RESUMEN
PURPOSE: The purpose of this work was to detail our center's experience in transitioning from a Co-60 treatment technique to an intensity modulated radiation therapy (IMRT) based lateral-field extended source-to-axis distance (e-SAD) technique for total body irradiation (TBI). MATERIALS AND METHODS: An existing beam model in RayStation v.10A was validated for the use of e-SAD TBI treatments. Data were acquired with an Elekta Synergy linear accelerator (LINAC) at an extended source-to-surface distance of 365 cm with an 18 MV beam. Beam model validation measurements included percentage depth dose (PDD), profile data, surface dose, build-up region and transmission measurements. End-to-end testing was carried out using an anthropomorphic phantom. Treatments were performed in a supine position in a whole-body Vac-Lok at an e-SAD of 400 cm with a beam spoiler 10 cm from the couch. Planning was achieved using IMRT, where multi-leaf collimators were used to modulate the beam and shield the organs at risk. Beam's eye view projection images were used for in-room patient positioning and in-vivo dosimetry was performed for every treatment. RESULTS: The percent difference between the measured and calculated PDD and profiles was less than 2% at all locations. Surface dose was 83.8% of the maximum dose with the beam spoiler at a 10 cm distance from the phantom. The largest percent difference between the treatment planning system (TPS) and measured data within the anthropomorphic phantom was approximately 2%. In-vivo dosimetry measurements yielded results within the 5% institutional threshold. CONCLUSION: In 2022, 17 patients were successfully treated using the new IMRT-based lateral-field e-SAD TBI technique. The resulting clinical plans respected the institutional standard. The commissioning process, as well as the treatment planning and delivery aspects were described in this work with the intention of supporting other clinics in implementing this treatment method.
RESUMEN
PURPOSE: The purpose of this study was to compare absorbed dose with the treated breast and organs at risks (OARs) with weekly image guidance using electronic portal imaging (EPI), complete kilovoltage cone beam computed tomography (kV CBCT), and partial kV CBCT. METHODS AND MATERIALS: Using a thorax female phantom, we determined absorbed doses to treated and contralateral breast, ipsilateral and contralateral lung, heart, and skin for tangential EPI, complete kV CBCT, and partial kV CBCT. Doses were measured by use of ionization chambers and compared with treatment planning system calculations. With simulation of breast tangential irradiation to a standard dose of 50 Gy in 25 fractions, dose to each organ was measured for each image guidance technique. RESULTS: Use of weekly EPI was associated with a significantly increased dose to the treated breast compared with weekly complete and partial kV CBCT (4.44 ± 0.04 vs 1.00 ± 0.07 vs 0.576 ± 0.003 cGy, respectively). Dose to the contralateral breast, ipsilateral and contralateral lung, heart, and contralateral skin was lower with EPI than with either complete or partial kV CBCT (0.042 ± 0.004 vs 0.36 ± 0.01 vs 0.23 ± 0.01 cGy, 0.06 ± 0.04 vs 0.42 ± 0.02 vs 0.31 ± 0.01 cGy, 0.004 ± 0.002 vs 0.29 ± 0.01 vs 0.22 ± 0.01 cGy, 0.03 ± 0.08 vs 0.36 ± 0.02 vs 0.25 ± 0.01 cGy, and 0.20 ± 0.02 vs 0.80 ± 0.06 vs 0.40 ± 0.03 cGy, respectively). Compared with complete CBCT, the use of partial CBCT allowed dose reductions of 42%, 37%, 27%, 24%, and 28% to the ipsilateral breast, contralateral breast, ipsilateral lung, contralateral lung, and heart, respectively. Additional dose from weekly CBCT was significantly lower than treatment-related scatter dose for all OARs. CONCLUSIONS: Use of CBCT was associated with decreased dose to ipsilateral breast and increased dose to all OARs compared with EPI. Significant dose reduction can be achieved with the use of partial CBCT, while generally maintaining image quality.