Two atmospheric circulation systems, the mid-latitude Westerlies and the Asian summer monsoon (ASM), play key roles in northern-hemisphere climatic changes. However, the variability of the Westerlies in Asia and their relationship to the ASM remain unclear. Here, we present the longest and highest-resolution drill core from Lake Qinghai on the northeastern Tibetan Plateau (TP), which uniquely records the variability of both the Westerlies and the ASM since 32 ka, reflecting the interplay of these two systems. These records document the anti-phase relationship of the Westerlies and the ASM for both glacial-interglacial and glacial millennial timescales. During the last glaciation, the influence of the Westerlies dominated; prominent dust-rich intervals, correlated with Heinrich events, reflect intensified Westerlies linked to northern high-latitude climate. During the Holocene, the dominant ASM circulation, punctuated by weak events, indicates linkages of the ASM to orbital forcing, North Atlantic abrupt events, and perhaps solar activity changes.

We propose a planning method to design true 4-dimensional (4D) intensity-modulated radiotherapy (IMRT) plans, called the t4Dplan method, in which the planning target volume (PTV) of the individual phases of the 4D computed tomography (CT) and the conventional PTV receive non-uniform doses but the cumulative dose to the PTV of each phase, computed using deformable image registration (DIR), are uniform. The non-uniform dose prescription for the conventional PTV was obtained by solving linear equations that required motion-convolved 4D dose to be uniform to the PTV for the end-exhalation phase (PTV50) and by constraining maximum inhomogeneity to 20%. A plug-in code to the treatment planning system was developed to perform the IMRT optimization based on this non-uniform PTV dose prescription. The 4D dose was obtained by summing the mapped doses from individual phases of the 4D CT using DIR. This 4D dose distribution was compared with that of the internal target volume (ITV) method. The robustness of the 4D plans over the course of radiotherapy was evaluated by computing the 4D dose distributions on repeat 4D CT datasets. Three patients with lung tumors were selected to demonstrate the advantages of the t4Dplan method compared with the commonly used ITV method. The 4D dose distribution using the t4Dplan method resulted in greater normal tissue sparing (such as lung, stomach, liver and heart) than did plans designed using the ITV method. The dose volume histograms of cumulative 4D doses to the PTV50, clinical target volume, lung, spinal cord, liver, and heart on the 4D repeat CTs for the two patients were similar to those for the 4D dose at the time of original planning.

Purpose

To compare dose-volume histograms (DVHs) for intensity-modulated proton therapy (IMPT) with intensity-modulated radiation therapy (IMRT) and passive scattering proton therapy (PSPT) for stage IIIB non-small cell lung cancer (NSCLC) and explore the possibility of individualized radical radiotherapy.

Methods and Materials

DVHs for IMPT, PSPT, and IMRT designed to deliver IMRT at 60 to 63 Gy, PSPT at 74 Gy, and IMPT at the same doses and individualized radical radiotherapy in patients with extensive stage IIIB NSCLC (N = 10 for each approach) were compared. These patients were selected based on their extensive disease and considered to have no or borderline tolerance of IMRT at 60 to 63 Gy based on normal tissue dose-volume constraints (lung V20<35%, total mean lung dose <20 Gy; spinal cord dose, <45 Gy). The possibility of increasing the total tumor dose with IMPT for each patient without exceeding the dose-volume constraints (maximum tolerant dose, MTD) was also investigated.

Results

Compared with IMRT, IMPT spared more lung, heart, spinal cord, and esophagus even with dose escalation from 63 Gy to 83.5 Gy, with a mean MTD of 74 Gy. Compared with PSPT, IMPT allowed further dose escalation from 74 Gy to mean MTD of 84.4 Gy (range 79.4-88.4 Gy) while keeping all parameters of normal tissue sparing lower or similar. In addition, IMPT prevented lower target coverage in patients with complicated tumor anatomies. Conclusions: IMPT reduces the normal tissue dose and allows individualized radical radiotherapy for extensive stage IIIB NSCLC.