Clinical Implementation of an In vivo Dose Verification System Based on a Transit Dose Calculation Tool for 3D-CRT

We developed and evaluated an algorithm to calculate the target radiation dose in cancer patients by measuring the transmitted dose during 3D conformal radiation treatment (3D-CRT) treatment. The patient target doses were calculated from the transit dose, which was measured using a glass dosimeter positioned 150 cm from the source. The accuracy of the transit dose algorithm was evaluated using a solid water phantom for five patient treatment plans. We performed transit dose-based patient dose verification during the actual treatment of 34 patients who underwent 3D-CRT. These included 17 patients with breast cancer, 11 with pelvic cancer, and 6 with other cancers. In the solid water phantom study, the difference between the transit dosimetry algorithm with the treatment planning system (TPS) and the measurement was −0.10 ± 1.93%. In the clinical study, this difference was 0.94 ± 4.13% for the patients with 17 breast cancers, −0.11 ± 3.50% for the eight with rectal cancer, 0.51 ± 5.10% for the four with bone cancer, and 0.91 ± 3.69% for the other five. These results suggest that transit-dosimetry-based in-room patient dose verification is a useful application for 3D-CRT. We expect that this technique will be widely applicable for patient safety in the treatment room through improvements in the transit dosimetry algorithm for complicated treatment techniques (including intensity modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT)).