Advanced Techniques:

Tomotherapy, GammKnife, CyberKnife, MR-Linac,

Proton Therapy, Vero

Jason Yan, MS, DABR, MCCPM

05/2015. Yanxxs at gmail dot com

Radiation Oncology & CyberKnife, U of Arizona Cancer Center at St Joseph’s Hospital & MC

GammaKnife, Barrow Neurological Insitute.

Big Picture:

World wide: # of machines # of pts treated Existing in market Main sites treated

Linac ~8000 50,000,000 58 yrs 56%: lung, prostate, breast. 44%: all others

Tomo ~300 ~100,000 ?? 12 yrs Mainly pelvis, prostate, H&N, etc.

GammaKnife ~550 700,000 28 yrs Brain SRS (1 fx)

CyberKnife ~500 100,000 14 yrs 50% Brain SRS, 50% SBRT: lung, spine,

prostate, liver, pancreas, etc.

Proton Therapy 14(+11) in US ~30,000 24 yrs

Vero <5 ?? ~4 yrs

Some facts:

--- there are ~2000 cancer centers in US. 60% cancer patients were treated with RT. (in China, only ~15% cancer patients

were treated with RT).

--- for RT patients: ~75% is curative. Lowest cure rate including: 59% for lung, 50% for brain.

--- for RT patient: ~88% treated with EBRT (Linac, Tomo), ~6% GammaKnife, ~4% CyberKnife, ~6% brachy, etc.

--- on average, every RT patient will be treated with 23.4 fractions.

Tomotherpy (competitor with Linac)

Miniature Linac: X-band, 6MV only. Beam stopper as weight balance. (Linac: S-band, more stable)

Helical beam: gantry rotation + table moving in. It can treat 160cm length in Sup/Inf direction instead of 40cm.

Pneumatic driven MLC leaf:

-- 20 ms to close or open (binary MLC). More stable.

-- Higher dynamic range of intensities leads to better plan. (No rounded leaf end effect, no DLG, no sliding).

Jaw opening: 5mm – 50mm (equivalent to MLC leaf thickness of Linac)

Structure: Leaf height 10cm (MLC 6.3cm), collimator height 22cm.

Tomotherapy machine structure: every compacted into the „donut‟. Shielding design requirement is much less stringent.

Fan beam irradiation: sharper penumbra better plan. (similar to: CT has lesser noise than CBCT)

Linac Tomotherapy

Iso wobbling ~1mm 0.2mm (mini-linac on ring)

Table accuracy ~1mm 0.25mm

Gantry speed 5.6o/sec 30o/sec

Field size 40cm * 40cm 160cm * 38cm

MLC -- (60 leaves) x (2 banks), along Y direction.

-- Leaf thickness: 5mm/10mm

-- Modulation at rotational direction:

leaf speed 2.5cm/sec

-- leaf sliding 2.5cm/sec max.

-- prone to mechanical failure.

-- 64 leaves, along X direction.

-- Jaw opening: 5mm-50mm

-- Modulation at rotational direction:

binary at 6.25mm leaf thickness.

-- binary MLC (20 ms)

-- stable

Beam penumbra: Moderate Small better plan

Intensity level: Moderate Big dynamic range better plan

Non-coplanar beams: Yes better plan for brain cases. No

Delivery accuracy: Good May be better, but largely depends on setup

uncertainty, and organ motions.

SRS plans Yes No (no cone)

CBCT KV-CBCT has better soft-tissue contrast MVCT has less image noise (fan beam).

3D-CRT plans Simple. Has to use helical IMRT, but comparable.

CNS, TBI plans Need field junction Easier

Breast plans Easy More complicated?

Electron field plans Yes, simple. Has to use helical IMRT, but could be

comparable.

Room shielding

requirement

~2m concrete wall Much less requirement (beam stopper).

Portal dosimetry EPID panel (not really measuring dose) 511 Xenon ion chamber ring easy for

dose reconstruction.

二. GammaKnife

2.1) GK model 4C (up to 2006):

Principle:

-- 201 Co-60 sources. 4 helmets with 4, 8,

14, 18mm collimator sizes respectively. All

collimator central axis focus on the center

of helmet (iso). Each helmet has 201

source holding chambers, with some

chambers empty and some loaded, it can

create different shape of isodose lines (at

prescription dose level).

