Résumé
To compare the dose coverage of planning and clinical target volume (PTV, CTV), and organs-at-risk (OAR) between intensity-modulated (3D-IMRT) and conventional conformal radiotherapy (3D-CRT) before and after internal organ variation in prostate cancer.
We selected 10 patients with clinically significant interfraction volume changes. Patients were treated with 3D-IMRT to 80
Gy (minimum PTV dose of 76
Gy, excluding rectum). Fictitious, equivalent 3D-CRT plans (80
Gy at isocenter, with 95% isodose (76
Gy) coverage of PTV, with rectal blocking above 76
Gy) were generated using the same planning CT data set (“CT planning”). The plans were then also applied to a verification CT scan (“CT verify”) obtained at a different moment. PTV, CTV, and OAR dose coverage were compared using non-parametric tests statistics for V95, V90 (% of the volume receiving ⩾95 or 90% of the dose) and D50 (dose to 50% of the volume).
Mean V95 of the PTV for “CT planning” was 94.3% (range, 88–99) vs 89.1% (range, 84–94.5) for 3D-IMRT and 3D-CRT (
p
=
0.005), respectively. Mean V95 of the CTV for “CT verify” was 97% for both 3D-IMRT and 3D-CRT. Mean D50 of the rectum for “CT planning” was 26.8
Gy (range, 22–35) vs 43.5
Gy (range, 33.5–50.5) for 3D-IMRT and 3D-CRT (
p
=
0.0002), respectively. For “CT verify”, this D50 was 31.1
Gy (range, 16.5–44) vs 44.2
Gy (range, 34–55) for 3D-IMRT and 3D-CRT (
p
=
0.006), respectively. V95 of the rectum was 0% for both plans for “CT planning”, and 2.3% (3D-IMRT) vs 2.1% (3D-CRT) for “CT verify” (
p
=
non-sig.).
Dose coverage of the PTV and OAR was better with 3D-IMRT for each patient and remained so after internal volume changes.