Session Item

Radiation therapy is an effective therapeutic strategy for pancreatic cancer (PC), especially in terms of local-regional control, and stereotactic body radiation therapy (SBRT) is gaining more importance as treatment option, thanks to high spatial precision. This study was conducted to analyse the results of a dose-painting SBRT approach with higher biologically effective doses released on tumour-vessel interface (TVI) to increase surgical resectability and reduced doses on simultaneous integrated protection (SIP) to protect duodenum for unresectable PC.

Frameless set-up was used for CT simulation. Gross Tumor Volume (GTV) and involved major blood vessels were contoured by a dynamic co-registration of CT simulation with contrast medium diagnostic CT scan. CTV was delineated including tumour-vessel interface (CTV= GTV+TVI) obtained by expanding of 5mm blood vessels volume. A Planning target volume (PTV) was obtained adding 5mm to Internal Target Volume (ITV), generated by 4DCBCT (Symmetry^TM). Within the PTV, two volumes were delineated: a PTV boost created to cover the tumor-vessel interface inside the GTV with higher dose and a PTV_SIP  (Simultaneous integrated protection) defined as the intersection between the PTV and the Planning Organ at Risk (PRV) for the duodenum (duodenum + 3mm), inside which the prescription dose was reduced according to OAR dose constraints (UK Consensus SBRT 2018), and.  A differential dose distribution by a Simultaneous Integrated Boost (SIB) technique was planned.

Four pilot cases have been analyzed. Dose constraint for duodenum was set as maximum dose (0.5cc) <33Gy (5 fractions). Dose prescription on all cases was 35Gy (5 consecutive daily fraction, 60Gy BED10), with minimal dose to PTVs of 25Gy, and 40Gy on PTV boost (72Gy BED10). Case1: PTV volume =52cc, PTV_SIP volume =12cc, PTV boost volume =8cc. Case2: PTV volume =126cc, PTV_SIP volume =15cc, PTV boost volume =57cc. Case3: PTV volume =107cc, PTV_SIP volume =10cc, PTV volume boost=44cc; Case4: PTV volume =109cc, PTV_SIP volume =22cc, PTV boost volume =21cc.

In the four cases, the mean dose on PTV were 35.5, 36.7, 37.1, 35Gy, the mean dose on PTV_SIP were 32, 31, 33, 30Gy, the mean dose on PTVs boost were 40, 41, 39, 41Gy and the maximum dose on PTVs boost were 41.7, 42.3, 41, 42Gy, respectively. Volumes and dose distribution of Case1 is showed in Figure 1.

Our preliminary results showed that SIB/ SIP approach in pancreatic SBRT is feasible and may prevent damage to duodenum giving a safe administration of ablative doses to the tumor. This dose-painting could facilitate the conversion to negative margin resection and to enhance local tumour control and survival, increasing the therapeutic window of clinical benefit. Despite the volume difference among the clinical presentations, the technique is also proving to be reproducible through its optimization. A prospective clinical study is currently ongoing to confirm the efficacy on outcomes.