KV Cone-Beam TC LA SOLUZIONE ELEKTA. F. Casamassima U.O. RADIOBIOLOGIA CLINICA UNIVERSITA DI FIRENZE

KV Cone-Beam TC LA SOLUZIONE ELEKTA F. Casamassima U.O. RADIOBIOLOGIA CLINICA UNIVERSITA DI FIRENZE

KV Cone-Beam TC Immagine volumetrica acquisita con Tubo X a 90 rispetto alla sorgente MV + Pannello di silicio amorfo Sistema che ruota attorno al paziente

CONE - BEAM Tc A single rotation around the patient produces a complete 3D volumetric data set 1 rotation = 3 minute = 650 projections More projections = higher-quality CT z Volumetric Image 17 cm Cone Beam

KV Cone-Beam TC Le proiezioni da ogni singolo angolo sono acquisite e ricostruite con algoritmo modificato di Feldkamp Si ottengono immagini tridimensionali con visualizzazione anatomiche parti molli e scheletro

Immagine 3D Cone - Beam TC

KV Cone-Beam TC La qualità dell immagine volumetrica dipende dai parametri di acquisizione KV ma N totale proiezioni acquisite Velocita rotazione del gantry Angolo totale di rotazione

KV Cone-Beam TC I parametri di acquisizione debbono essere ottimizzati secondo l area anatomica da trattare

KV Cone-Beam TC PARAMETRI TIPICI 650 ACQUISIZIONI 360 ROTAZIONE 120 KV 40 ma 40 ms

KV Cone-Beam TC E possibile scegliere il FOV GRANDE VOLUME DEL PICCOLO CILINDRO ACQUISITO

Cone Beam CT Mode Acuity FDA 510(k)

KV Cone-Beam TC DOSI EROGATE AL PAZIENTE Da 1 cgy a 4 cgy (inferiore a 2 immagini portali 0-90 )

KV Cone-Beam TC Tempi di acquisizione-ricostruzione dell immagine 3-4 minuti Tempi per valutazione clinica e correzione on - line 5-10 minuti

La Cone-Beam TC è registrata con La TC di pianificazione

La sovrapposizione ed il confronto Cone-Beam TC e TC di pianificazione è eseguito su un area scelta dall operatore (clip-box)

Il confronto-sovrapposizione delle due TC può avvenire: Manualmente In automatico basandosi sulla densita dell osso Sui livelli di grigio (mutua informazione)

La sovrapposizione-confronto della CBCT sulla TC di pianificazione in automatico su formazioni scheletriche consente una correzione on-line del Set-up

I contorni dei VOI disegnati sulla TC di pianificazione sono anatomicamente trasferiti sulle CBCT

La visualizzazione dei contorni del VOI sulla CBCT può rendere possibile la correzione inter-frazione della mobilità d organo on-line

LA CBTC PUO MOSTRARE RISPOSTA PRECOCE DELLA LESIONE IRRADIATA DURANTE IL TRATTAMENTO

Deformazione OAR vescica Deformazione dll OAR retto

RCCBCT (Respiratory Correlated cone beam Tc) Durante l acquisizione fluoroscopica vengono selezionate serie di data sets ciascuna in relazione con 8 diverse fasi respiratorie (Utilizzando le diverse posizioni del diaframma) Un apposito sistema è stato sviluppato per utilizzare la RCCBCT per valutare le modificazioni indotte nella distribuzione della dose in confronto alla pianificazione statica basata sulla Tc di centraggio

KV Cone-Beam TC ESPERIENZE CLINICHE F. Casamassima L.Masi I.Bonucci C.Polli C.Menichelli U.O. RADIOBIOLOGIA CLINICA UNIVERSITA DI FIRENZE

On-line positioning corrections using a cone beam CT for extracranial stereotactic treatments Four years experience in extracranial stereotactic treatments; A body frame used for generating isocenter coordinates and for patient set-up. Prior to January 2006 positioning checked by CT simulation and electronic portal imaging. From January we started to acquire at each fraction a cone beam CT volumetric image (Synergy-Elekta XVI). The CBCT is registered to the reference CT used for planning (GE Lightspeed 16 slices): corrections for isocenter positioning The displacements predicted by XVI are compared with the isocenter position found by the Body Frame

