Abstract
Materials/Methods: The study included volumetric modulated arc plans obtained with an Eclipse planning system from 11 localized prostatecancer cases. The clinical targetvolume (CTV) was the prostategland. The planningtargetvolume (PTV) was an expansion of CTV by 3 mm posteriorly and 4 mm in other directions. The prescribed dose (PD) to the PTV was 40 Gy (100%) to be delivered in 5 fractions with a RapidArc technique, similar to an ongoing SBRT protocol in our department. The intent in this exercise was to perform dose escalation within the PTV by increasing mean doses, rather than the minimum or peripheral doses. To create PTV dose inhomogeneity, a PTV sub-volume was defined to receive a higher dose. This high-dose volume (HDV) was created by shrinking the CTV by 5 mm and subtracting the urethral volume with a margin of 3 mm. The HDV was intended to receive at least 150% of the PD with no maximal dose limit. The mean PTV was 90 cc (range 54 to 127 cc). The HDV represented an average of 24% of the prostate PTV volume (range 15 to 38%). Rectal and bladder constraints were the same at: 50%\40 Gy, 20%\32 Gy, 12%\36 Gy, and 8%\40 Gy. Results: The profiles of the PTV dosevolume histograms resemble those achieved with high dose rate brachytherapy of the prostate. With respect to the target areas, the average PTV dose was 132% of the PD (range 110 to 140%). The HDV received an average of 155% of the PD (range 120 to 183%). The average of the HDV maximal doses was 195% of the PD (range 128.3 to 236.3%). Critical structure constraints were met in all cases. Overall, the mean rectal volume receiving 36 Gy was\5% (range 3 to 11%); the mean bladder volume receiving 36 Gy was\3% (range 1 to 12%) The urethral mean dose was 106% of the PD (range 91 to 128%). Conclusions:In this study, allowing dose inhomogeneity within the prostategland resulted in large dose escalation without compromiseofcriticalnormaltissues.Brachytherapytargetdose/volumeprofilescanbesafelyachievedwiththisnovelexternalbeam technique. Author Disclosure: N.G. Nickols: None. N. Agazaryan: None. C. King: None. P. Lee: None. M. Steinberg: None. P. Kupelian: None.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have