No abstract

Total body irradiation (TBI) is a special radiotherapy technique, administered prior to bone marrow transplantation. Due to the complex nature of the treatment setup, in vivo dosimetry for TBI is mandatory to ensure proper delivery of the intended radiation dose throughout the body. Lithium fluoride (LiF) TLD-100 chips are used for the TBI in vivo dosimetry. Results obtained from the in vivo dosimetry of 20 patients are analyzed. Results obtained from forehead, abdomen, pelvis, and mediastinum showed a similar pattern with the average measured dose from 96 to 97% of the prescription dose. Extremities and chest received a dose greater than the prescription dose in many instances (more than 20% of measurements). Homogeneous dose delivery to the whole body is checked by calculating the mean dose with standard deviation for each fraction. Reasons for the difference between prescription dose and measured dose for each site are discussed. Dose homogeneity within ±10% is achieved using our in-house TBI protocol.

No abstract

This work was undertaken with the intention of investigating the possibility of clinical use of commercially available self-developing radiochromic film – Gafchromic EBT film – for IMRT dose verification. The dose response curves were generated for the films using VXR-16 film scanner. The results obtained with EBT films were compared with the results of Kodak EDR2 films. It was found that the EBT film has a linear response between the dose ranges of 0 and 600 cGy. The dose-related characteristics of the EBT film, like post-irradiation color growth with time, film uniformity and effect of scanning orientation, were studied. There is up to 8.6% increase in the color density between 2 and 40 h after irradiation. There was a considerable variation, up to 8.5%, in the film uniformity over its sensitive region. The quantitative difference between calculated and measured dose distributions was analyzed using Gamma index with the tolerance of 3% dose difference and 3 mm distance agreement. EDR2 films showed good and consistent results with the calculated dose distribution, whereas the results obtained using EBT were inconsistent. The variation in the film uniformity limits the use of EBT film for conventional large field IMRT verification. For IMRT of smaller field size (4.5 × 4.5 cm), the results obtained with EBT were comparable with results of EDR2 films.

CyberKnife radiosurgery treatment of Trigeminal neuralgia (TN) is performed as a non-invasive image guided procedure. The prescription dose for TN is very high. The brainstem is the adjacent critical organ at risk (OAR) which is prone to receive the very high target dose of TN. The present study is to analyze the dose distribution inside the tiny trigeminal nerve target and also to analyze the dose fall off in the brain stem. Seven TN cases treated between November 2010 and January 2012 were taken for this study retrospectively. The treatment plans were analyzed for target dose conformity, homogeneity and dose coverage. In the brainstem the volume doses D1%, D2% were taken for analyzing the higher doses in the brain stem. The dose fall off was analyzed in terms of D5% and D10%. The mean value of maximum dose within the trigeminal nerve target was 73.5±2.1Gy (P=0.0007) and the minimum dose was 50.0±4.1Gy (P=0.1315). The mean conformity index was 2.19 and the probable reason could be the smallest CyberKnife collimator of 5mm used in the treatment plan. The mean D1%, of the brainstem was 10.5± 2.1Gy (P=0.5316) and the mean value of the maximum point dose within the brainstem was 35.6±3.8Gy. This shows the degree of dose fall off within the brainstem. Though the results of the present study are showing superior sparing of brain stem and reasonable of target coverage, it is necessary to execute the treatment plan with greater accuracy in CyberKnife as the immobilization is noninvasive and frameless.