Universal field matching in craniospinal irradiation by a background‐dose gradient‐optimized method

Abstract

PurposeThe gradient‐optimized methods are overcoming the traditional feathering methods to plan field junctions in craniospinal irradiation. In this note, a new gradient‐optimized technique, based on the use of a background dose, is described.MethodsTreatment planning was performed by RayStation (RaySearch Laboratories, Stockholm, Sweden) on the CT scans of a pediatric patient. Both proton (by pencil beam scanning) and photon (by volumetric modulated arc therapy) treatments were planned with three isocenters. An ‘in silico’ ideal background dose was created first to cover the upper‐spinal target and to produce a perfect dose gradient along the upper and lower junction regions. Using it as background, the cranial and the lower‐spinal beams were planned by inverse optimization to obtain dose coverage of their relevant targets and of the junction volumes. Finally, the upper‐spinal beam was inversely planned after removal of the background dose and with the previously optimized beams switched on.ResultsIn both proton and photon plans, the optimized cranial and the lower‐spinal beams produced a perfect linear gradient in the junction regions, complementary to that produced by the optimized upper‐spinal beam. The final dose distributions showed a homogeneous coverage of the targets.DiscussionOur simple technique allowed to obtain high‐quality gradients in the junction region. Such technique universally works for photons as well as protons and could be applicable to the TPSs that allow to manage a background dose.

Impact of setup errors on multi‐isocenter volumetric modulated arc therapy for craniospinal irradiation

“…5,8,10,13 Due to its advantage of less treatment time and potential decrease of movement uncertainty, especially for pediatric patients, linac-based VMAT CSI has been investigated and applied in clinical practice. Controlling linear dose gradient across the junction, 14 silico ideal-based universal field matching solution, 15 low gradient junction technique, 16 etc., have been investigated specifically for VMAT CSI to optimize the junction doses. However, as an inversely optimized technique, careful planning of field junctions may complicate the VMAT planning process.…”

Avaliação dosimétrica de erros de posicionamento para implementação da técnica de neuroeixo com arcoterapia volumétrica modulada (VMAT)

“…Com resultado similar a estes estudos (6,7,8,9,10,11), este trabalho demonstrou que a técnica de sobreposição é mais influenciada por erros de posicionamento, de tal forma que erros de 3 mm podem, em alguns casos, chegar, a 20% acima da dose de prescrição na junção dos arcos, lembrando que os valores encontrados são para erros de posicionamento em todas as frações do tratamento. Da mesma forma, a técnica gradiente escada com 6 cm de junção também apresentou grande impacto dosimétrico com magnitude semelhante à sobreposição de 3 cm de junção.…”

“…Da mesma forma, a técnica gradiente escada com 6 cm de junção também apresentou grande impacto dosimétrico com magnitude semelhante à sobreposição de 3 cm de junção. Um resultado diferente para essa técnica de gradiente foi encontrado no estudo de Myers e colaboradores [8], em que o gradiente de dose criado por quatro anéis, ou seja do tipo escada, com junção maior que 3,5 cm diminui significativamente diferenças dosimétricas em erros de posicionamento.…”

“…Assim, considerando os diferentes modelos de planejamento para a junção de campos encontrados na literatura (6,7,8,9,10,11) e seus respectivos impactos dosimétricos de erros de posicionamento em cada técnica, o objetivo do presente trabalho é estudar de forma retrospectiva a magnitude de erros de posicionamentos diários de CSI, avaliar a qualidade de planejamento de dois modelos de técnicas VMAT e os impactos dosimétricos de erros de posicionamento. Dessa forma, o trabalho visa encontrar a técnica que apresenta qualidade de planejamento e menor impacto dosimétrico para ser implementada na prática clínica.…”

Improved Volumetric Modulated Arc Therapy Field Junctions Using In Silico Base Plans: Application to Craniospinal Irradiation

“…Recently, Traneus et al briefly introduced a universal field matching solution that used an in silico ideal base plan dose to guide inverse optimization of junctioned VMAT for CSI [16]. However, to generate acceptable in silico base plans, Traneus et al needed to divide the PTV into five segments.…”