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Year : 2019  |  Volume : 8  |  Issue : 3  |  Page : 180-186

Adaptive radiotherapy in non-small cell lung cancers: Is there a dosimetric benefit of volumetric modulated arc radiotherapy over three-dimensional conformal radiotherapy?

Department of Radiotherapy, PGIMER, Chandigarh, India

Correspondence Address:
Dr. Anshuma Bansal
Department of Radiotherapy, PGIMER, Chandigarh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijhas.IJHAS_14_19

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AIM: The study aimed to evaluate the change in gross tumor volume (GTV) in pretreatment and mid-treatment planning computed tomography (CT) scans, to find its dosimetric impact on normal tissue sparing when doing adaptive radiotherapy in lung cancers, and to do dosimetric comparison between volumetric modulated arc radiotherapy (VMAT) and three-dimensional conformal radiotherapy (3DCRT) plans. MATERIALS AND METHODS: Fifteen patients with advanced non-small cell lung cancer, planned for radical radiotherapy, underwent planning CT scans at baseline and after 40 Gy. Target volumes were delineated on both scans, and both 3DCRT and VMAT plans were made. Phase I delivered 40 Gy to initial planning target volume (PTV). Two Phase II plans for 20 Gy to PTV boost were developed on initial and mid-treatment scans. Plan sums were made. Volumetric and dosimetric changes in target volumes and normal structures were analyzed. RESULTS: There was a significant reduction in primary GTV (31.26%; P = 0.001) and PTV (28.07%; P = 0.001) in mid-treatment CT scan. VMAT plans were superior to 3DCRT plans in terms of lesser V20 and V5 doses to the ipsilateral lung (V20: 33.03% vs. 58.89%; P = 0.00 and V5: 63.62% vs. 77.20%; P = 0.001), lesser V5 doses to the contralateral lung (V5: 19.12% vs. 32.16%; P = 0.03), and lesser mean doses to the heart (12.61 Gy vs. 15.06 Gy; P = 0.02); however, PTV coverage was similar in both the plans. Among the two Phase II VMAT plans, those made on mid-treatment CT scans were superior in terms of V5 doses to the contralateral lung (5.23% vs. 7.99%; P = 0.001), mean dose to bilateral combined lung (3.57 Gy vs. 5.10 Gy; P = 0.03), and Dmax spinal cord (7.90 Gy vs. 11.36 Gy; P = 0.05). CONCLUSION: The study demonstrates the superiority of VMAT plans over 3DCRT plans and emphasizes the need for adaptive radiotherapy planning with VMAT in lung cancers for minimizing normal tissue toxicity without compromising local control.

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