[High dose for prostate irradiation with image guided radiotherapy: contribution of intensity modulation arctherapy].
OBJECTIVE
To compare two Intensity Modulated Radiation Therapy (IMRT) techniques for prostate cancer: the Volumetric Modulated Arc Therapy (VMAT) and the "Step and Shoot" technique (S&S).


METHODS
VMAT and S&S plans (RX 18MV) were created and compared (Wilcoxon test) for 10 patients. The dosimetric goal of both treatments was to deliver 46 Gy to the seminal vesicles and 80 Gy to the prostate, while respecting the dose constrains in the organs at risk of toxicity. For one patient, the two techniques were compared for dose painting and escalation in target volumes defined on MRI and registered thanks to intraprostatic fiducials.


RESULTS
VMAT, compared to S&S, offered: an increase of the PTV2s (prostate) volume receiving 77 to 80 Gy and a decrease of V(82) and V(83); a decrease of V(4) to V(6), V(16) to V(23), and V(69) to V(73) for the rectal wall; a decrease of V(25) for the bladder wall; a decrease of V(21) to V(43) for the femoral heads; a decrease of V(26) to V(44) and V(72) to V(80) but an increase of V(1) to V(21) and V(49) to V(60) for the healthy tissues. The Conformal Index "COIN" was better with VMAT than S&S (0.60 to 0.66). The delivered MU were significantly reduced with VMAT (8% mean) as well as the delivery time (4 min to 1.5 min). VMAT allowed delivering theorically 90Gy in the peripheral zone and 100 Gy in the tumor.


CONCLUSIONS
In case of prostate irradiation, VMAT shows improvement compared with S&S. In particular, organs at risk are better spared, the delivery time is shortened and the number of delivered UM is decreased.
Jouyaux
F
F
Centre Eugène-Marquis, rue de La Bataille-Flandres-Dunkerque, CS 44229, 35042 Rennes cedex, France.
De Crevoisier
R
R
Manens
J-P
JP
Bellec
J
J
Cazoulat
G
G
Haigron
P
P
Chira
C
C
Le Prisé
E
E
Lafond
C
C
D000230:Adenocarcinoma / Q000532:radiotherapy*; D005270:Femur Head / Q000473:pathology / Q000528:radiation effects; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009929:Organ Size; D058958:Organs at Risk / Q000473:pathology / Q000528:radiation effects*; D011467:Prostate / Q000473:pathology / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000473:pathology / Q000528:radiation effects; D012669:Seminal Vesicles / Q000473:pathology / Q000528:radiation effects; D001743:Urinary Bladder / Q000473:pathology / Q000528:radiation effects