ESTRO 2023 - Abstract Book

S62

Saturday 13 May

ESTRO 2023

fraction. Reduction of pain medication was seen in 16 patients (55.2%), pain medication remained unchanged in six patients (20.7%), and five (17.2%) required ≥ 25% increase of strong opioids. Global QoL significantly improved from 50.9 to 62.7 during the study period, p=<0.001. Joint model analysis showed better global QoL (p=0.039), decrease of nausea/vomiting (p=0.005) and lower insomnia symptoms (p=0.002) in patients treated with three (n=21) versus less than three (n=8) radiotherapy fractions. Grade 3 acute toxicity occurred in three patients, reporting transient flare-up combined with nausea and/or vomiting after the first fraction. No grade 4-5 acute toxicity was observed. Median OS was 11.8 weeks (range 0.9 238.8 weeks), with a 13.3% one-year actuarial OS rate. Conclusion This prospective phase II study of a short course palliative radiotherapy for pancreatic cancer-related pain showed a significant reduction of pain severity, for 70% of patients until death or last follow-up and an increase in global QoL over time, accompanied by mostly mild toxicities.

OC-0101 First randomized evidence of the lymphocyte-sparing effect of proton beam therapy (NCT01512589) X. Wang 1,2 , P. van Rossum 2 , Y. Chu 3 , B. Hobbs 4 , C. Grassberger 5 , T. Hong 6 , Z. Liao 2 , R. Mohan 7 , S. Lin 2 1 Tianjin Medical University Cancer Institute and Hospital, National Clinical Research Center for Cancer, Tianjin’s Clinical Research Center for Cancer, Key Laboratory of Cancer Prevention and Therapy, Radiation Oncology, Tianjin, China; 2 The University of Texas MD Anderson Cancer Center, Radiation Oncology, Houston (TX), USA; 3 The University of Texas at Houston, UTHealth, Houston (TX), USA; 4 The University of Texas at Austin, Population Health, Dell Medical School, Austin (TX), USA; 5 Massachusetts General Hospital, Radiation-Drug Treatment Design Lab, Boston (MA), USA; 6 Massachusetts General Hospital, Radiation Oncology, Boston (MA), USA; 7 The University of Texas MD Anderson Cancer Center, Radiation Physics, Houston (TX), USA Purpose or Objective While lymphocytes play an important role in anti-tumor immunity, they are also especially vulnerable to depletion during chemoradiotherapy (CRT). Since the extent of radiation dose scatter within the irradiated region has been implicated in the degree of radiation-induced lymphopenia (RIL), the primary purpose of this study was to compare the incidence of grade 4 lymphopenia (G4L) between proton beam therapy (PBT) and intensity-modulated photon RT (IMRT) in esophageal cancer patients treated with CRT in a completed randomized trial. A second purpose was to ascertain patient heterogeneity to G4L risk based on treatment factors and established prognostic factors. Materials and Methods Between April 2012 and March 2019, a single-institutional, open-label, nonblinded, phase II randomized trial was conducted at The University of Texas MD Anderson Cancer Center. Patients with locally advanced esophageal cancer were randomly assigned to IMRT or PBT, either definitively or pre-operatively. The primary endpoint of this post-hoc analysis was grade 4 lymphopenia (G4L) during concurrent CRT according to CTCAE version 5.0. Results In total, 105 patients were evaluable for analysis with a median follow-up of 46 months. Among them, 44 patients (42%) experienced G4L at a median of 28 days after the start date of concurrent CRT. Figure 1 illustrates the absolute lymphocyte counts for the patients over the 5-week monitoring period during CRT stratified by treatment arm. The incidence of G4L for PBT versus IMRT was 27.3% versus 52.5%, respectively (relative risk 0.52, p =0.010). Induction chemotherapy (hazard ratio [HR] = 3.78, 95% confidence interval [CI] 1.59-8.97, p =0.003), baseline absolute lymphocyte count (ALC in K/µL; HR = 0.19, 95%CI 0.09-0.38, p <0.001), radiotherapy modality (IMRT vs. PBT; HR = 3.00, 95%CI 1.48-6.07, p =0.002), and planning