Both authors contributed equally to this work.
A hybrid-dynamic conformal arc therapy (HDCAT) technique consisting of a single half-rotated dynamic conformal arc beam and static field-in-field beams in two directions was designed and evaluated in terms of dosimetric benefits for radiotherapy of lung cancer.
This planning study was performed in 20 lung cancer cases treated with the VERO system (BrainLAB AG, Feldkirchen, Germany). Dosimetric parameters of HDCAT plans were compared with those of three-dimensional conformal radiotherapy (3D-CRT) plans in terms of target volume coverage, dose conformity, and sparing of organs at risk.
HDCAT showed better dose conformity compared with 3D-CRT (conformity index: 0.74 ± 0.06 vs. 0.62 ± 0.06, p < 0.001). HDCAT significantly reduced the lung volume receiving more than 20 Gy (V20: 21.4% ± 8.2% vs. 24.5% ± 8.8%, p < 0.001; V30: 14.2% ± 6.1% vs. 15.1% ± 6.4%, p = 0.02; V40: 8.8% ± 3.9% vs. 10.3% ± 4.5%, p < 0.001; and V50: 5.7% ± 2.7% vs. 7.1% ± 3.2%, p < 0.001), V40 and V50 of the heart (V40: 5.2 ± 3.9 Gy vs. 7.6 ± 5.5 Gy, p < 0.001; V50: 1.8 ± 1.6 Gy vs. 3.1 ± 2.8 Gy, p = 0.001), and the maximum spinal cord dose (34.8 ± 9.4 Gy vs. 42.5 ± 7.8 Gy, p < 0.001) compared with 3D-CRT.
HDCAT could achieve highly conformal target coverage and reduce the doses to critical organs such as the lung, heart, and spinal cord compared to 3D-CRT for the treatment of lung cancer patients.
Radiotherapy (RT) alone or with chemotherapy is an important treatment for locally advanced lung cancer. Although a radiation dose higher than 60 Gy is important for better tumor control [
Recently, intensity-modulated radiotherapy (IMRT) is being used for the treatment of lung cancer because it can improve dose conformity and lower radiation doses to OARs compared with 3D-CRT [
Therefore, we designed a new technique, hybrid-dynamic conformal arc radiotherapy (HDCAT), to improve the quality of 3D-CRT. HDCAT is a type of conformal arc RT technique that delivers a single arc with static conformal fields. In this study, we evaluated the dosimetric advantages of HDCAT over 3D-CRT for the treatment of lung cancer.
The Institutional Review Board of Kyungpook National University Chilgok Hospital approved this study and waived the requirement for informed patient consent (No. 2016-12-026).
Twenty consecutive patients who were treated with HDCAT for lung cancer using the VERO system (BrainLAB AG, Feldkirchen, Germany) from November 2015 to March 2016 were retrospectively enrolled for this planning study. According to the discretion of physicians in this institution, patients with central tumors or tumors close to or invading into the mediastinum were treated with HDCAT unless the target volume exceeded the field size of the VERO system (maximum, 15 cm × 15 cm). Fourteen patients had tumors abutting on or invading into large bronchi with or without regional lymph node metastasis. Four patients had tumors close to or invading into the mediastinum. One patient had subcarinal lymph node recurrence, and one patient had left hilar lymph node recurrence. Nineteen patients had non-small cell lung cancer and one had small cell lung cancer. All patients had locally advanced disease (c/rT1-4N0-2) in the thorax based on the 7th edition of the American Joint Committee on Cancer staging system [
Patients lay in a supine position with both arms raised and were immobilized with a wing board and a vacuum bag. All patients underwent four-dimensional computed tomography (4D-CT) scans with slices of 3-mm thickness from the mandible to the mid-abdomen to include the whole lung using a Brilliance CT Big Bore (Philips, Amsterdam, the Netherlands). During 4D-CT scanning, the respiration of the patient was monitored with a Real-time Positioning Management (RPM) respiratory gating system (Varian Medical Systems, Palo Alto, CA, USA). The gross tumor volume (GTV) was defined as the primary tumor and involved regional lymph nodes. To generate the internal target volume (ITV), GTVs were manually delineated while reviewing all 10 respiratory phases of 4D-CT and expanded with a 6-mm margin considering the anatomical boundaries. The planning target volume (PTV) was generated by adding a 5-mm margin to the ITV. The target volumes and normal organs, including the total lung, heart, and spinal cord, were delineated on the untagged image set of 4D-CT images, which is a time weighted reconstruction with a true Hounsfield unit representation.
HDCAT plans used for the treatment of patients were not modified for this study except the dose prescription for dosimetric comparisons and 3D-CRT plans were generated with an effort to minimize the doses to OARs as much as possible. All plans were generated considering the recommended normal tissue dose-volume constraints [
The prescribed dose to the PTV was 66 Gy in 33 fractions. The planning objective was to achieve a minimum dose to ITV greater than 98% prescribed dose. The HDCAT plan consisted of a single dynamic conformal arc (DCA) rotating 180° and static conformal fields with the same isocenter (
For the comparison of target dose coverage between HDCAT and 3D-CRT plans, he conformity index (CI) used by MacFarlane et al. [
where V95PTV and V95body are the volumes of the PTV and body, respectively, receiving at least 95% of the prescription dose, and VPTV is the volume of the PTV. The better the dose conformity is, the closer the CI value approaches 1. The HI was defined as
where D5PTV and D95PTV correspond to the dose delivered to 5% and 95% of the PTV volume, respectively. The lower (closer to 1) HI is, the better the dose homogeneity.
