|Year : 2020 | Volume
| Issue : 1 | Page : 73-74
Patient setup variations for treatment planning for breast cancer
Department of Radiotherapy, Burdwan Medical College, Purba Bardhaman, West Bengal, India
|Date of Submission||10-Nov-2019|
|Date of Decision||13-Nov-2019|
|Date of Acceptance||07-Dec-2019|
|Date of Web Publication||03-Mar-2020|
Dr. Rajat Bandyopadhyay
Professor, Department of Radiotherapy, Burdwan Medical College, Purba Bardhaman, West Bengal
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Bandyopadhyay R. Patient setup variations for treatment planning for breast cancer. J Mar Med Soc 2020;22:73-4
Radiotherapy to the chest wall or breast improves the outcome after mastectomy and breast conservation surgery for breast cancer.,, External beam radiotherapy is an essential component of multimodality treatment of breast cancer along with chemotherapy and hormone therapy/Her2 neu-directed therapy if indicated for all breast conservation surgeries and many postmastectomy patients.
Breast irradiation is one of the most challenging problems in radiotherapy due to complex shape of the target volume, proximity of radiation-sensitive normal structures, and breathing motion. Problems in delivering external beam radiotherapy apart from curvature of the chest wall, breathing motion issues, and fixation issues are the unwarranted doses to lungs and heart. Doses to lungs are minimized by employing tangential fields. Treatment of left-sided breast tumor creates special problems due to excessive doses to heart. Image-guided three-dimensional (3D) conformal radiotherapy or intensity-modulated radiation therapy (IMRT) attempts to minimize the dose to heart and lung. Inhomogeneous dose distribution due to anatomic shape of postmastectomy chest wall and unwarranted dose to heart are major challenges for treating radiation oncologists.
Another aspect of major concern is setup errors. Basic principle of radiation therapy is to deliver planned dose to the defined treatment volume accurately daily during treatment delivery without any variation. This would enable us to achieve our treatment goal and also minimize dose to organs at risk (OARs). Ideally, there should not be any setup variations but that is not practical. Both systematic and random errors are part of all radiation treatments.
Studies have been done to use electronic portal imaging (EPI) during treatment to determine intra- and inter-fraction motion in patients undergoing radiotherapy and to correlate the magnitude of motion with patient-specific parameters. EPI is easily performed daily with minimal increase in treatment time.
Random error is the measurement caused during daily setup reproducibility of treatment fields for matching of coordinates. It is calculated as the standard deviation of the mean.
The systematic error is a deviation that occurs in the same direction and is of a similar magnitude for each fraction throughout the treatment course. It occurs during image registration, target delineation, and target reconstruction.
Computed tomography (CT)-based modern planning systems which are widely used nowadays in 3D conformal radiotherapy and IMRT attempt to deliver the planned dose to the target volume minimizing dose to OARs. Reduction in setup variations to an acceptable standard is necessary to achieve the desired goal.
Cone-beam CT (CBCT) and electronic portal image devices (EPIDs) are two common methods for assessing inter- and intra-fraction setup variations in breast cancer patients. Topolnjak et al. compared breast setup error assessments by CBCT and EPID in 20 breast cancer patients. EPID-based setup errors were smaller than the CBCT-based setup errors. The authors concluded that EPID registration underestimated the actual bony anatomy setup error in breast cancer patients by 20%–50%. Using CBCT, decreased setup uncertainties significantly.
Batumalai et al. compared the setup accuracy of three different image assessment methods for tangential breast radiotherapy in 25 postoperative breast cancer patients. The authors concluded that the CBCT and EPI show insignificant variation in their ability to detect setup error. These findings suggest no significant differences that would make one modality considered superior over the other and EPI should remain the standard of care for most patients.
The article presented in this issue deals with patient setup variations in 25 postmastectomy patients who had CT-based treatment planning for left-sided breast cancer using EPIs. The reported setup deviations in this study are the uncorrected random and systematic errors as the patient setup was not adjusted during the first three fractions. The authors conclude that the setup variations detected are within the standard institutional parameters.
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