12th Varian Oncology Summit

Adaptive treatment strategies in head & 

neck and pelvic regions - The Aarhus 

experience with the DART prototype 

U. V. Elstrøm, M. Thor, S. Thörnqvist, L. P. Muren, 

J. B.B. Petersen and C. Grau 

Department of Oncology & Department of Medical Physics 

Aarhus University Hospital, Aarhus 

Denmark 

12 th Varian Oncology Summit 

Berlin, October 2011

Outline 

� Dynamic Adaptive Radiotherapy – DART 

� Short introduction 

� Illustrative case 

� Ongoing evaluation 

� Head and neck 

� Pelvis 

� Conclusions 


2

Background 

Adaptation (ART): 

� Treatment process in which subsequent delivery can be 

modified using a systematic feedback of the geometric and 

dosimetric information from previous fractions. 

� Based on 3D volumetric information (soft tissue contrast) 

� Requires many techniques such as 

� image registration (deformable!) 

� re-contouring volumes (auto-segmentation!) 

� dose reconstruction 

� dose accumulation 

� treatment evaluation (thresholds!) 

� re-optimization (new treatment plan) 


3

The DART prototype 

� Eclipse 10.0 treatment planning (incl. Acuros) 

� SmartAdapt 10.0 

� CBCT to pCT registration: 

• Rigid online match (for plan copy) 

• Deformable for dose accumulation 

� pCT to CBCT registration: 

• Rigid (for structure COM) 

• Deformable for structure propagation 

� Dose accumulation tool 

� Improved CBCT image reconstruction 

Manual import of planning and repeat CT’s, treatment plan, CBCT’s with online 

registrations and/or raw CBCT projections for improved reconstruction 


4

Head and neck case 

� 70 years old male 

� Recurrent lip cancer - T1N2M0 

� 6-field IMRT SIB - 66/60/50 Gy in 33 fx. 

� Daily CBCT for setup correction; mid-course CT 

� All relevant structures in CBCT field-of-view 


5

Registrations in SmartAdapt 

pCT 

Daily 

CBCT’s 

Rigid 

pCT vs. 

CBCTfx33 


6

Registrations in SmartAdapt – smooth algorithm 

Deform 

pCT vs. 

CBCTfx33: 

Contourpropagation 


7

Registrations in SmartAdapt 


Rigid (ONLINE) + Deform for dose accumulation 

Rigid + Deform for contour propagation 

• 4 x 33 registrations ! 

• Average 8:30 min per fx incl. review & DFC 

• Time per fx increases with deformation 

(system crash after 2-3 registrations �) 

8

Volume statistics in SmartAdapt 


9

DART prototype – dose accumulation 

Dose Record1: Re-calculated 

fractional dose on CBCTfx1 


Original treatment plan 

Non Adapted plans 

=> Re-calculation 

Cumulative1: fx1 dose on pCT 

10


Original treatment plan 


• 3 x 33 plans in Eclipse 

• Approx. 1 min per fx 

Using Adapted plans the consequences of 

various adaptive strategies can be simulated 

- difficult in current version due to 

system crashes � 

Cumulative33: All fx doses on pCT 

11


Daily dose & 

accumulated dose 

in less than 10 min 

per fraction !!! 

Similar evaluation using external DIR software: 

approx. 45 min per treatment fraction 

Elstrøm et al., 2010 


12

Dose accumulation – what was delivered ? 


left parotid 

right parotid 

spinal cord 

PVT/ 

CTV 50 

PRV spinal cord 

PVT/ 

CTV 60 

PVT/ 

CTV 66 

13

Effect of CBCT image quality ? 

