From Impossible to Feasible- A Dosimetric Study Comparing Four Different Treatment Techniques in a Lung Cancer Patient Presenting with Diffuse Pleural Seeding

Abstract

Purpose: To investigate the performance and feasibilities of four different linac-based radiation therapy devices in palliating a lung adenocarcinoma patient presenting with diffuse pleural seeding and intractable pain. Patients and Methods: Treatment plans were generated for three dimensional conformal radiotherapy (3D-CRT), Intensity-modulated radiation therapy (IMRT), Volumetric- modulated arc therapy (VMAT) and Helical Tomotherapy (HT) using 6 MV photon beam with adequate optimization criteria. The total prescribed dose to planning target volume (PTV) was 50 Gy in 20 fractions. Dose distributions to PTV and organs at risk (OAR) were compared using dose-volume histograms (DVHs), conformity indexes (CIs), and homogeneity indexes (HIs). Results: In general, IMRT, VMAT and HT all resulted in comparable PTV coverage. The D98 of all four techniques were all greater than 48.5 Gy. HT had the highest CI (0.982) and the lowest HI (0.035), whereas 3D-CRT had the highest D2% (56.82 Gy) and Dmax (58 Gy). HT had the lowest ipsilateral lung V45 (55%) and ipsilateral mean lung dose (45 Gy). 3D-CRT had the lowest contralateral lung V18 (0%) and contralateral mean lung dose (1.14 Gy). The integral dose (L.Gy) for total lung tissue was VMAT ＞ HT ＞ IMRT ＞ 3D-CRT. HT delivered the most monitor units (MUs) and needed the longest treatment time. Conclusion: IMRT, VMAT and HT all could attain over 95% PTV coverage and had superior OAR sparing compared to 3D-CRT. However, larger volumes of some healthy tissues (especially contralateral lung) received low-to-intermediate doses, which contributed to a higher integral dose in VMAT, HT and IMRT. The superiority of one technique over another needed further clinical correlation.