On-line positioning corrections using a cone beam CT for extracranial stereotactic treatments From January 2006: 40 Patients treated ( 22 lung; 10 abdomen (liver and pancreas); 4 vertebral metastases; 4 other). Fraction ranging from 1 to a maximum of 4 Total doses ranging from 22Gy to 30 Gy

On-line positioning corrections using a conebeam CT for stereotactic treatments A Body Frame is used for generating the isocenter coordinates and for patient set-up Corrections for patient set-up and target motion performed acquiring a kv volumetric imaging with a cone beam CT (XVI-Elekta Synergy) On-line corrections before each fraction (a total of 83 fractions) Analysis of the displacements along the three major axis (lateral, longitudinal, vertical) obtained by the XVI system, respect to the body frame isocenter position

Respiratory organ motion: PTV segmentation 1. Acquisition of two CT data sets respectively in light inhale and exhale 2. Two CTVs created on each CT data set 3. A third CTV created encompassing the previous two 4. PTV obtained adding a further uniform 3 mm margin

Procedures for patient repositioning A group of patients remained immobilized inside the body frame after the reference CT acquisition (used for TPS) and were transported to the Linac using a rigid table. Group A (for a total of 30 sessions) A second group was completely repositioned in the vacuum pillow or the body cast at the linac immediately before treatment delivery. Group B (for a total of 53 sessions)

RESULTS XVI displacements vs. Body Frame isocenter Lateral displacements distribution: Patients who remained immobilized groupa Patients re-positioned group B A Mean=0.12 cm; std.dev=0.33 cm B Mean=-0.09 cm; std.dev=0.58 cm Lateral displacements (X axis) distribution Probability 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0-2.5-2 -1.5-1 -0.5 0 0.5 1 1.5 2 2.5 X displacement cm A B

RESULTS XVI displacements vs. Body Frame isocenter Longitudinal displacements distribution: Patients who remained immobilized group A Patients re-positioned group B A Mean=-0.02 cm; std.dev=0.42 cm B Mean=0.09 cm; std.dev=0.77 cm Longitudinal displacements (Y axis) distribution probability 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0-2.5-2 -1.5-1 -0.5 0 0.5 1 1.5 2 2.5 Y displacement cm A B

RESULTS XVI displacements vs. Body Frame isocenter Vertical displacements distribution: Patients who remained immobilized group A Patients re-positioned group B A Mean=-0.14 cm; std.dev=0.31 cm B Mean=-0.06 cm; std.dev=0.32cm Vertical displacement (Z axis) distribution 0.5 probability 0.4 0.3 0.2 0.1 0-3 -2-1 0 1 2 3 Z displacement cm A B

Extracranial stereotactic treatments: XVI predicted displacements vs. SBF set-up 44 patients Xtot Ytot Ztot (104 fractions) Mean (cm) -0.07-0.08-0.05 St.dev (cm) 0.496 0.56 0.267 Set A: no re-positioning performed XA YA ZA (34 fractions) Mean (cm) 0.10-0.02-0.14 St.dev (cm) 0.315 0.403 0.305 Set B: patient completely re-positioned at the linac XB YB ZB (70 fractions) Mean (cm) -0.15-0.12-0.01 St.dev (cm) 0.546 0.622 0.238

XVI displacements vs Body frame isocenter possible explanations for observed differences Repositioning the patient: The distributions of displacements along the lateral (X) and longitudinal (Y) directions show larger std.dev for group B (repositioned at the linac) than for group A. No effect observed for the vertical (Z) direction. organ motion: even if the set-up is correct, the cone beam CT can discriminate displacements due to the target motion leading to a different position respect to the Body frame coordinates

Shift of the vacuum pillow inside the body frame, after patient repositioning: reference CT vs. second simulation CT

Shift of the vacuum pillow inside the body frame, after repositioning: reference CT vs. Cone beam CT volumetric acquisition 1. Fiducial bars concide, but the patient is shifted inside the Body-frame 2. After registration fiducial bars are no more coincident. The lateral displacement predicted by XVI coincides with the distance between the bars.

