Treatment Delivery Verification Using Thimble Chamber and IMRT Phantom

Background In external beam radiotherapy, over radiation dose results in severe side-effects, but under radiation dose decreases the probability of treatment for cancer patients. The purpose of the article was to verify treatment delivery in radiotherapy of the cancer patients using single point dose verification method. Methods Computed tomography (CT) simulation of intensity-modulated radiation therapy (IMRT) phantom with slot-in ion chamber was done. The IMRT phantom was set on the treatment table of LINAC (Siemens) with FC65-P Farmer type thimble chamber for radiation dose measurement. Different plans were prepared on prowess panther treatment planning system (TPS) using CT images of IMRT Phantom. The monitor units (MU) and doses were calculated for both photon algorithms i.e. Collapsed Cone Convolution Superposition (CCCS) and Fast Photon (FP) algorithms. The calculations for treatment verification were done for both 6MV and 15MV energies produced by LINAC (Siemens) at central axis as well as off axis beams. Results The percentage difference between the measured and calculated dose was less than 1% except for those plans which have greater number of posterior beams. These percentage errors were slightly greater than 1% but well within international recommended limits of ± 3%. Conclusion The percentage error in radiotherapy treatment delivery within limit confirms the best quality of radiotherapy treatment at the institute. The couch attenuation lessens the posterior beams’ dose slightly which can be reduced by incorporating the couch attenuation correction factor while calculating dose on treatment planning system.