Direct segment aperture and weight optimization for intensity-modulated radiotherapy of prostate cancer.
OBJECTIVE
To describe the implementation and to evaluate the results of direct segment aperture optimization using the segment outline and weight adapting tool (SOWAT) in intensity-modulated radiotherapy (IMRT) for prostate cancer.


METHODS
14 consecutive, unselected patients with localized prostate cancer were entered in a planning study comparing IMRT without and with the use of SOWAT. The clinical target volume (CTV) consisted of the prostate and seminal vesicles in all cases. To create the planning target volume (PTV), a three-dimensional anisotropic margin (10 mm in craniocaudal direction, 7 mm in both other directions) was used. To compare both plans, physical as well as biological endpoints were considered.


RESULTS
Considering the CTV, SOWAT resulted in a significantly higher minimal dose together with a higher dose to 95% (D(95)) and 90% (D(90)) of the CTV volume (p < 0.05; Figure 2). Target dose homogeneity was significantly improved (p < 0.001). Tumor control probability (TCP) was significantly increased (p < 0.05). Considering the PTV, D(90) was significantly increased (p < 0.05). Target dose homogeneity was significantly improved (p < 0.05; Figure 1). For rectum, the volumes receiving 50 Gy (R(vol50)), 60 Gy (R(vol60)), or 65 Gy (R(vol65)) as well as the mean dose were significantly lowered after SOWAT (p = 0.0001; Figure 3). Rectal normal tissue complication probability (NTCP) was significantly lower after SOWAT (p = 0.005). Probability of uncomplicated local control (P+) was significantly higher after SOWAT (p < 0.0001).


CONCLUSIONS
SOWAT is a powerful planning tool to increase the therapeutic ratio of IMRT for prostate cancer. It leaves the delivery time unchanged, so that treatments can still be delivered within a time slot of 8 min.
Department of Radiotherapy, Gent University Hospital, Belgium. gert@krtkg1.rug.ac.be
Gert
G
De Meerleer
Luc
L
Vakaet
Werner
W
De Gersem
Geert
G
Villeirs
Wilfried
W
De Neve
D012809:Colon, Sigmoid / Q000528:radiation effects; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008962:Models, Theoretical; D011336:Probability; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation; D020266:Radiotherapy, Conformal; D012007:Rectum / Q000528:radiation effects; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder / Q000528:radiation effects