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Hypofractionated Prostate Treatment in a Single VMAT Arc

F Clemente*, C Perez-Vara, M Couselo, C Lopez-Carrizosa, C Ibanez, M Martin de Miguel, J Saez, J Zapatero, V Jerviz, M Dominguez, Hospital Central de la Defensa Gomez Ulla, Madrid, Madrid

SU-E-T-633 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Several publications have proposed during the last years hypofractionated treatment schedules in prostate cancer. Such schedules have been possible because the α/β ratio for prostate carcinoma is comparable to, and even lower than, the surrounding late-responding normal tissues. This work shows the scheme adopted in our institution for hypofractionated prostate cancer treatment and plan evaluation based in DVH parameters.

Methods: Monaco 3.10 (CMS, Elekta) is the inverse planning system used for volumetric-modulated arc therapy (VMAT). Treatments are delivered with an Elekta Synergy linac. Daily cone-beam CT corrections are performed as image-guided radiation therapy technique. The fractionation schedule, with the assumption that α/β = 1.5 for targets and 3.0 Gy for OARs, consists on 28 fractions, delivering 2.5 Gy to prostate gland, 2.0 Gy to seminal vesicles and 1.8 Gy if lymph nodes are included. Dose-volume constraints are taken from QUANTEC reviews and they are adapted to our fractionation scheme according the linear-quadratic model (assuming the previous α/β ratios): V45.4<50%, V54.5<35%, V59.0<25%, V63.6<20%, V68.2<50% for rectum; V59.0<50%, V63.6<35%, V68.2<25%, V72.7<15% for bladder; Dmax<45.4 Gy for femoral heads; Dmean<45.4 Gy for penile bulb

Results: Valid single VMAT arc plans are generated by the TPS. Target volumes preserve the optimal homogeneity and coverage, as well as OARs maintain their dose-volume parameters under those imposed by QUANTEC: V45.4=(20.3±5.9)%, V54.5=(11.7±4.4)%, V59.0=(8.9±4.0)%, V63.6=(6.5±3.1)%, V68.2=(4.1±2.4)% for rectum; V59.0=(12.2±7.3)%, V63.6=(9.5±6.5)%, V68.2=(6.5±5.6)%, V72.7=(2.7±4.0)% for bladder; Dmax=(35.3±4.6) Gy for femoral heads; Dmean=(42.3±3.7) Gy for penile bulb. Mean treatment time is 310±43 s.

Conclusion: VMAT in conjunction with IGRT techniques are powerful tools to cover a hypofractionated prostate cancer treatment program. It is possible to generate optimal plans to treat target volumes as well as to accomplish QUANTEC constraints. VMAT technique allows the delivery of the treatment in a single arc, with a significant reduction in treatment time.

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