Adjuvant radiation therapy for bladder cancer: a dosimetric comparison of techniques.

Trials of adjuvant radiation after cystectomy are under development. There are no studies comparing radiation techniques to inform trial design. This study assesses the effect on bowel and rectal dose of 3 different modalities treating 2 proposed alternative clinical target volumes (CTVs). Contours of the bowel, rectum, CTV-pelvic sidewall (common/internal/external iliac and obturator nodes), and CTV-comprehensive (CTV-pelvic sidewall plus cystectomy bed and presacral regions) were drawn on simulation images of 7 post-cystectomy patients. We optimized 3-dimensional conformal radiation (3-D), intensity-modulated radiation (IMRT), and single-field uniform dose (SFUD) scanning proton plans for each CTV. Mixed models regression was used to compare plans for bowel and rectal volumes exposed to 35% (V35%), 65% (V65%), and 95% (V95%) of the prescribed dose. For any given treatment modality, treating the larger CTV-comprehensive volume compared with treating only the CTV-pelvic sidewall nodes significantly increased rectal dose (V35% rectum, V65% rectum, and V95% rectum; p < 0.001 for all comparisons), but it did not produce significant differences in bowel dose (V95% bowel, V65% bowel, or V35% bowel). The 3-D plans, compared with both the IMRT and the SFUD plans, had a significantly greater V65% bowel and V95% bowel for each proposed CTV (p < 0.001 for all comparisons). The effect of treatment modality on rectal dosimetry differed by CTV, but it generally favored the IMRT and the SFUD plans over the 3-D plans. Comparison of the IMRT plan vs the SFUD plan yielded mixed results with no consistent advantage for the SFUD plan over the IMRT plan. Targeting a CTV that spares the cystectomy bed and presacral region may marginally improve rectal toxicity but would not be expected to improve the bowel toxicity associated with any given modality of adjuvant radiation. Using the IMRT or the SFUD plans instead of the 3-D conformal plan may improve both bowel and rectal toxicity.

An integrated method for reproducible and accurate image-guided stereotactic cranial irradiation of brain tumors using the small animal radiation research platform.

Preclinical studies of cranial radiation therapy (RT) using animal brain tumor models have been hampered by technical limitations in the delivery of clinically relevant RT. We established a bioimageable mouse model of glioblastoma multiforme (GBM) and an image-guided radiation delivery system that facilitated precise tumor localization and treatment and which closely resembled clinical RT. Our novel radiation system makes use of magnetic resonance imaging (MRI) and bioluminescent imaging (BLI) to define tumor volumes, computed tomographic (CT) imaging for accurate treatment planning, a novel mouse immobilization system, and precise treatments delivered with the Small Animal Radiation Research Platform. We demonstrated that, in vivo, BLI correlated well with MRI for defining tumor volumes. Our novel restraint system enhanced setup reproducibility and precision, was atraumatic, and minimized artifacts on CT imaging used for treatment planning. We confirmed precise radiation delivery through immunofluorescent analysis of the phosphorylation of histone H2AX in irradiated brains and brain tumors. Assays with an intravenous near-infrared fluorescent probe confirmed that radiation of orthografts increased disruption of the tumor blood-brain barrier (BBB). This integrated model system, which facilitated delivery of precise, reproducible, stereotactic cranial RT in mice and confirmed RT's resultant histologic and BBB changes, may aid future brain tumor research.