Two of the nine post-operative breast cancer patients defaulted for radiotherapy after computed tomography (CT) simulation. (Table 1) Therefore, case-records of only seven patients were reviewed for data collection and analysis. Informed consent for CT simulation and VMAT was obtained from all the nine consecutive post-operative breast cancer patients presenting for radiotherapy. Confidentiality and privacy of all the patients were maintained throughout the study. Study adhered to principles of the Declaration of Helsinki 1975 (as revised in 2000). Consent was obtained for clinical photographs taken during study and utmost care was take to conceal the identity of patients. The study is outcome of real-world practice of VMAT for post-operative irradiation of chest wall / breast and regional lymph node areas. The work-flow for implementation of VMAT is as follows: a) arranging of breast and lung board on CT simulator couch b) position of patients on breast and lung board c) Ascertaining the position of patients for reproducibility d) tattooing and fidicual placement at point of three laser cross hair on skin surface .i.e. one each on anterior midline, right lateral and left lateral chest wall d) acquisition of non-contrast CT e) Importing of simulation CT and contouring of target and normal structures f) VMAT planning by medical physicists g) Plan approval by radiation oncologists and registration of patient details h) exporting of VMAT plan for implementation on linac and scheduling the same along with AP and lateral digitally reconstructed radiograph (DRR) for set-up verification of treatment position. Simulation CT data set were also scheduled with VMAT plan for matching with CBCT based on-board imaging for set-up verification. However, planar x-ray image based matching was planned mode of set-up verification i) positioning of patients on breast and lung board following procedure similar to that for CT simulation, matching of body tattoo with laser cross-hair on linac, shifting of couch in x-,y-, z- axis if needed and checking SSD j) online 2-D based image matching and final shifting of couch in x-, y- and z- axis k) Execution of VMAT.
Table 1
Clinical profile of patients
Age range | 30–56 years |
| | No. of patients |
Menopausal status | Pre-menopausal | 5‡‡ |
Post-menopausal | 4 |
Body habitus | Thin | 3‡ |
Normal | 3‡ |
Obese | 3 |
Stage of the disease | Early | 2 |
Locally advanced | 6‡‡ |
Metastatic | 1 |
Histology | Invasive Ductal Carcinoma | 7 |
Malignant / borderline phyllodes tumor | 2‡‡ |
Comorbidities | Retroviral disease | 1‡ |
Nature of surgery | Modified Radical Mastectomy | 5 |
Breast conservation surgery (BCS) | 2 |
Simple mastectomy | 2‡‡ |
Intent of therapy | Post-operative | 8‡‡ |
Palliative | 1 |
Clinical Target Volume (CTV)* | Chest wall alone | 2‡‡ |
Chest wall and regional lymph node area | 5 |
Whole breast | 1 |
Whole breast and regional lymph node area | 1 |
* All patients were planned by a pair of partial arc VMAT technique with online 2-D matching of images for set-up verification. |
‡ indicates default of patients to therapy in that particular group. Number of ‘‡’ superscripted after the Arabic numeral indicates number of patients defaulting radiotherapy. |
Immobilization of patients on Klarity base plate and thermoplastic immobilization mask was the clinical practice before introduction of breast and lung board immobilization. Patients were initially simulated, planned and VMAT was executed on Klarity base plate and thermoplastic immobilization mask in the transition period of changing over from one kind of immobilization to another different type of immobilization. Once the work flow for immobilization on breast and lung board was established, patients were completely switched over from klarity immobilization system with thermoplastic mask to breast and lung board immobilization system without thermoplastic mask.
Coming to the present study, nine consecutive post-operative breast cancer patients were immobilized on Breast and Lung board without thermoplastic mask. Patients were immobilized on combination of 0°, one of 5° / 10° / 15° angle wedge, low or high arm rest (20° or 30° angle respectively), feet and knee cushions. Indexed head support by using one of the head rest ranging from number 1 to 6 was used to position the head in reproducible manner. A pair of grip pole mounted over grip pole collar to provide hand grip for over-head abducted arms were also utilized. L shaped hand grip projecting from one of the grip pole was used in case of painful limitation of / difficulty in abduction of arm due to post-operative fibrosis. The cushion set and accessories were used with base plate that was secured to couch top using two-pin indexing bar. Patient was relaxedly positioned supine over breast and lung board with head placed over appropriate head rest fixed to slot on the board after asking them to remove all clothes and jewels till pubis. Arms were abduced over-head and positioned over arm rest with hands holding hand grip. Central laser passed exactly along midline of patients’ body from root of nose through neck, thorax and abdomen to pubis. Positioning patients in this manner ensured that the same can be reproduced during set-up and treatment. No thermoplastic mask was used for immobilization of patients as the same was not procured and supplied.
