Purpose The purpose of the study was to investigate if surface guided radiotherapy (SGRT) can decrease setup deviations for tangential and locoregional breast cancer patients compared to conventional laser‐based setup (LBS). Materials and Methods Both tangential (63 patients) and locoregional (76 patients) breast cancer patients were enrolled in this study. For LBS, the patients were positioned by aligning skin markers to the room lasers. For the surface based setup (SBS), an optical surface scanning system was used for daily setup using both single and three camera systems. To compare the two setup methods, the patient position was evaluated using verification imaging (field images or orthogonal images). Results For both tangential and locoregional treatments, SBS decreased the setup deviation significantly compared to LBS (P < 0.01). For patients receiving tangential treatment, 95% of the treatment sessions were within the clinical tolerance of ≤ 4 mm in any direction (lateral, longitudinal or vertical) using SBS, compared to 84% for LBS. Corresponding values for patients receiving locoregional treatment were 70% and 54% for SBS and LBS, respectively. No significant difference was observed comparing the setup result using a single camera system or a three camera system. Conclusions Conventional laser‐based setup can with advantage be replaced by surface based setup. Daily SGRT improves patient setup without additional imaging dose to breast cancer patients regardless if a single or three camera system was used.

The aim of this study was to investigate potential dose reductions to the heart, left anterior descending coronary artery (LAD), and ipsilateral lung for left‐sided breast cancer using visually guided deep inspiration breath‐hold (DIBH) with the optical surface scanning system Catalyst™, and how these potential dosimetric benefits are affected by intrafractional motion in between breath holds. For both DIBH and free breathing (FB), treatment plans were created for 20 tangential and 20 locoregional left‐sided breast cancer patients. During DIBH treatment, beam‐on was triggered by a region of interest on the xiphoid process using a 3 mm gating window. Using a novel nonrigid algorithm, the Catalyst™ system allows for simultaneous real‐time tracking of the isocenter position, which was used to calculate the intrafractional DIBH isocenter reproducibility. The 50% and 90% cumulative probabilities and maximum values of the intrafractional DIBH isocenter reproducibility were calculated and to obtain the dosimetric effect isocenter shifts corresponding to these values were performed in the treatment planning system. For both tangential and locoregional treatment, the dose to the heart, LAD and ipsilateral lung was significantly reduced for DIBH compared to FB. The intrafractional DIBH isocenter reproducibility was very good for the majority of the treatment sessions, with median values of approximately 1 mm in all three translational directions. However, for a few treatment sessions, intrafractional DIBH isocenter reproducibility of up to 5 mm was observed, which resulted in large dosimetric effects on the target volume and organs at risk. Hence, it is of importance to set tolerance levels on the intrafractional isocenter motion and not only perform DIBH based on the xiphoid process.

above the chamber for adjusting the mean electron energy incident on the lead solid-water interface. Such measurements were repeated with the removal of lead sheet. By comparing the measured dose with and without the lead sheet, the backscatter effect of electrons from the lead interface could be derived experimentally at different depths away from the lead interface. To investigate the impact of lead heterogeneity in the eMC calculation, metallic artefact-free MVCTs were done on all setups used in previous dose measurements. and imported into the planning system for eMC dose calculations. Finally, the impact on the accuracy of the eMC algorithm due to backscatter effect from lead heterogeneity can be found by comparing the measured and calculated dose in different setups. Results: At the lead-solid water interface (depth Z 0 cm), the eMC calculation underestimated the dose in the range between 61.5 AE 4.4% to 47.5 AE 3.3% for the mean energy of the electron incident on the interface ranging from 2 to 11 MeV. Such underestimation was reduced to between 12 AE 0.8% and 14.5 AE 0.9% at the depth 1 cm away from the interface. It was further reduced to between 5.6 AE 0.4% and 8.5AE 0.6 % at the depth 1.5 cm away from the interface. Conclusion: When there is a presence of lead heterogeneity in an electron beam, eMC dose calculation underestimates the dose depending on treatment depth. Special attention must be paid in the eMC plan when lead is used as an inner shield.

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