Stereotactic Body Radiotherapy (SBRT) for Prostate Cancer:Practical Considerations for

Treatment Planning

Minsong Cao, Ph.D.Department of Radiation Oncology

David Geffen School of Medicine at UCLAminsongcao@mednet.ucla.edu

Outline of Presentation• Introduction• Simulation and immobilization• Treatment planning process

– Target and OAR contours– Beam design– Dose optimization/calculation – Plan evaluation

• Patient treatment setup and verification

Learning Objectives

• Summarize and discuss the clinical issues involved when planning prostate patient with SBRT treatment including target volume delineation, contouring critical structure, dose prescription strategies, and plan evaluation

• Summarize and discuss the clinical issues associated plan simulation, motion management and treatment verification for prostate SBRT

SBRT – Prostate

Alongi et al. Radiation Oncology 2013, 8:171

Common treatment techniques• Isocenter

– Isocentric (Linac gantry based) vs. non-isocentric (Cyberknife)

• Beam arrangement– Coplanar vs. non-coplanar beams

– Static gantry angle IMRT vs. Volumetric arc modulated treatment (VMAT)

• PTV dose distribution– Homogenous vs. Heterogeneous vs. Simultaneous boost

Isocentric vs. non-isocentric

Courtesy of BrainLab® Courtesy of Accuray®

PTV dose coverage

Uniform distribution

D. B. FULLER et al., IJROBP. V70(5), 2008

Udrescu et al. Physica Medica.2013( in press)

Clinical Workflow• Patient immobilization and simulation

• Target and organ at risk (OAR) delineation

• Isocenter placement and beam design

• Dose optimization and calculation

• Plan evaluation and quality assurance

• Patient setup and verification

• Treatment delivery

Special considerations - Challenges

• Close proximity of OARs

• High dose gradient / conformity

• Organ motion

Patient immobilization

Body frame

Vacuum bag

CT simulation• Placement of 3 gold markers via trans-rectal ultrasound

• Patient instructed to have comfortably full bladder

• Patient in supine position in the immobilization device

• Non-contrast CT scan and MRI of the pelvis

– from above the iliac crest to below the ischium

– 1.5mm slice thickness

Rectal Balloon

Both S etc. TCR, Vol.1(3), 2012

B L Jones et al, Phys. Med. Biol. 58 (2013)

Spacer between Prostate and Rectum• Biocompatible liquid gel injected between the prostate

and rectum under ultrasound guidance

Alongi et al. Radiation Oncology 2013, 8:171

Target localization

MRI Prostate Anatomy Atlas: http://www.prostadoodle.com/

OAR contours

• Bladder • Rectum• Penile bulb• Femoral heads• Urethra (optional)• Bowel (optional) • Testes (optional)

Planning dose constraints

Descovich et al. JACMP Vol. 14 (5), 2013

Dose conformity and Homogeneity

Feuvret L. et. al., IJROBP, V64(2), 2006

Cyberknife plan• Typical treatments consist of about

100-120 non-coplanar beams• Total treatment 40-60 minutes• Imaging correction every 5–7

beams (about every 30–90s)

Chen et al. Radiation Oncology 2013, 8:58

Cyberknife vs. Linac IMRT• No posterior beams in cyberknife

plan. More anterior beams transvers the bladderHigher bladder dose

• Fewer beams to enter from the left side of patient due to the robotic kinematic constraintsHigher dose to right femur

compared with left femur

Pawlicki et al. Med Dosi 32(2), 2007

Cyberknife vs. Linac IMRT

S. Hossain et al. IJROBP.78(1), 2010

King. Front Radiat Ther Oncol. V43. 2011

Volumetric Modulated Arc for SBRT• Volumetric arc modulated therapy that

simultaneously changes: – Gantry rotation speed– Treatment aperture shape (MLC) – Delivery dose rate

• Improved conformity • Fast plan delivery

Linac VMAT and IMRT plan

Beam parameter selection• Prostate SBRT plans developed for different number of

arcs collimator angels, beam energies and couch rotations for ten patients – Plans with ±45º collimator angles required 38% less

MU with no collimator rotations and 20% less than ±22.5º

– Plans with ±45º collimator angles provided more homogeneous dose distribution

– Plans with two arcs provided improved conformity and homogeneity compared with single arc

Agazaryan N. et. al. ASTRO 2010

Beam parameter selection

• Increasing the number of arcs to 3 did not provide significant improvement

• ±5º couch rotations between arcs did not improve the plan dosimetry significantly

• Selection of beam energy between 6MV and 10MV did not show notable dosimetric difference

Agazaryan N. et. al. ASTRO 2010

Current planning protocol

• Prescription: 8Gy x 5 fractions• Beam energy: 6MV SRS (1000MU/Minute) • Arc: 2 full arcs split to 4 half arcs• Collimator rotation: ±45º • No couch rotation

Plan optimization

• Goals:– PTV:

• V100≥95% R50 < 4.0

– Rectum:• V20Gy < 50% V32Gy < 20%• V36Gy < 10% V40Gy < 5%

– Bladder:• V20Gy < 40% V40Gy<10%

– Femur header: • V16Gy < 5%

Flattering Filter Free (FFF)

MLC Size

Standard MLC HD120 MLC

Plan evaluation – where you stand?

