Serious complications associated with stereotactic ablative radiotherapy and strategies to mitigate the risk.

The clinical applications of stereotactic body radiotherapy or stereotactic ablative radiotherapy (SABR) for the treatment of primary and metastatic tumours of different organ sites have been expanding rapidly in the recent decade. SABR requires advanced technology in radiotherapy planning and image guidance to deliver a highly conformal ablative dose precisely to targets (or tumours) in the body. Although this treatment modality has shown promising results with regard to tumour control, some serious complications have been observed and reported. In order to achieve a favourable therapeutic ratio, strategies to mitigate the risk of complications must be in place. This overview will summarise the reported serious complications caused by SABR and strategies to mitigate the risk will be discussed.

Which MR imaging sequences are necessary in determining the need for radiation therapy for cord compression? A prospective study.

BACKGROUND AND PURPOSE: To determine which MR imaging sequences are necessary to assess for spinal metastases. METHODS: Hypothetical MR imaging interpretations and management plans were made prospectively for consecutive adult cases acquired retrospectively. Standardized MR imaging protocols were independently interpreted by 2 neuroradiologists. MR imaging protocol types varied: 1) T1-weighted images only; 2) T1-weighted and T2-weighted images; 3) T1-weighted and postcontrast T1-weighted images; and 4) T1- and T2-weighted images and postcontrast T1-weighted images. Hypothetical management plans were created by 2 radiation oncologists. Logit model was used to investigate the effect of MR imaging protocol type on the probability of recommending radiation therapy (RT). Mixed effect models were used to investigate whether median spinal level or total number of spinal levels of planned RT was associated with MR imaging protocol type. RESULTS: Thirty-one subjects were evaluated, each with multiple scan interpretations. Logit model showed that neither MR imaging protocol type nor neuroradiologist reader affected the probability that the oncologist would recommend RT (all P > .50). Mixed models showed that neither ML nor NL was affected by MR imaging protocol type or by neuroradiologist reader (all P > .12). CONCLUSION: Although MR imaging is known to be the most useful diagnostic test in suspected spinal cord compression, which particular MR images are necessary remain unclear. Compared with T1-weighted images alone, the additional use of T2-weighted and/or postcontrast T1-weighted sequences did not significantly affect the probability that RT would be recommended or the levels that would be chosen for RT in our study. Our data suggest that unenhanced T1-weighted images may be sufficient for evaluation of possible cord compression.

Quantitative analysis of three-dimensional conformal radiotherapy techniques for posterior fossa treatment in children.

Numerous beam directions using 3-D conformal techniques can be employed in treating tumors in the posterior fossa, each with characteristic normal tissue exposure along the entrance and exit trajectory. A representative variety of beam configurations were modeled in a modern computer planning system initially with the entire posterior fossa as the target. These beams were quantitatively scored using criteria based on integral doses for both low dose and high dose effects encompassing a variety of critical normal structures, thus identifying strengths and weaknesses of each beam. By blocking portions of a particular beam accounting for unfavorable scores, a map of "zones" within the posterior fossa ideally treated by a certain beam or beams could be constructed. No universally ideal photon beam arrangement for the entire posterior fossa target could be identified. However, using single beam analysis, the strengths and weaknesses of particular strategies could be quantified. For example, vertex beams treating the cerebellar hemispheres allow the greatest sparing of cochlea and hypothalamus but at the cost of increased low to moderate dose to the supratentorial brain. Using the constructed maps identifying "zones" appropriately treated by a given beam or beams, three-dimensional conformal treatment plans with favorable dose-volume statistics can be designed based on previously defined normal tissue tolerance considerations. It is shown how this approach can be individualized based on specific patient characteristics (e.g., age). We conclude that radiotherapy directed to the posterior fossa can be optimized based on systematic assessment of individual beam contributions to normal tissues. This technique allows fast selection of treatment beams based on known normal tissue anatomical and tolerance information. Further studies will be required regarding long term effects of various radiation doses on specific volumes of normal tissue in order to individualize beam selection. When treating children, knowledgeable consideration of these beam characteristics can help avoid late effects.

