Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_6_3170 - CPAP Improves the Anatomy and Dosimetry of Patients Undergoing Breath-Hold Motion Management for Thoracic SBRT.

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

CPAP Improves the Anatomy and Dosimetry of Patients Undergoing Breath-Hold Motion Management for Thoracic SBRT.
I. Sadetskii1, I. Darras2, S. Appel3, T. Rabin2, U. Amit4, I. Weiss4, M. ben-Ayun4, D. Alezra4, L. Tsvang4, Z. Symon4, and Y. Lawrence4; 1Sheba Medical Center, Ramat Gan, Israel, 2sheba medical centre, ramat gan, Israel, 3Radiation Oncology, Sheba Medical Center, Tel Hashomer, Israel, 4Radiation Oncology, Sheba Medical Center, Ramat Gan, Israel

Purpose/Objective(s): Intra-fraction tumor motion during thoracic radiation remains a major challenge. Two alternative approaches to motion management during radiation therapy are the 4D-ITV approach and maximal inspiratory breath hold (MIBH). We have previously reported on the ability of CPAP to improve thoracic anatomy for lung irradiation using 4D-ITV: enlarging lung volumes and decreasing tumor movement compared to free breathing. We hypothesized that CPAP during MIBH would further optimize SBRT dosimetry compared with MIBH without CPAP.

Materials/Methods: We performed a prospective study: patients underwent simulation twice - ‘regular’ MIBH, and MIBH combined with CPAP, for the latter patients were connected to the CPAP machine for 15 minutes prior to, and during the simulation. Contouring and planning were performed on both scans. Critical structures were defined as: heart, ribs, proximal bronchial tree. Radiation planning was performed using a commercially available treatment planning system, VMAT technique

Results: Eight patients underwent two simulations, 5 men and 3 women, mean age 67.5 age (49-74 years of age). Seven suffered from metastatic colorectal cancer, one thyroid cancer. CPAP+MIBH increased lung height by a median of 7%, width and breadth both by 2% compared to MIBH alone. Median lung volumes for MIBH and CPAP+MIBH were 4444cc (3913-6281) vs. 5265cc (4182-6441) respectively, p = 0.003. Hence CPAP increased BH volumes by a median 596cc (140cc-1275cc; 11.6%). Distance to closest critical structure increased from median 1.9cm (0.62-4.29cm) with MIBH to 2.4cm (0.65-4.9cm) for CPAP+MIBH, a median improvement 4.8mm (min 0.3mm; max 6.1mm) 25%, (p<0.03). Regarding dosimetric outcomes: the absolute mean decrease in lung V10 was 0.8% (range 0 – 1.3%; a 14% relative decrease, p<0.001)

Conclusion: Compared to MIBH alone, CPAP combined with MIBH significantly improves thoracic geometry and dosimetry for thoracic SBRT by improving lung expansion, and increasing the distance between the GTV and critical structures. These improvements are likely to be critical in patients with large GTVs or multiple lung metastases. Further clinical investigation of reproducibility, functional and clinical outcomes is currently underway.

Author Disclosure: I. Sadetskii: Travel Expenses; Sheba medical centre. I. Darras: None. S. Appel: None. U. Amit: None. M. ben-Ayun: None. Y. Lawrence: Research Grant; Gateway for Cancer research. Advisory Board; celgene. committee member; RTOG.

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