Open AccessMinimizing dose variation from the interplay effect in stereotactic radiation therapy using volumetric modulated arc therapy for lung cancer
Author(s) -
Kubo Kazuki,
Monzen Hajime,
Tamura Mikoto,
Hirata Makoto,
Ishii Kentaro,
Okada Wataru,
Nakahara Ryuta,
Kishimoto Shun,
Kawamorita Ryu,
Nishimura Yasumasa
Publication year - 2018
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1002/acm2.12264
Subject(s) - nuclear medicine , multileaf collimator , radiation therapy , medicine , dosimetry , respiratory quotient , imaging phantom , lung cancer , radiation treatment planning , materials science , radiology
It is important to improve the magnitude of dose variation that is caused by the interplay effect. The aim of this study was to investigate the impact of the number of breaths ( NB s) to the dose variation for VMAT ‐ SBRT to lung cancer. Data on respiratory motion and multileaf collimator ( MLC ) sequence were collected from the cases of 30 patients who underwent radiotherapy with VMAT ‐ SBRT for lung cancer. The NB s in the total irradiation time with VMAT and the maximum craniocaudal amplitude of the target were calculated. The MLC sequence complexity was evaluated using the modulation complexity score for VMAT ( MCS v). Static and dynamic measurements were performed using a cylindrical respiratory motion phantom and a micro ionization chamber. The 1 standard deviation which were obtained from 10 dynamic measurements for each patient were defined as dose variation caused by the interplay effect. The dose distributions were also verified with radiochromic film to detect undesired hot and cold dose spot. Dose measurements were also performed with different NB s in the same plan for 16 patients in 30 patients. The correlations between dose variations and parameters assessed for each treatment plan including NB s, MCS v, the MCS v/amplitude quotient ( TMMCS v), and the MCS v/amplitude quotient × NB s product ( IVS ) were evaluated. Dose variation was decreased with increasing NB s, and NB s of >40 times maintained the dose variation within 3% in 15 cases. The correlation between dose variation and IVS which were considered NB s was shown stronger ( R 2 = 0.43, P < 0.05) than TMMCS v ( R 2 = 0.32, P < 0.05). The NB s is an important factor to reduce the dose variation. The patient who breathes >40 times during irradiation of two partial arcs VMAT (i.e., NB s = 16 breaths per minute) may be suitable for VMAT ‐ SBRT for lung cancer.