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
Renzo Mazzarotto, Nicola Simoni, Stefania Guariglia, Gabriella Rossi, R. Micera, Riccardo De Robertis, A. Pierelli, Emanuele Zivelonghi, Giuseppe Malleo, Salvatore Paiella, Roberto Salvia, Carlo Cavedon, Michèle Milella, Claudio Bassi
Abstract
Background and Objective 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). Material and Methods 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 sib (tumor-vessel interface [TVI])/PTV t (tumor volume)/PTV sip (overlap area between PTV t and planning organs at risk volume [PRV oars ]), respectively. At re-planning, the prescribed dose was escalated up to 60/40/33 Gy in five fractions to PTV sib /PTV t /PTV sip , 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 0.5cc < 33 Gy for luminal OARs and D 0.5cc < 38 Gy for corresponding PRV oars ). The primary end-point was to achieve a median dose equal to the prescription dose for the PTV sib with D 98 ≥ 95% (95% of prescription dose is the minimum dose), and a coverage for PTV t and PTV sip of D 95 ≥95%, with minor deviations in OAR dose constraints in < 10% of the plans. Results PTV sib median (± SD) dose/D 95 /conformity index (CI) were 60.54 (± 0.85) Gy/58.96 (± 0.86) Gy/0.99 (± 0.01), respectively; whilst PTV t median (± SD) dose/D 95 were 44.51 (± 2.69) Gy/38.44 (± 0.82) Gy, and PTV sip median (± SD) dose/D 95 were 35.18 (± 1.42) Gy/33.01 (± 0.84) Gy, respectively. With regard to OARs, median (± SD) maximum dose (D 0.5cc ) 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 0.5cc =34.8 Gy). V38 < 0.5 cc was achieved for all PRV luminal OARs. Conclusions In LAPC patients SBRT, with a SIB/SIP dose escalation approach up to 60/40/33 Gy in five fractions to PTV sib /PTV t /PTV sip , respectively, is dosimetrically feasible with adequate PTVs coverage and respect for OAR dose constraints.