Comparison of the Effect of Prone versus Supine Patient Immobilization on Intrafraction Prostate Displacement Monitored by Real-time Electromagnetic Tracking

Abstract

following parameters were analyzed: age, history of pelvic surgery, anticoagulant therapy (ACT), diabetes, tumor characteristics, total dose, dose/fr, CTV, PTV and DVHs. Univariate (UVAs) and multivariate analysis (MVAs) were used to identify parameters impacting on RTOG grade $2 toxicity and bleeding. Logistic regression was used for the analysis of 5-year toxicity and bleeding. Significant thresholds were identified by ROC analysis. Results:Median follow-upwas65 months(range: 6to161).Medianage was70years(45-83). Historyofpelvicsurgery, ACTand diabetes were observedin 12%, 21% and 6% of pts, respectively. Five-year grade $2 toxicity probabilities were: 15% (IC 95%: 822%),18%(IC 95%:10-25%)and26%(IC 95%:16-36%)forptsreceiving70Gy(2Gy/fr), 70Gy(2.5Gy/fr)and80Gy(2Gy/fr), respectively.Intheentireseries:ACTincreasedtheriskofrectalbleeding(p= 0.03;RR= 1.7).Totaldoseof80Gycomparedto70 Gy increased the 5-year grade $ 2 toxicity risk (OR = 3.35; p = 0.04). In the 70 Gy (2 Gy/fr) pts series, UVAs revealed that rectal wall volumes (in %) corresponding to 70 Gy (V70) increased the risk of bleeding (p = 0.04; RR = 1.1). Rectal wall V69 in % (p = 0.03; RR = 1.1) as well as age (p = 0.04; RR = 1.2) increased the risk of grade $ 2 toxicity. In the 80 Gy pts series, UVAs shows that rectal wall V41 to V73 (in %) and V52 to V69 (in %) increased the risk of grade $ 2 toxicity and bleeding, respectively (p\0.05). Rectal wall V63 (in %, as continuous variable) was predictor of toxicity (p = 0.002; RR = 1.1) and rectal bleeding (p\0.02; RR = 1.1). The RR for grade $ 2 toxicity and bleeding were 5.3 and 3.2 respectively, if V63.32% (p\0.02); median value of V63 being 32%. Whole rectal volume DVHs were not correlated with toxicity. Conclusions: Use of ACT increased the risk of rectal bleeding. Total dose of 80 Gy increased the risk of late rectal toxicity. Rectal wallDVHs(in%onlyandnotinwholevolume)weresignificantlycorrelatedwithtoxicity(V69incaseofatotaldoseof70Gyand V41 to V73 in case of 80 Gy). Recent techniques such as intensity modulated and image guided radiotherapy should be used to decrease rectal dose and therefore complications.