Dosimetric evaluation of photons versus protons in postmastectomy planning for ultrahypofractionated breast radiotherapy

Puntiwa Oonsiri,Thanaporn Sarsitthithum,Kitwadee Saksornchai,Chawalit Lertbutsayanukul,Chonnipa Nantavithya,Tanawat Tawonwong,Mananchaya Vimolnoch

doi:10.1186/s13014-022-01992-w

Abstract

BackgroundUltrahypofractionation can shorten the irradiation period. This study is the first dosimetric investigation comparing ultrahypofractionation using volumetric arc radiation therapy (VMAT) and intensity-modulated proton radiation therapy (IMPT) techniques in postmastectomy treatment planning.Materials and methodsTwenty postmastectomy patients (10-left and 10-right sided) were replanned with both VMAT and IMPT techniques. There were four scenarios: left chest wall, left chest wall including regional nodes, right chest wall, and right chest wall including regional nodes. The prescribed dose was 26 Gy(RBE) in 5 fractions. For VMAT, a 1-cm bolus was added for 2 in 5 fractions. For IMPT, robust optimization was performed on the CTV structure with a 3-mm setup uncertainty and a 3.5% range uncertainty. This study aimed to compare the dosimetric parameters of the PTV, ipsilateral lung, contralateral lung, heart, skin, esophageal, and thyroid doses.ResultsThe PTV-D95 was kept above 24.7 Gy(RBE) in both VMAT and IMPT plans. The ipsilateral lung mean dose of the IMPT plans was comparable to that of the VMAT plans. In three of four scenarios, the V5 of the ipsilateral lung in IMPT plans was lower than in VMAT plans. The Dmean and V5 of heart dose were reduced by a factor of 4 in the IMPT plans of the left side. For the right side, the Dmean of the heart was less than 1 Gy(RBE) for IMPT, while the VMAT delivered approximately 3 Gy(RBE). The IMPT plans showed a significantly higher skin dose owing to the lack of a skin-sparing effect in the proton beam. The IMPT plans provided lower esophageal and thyroid mean dose.ConclusionDespite the higher skin dose with the proton plan, IMPT significantly reduced the dose to adjacent organs at risk, which might translate into the reduction of late toxicities when compared with the photon plan.

Highlights

There are many techniques and schedule schemes of treatment for breast irradiation [1]
The planning target volume (PTV)-D95 was kept above 24.7 Gy(RBE) in both volumetric arc radiation therapy (VMAT) and intensity-modulated proton radiation therapy (IMPT) plans
Despite the higher skin dose with the proton plan, IMPT significantly reduced the dose to adjacent organs at risk, which might translate into the reduction of late toxicities when compared with the photon plan

Summary

Introduction

There are many techniques and schedule schemes of treatment for breast irradiation [1]. Routine breast irradiation using three-dimensional conformal radiotherapy (3D-CRT) is associated with long-term toxicity in organs at risk (OARs), such as the heart, the lungs, and the contralateral breast, Oonsiri et al Radiation Oncology (2022) 17:20 especially when regional node irradiation is required [6]. By using advanced techniques, such as intensity modulation radiotherapy (IMRT) or volumetric arc radiation therapy (VMAT), a high radiation dose could be delivered to the planning target volume (PTV) with high conformity. The high-dose regions of the lungs and heart are spared using these methods [7], but a higher volume of the adjacent OARs receives a low dose radiation, which can cause long term toxicities and secondary cancer [8]. This study is the first dosimetric investigation comparing ultrahypofractionation using volumetric arc radiation therapy (VMAT) and intensity-modulated proton radiation therapy (IMPT) techniques in postmastectomy treatment planning

Objectives

Methods

Results

Discussion

Conclusion