ptcog 49 educational workshop of head & neck cancer

PTCOG 49 Educational Workshop

Proton Therapy of Head & Neck Cancer

Robert S Malyapa, MD, PhD

Malyapa – PTCOG 49 Educational Workshop

Clinical experiences of H&N proton therapy

Loma Linda oropharynx study using the concomitant boost technique (IJROBP, 2005)

MGH study for skull base adenoid cystic carcinoma (Arch Otolaryngol Head Neck Surg, 2006)

UFPTI study on maxillary sinus cancer (AJCO, 2008)


Why protons for H&N cancer?

Protons are attractive to radiotherapy because of their physical dose distributionThe RBE of protons are indistinguishable from 250 kV X-rays, which means that they are 10-15% more effective than 60Co (RBE=1.1)The OER of proton beams is not distinguishable from X-rays (2.5 – 3)Protons are sparsely ionizing, except for a region at the end of particles’ rangeThis high LET component is restricted to a tiny portion of the terminal track, it does not have any significant effect (this should be kept in mind when planning treatment close to critical structures)


Why protons for H&N cancer?

Preservation of visual function by reduction in dose to optic appartusPotential to further improve quality of life

Improved salivary gland function by sparing of parotid and submandibular glandsImproved swallowing function

Potential to escalate dose for hypoxic tumors while maintaining improvement in quality of life


UFPTI approach to H&N proton therapy

Large amount of H&N conventional and IMRT radiotherapy experience at UFEstablished H&N outcome database for comparisonEstablished IMRT H&N protocolsProton therapy H&N protocols designed to maximize utilization of these experiences


Concomitant Boost with PROTONS -Ca Oropharynx (tonsil, soft palate, base of tongue)

Aim: Preservation of salivary gland function and swallowing function

TREATMENT

REGISTER

STRATIFY

a) Stage I (T1N0) - RT alone

b) Stage II (T2N0) Š RT alone

c) Favorable Stage III (T1N1/T2N1) and IV (T1-T2 early N2b) ≤ 2 LN and ≤ 2 cm diameter LN Š RT alone

d) Unfavorable Stage III (T3N0) & IV (any T, N2c/N3) Š RT + chemo*

DOSEPTV Photon

(IMRT-Initial Volume)

Photon/Proton(CC Boost)*

Standard Risk

1.65 x 30=49.5Gy

__

IntermediateRisk

1.8 x 30=54 Gy __

High Risk 1.8 x 30=54 Gy 1.5 x 12 = 18 Gy

Total Dose = 72 Gy

* 6 hours interval between fractions on same day

*Chemo: CDDP 30 mg/m2 q weeklyOR

CDDP 100 mg/m2 q 3 weeks

Low Neck: Photons


Hyperfractionation with PROTONS –Carcinoma Nasal Cavity & Paranasal Sinuses

Aim: Preservation of visual functions (optic nerves, chiasm) andreduction of radiation dose to brain

•Hyperfractionation @ 1.2 CGE BID•68.4 -69.6 CGE: post-op negative margins•74.4 CGE: post-op positive margins

close marginperineural invasion

•Low neck: photons•CHEMO: 30 mg/m2 weekly CDDP


TREATMENT

REGI STER

STRATIFY a) T1, T2, N0 → RT alone

b) T3 and any N+ →RT+Chemo

DOSE

Photon (IMRT-Initial Volume)

BID Tx

Photon/Proton (Boost) BID Tx

50.4 Gy (1.2 Gy BID)*

24.0 Gy (1.2 Gy BID)*

TOTAL DOSE = 74.4 Gy

* 6 hours interval between fractions on same day

*Chemo: CDDP 30 mg/m2 q weekly OR CDDP 100 mg/m2 q 3 weeks Neck Nodes: Photons

Aim: Preservation of visual functions (optic nerves, chiasm) andreduction of radiation dose to brain

Hyperfractionation with PROTONS- Ca Nasopharynx


Hyperfractionation with PROTONS -H&N Skin Cancer with Perineural Invasion

REGI STER

STRATIFY a) Negative margins and focal perineural ⇒

invasion b) Incidental/positive per ineural invasion ⇒

TREATMENT

Local RT: (-) margin: 60 Gy/30 fx Focally (+) margin: 66 Gy/33 fx Local RT + RT of involved nerve to skull base:

Photons Proton (Boost) 60 Gy @1.2 Gy

BID* 14.4 Gy @ 1.2 Gy

BID* * 6 hours interval between fractions on same day

Aim: Preservation of visual functions (optic nerves, chiasm) and reduction of radiation dose to brain


Patient selection criteria for H&N proton therapy

Oropharynx:Must have only ipsilateral lymph nodes involved

Tumor extent that may require overly complex beam arrangements

Tumors extending from oropharynx to anterior cranial fossaTumors extending into low neck

Tumor location relative to high-Z dental implants


Patient immobilization and simulation

Patient immobilization devices must be proton-friendlyHomogeneous radiological lengths through potential beam pathsAll patient immobilization devices must be carefully evaluated for their physical properties


Evaluation of Immobilization Devices for Proton Therapy

Dosimetric Tests:CT scan of device to evaluate WET uniformityCompared TPS-calculated range pullback vs. measured range pullback at multiple locations on deviceThese tests must be performed with consideration of TPS dose calculation grid sizes, compensator smearing used, and proton scattering at depths of target after passing through device

