Combining deep-inspiration breath hold and intensity-modulated radiotherapy for gastric mucosa-associated lymphoid tissue lymphoma: Dosimetric evaluation using comprehensive plan quality indices

Abstract

Background: Although there have been many attempts to increase the therapeutic ratio of radiotherapy for gastric mucosa-associated lymphoid tissue lymphoma (MALToma), only a few planning studies have reported the efficacy of the modern radiotherapy technique till date. Therefore, we performed the dosimetric comparison among 3-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) plans, using deep-inspiration breath hold (DIBH) or free-breathing (FB) techniques, to determine the most optimal plan for gastric MALToma.

Methods: We evaluated 9 patients with gastric MALToma for whom 3D-CRT, step-and-shoot IMRT (_SIMRT), volumetric-modulated arc therapy (VMAT), and tomotherapy plans with identical prescribed doses were generated using DIBH or FB computed tomography (CT). Planning target volume (PTV) coverage and non-target doses were calculated for each plan and compared with plan quality metric (PQM) scores.

Results: All 72 plans of 9 patients satisfied our dosimetric goals, and the IMRT plans and 3D-CRT plans had similarly good conformity index values with no differences related to respiratory movement. IMRT plans yielded significantly better doses to the organs-at-risk, and DIBH plans yielded significantly lower liver, heart, and lung D_mean and spinal cord D_max with smaller irradiated volumes compared to FB plans. For the mean PQM scores, VMAT-DIBH and _SIMRT-DIBH yielded the best scores, whereas 3D plans provided reduced beam monitor unit values.

Conclusion: Our findings demonstrate that modern RT technologies (DIBH with VMAT or _SIMRT) could potentially provide excellent target coverage for gastric MALToma while reducing doses to organs-at-risk. However, the relevance of the most optimal plan considering clinical outcomes should be confirmed further in a larger patient cohort.

Keywords: Deep inspiration breath hold; Intensity modulated radiotherapy; Mucosa-associated lymphoid tissue lymphoma; Planning study; Radiotherapy.

Fig. 1

Boxplots of (a) the doses to 95% of the PTV (D₉₅), (b) percent volume of the PTV receiving at least 95% of the prescription dose (TV₉₅), (c) homogeneity index (HI), (d) conformity index (CI), (e) D_max of the spinal cord, and (f) D_max of the small bowel of the 8 different plan groups. *The significant differences between groups are shown in the Supplementary text

Fig. 2

Treatment plans for 1 patient; (a) isodose lines in the image showing the curvature of the stomach, (b) isodose lines in the image showing the irradiation dose to both the kidneys. In Fig. 2(a), the difference in D₉₅, TV₉₅, HI, and CI values among treatment plans can be compared visually to some extent. In Fig. 2(b), the difference between the right and left kidney D_mean, liver D_mean, and bowel D_max doses among treatment plans can be compared visually to some extent

Fig. 3

Boxplots of (a) plan quality metric (PQM) scores and (b) motor units (MU) of the 8 different plan groups. DIBH, deep-inspiration breath hold; FB, free-breathing; 3D, 3-dimensional conformal radiotherapy; IMRT, intensity-modulated radiotherapy; VMAT, volumetric-modulated arc therapy; Tomo, tomotherapy