Beam Deliveries Research Articles

A Multiple acquisition sequence for IMRT verification with a 2D ion chamber array

This investigation deals with the implementation of a multiple acquisition (MA) sequence for radiotherapy beam verification with a 2-dimensional (2D) ion chamber array. The acquisition is carried out through multiple beam deliveries with the 2D detector array in different positions. The MA sequence is performed through remote-controlled movements of the treatment couch. In this work, the MA dose map of an intensity-modulated radiotherapy (IMRT) modulated beam is presented and compared to standard acquisition mode data and ion chamber measurements. The implementation of MA sequence increases the number of measurement points and therefore the efficiency of the detection system and the final imaging resolution. Results from this investigation show that the imaging resolution of the system used in standard acquisition mode can be increased up to 4 times. The procedure described in this work can be automated, including couch movements in the radiotherapy plan sent to the treatment workstation. Furthermore, this specific solution could be successfully applied to matrices of detector with a different construction design.

Verification of dynamic intensity-modulated beam deliveries in canine subjects.

Our objective in this work was to assess the precision and degree of accuracy with which intensity modulated radiation therapy (IMRT) can deliver highly localized dose distributions to tumors near critical structures using the dynamic sliding window technique. Measurements of dose distribution were performed both in vivo and in vitro using a combination of dosimeters [thermoluminescent dosimeters (TLD's), films, and diodes]. In vivo measurements were performed in two groups of purpose-bred dogs: one receiving four-field three-dimensional (3D) conformal treatment and the other receiving IMRT. The algorithms used in the inverse planning process included the Macro Pencil Beam (MPB) model and Projections onto Convex Sets (POCS). Single beam measurements were performed in phantoms to verify the accuracy of monitor unit settings required for delivering the desired doses. The composite doses from the delivery of the seven beam intensity modulated plans were measured in phantoms and cadavers, Biological end points (spinal cord toxicity and neurologic deficits due to irradiation) were evaluated at the end of one year to determine the spatial accuracy of the IMRT treatments over a fractionated course in live subjects. Results in single beam measurements were used at first to improve the dose calculation and translation algorithms. Results of the measurements for the delivery of all seven beams in phantoms confirmed that the system was capable of accurate spatial and dosimetric IMRT delivery. The in vivo results showed dramatic differences between control and IMRT-treated dogs, with the IMRT group showing no adverse effects and the control animals showing severe spinal cord injuries due to irradiation. The measurements presented in this paper have helped to verify the successful and accurate delivery of IMRT in a clinically related model using the University of Washington Medical Center (UWMC) system.