Abstract
The correlation between the pancreatic and external abdominal motion due to respiration was investigated on two patients. These studies utilized four dimensional computer tomography (4D CT), a four dimensional (4D) electromagnetic transponder system, and a gating belt system. One 4D CT study was performed during simulation to quantify the pancreatic motion using computer tomography images at eight breathing phases. The motion under free breathing and breath‐hold were analyzed for the 4D electromagnetic transponder system and the gating belt system during treatment. A linear curve was fitted for all data sets and correlation factors were evaluated between the 4D electromagnetic transponder system and the gating belt system data. The 4D CT study demonstrated a modest correlation between the external marker and the pancreatic motion with R‐square values larger than 0.8 for the inferior–superior (inf‐sup). Then, the relative pressure from the belt gating system correlated well with the 4D electromagnetic transponder system's motion in the anterior–posterior (ant‐post) and the inf–post directions. These directions have a correlation value of −0.93 and 0.76, while the lateral only had a 0.03 correlation coefficient. Based on our limited study, external surrogates can be used as predictors of the pancreatic motion in the inf–sup and the ant–post directions. Although there is a low correlation on the lateral direction, its motion is significantly shorter. In conclusion, an appropriate treatment delivery can be used for pancreatic cancer when an internal tracking system, such as the 4D electromagnetic transponder system, is unavailable.PACS number: 87.55.kh
Highlights
Correlation using 4D CT The 4D CT studies for both patients indicated that breathing affects pancreatic motion mainly in two directions, inf–sup and ant–post
Its position was given as a function of the external marker position from 4D CT studies for both patients, namely Patient A and Patient B
The highest R-square values resulted from the inf–sup direction, which had the highest range of ± 0.90 cm according to 4D CT
Summary
Pancreatic cancer is one of the most deadly cancers, with a 1% five-year overall survival.[1,2] At the time of diagnosis, around 60% of the patients have locally advanced disease and/or distant metastasis.[3,4,5] Even when patients have metastatic disease, a significant percentage will die of local complications, according to a John Hopkins Rapid Autopsy Program in Pancreatic Cancer.14 Betancourt et al.: Abdominal and pancreatic motion correlation radiation therapy (IMRT), volumetric-modulated arc therapy (VMAT), stereotactic body radiation therapy (SBRT) advance, knowledge of target position become more crucial.[6,7,8,9,10]For example, tumor motion may result in a different dose distribution if motion is not correctly accounted for. Langen and Jones reviewed the literature for pancreatic motion and concluded that the pancreas can move up to 3.0 cm during normal breathing and up to 8.0 cm in deep breathing. Covering such motion with wide margins would be inappropriate, since a large volume of healthy organs, such as bowel and kidneys, might receive therapeutic doses.[6] it is important to understand how the pancreas moves. One approach is to use breath-hold or to modify the breath cycle.[19,20,21,22,23] Other methods include synchronizing the radiation beam on time to the breathing cycle to deliver the dose when the target moved the least,(24-28) and allowing the patient to breathe normally and track the tumor position during treatment.[29,30,31] the motion of an external marker is often used as a reference to deduce the internal motion of the tumor.[32,33,34]
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