No abstract

This study is aimed at providing a dosimetric evaluation of the irregular motion of lung tumors due to variations in patients' respiration. Twenty-three lung cancer patients are retrospectively enrolled in this study. The motion of the patient clinical target volume is simulated and two types of irregularities are defined: characteristic and uncharacteristic motions. Characteristic irregularities are representative of random fluctuations in the observed target motion. Uncharacteristic irregular motion is classified as systematic errors in determination of the target motion during the planning session. Respiratory traces from measurement of patient abdominal motion are also used for the target motion simulations. Characteristic irregular motion was observed to cause minimal changes in target dosimetry with the largest effect of 2.5% ± 0.9% (1σ) reduction in the minimum target dose (D(min)) observed for targets that move 2 cm on average and exhibiting 50% amplitude variations within a session. However, uncharacteristic irregular motion introduced more drastic changes in the clinical target volume (CTV) dose; 4.1% ± 1.7% reduction for 1 cm motion and 9.6% ± 1.7% drop for 2 cm. In simulations with patients' abdominal motion, corresponding changes in target dosimetry were observed to be negligible (<0.1%). Only uncharacteristic irregular motion was identified as a clinically significant source of dosimetric uncertainty.

Calcification was demonstrated radiographically within newly diagnosed lymphoma of the mediastinum in two patients. These patients and those in other isolated reports show that radiographic examinations may, rarely, reveal calcification in lymphomatous tissue prior to treatment.

No abstract

Purpose: The aim of this study is to investigate the dosimetric effects of the irregular respiratory motion of lung tumors treated using respiratory gating techniques. Several treatment parameters such as the gating window, average target motion, and the inclusion of respiratory coaching techniques are also investigated for their effect on target dosimetric coverage. Methods and Materials: Respiratory motion traces of 11 lung cancer patients are used to reflect the typical respiratory irregularities. From the entire respiratory motion data, an average respiratory cycle is calculated to represent the corresponding regular motion for the patient. Using the regular motion amplitude, target volume is expanded by the amount of residual motion observed within the gating window and a treatment plan is generated. The target is then subjected to both regular and irregular motions without affecting anatomical topology. Target dosimetry under regular and irregular motion conditions is compared for quantitative evaluations Results: The reduction in Dmin due to irregular motion was less than 1% (4%) for a mean target motion of 1.0 cm (2.0 cm) when no gating technologies utilized. The drop in target Dmin increased as the shorter gating window sizes are implemented. For gated treatments with 50% duty cycle, largest change in Dmin was 2% and 9% for 1.0 and 2.0 cm mean target motions respectively. More importantly, gated treatments were observed to undermine target dosimetry in cases where the synchronization between the target motion and the external respiratory signal doesn't stay constant as observed by other investigators. Within the parameter space investigated here, up to 35% reduction in target Dmin was observed. Conclusion: Being a more aggressive treatment strategy, respiratory gated treatments were observed to be more susceptible to dosimetric uncertainties as compared to traditional delivery techniques in presence of irregular respiratory motion.