Treatment Planning for Lung Kristi Hendrickson, PhD, DABR University of Washington Dept. of Radiation Oncology
Outline of Presentation Dosimetric planning strategies for SBRT lung Delivery techniques Examples for central and peripheral tumor locations Summary
Learning Objectives To understand how SBRT lung planning differs from conventional lung RT planning To know the objectives for target coverage and normal tissue sparing To understand the strategies for creating linacbased 3DCRT and IMRT/VMAT plans that will meet target coverage and normal tissue sparing goals
Dosimetric planning strategies for SBRT lung Target dose coverage Large doses in few fractions to achieve BED of 100 Gy + Inhomogeneous, not uniform, high hot spots in GTV Place penumbra at target boundary Dose prescription line is low (60-90%) Steep dose gradient outside the target to improve sparing of surrounding normal tissues
Dosimetric planning strategies for Normal tissue sparing SBRT lung Non conventional dose limits due to high daily doses and few fractions (short total time for treatment)
General lung planning guidelines 6 MV Heterogeneity corrections for tissue density variations Multiple beam angles (6-12 or more) Noncoplanar beam arrangements common Accurate dose calculation algorithm 2-mm calculational grid size
3DCRT Choose beam angles to produce conformal target coverage and to avoid critical structures Non opposing beams Blocking without margins: zero or negative Forward planned: manually optimize beam weights and tweak MLC positions
3DCRT
IMRT/VMAT Inverse-planned fixed-gantry IMRT / Modulated arc List optimization objectives for target coverage and NT sparing as usual Place high weight on target coverage objectives Do NOT include uniform dose objectives for target; no upper limit or high upper limit (60-90% isodose line) Create rings to create steep dose gradients
IMRT vs 3DCRT Benefits: Improved sculpting of dose around critical structures Easier to plan? Disadvantages: Longer treatment time Interplay effects between target and MLC motion (low modulation recommended)
VMAT vs IMRT 1 or more arcs akin to many many beams Benefits: IMRT benefits plus reduced treatment time Increased high dose conformality Disadvantages: Increased low dose bath
Cyberknife and other Cyberknife Tomotherapy Proton therapy
Plan Evaluation Includes careful review of target and normal tissue doses TG-101, RTOG 0831 and 0915 and other sources suggest practical guidelines and a variety of possible metrics to access plan quality
Plan Evaluation: Normal Tissues Dose statistics: min, max, mean, dose/volume parameters
Plan Evaluation: Target Target coverage, heterogeneity indices, conformality indices Target coverage
Plan Evaluation Dose spillage outside the target Volume at 52.5 Gy - PTV Volume at 50 Gy / PTV volume Volume at 25 Gy / PTV volume
Plan Evaluation
Peripheral Lung Example 3DCRT IMRT VMAT
PTV Trachea Spinal Canal Total Lung Medium solid line 3DCRT Thin solid line IMRT Dashed line VMAT
3DCRT IMRT
Central Lung Example 3DCRT IMRT VMAT
Central Lung Plan Comparison Bronchial Tree PTV Total Lung Spinal Canal Medium solid line 3DCRT Thin solid line IMRT Dashed line VMAT
Central Lung Isodose Comparison IMRT VMAT
Lung SBRT Planning Summary Conclusion Planning strategies: Conformal target coverage Steep dose gradients to spare NT Delivery techniques: 3DCRT IMRT/VMAT other
References Bortfeld T, Jokivarsi K, Goitein M, Kung J, Jiang SB (2002) Effects of intra-fraction motion on IMRT dose delivery: statistical analysis and simulation. Phys Med Biol 47:2203. Bortfeld T, Webb S (2009) Single-arc IMRT? Phys Med Biol 54:N9. Jiang SB, Pope C, Jarrah KMA, Kung JH, Bortfeld T, Chen GTY (2003) An experimental investigation on intra-fractional organ motion effects in lung IMRT treatments. Phys Med Biol 48:1773. Lo, S. S., Teh, B. S., Lu, J. J., Schefter, T. E. (Eds.). (2012). Stereotactic Body Radiation Therapy. Berlin: Springer-Verlag. Lo, S., Teh, B. S., Mayr, N. A., & Machtag, M. (Eds.). (2013) Stereotactic body radiation therapy: lung cancer. London: Future Medicine Ltd. RTOG 0813 Seamless PhaseI/II Study of Stereotactic Lung Radiotherapy for Early Stage, Centrally Located, Non-Small Cell Lung Cancer in Medically Inoperable Patients. RTOG 0915 A Randomized Phase II Study Comparing 2 Stereotactic Body Radiation Therapy Schedules for Medically Inoperable Patients with Stage I Peripheral Non-Small Cell Lung Cancer. Solberg, T. D. et. Al Practical Radiation Oncology (2012) 2, 2-9. TG-101
Acknowledgements Thanks to: Summer School Organizing Committee and Faculty SBRT Colleagues at Univ of Washington: Juergen Meyer, Minsun Kim, Shilpen Patel, Ramesh Rengan