A dosimetric comparison of tomotherapy and volumetric modulated arc therapy in the treatment of high-risk prostate cancer with pelvic nodal radiation therapy.
OBJECTIVE
To compare the dosimetric results of volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) in the treatment of high-risk prostate cancer with pelvic nodal radiation therapy.


METHODS
Plans were generated for 10 consecutive patients treated for high-risk prostate cancer with prophylactic whole pelvic radiation therapy (WPRT) using VMAT and HT. After WPRT, a sequential boost was delivered to the prostate. Plan quality was assessed according to the criteria of the International Commission on Radiation Units and Measurements 83 report: the near-minimal (D98%), near-maximal (D2%), and median (D50%) doses; the homogeneity index (HI); and the Dice similarity coefficient (DSC). Beam-on time, integral dose, and several organs at risk (OAR) dosimetric indexes were also compared.


RESULTS
For WPRT, HT was able to provide a higher D98% than VMAT (44.3 ± 0.3 Gy and 43.9 ± 0.5 Gy, respectively; P=.032) and a lower D2% than VMAT (47.3 ± 0.3 Gy and 49.1 ± 0.7 Gy, respectively; P=.005), leading to a better HI. The DSC was better for WPRT with HT (0.89 ± 0.009) than with VMAT (0.80 ± 0.02; P=.002). The dosimetric indexes for the prostate boost did not differ significantly. VMAT provided better rectum wall sparing at higher doses (V70, V75, D2%). Conversely, HT provided better bladder wall sparing (V50, V60, V70), except at lower doses (V20). The beam-on times for WPRT and prostate boost were shorter with VMAT than with HT (3.1 ± 0.1 vs 7.4 ± 0.6 min, respectively; P=.002, and 1.5 ± 0.05 vs 3.7 ± 0.3 min, respectively; P=.002). The integral dose was slightly lower for VMAT.


CONCLUSIONS
VMAT and HT provided very similar and highly conformal plans that complied well with OAR dose-volume constraints. Although some dosimetric differences were statistically significant, they remained small. HT provided a more homogeneous dose distribution, whereas VMAT enabled a shorter delivery time.
Département Universitaire de Radiothérapie, Centre O. Lambret, Lille, France. d-pasquier@o-lambret.fr
David
D
Pasquier
Fabrice
F
Cavillon
Thomas
T
Lacornerie
Claire
C
Touzeau
Emmanuelle
E
Tresch
Eric
E
Lartigau
D006801:Humans; D015182:Lymphatic Irradiation / Q000379:methods; D008297:Male; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D010388:Pelvis; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D012669:Seminal Vesicles / Q000000981:diagnostic imaging; D013997:Time Factors; D036542:Tomography, Spiral Computed / Q000379:methods; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000528:radiation effects