Comparing planning time, delivery time and plan quality for IMRT, RapidArc and Tomotherapy

Abstract

The purpose of this study is to examine plan quality, treatment planning time, estimated treatment delivery time and other dose metrics for 5 and 9 field sliding window IMRT (IMRT5 and IMRT9), single and dual arc Rapid Arc (RA1 and RA2) and Tomotherapy (TOMO). Four cylindrical virtual phantoms were created each with its own distinct set of contours. The contour sets were 2D contours on the axial slice extended in the superior-inferior direction. The prescription dose in all cases was 2 Gy per fraction. IMRT plans were created with 5 or 9 equally spaced beams and RA plans were created with either 1 or 2 complete rotations of the gantry. TOMO plans were created with typical planning parameters. Plans were evaluated based on the ability to meet dose-volume constraints, dose homogeneity index (DHI), radiation conformity index (RCI), planning time, estimated delivery time, integral dose and volume receiving more than 2 and 5 Gy. For all of the phantoms, TOMO was able to meet the most optimization criteria during planning (2/4 for P1, 4/6 for P2, 0/8 for P3 and 2/4 for P4), the second most were met by RapidArc (1/4 for P1, 1/6 for P2, 0/8 for P3 and 0/4 for P4) while IMRT was never able to meet any of the constraints. In addition, TOMO plans were able to produce the most homogeneous dose (DHITomo=0.88±0.02, DHIRA2=0.87±0.02, DHIRA1=0.85±0.01, DHIIMRT9=0.82±0.01, DHIIMRT5=0.82±0.06). This improved plan quality comes with some costs including longer planning time (tplan,Tomo= 58.5±28.3 min, tplan,RA2= 54.8±7.3 min, tplan,RA1= 41.5±9.8 min, tplan,IMRT9 = 8.1±0.7 min, tplan,IMRT5= 6.9±0.3 min), longer estimated treatment times (ttreat,Tomo= 3.5±0.7 min, ttreat,RA2= 2.8±0.0 min, ttreat,RA1= 1.5±0.2 min, ttreat,IMRT9 = 5.5±0.4 min, ttreat,IMRT5= 4.0±0.2 min), lower conformity index (RCITomo=0.81±0.07, RCIRA2=0.92±0.01, RCIRA1=0.90±0.01, RCIIMRT9=0.88±0.07, RCIIMRT5=0.81±0.06) and higher integral dose (about 1.2 times higher than RA and IMRT). Tomotherapy plans can produce plans of higher quality and have the capability to conform dose distributions more than IMRT or RA in the axial plane but exhibit increased dose superior and inferior to the target volume. RA however is capable of producing better plans than IMRT for the test cases examined in this study. Users should understand that TOMO plans come with some costs that may impact efficiency. Further studies are necessary to validate these conclusions for clinical geometries and phantom studies where the target and organ at risk shapes vary in the superior-inferior direction.