Deep-inspiration breath-hold - Development and utilization of a deep-inspiration breath-hold system for breast cancer radiotherapy
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The purpose of this thesis was to develop a deep-inspiration breath-hold (DIBH) system and study the performance and clinical implications in the treatment of leftsided breast cancer and radiotherapy. This was investigated in several individual clinical studies. Study I described the development of the in-house system and the experiments that were conducted to compare the in-house system to a commercial system. Initially, the in-house system performed measurements from a fixed point in the treatment room, but implementing a FlexArm allowed adjustment of the measuring location of the laser to a suitable region regardless of the isocenter position. The study found that the in-house system had a high reproducibility, was intuitive to use, and was cost-effective for performing DIBH. Study II described the clinical results from a pilot study with the fixed-isocenter DIBH system. Twenty-two breast-only patients complied with the requirements and performed a free-breathing and a DIBH CT-scan. All patients were treated by DIBH with the in-house system. Significantly reduced doses were found for the heart and left ascending coronary artery (LAD) using the in-house system compared to freebreathing radiotherapy. The reproducibility and stability of the in-house DIBH system were good; the mean patient setup deviation was less than 0.6 mm, with systematic and random errors in the order of 2 mm. Study III described the clinical results from using the in-house system mounted on a FlexArm. Twenty loco-regional patients participated in the clinical study. They were treated with a standard three-dimensional conformal technique (3DCRT), while a volumetric modulated arc therapy (VMAT) plan was generated retrospectively. The robustness of each technique was assessed by calculating a perturbed overall dose considering the patient’s actual location during the treatment sessions. VMAT plans provided significantly better target coverage as well as lower doses to the heart than 3DCRT. The perturbed doses were less variable, and homogeneity was significantly improved with VMAT plans compared to 3DCRT. Study IV described baseline drift and its incidence in free-breathing right-sided breast cancer patients. Twenty patients participated in the clinical study, and 357 patient respiratory traces were analyzed. The mean overall baseline drift at the end of each treatment session was -1.3 mm. More than 90% of the baseline drift occurred during the first 3 min of each treatment session, and 4% of the treatment sessions had a 5-mm or larger baseline drift 5 min after patient setup in the posterior direction. A total of 75 patients were recruited for the 3 cohorts, but in the process of writing Paper III, a control group of 13 patients was not included in the results due to the length of the manuscript and the focus of the paper. All 3 clinical studies have been approved by the Regional Ethics Committee under approval numbers REK2011/111, REK2014/492 and REK2014/181. The results of these studies showed that the in-house laser distance measurer system performed very well in the clinical setting and that DIBH could potentially improve the quality of life of breast cancer patients by reducing normal tissue doses and improving the dose to the target with the 3DCRT technique. The VMAT technique will increase doses to surrounding tissues, but this can possibly be counterbalanced by the improved target coverage, increased target homogeneity and decreased tissue volume receiving high doses. The system also has the potential to monitor the patient position in 1D.