When no shifts of the patient inside the Body frame occurs, the fiducial bars coincide after registration.

kv volumetric images registered on TPS reference CT: Our initial clinical experience for target positioning Lung cases Organ boundary blurred by respiratory motion (CBCT acquisition 90 s) CBCT reproduced a target averaged image over several breathing cycles Lung nodules: after registration visual check of the tumor match is possible (PTV enclosing the CBCT target volume) Registration in a large region (including the vertebrae) Grey-value registration in a restricted region around the target (clipbox)

kv volumetric images registered on TPS reference CT: Our clinical experience for target positioning Lung nodules. Grey values registration and visual check of the tumor and bony structure match. When necessary manual correction.

kv volumetric images registered on TPS reference CT: Our clinical experience for target positioning Lung nodules. Grey values registration and visual check of the tumor and bony structure match. When necessary manual correction.

kv volumetric images registered on TPS reference CT: Our clinical experience for target positioning Lung nodules. Grey values registration around the target: the vertebrae do not match.

kv volumetric images registered on TPS reference CT: Our initial clinical experience for target positioning Abdomen Soft tissue definition for liver and kidneys is fairly good. For target actual positioning definition the use of internal markers (post-surgical clips) may help, although they produce artefacts.

kv volumetric images registered on TPS reference CT: Our clinical experience for target positioning Abdomen. Grey values registration: when possible a check of matching using internal markers (post-chirurgical metal clips) can be very useful.

kv volumetric images registered on TPS reference CT: Our clinical experience for target positioning Abdomen. Manual matching using internal markers (post-chirurgical metal clips) ; bony structures do not match.

kv volumetric images registered on TPS reference CT: Our clinical experience for target positioning Vertebra X-ray volumetric imaging provides excellent definiton of bony structures.

Comparison of XVI and IviewGT results on Patients: Difference between KV and MV results along the three axes N= 16 X Y Z Mean mm -0.2 0.8 0.2 SD (mm) 2.6 1.6 2.0

CONCLUSIONS The use of a body frame is a good starting point for patient set-up. Since the Body Frame is not rigidly fixed to the patient, large errors can occur in set-up if the patient is completely re-positioned after the reference CTscan Image guidance is always needed to check the setup. X-ray volumetric image quality superior for bone and soft tissue definition respect to EPI X ray volumetric imaging permits a global correction: set-up and organ motion

cranial stereotactic treatments: XVI predicted displacements vs. stereotactic frame set-up X Y Z Total displacement 22 patients (47 fractions) Mean (cm) 0.01-0.20-0.08 0.44 St.dev (cm) 0.1 0.44 0.18 0.29

La CBCT può essere esportata al TPS per rivalutazione della distribuzione della dose programmata

Sulla CBCT può essere ripianificato il trattamento con relativi DVH ADAPTIVE RADIOTHERAPY

CTV e PTV iniziali

Conebeam CT in trattamento: copertura dei relativi CTV 1 2 3 4

Inviluppo Convesso dei 5 CTV

Inviluppo di 5 CTV senza margini ulteriori

DVH CTV0 e CTVenvelope

DVH parete rettale su 7 cone beam CT con piano iniziale

IGART : SCHEMA PROGETTO DI PROTOCOLLO ( Fase online ) Set-up del Paziente Registrazione della Cone-Beam Tc Registrazione della posizione attuale Correzione del set-up (Utilizzo dello scheletro) CORREZIONE ERRORI SISTEMATICI MEDI DOPO5 fx

SCHEMA PROGETTO DI PROTOCOLLO ( Fase offline ) Set-up del Paziente Registrazione della Cone-Beam Tc Registrazione della posizione attuale Correzione del set-up (Utilizzo della scala dei grigi) Nuovo contornamento Target e VOI su cone-beam Tc Nuovo PTV sul risultato del valore medio degli errori random su 5 Fx

Nuovo PTV sul risultato del degli errori random su 5 Fx valore medio della Posizione della prostata e shape medio del retto NUOVO PIANO CONTROLLO SETTIMANALE

Use of a motion tracking system in the thoracic and abdominal regions: evaluation of uncertainty in off-target dose distribution and optimization strategies Franco Casamassima,, MD University of Firenze, Italy SBRT2006 Copenhagen June 15-17, 2006

Treating moving targets The high conformity achievable with the CyberKnife may lead to problems with the coverage of targets that move during normal breathing.

