Effect of Lung Blocks Parameters on Lung and Cardiac Doses in Total Body Irradiation Using 3D Dosimetry

Abstract

Purpose/Objective(s): There are many studies findings on patient positioning efficiency using SGRT. In our clinic, we have 80 patients in average per linear accelerator. Hence, we would like to further develop the positioning method by combining the functions from both LINAC and SGRT system to investigate its potential in positioning accuracy and setup time. Materials/Methods: There was 40 thoracic cancer patients were selected randomly and divided into 2 groups. Controlled group (Group A) with a total of 20 patients who were aligned based on skin marking. The patient was aligned to the CT reference plane by the therapists using hands. Then, the therapists did the manual calculations for each patient for the isocenter shifts. The other 20 patients, the experimental group (Group B), who were first aligned to the reference plane along their nipples across the vac-bag marking to ensure patient's position in longitudinal direction and patient was nicely fit into the vac-bag. Next, the therapist introduced the first step of auto-positioning and second step with 'move couch' function to the isocenter position. CBCT images were taken in both groups and shifts in translational and rotational were recorded. All systematic and random errors were analyzed as well as setup time.Results: Total of 208 and 199 CBCT images in group A and B were analyzed. The mean shifts errors for group A and B were 0.36cm, 0.27cm and 0.44cm (lat, lng and vrt) and 0.898, 0.988 and 0.768 (pitch, roll and rtn) and 0.23cm, 0.10cm and 0.16cm (lat, lng and vrt) and 0.638, 0.58 and 0.578 (pitch, roll and rtn) respectively. Group B is superior in positioning accuracy than Group A in all directions. The results also shown the average setup time for Group A and B were 118 second and 89 seconds respectively. It is statistical significance (P < 0.05). Conclusion: New positioning method using combination of auto-positioning by both LINAC and SGRT system has proven to improve our workflow efficiency and setup accuracy greatly. It eliminates the need of isocenter shift manual calculation, which substantially reduced the potential of human error-induced radiation incidence. This new positioning method is adapted in our clinic to replace the current patient positioning workflow.

Impact of lung block shape on cardiac dose for total body irradiation

“…To assess the 3-dimensional dose distribution in tissues of interest, an 18 MV beam was commissioned in RayStation (RaySearch Laboratories; Stockholm, Sweden) for the standing TBI setup at an extended SSD. This model was validated for accuracy with clinical tissue-phantom ratio measurements, off-axis ratio measurements, and treatment monitor units following our current clinical treatment protocol, which was based on 2D hand calculation [7] . For this arrangement, the patient was treated as if standing on a platform at an extended SSD of 475 cm from source to patient midline and treated with AP and PA beams.…”

“…The risk of treatment-related death following these procedures is estimated to range from 10 to 30% [5]. Among these toxicities, cardiovascular disease (CVD) is several-fold higher than expected in TBI patients [6,7]. With lower survival rates in the past, late cardiovascular events received relatively little attention; however, with increasing numbers of longer-term survivors, late cardiovascular toxicities may be of interest in the management of TBI treatments [8].…”