Dosimetric comparison of volumetric-modulated arc therapy and helical tomotherapy for adjuvant treatment of bilateral breast cancer

Abstract

Purpose: Dosimetric comparison between volumetric-modulated arc therapy (VMAT) and helical tomotherapy (HT) in the treatment of bilateral breast cancer (BBC). Materials and methods: Ten patients treated on HT were selected retrospectively. Dose prescription was 50 Gy in 25 fractions to breast/chest wall and supraclavicular fossa (SCF) while tumour bed was simultaneously boosted to 61 Gy in 25 fractions. VMAT plans were made with four mono-isocentric partial arcs. The monitoring unit (MU) and treatment time were used to quantify the treatment efficiency. Target volumes were compared for homogeneity index (HI), conformity index (CI) while organs at risk (OARs) were compared for relevant dose volumes and integral doses (IDs). Result: For targets, no significant difference is observed between VMAT and HT in CI but VMAT could give better HI. The mean lung dose, V20 and V5 is 10·6 Gy versus 8·4 Gy (p-value 0·03), 12% versus 11·5% (p-value 0·5) and 78·1% versus 43·4% (p-value 0·005), respectively. The mean heart dose, V30 and V5 is 4·9 Gy versus 4·7 Gy (p-value 0·88), 0·5% versus 1·5% (p-value 0·18) and 26·2% versus 22·8% (p-value 0·4). Integral dose (ID) for the whole body and heart are comparable: 289 Gy kg versus 299 Gy kg (p-value 0·24) and 2·9 Gy kg versus 2·8 Gy kg (p-value 0·80). ID for lungs was significantly higher with VMAT: 7·9 Gy kg versus 6·3 Gy kg (p-value 0·03). There is a 53% reduction in treatment time and 78% in MU with VMAT against HT. Conclusion: VMAT can generate clinically acceptable plans comparable to HT for BBC. HT shows better control over low dose spillage in lungs compared to VMAT thereby increasing ID to lungs. VMAT shows better homogeneity and efficient treatment delivery than HT.

Can knowledge based treatment planning of VMAT for post-mastectomy locoregional radiotherapy involving internal mammary chain and supraclavicular fossa improve performance efficiency?

“…Model-generated plans are also likely to improve the workflow by giving consistent plans, especially in this group of post-mastectomy patients wherein complex treatment volumes are very common. In the CLI plans, many optimization structures were created to control the dose spill to the heart and lungs, and it is explained in the literature ( 4 ). However, for KBP plans, the creation of such optimization structures is not necessary with RapidPlan™ as predicted DVH objectives automatically take into account the dose spill and control it accordingly ( 26 ).…”

“…The combination of photon beam and electron beam has also been used for IMNI but with the limitations of over or under dosing at the photon-electron junction along with a high dose to the anterior myocardium. Rotational intensity modulated radiotherapy (IMRT) provides a viable solution in such a scenario by providing better target coverage, improved dose conformity, as well as homogeneity and better sparing of the OARs ( 3 , 4 ). The absence of any form of junction and ease of setup are the added advantages.…”