Simultaneous integrated boost on hypoxic region by means of setup errors for pancreatic cancer SBRT / 中华放射医学与防护杂志

ABSTRACT

Objective To assess the dosimetric impact on the target volumes and organs at risk ( OARs) using simultaneous integrated boost ( SIB ) for the hypoxic regions of the pancreatic cancer patients treated with stereotactic body radiotherapy ( SBRT ) , and to predict an optimal way of SIB. Methods The setup corrections guided by 100 sets of CBCT scans of 10 patients previously treated with SBRT were imported to the treatment planning system ( TPS ) to recalculate the dose to the target and OARs. Two tumor control probability ( TCP ) models were applied to calculate the TCP under various hypoxic situations. The correlations between the TCP and target dose were analyzed. Results Without setup corrections, the PTV and ITV were underdosed by 8. 9％ and 9. 2％ on average respectively relative to planed dose. With setup corrections, the mean dose to PTV and ITV coverage were 1. 6％ and 1. 3％lower than planned respectively. The mean deviations of OAR dose were between -0. 11 Gy and 0. 26 Gy for all plans. The predictive values of Dmean on hypoxic regions were 31. 4, 34. 0 and 37. 2 Gy (Niemierko model) or 31. 6, 33. 9 and 37. 2 Gy (Poisson model) when the oxygen enhancement ratios (OERs) were 1, 1. 5 and 3 respectively. Conclusions With CBCT setup corrections, the dosimetric impacts of setup errors on the target and OARs can be neglected. Significant deviations of TCP calculation were observed without accounting for tumor hypoxia. To counteract the impacts of hypoxia, the mean dose to the hypoxic regions should be at least 1. 24 times of prescribed dose.