Accumulation of rectum dose‐volume metrics for prostate external beam radiotherapy combined with brachytherapy: Evaluating deformably registered dose distribution addition using parameter‐based addition

Abstract

Distribution-adding was confounded by unsystematic inter/intra-observer rectum-contouring errors and registration accuracy near the anterior rectal wall. Consequently, clinical use of distribution-adding to assess rectal doses requires careful contour and registration evaluation.

Use of deformable image registration techniques to estimate dose to organs at risk following prostate external beam radiation therapy and high-dose-rate brachytherapy

“…HDR-BT doses were first converted to an equivalent dose in 2 Gy fractions (EQD 2 ) on a voxel-by-voxel basis, using α/β function in MIM software, which is based on the linear quadratic model [ 7 , 12 , 22 ] and given by:…”

“…where n is the number of fractions, d is the dose per fraction, and α/β is the cell fractionation sensitivity [ 23 , 24 ]. The prostate α/β was taken to be 1.5 Gy [ 7 , 24 , 25 ], and 3 Gy for the rectum [ 7 , 12 , 13 , 15 ].…”

“…One dose estimation approach called “parameter addition” includes full parameter addition (FPA) and partial parameter addition (PPA) [ 12 , 13 ]. FPA, also known as the “overlapping high-dose method”, adds together the maximum dose from the dose-volume histogram from each fraction in the dose accumulation approximations [ 12 , 13 , 14 , 15 ]. PPA is similar to FPA, except for the dose to target volume, which is considered homogeneously distributed [ 10 , 13 ].…”

“…There have been many studies in the field of brachytherapy in recent years that have investigated how DIR dose estimation compares to parameter addition methods. For example, DIR has been applied to dose accumulation for combined EBRT and BT treatments of the cervix [ 13 , 18 ], and the prostate [ 12 , 19 , 20 ]. However, the afore-mentioned studies dealt with image registrations between the same modality or computed tomography-magnetic resonance imaging (CT-MRI), which have the problem of anatomical differences such as rectal filling [ 12 , 13 , 18 , 19 ], rather than the unique challenge faced by deformation of TRUS probe placed in the rectum.…”

Deformable image registration for radiation therapy: principle, methods, applications and evaluation

“…The use of DIR has also allowed the decrease in rectal dose when using a rectal balloon to be quantified (70% of patients showed a decrease of more than 5% in the normal tissue complication probability, NTCP) [100]. Moreover, DIR can be used to accumulate the rectal dose of EBRT and high-dose-rate (HDR) BT [101]. The accumulated dose was higher when using DIR (21.3% for D 0.1cc , 6.3% for D 1cc and 3.5% for D 2cc ) than that given by the direct addition of the DVH.…”