Potential benefits of crawl position for prone radiation therapy in breast cancer

Abstract Purpose To investigate crawl position with the arm at the treated side alongside the body and at the opposite side above the head for prone treatment in patients requiring breast and regional lymph node irradiation. Methods Patient support devices for crawl position were built for CT simulation and treatment. An asymmetric fork design resulted from an iterative process of prototype construction and testing. The fork's large horn supports the hemi‐thorax, shoulder, and elevated arm at the nontreated side and the head. The short, narrow horn supports the arm at the treated side. Between both horns, the treated breast and its regional lymph nodes are exposed. Endpoints were pain, comfort, set‐up precision, beam access to the breast and lymph nodes, and plan dose metrics. Pain and comfort were tested by volunteers (n = 9); set‐up precision, beam access, and plan dose metrics were tested by means of a patient study (n = 10). The AIO™ (Orfit, Wijnegem, Belgium) prone breastboard (AIO™) was used as a reference regarding comfort and set‐up precision. Results Pain at the sternum, the ipsilateral shoulder, upper arm, and neck was lower in crawl position than with bilateral arm elevation on AIO™. Comfort and set‐up precision were better on the crawl prototype than on AIO™. In crawl position, beam directions in the coronal and near‐sagittal planes have access to the breast or regional lymph nodes without traversing device components. Plan comparison between supine and crawl positions showed better dose homogeneity for the breast and lymph node targets and dose reductions to all organs at risk for crawl position. Conclusions Radiation therapy for breast and regional lymph nodes in crawl position is feasible. Good comfort and set‐up precision were demonstrated. Planning results support the hypothesis that breast and regional lymph nodes can be treated in crawl position with less dose to organs at risk and equal or better dose distribution in the target volumes than in supine position. The crawl technique is a candidate methodology for further investigation for patients requiring breast and regional lymph node irradiation.


| INTRODUCTION
Radiotherapy after breast-conserving surgery improves loco-regional control and survival at the expense of acute and late toxicity to the treated region, radiation-induced cardiac events, lung cancer, and cancer in the nontreated breast. [1][2][3][4][5][6] Prone radiotherapy allows decreasing acute toxicity, cosmetic changes, risks of radiation-induced lung cancer, and cardiac toxicity. [7][8][9] However, several drawbacks of prone position are reported, including reduced set-up precision and discomfort. 10 Two classes of patient support devices for prone radiotherapy can be distinguished. Prone breastboards rest entirely on the treatment couch surface while prone breastcouches replace the couch blade (or its cranial part) so that no couch parts extend below the treated breast.
Commercial devices of both classes are designed to support the patient with both arms elevated. The arm position, the treatment couch when using breastboards, as well as device components that support the elevated arm at the treated side are in the way of anterior beam directions for breast and lymph node irradiation (B+LNI).
Although clinical experience using posterior beams to treat axillary and periclavicular lymph node chains has been described, 11 prone radiotherapy is rarely used in patients requiring B+LNI. This is unfortunate because patients requiring B+LNI receive substantially more lung dose than patients treated with breast irradiation only, due to irradiation of the lung top nearby the axillary and periclavicular lymph node regions. The correlation between lung dose and death due to second primary lung cancer is well documented. 3,4,6 Irradiation of the internal mammary chain increases heart dose and was shown to increase the rate of major cardiac events. 5,6,12 Hence, risk for radiation-induced heart disease or lung cancer induction might be reduced if heart and lung dose could be decreased by using prone B+LNI.
With reduction in lung and heart dose in the setting of B+LNI as main objective, we investigated a new prone position with the arm at the treated side alongside the body and the arm at the contralateral side above the head, further called crawl position because it resembles a phase of crawl swimming. Support devices for crawl position were built as breastboards (for CT simulation) and breastcouches (for treatment). Comparative assessment was performed with prone bilateral arm elevation regarding feasibility, comfort, and set-up precision and with supine position regarding dose to targets and organs at risk in B+LNI.

