RSNA 2013 

Abstract Archives of the RSNA, 2013


SSA22-01

Increased Risk of Chest Wall and Rib Toxicity in Lung SBRT Patients Treated with RTOG-0813 Protocol and Monte Carlo Based Planning

Scientific Formal (Paper) Presentations

Presented on December 1, 2013
Presented as part of SSA22: Radiation Oncology & Radiobiology (Lung I)

Participants

Supriya Jain MS, BA, Presenter: Nothing to Disclose
Anil Sethi PhD, Abstract Co-Author: Nothing to Disclose
Edward Melian MD, Abstract Co-Author: Nothing to Disclose
Bahman Emami MD, Abstract Co-Author: Nothing to Disclose

PURPOSE

To evaluate Monte Carlo (MC) based lung stereotactic body radiotherapy (SBRT) plans for dosimetric parameters correlated with the development of chest wall pain and rib fracture.

METHOD AND MATERIALS

Twenty consecutive lung SBRT patients treated from 2010-2012 with heterogeneity corrected Pencil Beam (PB) plans were selected. Chest wall (CW) was contoured as a 3 cm expansion of the ipsilateral lung. Treatment plans were normalized to deliver 50 Gy PTV dose in 5 fractions using 7-12 non-coplanar, conformal, 6 MV fields. Using MC dose algorithm, each plan was optimized for PTV dose coverage as per RTOG-0813 protocol. Patients were classified based on PTV location: island tumors (8), adjacent to CW (9), or mixed (3); and PTV size (cc): small (< 25), medium (25-60), or large (> 60). Treatment plans were evaluated for toxicity risk based on four dosimetric thresholds - CW: Dmax < 50 Gy, V30 < 30 cc,  V40 < 5 cc and Ribs: Dmax <50 Gy.

RESULTS

Tumor size and location were strong predictors of risk of toxicity to CW and ribs. With MC planning, 0% (0/6) of small, 50% (4/8) of medium, and 100% (6/6) of large tumors exceeded all four CW and ribs toxicity thresholds. 78% (7/9) of tumors located adjacent to CW surpassed every CW / ribs threshold vs. 67% (2/3) of mixed and 25% (2/8) of island tumors. Mean Dmax for ribs was significantly higher for tumors adjacent to CW than for island tumors (61.6±11.7 Gy vs. 45.00±11.7 Gy, p = .007). Transitioning from PB to MC planning resulted in a higher overall risk of toxicity. Mean relative dose increases from PB to MC plans were 32.4±12.7%, 24.8±10.4%, and 20.3±6.4% for small, medium, and large tumors, respectively, and 32.5±11.6%, 26.6%±8.8%, and 19.5±7.2% for island, mixed, and chest wall tumors respectively.

CONCLUSION

MC based lung SBRT plans that satisfy RTOG-0813 criteria for PTV dose coverage result in an increased risk of chest wall and rib toxicity. Large tumor size and proximity to CW predict highest absolute dose to CW and ribs. However, relative increase in CW / rib dose from PB to MC planning is directly proportional to tumor distance from CW and inversely proportional to tumor size. Low-risk small island tumors experience the greatest increase in CW/rib dose when planned with MC algorithm.

CLINICAL RELEVANCE/APPLICATION

With Monte Carlo based planning, revision of RTOG-0813 guidelines for PTV dose coverage may be necessary to prevent chest wall pain and rib fractures.

Cite This Abstract

Jain, S, Sethi, A, Melian, E, Emami, B, Increased Risk of Chest Wall and Rib Toxicity in Lung SBRT Patients Treated with RTOG-0813 Protocol and Monte Carlo Based Planning.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13015713.html