Parameters for OARs were acquired from the dose-volume histograms (DVHs) of the HDCAT and 3D-CRT plans [
The median volume of the PTV was 214.94 mL (range, 82.63 to 467.13 mL). The target coverage parameters of HDCAT and 3D-CRT are summarized in
Dosimetric parameters of OARs are shown in
This planning study confirmed that HDCAT had dosimetric advantages over 3D-CRT in terms of the conformity and the doses to OARs.
Several studies reported that IMRT or volumetric modulated arc therapy (VMAT) could enhance CI when they used the ratio of the volume of normal tissue and target receiving the prescribed dose for the calculation of CI [
The V20 of the total lung and MLD are well-known parameters to estimate the probability of radiation pneumonitis [
Cardiac complications can occur in 6%–29% of lung cancer patients [
HDCAT could reduce the Dmax of the spinal cord in comparison to 3D-CRT. Because the angles of the beams for 3D-CRT are limited for the treatment of lung cancer as shown in
As HDCAT combining arc and conformal beams, other techniques using more than one type of beam have been reported. Chan et al. [
There are some limitations in the current study, because this study was performed only with patients treated with VERO. The physical properties of VERO are slightly different from other treatment machines. Because of the maximum field size of 15 cm × 15 cm, we only treated patients with a relatively small tumor volume. Therefore, our results should be cautiously interpreted, keeping in mind that the volume of PTV in our study ranged from 82.6 mL to 467.1 mL (median, 214.9 mL). In this volume range, we could not see a trend in the absolute value of the difference in all dosimetric parameters between HDCAT and 3D-CRT according to the PTV volume. For patients with a larger target volume to be treated, further studies comparing HDCAT with other treatment techniques, including 3D-CRT, IMRT, and VMAT, are warranted.
In conclusion, the HDCAT technique using a single half-rotated conformal arc and static field-in-field beams showed better target coverage and less doses to OARs such as the lung, heart, and spinal cord compared with 3D-CRT. Therefore, HDCAT is expected to reduce radiation-induced toxicities for lung cancer.
No potential conflict of interest relevant to this article was reported.
Hybrid-dynamic conformal arc radiotherapy plan, consisting of a single dynamic conformal arc (dark green) and static conformal fields (gray).
Dose distributions of hybrid-dynamic conformal arc radiotherapy plan (left) and three-dimensional conformal radiotherapy plan (right). Internal target volume in red and planning target volume in cyan.
Average dose-volume histograms of hybrid-dynamic conformal arc radiotherapy (HDCAT, solid line) and three-dimensional conformal radiotherapy (3D-CRT, dashed line) plans.
Comparison of the target dose-volume parameters for HDCAT and 3D-CRT
HDCAT | 3D-CRT | p-value | |
---|---|---|---|
CI | 0.74 ± 0.06 | 0.62 ± 0.06 | <0.001a) |
HI | 1.10 ± 0.02 | 1.10 ± 0.02 | 0.616 |
Values are presented as mean ± standard deviation.
HDCAT, hybrid dynamic conformal arc radiotherapy; 3D-CRT, three-dimensional conformal radiotherapy; CI, conformity index; HI, homogeneity index.
Paired t-test.
Comparison of doses to organs at risk
HDCAT | 3D-CRT | p-value | |
---|---|---|---|
Total lung | |||
Mean dose (Gy) | 12.0 ± 3.6 | 12.2 ± 3.7 | 0.102 |
V5 (%) | 50.8 ± 14.7 | 41.6 ± 13.0 | <0.001 |
V10 (%) | 32.5 ± 11.9 | 32.3 ± 10.6 | 0.819 |
V13 (%) | 26.9 ± 10.2 | 28.5 ± 10.0 | 0.097 |
V20 (%) | 21.4 ± 8.2 | 24.5 ± 8.8 | <0.001 |
V30 (%) | 14.2 ± 6.1 | 15.1 ± 6.4 | 0.022 |
V40 (%) | 8.8 ± 3.9 | 10.3 ± 4.5 | <0.001 |
V50 (%) | 5.7 ± 2.7 | 7.1 ± 3.2 | <0.001 |
Heart | |||
V40 (%) | 5.2 ± 3.9 | 7.6 ± 5.5 | <0.001 |
V50 (%) | 1.8 ± 1.6 | 3.1 ± 2.8 | 0.001 |
Spinal cord | |||
Dmax (Gy) | 34.8 ± 9.4 | 42.5 ± 7.8 | <0.001 |
Values are presented as mean ± standard deviation.
HDCAT, hybrid dynamic conformal arc radiotherapy; 3D-CRT, three-dimensional conformal radiotherapy; Dmax, maximum dose.
Paired t-test.
Wilcoxon signed-rank test.