IMRT / Tomo / VMAT / Cyberknife / HDR Brachytherapy · 2014. 4. 8. · HDR Brachytherapy: RTOG0321...
Transcript of IMRT / Tomo / VMAT / Cyberknife / HDR Brachytherapy · 2014. 4. 8. · HDR Brachytherapy: RTOG0321...
1
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
2
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
3
Collaborators
Josephine Chen, PhDAdam Cunha, PhDMartina Descovich, PhDAaron Garcia, MSAlex Gottschalk, MDI-Chow Hsu, MDDilini Pinnaduwage, PhDMack Roach, MD
Monday, March 31, 14
Educational Objectives
- Understand that each modality follows a paradigm
- Understand when motion management is required
IMRT - VMAT - TOMO - CK - HDR
Monday, March 31, 14
Dose Distributions
Tomo
Ck
GammaK
Monday, March 31, 14
Dose Distributions
Tomo CkGammaK
HDR
Monday, March 31, 14
Dose Distributions
Monday, March 31, 14
Dose Profiles
HDR Brachy
Monday, March 31, 14
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
Monday, March 31, 14
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.
Monday, March 31, 14
Urethra-sparing dose distribution
Monday, March 31, 14
CK Urethra Sparing
Objective: Mean urethra dose < Prescription
Monday, March 31, 14
- 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
Monday, March 31, 14
- 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
Monday, March 31, 14
- 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).
Monday, March 31, 14
Tomotherapy
Fixed Jaw TomoEdge
Supperior
Inferior
Monday, March 31, 14
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.
Monday, March 31, 14
22
Thank You!
Questions?
Genitourinary Cancers Session, March 22nd, 2014
Monday, March 31, 14