AUTHOR=Mazzarotto Renzo , Simoni Nicola , Guariglia Stefania , Rossi Gabriella , Micera Renato , De Robertis Riccardo , Pierelli Alessio , Zivelonghi Emanuele , Malleo Giuseppe , Paiella Salvatore , Salvia Roberto , Cavedon Carlo , Milella Michele , Bassi Claudio 

TITLE=Dosimetric Feasibility Study of Dose Escalated Stereotactic Body Radiation Therapy (SBRT) in Locally Advanced Pancreatic Cancer (LAPC) Patients: It Is Time to Raise the Bar

JOURNAL=Frontiers in Oncology

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2020.600940

DOI=10.3389/fonc.2020.600940

ISSN=2234-943X

ABSTRACT=<sec><title>Background and Objective</title><p>To assess the dosimetric feasibility of a stereotactic body radiotherapy (SBRT) dose escalated protocol, with a simultaneous integrated boost (SIB) and a simultaneous integrated protection (SIP) approach, in patients with locally advanced pancreatic cancer (LAPC).</p></sec><sec><title>Material and Methods</title><p>Twenty LAPC lesions, previously treated with SBRT at our Institution, were re-planned. The original prescribed and administered dose was 50/30/25 Gy in five fractions to PTV<sub>sib</sub> (tumor-vessel interface [TVI])/PTV<sub>t</sub> (tumor volume)/PTV<sub>sip</sub> (overlap area between PTV<sub>t</sub> and planning organs at risk volume [PRV<sub>oars</sub>]), respectively. At re-planning, the prescribed dose was escalated up to 60/40/33 Gy in five fractions to PTV<sub>sib</sub>/PTV<sub>t</sub>/PTV<sub>sip</sub>, respectively. All plans were performed using an inspiration breath hold (IBH) technique and generated with volumetric modulated arc therapy (VMAT). Well-established and accepted OAR dose constraints were used (D<sub>0.5cc</sub> &lt; 33 Gy for luminal OARs and D<sub>0.5cc</sub> &lt; 38 Gy for corresponding PRV<sub>oars</sub>). The primary end-point was to achieve a median dose equal to the prescription dose for the PTV<sub>sib</sub> with D<sub>98</sub>≥ 95% (95% of prescription dose is the minimum dose), and a coverage for PTV<sub>t</sub> and PTV<sub>sip</sub> of D<sub>95</sub>≥95%, with minor deviations in OAR dose constraints in &lt; 10% of the plans.</p></sec><sec><title>Results</title><p>PTV<sub>sib</sub> median (± SD) dose/D<sub>95</sub>/conformity index (CI) were 60.54 (± 0.85) Gy/58.96 (± 0.86) Gy/0.99 (± 0.01), respectively; whilst PTV<sub>t</sub> median (± SD) dose/D<sub>95</sub> were 44.51 (± 2.69) Gy/38.44 (± 0.82) Gy, and PTV<sub>sip</sub> median (± SD) dose/D<sub>95</sub> were 35.18 (± 1.42) Gy/33.01 (± 0.84) Gy, respectively. With regard to OARs, median (± SD) maximum dose (D<sub>0.5cc</sub>) to duodenum/stomach/bowel was 29.31 (± 5.72) Gy/25.29 (± 6.90) Gy/27.03 (± 5.67) Gy, respectively. A minor acceptable deviation was found for a single plan (bowel and duodenum D<sub>0.5cc</sub>=34.8 Gy). V38 &lt; 0.5 cc was achieved for all PRV luminal OARs.</p></sec><sec><title>Conclusions</title><p>In LAPC patients SBRT, with a SIB/SIP dose escalation approach up to 60/40/33 Gy in five fractions to PTV<sub>sib</sub>/PTV<sub>t</sub>/PTV<sub>sip</sub>, respectively, is dosimetrically feasible with adequate PTVs coverage and respect for OAR dose constraints.</p></sec>