ESTRO 2024 - Abstract Book

S1531

Clinical - Lower GI

ESTRO 2024

The delivery of ablative radiation doses to pancreatic lesions has historically been challenged by limited soft tissue contrast of CBCT images, mobility of the target area, and closely related organs at risk. Consequently, the role of radiation therapy in the treatment of pancreatic ductal adenocarcinoma (PDAC) remains controversial. However, the introduction of MR-guided radiotherapy (MRgRT) systems such as the 1.5 Tesla (T) MR-Linac offers the important advantage of improved visibility along with a daily online adaptive workflow to account for interfraction motion. This has facilitated dose escalation in the treatment of primary and recurrent PDAC, without increasing the risk of toxicity. To date, only one small single-center study presented patient-reported outcomes after MRgRT for upper abdominal tumors 1 , and one study presented a heterogeneous group of (peri)pancreatic tumors 2 . Therefore, the aim of this study was to present updated toxicity and patient-reported Quality of Life (QoL) of the currently largest cohort of patients treated with MRgRT for PDAC who were enrolled in the ongoing cohort study ‘Multi-OutcoMe EvaluatioN of radiation Therapy Using the MR-Linac (MOMENTUM)’ study (NCT04075305). All patients with proven PDAC treated with hypofractionation (≤5 fractions) were selected, including primary and recurrent tumors. Patients were included from three centers, two in Europe and one in North America. Outcomes were measured at baseline, three, six, and twelve months following the end of MRgRT. High-grade toxicity was measured using Common Terminology Criteria for Adverse Events (CTCAE) defined as grade ≥3. QoL was measured using EORTC QLQ-C30, where scores were calculated according to the scoring manual. For functional domains, a high score represents high functioning. For symptom domains, a high score represents a high symptomatology level. Descriptive statistics and figures were obtained using R Studio. Toxicity rates were calculated in patients from which toxicity was prospectively assessed, and who reached a certain time point. For QoL, mean score with standard deviation per domain and time point was calculated. Patients who underwent tumor resection were censored at the date of surgery. In total, 130 patients with a median follow-up of 5 months (interquartile range 3-12) were included. Of these, 99 patients (76.2%) were treated for a primary tumor and 31 (23.8%) for a recurrence. Of the primary tumors, 14 were evaluated as resectable, 9 borderline resectable, 41 unresectable, and unknown in 35 patients. Patients were treated with a median dose of 50 Gy (range 32-50 Gy). 128 patients (98.5%) were treated using the online adaptive workflow (Adapt-to-shape, ATS), one (0.8%) using rigid registration (Adapt-to-position, ATP), and one (0.8%) using both workflows. One patient (0.8%) received re-irradiation. Four (3.0%) patients were not able to finish their treatment as initially planned, of which two (1.5%) after physician decision to stop or switch to a different modality, one (0.8%) due to progression of disease, and one (0.8%) due to comorbidities unrelated to radiotherapy. 99 patients (76.2%) patients received chemotherapy, of which 9 (6.9%) during MRgRT. Three patients (2.3%) received immunotherapy, of which two (1.5%) during MRgRT. In total, 14 patients (10.8%) had post-RT surgery within three months, and an additional two (1.5%) within 6 months following MRgRT. No grade 4 toxicity was reported. In 1/53 patients (1.9%), grade 3 anorexia was reported at three months follow-up. No other grade 3 toxicity was reported. Most functional scores of the EORTC QLQ-C30 improved at 12 months follow-up compared to baseline (Figure presented). In the symptom scores, we found a temporary increase in pain and diarrhea at three months, and insomnia at six months follow-up. Material/Methods: Results: