MAASTRO applicator, a novel rectal applicator for contact brachytherapy with 192Ir HDR sources
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Radiotherapy and Oncology
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Purpose or Objective: The standard care for rectal cancer includes surgery,
which may be avoided if complete response is achieved,
e.g. with chemoradiotherapy (EBCRT) or external beam
radiotherapy EBRT, adopting a watch and wait strategy.
Studies report a local regrowth reduction from 30% (EBCRT
alone) to 11% when EBCRT is associated with a radiation
boost using 50 kV x-rays (CXB), technique that allows a
high dose delivery to a highly selective volume, allowing
preservation of organs at risk (OAR) and low toxicity.
However, CXB is not widely adopted due to its low costeffectiveness.
Hence, the MAASTRO applicator was
developed to deliver a dose distribution similar to those
generated by CXB devices, but using HDR 192Ir sources, as
a cost-effective alternative to CXB, with possibility of
integration to treatment planning systems (TPS). Material and Methods: Fig 1-a shows the applicator design, a cylindrical
applicator with 5 channels and a slanted edge, using its tip. Results: Due to the applicator geometry, the most distal position
of the source in each channel doesn’t reach the sharp edge
of the applicator, resulting in an effective treatment
surface (high dose region shown in Fig 1 a and b) of
approximately 20 x 20 mm2, which is smaller than the
contact surface. The resulting dose falloff is steeper than
the one resulting from the P50 with a 22 mm applicator.
With the dose falloff normalized at 2mm, the relative dose
values delivered at depths of 0, 2, 5 and 10 mm are,
respectively, 130, 100, 70 and 43% for the P50 and 140,
100, 67 and 38% for the applicator. The time required to
deliver an average dose of 32 Gy to the treatment surface
of the applicator is 5m30s for a 40700 U source (new
source) and 8m30s for a 20350 U source (source to be
replaced), including the time required to
perform obstruction verification before irradiation. The
applicator delivers a high dose to a small target volume
while the lateral shielding spares normal tissues in all
directions other than the contact surface. Conclusion: The MAASTRO applicator was designed to deliver dose
distributions similar to those of CXB devices using 192Ir
HDR sources. The applicator has the advantage of TPS
integration, increasing the degrees of freedom to
modulate the dose distribution.
Como referenciar
BELLEZZO, M.; FONSECA, G.P.; VONCKEN, R.; VERRIJSSEN, A.; VAN BEVEREN, C.; ROELOFS, E.; YORIYAZ, H.; RENIERS, B.; VAN LIMBERGEN, E.J.; BARBEE, M.; VERHAEGEN, F. MAASTRO applicator, a novel rectal applicator for contact brachytherapy with 192Ir HDR sources. Radiotherapy and Oncology, v. 152, p. S1102-S1103, 2020. Supplement 1. DOI: 10.1016/S0167-8140(21)01990-3. Disponível em: http://repositorio.ipen.br/handle/123456789/32694. Acesso em: 27 Mar 2026.
Esta referência é gerada automaticamente de acordo com as normas do estilo IPEN/SP (ABNT NBR 6023) e recomenda-se uma verificação final e ajustes caso necessário.