| MATERIALS AND METHODS
To test crawl position, we constructed prone breastboards andcouches with an upper surface that supported the entire body except the treated breast, and the ventral body regions overlaying the axillary, periclavicular and internal mammary lymph node regions. Above the waist, the resulting support surface is shaped as an asymmetric fork [ Fig. 1(a)] with a short, narrow horn supporting the arm at the treated side and a large horn supporting the hemithorax, breast, shoulder, and elevated arm at the nontreated side as well as the head [ Fig. 1(b)]. The treated breast and its regional lymph nodes is positioned between both horns. The device is www.abro-bvro.be/index.php?option=com_content&view=categor-y&id=94&Itemid=940). 13 Ten patients received half of their WBI treatment sessions on the crawl breastcouch and the other half on AIO TM . The patients were selected as follows: female, 45 years or older, right-sided breast carcinoma, suitable for adjuvant radiotherapy after lumpectomy for breast cancer, and prone WB irradiation without LNI.
Laser-based set-up was performed in both positions and set-up errors were measured using daily cone-beam CT scanning as reference. 10,14 The magnitude of set-up errors was calculated as described before. 10 All studies were approved by the ethics committee of Ghent University Hospital and informed consent was obtained from the study participants.

| RESULTS
Comfort was optimized by an iterative process of prototype construction, testing, and redesign. AIO TM served as a reference. We report results obtained on AIO TM and on the crawl breastboard (prototype version shown in Fig. 1(d) which is presently used in clinical trials).
Ex-patients positioned on AIO TM reported discomfort caused by bilateral arm elevation and had to exert force by the arm at the operated side to maintain a stable position. The ipsilateral arm support of the crawl prototypes provides stability by preventing lateral and downward movement. The arm alongside the body was reported to be more comfortable than the elevated arm position, especially after axillary node dissection.
Pain was scored by nine volunteers (Fig. 2). On the AIO TM , pain was frequently reported at the sternum near the edge of the surface supporting the nontreated breast; at the ipsilateral shoulder, at both upper arms, and at the neck [ Fig. 2(a)]. On the crawl breastboard, sternal pain was reported less frequently and was less severe

| DISCUSSION
A review of the advantages, disadvantages, challenges, limitations of prone position for breast irradiation has been published by the investigators at New York University. 15 Prone radiotherapy is advantageous for the vast majority of patients requiring breast irradiation irrespective of breast size: lower dose to lung and heart, less acute toxicity, and better cosmesis. [7][8][9]15 Challenges of prone radiotherapy are numerous 15 and centers that wish acquiring prone breast radiotherapy face a substantial learning effort. The drawbacks and the learning effort necessary to acquire prone breast radiotherapy may explain the adherence to supine breast cancer radiotherapy in the vast majority of centers worldwide. We investigated prone radiotherapy for breast cancer since 2008, first using the Horizon prone breastboard (Civco Medical Solutions, Orange City, Iowa, USA) 13 and later the AIO TM breastboard which we modified 7 to become the device that we use in clinical practice. With AIO TM , no patients requiring B+LNI (about three of ten patients referred to our centre require B+LNI) were treated in prone position because of the restrictions regarding good beam directions. The aim of crawl positioning research was to offer a prone solution for these patient groups.
We generated proof that crawl position is a feasible alternative for prone position with bilateral arm elevation. We were able to construct prototypes that showed better patient comfort than the two commercial prone breastboards (Horizon and AIO TM ) that we used until now. We demonstrated that crawl position on properly designed devices allows a large, unobstructed beam access range to the breast and its regional lymph node regions (Fig. 3,  The prone crawl position seems promising, but several challenges and limitations of the crawl breastcouch prototype hamper its widespread use. First, the prototype is the result of an iterative process of tests and improvements which resulted in using many components and materials which makes it unsuitable for modern industrial pro-

| SUMMARY
Crawl position, with the arm at the treated side alongside the body and at the opposite side above the head, was investigated for prone breast cancer radiation therapy. As compared to the commonly used prone position with bilateral arm elevation, crawl position shows better comfort, stability, and set-up precision and permits a vast range of beam directions in the coronal and near-sagittal planes that reach the breast and regional lymph nodes without passage through components of the crawl positioning device. Near-sagittal beam directions seem valuable to reduce dose to heart, lung, and contralateral breast in patients who require irradiation of regional lymph nodes.