Volumetric modulated arc therapy (VMAT) is modern rotational intensity modulated therapy used for treatment of several sites. The study aimed to analyze partial tangential arc VMAT treatment planning and delivery, including analyzing the cardiac and contralateral breast doses resulting from this technique. A total of 153 consecutively treated breast cancer (conservation as well as mastectomy) patients were taken for this dosimetric study. All patients were planned using partial arc VMAT in the Monaco treatment planning system using two partial arc beams. All patients were divided into seven different categories: (1) all the patients in the study, (2) left sided whole breast and chest wall patients, (3) left Chest wall patients, (4) left whole breast patients, (5) right sided whole breast and chest wall patients, (6) right chest wall patients, and (7) right whole breast patients. We evaluated each treatment plan for PTV coverage and doses to OARs. SPSS version 16.0 software was used for statistical analysis. There were 91 left sided and 62 right sided breast cancer patients in the overall analysis. The percentage of PTV volume receiving 95% of the prescription dose (PTV V95%, mean ± SD) varied in the range of 91.2 ± 5.2-94.8 ± 2.1% with mean dose of 92.4 ± 5.2% for all cases. The (mean ± SD) cardiac dose for all the patients was 289 ± 23 cGy. The (mean ± SD) cardiac doses were higher for left sided patients (424 ± 33.8 cGy) as compared to right sided patients (123.9 ± 80 cGy) (p < 0.001). Cardiac mean doses were higher with arc angles >30° versus 30° (324.5 ± 247.1 vs. 234.4 ± 188.4 cGy) (p = 0.001). Similarly contralateral breast mean dose was higher with arc angles >30° versus 30° (126 ± 115 vs. 88.6 ± 76.1 cGy) (p = 0.001). However cardiac V20, V30 and V40 Gy did not exhibit any statistical difference between the two groups (p = 0.26, 0.057 and 0.054 respectively). This is the first large study of its kind that assesses the dosimetric outcome of tangential partial arc VMAT treatments in a large group of mastectomy and breast conservation patients. Our study demonstrates the efficacy of this technique in dose coverage of PTV as well as in minimizing dose to OARs. Further, based on our results, we conclude that the arc length for the bi-tangential arcs should be 30° since it helps to achieve the most optimal balance between target coverage and acceptable OAR doses.

The aim of this article is to derive and verify a mathematical formulation for the reduction of the six-dimensional (6D) positional inaccuracies of patients (lateral, longitudinal, vertical, pitch, roll and yaw) to three-dimensional (3D) linear shifts. The formulation was mathematically and experimentally tested and verified for 169 stereotactic radiotherapy patients. The mathematical verification involves the comparison of any (one) of the calculated rotational coordinates with the corresponding value from the 6D shifts obtained by cone beam computed tomography (CBCT). The experimental verification involves three sets of measurements using an ArcCHECK phantom, when (i) the phantom was not moved (neutral position: 0MES), (ii) the position of the phantom shifted by 6D shifts obtained from CBCT (6DMES) from neutral position and (iii) the phantom shifted from its neutral position by 3D shifts reduced from 6D shifts (3DMES). Dose volume histogram and statistical comparisons were made between [Formula: see text] and [Formula: see text]. The mathematical verification was performed by a comparison of the calculated and measured yaw (γ°) rotation values, which gave a straight line, Y  =  1X with a goodness of fit as R =  0.9982. The verification, based on measurements, gave a planning target volume receiving 100% of the dose (V100%) as 99.1  ±  1.9%, 96.3  ±  1.8%, 74.3  ±  1.9% and 72.6  ±  2.8% for the calculated treatment planning system values TPSCAL, 0MES, 3DMES and 6DMES, respectively. The statistical significance (p-values: paired sample t-test) of V100% were found to be 0.03 for the paired sample [Formula: see text] and 0.01 for [Formula: see text]. In this paper, a mathematical method to reduce 6D shifts to 3D shifts is presented. The mathematical method is verified by using well-matched values between the measured and calculated γ°. Measurements done on the ArcCHECK phantom also proved that the proposed methodology is correct. The post-correction of the table position condition introduces a minimal spatial dose delivery error in the frameless stereotactic system, using a 6D motion enabled robotic couch. This formulation enables the reduction of 6D positional inaccuracies to 3D linear shifts, and hence allows the treatment of patients with frameless stereotactic radiosurgery by using only a 3D linear motion enabled couch.

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