CT-guided intensity-modulated radiotherapy for bladder cancer: Isocentre shifts, margins and their impact on target dose

Dynamic contrast enhanced magnetic resonance imaging of bladder cancer and implications for biological image-adapted radiotherapy

“…The situation is further complicated by the considerable geometrical uncertainties taking place during RT (bladder/tumor motion) for the present patient group [22]. Methods to account for such uncertainties [23] would also need to be included to realize the full potential of a biological adaptive RT approach.…”

The normal tissue sparing potential of adaptive strategies in radiotherapy of bladder cancer

“…Clinically, translational correction of the isocentre is performed by moving the patient, and thus the CTV, in the three possible directions. The optimal CTV position used in strategy b) was found using a previously developed algorithm [7]. Starting with translation of two CTV structures such that their mid points coincided, the algorithm calculated if any further shifting of the repeat CTV relative to the planning CTV would increase the percentage volume overlap between the planning and the repeat CTV.…”

“…To further enable a reduction of the treatment margins used, Burridge et al [5] and Pos et al [6] have both suggested individual adaptation of the PTV based on multiple imaging of the CTV. In addition, a previous study has shown that correction of the isocentric position based on image guided RT (IGRT) could reduce the volume needed to enclose both planning and repeat CTVs [7].…”

The contribution of on-line correction for rotational organ motion in image-guided radiotherapy of the bladder and prostate

“…The planning CT and the related bladder and prostate repeat scan outlines were imported into in-house developed software where the IGRT translations were determined using a previously described methodology [13] and briefly, the following approach was taken. The 3D shift required to find the optimal isocentre position of the repeat scan bladder volume was determined as that which resulted in the smallest volume of the repeat scan bladder volume lying outside the planning scan volume and that was used as the objective function of a minimisation problem.…”

“…A technical solution that is currently given a lot of attention is cone-beam CT imaging (CBCT), where a full 3-D CT data set is reconstructed from multiple conebeam x-ray transmission projections through the patient. In a recent study we showed that there is considerable theoretical potential in terms of margin reduction resulting from the use of translational isocentre corrections based on CBCT-guidance in bladder RT [13]. However, rotations have been show to play a role in the geometric precision of pelvic RT [14] and could be accounted for if using both translational and rotational corrections based on on-line imaging.…”