How should we describe the radioblologic effect of extracranial stereotactic radlosurgery: equivalent uniform dose or tumor control probability?

Extracranial stereotactic radiosurgery (ESR) is now undergoing clinical investigation at numerous institutions as a treatment for solitary malignant lesions. Because there is no standard ESR technique, the same minimum dose might be applied through widely variable target dose-volume histograms. For multicenter trials of ESR or interinstitutional comparisons, a reliable index of radiobiological dose equivalency might facilitate the evaluation of dose-response relationships. Equivalent uniform dose (EUD) and tumor control probability (TCP) were considered for this application. While EUD appears more robust for the prospective description of ESR, TCP is expected to remain more valuable for a post hoc estimation of radiosensitivity parameters.

Brachytherapy for the prevention of stenosis in a canine hemodialysis graft model: preliminary observations.

PURPOSE: To determine whether gamma brachytherapy can prevent in-stent stenosis in hemodialysis grafts. MATERIALS AND METHODS: Six-millimeter polytetrafluoroethylene arteriovenous grafts were created bilaterally in six dogs. After 1 month, Wallstents spanning the venous anastomosis were placed to accelerate restenosis. Gamma irradiation (12 Gy) was delivered endoluminally to one of the two grafts by using an iridium 192 source; thus, each animal served as its own control. Fistulography was performed monthly for 10 months or until graft thrombosis, with measurement of stenosis at each time point. At the conclusion of the study period, the treated area was examined histologically, and a computer model was used to calculate the volume of intimal hyperplasia. RESULTS: Delayed stent migration resulted in exclusion of one dog. In the remaining five dogs; maximum stenosis across all time intervals was less for the treated side (P < .04), and the volume of intimal hyperplasia was less for the treated side (P < .045). In one animal studied at 1 year, this trend reversed in terms of percentage stenosis but not total neointimal volume. CONCLUSION: Brachytherapy with 192Ir (gamma) delivered at the time of stent placement reduces restenosis in this hemodialysis graft model, but, depending on the parameter evaluated (stenosis vs total volume of neointima), the benefit may wane or even reverse with time.

Wound complications associated with brachytherapy for primary or salvage treatment of head and neck cancer.

Brachytherapy can be employed in the primary or salvage treatment of head and neck cancer. The advantage of brachytherapy is the stereotactic limitation of radiation exposure to noninvolved tissues. Wound complications associated with brachytherapy have been discussed only sporadically in the literature. This retrospective study examines 28 patients, 20 for initial treatment and eight for salvage, with varying site and stage head and neck cancer treated with brachytherapy in addition to external beam radiation therapy and/or surgery. The overall complication rate was 50% (14/28), with infection and minor flap breakdown being the most common problems. Tumor site in the primary treatment group was the only significant factor in wound complications. In the salvage group complications were minor and primarily related to flap coverage of brachytherapy catheters.

Radiation therapy of external iliac lymph nodes with lateral pelvic portals: identification of patients at risk for inadequate regional coverage.

PURPOSE: To determine whether "standard" lateral pelvic radiation therapy portals provide adequate margins for treating the external iliac lymph nodes (EILNs). MATERIALS AND METHODS: With computed tomographic (CT) data and a computerized algorithm, the course of the EILN chain was reconstructed in 48 patients. The marginal distance between a consistently localized portion of the EILNs and the anterior field border that was placed at the front of the pubic symphysis was recorded for each patient. RESULTS: The EILNs were covered adequately in only 50% of both men and women. More adequate EILN margins were observed in (a) women older than 68 years, (b) women with small anteroposterior separations, (c) men older than 70 years, and (d) men and women with a low central obesity index. Less adequate margins were observed in men who were obese or men with large anteroposterior separations. In the study population, no correlation was observed for sex, race, or tumor site. CONCLUSION: The authors recommend portals that are designed specifically for patients rather than standard portals that may inadequately cover the intended targets.