Abstract
Stereotactic body radiation therapy (SBRT) is an option for selected patients with metastatic disease. However, sometimes these lesions are located in such close proximity to critical normal structures that the use of safe tumoricidal SBRT doses is not achievable. Here we present a case in which real-time imaging and tracking with a magnetic resonance linear accelerator (MR-LINAC) provided a novel treatment approach and enabled safe treatment of the tumor using SBRT. Our case is a 69-year-old female who presented with localized recurrent small cell lung cancer with a retroperitoneal (FDG-avid) soft tissue lesion measuring 2.4 x 4.1 cm that was causing pain and right hydronephrosis. A Food and Drug Administration (FDA)-approved MR-LINAC system was utilized for planning and the delivery of 21 Gy in three fractions to the retroperitoneal lesion planning target volume (PTV), limited by the neighboring small bowel tolerance. The gross tumor volume (GTV) itself received 27 Gy (9 Gy per fraction). Simulation was performed using a volumetric MR imaging study in treatment position co-registered to a 4D-computed tomography (CT) image set for contouring of the target and organs at risk (OAR). Treatment planning was performed using the primary CT dataset. We developed a reasonable SBRT treatment plan to deliver the prescribed dose without exceeding tolerance doses to the right kidney, the small bowel and all other OAR’s. Real-time MR imaging and tracking during treatment delivery enabled assessment of respiratory-induced target movement in relation to the small bowel and kidney. Gating was performed to halt treatment when PTV movement exceeded the 2-mm range as specified by the treating physician. The treatment course was concluded successfully. The patient denied any acute gastrointestinal or genitourinary toxicity. The pain was significantly improved within a short time following treatment. Follow-up CT showed a near complete response of the mass with total restoration of renal functions, allowing the ureteric stent to be removed. This response has been maintained for five months till the last follow-up. In conclusion, MR-guided planning and delivery using real-time MR imaging and tracking facilitated the treatment of the retroperitoneal mass accurately and efficiently with excellent clinical and radiological response and minimal to no toxicity. We would not discern it safe to treat this mass utilizing SBRT without this ability to accurately visualize the tumor boundary using magnetic resonance imaging (MRI), and offer tracking of the target within the millimeter of surrounding critical OAR’s.
Highlights
Small cell lung cancer (SCLC) represents approximately 14% of newly diagnosed lung cancer patients with 29,540 new cases expected in 2017 [1,2,3]
After achieving a good initial response, prophylactic cranial radiotherapy (PCI) and thoracic radiation therapy (RT) were both associated with much-improved outcomes for patients with good performance status according to the National Comprehensive Cancer Network (NCCN) guidelines [6]
We present a case report of a patient with relapsed ES-SCLC with oligometastatic disease who achieved an excellent response to Stereotactic body radiation therapy (SBRT) for a retroperitoneal lesion delivered using magnetic resonance imaging (MRI)-guided radiation therapy system with real-time MR-guided tracking and treatment gating
Summary
Small cell lung cancer (SCLC) represents approximately 14% of newly diagnosed lung cancer patients with 29,540 new cases expected in 2017 [1,2,3]. We present a case report of a patient with relapsed ES-SCLC with oligometastatic disease who achieved an excellent response to SBRT for a retroperitoneal lesion delivered using MRI-guided radiation therapy system with real-time MR-guided tracking and treatment gating. Follow-up PET-CT performed 110 days after treatment completion revealed multiple foci of increased activity in the right paratracheal region (maximum standardized uptake value (max SUV) = 6.1), a left hilar mass (max SUV = 5.2) and an enlarged right cervical LN (max SUV = 4.1) consistent with recurrent metastatic disease. Given the patient’s co-morbidities, soft tissue lesion, and proximity of the lesion to several critical organs, we surmised that the MRI-linear accelerator (MR-LINAC) system, incorporating MRIbased imaging, and real-time tumor tracking offered the assurance of being able to deliver hypofractionated doses to this patient safely. Renal functions returned to normal, the patient had her ureteric stent removed and she is still in a good performance status (ECOG-1) with minimal use of analgesics as per her last clinical encounter
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