SU-E-T-231: Comparison of Beam Characteristics of Small Field 6 MeV Electrons as Replacement for Superficial X Ray Beam.

Purpose: To compare beam characteristics of superficial X-rays with 6 MeV Electrons for the purpose of replacing superficial treatments with electron fields for skin lesions.

Methods: Electron beam cutouts were made with 12mm thickness cerrobend in diameters 2-5 cm to match superficial X-ray machine cones. Central axis depth doses and profiles were generated using 0.

Duplicating a tandem and ovoids distribution with intensity-modulated radiotherapy: a feasibility study.

Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiotherapy. In the present study, we investigated whether sliding-window intensity-modulated radiation therapy (IMRT) can achieve a pear-shaped distribution with a similar sharp dose falloff identical to that of brachytherapy. The computed tomography scans of a tandem and ovoid patient were pushed to both a high dose rate (HDR) and an IMRT treatment planning system (TPS) after the rectum, bladder, and left and right femoral heads had been outlined, ensuring identical structures in both planning systems.

Technical and dosimetric considerations in IMRT treatment planning for large target volumes.

The maximum width of an intensity-modulated radiotherapy (IMRT) treatment field is usually smaller than the conventional maximum collimator opening because of design limitations inherent in some multileaf collimators (MLCs). To increase the effective field width, IMRT fluences can be split and delivered with multiple carriage positions. However, not all treatment-planning systems and MLCs support this technique, and if they do, the maximum field width in multiple carriage position delivery is still significantly less than the maximum collimator opening.

Quantifying IOHDR brachytherapy underdosage resulting from an incomplete scatter environment.

Purpose: Most brachytherapy planning systems are based on a dose calculation algorithm that assumes an infinite scatter environment surrounding the target volume and applicator. Dosimetric errors from this assumption are negligible. However, in intraoperative high-dose-rate brachytherapy (IOHDR) where treatment catheters are typically laid either directly on a tumor bed or within applicators that may have little or no scatter material above them, the lack of scatter from one side of the applicator can result in underdosage during treatment.

Predictive value of linear-quadratic model in the treatment of cervical cancer using high-dose-rate brachytherapy.

Purpose: To determine whether a dose-response relationship exists between the biologic effective dose (BED) at Point A and the bladder and rectum and the clinical outcomes in our experience with external beam radiotherapy (EBRT) and high-dose-rate brachytherapy in the treatment of cervical carcinoma.

Methods And Materials: This was a retrospective study. A total of 49 patients with cervical cancer were treated with a combination of EBRT (median 45 Gy, range 41.

Dosimetric aspects of physical and dynamic wedge of Clinac 2100C linear accelerator.

Aim: To investigate variation of wedge factors on field size and depth for physical and dynamic wedges of identical wedge angles for Clinac 2100C linear accelerator and its clinical implementation.

Material And Methods: A computer controlled water phantom dosimetric system is used to generate profile data for physical wedges, whereas a 0.6 cm3 ion chamber is used for generation of profiles for dynamic wedge and wedge factors for both types of wedges.

Design and comparison of wedge shaped midline block with rectangular block used in early stage cervical cancers.

Purpose: Design of an universal wedge shaped midline block for early stage cervical cancers to get uniform dose distribution around the target volume.

Material And Methods: The method of fabrication of wedge shaped midline block is discussed for treatment of early stage cervical cancers based on the configuration of 137Cs pellets used in intracavitary applications and along with external photon beams obtained by using 60Co teletherapy machine and 6 and 10 MV linear accelerators.

Results: The dosimetric measurements are carried out to confirm the adequacy of thickness and shape of the block using radiation field analyzer for all the 3 energies.

The dependency of wedge factors on field size and depth in megavoltage beams.

Aim: To investigate the variation of wedge factors on field size, depth on 2 types of telecobalt units and 3 types of medical linear accelerators and to make a simplified approach for day to day calculation procedure.

Materials And Methods: A 0.125 cm3 ion chamber was used to determine the wedge factors which is connected to the computer controlled radiation field analyser.

A concave tray with divergent block for desired dose distribution around shielded region in megavoltage radiation therapy.

In clinical situations large numbers of rectangular divergent blocks are required at different off-axis positions from central axis to shield sensitive organs. Superiority of divergent blocks over non-divergent blocks on a flat tray lies in improving the dose homogeneity. A method has been developed to minimize the number of divergent shielding blocks by using a concave tray at the collimator.

CT assisted computation of collimator angle and importance of off-axis planning of inclined lesions.

In the radiation treatment of inclined lesions the longitudinal axis of beam should be always parallel to the longitudinal axis of lesion in the treatment plane. Hence the choice of correct collimator angle is of prime importance in the oblique field off-axis treatment planning of inclined lesions. In this paper a graphical method is discussed to determine the collimator angles from the CT scans taken at different off-axis planes.