� Head and Neck 

� (Thorax and pelvis under investigation) 


14

Improvements in CBCT (diagnostic) 

image quality 

� Two CBCT image reconstruction methods 

� Standard clinical (OBI) 

• Uses phantom for beam hardening and scatter correction 

� Pre-clinical “Full Fan Experimental” (FFE) using an 

adaptive pencil beam based scatter correction algorithm 

• Asymmetric scatter kernels to correct for object size, objects 

edge effects, detector scatter and anti-scatter grids 

• Analytical beam hardening correction based on models of beam 

spectrum, filtration in bow tie and object, and detector 

response 

Details in 

Sun and Star-Lack PMB 55 (2010) p6695 

Star-Lack et al. Proc SPIE (2009) p7258 


Elstrøm et al., 2011 

15

HU-EDR calibration 

in CT vs. CBCT 

Relative Electron Density Ratio (EDR) 

2.0 

1.8 

1.6 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

Catphan 

1.0 

the treatment planning system 

0.9 

-150 -100 -50 0 50 100 150 200 250 300 

0.0 

-1000 -500 0 500 1000 1500 2000 

12th Varian Oncology SummitCalculated 

CT-number (HU) 

Relative Electron Density Ratio (EDR) 

1.2 

1.1 

CT Gammex 

All these curves goes into 

for dose calculation 

Calculated CT-number (HU) 

Elstrøm et al., submitted 2011 

CT PMMA16cm 

CT CIRS 

HQHOBI PMMA16cm 

HQHFFE PMMA16cm 

HQHFFE CIRS 

HQHOBI CIRS 

16

CBCT vs. CT dose calculation 

� 8 head and neck cancer patients 

� Treated July09 – Nov10 on the same Trilogy unit with IMRT 

and daily CBCT (OBI v1.4) 

� A high-quality head (100kV/80mA/25ms) CBCT were 

performed within hours of the mid-course CT 

� CT and CBCT in OBI and FFE reconstruction auto-segmented 

from pCT 


Patient Gender Age Site T N 

Dose (Gy) 

CTV1/CTV2 

1 male 70 Recurrent lip cancer T1 N2 66/60 

2 female 68 Right parotid T2 N1 66/60 

3 male 59 Oropharynx (tonsil) T3 N2b 68/60 

4 male 56 Oral cavity (retromolar) T3 N2b 68/60 

5 male 45 Unknown primary Tx N2a 66/60 

6 female 65 Unknown primary Tx N2b 66/60 

7 female 54 Unknown primary Tx N3 68/-- 

8 male 64 Hypopharynx T3 N2b 68/60 

17

Auto-segmented volumes in CBCT vs. CT 

Volumes in CBCT were generally 2-5% smaller 

than CT volumes, largest for the mandible. The 

experimental FFE reconstruction algorithm 

reduced the difference slightly. 


18

Dose calculation in CBCT vs. CT 

The average difference between CT-based and CBCT-based 

dose calculation were well within 2% for all relevant DVH 

parameters in both CTVs and normal tissues 


19

Auto-segmentation in Pelvis CT’s 

� 4 prostate cancer patient with 8-10 repeat CT’s 

� Manual segmentation vs. SmartAdapt 


Thörnqvist et al., 2010 

20

Auto-segmentation in Pelvis CBCT’s 

� 5 prostate cancer patient with 6-8 repeat CBCT’s 

� Manual segmentation vs. SmartAdapt 


Thor et al., 2011 

21

Association between quantitative and 

qualitative scoring in both studies 

� Bladder 


CT CBCT 

22

Dose accumulation 


23

Conclusions 

� DART prototype offers considerable improvements 

in the workflow involved in ART 

� Tool for developing future adaptive strategies 

� First step – what do we deliver today? 

� Improvements needed: 

� Stability 

� Larger FOV in CBCT – stitching of more scans 

� Further developed deformable image registration 

� Diagnostic image quality in CBCT 


24

“Future aspect” – Adaptive proton therapy? 

� Proton range decisive for dose distribution -> anatomical 

changes may cause major change in target and organ 

DVH 

� Treatment adaptation very important in proton therapy 

� Modern hospital based proton facilities: 

� Huge investment - calls for high throughput 

� Integrated software to handle workflow (re-planning) 

efficiently. Like DART… 

� Varian ProBeam equipped with CBCT for patient setup 

approaching diagnostic image quality for direct 

calculation of proton range 


25

12th Varian Oncology Summit

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