Zhongguo aizheng zazhi (Jan 2023)
Radiation therapy in locally advanced pancreatic cancer with 75 Gy simultaneous integrated boost: a dosimetric feasibility study
Abstract
Background and purpose: The incidence of pancreatic cancer has increased annually. Intensity-modulated radiotherapy (IMRT) has been widely used in the treatment of pancreatic cancer, however most dosimetric studies for pancreatic cancer have prescribed doses less than 60 Gy. The purpose of this study was to investigate the feasibility and dosimetric differences between coplanar IMRT (CO-IMRT) and non-coplanar IMRT (NC-IMRT) when using 75 Gy simultaneous integrated boost for patients with locally advanced pancreatic cancer (LAPC). Methods: Ten patients with LAPC treated with simultaneous integrated boost at Fudan University Shanghai Cancer Center from January 2018 to December 2021 were included. The prescribed dose for the planning target volume (PTV)50 Gy was 50 Gy in 25 fractions, and 75 Gy in 25 fractions for the simultaneous integrated boost PTV75 Gy. CO-IMRT and NC-IMRT plans were designed for each patient separately, with identical number of fields, prescription doses and OAR constrains for the same patient. The PTV dose distribution, conformability index (CI), homogeneity index (HI), indices to organs at risk (OAR) for multiple end points, beam-on time and monitor units (MU) were analyzed. We evaluated whether the PTV met clinical requirements and quantitative analysis of normal tissue effects in the clinic (QUANTEC) limits, and compared dosimetric differences between the two plans. Results: Both CO-IMRT and NC-IMRT could achieve the required dose coverage of PTV and meet the QUANTEC dose limits for OAR. The differences in CI, HI, beam-on time and MU between the two plans were not statistically significant (P>0.05). NC-IMRT was significantly decreased left kidney Dmean[(10.15±1.53) Gy vs (9.29±1.78) Gy, P<0.05], left kidney V12[(32.74±7.45)% vs (26.03±8.97)%, P<0.05], right kidney Dmean[(7.37±2.41) Gy vs (6.62±2.37)Gy, P<0.05], right kidney V12[(22.27±10.30)% vs (14.94±8.62)%, P<0.05], liver V30[(6.37±4.05)% vs (5.47±3.70)%, P<0.05], small intestine V30[(9.96±6.66)% vs (8.73±6.19)%, P<0.05], small intestine V45[(1.15±0.71)% vs (0.96±0.61)%, P<0.05], stomach V45[(5.37±3.96)% vs (4.52±3.32)%, P<0.05] and large bowel V30[(13.18±4.95)% vs (9.19±4.94)%, P<0.05]. There was no significant difference between CO-IMRT and NC-IMRT in spinal cord Dmax, liver Dmean, bilateral renal V20, bilateral renal V28, small intestinal Dmax, gastric Dmax and duodenal V55(mL) (P >0.05). Conclusion: In the treatment of LAPC using 75 Gy simultaneous integrated boost, both CO-IMRT and NC-IMRT can achieve excellent PTV coverage and meet the OAR constraints in all patients. Without affecting the quality of PTV coverage, NC-IMRT has more advantages in the dose distribution of OAR, which can better protect the OAR and reduce the toxicity to the gastrointestinal tract, liver and kidneys.
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