External Beam Radiotherapy Sidsel Damkjr Medical physicist, PhD - - PowerPoint PPT Presentation

A modeling Study of Functional MRI to Individualize Target Definition of Seminal Vesicles for External Beam Radiotherapy Sidsel Damkjær

Medical physicist, PhD NACP, 6-8th of Febuary 2017, Oslo

Motivation

• Prostate cancer pts (high-risk)
• Increased risk of SV invol.
• 78 Gy in 39 frac.
• Internal markers
• SV PTV 11.4 mm*
• Rectal tox
• Subvol of SV with tumor

characteristics

• T2w, DWI & DCE MRI
• Treatment plans (24 pt)
• Evaluate rectal NTCP ≥ 2 & TCP

* de Boer J, Herk M, Pos FJ, et al., Int J Radiat Oncol Biol Phys 2012:86; 177-182.

Craniel Caudal Anterior Posterior

Identify the subvol. with MRI

MRI positive vol → pt T2 and DWI/DCE MRI negative pt Remaining Not trying to identify the true vol

T2 weighted DWI (ADC map) DCE (Ktrans map)

MRI positive patient – transverse view

Bladder Rectum

DWI (ADC map) DCE (Ktrans map) T2 weighted

Treatment plans

GTVs transferred from MRI

• CTV: MRI+ in SV & P
• CTV: SV & P
• CTV: SV & P
• PTV: MRI+ SV 11 mm
• PTV: SV 11 mm
• PTV: SV 7 mm ‘std’

PTV prostate: 5 mm (LR),5 mm (AP),7 mm (CC)

CT, transverse view

Comparison

NTCP: rectal tox. grade ≥ 2, LKB model TCP: logistic model with TCP(78Gy)=0.80 Assume: TCP is driven by the coverage of the PTV for the MRI positive volume Reason: to include motion of SV over a treat. course

MRI+ 11 mm plan:

• No difference to NTCP SV 7 mm, p > 0.6
• Lower NTCP compared to SV 11 mm, p < 0.001

NTCP ≥ 2

TCP

MRI+ 11 mm plan:

• Higher TCP compared to SV 7 mm, p < 0.001

Conclusion

• Maintain rectal NTCP ≥ 2

but gain higher TCP

• Would like to identify specific

taget vol. in SV in the clinic from fMRI to benefit from this approach.

Acknowlegements Jakob Borup Thomsen Peter Meidahl Petersen Ivan Vogelius Svetlana Petersen Marianne C. Aznar Jens Peter Bangsgaard Anne Kiil Berthelsen Joen sveistrup

Thank you for your attention

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