Mr‐guided adaptive radiotherapy for gastric lymphoma, preliminary results from ongoing study

Radiotherapy is a curative treatment in indolent lymphoma and an important part of the combined treatment for aggressive gastric lymphoma. New technologies have changed the options for normal tissue sparing with same target dose coverage substantially. One of the new technologies, MR-guided daily adaptive radiotherapy (MR-ART) is a modality that could be advantageous for patients who need radiotherapy for gastric lymphoma due to the improved soft tissue contrast for daily image guidance, possibility of tracking and gating on internal anatomy, and the ability to account for large daily anatomical variations, so the treatment can be delivered with the intended dose to the stomach with reduced dose to the heart and left kidney. The purpose of this study is to report a preliminary analysis from an ongoing protocol for MR-ART for patients with gastric lymphoma and investigate if daily adaption with MR-ART improves target coverage relative to no adaption. Materials/Methods: At present 4 patients with gastric lymphoma have been recruited to participate in our protocol for MR-ART and provided written informed consent. All patients were planned in (comfortably deep) inspiration breath-hold on the MR-linac (MRIdian, ViewRay) using intensity modulated radiotherapy (IMRT) for the base plan. The prescription dose was 24 Gy in 12 fractions in 3 patients and 2 Gy × 20 in one patient. All patients were treated on the MR-linac with MR-ART, with internal gating on the superior region of the stomach near the heart. Results: In this ongoing trial, we have performed analyses of the treatment with daily adaption with MR-ART improved target coverage relative to the predicted plan for the first two patients (base plan recalculated on the daily anatomy) (Figure 1). For example, the dose to 95% of the target (D95%) improved from 77% to 95% of the prescription dose for the predicted plan compared to the adapted plan for patient 1 and from 72% to 98% for patient 2 (mean of all fractions). The results for the volume (cubic centimeters) of the heart and kidneys risk receiving 5 Gy or 10 Gy (V5Gy or V10Gy) were kept at the same level when comparing the predicted plan to the reoptimized adapted plan (Figure 2). Keywords: extranodal non-Hodgkin lymphoma, ongoing trials, radiation therapy No conflicts of interests pertinent to the abstract.