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. 2021 Apr 20;16(1):77.
doi: 10.1186/s13014-021-01800-x.

Split-VMAT technique to control the deep inspiration breath hold time for breast cancer radiotherapy

Sara Poeta  1 , Younes Jourani  2 , Alex De Caluwé  3 , Robbe Van den Begin  3 , Dirk Van Gestel  3 , Nick Reynaert  2
Affiliations

Split-VMAT technique to control the deep inspiration breath hold time for breast cancer radiotherapy

Sara Poeta et al. Radiat Oncol. .

Abstract

Background: To improve split-VMAT technique by optimizing treatment delivery time for deep-inspiration breath hold (DIBH) radiotherapy in left-sided breast cancer patients, when automatic beam-interruption devices are not available.

Methods: Ten consecutive patients were treated with an eight partial arcs (8paVMAT) plan, standard of care in our center. A four partial arcs (4paVMAT) plan was also created and actual LINAC outputs were measured, to evaluate whether there was a dosimetric difference between both techniques and potential impact on the delivered dose. Subsequently, ten other patients were consecutively treated with a 4paVMAT plan to compare the actual treatment delivery time between both techniques. The prescribed dose was 40.05 Gy/15 fractions on the PTV breast (breast or thoracic wall), lymph nodes (LN) and intramammary lymph node chain (IMN). Treatment delivery time, PTVs coverage, conformity index (CI), organs at risk (OAR) dose, monitor units (MU), and gamma index were compared.

Results: Both split-VMAT techniques resulted in similar dose coverage for the PTV Breast and LN, and similar CI. For PTV IMN we observed a 5% increased coverage for the volume receiving ≥ 36 Gy with 4paVMAT, with an identical volume receiving ≥ 32 Gy. There was no difference for the OAR sparing, with the exception of the contralateral organs: there was a 0.6 Gy decrease for contralateral breast mean (p ≤ 0.01) and 1% decrease for the volume of right lung receiving ≥ 5 Gy (p = 0.024). Overall, these results indicate a modest clinical benefit of using 4paVMAT in comparison to 8paVMAT. An increase in the number of MU per arc was observed for the 4paVMAT technique, as expected, while the total number of MU remained comparable for both techniques. All the plans were measured with the Delta4 phantom and passed the gamma index criteria with no significant differences. Finally, the main difference was seen for the treatment delivery time: there was a significant decrease from 8.9 to 5.4 min for the 4paVMAT plans (p < .05).

Conclusions: This study is mainly of interest for centers who are implementing the DIBH technique without automatic beam-holding devices and who therefore may require to manually switch the beam on and off during breast DIBH treatment. Split-VMAT technique with 4 partial arcs significantly reduces the treatment delivery time compared to 8 partial arcs, without compromising the target coverage and the OAR sparing. The technique decreases the number of breath holds per fraction, resulting in a shorter treatment session.

Keywords: Deep inspiration breath-hold; SGRT; Split-VMAT.

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Conflict of interest statement

Dr. Poeta has nothing to disclose. Dr. Jourani has nothing to disclose. Dr. De Caluwé reports grants from AstraZeneca, outside the submitted work. Dr. Van den Begin has nothing to disclose. Dr. Van Gestel reports being a member of the Advisory board or receiving honoraria from Sanofi, Accuray, Takeda, Merck-Pfizer and Novartis. Dr. Reynaert has nothing to disclose.

Figures

Fig. 1
Fig. 1
Axial caption of the treatment arcs set up for one of the selected patients. On the left the 8paVMAT is displayed and on the right the 4paVMAT
Fig. 2
Fig. 2
The mean DVH for right lung (left figure) and contralateral breast (right figure) using 8paVMAT and 4paVMAT. The colored shadows show the interquartile ranges (IQRs) from the mean values
Fig. 3
Fig. 3
Boxplots of MU for 8paVMAT and 4paVMAT (total MU of all arcs, maximum MU per arc, minimum MU per arc)
Fig. 4
Fig. 4
Mean treatment delivery time in minutes for 8paVMAT and 4paVMAT
Fig. 5
Fig. 5
Measurement results with the gamma index for 8paVMAT and 4paVMAT with and without treatment interruption
See this image and copyright information in PMC

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