Abstract
We have constructed a computer controlled translational couch to administer total body irradiation reproducibly and safely. The system has replaced the previous stationary anterior‐posterior technique in our institution and 30 plus patients have been treated with it so far. In this technique, patients comfortably lie on a couch in supine and prone positions and are transported slowly through a narrow beam with the gantry in an upright position. Dose to the patient is determined by the couch velocity that is calculated based on physical parameters such as patient's dimensions, beam geometry, and machine dose rate. In our design, the couch velocity is continuously updated to compensate for machine dose rate fluctuations. The translational couch technique provides better dose uniformity within the patient compared to fixed beam techniques, and allows a more precise shielding block placement for organs at risk. At the same time, it presents a special challenge for dosimetry calculations. A dosimetry parameter is introduced that converts the moving beam output to the fixed beam output factor. Based on this factor, a simple dosimetry calculation method has been developed that takes advantage of conventional dosimetry parameters, eliminating extensive dosimetry measurements. Multiple point dose measurements within a phantom confirmed the validity of the calculation method.PACS number(s): 87.53.–j, 87.66.–a
Highlights
Total body irradiationTBIwith photon beams is administered in radiation therapy centers for variety of the clinical situations with different techniques.[1–4]
The radiotherapy is usually combined with comprehensive chemotherapy either prior to or concurrent with the radiation
The dose to the patient is determined by the couch velocity assuming constant machine dose rate
Summary
Total body irradiationTBIwith photon beams is administered in radiation therapy centers for variety of the clinical situations with different techniques.[1–4] The radiotherapy is usually combined with comprehensive chemotherapy either prior to or concurrent with the radiation. The most common irradiation technique consists of anterior-posterior fixed beams with the patient in standing position. This technique requires a source to surface distanceSSDin excess of 3 m to encompass the patient within the large beams. To alleviate patient discomfort to some extent and to overcome the limitation of treatment room dimensions, patients are treated in a semiseated position with bilateral beams. This technique suffers from poor dose uniformity and does not allow for effective shielding of the lungs and kidneys. It is found that kidneys outlined on computed tomographyCTscans show a dramatic shift in all directions during treatment in the above mentioned techniques,[5] creating a serious shielding problem
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