Dosimetric feasibility of an “off-breast isocenter” technique for whole-breast cancer radiotherapy

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• 作者：Juan-Francisco Calvo-Ortega ; ^{jfcdrr@yahoo.es" class="auth_mail" title="E-mail the corresponding author} ; Sandra Moragues ; Miquel Pozo ; Joan Casals
• 关键词：Off-breast ; Isocenter ; Collision ; IMRT ; SIB
• 刊名：Reports of Practical Oncology & Radiotherapy
• 出版年：2016
• 出版时间：November-December 2016
• 年：2016
• 卷：21
• 期：6
• 页码：500-507
• 全文大小：1589 K

文摘

To investigate the viability of placing the treatment isocenter at the patient midline for breast cancer radiotherapy in order to avoid the risk of collisions during image-guided setup and treatment delivery.

Background

The use of kilovoltage orthogonal setup images has spread in last years in breast radiotherapy. There is a potential risk of an imaging system–patient collision when the isocenter is laterally placed.

Materials and methods

Twenty IMRT plans designed by placing the isocenter within the breast volume (“plan_ref”), were retrospectively replanned by shifting the isocenter at the patient's midline (“plan_off-breast”). An integrated simultaneous boost (SIB) technique was used. Multiple metrics for the planning target volumes (PTVs) and organs at risk (OARs) were compared for both approaches using a paired t test.

Results

Comparing plan_ref vs. plan_off-breast, no significant differences in PTV coverage (V95%) were found (96.5% vs. 96.2%; p = 0.361 to PTVbreast; 97.0% vs. 97.0%; p = 0.977 to PTVtumor_bed). With regard to OARs, no substantial differences were observed in any analyzed metric: V5Gy (30.3% vs. 31.4%; p = 0.486), V20Gy (10.3% vs. 10.3%; p = 0.903) and mean dose (7.1 Gy vs. 7.1 Gy; p = 0.924) to the ipsilateral lung; V5Gy (11.2% vs. 10.0%; p = 0.459), V30Gy (0.7% vs. 0.6%; p = 0.251) and mean dose (2.3 Gy vs. 2.2 Gy; p = 0.400) to the heart; and average dose to the contralateral breast (0.4 Gy vs. 0.5 Gy; p = 0.107).

Conclusions

The off-breast isocenter solution resulted in dosimetrically comparable plans as the reference technique, avoiding the collision risk during the treatment session.