Abstract # 1068 In Vivo Verification of Dose Delivery to Prostate Cancer by Utilizing PET/CT Images Taken after Proton Therapy

Presenter: Lin, Liyong

< Back to topics

> Cover Page, Authors, Institutions

> Purpose/Objective

> Materials/Methods

> Results/Discussion

> Conclusions

> View tables/images/videos

Positron emitters activated in low‐perfusion bone and fat after proton therapy reportedly can verify proton beam path. Relatively long‐lived 11C are produced by nuclear interactions between proton beam and tissue nuclei, mainly 12C. Consequently, tissues rich in carbon, such as fat, are dominantly detected on offline PET images. Immediately after one‐field 2 CGE proton treatment, patients walked to the PET/CT scanner and their position was replicated using the same immobilization device as for treatment. 36 scans were performed for 8 prostate cancer patients. PET image acquisition lasted 30 minutes after CT. The duration between the start of proton irradiation and the start of PET acquisition was 16.6 ± 4.2 minutes. The activated retropubic, ischioanal and perivesical fat boundaries served as surrogates for the treatment target, rectal wall, and bladder wall positions, respectively. For each patient, the proton beam path visualized on CT was aligned with positron activation in the subcutaneous fat and pelvic bones visualized on PET. Doses were recalculated accordingly for each PET/CT study. Recalculated volumes of 95% and 50% of 78 Gy prescription dose (i.e., V74 and V39) were compared to the initial planned volumes for prostate, rectal wall, and bladder wall.