Experimental dosimetry in locally fabricated phantom for endobronchial brachytherapy plan: A phantom study

This study is to perform dosimetric analysis in a locally fabricated thorax phantom with the help of radiochromic film.

A thorax human body tissue equivalent phantom was fabricated. This phantom was scanned in the positron emission tomography/computed tomography (PETCT) machine and transferred the CT data into the Oncentra Master Plan treatment planning system (TPS). A brachytherapy (BT) plan created in TPS, exported to the high dose rate (HDR) BT machine. Placed Radiochromic EBT3 film dosimeter at the desired locations in the phantom and irradiate on machine with Ir-192 source. The TPS calculated values were compared with film measured values in the Phantom. Doses at five points in each film for each organ at risk were measured and compared with the TPS calculated doses to see the effects of distance on dose variation for analysis purpose.

The film measured doses deviate from TPS calculated doses with -2.5%, -3.2%, 3.8%, 2.4%, 5.3%, 17.75%, -7.1%, -9.4%, and 7.1% variation to Heart, Esophagus, Spinal Cord, descending Aorta, Ipsilateral Lung, Ipsilateral Lung 2 cm depth, pulmonary trunk, coronary artery, and contralateral Lung doses, respectively. In each film out of five points the center point and point closure to the source was having less variation between TPS calculated and film measured doses then other points.

This variation is due to the algorithm used in BT TPS so it is important to perform a verification of the treatment plan before execution in the patient to assure accuracy of treatment delivery. It is cheaper and used as a quality assurance Tool.