Development and Validation of a MATLAB Software Program for Decoding the Treatment Errors in Real-time Position Management™ Gating-generated Breathing Trace.

INTRODUCTION: The Real-time Position Management™ (RPM) is used as a motion management tool to reduce normal tissue complication. However, no commercial software is available to quantify the "beam-on" errors in RPM-generated breathing traces. This study aimed to develop and validate an in-house-coded MATLAB program to quantify the "beam-on" errors in the breathing trace. MATERIALS AND METHODS: A graphical user interface (GUI) was developed using MATLAB (Matrix Laboratory Ra2016) software. The GUI was validated using two phantoms (Varian-gated phantom and Brainlab ET gating phantom) with three regular motion profiles. Treatment time delay was calculated using regular sinusoidal motion profile. Ten patient's irregular breathing profiles were also analyzed using this GUI. RESULTS: The beam-on comparison between the recorded reference trace and irradiated trace profile was done in two ways: (1) beam-on time error and (2) beam-on displacement error. These errors were ≤1.5% with no statistical difference for phase- and amplitude-based treatments. The predicated amplitude levels of reference phase-based profiles, and the actual amplitude levels of amplitude-based irradiated profiles were almost equal. The average treatment time delay was 47 ± 0.003 ms. The irregular breathing profile analysis showed that the amplitude-based gating treatment was more accurate than phase based. CONCLUSION: The developed GUI gave the same and acceptable results for all regular profiles. These errors were due to the lag time of the linear accelerator with gating treatment. This program can be used as to quantifying the intrafraction "beam-on" errors in breathing trace with both mode of gating techniques for irregular breathing trace, and in addition, it is capable to convert phase-based gating parameters to amplitude-based gating parameters for treatment.

The Composite Planning Technique in Left Sided Breast Cancer Radiotherapy: A Dosimetric Study.

OBJECTIVE: The aim of this retrospective study is to reduce the dose of heart, both lung and opposite breast and left anterior descending artery (LAD) and avoid long term complication and radiation induced secondary malignancies in radiotherapy left breast/chest wall without losing homogeneity and conformity of the Planning Target Volume (PTV), contoured using Radiotherapy Oncology Group (RTOG 1005) guideline. MATERIALS AND METHODS: The treatment plans were generated retrospectively by TFIF, VMAT and Composite techniques for 30 patients. Dose-Volume Histograms (DVHs) were evaluated for PTV and organs at risk (OAR's) and analyzed in two groups BCS and MRM using Wilcoxon signed rank test. RESULTS: The homogeneity index (HI) was improved in Composite technique by 32.72% and 21.81% of VMAT, 50.66% and 49.41% of TFIF in BCS and MRM group respectively. The Conformity Index (CI) for composite plan was statistically same as VMAT and superior by 27.94% and 41.37% of TFIF in BCS and MRM group respectively. The low dose volume V5Gy and V10Gy of the heart were improved in Composite plan by 47.9% and 26.1% of VMAT respectively in BCS group and in MRM group, improved by 21.2% and 45.6% of VMAT. The V5Gy and V10Gy of ipsilateral lung were improved in Composite plan by 16% and 13.7% of VMAT respectively in BCS and 8.4% and 3% of VMAT respectively in MRM group. CONCLUSION: The Composite plan consisting of VMAT and TFIF plan with an optimum selection of fractions can achieve lower low dose exposure to the OAR's without compromising coverage compared to VMAT.

Fractionated stereotactic radiosurgery with volumetric modulated arc therapy (Rapid Arc) for reradiation in recurrent high grade gliomas.

BACKGROUND: To evaluate 'Rapid Arc (RA)' technique for delivering fractionated stereotactic radiosurgery (FSRS) in patients with recurrent high grade gliomas (HGGs) for minimizing the dose to previously radiated high dose brain volume. MATERIALS AND METHODS: Between April 2010 and February 2011, 16 consecutive patients with recurrent HGGs and previously treated with intensity modulated radiation therapy (IMRT) and Temozolamide received FSRS. The median time between IMRT and FSRS was 10.72 months. FSRS to a dose of 30 Gy in a median of 5 fractions was delivered to the recurrent tumor (gross tumor volume [GTV]). Brain volume around the GTV and previously treated to a mean dose >50 Gy was delineated as "Avoidance Volume (AV)." Patients were planned with both RA and Dynamic Conformal Arc (DCA) to achieve minimum dose to AV. Dose received by GTV, AV, rest of the normal brain (brain minus PTV) and conformity index (CI) and heterogenecity index (HI) were compared by the two techniques. RESULTS: At a median follow up of 7.33 months, median progression free and overall survival was 6.4 and 9.3 months, respectively. Mean dose to AV was significantly lower with RA as compared with DCA (10.8 Gy vs. 15.5 Gy, P - 0.0001) with no significant difference in the dose delivered to GTV. No patient developed radiation necrosis. CONCLUSION: As compared with DCA, RA delivered significantly less dose to previously radiated high dose brain volume. It may contribute to minimizing the risk of radionecrosis with stereotactic radiosurgery (SRS) in patients with recurrent HGG.

A comparison between four immobilization systems for pelvic radiation therapy using CBCT and paired kilovoltage portals based image-guided radiotherapy.

INTRODUCTION: We commonly use 6- and 4-clamped thermoplastic molds (TMs) for rigid immobilization during pelvic radiotherapy (RT), sometimes a vacuum cushion (VC) is also used as leg support with TM. Our objective was to report the setup margins (SMs) associated with the different systems, to analyze whether any of these systems is superior, and to analyze whether any of them showed better reproducibility in any particular direction. MATERIALS AND METHODS: Retrospective analysis was done by dividing the patients into four groups: 6-clamp with VC (6CVC), 6-clamp without VC (6CNC), 4-clamp with VC (4CVC), and 4-clamp without VC (4CNC). A repeat offline review was done for all patients and errors were tabulated. Statistical methods were then applied. RESULTS: Total 24 patients had 413 image-guided RT (IGRT) sessions, 312 were cone beam computed tomography scan (CBCT) scans and 101 were paired kilovoltage portals (kVp). There was no statistically significant difference between 6CVC and 6CNC. However, while comparing 4CVC and 4CNC, a statistically significant difference was seen in all directions. VC improved precision in vertical and lateral direction mainly, while the 6-clamped TM improved reproducibility in longitudinal direction. CONCLUSIONS: SM was low for all the four immobilization systems studied. There is no added benefit of using a VC with 6-clamped TM for pelvic RT. Use of a VC is recommended with 4-clamped TM to improve overall reproducibility. 6-clamped TM helps keep the errors low.