In electron beam therapy, lead or low melting point alloy (LMA) sheet cutouts of sufficient thickness are commonly used to shape the beam. In order to avoid making cutouts for each patient, an attempt has been made to develop a manual multi-leaf collimator for electron beams (eMLC). The eMLC has been developed using LMA for a 15 x 15 cm2 applicator. Electron beam characteristics such as depth dose, beam profiles, surface dose, output factors and virtual source position with the eMLC have been studied and compared with those of an applicator electron beam. The interleaf leakage radiation has also been measured with film dosimetry. Depth dose values obtained using the eMLC were found to be identical to those with the applicator for depths larger than Dmax. However, a decrease in the size of the beam penumbra with the eMLC and increase in the values of surface dose, output factors and virtual source position with eMLC were observed. The leakage between the leaves was less than 5% and the leakage between the opposing leaves was 15%, which could be minimized further by careful positioning of the leaves. It is observed that it is feasible to use such a manual eMLC for patients and eliminate the fabrication of cutouts for each patient.

As complex treatment techniques such as intensity modulated radiotherapy (IMRT) entail the modeling of rounded leaf-end transmission in the treatment planning system, it is important to accurately determine the dosimetric leaf gap (DLG) value for a precise calculation of dose. The advancements in the application of the electronic portal imaging device (EPID) in quality assurance (QA) and dosimetry have facilitated the determination of DLG in this study. The DLG measurements were performed using both the ionization chamber (DLGion) and EPID (DLGEPID) for sweeping gap fields of different widths. The DLGion values were found to be 1.133 mm and 1.120 mm for perpendicular and parallel orientations of the 0.125 cm3 ionization chamber, while the corresponding DLGEPID values were 0.843 mm and 0.819 mm, respectively. It was found that the DLG was independent of volume and orientation of the ionization chamber, depth, source to surface distance (SSD), and the rate of dose delivery. Since the patient-specific QA tests showed comparable results between the IMRT plans based on the DLGEPID and DLGion, it is concluded that the EPID can be a suitable alternative in the determination of DLG.

Aim: This study reveals the characteristic nature and the use of optically stimulated luminescence dosimeters (OSLD) as an in vivo dosimetry tool for head and neck intensity-modulated radiation therapy (IMRT). Materials and methods: Calibration and characterisation of OSLD such as sensitivity, reproducibility, dose-rate dependence, beam quality dependence, output factor measurement and comparison of two bleaching techniques using halogen and compact fluorescent lamp (CFL) were initially performed. Later, eye dose measurements were performed for head and neck IMRT patients using OSLD and were compared with the corresponding dose calculated by the treatment planning system (TPS). Results: While the sensitivity was found to be within ±5%, the dose-rate dependence and reproducibility were found to be within ±3%. The OSLD showed an under-response of 3% for 15 MV and an increase in response by 5% for Co60 (1·25 MeV) when compared with the 6 MV X-ray beam. Therefore, a separate calibration for different beam energies is required. The percentage deviation of OSLD to that of TPS was found to be within ±2·77%. The OSLD has been successfully used for the in vivo dosimetry of patients who received IMRT. Hence, it is concluded that OSLDs can serve as effective dosimeters for in vivo dosimetry.

A manual multileaf collimator developed for telecobalt unit was motorized to accomplish the easy movement of the leaves. The required field shaping using MLC could be achieved by either using template or display. The beam characteristics were investigated and then compared with those of customized blocks. The maximum interleaf leakage and the percentage of transmission measured at the depth of maximum ionization (0.5cm) were found to be 2.7% and 2.4%, respectively. The field shaping performed by the MLC was verified using film dosimetry. The comparative study of treatment plans of 3DCRT and IMRT between 60 Co beam and 6 MV beams was carried out. This MLC could be used as a substitute for conventional blocks in static fields, there by eliminating the effort and cost of fabricating customized blocks, the need for storage space for blocks and other practical difficulties during the process of the block making. It is also demonstrated that if a provision for IMRT delivery with MLC for 60 Co is made, could be a cost effective alternative to IMRT with 6 MV beam.

The distinctive features of a well-known NaI(Tl) scintillation detector, by virtue of its crystal size, are experimentally investigated by observing changes in parameters such as intrinsic efficiency (εi), photo-peak efficiency (εp), resolution, and response function to incident gamma photon energy. This study provides a better understanding for the choice of crystal size of the scintillation detector in Compton scattering experiments. The response function of the NaI(Tl) detector is in the form of an inverse matrix focusing on the retort of the crystal when gamma photons are incident upon it. The response function of the NaI(Tl) detector depends upon the distance between the source and the detector, composition of the material for the crystal itself, photo-fraction, solid angle, incident gamma energy, and geometry of the experimental setup. The factors responsible for broadening of full energy and backscattered peaks are discussed for present investigations. The observed results indicate that the resolution of the detector varies with the incident energy of gamma radiation, and it also depends upon the size of the crystal of the detector. Statistical fluctuations related with the scintillation mechanism are found to be responsible for broadening of instrumental line width (photo-peak). The signal-to-noise ratio and photo-fraction for different crystal sizes of the scintillation detector corrected for efficiency of the detector are also discussed.