Persistently better treatment planning results of intensity-modulated (IMRT) over conformal radiotherapy (3D-CRT) in prostate cancer patients with significant variation of clinical target volume and/or organs-at-risk.
OBJECTIVE
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.


METHODS
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).


RESULTS
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.).


CONCLUSIONS
Dose coverage of the PTV and OAR was better with 3D-IMRT for each patient and remained so after internal volume changes.
Fenoglietto
Pascal
P
Département d'Oncologie Radiothérapie, CRLC Val d'Aurelle-Paul Lamarque, Montpellier, France. pfenoglietto@valdorel.fnclcc.fr
Laliberte
Benoit
B
Allaw
Ali
A
Ailleres
Norbert
N
Idri
Katia
K
Hay
Meng Huor
MH
Moscardo
Carmen Llacer
CL
Gourgou
Sophie
S
Dubois
Jean-Bernard
JB
Azria
David
D
D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D015641:Radiography, Interventional; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D012007:Rectum / Q000528:radiation effects; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D001743:Urinary Bladder / Q000528:radiation effects