-- Alloy frame with sharp pins that are

screwed into patient skull after local

anesthesia. Frame acts as the origin and

coordinate system for the head and tumor

in MR Image.

-- cap with image marker lines helps to

determine frame position in 3D space.

-- most GK SRS cases are done with MR

image, not CT. Assuming water in head.

-- TG 51 output? NO!

Task Group No. 178 – Gamma Stereotactic Radiosurgery Dosimetry and Quality Assurance

2.2) GK Perfexion (2006)

-- built-in auto collimator size change, auto plugging by sectors.

-- sector: 6+4+5+4+5=24 sources/sector * 8 sectors = 192 sources.

-- By moving a sector, the corresponding set of sources is aligned with a specific size of collimator set (16mm, 4mm, off, 8mm), or beam off.

-- couch positioning system: LGK 4C -- auto positioning, or manual trunnion(炮耳) setting positions pt head. LGK Perfexion:

whole body movement, the couch is the positioning system.

-- head frame and caps are the same.

GK Perfexion Video https://www.youtube.com/watch?v=mAktF38ALus Safety:

US Homeland Security: camera, alarm disable when going in, iris scan (background investigation by FBI), etc.

三. CyberKnife

-- Fixed 133 “nodes” in 3D space (114 nodes for body)

-- SAD = 80cm (or 65 cm)

Various Tracking methods with CyberKnife:

Tumor site Algorithm of tracking Tracking accuracy* Remark

6D Skull Tracking Brain KV image pairs of bone 0.44±0.12mm

Spine Tracking Near spine (C,

T, L, sacral) KV image pairs of spine 0.52±0.22mm Spine is distortable

Lung Tracking in lung KV image pairs of tumor

in lung, if visible.

0.73±0.33mm

(1.4±1.1mm for patient)

Moving tumor. MC optimization.

MC dose calculation.

Fiducial Tracking

in lung,

prostate, liver,

etc.

KV image pairs of

fiducials (1, or ≥3)

0.70±0.33mm

(dynamic)

0.29±0.10mm (static)

Fiducials on the perimeter of

tumor. Wait 5-7 days after

implant to stabilize fiducials.

*. Error includes planning CT image error, TPS error, KV image pair error, and robot tracking error.

Comparison between GammaKnife and CyberKnife:

GammaKnife CyberKnife

Frame? Frame No frame, use mask.

Fractionation possible? No Yes

Real-time tracking? No Yes

Overall pt positioning accuracy? <1mm <1.0-1.5mm

Biggest cone size 16mm 60mm (G6 has Micro-MLC)

Gradient Index (GI=V50%Rx/V100%Rx) 2.5-3.0 for brain (better) 3.0-3.5 for brain

Treat body No Yes (lung, liver, prostate, etc.)

Dose Prescription 50% of Dmax 70% of Dmax

Cost of machine 2.5 million,

change sources 1.5 million/5 yrs.

3.5 million, service 0.3 million/yr.

Cost per patient ~$25,000 (surgery ~80,000?) ~$40,000 (regular EBRT: ~$20,000)

TG 135. quality assurance for robotic radiosurgery.

四. MR-Linac

4.1) MR: great soft tissue contrast.

-- Imaging frequency of MR: 2/sec (at best). 4D-MR (multi-cycle) much better than 4D-CT (single cycle). No dose!!

-- CBCT has good soft tissue contrast, but imaging frequency is 1/min (due to gantry speed limit).

-- opens the possibility of “see what you treat”!

-- Computer technology will make the real-time contour and real-time tracking possible!! Math model from 4D-CT is only

for one cycle of motion, not representative, need real-time tracking.

-- can also see tumor response, adjust dose on the fly customized RT.

4.2) 1999 invention, 2004 design, 2009 first prototype, now 3rd generation in clinic.

4.3) Bright future:

GTV CTV Distant tumors

chemo - +/- +

RT (with MR-linac) ++ ++ -

surgery + +/- --

4.4) One of the pioneers in MR-Linac development family with Elekta company:

-- UMC Utrecht: 150 PhD’s, 80% with MRI titles. 20 MR-Linac research physicists, and 20 clinical physicists. 13 professors.

