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