Simulation was performing by spiral CT scan obtaining slice thickness of 5 mm (images spaced from base of skull to lower edge of liver) without contrast on Philips Brilliance BigBore™ (Philips Medical Systems, Madison, WI). Midline laser of CT simulator was used to position the patients in straight line on the set of cushions before acquisition of scan. Three skin tattoos, two lateral and one anterior, were marked for position verification by alignment to the 3 laser system. Three 2 mm lead ball on 15 mm skin marking label [KSU-SL-20 - SureMark™, Newark, OH] was placed on tattooed laser cross-hair on anterior midline and lateral thoracic wall. Positional quality of simulation CT scan was ascertained by scrolling through the CT dataset by placing TPS crosshair over the tip of spinous process. If consecutive tip of spinous process had deviated > 2 mm from the TPS crosshair, then re-simulation was performed after re-aligning of patients’ midline with midline laser by technologist / radiation oncologist. If the deviation persisted despite re-positioning, it was anticipated that the same would be reproducible during treatment. The images with DICOM 3 format were transferred to the treatment planning system (TPS) by local network. Simulation CT so transferred was imported to Monaco TPS version 5.1 (Elekta CMS, Maryland Heights, MO, USA) and RTOG consensus guidelines were used for contouring chest wall / breast and draining lymph node areas.
Medical physicists planned VMAT on simulation CT and same was approved by radiation oncologists if the plans were satisfactory with respect to target volume coverage and dose to critical normal tissue. Next step is registration of patient, scheduling of approved plan along with AP / lateral DRRs and simulation CT into Radiation Oncology Information System (interface software) MOSAIQ ® Radiation Oncology (Elekta IABS, Kungstensgatan, SE, Stockholm). During the first treatment session, the patient was aligned by the laser system with the three skin tattoos and two orthogonal 2D images (one each of EPID images and flat panel kV image acquired simultaneously) were acquired, typically anterior-posterior and latero-lateral. Tattoo-based set-up of patients immobilized on breast and lung board and online 2D image matching was performed for set-up verification before implementation of VMAT. Set-up verification was performed using orthogonal kV and MV image (flat panel detector and EPID generated kV and MV images by using CBCT-generated and linac-generated x-ray respectively). The images were matched with the digitally reconstructed radiographs (DRRs) from the CT simulation using a dedicated software. The alignment was validated by a radiation oncologist on the basis of bone anatomy. The region of interest (ROI) of the patient for 2D image matching was from base of skull to lower extent of rib cage. Vertebra bodies, interface of pleura with ribs, clavicle, head, neck and upper shaft of humerus were matched in online 2D AP images. Vertebra bodies, intervertebral foramina, spinous process, manubrio-sternal joint, outer and inner cortex of sternum were matched in online 2D lateral images. Active Breathing Coordinator or 4-D CT was not utilized for simulation.
Treatment of chest wall / breast with or without draining lymph node areas was planned by VMAT to a total dose of 50 Gy in 25 fractions of 2 Gy by a pair of partial arc (one clockwise and another counter-clockwise) technique over a period of 5 weeks. The planning target volume (PTV) was obtained by a 5 mm expansion around the CTV except for the posterior margin where the PTV expansion was trimmed anticipating dose to ipsilateral lung. All patients were treated in supine position with both arm abducted over-arm and hand held hand grip fixed to grip collar on base plate. Knee joints were placed in flexed position over knee rest that was placed over ankle board to facilitate setup reproducibility.
In the entire study, tattoo-based set-up and online 2D matching was the planned and primary mode of set-up verification. However, based on in-puts from medical physicists and technologists, it was subsequently planned to check for collusion of gantry with couch by moving the gantry 360° around iso-centre (simulating on-board acquisition of CBCT) in the in-room presence of two radiotherapy technologists and radiation oncologist after shifting the patients’ couch in x-, y- and z-axis as determined by Treatment Planning System (TPS) necessary for implementingiso-centric treatment by VMAT. All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008 (5). Informed consent was obtained from all patients for being included in the study.