4.5) expect 510K approved by FDA in 2017.

4.6) ViewRay MR-Linac: 3 Co-60 sources at 120o apart. Not-popular: penumbra big??

Elekta MR-Linac Research Consortium:

The consortium includes the University Medical Center Utrecht (Utrecht, the Netherlands), The University of Texas MD

Anderson Cancer Center (Houston, Texas), The Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital

(Amsterdam, the Netherlands), Sunnybrook Health Sciences Centre (Toronto, Ontario), The Froedtert & Medical College of

Wisconsin Cancer Center (Milwaukee, Wisconsin), The Institute of Cancer Research (London, UK), and The Royal Marsden

NHS Foundation Trust (London, UK). http://www.hotspot.philips.com/article/mr-linac/

五. Proton Therapy

5.1) Brag Peak magic:

5.2) principles and Proton Center layout:

5.3) Since the first medical center of PBT (Photon Beam Therapy), at least 2/3 of all radiation oncologists and physicists

have been discouraging its use in clinics. Reasons are:

-- Photon therapy has already achieved very successful curative rate for most type of cancers. It is very unlikely PBT will achieve

significant better curative rate.

-- Bottle neck for radiation therapy is imaging of soft tissue in real time, hence tracking organ motions in real time, which is not

solved at all by PBT. Rather, this will largely diminish the effect of PBT.

-- PBT is significantly more expensive than photon therapy (at least 4 times higher cost), especially the initial investment (at least

10 times higher).

5.4) Publications constantly warning our society to discourage PBT:

JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS, VOLUME 16, NUMBER 3, 2015. Proton-beam therapy: are

physicists ignoring clinical realities? R. J. Schulz, Ph.D. Department of Therapeutic Radiology, Yale University

Summary It is eminently clear from phase II evaluations of the more common cancers that the clinical outcomes of PBT are

no better — nor any worse — than those achieved by IMRT or SBRT. This broad statement is supported by the reviews of

Brada et al.,(22) Lodge et al.,(23) Olsen et al.,(24) and Brada et al.(25) that compare the clinical results achieved by PBT for

a wide variety of disease sites with those achieved by more conventional means.

The conclusions reached by Lodge and Olsen and their colleagues are essentially the same as those of Brada et al.:(22) ―An

uncontrolled expansion of clinical units offering as yet unproven and expensive proton therapy is unlikely to advance the field

of radiation oncology or be of benefit to cancer patients.‖

22. Brada M, Pijls-Johannesma M, De Ruysscher D. Proton therapy in clinical practice: current clinical evidence. J Clin Oncol.

2007;25(8):965–70.

23. Lodge M, Pijls-Johannesma M, Stirk L, Munro AJ, De Ruysscher D, Jefferson T. A systematic literature review of the

clinical and cost-effectiveness of hadron therapy in cancer. Radiother Oncol. 2007;83(2):110–22.

24. Olsen DR, Bruland OS, Frykholm G, Norderhaug IN. Proton therapy — a systematic review of clinical effectiveness.

Radiother Oncol. 2007;83(2):123–32.

5.4) Massive market capitalization can confuse people for a period of time, but won’t be long.

-- Smoking was a fashion and 70% of people in US smokes for almost 40 years until 1930, which is ~20 years later than

medical and scientific findings that smokers are 5-25 times more related to lung cancer than non-smokers!

-- smoking was considered a fashion, an energy booster, a mental soother, and even good to health in the past in US.

六. Vero

6.1) Video of VERO machine: https://www.youtube.com/watch?v=YFoAC_nmPdg

6.2) A “combination” of Tomotherapy and CyberKnife：

-- miniature linac rotates in a donut shape gantry (similar to Tomotherapy).

-- it has two KV-imager for 3D positioning of patient bone structure (similar to CyberKnife or ExacTrac, but KC-imager

moving with linac head instead of fixed on ceiling or under floor.)

-- Linac head can rotate itself in a certain cone range, donut shaped gantry can also rotate in a certain angle range, with 6D

couch (similar to CyberKnife).

-- less than 10 machines sold in the world.