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IMRT: Improvement in treatment planning efficiency using NTCP calculation independent of the dose‐volume‐histogram
Author(s) -
Grigorov Grigor N.,
Chow James C. L.,
Grigorov Lenko,
Jiang Runqing,
Barnett Rob B.
Publication year - 2006
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 - 10.1118/1.2181301
Subject(s) - radiation treatment planning , nuclear medicine , rectum , medicine , dose volume histogram , dosimetry , pinnacle , radiation therapy , prostate , tomotherapy , medical physics , radiology , cancer , surgery
The normal tissue complication probability (NTCP) is a predictor of radiobiological effect for organs at risk (OAR). The calculation of the NTCP is based on the dose‐volume‐histogram (DVH) which is generated by the treatment planning system after calculation of the 3D dose distribution. Including the NTCP in the objective function for intensity modulated radiation therapy (IMRT) plan optimization would make the planning more effective in reducing the postradiation effects. However, doing so would lengthen the total planning time. The purpose of this work is to establish a method for NTCP determination, independent of a DVH calculation, as a quality assurance check and also as a mean of improving the treatment planning efficiency. In the study, the CTs of ten randomly selected prostate patients were used. IMRT optimization was performed with a PINNACLE 3 V 6.2b planning system, using planning target volume (PTV) with margins in the range of 2 to 10 mm . The DVH control points of the PTV and OAR were adapted from the prescriptions of Radiation Therapy Oncology Group protocol P‐0126 for an escalated prescribed dose of 82 Gy . This paper presents a new model for the determination of the rectal NTCP ( NTCP R) . The method uses a special function, named GVN (from G y, V olume, N TCP), which describes theNTCP Rif 1cm 3of the volume of intersection of the PTV and rectum ( R int ) is irradiated uniformly by a dose of 1 Gy . The function was “geometrically” normalized using a prostate‐prostate ratio (PPR) of the patients’ prostates. A correction of theNTCP Rfor different prescribed doses, ranging from 70 to 82 Gy , was employed in our model. The argument of the normalized function is theR int , and parameters are the prescribed dose, prostate volume, PTV margin, and PPR. TheNTCPs Rof another group of patients were calculated by the new method and the resulting difference was < ± 5 % in comparison to the NTCP calculated by the PINNACLE 3 software where Kutcher's dose‐response model for NTCP calculation is adopted.