Adaptive SBRT by 1.5 T MR-linac for prostate cancer: On the accuracy of dose delivery in view of the prolonged session time. (December 2020)

• Record Type: Journal Article
• Authors: Ruggieri, Ruggero; Rigo, Michele; Naccarato, Stefania; Gurrera, Davide; Figlia, Vanessa; Mazzola, Rosario; Ricchetti, Francesco; Nicosia, Luca; Giaj-Levra, Niccolò; Cuccia, Francesco; Vitale, Claudio; Stavreva, Nadejda; Pressyanov, Dobromir S.; Stavrev, Pavel; Pellegrini, Roberto; Alongi, Filippo
• Is Part Of: Physica medica. Volume 80(2021)
• Page Start: 34
• Page End: 41
• Publication Date: 2020-12
• Subjects: Prostate SBRT -- 1.5T MR-linac -- MRi-guided adaptive radiotherapy -- Delivered dose -- Cumulative dose; Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2020.09.026
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: Daily fully adaptive RT (dART) by 1.5 T MR-linac removes the effects of inter-fraction motion. However, the dART session time is prolonged with respect to not-adaptive RT. Intra-fraction target motion is then likely increased by the use of dART. The trade-off between these two opposite effects of dART needs of a quantification. For 5-fx Prostate-SBRT, the accuracy of dART dose delivery by 1.5 T MR-linac was estimated. Abstract: Purpose: Adaptive Stereotactic Body Radiotherapy (SBRT) of prostate cancer (PC) by online 1.5 T MRi-guidance prolongs session-time, due to contouring and planning tasks, thus increasing the risk of prostate motion. Hence, the interest to verify the adequacy of the delivered dose. Material and methods: For twenty PC patients treated by 35 Gy (Dp ) in five fractions, daily pre- and post- delivery MRi scans were respectively used for adapt-to-shape (ATS) optimization, and re-computation of the delivered irradiation (D rec ). Two expansion recipes, from Clinical (CTV) to Planning target volume (PTV), which slightly differed in the posterior margin were used for groups I and II, of ten patients each. Plans had to assure D95% ≥ 95%Dp to PTV, and D1cc ≤ Dp to rectum, bladder, penile bulb, and urethral planning-risk-volume (urethral-PRV). The adequacy of the delivered dose was estimated by inter-fraction average ( ifa ) of dose-volume metrics computed from D rec . A cumulative dose (D sum ) was calculated from the five daily D rec deformed onto the simulation MRi. Results: For each patient, CTV coverage resulted in D95% > 95%Dp when estimated as ifa by D rec . No significant difference for D95% and D99% metrics to CTV resulted between groups I and II. D1cc was < Dp for rectum, urethral-PRV, and penile bulb, whereas < 103.5%Dp for the bladder. Significant correlations resulted between metrics computed by D sum and as ifa by D rec, by both linear-correlation analysis, and Receiver-Operating-Characteristic curve analysis. Conclusions: Our results for PC-SBRT confirm the adequacy of the delivered dose by ATS with 1.5 T MR-linac, and the consistency between dose-volume metrics computed by D rec and D sum .