Objectives:

Stereotactic treatment for pancreatic carcinoma is challenging due to immediate proximity of organ at risk (OAR). Dose escalation is difficult without exceeding normal tissue dose constraints leading to an unfavorable therapeutic ratio. In our department, we are often forced to reduce the prescribed dose to 25Gy in 5 fractions. Stereotactic Centralized Ablative Radiation Therapy (SCART) has the potential to escalate the dose in central position of the target while maintaining fractionation and meeting OAR dose constraints. The aim is to assess feasibility and options for treatment planning with the first fraction delivered using SCART technique.

Methods:

A clinical case treated previously with stereotactic body radiotherapy (SBRT) using CyberKnife system was selected. A new target volume (CTVcentral) was created by reducing original clinical target volume (CTV) by 1cm. The aim was to prepare a plan with the CTVcentral receiving uniform dose of 15Gy. The surrounding tissue dose constraint was set to 5Gy. Finally, the original treatment prescription was changed to 4x5Gy and the plan was summed with the SCART single fraction plan, The OAR doses of the combined plan were evaluated.

Results:

Doses to closest OARs were slightly lower compared to original treated (5x5Gy SBRT) plan. Final coverage of the planning target volume (PTV) by 25Gy isodose dropped to 88.6% due to the dose prescription to the CTVcentral. Biologically effective dose (BED10) calculated from mean dose increased from 48Gy10 to 80Gy10, 47.7Gy10 to 57Gy10 and 45Gy10 to 51Gy10 for CTVcentral, CTV and PTV respectively.

Conclusion(s):

Dose escalation using SCART for the 1st fraction in SBRT of pancreatic cancer is technically feasible without exceeding the dose constraints for OARs. The BED10 in the central part of CTV increased by 66%.