1. No category

CTOS 14.11.08
Soft Tissue Sarcoma of the Extremity
Comparison of Conformal Post-operative
Radiotherapy (CRT) and Intensity Modulated
Radiotherapy (IMRT)
Young K Lee1, Alexandra J Stewart2, Frank H Saran3
1Joint
Department of Physics, Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK
2St Luke’s Cancer Centre, Royal Surrey County Hospital, Guildford, Surrey, UK
3Department of Radiotherapy, Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK
CRT and IMRT for extremity STS
 Background
 Materials and Methods
 Results
 Summary
CRT and IMRT for extremity STS
 Background
 Materials and Methods
 Results
 Summary
Background
 Limb-sparing surgery in combination with focal
radiotherapy - standard of care in patients with
intermediate and high grade limb and limb girdle
soft tissue sarcomas (STS)
 Normal tissue toxicity increases with escalating
total and integral dose
 Dose prescription limited by organs-at-risk (OAR)
surrounding the PTV
Aims
 To define a reproducible and comparable target
volume definition for CT planning
 To define reproducible prospective planning dose
volume constraints
 To assess the ability of inversely-planned IMRT
plans to minimise the dose to surrounding OAR
 To assess efficacy of ‘simple’ IMRT compared to
‘complex’ IMRT planning
CRT and IMRT for extremity STS
 Background
 Materials and Methods
 Results
 Summary
Patient data
 T2 and G2/3 STS of the thigh (n=10)
 No tumours invading bone
 Entire surgical scar and all drain sites marked
 Planning CT scan (GE HiSpeed QX/i, Milwaukee, WI)
• pelvic brim to below knee
• customised immobilisation
• slice thickness = 2.5mm
Target volume definition
 Phase I volume
PTV1 = tumour bed + 5cm SI and 3cm
circumferentially
 Phase II volume
PTV2 = tumour bed + 2cm isotropically
 OAR defined as whole femur, neurovascular
bundle, normal tissue corridor and normal tissue
outside PTV1
Planning target volumes
PTV1
PTV2
Organ definition
neurovascular bundle
PTV2
PTV1
whole femur
normal tissue
outside PTV1
tissue corridor
Radiotherapy planning
 Primary planning objective
• PTV dose
• femur
• skin corridor
 Other planning objectives
• neurovascular bundle
• soft tissue outside PTV
Dose prescription
 Pinnacle3 v7.4f (Philips Radiation Oncology
Systems, Madison, WI)
 2-phase 3D-CRT
• Ph I - 50 Gy/25# (5 weeks)
• Ph II - 16 Gy/8# (1½ weeks)
 IMRT with simultaneous integrated boost (SIB)
• Ph I - 50 Gy/25# (5 weeks)
• Ph II - 62.5 Gy/25# (5 weeks) (/ = 10 Gy)
Analysis
 cumulative dose volume histograms (DVH)
 Dmean, Dmax, Dmin
 Conformity Index (CI)
 Heterogeneity Index (HI)
CRT and IMRT for extremity STS
 Background
 Materials and Methods
 Results
 Summary
Conformal
2-34-5
field
(simple)
Radiotherapy
field
IMRT IMRT
sagittal view
conformal
2-3f
4-5f IMRT
coronal view
conformal
2-3f IMRT
4-5f IMRT
Conformity and Heterogeneity
3DCRT
Mean
Conformity p-value
Index (range)
1.76
(1.48-2.47)
2/3f
IMRT
1.59
(1.15-2.67)
4/5f
IMRT
1.33
(1.08-1.84)
Mean
Heterogeneity p-value
Index (range)
1.052
(1.031-1.065)
0.02
1.045
(1.029-1.063)
0.06
0.0002
1.036
(1.027-1.049)
0.001
DVH summary
‘Simple’ 2-3f IMRT?
 Median number of segments
• 26 (range 13-37) for 2-3f IMRT
• 36 (range 34-56) for 4-5f IMRT
 Both IMRT plans were more conformal and less
heterogeneous than 3D-CRT
 Both IMRT delivered significantly lower femur V45
compared to 3D-CRT plans
 HOWEVER, 4/5f IMRT resulted in significantly
lower femur V45 when compared directly to 2/3f
IMRT (p=0.04)
CRT and IMRT for extremity STS
 Background
 Materials and Methods
 Results
 Summary
Summary
 Reproducible, comprehensive planning guidelines
and dose-volume constraints for 3D planning for
extremity sarcomas devised
 4/5f IMRT plan - lowest clinically relevant doses to
OAR whilst delivering conformal doses to PTV
 Large primary tumour
• 4/5f preferable to a 2/3f IMRT approach
 Small, superficial disease
• 3D-CRT may provide adequate
added cost and complexity
treatment
without
Further work
 Results from this study may not be directly
translated to all other primary locations of STS of
the extremity
 IMRT approach should be assessed prospectively
with respect to late toxicity within the confines of
a prospective clinical trial
Acknowledgment
Radiotherapy Department
Royal Marsden NHS Foundation Trust