Empirical planning target volume modeling for high precision MRI guided intracranial radiotherapy

Purpose

Magnetic resonance image-guided radiotherapy for intracranial indications is a promising advance; however, uncertainties remain for both target localization after translation-only MR setup and intrafraction motion. This investigation quantified these uncertainties and developed a population-based planning target volume (PTV) model to explore target and organ-at-risk (OAR) volumetric coverage tradeoffs.

Methods

Sixty-six patients, 49 with a primary brain tumor and 17 with a post-surgical resection cavity, treated on a 1.5T-based MR-linac across 1329 fractions were included. At each fraction, patients were setup by translation-only fusion of the online T1 MRI to the planning image. Each fusion was independently repeated offline accounting for rotations. The six degree-of-freedom difference between fusions was applied to transform the planning CTV at each fraction (CTV_fx). A PTV model parameterized by volumetric CTV_fx coverage, proportion of fractions, and proportion of patients was developed. Intrafraction motion was quantified in a 412 fraction subset as the fusion difference between post- and pre-irradiation T1 MRIs.

Results

For the left-right/anterior-posterior/superior-inferior axes, mean ± SD of the rotational fusion differences were 0.1 ± 0.8/0.1 ± 0.8/-0.2 ± 0.9°. Covering 98 % of the CTV_fx in 95 % of fractions in 95 % of patients required a 3 mm PTV margin. Margin reduction decreased PTV-OAR overlap; for example, the proportion of optic chiasm overlapped by the PTV was reduced up to 23.5 % by margin reduction from 4 mm to 3 mm.

Conclusions

An evidence-based PTV model was developed for brain cancer patients treated on the MR-linac. Informed by this model, we have clinically adopted a 3 mm PTV margin for conventionally fractionated intracranial patients.

Leukocyte adhesion deficiency

Leukocyte adhesion deficiency is a rare syndrome with autosomal recessive pattern of inheritance. An eleven-month-old boy, whose parents were first degree relatives, was referred to clinic with recurrent episodes of pneumonia, otitis and extensive necrotic wounds of perianal area since neonatal period. His umbilical cord had separated 30 days after birth. Laboratory findings included marked leukocytosis, chemotaxis abnormality, and very low levels of CD 11 (0.5%) and CD 18 (2%). Leukocyte Adhesion Defect (LAD) is rare genetic defect of a group of leukocyte membrane glycoproteins. LAD affects nearly one out of every million individuals and is characterized by recurrent bacterial and fungal infections of skin and mucous membranes, diminished pus formation, delayed umbilical cord separation, granulocytosis, poor wound healing and progressive periodontitis. This is the first report of a case of LAD in Isfahan of Iran.

Influenza outbreak detection and control measures in nursing homes in the United States

OBJECTIVE

To evaluate the use of influenza vaccine, rapid influenza testing, and influenza antiviral medication in nursing homes in the US to prevent and control outbreaks.

METHODS

Survey questionnaires were sent to 1017 randomly selected nursing homes in nine states. Information was collected on influenza prevention, detection and control practices, and on outbreaks during three influenza seasons (1995-1998).

RESULTS

The survey response rate was 78%. Influenza vaccine was offered to residents and staff by 99% and 86%, respectively, of nursing homes. Among nursing homes offering the influenza vaccine, the average vaccination rate was 83% for residents and 46% for staff. Sixty-seven percent of the nursing homes reported having access to laboratories with rapid antigen testing capabilities, and 19% reported having a written policy for the use of influenza antiviral medications for outbreak control. Nursing homes from New York, where organized education programs on influenza detection and control have been conducted for many years, were more likely to have reported a suspected or laboratory-confirmed influenza outbreak (51% vs 10%, P = .01), to have access to rapid antigen testing for influenza (92% vs 63%, P = .01), and to use antivirals for prophylaxis and treatment of influenza A for their nursing home residents (94% vs 55%, P = .01) compared with nursing homes from the other eight states.

CONCLUSIONS

Influenza outbreaks among nursing home residents can lead to substantial morbidity and mortality when prevention measures are not rapidly instituted. However, many nursing homes in this survey were neither prepared to detect nor to control influenza A outbreaks. Targeted, sustained educational efforts can improve the detection and control of outbreaks in nursing homes.