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Treatment Planning for Lung
Kristi Hendrickson, PhD, DABRUniversity 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 linac-based 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 SBRT lung
• Normal tissue sparing– 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/VMATInverse-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 3DCRTBenefits:• 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 IMRT1 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, conformalityindices
Target coverage
Plan Evaluation
• Dose spillage outside the target
Volume at 50 Gy / PTV volume
Volume at 25 Gy / PTV volume
Volume at 52.5 Gy - PTV
Plan Evaluation
Peripheral Lung Example
• 3DCRT• IMRT• VMAT
PTV
Trachea
Spinal Canal
Total Lung
Medium solid line 3DCRTThin solid line IMRTDashed line VMAT
3DCRT IMRT
Central Lung Example
• 3DCRT• IMRT• VMAT
Central Lung Plan Comparison
Medium solid line 3DCRTThin solid line IMRTDashed line VMAT
PTV
Spinal CanalTotal Lung
Bronchial Tree
Central Lung Isodose Comparison
IMRT VMAT
Lung SBRT Planning Summary|Conclusion
Planning strategies:• Conformal target coverage• Steep dose gradients to spare NTDelivery techniques:• 3DCRT• IMRT/VMAT• other
ReferencesBortfeld 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
AcknowledgementsThanks to:• Summer School Organizing Committee and
Faculty• SBRT Colleagues at Univ of Washington:
Juergen Meyer, Minsun Kim, Shilpen Patel, Ramesh Rengan