Phase ǀ Study on Pancreatic Cancer Treated by CyberKnife

Pancreatic cancer is the fourth-leading cause of cancer-related death in the world. It is characterized by metastatic spread and local failure and seldom detected in its earlier stages. For locally advanced stage pancreatic cancer, the complete surgical removal is hard to achieve. Stereotactic body radiotherapy (SBRT) with CyberKnife for unresectable pancreatic tumor is a relatively new treatment option made available because of significant improvements in diagnostic imaging and radiation delivery techniques. Different from the conventional radiotherapy, radiation dose is delivered in fewer fractions and higher fractional doses in SBRT. Gurka (1) reported that 14 patients received SBRT with prescription dose of 25 Gy in five fractions with biologically equivalent doses (BED) of α/β=10 in correspondence to 37.5Gy. Grade 1 to 2 gastrointestinal toxicity (no grade 3 or 4 radiation-related toxicities) was observed two weeks after treatment. Two patients had a partial response, and 12 patients were with stable diseases. In the previous dose escalation study, a single fraction up to15 Gy, 20 Gy, 25 Gy which is an equivalent BED10 to 37.5 Gy, 60 Gy, 87.5 Gy respectively is recommended by Koong AC (2) and his team. Even though the local control rate is 100%, the follow up is short and the sample size of 15 patients is relatively small. Moreover, the late toxicity is not investigated. And with single fraction scheme, higher late gastrointestinal (GI) toxicities were reported (2,3,4). In the meanwhile, investigators (5, 6) from South Korea examined that a Dmax of 35Gy and 38Gy in 3 fractions (BED10 to 75.8Gy and 86.1Gy) of SBRT correlated with a 5% and 10% rate of grade 3 of gastroduodenal toxicity for abdominal malignant tumor, respectively. Chuong (7) used 5 fractions to potentially decrease the risk of late normal tissue injury compared with 1 to 3 fractions commonly used in other institutions. Assuming α/β=3, the BED3 delivered to normal tissue in this study (using a mean 36.4 Gy in 5 fractions to the high dose PTV) was 125 Gy, which is lower than the mean BED3 from other series, the corresponding values from Boston and Stanford were 153.7 Gy (mean, 32.96 Gy in 3 fractions) and 233.3 Gy (mean, 25Gy in 1 fraction), respectively (8, 9). And a relatively lower incidence of grade ≥3 late adverse effects (5.3% VS 9%) was observed. Since the treatment modality and dose are still under exploratory stage, we propose to conduct a Phase I study determining the maximum tolerated dose of CyberKnife SBRT on dose escalation for the treatment of locally advanced pancreatic tumor based on a 5 fractions treatment regimen. A prescription dose of 35-47.5 Gy in five fractions was chosen, with an equivalent to the traditional dose of 2 Gy in 25-39 fractions of BED10. And this is assumed to be the safe and effective dose for unresectable pancreatic cancer patients. Study Procedure: CyberKnife SBRT body fixation (vacuum-bag) will be used in immobilizing the body, the arms and the legs. * Patients will undergo a plain CT as well as an enhanced pancreatic parenchymal CT for radiation treatment planning and target delineation. * SBRT will be delivered on CyberKnife with Synchrony Respiratory Tracking system. The tumor will be tracked with implanted fiducial markers by Fiducial Tracking System. Treatment will be delivered in 5 fractions within 1 to 2 weeks at the discretion of the investigator. * A body fixation (vacuum-bag) will be used in immobilizing the body, the arms (both arms are along the body) and the legs.