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

Identify the subvol. with MRI T2 weighted DWI (ADC map) MRI positive vol → pt T2 and DWI/DCE MRI negative pt Remaining DCE (Ktrans map) Not trying to identify the true vol

MRI positive patient – transverse view Bladder DWI (ADC map) Rectum T2 weighted DCE (K trans map)

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: CT, transverse view 5 mm (LR),5 mm (AP),7 mm (CC)

Comparison NTCP : rectal tox. g rade ≥ 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

NTCP ≥ 2 MRI+ 11 mm plan: • No difference to NTCP SV 7 mm, p > 0.6 • Lower NTCP compared to SV 11 mm, p < 0.001

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.

Thank you for your attention Acknowlegements Jakob Borup Thomsen Peter Meidahl Petersen Ivan Vogelius Svetlana Petersen Marianne C. Aznar Jens Peter Bangsgaard Anne Kiil Berthelsen Joen sveistrup http://iheartguts.com/collections/plush-organs/products/prostate-plush