TY - JOUR
T1 - On the feasibility of cardiac substructure sparing in magnetic resonance imaging guided stereotactic lung radiotherapy
AU - van der Pol, Luuk H.G.
AU - Hackett, Sara L.
AU - Hoesein, Firdaus A.A.Mohamed
AU - Snoeren, Louk M.W.
AU - Pomp, Jacqueline
AU - Raaymakers, Bas W.
AU - Verhoeff, Joost J.C.
AU - Fast, Martin F.
N1 - Funding Information: We would like to acknowledge: H. Ligtenberg for creating the mid‐position images, L.G. Merckel, who delineated OARs and targets on the mid‐position images and P.R.S. Stijnman for automating the iOVH calculation. Martin F. Fast acknowledges funding by the Dutch Research Council (NWO) through project no. 17515 (BREATHE EASY). Publisher Copyright: © 2022 The Authors. Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.
PY - 2023/1
Y1 - 2023/1
N2 - Background: Lung stereotactic body radiotherapy (SBRT) has proven an effective treatment for medically inoperable lung tumors, even for (ultra-)central tumors. Recently, there has been growing interest in radiation-induced cardiac toxicity in lung radiotherapy. More specifically, dose to cardiac (sub-)structures (CS) was found to correlate with survival after radiotherapy. Purpose: Our goal is first, to investigate the percentage of patients who require CS sparing in an magnetic resonance imaging guided lung SBRT workflow, and second, to quantify how successful implementation of cardiac sparing would be. Methods: The patient cohort consists of 34 patients with stage II–IV lung cancer who were treated with SBRT between 2017 and 2020. A mid-position computed tomography (CT) image was used to create treatment plans for the 1.5 T Unity MR-linac (Elekta AB, Stockholm, Sweden) following clinical templates. Under guidance of a cardio-thoracic radiologist, 11 CS were contoured manually for each patient. Dose constraints for five CS were extracted from the literature. Patients were stratified according to their need for cardiac sparing depending on the CS dose in their non-CS constrained MR-linac treatment plans. Cardiac sparing treatment plans (CSPs) were then created and dosimetrically compared with their non-CS constrained treatment plan counterparts. CSPs complied with the departmental constraints and were considered successful when fulfilling all CS constraints, and partially successful if some CS constraints could be fulfilled. Predictors for the need for and feasibility of cardiac sparing were explored, specifically planning target volume (PTV) size, cranio-caudal (CC) distance, 3D distance, and in-field overlap volume histograms (iOVH). Results: 47% of the patients (16 out of 34) were in need of cardiac sparing. A successful CSP could be created for 62.5% (10 out of 16) of these patients. Partially successful CSPs still complied with two to four CS constraints. No significant difference in dose to organs at risk (OARs) or targets was identified between CSPs and the corresponding non-CS constrained MR-linac plans. The need for cardiac sparing was found to correlate with distance in the CC direction between target and all of the individual CS (Mann–Whitney U-test p-values <10−6). iOVHs revealed that complying with dose constraints for CS is primarily determined by in-plane distance and secondarily by PTV size. Conclusion: We demonstrated that CS can be successfully spared in lung SBRT on the MR-linac for most of this patient cohort, without compromising doses to the tumor or to other OARs. CC distance between the target and CS can be used to predict the need for cardiac sparing. iOVHs, in combination with PTV size, can be used to predict if cardiac sparing will be successful for all constrained CS except the left ventricle.
AB - Background: Lung stereotactic body radiotherapy (SBRT) has proven an effective treatment for medically inoperable lung tumors, even for (ultra-)central tumors. Recently, there has been growing interest in radiation-induced cardiac toxicity in lung radiotherapy. More specifically, dose to cardiac (sub-)structures (CS) was found to correlate with survival after radiotherapy. Purpose: Our goal is first, to investigate the percentage of patients who require CS sparing in an magnetic resonance imaging guided lung SBRT workflow, and second, to quantify how successful implementation of cardiac sparing would be. Methods: The patient cohort consists of 34 patients with stage II–IV lung cancer who were treated with SBRT between 2017 and 2020. A mid-position computed tomography (CT) image was used to create treatment plans for the 1.5 T Unity MR-linac (Elekta AB, Stockholm, Sweden) following clinical templates. Under guidance of a cardio-thoracic radiologist, 11 CS were contoured manually for each patient. Dose constraints for five CS were extracted from the literature. Patients were stratified according to their need for cardiac sparing depending on the CS dose in their non-CS constrained MR-linac treatment plans. Cardiac sparing treatment plans (CSPs) were then created and dosimetrically compared with their non-CS constrained treatment plan counterparts. CSPs complied with the departmental constraints and were considered successful when fulfilling all CS constraints, and partially successful if some CS constraints could be fulfilled. Predictors for the need for and feasibility of cardiac sparing were explored, specifically planning target volume (PTV) size, cranio-caudal (CC) distance, 3D distance, and in-field overlap volume histograms (iOVH). Results: 47% of the patients (16 out of 34) were in need of cardiac sparing. A successful CSP could be created for 62.5% (10 out of 16) of these patients. Partially successful CSPs still complied with two to four CS constraints. No significant difference in dose to organs at risk (OARs) or targets was identified between CSPs and the corresponding non-CS constrained MR-linac plans. The need for cardiac sparing was found to correlate with distance in the CC direction between target and all of the individual CS (Mann–Whitney U-test p-values <10−6). iOVHs revealed that complying with dose constraints for CS is primarily determined by in-plane distance and secondarily by PTV size. Conclusion: We demonstrated that CS can be successfully spared in lung SBRT on the MR-linac for most of this patient cohort, without compromising doses to the tumor or to other OARs. CC distance between the target and CS can be used to predict the need for cardiac sparing. iOVHs, in combination with PTV size, can be used to predict if cardiac sparing will be successful for all constrained CS except the left ventricle.
KW - MR-linac
KW - cardiac (sub-)structures
KW - cardiac sparing
KW - lung SBRT
KW - treatment planning
UR - http://www.scopus.com/inward/record.url?scp=85140403233&partnerID=8YFLogxK
U2 - https://doi.org/10.1002/mp.16028
DO - https://doi.org/10.1002/mp.16028
M3 - Article
C2 - 36210631
SN - 0094-2405
VL - 50
SP - 397
EP - 409
JO - Medical physics
JF - Medical physics
IS - 1
ER -