Utilize in-vivo offline PET/CT imaging to evaluate range deviations of implanted metal-clips in whole-breast proton radiotherapy.

This study presented a quantitative analysis of the differences in the depths of the distal 50% of acquired and estimated positron emission tomography (PET) images for 18 patients who had a total of 109 titanium (Ti) metal-surgical clips implanted after breast-conserving surgery. Offline PET/computed tomography (PET/CT) images were acquired after proton irradiation. Hounsfield Unit modifications were applied to correct for metal artifacts induced by the Ti clips in the planning CT scans of the soft tissues surrounding the clips. The positron-emitting-isotope PET distribution was calculated through Range-Verification scripting. Quantitative analysis was conducted on the depth differences at the distal 50% R50 of the PET and the calculated PET distribution. Using the R50 method, the depth verification results of the clips and the normal tissues were compared. The R50 method calculates the positional difference at the half-maximum value 2 cm from the skin, with clips beyond this position not affecting the results. Analyses of the regions around the Ti clips were conducted. The depth difference for Ti < 2 cm (where the depth of the clips from the skin was <2 cm) was -1.63 ± 1.08 mm, while the corresponding normal tissue (Ticont) showed a depth difference of -1.79 ± 1.15 mm. There was no statistically significant difference in the depth differences between Ti < 2 cm and the corresponding Ticont. This study utilized offline PET verification to demonstrate that applying tissue corrections based on surgical clips and surrounding muscle tissues in clinical practice ensures that the presence of surgical clips does not compromise the precision of proton dose delivery at the surgical site.