Automated Weekly Online Replanning for IMRT of Cervix Cancer

Abstract

Gy/2-2.5 weeks), and mid-RT (at 45-50 Gy/4-5 weeks). The time-signal intensity (SI) curve and the plateau SI were derived for each tumor pixel of each DCE MRI. The poorly perfused tumor subregions were quantified as lower 10th percentiles of SI among the tumor pixels (SI10). Outcome endpoints, local tumor control and disease-free survival, were correlated with perfusion parameters of the pre-RT, early RT, and mid-RT MRI. Median follow was 4.6 (range: 0.2-9.0) years. Results: Patterns of DCE of the tumor pixels changed during treatment, and the change influenced therapy outcome: In the pre-RT MRI, 16 patients with initial high perfusion (SI10 $ 2.1) had excellent outcome (100% local control and 81% disease-free survival).In28(34%)ofthe82patientswithinitiallylow perfusion(SI10\2.1) onpre-RTMR, thepatternchangedto highperfusion in early-RT (at 20-25 Gy). These patients had an improved local control rate of 93%, compared to those with persistently low perfusion in pre-RT and early-RT MRIs (72%, p = 0.014). If low perfusion persisted to the mid-RT phase (at 45-50 Gy), local control rate decreased further to 66% (p = 0.008). Patients with persistently low perfusion had a disease-free survival rate of 44%, compared to 81% in those with high pre-RT perfusion, and 72% in those with low pre-RT and subsequently high perfusion (p = 0.01). In patients with initially high perfusion pre-RT, a subsequent decrease in SI did not negatively impact on outcome. Conclusions: Tumor perfusion pattern varies during treatment, and such changes critically influence treatment outcome. Persistently low perfusion from the pre-RT through mid-RT phase indicates high risk of treatment failure, while better outcome is associatedwithhighinitial,orhighsubsequentperfusionpatterns,evenwithpriorstatusofpoorperfusion.Ourlimiteddatasuggest thatDCEMRIisaneffectiveandnon-invasivemeanstoassessthetemporalchangesoftumorperfusionstatusduringthetreatment, which may play an essential role in tumor reoxygenation and radioresponsiveness.