Small‐spot intensity‐modulated proton therapy and volumetric‐modulated arc therapies for patients with locally advanced non‐small‐cell lung cancer: A dosimetric comparative study

Abstract

PurposeTo compare dosimetric performance of volumetric‐modulated arc therapy (VMAT) and small‐spot intensity‐modulated proton therapy for stage III non‐small‐cell lung cancer (NSCLC).Methods and MaterialsA total of 24 NSCLC patients were retrospectively reviewed; 12 patients received intensity‐modulated proton therapy (IMPT) and the remaining 12 received VMAT. Both plans were generated by delivering prescription doses to clinical target volumes (CTV) on averaged 4D‐CTs. The dose‐volume‐histograms (DVH) band method was used to quantify plan robustness. Software was developed to evaluate interplay effects with randomized starting phases of each field per fraction. DVH indices were compared using Wilcoxon rank sum test.ResultsCompared with VMAT, IMPT delivered significantly lower cord Dmax, heart Dmean, and lung V5 Gy[ RBE ] with comparable CTV dose homogeneity, and protection of other OARs. In terms of plan robustness, the IMPT plans were statistically better than VMAT plans in heart Dmean, but were statistically worse in CTV dose coverage, cord Dmax, lung Dmean, and V5 Gy[ RBE ]. Other DVH indices were comparable. The IMPT plans still met the standard clinical requirements with interplay effects considered.ConclusionsSmall‐spot IMPT improves cord, heart, and lung sparing compared to VMAT and achieves clinically acceptable plan robustness at least for the patients included in this study with motion amplitude less than 11 mm. Our study supports the usage of IMPT to treat some lung cancer patients.

Dosimetric comparison of distal esophageal carcinoma plans for patients treated with small‐spot intensity‐modulated proton versus volumetric‐modulated arc therapies

“…Compared with IMRT, large‐spot IMPT using three beam angles (anteroposterior, right posterior oblique, and left posterior oblique) has been shown to deliver significantly lower lung D mean , lung V 5Gy[RBE] , V 10Gy[RBE] , and V 20Gy[RBE] , and heart D mean for distal esophageal cancer patients . Compared with large‐spot IMPT, small‐spot IMPT is considered to have two benefits: (a) sharper penumbra, which results from smaller spot sizes, can improve the sparing of organs‐at‐risk and lead to lower radiation toxicities; (b) a larger number of spots, which are needed to cover the same tumors compared to large‐spot IMPT, provides the TPS more freedom to compensate for the impact of uncertainties and interplay effects …”

“…It is composed of 27 energy layers (120–173.6 MeV), 289 spots in each layer with 6 mm spot spacing, a total of 200 MU. In IMPT treatment planning, we also used the iso‐layer repainting to mitigate interplay effects . For respiratory motion less than or equal to 5 mm, the minimum and maximum MU limits in the proton machine were 0.003 and 0.04 MU, respectively.…”

“…A smaller maximum MU limit of 0.01 MU was used for cases with respiratory motion greater than 5 mm. The purpose of a smaller maximum MU limit was to make the delivery system perform a larger number of iso‐layer repainting, which in turn mitigated the impact of interplay effects . During the delivery process, if the intensity of one spot was larger than the maximum MU limit, the spot was split into multiple spots, and the split spots were appended in the spot list of the same energy layer and delivered individually.…”

Fraction‐variant beam orientation optimization for intensity‐modulated proton therapy

“…4 Further increase in the number of beams to form arc delivery may lead to substantial improvement in dose conformity and adjacent organ sparing. [5][6][7][8][9][10][11][12][13][14] In addition to the dose conformity, the plan robustness can improve as well. We showed that beams from different angles could be compensatory toward range and positioning uncertainties.…”

3D‐printable lung phantom for distal falloff verification of proton Bragg peak

“…The Bragg peak in the radiation dose distribution in proton therapy allows for better dose distribution compared to other radiation treatments, so proton therapy is one of the important options for cancer treatment. However, researchers have reported that passage of the proton beam through heterogenous regions, such as the human lung, causes the Bragg peak to be amplified, deteriorating the distal falloff .…”