Ruan et. al. Medical Physics, Vol. 39(5), 2012

Ruan et. al. Medical Physics, Vol. 39(5), 2012

Planner

No

Re-plan Plan Evaluation

Yes

Published standards

Treatment Planning

Planning Scripts(Parser)

Patient plan database

Physics Check QA…

Yes

Update

Plan Quality Report

(Planning goals, achieves, ranks)

Cao et. al. AAPM 2013

Dynamic Static

Patient Treatment Setup and Verification

• Patient inter-fractional positioning correction:– 2D image pairs (OBI, ExacTrac …)– 3D volumetric image (CBCT)

• Patient intra-fractional motion tracking: – Electromagnetic tracking (Calypso) – Stereoscopic imaging (ExacTrac)

Prostate moves!

Courtesy of ViewRay®

Kupelian, IJROBP, 67: 1088-1098, 2007

Intra-fractional motion

“If large movements (>5mm) could be excluded by some activecorrection strategies, then the average V100% for the simulated plan could be restored to within approximately 2% of the ideal treatment plans.”

Hossain et al., Med. Phys. 35 (9), 2008

Agazaryan N. et. al. ASTRO 2010

MRI guided radiotherapy

Courtesy of ViewRay®

References1. Alongi, F., et al., Linac based SBRT for prostate cancer in 5 fractions with VMAT and flattening filter

free beams: preliminary report of a phase II study. Radiat Oncol, 2013. 8(1): p. 171.2. Benedict, S.H., et al., Stereotactic body radiation therapy: the report of AAPM Task Group 101. Med

Phys, 2010. 37(8): p. 4078-101.3. Buyyounouski, M.K., et al., Stereotactic body radiotherapy for primary management of early-stage,

low- to intermediate-risk prostate cancer: report of the American Society for Therapeutic Radiology and Oncology Emerging Technology Committee. Int J Radiat Oncol Biol Phys, 2010. 76(5): p. 1297-304.

4. Chen, L.N., et al., Stereotactic body radiation therapy (SBRT) for clinically localized prostate cancer: the Georgetown University experience. Radiat Oncol, 2013. 8: p. 58.

5. Descovich, M., et al., Improving plan quality and consistency by standardization of dose constraints in prostate cancer patients treated with CyberKnife. J Appl Clin Med Phys, 2013. 14(5): p. 162-72.

6. Fuller, D.B., et al., Virtual HDR CyberKnife treatment for localized prostatic carcinoma: dosimetry comparison with HDR brachytherapy and preliminary clinical observations. Int J Radiat Oncol BiolPhys, 2008. 70(5): p. 1588-97.

7. Hossain, S., et al., Simulated real time image guided intrafraction tracking-delivery for hypofractionated prostate IMRT. Med Phys, 2008. 35(9): p. 4041-8.

8. Hossain, S., et al., Dose gradient near target-normal structure interface for nonisocentricCyberKnife and isocentric intensity-modulated body radiotherapy for prostate cancer. Int J RadiatOncol Biol Phys, 2010. 78(1): p. 58-63.

References9. Jones, B.L., et al., Effect of endorectal balloon positioning errors on target deformation and

dosimetric quality during prostate SBRT. Phys Med Biol, 2013. 58(22): p. 7995-8006.10. King, C., Stereotactic body radiotherapy for prostate cancer: current results of a phase II trial.

Front Radiat Ther Oncol, 2011. 43: p. 428-37.11. King, C.R., et al., Long-term outcomes from a prospective trial of stereotactic body radiotherapy

for low-risk prostate cancer. Int J Radiat Oncol Biol Phys, 2012. 82(2): p. 877-82.12. King, C.R., et al., Stereotactic body radiotherapy for localized prostate cancer: pooled analysis

from a multi-institutional consortium of prospective phase II trials. Radiother Oncol, 2013. 109(2): p. 217-21.

13. Kupelian, P., et al., Multi-institutional clinical experience with the Calypso System in localization and continuous, real-time monitoring of the prostate gland during external radiotherapy. Int J Radiat Oncol Biol Phys, 2007. 67(4): p. 1088-98.

14. Pawlicki, T., et al., Investigation of linac-based image-guided hypofractionated prostate radiotherapy. Med Dosim, 2007. 32(2): p. 71-9.

15. Ruan, D., et al., Evolving treatment plan quality criteria from institution-specific experience. Med Phys, 2012. 39(5): p. 2708-12.

16. Udrescu, C., et al., Potential interest of developing an integrated boost dose escalation for stereotactic irradiation of primary prostate cancer. Phys Med, 2014. 30(3): p. 320-5.

Summary|Conclusion• Hypofractionation has the potential to biologically dose-

escalate radiotherapy for prostate cancer.• Establishing SBRT procedures and guidelines from CT

simulation to treatment planning, verification, delivery, and reporting methodology is essential to the success of the implementation of prostate SBRT treatment

• Personal training is another important aspect of implementation of a SBRT prostate program

AcknowledgementsChristopher King, MD, PhDPatrick Kupelian, MDMichael Steinberg, MDDaniel Low, Ph.D. Nzhde Agazaryan, Ph.D.John DeMarco, Ph.D.Steve Tenn, Ph.D.Dan Ruan, Ph.D.Ke Sheng, Ph.D.Chul Lee, M.S.