Effect of contrast medium on treatment modalities planned with different photon beam energies: a planning study.

BACKGROUND: Routinely, patient's planning scans are acquired after administration of iodinized contrast media but they will be treated in the absence of that. Similarly, high energy photons have a better penetrating power, while low energy photons will result in tighter dose distribution and negligible neutron contamination. The aim of the study was to investigate a suitable photon beam energy in the presence of intravenous contrast medium. MATERIALS AND METHODS: An indigenously made original-contrast (OC) phantom was mentioned as virtual-contrast (VC) and virtual-without-contrast (VWC) phantom were generated by assigning the Hounsfield Units (HU) to different structures. Intensity-modulated (IMRT) and volumetric-modulated-arc (VMAT) plans were generated as per criteria of the TG-119 protocol. RESULTS: It was observed that the maximum dose to the spinal cord was better with 6 mega-voltage (MV) in IMRT. The coverage of Prostate PTV (PR PTV) was similar with all the photon energies and was comparable with TG-119, except for original-contrast (OC) phantom using the VMAT technique. Homogeneity-index (HI) was comparatively better for VMAT plans. CONCLUSION: The contrast CT images lower the dose to targets. IMRT or VMAT plans, generated on such CT images will be delivered with higher doses than evaluated. However, the overdose remains non-significant.

Dosimetric Analysis of Unflattened (FFFB) and Flattened (FB) Photon Beam Energy for Gastric Cancers Using IMRT and VMAT-a Comparative Study.

PURPOSE: To evaluate the feasibility of flattening filter free beam (FFFB) for the treatment of gastric tumors and to review their benefits over 6MV flatten beam (6MV_FFB). METHODS: Fifteen patients with histologically proven gastric carcinoma were selected. CT scans with slice thickness of 0.3 cm were acquired and planning target volume (PTV) and organ at risk (OAR) were delineated. Plans were made retrospectively for each patient for the prescription dose of 45 Gy/25 fractions to the PTV. Four isocentric plans were compared in the present study on Varian TrueBeam linear accelerator (Varian Medical Systems, Palo Alto, CA, USA). RESULTS: PTV D98% was 44.41 ± 0.12, 44.38 ± 0.13, 44.59 ± 0.14, and 44.49 ± 0.19 Gy for IMRT 6MV_FFB, IMRT 6MV_FFFB, VMAT 6MV_FFB, and VMAT 6MV_FFFB respectively. 6MV_FFFB beam minimizes the mean heart dose Dmean (P = 0.001). VMAT dominates over IMRT when it came to kidney doses V12Gy (P = 0.02), V23Gy (P = 0.015), V28Gy (P = 0.011), and Dmax (P < 0.01). VMAT has significantly reduced the doses to kidneys. It was analyzed that 6MV_FFFB significantly reduces the dose to normal tissues (P = 0.006 and P = 0.018). VMAT significantly reduces the TMU, which is required to deliver the similar dose by IMRT (P < 0.01). CONCLUSIONS: Unflattened beam spares the organs at risk significantly to avoid the chances of secondary malignancies and reduces the intra-fraction motion during treatment due to provision of higher dose rate. Hence, we conclude that 6MV unflattened beam can be used to treat gastric carcinoma.

Reirradiation with IMRT for recurrent head and neck cancer: A single-institutional report on disease control, survival, and toxicity.

AIM: To study and explores the feasibility and efficacy of re-irradiation (Re-RT) for locally recurrent head and neck cancer (HNC) and second primary (SP) malignancies. BACKGROUND: The most common form of treatment failure after radiotherapy (RT) for HNC is loco-regional recurrence (LRR), and around 20-50% of patients develop LRR. Re-irradiation (Re-RT) has been the primary standard of care in the last decade for unresectable locally recurrent/SP HNC. MATERIALS AND METHODS: It was a retrospective analysis in which we reviewed the medical records of 51 consecutive patients who had received Re-RT to the head and neck region at our institute between 2006 and 2015. RESULTS: Forty-eight patients were included for assessment of acute and late toxicities, response evaluation at 3 months post Re-RT, and analyses of locoregional control (LRC) and overall survival (OS). The median LRC was 11.2 months, and at 2 and 5 years the LRC rates were 41% and 21.2%, respectively. A multivariate analysis revealed two factors: initial surgical resection performed prior to Re-RT, and achievement of CR at 3 months after completion of Re-RT to be significantly associated with a better median LRC. The median OS was 28.2 months, and at 1, 2, and 5 years, OS were 71.1%, 55.9% and 18%, respectively. A multivariate analysis revealed initial surgical resection performed prior to Re-RT, and achievement of CR at 3 months post completion of Re-RT being only two factors significantly associated with a better median OS. Acute toxicity reports showed that no patients developed grade 5 toxicity, and 2 patients developed grade 4 acute toxicities. CONCLUSION: Re-RT for the treatment of recurrent/SP head and neck tumors is feasible and effective, with acceptable toxicity. However, appropriate patient selection criteria are highly important in determining survival and treatment outcomes.