Impact of varying air cavity on planning dosimetry for rectum patients treated on a 1.5 T hybrid MR-linac system Journal Article
| Authors: | Godoy Scripes, P.; Subashi, E.; Burleson, S.; Liang, J.; Romesser, P.; Crane, C.; Mechalakos, J.; Hunt, M.; Tyagi, N. |
| Article Title: | Impact of varying air cavity on planning dosimetry for rectum patients treated on a 1.5 T hybrid MR-linac system |
| Abstract: | Purpose: To investigate the dosimetric impact of magnetic (B) field on varying air cavities in rectum patients treated on the hybrid 1.5 T MR-linac. Methods: Artificial air cavities of varying diameters (0.0, 1.0, 1.5, 2.0, 2.5, 3.0, and 5.0 cm) were created for four rectum patients (two prone and two supine). A total of 56 plans using a 7 MV flattening filter-free beam were generated with and without B-field. Reference intensity-modulated radiation therapy treatment plans without air cavity in the presence and absence of B-field were generated to a total dose of 45/50 Gy. The reference plans were copied and recalculated for the varying air cavities. D95(PTV45–PTV50), D95(PTV50–aircavity), V50(PTV50–aircavity), Dmax(PTV50–aircavity), and V110%(PTV50–aircavity) were extracted for each patient. Annulus rings of 1-mm-diameter step size were generated for one of the air cavity plans (3.0 cm) for all four patients to determine Dmax (%) and V110% (cc) within each annulus. Results: In the presence of B-field, hot spots at the cavity interface start to become visible at ~1 cm air cavity in both supine and prone positioning due to electron return effect (ERE). In the presence of B-field Dmax and V110% varied from 5523 ± 49 cGy and 0.09 ± 0.16 cc for 0 cm air cavity size to 6050 ± 109 cGy and 11.6 ± 6.7 cc for 5 cm air cavity size. The hot spots were located within 3 mm inside the rectal-air interface, where Dmax increased from 110.4 ± 0.5% without B-field to 119.2 ± 0.8 % with B-field. Conclusions: Air cavities inside rectum affects rectum plan dosimetry due ERE. Location and magnitude of hot spots are dependent on the size of the air cavity. © 2020 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine |
| Keywords: | rectal cancer; mr-guided radiation therapy; 1.5 t magnetic field; electron return effect (ere) |
| Journal Title: | Journal of Applied Clinical Medical Physics |
| Volume: | 21 |
| Issue: | 7 |
| ISSN: | 1526-9914 |
| Publisher: | American College of Medical Physics |
| Date Published: | 2020-07-01 |
| Start Page: | 144 |
| End Page: | 152 |
| Language: | English |
| DOI: | 10.1002/acm2.12903 |
| PUBMED: | 32445292 |
| PROVIDER: | scopus |
| PMCID: | PMC7386179 |
| DOI/URL: | |
| Notes: | Article -- Export Date: 1 September 2020 -- Source: Scopus |
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