Main Session
Sep
29
PQA 07 - Head and Neck Cancer, Lung Cancer/Thoracic Malignancies, and Nursing and Supportive Care
Presenter(s)
Sarit Appel, MD - Sheba Medical Center, Ramat Gan, Center Israel
S. Appel1,2, D. Roizen3, J. D. Goldstein4, and Y. Lawrence5,6; 1Chaim sheba medical center, RAMAT-GAN, Israel, 2Radiation Oncology, Sheba Medical Center, Ramat Gan, Israel, 3Sheba Medical Center, Ramat Gan, Israel, 4Radiation Oncology, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel, 5Radiation Oncology Department, Sheba Medical Center, Ramat Gan, Israel, 6Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
Purpose/Objective(s):
Centrally located tumors often cause distal atelectasis and pleural effusions that mask the underlying tumor, resulting in overestimation of the gross tumor volume (GTV) on CT-SIM. FDG-PET scans may help, but are confounded by post-obstruction pneumonia, which can be mistaken for tumors. Prior studies, ours and others, have shown that chest MRI provides superior spatial resolution compared with CT, allowing differentiation of residual tumors from fibrosis in follow-up scans after lung SBRT. We hypothesized that MRI-sim of the thorax can differentiate tumor from atelectasis and pleural fluid, reducing the GTV size.Materials/Methods:
Following the CT-sim, patients with tumors suspected of having atelectasis or pleural fluid accumulation underwent MRI-sim in the treatment position using a 1.5T magnet (Philips Ingenia MR system) with gadolinium contrast. The series included T1, respiratory-gated T2, and diffusion-weighted sequences. We examined each sequence to identify the MRI dataset with the best resolution. After image registration with CT-sim using Eclipse software (Varian, 15.6), we contoured the GTV on the optimal MRI-sim sequence. We used paired two-sided t-tests to compare GTVs from CT and MRI-sims.Results:
Between 4/24 and 1/26, 24 patients underwent thoracic MRI-sim at our institution. Patient characteristics: mean age 73 years, 12/24 male, 22/24 NSCLC, 19/24 metastatic disease, RT intent palliative 19/24. Despite dyspnea and suspected atelectasis with pleural fluid accumulation, all patients completed a chest MRI-sim lasting 20 minutes (range 15-25). Respiratory-gated T2-weighted imaging provided the best image quality (22/24). Poor image quality due to respiratory motion hindered the use of non-respiratory gated images. MRI-sim detected tumors, atelectasis, and pleural fluid with better resolution than CT-sim in 16/24 cases and had smaller GTVs than tumors contoured with CT-sim (mean GTV-CT: 202cc, SD 99.4, vs. mean GTV-MRI: 92cc, SD 68, P= 0.0002). MRI-sim offered no advantage over CT-sim in 8 cases due to tumors involving the entire region without atelectasis (N=3), small tumor size and distal location (N=3), or poor resolution due to prior radiation induced fibrosis (N=2).Conclusion:
MRI-sim offers advantages when planning RT in centrally located tumors with large atelectasis or pleural fluid accumulation. Respiratory-gated T2-weighted MRI images provided the best resolution for distinguishing tumors from normal tissue, enabling a 50% reduction in GTV volume. Additional studies using respiratory-gated MRI imaging are warranted.