Mechanical TestsDevice sagging as a function of time and weight on device


Data of R.Slopsema, 2008

Evaluation of Radiological Uniformity


Immobilization: Base of Skull Frame


CT simulation for H&N proton therapy

CT scanning technique optimized for appropriate patient size and siteCT-HU to proton stopping power conversion curves are optimized for FOV because HU is dependent on FOV

large FOV on large-bore CT scannersmall FOV e.g. H&N/CNS on small-bore

Approx 1.5% difference in HU was observed between small and large FOVCT with contrast injection used for segmentation but not for dose calculation


Aperture Margin Selection

Aperture margins account for beam penumbra at target depthOverly tight aperture margins increase dose distribution inhomogeneity and reduce dose distribution calculation accuracyBeam penumbra is a function of beam option used for treatment, as well as target depth


R.Slopsema, 2007

Beam Penumbra in Air andin Water

Malyapa – PTCOG 49 Educational WorkshopR. Slopsema, 2008

Double-Scattering Uniform Scanning

Uniform scanning for H&N


DVH for four-field nasopharynx plan, comparing US ( ) and DS ( )delivery. Pink shows target coverage; the inset (blue) the dose to the brain stem.

Slopsema, 2008

DSUS

DS

US

Uniform scanning for H&N


Proton-Specific Treatment Planning Concepts

Distal MarginRelative Biological Effect (RBE): accounting for higher RBE near distal rangeAccounting for range uncertainties

Proximal MarginCompensator smearing: 5 mm for H&NCompensator border smoothing: 10 mm for H&NThrough-patch fields (match fields preferred)


Patch

Through

Patch-field to form convex dose distribution

Criticalorgan

tumor


Metal Artifacts

Metal artifacts are often present within or near target region on CT images of H&N tumors

These need to be manually contoured and assigned appropriate HU for correct proton range calculations


•Appropriate auto-contouring technique selected to match the physical dimension of titanium rod

•All of artifacts outside titanium rod overridden with tissue HU

•Beam paths chosen to avoid dental implant alloy

Metal Artifacts


Other considerations of treatment planning for H&N proton therapy

High skin dose: Selection of beam angles to minimize field overlap on skinHigher dose inhomogeneity at air-bone or tissue/implanted metal interfaces: Selection of beam angles to minimize beam parallel to such interfacesRange and penumbra uncertainties due to presence of metal objects: avoid beams passing through and stopping on cordIncreased RBE at the end of range:

Allow additional distal margin when beam exits on critical organsMinimize number of beams exiting on critical organs


Treatment


Clinical Examples

OropharynxNasal cavity and Paranasal sinus NasopharynxSkin with perineural invasionLacrimal glandRE-IRRADIATION


IMRTIMRT PROTONSPROTONS

Oropharyngeal Carcinoma 72 Gy

Clinical Examples


IMRT ProtonTherapy

% PRV Dose ↓

PTV coverage: ≥95% of PTV receives Rx dose

101.6% 99.7%

PTV coverage: 99% of PTV receives ≥ 93% of Rx dose

100.3% 96.7%

Hot spot in PTV72 (≤20% of PTV 72 receives 110% of prescribed dose )

107.3% 106%

Contralateral Parotid (mean dose <2600 cGy

2529 1482 43%

Brainstem (5500 cGy to 0.1 c.c.)

5020 2685 46%

Spinal cord (5000 cGy to 0.1 c.c.)

4400 546 87%

Ca Oropharynx


IMRT Proton TherapyComposite

72 GyCCB only

1.5x12=18 Gy

Composite72 CGE

CCB only1.5x12=18 CGE

Contralateral parotid (mean dose ≤ 2600 cGy

2529 460 1482 0

Brainstem (5500 cGy to 0.1 c.c.)

5020 890 2685 0

Spinal cord (5000 cGy to 0.1 c.c.)

4400 1106 546 0

Contralateral submandibular gland

6928 1533 6148 820

Ca Oropharynx


Maxillary Sinus IMRT vs Protons


SNUC


IMRT: 1.2 Gy/FX BID to 50.4 Gy

Proton Boost: 1.2 CGE/FX BID to 24.0 CGE

Total Dose: 74.4 CGE

SNUC: IMRT+Protons


30 year male with adenoid cystic carcinoma Lt ethmoid and extension to base of skull

Adenoid Cystic Ca EthmoidPre-Treatment


74.4 CGE @ 1.2 CGE BID

Adenoid Cystic Ca Ethmoid


Adenoid Cystic Ca EthmoidPost-Treatment


IMRT: 50.4 + Proton Boost 24 = 74.4 CGE

LAN = 50.4 Gy

Ca Nasopharynx: IMRT + Protons


Ca Nasopharynx: Proton FieldArrangement


Ca Skin with Perineural Invasion


Lacrimal Gland Adenoid Cystic Carcinoma


Lacrimal Gland Adenoid CysticCarcinoma


50407440

PTV50.4

RON

BS

Lacrimal Gland Adenoid CysticCarcinoma


Lacrimal Gland Adenoid CysticCarcinoma – Post Treatment


IMRT

74.4 Gy

Protons

69.6 CGE

RE-IRRADIATION-Nasopharynx


H/O Multiple Cancers and RadiationTreatments Presented withCa Base of tongue


Acknowledgement

Daniel Yueng, PhDCraig McKenzie, CMDWilliam M. Mendenhall, MDZuofeng Li, DScNancy P. Mendenhall, MD

ptcog 49 educational workshop of head & neck cancer

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