Treating moving targets before Synchrony Three possible solutions: 1. PTV ENLARGEMENT bigger volumes 2. GATED X-RAY X DELIVERY longer times 3. TRACKING ideal solution?

Treating moving targets before Synchrony Before introduction of Synchrony, we solved the problem of respiration by drawing the target contours on the basis of two different CT data sets: 1. breath holding at the end of normal inspiration 2. breath holding at the end of normal expiration

Treating moving targets before Synchrony The final contour of the PTV is obtained by joining the contours outlined on the two CT data sets corresponding to inspiration and expiration. By this solution the final PTV is obviously enlarged.

Treating moving targets with Synchrony With Synchrony, the problem of target motion during the respiratory cycle is overcome by real-time tracking. As we don t t need to draw expanded target contours, the PTV is reduced.

Treating moving targets with Synchrony We evaluated the mean reduction of PTV allowed by Synchrony with respect to the join of targets in some significant clinical situations: LIVER mean reduction 38% (3 cases) LUNG mean reduction 44% (4 cases) PANCREAS mean reduction 8.5% (3 cases)

Treating moving targets with Synchrony The reduction of PTV leads to reduction of NTCP Organs at risk that were considered: LIVER KIDNEY LUNG DUODENUM ESOPHAGUS SPINAL CORD

Treating moving targets with Synchrony Normal Tissue Complication Probability (NTCP) OAR Liver (liver treat.) average Lung most significant reduction Join of targets 23.1 % 2.5 % Synchrony 14.5 % 0.1 % NTCP for organs at risk was calculated using the Lyman model with correction for fractionation.

Treating moving targets with Synchrony Equivalent Uniform Dose (EUD) OAR Kidney most significant reduction Spinal cord most significant reduction Join of targets 3.0 Gy 31.8 Gy Synchrony 0.0 Gy 0.0 Gy EUD (corrected for fractionation) was compared in the cases that showed negligible NTCP in both join of targets and Synchrony methods.

PTV enlargement vs. Synchrony: possible uncertainty on dose to OAR Join of targets Synchrony

PTV enlargement vs. Synchrony: possible uncertainty on dose to OAR 25 20 Volume (cc) 15 10 5 0 0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 Dose (Gy)

Target tracking: uncertainty on the dose to OAR 6 patients including lung with Synchrony Treatment plan on full exhalation CT Dose distribution recalculated on full inhalation CT by relocating the set of beams according to the displacement of fiducial markers Dose to OAR: D ave ave =1/3D inh +2/3D exh

Target tracking: uncertainty on the dose to OAR max Dose spinal cord (cgy) D Exh 73.8 D Inh 109.8 D ave 82.1

PTV enlargement vs. Synchrony: need for a CT time series Expiration Inspiration

Treating moving targets Particular attention should be paid to the sum of lower isodose values in the treatment of multiple targets that move with respect to each other (typically for treatments of pancreas with concurrent liver metastases). with Synchrony In such cases dynamic treatment planning is expected to give major contributions.

PTV enlargement vs. Synchrony: need for a CT time series The situation is more complex when the PTV moves with respect to more than one OAR. A more accurate estimation of dose to OAR may be calculated using a full 4DCT time series, allowing dynamic treatment planning to be performed.

Conclusions In our experience the CyberKnife confirms itself as a high accuracy, high precision therapy system thanks to: image guided inter- and intra-fraction control automatic correction of setup inaccuracies Non-isocentric treatment delivery allows high conformity to be achieved for irregular targets

Conclusions Synchrony is an additional tool that improves the precision of the CK system, overcoming the problem of organ motion, but we must remember that: only respiratory motion is corrected for if treatment planning is not based on a full 4D dataset, uncertainty on the dose distribution may take place due to lack of coherence between movements of PTV and OAR Needed solution: : DYNAMIC TREATMENT PLANNING