Low-Dose Image-Guided Pediatric CNS Radiation Therapy: Final Analysis From a Prospective Low-Dose Cone-Beam CT Protocol From a Multinational Pediatrics Consortium.

BACKGROUND: Lower-dose cone-beam computed tomography protocols for image-guided radiotherapy may permit target localization while minimizing radiation exposure. We prospectively evaluated a lower-dose cone-beam protocol for central nervous system image-guided radiotherapy across a multinational pediatrics consortium. METHODS: Seven institutions prospectively employed a lower-dose cone-beam computed tomography central nervous system protocol (weighted average dose 0.7 mGy) for patients ≤21 years. Treatment table shifts between setup with surface lasers versus cone-beam computed tomography were used to approximate setup accuracy, and vector magnitudes for these shifts were calculated. Setup group mean, interpatient, interinstitution, and random error were estimated, and clinical factors were compared by mixed linear modeling. RESULTS: Among 96 patients, with 2179 pretreatment cone-beam computed tomography acquisitions, median age was 9 years (1-20). Setup parameters were 3.13, 3.02, 1.64, and 1.48 mm for vector magnitude group mean, interpatient, interinstitution, and random error, respectively. On multivariable analysis, there were no significant differences in mean vector magnitude by age, gender, performance status, target location, extent of resection, chemotherapy, or steroid or anesthesia use. Providers rated >99% of images as adequate or better for target localization. CONCLUSIONS: A lower-dose cone-beam computed tomography protocol demonstrated table shift vector magnitude that approximate clinical target volume/planning target volume expansions used in central nervous system radiotherapy. There were no significant clinical predictors of setup accuracy identified, supporting use of this lower-dose cone-beam computed tomography protocol across a diverse pediatric population with brain tumors.

HDR 192Ir source speed measurements using a high speed video camera.

PURPOSE: The dose delivered with a HDR (192)Ir afterloader can be separated into a dwell component, and a transit component resulting from the source movement. The transit component is directly dependent on the source speed profile and it is the goal of this study to measure accurate source speed profiles. METHODS: A high speed video camera was used to record the movement of a (192)Ir source (Nucletron, an Elekta company, Stockholm, Sweden) for interdwell distances of 0.25-5 cm with dwell times of 0.1, 1, and 2 s. Transit dose distributions were calculated using a Monte Carlo code simulating the source movement. RESULTS: The source stops at each dwell position oscillating around the desired position for a duration up to (0.026 ± 0.005) s. The source speed profile shows variations between 0 and 81 cm/s with average speed of ∼ 33 cm/s for most of the interdwell distances. The source stops for up to (0.005 ± 0.001) s at nonprogrammed positions in between two programmed dwell positions. The dwell time correction applied by the manufacturer compensates the transit dose between the dwell positions leading to a maximum overdose of 41 mGy for the considered cases and assuming an air-kerma strength of 48 000 U. The transit dose component is not uniformly distributed leading to over and underdoses, which is within 1.4% for commonly prescribed doses (3-10 Gy). CONCLUSIONS: The source maintains its speed even for the short interdwell distances. Dose variations due to the transit dose component are much lower than the prescribed treatment doses for brachytherapy, although transit dose component should be evaluated individually for clinical cases.

Implementation of a quality assurance program for computerized treatment planning systems.

In the present investigation, the necessary tests for implementing a quality assurance program for a commercial treatment planning system (TPS), recently installed at Sao Paulo University School of Medicine Clinicas Hospital-Brazil, was established and performed in accordance with the new IAEA publication TRS 430, and with AAPM Task Group 53. The tests recommended by those documents are classified mainly into acceptance, commissioning (dosimetric and nondosimetric), periodic quality assurance, and patient specific quality assurance tests. The recommendations of both IAEA and AAPM documents are being implemented at the hospital for photon beams produced by two linear accelerators. A Farmer ionization chamber was used in a 30 x 30 x 30 cm3 phantom with a dose rate of 320 monitor unit (MU)/min and 50 MU in the case of the dosimetric tests. The acceptance tests verified hardware, network systems integration, data transfer, and software parameters. The results obtained are in good agreement with the specifications of the manufacturer. For the commissioning dosimetric tests, the absolute dose was measured for simple geometries, such as square and rectangular fields, up to more complex geometries such as off-axis hard wedges and for behavior in the build up region. Results were analysed by the use of confidence limit as proposed by Venselaar et al. [Radio Ther. Oncol. 60, 191-201 (2001)]. Criteria of acceptability had been applied also for the comparison between the values of MU calculated manually and MU generated by TPS. The results of the dosimetric tests show that work can be reduced by choosing to perform only those that are more crucial, such as oblique incidence, shaped fields, hard wedges, and buildup region behavior. Staff experience with the implementation of the quality assurance program for a commercial TPS is extremely useful as part of a training program.

Análises de protocolos teleterápicos de controle de qualidade de alguns serviços locais, baseados no TG40 e ARCAL XXX / Routine teletherapy quality control protocols based on TG40 and ARCAL XXX

Considerando a importância da garantia da qualidade nos serviços de radioterapia, este trabalho tem como primeiro objetivo fazer uma avaliação dos testes propostos pelos protocolos oficiais internacionais TG40 e ARCAL XXX para os equipamentos de cobalto, acelerador linear e simulador. O segundo objetivo consistiu em se fazer uma avaliação dos testes que atualmente são realizados por alguns serviços de radioterapia nacionais e da América Latina, comparando-os com os apresentados nos protocolos citados. Dos resultados obtidos, observou-se que embora o TG40 apresente os testes básicos necessários para um controle de qualidade adequado, o ARCAL ainda sugere testes complementares. Dos resultados e discussões, concluiu-se que é necessário que os serviços de radioterapia implementem os testes de controle de qualidade básicos e indispensáveis aos seus equipamentos, e que os demais testes sejam implementados de acordo com as suas necessidades e disponibilidades. Como produto deste estudo, sugestões de protocolos são apresentadas para o trabalho de rotina, provenientes da fusão dos protocolos analisados.