A New Delineation Method Research Of The Clinical Target Volume In Pancreatic Cancer Adjuvant Radiotherapy

Purpose:To establish a map model of the local recurrence(LR)location after pancreatic cancer(PC)resection and to generate a new delineation method of clinical target volume(CTV)to effectively improve the adjuvant radiotherapeutic gain ratio.Methods and Materials:The clinical and imaging data of 48 resected pancreatic cancer patients with local recurrence were collected.Thirty patients with pancreatic head cancer and 18 patients with pancreatic body cancer were enrolled in this study.Local recurrences were all plotted with reference to the geometric center of the local recurrent foci outlined by oncologists.Based on the coordinates of the local recurrence foci with respect to the celiac artery(CA)or the superior mesenteric artery(SMA),a 3-demensional local recurrence map model was established on the template image of one post-pancreaticoduodenectomy(PD)patient.The adjuvant clinical target volumes(CTVs),defined as CTV-90 encompassing 90% of all local failures and CTV-90_H encompassing 90% of only postoperative pancreatic head cancer local failures,were created by expanding the combined CA and SMA contour.Then,we simulated 5 post-pancreaticoduodenectomy(PD)patients to generate two “new” target volumes using the above expansion data and the standard target volume per the Radiation Therapy Oncology Group(RTOG)0848 protocol.Simulated “new” plans and standard plans were generated,adopting the “new” target volume CTV-90_H and the standard target volume,respectively.Finally,we compared the target volumes and plans described above.Results:CTV-90 was generated by expanding the combined CA and SMA contour by 1.4 cm superior,1.9 cm inferior,2.6 cm left-lateral,3.1 cm right-lateral,1.9 cm anterior and 1.6 cm posterior.The corresponding expansions of CTV-90_H in the six directions were 1.4 cm,1.4 cm,2.1 cm,3.1 cm,1.6 cm and 2.0 cm,respectively.The final generated “new” target PTV-90_edited and PTV-90_H_edited had volumes of 217.64±58.67 cc and 207.78±50.94 cc,respectively,and the volume of the standard target PTV_edited was 320.72±50.94 cc in simulated cases.Comparison of the simulated target volumes showed that the “new” planning target volume based on only the local recurrences of postoperative patients with pancreatic head cancer was slightly smaller but not significantly different than the “new” planning target based on all local failures(t=0.28,P=0.78),but the “new” planning target volume for pancreatic head cancer was much smaller than the standard target volume(t=3.18,P=0.013).The dose received by organs at risk was also lower in the “new” plans than in the standard plans.Conclusions:A majority of local recurrences in postoperative patients with pancreatic head and body cancer is contained within a region surrounding the CA and the SMA,which is much smaller than the standard target volume.The target volume for only postoperative pancreatic head cancer determined by the new method is greatly decreased,which may allow dose escalation and enhanced local control while minimizing radiation-related toxicities.