Dosimetric evaluation and comparison of small-field non-coplanar multi-arc radiotherapy (SMART) and intensity-modulated radiotherapy (IMRT) in treatment of tumor-related bronchial/superior vena cava (SVC) obstructions

Abstract

19668 Background: Rapid and cost-effective palliation is of great importance in patients with complications from lung cancer progression. To offer immediate treatment for a tumor-related obstructed bronchus or SVC, we have implemented the SMART technique which has been shown to be effective and safe in the primary and re-treatment of malignant bronchial/SVC obstructions. The purpose of this study was to determine if the dose coverage to the obstructed bronchus/SVC and normal tissue sparing achieved by SMART compare favorably to the lengthier and more expensive IMRT technique. Methods: Treatment planning CT’s from 9 patients with a bronchial obstruction and 1 with SVC were studied. The planning target volume (PTV) consisted of the clinical target volume (CTV = obstructed bronchus or SVC) plus a 1 cm margin. For SMART, a dose of 10 Gy in a single treatment to the target was computed using 18 MV photons with 5 to 8 non-coplanar arcs with field sizes ranging from 4 cm2 to 8 cm2. For a dosimetric comparison using the same planning CT, an IMRT plan with 5 to 9 fields using 6 MV photons with 95% CTV coverage was computed to deliver the same dose. Dose volume histograms (DVH), treatment delivery time based on monitor units (MUs), and mean doses to the CTV, PTV, heart, lungs, spinal cord, and total body dose were compared using Student’s t-test. Results: Pooled DVH analysis of SMART and IMRT showed that SMART provided slightly better, but not statistically significant, coverage of the CTV (97±1.1 vs. 92±5%) and PTV (94±2 vs. 89±5%). There was no difference in normal tissue sparing between SMART and IMRT with respect to the mean lung dose (9±7 vs. 9±7%), heart dose (7±10 vs. 3±5%), cord dose (37±13 vs.30±13%), and total body dose (8±4 vs.7±4 Joules). However, SMART delivery was faster requiring significantly less MUs compared to IMRT (1,284±65 vs.1984±90, p<0.002). Conclusions: IMRT showed no advantage over SMART in dose coverage of the CTV/PTV and sparing of critical normal tissues. Therefore, less complex planning and faster treatment delivery of SMART maybe clinically preferable for rapid palliation of critically ill patients with an obstructed bronchus/SVC. No significant financial relationships to disclose.