Evaluating the use of planning PET in radiotherapy treatment planning for rectal cancer
Yujia Gao,
United Kingdom
PO-2326
Abstract
Evaluating the use of planning PET in radiotherapy treatment planning for rectal cancer
Authors: Yujia Gao1, Glen Blackman2, Thomas Richards2, Maria Hawkins3, Douglas Brand3
1University College London , Department of Medical Physics and Bioengineering, London, United Kingdom; 2University College London Hospitals, Oncology, London, United Kingdom; 3University College London, Department of Medical Physics and Bioengineering, London, United Kingdom
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Purpose or Objective
Radiotherapy for rectal cancer is typically contoured using clinical, endoscopic, CT and MRI data. Staging PET usage is infrequent, so a planning FDG-PET scan, examining tumour metabolic activity, might aid both staging and the contouring process. University College London Hospital (UCLH) has been using planning FDG-PET and here we examine its influence on treatment pathways. Additionally, given novel total neoadjuvant strategies, we examine planning FDG-PET activity post neoadjuvant chemotherapy.
Material and Methods
From the UCLH treatment planning system (TPS), 327 consecutive rectal adenocarcinoma patients were identified (radiotherapy dates: 13/02/2015–20/04/2022). Those who underwent planning FDG-PET prior to long (45–53.2Gy in 25–28 fractions, n=112) or short (25–30Gy in 5 fractions, n=12) course radical neoadjuvant rectal radiotherapy without staging FDG-PET were included (n=124). Patient demographics, disease characteristics and radiation treatment parameters were retrieved from health records and the TPS. We hypothesised firstly that planning FDG-PET would alter 20% of patients' treatment pathways: change of radical intent or new metastases. Secondly, that neoadjuvant chemotherapy, prior to radiotherapy, might cause zero biological activity on planning FDG-PET.
Results
Baseline characteristics are summarized in Table 1. The cancer pathway was altered in four patients (4/124, 3.2%, 95%CI: 1.3–8.0%) due to previously unknown metastases on planning FDG-PET (liver metastases, n=4). This was statistically significantly less than the hypothed 20% treatment pathway alteration rate (proportion z-test, p<0.001). Regarding FDG-PET scans with zero biological activity, this occurred in zero (0/109, 0%) patients without neoadjuvant chemotherapy and two (2/15, 13.3%, 95%CI: 3.7–38%) who received it (Fisher’s Exact, p=0.014).
Conclusion
At our centre, planning FDG-PET scans have unexpected findings, altering treatment strategy, in a low number of patients. With regards to patients having total neoadjuvant therapy, zero FDG-PET activity was observed more frequently than those not receiving neoadjuvant chemotherapy, although the rate was still low.