Abstract
Adequate matching methods are critical for accurate volumetric-modulated arc therapy (VMAT). We investigated the dosimetric differences in the target and organs at risk (OARs) between bone matching and target matching in patients with prostate cancer treated with VMAT. The relationship between the dosimetric differences and interfractional motion of the prostate was also evaluated. Forty patients with prostate cancer classified as intermediate risk were enrolled in a study to assess the differences in dosimetry between two matching methods. These patients were treated with VMAT and prescribed dose was 78 Gy. The dose distribution was calculated using cone-beam computed tomography (CBCT) for this study. We selected clinical target volume (CTV) as the target, and the rectum and bladder as the OARs. The Dmean, D98, D95, and D2 to the target and V10-V70 to the OARs were calculated as different dose from target matching value minus bone matching value. Multiple regression analysis was used to evaluate the effect of interfractional motion of the prostate on the differences in dose. The CTV D95 values differed by -0.22 ± 1.01 Gy (mean ± standard deviation). Rectum and bladder V70 values differed by 4.6% ± 7.2% and -2.6% ± 7.2%, respectively. There was a correlation between interfractional motion of the prostate and the dose differences to OARs (R2 = 0.73 - 0.94). The dose differences to OARs also varied depending on the direction of the prostate’s motion. We found that bone matching resulted in an increased rectal dose and high risk of decreasing dose to the CTV.
Highlights
Intensity-modulated radiotherapy (IMRT) for prostate cancer can deliver a more adequate dose distribution to the target while sparing normal tissue compared with conventional irradiation methods
We investigated the dosimetric differences in the target and organs at risk (OARs) between bone matching and target matching in patients with prostate cancer treated with volumetric-modulated arc therapy (VMAT)
The bone matching dose produced higher increases in all dosimetric indicators to the rectum compared to the target matching dose, and resulted in lower doses to the clinical target volume (CTV) and bladder than the target matching dose
Summary
Intensity-modulated radiotherapy (IMRT) for prostate cancer can deliver a more adequate dose distribution to the target while sparing normal tissue compared with conventional irradiation methods. Rijkhorst et al [17] reported that the dosimetric effect of different matching methods is dependent on interfractional motion of the prostate in the anteroposterior direction. Knowledge of this effect is important when choosing a matching method. We assessed interfractional motion of the prostate and the resulting dosimetric effects on the target and organs at risk (OARs) using the bone and target matching methods
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