-tracers to the patient. A positive clinical impact of in-beam (i.e. during the irradiation) PET monitoring has been demonstrated for carbon ion therapy in the pilot project at GSI Darmstadt, Germany, and promising clinical data of post-radiation PET/CT imaging have been recently reported for passive proton beam delivery in USA and Japan. Therefore, a pilot clinical study is hereby proposed at the Heidelberg Ion Therapy Center in order to 1) assess the applicability of post-radiation PET imaging to scanned ion beam delivery, 2) identify the patient population which may benefit from it and 3) extract population-based information on the reliability of the beam range in different tumour locations for all the ion species clinically available at HIT.
The investigated patients are expected to benefit from this study, since in case of detected deviations between planned and actual treatment delivery a proper correction could be applied in the next irradiation fraction, assuring an overall better treatment than without any monitoring. Moreover, site-specific patient-population information on the ion range precision at HIT might enable improvement of the CT-range calibration curve as well as safe reduction of the treatment margins to promote enhanced treatment plan conformality for full clinical exploitation of the promises of ion beam therapy.