Robustness of VMAT and 3DCRT plans toward setup errors in radiation therapy of locally advanced left-sided breast cancer with DIBH.

PURPOSE: The aim of our study was to evaluate and compare the robustness of treatment plans produced using the volumetric modulated arc-therapy (VMAT) and the standard three-dimensional conformal radiotherapy (3DCRT) techniques by estimating perturbed doses induced by localization offsets for deep inspiration breath-hold (DIBH) in locally advanced breast cancer radiation therapy. METHODS: Twenty patients with left breast carcinoma requiring radiation therapy were analysed in this planning study. Robust VMAT plans regarding minimum CTV doses and standard 3DCRT plans were produced, and perturbed doses were calculated in accordance with localization values from the weekly offline imaging protocol. Offsets from 5 weeks were summed to a perturbed overall treatment plan. Dose criteria for evaluation were coverage and homogeneity of the target, as well as doses to organs at risk. RESULTS: VMAT plans resulted in significantly better target coverage compared to 3DCRT, as well as lowered doses to heart and left anterior descending artery, while the perturbed doses were less variable for VMAT than 3DCRT plans. Homogeneity was significantly improved in VMAT plans. The statistical analysis taking all organs into account found that VMAT plans were more robust than 3DCRT to localization offsets (p = .001). The overall mean setup-deviation for the DIBH-patients was less than 2 mm in all directions. CONCLUSIONS: VMAT plans were more robust on average than conventional 3DCRT plans for DIBH when localization errors were taken into consideration. The combination of robust VMAT planning and DIBH generally improves the homogeneity and target doses.

Tumors exposed to acute cyclic hypoxia show increased vessel density and delayed blood supply.

The purpose of this study was to investigate the effect of acute cyclic hypoxia on tumor vasculature. A-07 human melanoma xenografts growing in dorsal window chambers were used as tumor model. Acute cyclic hypoxia was induced by periodically exposing tumor-bearing mice to a low oxygen atmosphere. The hypoxia treatment consisted of 12 cycles of 10 min of low O(2) (8% O(2) in N(2)) followed by 10 min of air for a total of 4 hr. The treatment started the first day after tumor initiation, and was given daily for 9 days. Vascular morphology was assessed from high-resolution transillumination images, and tumor blood supply was assessed from first-pass imaging movies recorded after a bolus of 155 kDa tetramethylrhodamine isothiocyanate-labeled dextran had been administered intravenously. Hypoxia-treated tumors showed increased vessel density, decreased interstitial distance, and delayed blood supply compared to control tumors. The increase in vessel density was attributed to an increased number of small vessels. In conclusion, acute cyclic hypoxia induced angiogenesis in A-07 tumors resulting in increased density of small-diameter vessels and delayed tumor blood supply.