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3 Polish Journal of Medical Physics and Engineering

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Evaluation of dosimetric implications of Pareto and constrained mode of optimization for Monaco TPS generated VMAT plans in post operated carcinoma of the left breast

Srivastava Anoop Kumar, Bharati Avinav, Rastogi Madhup, Mishra Surendra Prasad, Khurana Rohini, Hadi Rahat, Gandhi Ajeet Kumar, Mishra Lalatendu

Polish Journal of Medical Physics and Engineering

2021

Vol. 27, Iss. 1

11--18

Intensity-modulated radiotherapy (IMRT) is being practiced for the last several years with a special approach for radiation therapy in post-mastectomy breast cancer patients. Meeting the cardiac dose constraints has always been a challenge during radiotherapy planning by both IMRT and VMAT (volumetric modulated arc therapy) of postmastectomy left breast patients. With the advancement in IMRT planning techniques, it has been modified to VMAT with more degrees of freedom for modulation and is being utilised more frequently. This helps in obtaining a suitable plan for achieving both the dose homogeneity in target volume and dose constraints to Organ at Risk (OAR). 10 Patients with carcinoma of the left breast (post-mastectomy) were selected for this study. VMAT treatment plans for these patients were generated for 6 MV photons on the Monaco treatment planning system (TPS) using two types of optimization modes i.e. Pareto and Constrained mode available in Monaco TPS. For comparative dosimetric evaluation of the efficacy of these two types of optimization modes similar calculation algorithms, calculation grids, arcs, and beam sequencing parameters were used for generating treatment plans. The dosimetric quantities such as volume receiving more than 95% of the prescribed dose (V95), volume receiving more than 107% of the prescribed dose (V107) and Maximum dose (Dmax) for target volume, mean dose (Dmean) for heart, volume receiving more than 30 Gy (V30) volume receiving more than 20 Gy (V20) volume receiving more than 5 Gy (V5) for ipsilateral lung and total monitor units delivered were analysed for both optimization modes. A judicious mix of multiple planning parameters and variables using these two modes of optimization was applied and recorded. Both optimization modes yielded similar outcomes. However, Pareto mode has shown better coverage for planning target volume (PTV) with comparable doses to OARs.

Evaluation of clinical implications in the use of dose to water versus dose to medium by using NTCP and TCP models for urinary bladder tumours

Bharati Avinav, Mandal Susama R., Srivastava Anoop K., Rastogi Madhup, Khurana Rohini, Hadi Rahat, Gandhi Ajeet K., Mishra Lalatendu, Mishra Surendra P.

Polish Journal of Medical Physics and Engineering

2021

Vol. 27, Iss. 1

19--24

Purpose: To analyze the dosimetric and radiobiological differences between dose to water versus dose to medium for patients with carcinoma of the urinary bladder. Materials and Methods: 15 patients with cancer of urinary bladder were selected for the study. VMAT plans were generated for each patient. The dose distributions were calculated in the modes dose to water and to medium with the Monaco treatment planning system. A dosimetric comparative analysis has been made between the two modes of planning in this study. Subsequently, NTCP and TCP were determined for OARs and targets respectively. Results: The mean dose to 2 cc of the rectum, small bowel, left and right femoral heads respectively was higher by 0.8, 1.2, 2.7, and 2.2% for the dose to water calculation. Similarly, the mean dose to D2, D50, and D98 for PTV was higher by 0.4, 0.3, and 0.3% for dose to water calculation. Such small dose differences had little effect on the values of TCP and NTCP. Conclusion: For patients with the urinary bladder there were very small differences between results between calculations carried out in dose to medium and dose to water modes.

Evaluation of the effect of random setup errors on dose delivery in Intensity Modulated Radiotherapy

Bharati Avinav, Mandal Susama Rani, Srivastava Anoop Kumar, Rastogi Madhup, Khurana Rohini, Hadi Rahat, Sapru Shantanu, Gandhi Ajeet Kumar, Mishra S.P.

Polish Journal of Medical Physics and Engineering

2020

Vol. 26, Iss. 1

55--60

Aim: To conduct a study on the effect of random setup errors inpatient for dose delivery in Intensity Modulated Radiotherapy plans using Octavius 4D phantom. Materials and methods: 11 patients with cancer of H&N were selected for this study. An IMRT plan was created for each patient. The IMRT quality assurance plans were transferred to Mosaiq workstation in a linear accelerator. These plans were delivered at the reference treatment position. Subsequently, the QA plans were delivered on the Octavius 4D phantom after introducing errors in various translational and rotational directions. The setup inaccuracies introduced varied from 1 mm to 5 mm along X, Y. These setup uncertainties were then introduced along X and Y direction simultaneously in equal measures. Similarly, IMRT plans were delivered also after introducing roll and yaw rotation of 1, 2 and 3 degrees in phantom. The deviation of gamma indices at all these positions was analyzed with respect to the reference setup position. Results: The percentage of points passing the gamma acceptance criterion decrease as we increase the setup error. The change is found to be very insignificant with setup error up to 2 mm along X, Y or XY direction. Similarly, the rotational error of up to 3 degrees is found to be acceptable. Conclusions: Small setup (< 2 mm) correction in patients may not adversely affect the dose delivery. But an error of similar magnitude in 2 directions simultaneously has a much greater impact on IMRT dose delivery.