Computer visualization techniques (CVTs) foster evidence-based target delineation

Use of a deformable atlas to identify cryptic critical structures in the treatment of glioblastoma multiforme

Dose constraints for traditional neural critical structures (e.g. optic chiasm, brain stem) are a standard component of planning radiation therapy to the central nervous system. Increasingly, investigators are becoming interested in accounting for the dose delivered to other non-target neural structures (e.g. hippocampi), which are not easily identified on axial imaging. In this pilot study, a commercially available digital atlas was used to identify cryptic neural structures (hippocampus, optic radiations, and visual cortices) in 6 patients who received intensity modulated radiation therapy (IMRT) as part of multimodal management of glioblastoma multiforme (GBM). The patient's original IMRT plans were re-optimized, with avoidance parameters for the newly identified critical structures. Re-optimization was able to reduce both mean and maximum dose to the volumes of interest, with a more pronounced effect for contralateral structures. Mean dose was reduced by 11% and 3% to contralateral and ipsilateral structures, respectively, with comparable reduction in maximum dose of 10% and 2%, respectively. Importantly, target coverage was not compromised, with an average change in coverage of 0.2%. Overall, our results demonstrate the feasibility of incorporating tools for cryptic critical structure identification into the treatment planning process for GBM.

Helical Tomotherapy Significantly Reduces Dose to Normal Tissues When Compared to 3D-CRT for Locally Advanced Rectal Cancer

Combined modality treatment (neoadjuvant chemoradiotherapy followed by surgery) for locally advanced rectal cancer requires special attention to various organs at risk (OAR). As a result, the use of conformal dose delivery methods has become more common in this disease setting. Helical tomotherapy is an image-guided intensity modulated delivery system that delivers dose in a fan-beam manner at 7 degree intervals around the patient and can potentially limit normal tissue from high dose radiation while adequately treating targets. In this study we dosimetrically compare helical tomotherapy to 3D-CRT for stage T3 rectal cancer. The helical tomotherapy plans were optimized in the TomoPlan system to achieve an equivalent uniform dose of 45 Gy for 10 patients with T3N0M0 disease that was at least 5cm from the anal verge. The GTV included the rectal thickening and mass evident on colonoscopy and CT scan as well as with the help of a colorectal surgeon. The CTV included the internal iliac, obturator, and pre-sacral lymphatic chains. The OAR that were outlined included the small bowel, pelvic bone marrow, femoral heads, and bladder. Anatom-e system was used to assist in delineating GTV, CTV and OAR. These 10 plans were then duplicated and optimized into 3-field 3D-CRT plans within the Pinnacle planning system. The V[45], V[40], V[30], V[20], V[10], and mean dose to the OAR were compared between the helical tomotherapy and 3D-CRT plans. Statistically significant differences were achieved in the doses to all OAR, including all volumes and means except for V[10] for the small bowel and the femoral heads. Adequate dosimetric coverage of targets were achieved with both helical tomotherapy and 3D-CRT. Helical tomotherapy reduces the volume of normal tissue receiving high-dose RT when compared to 3D-CRT treatment. Both modalities adequately dose the tumor. Clinical studies addressing the dosimetric benefits are on-going.