Total body irradiation with volumetric modulated arc therapy: Dosimetric data and first clinical experienceReport as inadecuate




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Radiation Oncology

, 11:46

Clinical Radiation Oncology

Abstract

BackgroundTo implement total body irradiation TBI using volumetric modulated arc therapy VMAT. We applied the Varian RapidArc™ software to calculate and optimize the dose distribution. Emphasis was placed on applying a homogenous dose to the PTV and on reducing the dose to the lungs.

MethodsFrom July 2013 to July 2014 seven patients with leukaemia were planned and treated with a VMAT-based TBI-technique with photon energy of 6 MV. The overall planning target volume PTV, comprising the whole body, had to be split into 8 segments with a subsequent multi-isocentric planning. In a first step a dose optimization of each single segment was performed. In a second step all these elements were calculated in one overall dose-plan, considering particular constraints and weighting factors, to achieve the final total body dose distribution. The quality assurance comprised the verification of the irradiation plans via ArcCheck™ Sun Nuclear, followed by in vivo dosimetry via dosimeters MOSFETs on the patient.

ResultsThe time requirements for treatment planning were high: contouring took 5–6 h, optimization and dose calculation 25–30 h and quality assurance 6–8 h. The couch-time per fraction was 2 h on day one, decreasing to around 1.5 h for the following fractions, including patient information, time for arc positioning, patient positioning verification, mounting of the MOSFETs and irradiation. The mean lung dose was decreased to at least 80 % of the planned total body dose and in the central parts to 50 %. In two cases we additionally pursued a dose reduction of 30 to 50 % in a pre-irradiated brain and in renal insufficiency. All high dose areas were outside the lungs and other OARs. The planned dose was in line with the measured dose via MOSFETs: in the axilla the mean difference between calculated and measured dose was 3.6 % range 1.1–6.8 %, and for the wrist-hip-inguinal region it was 4.3 % range 1.1–8.1 %.

ConclusionTBI with VMAT provides the benefit of satisfactory dose distribution within the PTV, while selectively reducing the dose to the lungs and, if necessary, in other organs. Planning time, however, is extensive.

KeywordsTotal body irradiation TBI Total marrow irradiation TMI Volumetric modulated arc therapy VMAT Leukaemia Organs at risk OAR Dose sparing Dose homogenising Andreas Springer and Josef Hammer are co - first authors.

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Author: Andreas Springer - Josef Hammer - Erwin Winkler - Christine Track - Roswitha Huppert - Alexandra Böhm - Hedwig Kasparu - A

Source: https://link.springer.com/



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