Lung stereotactic body radiation therapy: personalized PTV margins according to tumor location and number of four-dimensional CT scans

Pierre Trémolières; Ana Gonzalez-Moya; Amaury Paumier; Martine Mege; Julien Blanchecotte; Christelle Theotime; Damien Autret; Stéphane Dufreneix

doi:10.1186/s13014-021-01973-5

Lung stereotactic body radiation therapy: personalized PTV margins according to tumor location and number of four-dimensional CT scans

Radiat Oncol. 2022 Jan 10;17(1):5. doi: 10.1186/s13014-021-01973-5.

Authors

Pierre Trémolières¹, Ana Gonzalez-Moya², Amaury Paumier², Martine Mege², Julien Blanchecotte², Christelle Theotime³, Damien Autret³, Stéphane Dufreneix³

Affiliations

¹ Department of Radiation Oncology, Institut de Cancérologie de L'Ouest Angers, 15 Rue A Boquel, 49055, Angers Cedex 02, France. pierre.tremolieres@ico.unicancer.fr.
² Department of Radiation Oncology, Institut de Cancérologie de L'Ouest Angers, 15 Rue A Boquel, 49055, Angers Cedex 02, France.
³ Department of Medical Physics, Institut de Cancérologie de L'Ouest Angers, 15 Rue A Boquel, 49055, Angers Cedex 02, France.

Abstract

Objectives: To characterise the motion of pulmonary tumours during stereotactic body radiation therapy (SBRT) and to evaluate different margins when creating the planning target volume (PTV) on a single 4D CT scan (4DCT).

Methods: We conducted a retrospective single-site analysis on 30 patients undergoing lung SBRT. Two 4DCTs (4DCT1 and 4DCT2) were performed on all patients. First, motion was recorded for each 4DCT in anterior-posterior (AP), superior-inferior (SI) and rightleft (RL) directions. Then, we used 3 different margins (3,4 and 5 mm) to create the PTV, from the internal target volume (ITV) of 4DCT1 only (PTV D1 + 3, PTV D1 + 4, PTV D1 + 5). We compared, using the Dice coefficient, the volumes of these 3 PTVs, to the PTV actually used for the treatment (PTV_ttt). Finally, new treatment plans were calculated using only these 3 PTVs. We studied the ratio of the D2%, D50% and D98% between each new plan and the plan actually used for the treatment (D2% PTV_ttt, D50% PTV_ttt, D50% ITVttt D98% PTV_ttt).

Results: 30 lesions were studied. The greatest motion was observed in the SI axis (8.8 ± 6.6 [0.4-25.8] mm). The Dice index was higher when comparing PTVttt to PTV D1 + 4 mm (0.89 ± 0.04 [0.82-0.98]). Large differences were observed when comparing plans relative to PTVttt and PTV D1 + 3 for D98% PTV_ttt (0.85 ± 0.24 [0.19-1.00]). and also for D98% ITV_ttt (0.93 ± 0.12 [0.4-1.0]).D98% PTV_ttt (0.85 ± 0.24 [0.19-1.00], p value = 0.003) was statistically different when comparing plans relative to PTV_ttt and PTV D1 + 3. No stastistically differences were observed when comparing plans relative to PTV_ttt and PTV D1 + 4. A difference greater than 10% relative to D98% PTV_ttt was found for only in one UL lesion, located under the carina.

Conclusion: A single 4DCT appears feasible for upper lobe lesions located above the carina, using a 4-mm margin to generate the PTV.

Advance in knowledge: Propostion of a personalized SBRT treatment (number of 4DCT, margins) according to tumor location (above or under the carina).

Keywords: Four dimensional computed tomography; Lung tumors; Motion study; PTV margin; Stereotactic body radiation therapy.

MeSH terms

Four-Dimensional Computed Tomography*
Humans
Lung Neoplasms / diagnostic imaging*
Lung Neoplasms / pathology
Lung Neoplasms / radiotherapy*
Radiosurgery*
Radiotherapy Planning, Computer-Assisted*
Retrospective Studies