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Jean Pouliot, PhDProfessor and Vice Chair,Department of Radiation Oncology,Director of Physics Division

UC-Berkeley - UCSF Graduate Program in Bioengineering

IMRT / Tomo / VMAT / Cyberknife / HDR Brachytherapy:

Should Choices be Basedon Dosimetric and Motion Considerations?

Genitourinary Cancers Session, March 22nd, 2014

Monday, March 31, 14

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Disclosure

Industrial Research ContractsAccuray, Dosisoft, Philips, Siemens, Varian

GrantsUC-Proof of Concept 12-PC-247UCSF CTSI Catalyst Award 2014

Licensing AgreementNucletron/Elekta

Monday, March 31, 14

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Collaborators

Josephine Chen, PhDAdam Cunha, PhDMartina Descovich, PhDAaron Garcia, MSAlex Gottschalk, MDI-Chow Hsu, MDDilini Pinnaduwage, PhDMack Roach, MD

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Educational Objectives

- Understand that each modality follows a paradigm

- Understand when motion management is required

IMRT - VMAT - TOMO - CK - HDR

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Dose Distributions

Tomo

Ck

GammaK

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Dose Distributions

Tomo CkGammaK

HDR

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Dose Distributions

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Dose Profiles

HDR Brachy

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DOSIMETRIC COMPARISON

IMRT - VMAT - TOMO - CK - HDR

- 3 Patients (prostate volumes: 35, 36 & 40 cc)- Prostate, bladder, rectum, bladder, and urethra- All structures segmented by same physician- Specific clinical planning team for each modality was asked to plan as usual.

- Prostate only- No consideration of RBE

Monday, March 31, 14

Average Dose Comparison

TOMO IMRT VMAT CK HDRBrachytherapy

Average Dose to Targetfor a Constant D95 103% 104% 105% 116% 147%

Falloff (V100/V50) 0.24 0.19 0.26 0.25 0.39

UrethraV120%(cc) 0 0 0 0 0

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HDR Brachytherapy: RTOG0321

Percent Dose of Prescription Dose

Acute adverse event

Late adverse event... the dose-limiting structure for prostate HDR brachytherapy is in the target volume (urethra).

This is in contrast to external beam radiation therapy where the rectum is the dose-limiting structure.

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Urethra-sparing dose distribution

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CK Urethra Sparing

Objective: Mean urethra dose < Prescription

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- 3 gold fiducial markers in prostate

- T1 and T2-weighted MRI (T1 for markers, T2 for urethra and prostate)

- Planning CT (1.5mm) and T2-weighted MRI are co-registered

- PTV = Prostate + 2mm expansion* (except posteriorly)

- OAR: Bladder, rectum, urethra, penis, testicles, bowel & femoral heads

UCSF Protocol for Prostate Robotic - SBRT

*  due  to  intrafraction  motion  

- Field sizes (Iris) ranging from largest aperture that fits the PTV contour to 12.5 mm-diameter opening are selected.

- Maximum of 200 MU per beam per fraction

- Four asymmetric shells are created around the PTV

Monday, March 31, 14

Intra-fraction Prostate Motion

Study: 2438 alignment shifts/rotations during Y fractions for 13 consecutive prostate patients, with a 90 sec average time between image verifications.

- PTV Margin of 2mm- Time between images < 60 sec

Monday, March 31, 14

Dose Planning Problematic: Difficult to predict level of OAR protection -> plan might not be optimal

Evidence-based dose constraintsfor prostate Ck-SBRT

Favorable Unfavorable

Objective: Use anatomy to determine possible level of sparing

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- Dose limits depend on anatomy

- Expansion-Interception-Volume (EIV) EIV = intersection volume between the target and the organ at risk expanded by 5 mm.

Evidence-based dose constraintsfor prostate Ck-SBRT

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- Clinical Use

Evidence-based dose constraintsfor prostate Ck-SBRT

nCi<1.25nCi≥1.25

-­‐  EIV  vs  V75

Descovich  et  al.,  “Improving  plan  quality  and  consistency  by  standardization  of  dose  constraintsin  prostate  cancer  patients  undergoing  stereotactic  body  radiation  therapy”,  JACMP  2014  (In  Press).

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Tomotherapy

Fixed  Jaw TomoEdge

Supperior

Inferior

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TOMO / IMRT / VMAT / CK / HDR

TOMO

IMRT

VMAT

CK

HDR

Target coverage and urethra protectioninsured by IGRT and dose uniformity

Urethra defined on MRI and intrafraction motion compensated via tracking

Urethra (defined via Foley) sparing via dose tunnel

⎫⎬⎭

Monday, March 31, 14

TOMO / IMRT / VMAT / CK / HDR

TOMO

IMRT

VMAT

CK

HDR

Most uniform dose of linac IMRT techniques

Hypofractionated Tx, intra-fx tracking, ~long Tx time

One-fx Tx, long clinical experience, caution with catheter motion

Most clinical experience

Efficient way to deliver radiation, more than one arc needed.

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Thank You!

Questions?

Genitourinary Cancers Session, March 22nd, 2014

Monday, March 31, 14