Dosimetric study of the plan quality and dose to organs at risk on tangential breast treatments using the Halcyon linac.

Everardo Flores‐Martinez,Laura I. Cerviño,Gwe‐Ya Kim,Catheryn M. Yashar

doi:10.1002/acm2.12655

Everardo Flores‐Martinez, Laura I. Cerviño + Show 2 more

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https://doi.org/10.1002/acm2.12655

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Abstract

PurposeTo investigate the plan quality and doses to the heart, contralateral breast (CB), ipsilateral lung (IL), and contralateral lung (CL) in tangential breast treatments using the Halcyon linac with megavoltage setup fields.MethodsRadiotherapy treatment plans with tangential beams from 25 breast cancer patients previously treated on a C‐arm linac were replanned for Halcyon. Thirteen corresponded to right‐sided breasts and 12 to left‐sided breasts, all with a dose prescription of 50 Gy in 25 fractions. Plans were created with the following setup imaging techniques: low‐dose (LD) MVCBCT, high‐quality (HQ) MVCBCT, LD‐MV and HQ‐MV pairs and the imaging dose was included in the plans. Plan quality metric values for the lumpectomy cavity, whole‐breast and doses to the organs at risk (OARs) were measured and compared with those from the original plans.ResultsNo significant differences in plan quality were observed between the original and Halcyon plans. An increase in the mean dose (Mean) for all the organs was observed for the Halcyon plans. For right‐sided plans, the accumulated Mean over the 25 fractions in the C‐arm plans was 0.4 ± 0.3, 0.2 ± 0.2, 5.4 ± 1.3, and 0.1 ± 0.1 Gy for the heart, CB, IL, and CL, respectively, while values in the MVCBCT‐LD Halcyon plans were 1.2 ± 0.2, 0.6 ± 0.1, 6.5 ± 1.4, and 0.4 ± 0.1 Gy, respectively. For left‐sided treatments, Mean in the original plans was 0.9 ± 0.2, 0.1 ± 0.0, 4.2 ± 1.2, and 0.0 ± 0.0 Gy, while for the MVCBCT‐LD Halcyon plans values were 1.9 ± 0.2, 0.6 ± 0.2, 5.1 ± 1.2, and 0.5 ± 0.2 Gy, respectively.ConclusionsPlan quality for breast treatments using Halcyon is similar to the quality for a 6 MV, C‐arm plan. For treatments using megavoltage setup fields, the dose contribution to OARs from the imaging fields can be equal or higher than the dose from treatment fields.

Highlights

1.A | Breast cancerBreast cancer is the cancer with the highest incidence in women in the US after skin cancer.[1]
For breast cancer patients, reducing the dose to organs at risk (OARs) from radiotherapy treatments is important as the 10‐year survival probability for diagnosed stage I and II patients treated with radiation after breast‐conserving therapy is higher than 60%
The values of D98%[Gy] and H.I. for the Halcyon plans showed a statistically significant difference as compared with the C‐arm plans, given that those differences are less than 1%, we do not consider them of clinical relevance and could be related with the planner’s skill when editing fluence

Summary

Introduction

1.A | Breast cancerBreast cancer is the cancer with the highest incidence in women in the US after skin cancer.[1]. Breast cancer treatment options depend on the stage of the disease, and include mastectomy, breast conserving surgery (BCS), chemotherapy, and radiation. For patients receiving radiation therapy, image‐guided radiotherapy (IGRT) is used to provide an accurate setup at the treatment machine ensuring adequate coverage of the target volume. Different imaging techniques have been used for IGRT, such as orthogonal kilovoltage (kV) or megavoltage (MV) pairs, kV or MV cone beam computed tomography (CBCT), ultrasound, surface‐guided radiotherapy (SGRT), or magnetic resonance imaging. For MV‐based imaging techniques, the dose from the imaging fields to organs at risk (OARs) can be significant, and needs to be evaluated. For breast cancer patients, reducing the dose to OARs from radiotherapy treatments is important as the 10‐year survival probability for diagnosed stage I and II patients treated with radiation after breast‐conserving therapy is higher than 60%.5. For breast cancer patients, reducing the dose to OARs from radiotherapy treatments is important as the 10‐year survival probability for diagnosed stage I and II patients treated with radiation after breast‐conserving therapy is higher than 60%.5 Several studies have reported dose to the OARs from the different modalities available for radiation delivery including three dimensional conformal therapy (3D‐CRT),[6,7] tomotherapy,[8–13] static‐field intensity‐modulated radiation therapy (IMRT)[10,12,14,15] and volumetric arc therapy (VMAT).[8,10,15–18]

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