The dosimetric effect of residual breath-hold motion in pencil beam scanned proton therapy - An experimental study.

BACKGROUND AND PURPOSE: Motion management in the treatment of lung cancer is necessary to assure highest quality of the delivered radiation therapy. In this study, the breath-hold technique is experimentally investigated for pencil beam scanned (PBS) proton therapy, with respect to the dosimetric effect of residual breath-hold motion. MATERIAL AND METHODS: Three-dimensional (3D)-printed tumours extracted from CT scans of three patients were inserted into a dynamic anthropomorphic breathing phantom. The target was set up to move with the individual patient's tumour motion during breath-hold as previously assessed on fluoroscopy. Target dose was measured with radio-chromic film, and both single field uniform dose (SFUD) and intensity-modulated proton therapy (IMPT) plans were delivered. Experiments were repeated for each patient without any motion, to compute the relative dose deviation between static and breath-hold cases. RESULTS: SFUD plans showed small dose deviations between static and breath-hold cases, as evidenced by the gamma pass rate (3%, 3 mm) of 85% or higher. Dose deviation was more evident for IMPT plans, with gamma pass rate reduced to 50-70%. CONCLUSIONS: The breath-hold technique is robust to residual intra-breath-hold motion for SFUD treatment plans, based on our experimental study. IMPT was less robust with larger detected dose deviations.

Retrospective estimation of heart and lung doses in pediatric patients treated with spinal irradiation.

BACKGROUND AND PURPOSE: The purpose of this study was to investigate whether treatment information from medical records can be used to estimate radiation doses to heart and lungs retrospectively in pediatric patients receiving spinal irradiation with conventional posterior fields. MATERIAL AND METHODS: An algorithm for retrospective dosimetry in children treated with spinal irradiation was developed in a cohort of 21 pediatric patients with available CT-scans and treatment plans. We developed a multivariable linear regression model with explanatory variables identifiable in case note review for retrospective estimation of minimum, maximum, mean and V10%-V80% doses to the heart and lungs. Doses were estimated for both linear accelerator (Linac) and 60Co radiation therapy modalities. RESULTS: Age and spinal field width were identified as statistically significant predictors of heart and lung doses in multivariable analyses (p < 0.01 in all models). Models showed excellent predictive performance with R2 = 0.70 for mean heart dose and 0.79 for mean lung dose, for Linac plans. In leave-one-out cross-validation analysis the average difference between predicted and actual mean heart dose was 6.7% and 7.6% of the prescription dose for Linac and 60Co plans, respectively, and 5.2% and 4.9% for mean lung dose. Due to the small sample size and large inter-patient variation in heart and lung dose, prospective studies validating these findings are highly warranted. CONCLUSIONS: The models presented here provide retrospective estimates of heart and lung doses for historical cohorts of pediatric patients, thus facilitating studies of long-term adverse effects of radiation.

Liquid fiducial marker performance during radiotherapy of locally advanced non small cell lung cancer.

BACKGROUND AND PURPOSE: We analysed the positional and structural stability of a long-term biodegradable liquid fiducial marker (BioXmark) for radiotherapy in patients with locally advanced lung cancer. MATERIAL AND METHODS: Markers were injected via endoscopic- or endobronchial ultrasound in lymph nodes and reachable primary tumours. Marker volume and Hounsfield Units (HU) changing rates were estimated using breath-hold CBCT. Inter-fraction variation in marker position relative to gross tumour volume (GTV) position was established, as well as the inter-fraction variation in mediastinal marker registration relative to a carina registration through the treatment. RESULTS: Fifteen patients were included and 29 markers analysed. All markers that were in situ at planning were visible through the treatment. Mean HU was 902±165HU for lymph node and 991±219HU for tumour markers. Volume degradation rates were -5% in lymph nodes and -23% in primary tumours. Three-dimensional inter-fraction variation for marker position relative to the GTV position was -0.1±0.7mm in lymph nodes and -1.5±2.3mm in primary tumours. Inter-fraction variations in marker registration relative to carina registration were -0.4±1.2mm in left-right, 0.2±2.0mm in anterior-posterior and -0.5±2.0mm in cranio-caudal directions. CONCLUSIONS: The liquid fiducial markers were visible and stable in size and position throughout the treatment course.

The effect on esophagus after different radiotherapy techniques for early stage Hodgkin's lymphoma.

INTRODUCTION: The cure rate of early stage Hodgkin's lymphoma (HL) is excellent; investigating the late effects of treatment is thus important. Esophageal toxicity is a known side effect in patients receiving radiotherapy (RT) to the mediastinum, although little is known of this in HL survivors. This study investigates the dose to the esophagus in the treatment of early stage HL using different RT techniques. Estimated risks of early esophagitis, esophageal stricture and cancer are compared between treatments. MATERIAL AND METHODS: We included 46 patients ≥ 15 years with supradiaphragmatic, clinical stage I-II HL, who received chemotherapy followed by involved node RT (INRT) to 30.6 Gy at our institution. INRT was planned with three-dimensional conformal RT (3DCRT). For each patient a volumetric modulated arc therapy (VMAT), proton therapy (PT) and mantle field (MF) treatment plan was simulated. Mean, maximum and minimum dose to the esophagus were extracted from the treatment plans. Risk estimates were based on dose-response models from clinical series with long-term follow-up. Statistical analyses were performed with repeated measures ANOVA using Bonferroni corrections. RESULTS: Mean dose to the esophagus was 16.4, 16.4, 14.7 and 34.2 Gy (p < 0.001) with 3DCRT, VMAT, PT and MF treatment, respectively. No differences were seen in the estimated risk of developing esophagitis, stricture or cancer with 3DCRT compared to VMAT (p = 1.000, p = 1.000, p = 0.356). PT performed significantly better with the lowest risk estimates on all parameters compared to the photon treatments, except compared to 3DCRT for stricture (p = 0.066). On all parameters the modern techniques were superior to MF treatment (p < 0.001). CONCLUSIONS: The estimated dose to the esophagus and the corresponding estimated risks of esophageal complications are decreased significantly with highly conformal RT compared to MF treatment. The number of patients presenting with late esophageal side effects will, thus, likely be minimal in the future.