Rectal complication probability from composite volumes derived from daily cone beam computed tomography in prostate...

The aim of this study is to investigate the rectal complication probabilities for various rectum volumes with intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiotherapy (3D-CRT) in patients undergoing prostate cancer radiotherapy.

Thirteen patients undergoing prostate cancer radiotherapy were consecutively selected for this study. All patients were treated with IMRT to a dose of 78 Gy in 39 fractions. Three different rectum volumes: (i) planned rectum (plan-rectum) (ii) Boolean sum of rectum volume based on the cone-beam computed tomography (CBCT) for first five fractions (planning organ at risk volumes [PRV]-CBCT-5), (iii) Boolean sum of rectum volume from all the CBCTs (PRV-CBCT-All) in addition to an average rectal complication (PRV-CBCT-AV) were used for computing the probabilities of rectal complications. To assess the rectal complications with 3D-CRT, a five-field plan was generated for comparison with IMRT. The Lyman-Kutcher-Burman (LKB) normal tissue complication probability (NTCP) model was used to assess the rectal complications for all of the defined rectal volumes.

The NTCPs for rectum as assessed from plan-rectum, PRV-CBCT-5, PRV-CBCT-All, and PRV-CBCT-AV with IMRT were 9.71% ±4.69%, 16.34% ±9.51%, 19.39% ±9.71%, and 12.81% ±7.22%, respectively. Similarly, with 3D-CRT, the NTCPs were 17.41% ±10.44%, 19.61% ±11.08%, 21.03% ±11.06%, and 17.72% ±10.29%, respectively.

Our results showed that the rectal complications are reduced significantly with IMRT as compared to 3D-CRT. As such, the analyses of NTCP with various defined composite rectum volumes indicate that IMRT requires image-guided adaptive radiotherapy as opposed to 3D-CRT.