Premium
SU‐GG‐T‐03: A Distance to Dose Difference Tool for Estimating the Required Spatial Accuracy of a Displacement Vector Field
Author(s) -
SalehSayah N.K.,
Weiss E.,
Salguero F.J.,
Siebers J.V.
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3468388
Subject(s) - nuclear medicine , dosimetry , mathematics , radiation treatment planning , statistics , computer science , physics , radiation therapy , medicine , surgery
Purpose : To introduce a tool, termed distance to dose difference (DTD), which estimates the required spatial accuracy of displacement vector fields (DVFs) used for mapping lung treatment 4D dose values. Method and Materials : 4D dose mapping pulls dose values from the irradiated geometry to the reference geometry. DVF errors result in dose being pulled from the wrong spatial location in the irradiated geometry, with a dose error equal to the dose difference between the error‐free and sampled spatial locations. The DTD, defined as the distance to observe a given dose or percentage dose difference in the irradiated geometry, quantifies the permitted DVF error to ensure a pre‐specified desired dose mapping accuracy is achieved. To demonstrate the DTD and its dependence on dose conformity, plans are generated with the CTV as the target and with a 1 cm CTV‐PTV margin for an IMRT lung patient. DTD is evaluated for 330 cGy, 5 % of the 66 Gy prescription dose. DTDs are loaded into the treatment planning system to visualize positional dependencies of permissible DVF errors overlaid on the patient's anatomy. DTD‐volume‐histograms are generated. Results : Tolerated DVF errors vary with plan conformity. Outside of irradiated geometric regions, DVF uncertainties up to 9 mm are tolerated before introducing 330 cGy dose mapping errors. Inside the irradiated volume, excluding the CTV, 1–4 mm errors are tolerated for the PTV plan and 1–2 mm for the CTV plan. Within the CTV, the CTV‐based plan tolerated larger DVF errors than the PTV plan due to better target dose homogeneity in the CTV plan. Conclusions : The DTD tool provides a first estimate of DVF required spatial accuracy. Accurate DVF's (∼1 mm) are required in dose gradient regions, but large DVF errors are acceptable in homogenous dose regions. Conflict of Interest : Supported by NIH‐P01CA116602 and Philips Medical Systems