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Dosimetric effects of swelling or shrinking tissue during helical tomotherapy breast irradiation. A phantom study.

ABSTRACT: During radiation therapy of the female breast, the actual target volume compared to the planning target volume may change due to swelling or shrinking of the tissue. Under- or overdosage is to be expected, especially when performing IMRT or tomotherapy techniques. The objective of this study is to develop a model-based quantification of these dose effects, with a particular focus on the changes in the surface dose. A cylindrical phantom was used as an artificial surrogate of the human torso. By adding and removing Superflab layers of various thicknesses, both radial breast swelling and shrinking could be simulated. The effects on dose distribution were evaluated using film dosimetry. The results were compared to dose calculations. To estimate the true surface doses, we subtracted the influence of the film material on air measurements. During a swelling of 5, 10, and 15 mm, the planning target volume was consistently underdosed by 2%, 5%, and 7% of the prescribed dose, respectively. Swelling led to reduced dose values of up to 72%, 55%, and 50% at the outer edge of the actual target volume. The measured surface dose decreased successively from 31% to 23%. During shrinking, the dose in the planning target volume increased successively from 100% to 106%. The measured surface doses increased from 29% to 36%. The calculated dose values agreed with the measured values within error limits. During radiotherapy of the female breast, new planning appears to be essential for radial tissue swelling of 5 mm or more because of severe underdosing. Shrinking leads to moderate overdosing and an increased surface dose. In addition, caution is advised when removing bolus material with respect to the planned situation.

SUBMITTER: Klepper R

PROVIDER: S-EPMC5875514 | biostudies-literature | 2014 Jul

REPOSITORIES: biostudies-literature

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Dosimetric effects of swelling or shrinking tissue during helical tomotherapy breast irradiation. A phantom study.

Klepper Rudolf R Höfel Sebastian S Botha Ulrike U Köhler Peter P Zwicker Felix F

Journal of applied clinical medical physics 20140708 4

During radiation therapy of the female breast, the actual target volume compared to the planning target volume may change due to swelling or shrinking of the tissue. Under- or overdosage is to be expected, especially when performing IMRT or tomotherapy techniques. The objective of this study is to develop a model-based quantification of these dose effects, with a particular focus on the changes in the surface dose. A cylindrical phantom was used as an artificial surrogate of the human torso. By ...[more]

PMID: 25207418

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Project description:Purpose:Because of the poor prognosis for high-grade glioma (HGG) patients, it is important to increase the dose of the tumor to improve the efficacy while minimizing the dose of organs at risk (OARs). Thus, we evaluated the potential dosimetric gains of helical tomotherapy (HT) versus intensity-modulated radiotherapy (IMRT) or volume-modulated arc therapy (VMAT) for high-grade glioma (HGG). Methods:A total of 42 HGG patients were retrospectively selected who had undergone helical tomotherapy; then, IMRT and VMAT plans were generated and optimized for comparison after contouring crucial neuronal structures for neurogenesis and neurocognitive function. IMRT and VMAT were optimized with the Eclipse treatment planning system (TPS) (Version 11.0.31) and HT using TomoTherapy Hi-Art Software (Version 2.0.7) (Accuray, Madison, WI, USA). All three techniques were optimized for simultaneously delivering 60?Gy to planning target volume (PTV) 1 and 50-54?Gy to PTV2. We also analyzed the homogeneity index (HI) and conformity index (CI) of PTVs and organ at risk (OAR) sparing. Results:There was no significant difference in the PTV coverage among IMRT, VMAT, or HT. As for the HI, HT plans (PTV1 HI: 0.09 ± 0.03, PTV2 HI: 0.17 ± 0.05) had the best homogeneity when compared to IMRT plans (PTV1 HI: 0.10 ± 0.04, PTV2 HI: 0.18 ± 0.04) and VMAT plans (PTV1 HI: 0.11 ± 0.03, PTV2 HI: 0.20 ± 0.03). The CI value of HT (PTV1 CI: 0.98 ± 0.03, PTV2: 0.98 ± 0.05) was closest to the optimal value. Except for the IMRT and VMAT groups, there were statistically significant differences between the other two groups of the CI values in both PTV1 and PTV2. The other comparison values were statistically significant except for the optic nerve, and VMAT had the best sparing of the optic chiasm. The mean and max doses of OARs declined significantly in HT. Conclusions:For high-grade glioma patients, HT had superior outcomes in terms of PTV coverage and OAR sparing as compared with IMRT/VMAT.

Project description:ObjectiveAs craniospinal irradiation (CSI) is delivered more frequently by helical tomotherapy (HT) with few reports about late effects, we analysed all patients treated in our centre over an 11-year period.Methods and materialsOur study included all patients that underwent CSI by HT, between September 2009 and January 2020, in the Department of Radiation Oncology of the Toulouse Cancer Institute. Acute radiotherapy toxicities were reported and medium- to long-term outcomes analysed.ResultsAmong the 79 patients included, 70.9 % were younger than 18 years at diagnosis, the median age was 13 (range: 1-52) at the time of radiation therapy, 67.1 % of patients had medulloblastoma. Half of them (49.4 %) had a metastatic disease at diagnosis. The median dose of CSI was 36 Gy (range, 18-36). Seventy-seven patients received a radiation boost to the original location of the primary tumour (97.5 %), 32 patients also received a boost to their metastatic sites (40.5 %). Median follow-up was 55.5 months (95 %CI = [41.2; 71.8]). The 3-year event-free survival rate was 66.3 % (95 %CI = [54.2; 75.9]). Most patients presented with acute haematological toxicities during CSI (85.9 %), predominantly severe thrombocytopenia (39.7 %). Among the 64 patients assessed for medium- and long-term outcomes, 52 survived and 47 were alive and disease-free at the latest follow-up visit on record. There were 3.8 % secondary tumours: two meningiomas and one diffuse intrinsic pontine glioma. Adult and paediatric patients respectively presented with secondary cataract (4.3 % vs 22.0 %), persistent hearing disorders (26.1 % vs 29.3 %), pulmonary or cardiac late effects (4.3 % vs 2.4 %), hormonal pituitary gland deficiencies (30.0 % vs 56.8 %) and psycho-cognitive disorders (56.5 % vs 53.7 %).ConclusionCSI dispensed by HT, did not result in any additional acute or late toxicities when compared to 3D-CSI. There was no increase in the secondary tumour rate compared to that reported in the literature.

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Dosimetric effects of swelling or shrinking tissue during helical tomotherapy breast irradiation. A phantom study.

Publications

Dosimetric effects of swelling or shrinking tissue during helical tomotherapy breast irradiation. A phantom study.

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