Direct aperture optimization as a means of reducing the complexity of intensity modulated radiation therapy plans

Intensity Modulated Radiation Therapy (IMRT) is a means of delivering radiation therapy where the intensity of the beam is varied within the treatment field. This is done by dividing a large beam into many small beamlets. Dose constraints are assigned to both the target and sensitive structures and computerised inverse optimization is performed to find the individual weights of this large number of beamlets. The computer adjusts the intensities of these beamlets according to the required planning dose objectives. The optimized intensity patterns are then decomposed into a series of deliverable multi leaf collimator (MLC) shapes in the sequencing step

Application of volumetric modulated arc therapy (VMAT) in a dual-vendor environment

Background and Purpose The purpose of this study was to assess plan quality and treatment time achievable with the new VMAT optimization tool implemented in the treatment planning system Oncentra MasterPlan® as compared to IMRT for Elekta SynergyS® linear accelerators. Materials and methods VMAT was implemented on a SynergyS® linear accelerator (Elekta Ltd., Crawley, UK) with Mosaiq® record and verify system (IMPAC Medical Systems, Sunnyvale, CA) and the treatment planning system Oncentra MasterPlan® (Nucletron BV, Veenendaal, the Netherlands). VMAT planning was conducted for three typical target types of prostate cancer, hypopharynx/larynx cancer and vertebral metastases, and compared to standard IMRT with respect to plan quality, number of monitor units (MU), and treatment time. Results For prostate cancer and vertebral metastases single arc VMAT led to similar plan quality as compared to IMRT. For treatment of the hypopharynx/larynx cancer, a second arc was necessary to achieve sufficient plan quality. Treatment time was reduced in all cases to 35% to 43% as compared to IMRT. Times required for optimization and dose calculation, however, increased by a factor of 5.0 to 6.8. Conclusion Similar or improved plan quality can be achieved with VMAT as compared to IMRT at reduced treatment times but increased calculation times

Comparison of simple and complex liver intensity modulated radiotherapy

<p>Abstract</p> <p>Background</p> <p>Intensity-modulated radiotherapy (IMRT) may allow improvement in plan quality for treatment of liver cancer, however increasing radiation modulation complexity can lead to increased uncertainties and requirements for quality assurance. This study assesses whether target coverage and normal tissue avoidance can be maintained in liver cancer intensity-modulated radiotherapy (IMRT) plans by systematically reducing the complexity of the delivered fluence.</p> <p>Methods</p> <p>An optimal baseline six fraction individualized IMRT plan for 27 patients with 45 liver cancers was developed which provided a median minimum dose to 0.5 cc of the planning target volume (PTV) of 38.3 Gy (range, 25.9-59.5 Gy), in 6 fractions, while maintaining liver toxicity risk <5% and maximum luminal gastrointestinal structure doses of 30 Gy. The number of segments was systematically reduced until normal tissue constraints were exceeded while maintaining equivalent dose coverage to 95% of PTV (PTVD95). Radiotherapy doses were compared between the plans.</p> <p>Results</p> <p>Reduction in the number of segments was achieved for all 27 plans from a median of 48 segments (range 34-52) to 19 segments (range 6-30), without exceeding normal tissue dose objectives and maintaining equivalent PTVD95 and similar PTV Equivalent Uniform Dose (EUD(-20)) IMRT plans with fewer segments had significantly less monitor units (mean, 1892 reduced to 1695, p = 0.012), but also reduced dose conformity (mean, RTOG Conformity Index 1.42 increased to 1.53 p = 0.001).</p> <p>Conclusions</p> <p>Tumour coverage and normal tissue objectives were maintained with simplified liver IMRT, at the expense of reduced conformity.</p

Reprodutibilidade do teste de 1-RM em indivíduos com doença arterial obstrutiva periférica Reproducibility of the 1-RM test in individuals with peripheral obstructive arterial disease

INTRODUÇÃO: Indivíduos com doença arterial obstrutiva periférica (DAOP) apresentam atrofia muscular e redução da força de membros inferiores que, por sua vez, estão associadas às limitações na capacidade funcional. Consequentemente, a mensuração da força muscular pode ser útil na identificação dos níveis de força muscular e para monitorar as alterações na força em programas de intervenção. OBJETIVO: Analisar a reprodutibilidade do teste de uma repetição máxima (1-RM) em indivíduos com DAOP. Métodos: Fizeram parte da amostra 26 indivíduos com DAOP e sintomas de claudicação intermitente. Os indivíduos realizaram quatro sessões de teste de 1-RM no exercício extensão de joelhos unilateral, no membro com maior índice tornozelo-braço (ITB) e no membro com menor ITB. RESULTADOS: A força máxima aumentou significantemente da primeira para a segunda sessão de teste nos dois membros (4,1 ± 14,3% na perna com menor ITB e 5,9 ± 13,1% na perna com maior ITB). A análise dos limites de concordância revelou que, nos dois membros, as maiores diferenças médias e os maiores limites de concordância foram observados quando comparadas as sessões 1 e 2. CONCLUSÃO: A medida acurada da força máxima usando o teste de 1-RM, no exercício extensão de joelhos, em indivíduos com DAOP e sintomas de claudicação intermitente, é obtida quando duas sessões de testes de 1-RM são realizadas.<br>INTRODUCTION: Patients with peripheral obstructive arterial disease (PAD) present muscle atrophy and reduced strength in the legs which have been associated with impairment in physical function. Consequently, the assessment of leg strength can be useful for identifying muscle weakness and analyzing the efficacy of intervention programs for patients with PAD. OBJECTIVE: To assess the reliability of the 1-RM test in patients with PAD. Methods: The sample was composed of twenty-six patients with PAD and symptoms of mild intermittent claudication. Patients performed the 1-RM tests in the knee extension exercise in the leg with lower ankle brachial index (ABI) and in the leg with higher ABI. This protocol was repeated in four sessions to assess the reliability of the maximum strength measurements. RESULTS: Maximal strength increased significantly from session 1 to session 2 in both legs (4.1 ± 14.3% in the leg with lower ABI and 5.9 ± 13.1% in the leg with higher ABI). The analysis of agreement revealed that higher bias and higher limits of agreement were observed in both legs when sessions 1 and 2 were compared. CONCLUSION: Reliable assessment of strength using 1-RM test in knee extension exercise in patients with PAD and symptoms of intermittent claudication is obtained when 2 test sessions are performed