In-vivo range verification analysis with in-beam PET data for patients treated with proton therapy at CNAO

Abstract

Morphological changes that may arise through a treatment course are probably one of the most significant sources of range uncertainty in proton therapy. Non-invasive in-vivo treatment monitoring is useful to increase treatment quality. The INSIDE in-beam Positron Emission Tomography (PET) scanner performs in-vivo range monitoring in proton and carbon therapy treatments at the National Center of Oncological Hadrontherapy (CNAO). It is currently in a clinical trial (ID: NCT03662373) and has acquired in-beam PET data during the treatment of various patients. In this work we analyze the in-beam PET (IB-PET) data of eight patients treated with proton therapy at CNAO. The goal of the analysis is twofold. First, we assess the level of experimental fluctuations in inter-fractional range differences (sensitivity) of the INSIDE PET system by studying patients without morphological changes. Second, we use the obtained results to see whether we can observe anomalously large range variations in patients where morphological changes have occurred. The sensitivity of the INSIDE IB-PET scanner was quantified as the standard deviation of the range difference distributions observed for six patients that did not show morphological changes. Inter-fractional range variations with respect to a reference distribution were estimated using the Most-Likely-Shift (MLS) method. To establish the efficacy of this method, we made a comparison with the Beam’s Eye View (BEV) method. For patients showing no morphological changes in the control CT the average range variation standard deviation was found to be 2.5 mm with the MLS method and 2.3 mm with the BEV method. On the other hand, for patients where some small anatomical changes occurred, we found larger standard deviation values. In these patients we evaluated where anomalous range differences were found and compared them with the CT. We found that the identified regions were mostly in agreement with the morphological changes seen in the CT scan.

Analysis methods for in-beam PET images in proton therapy treatment verification: a comparison based on Monte Carlo simulations

“…On the other hand, it is be somewhat less sensitive to fluctuations in the values in distal activity, since it does not look at a threshold value, but tries to find the best matching δR value for the end-of-range profile. This method is being tested on data, as reported in [21].…”

Synthetic CT imaging for PET monitoring in proton therapy: a simulation study

“…The treatment plan for each patient was simulated, additionally with the last part of the CNAO beam line, including the exit window and nozzle (Molinelli et al 2013, Magro et al 2015, Mirandola et al 2015, the patient geometry (from the CT scan to a voxel FLUKA geometry), radiation transport and interactions of protons in the patient. These data are then used to reconstruct the AMs in a field of view of 140 × 70 × 165 and with a resolution of 1.6 mm × 1.6 mm × 1.6 mm (Fiorina et al 2021, Kraan et al 2022, Moglioni et al 2022, as displayed in figure 2.…”

“…A small cohort of them (clinical trial registered under ID: NCT03662373) has been monitored with the INSIDE IB-PET scanner (Bisogni et al 2016, Bisogni 2019. Recent studies based both on MC simulation and the acquired INSIDE IB-PET data have shown the possibility of detecting morphological changes using range variation or 3D methods (Fiorina et al 2021, Kraan et al 2022, Moglioni et al 2022, Moglioni et al 2023. To the best of our knowledge, these are the most recent papers regarding attempts to correctly locate and identify the morphological change in patients starting from PET data.…”

Design and performance evaluation of a slit‐slat camera for 2D prompt gamma imaging in proton therapy monitoring: A Monte Carlo simulation study

“…PET provides 3D information about the activity distribution based on the produced radioisotopes during the PT 10 . Several studies have demonstrated the feasibility of range verification, dose quantification, and inter‐fractional morphological changes of patient using the PET system 3,11 . However, PET imaging suffers from certain limitations such as delayed signal emission and wash out effects which reduce its spatial resolution, thereby limiting its applicability for the online imaging of the single spots 12 .…”