ABSTRACT
Aim: The aim of the present study was to access the need of daily cone-beam computed tomography (CBCT) and the requirement of in-house protocols of image acquisition frequency to reduce unnecessary exposure to the patients undergoing radiotherapy treatment. Materials and Methods: The dose delivered during CBCT procedure (On-Board Imager, Trilogy, Varian medical system, Inc., Palo Alto, California) was assessed for pelvic and head and neck region. For dose estimation, cylindrical polymethyl methacrylate phantoms of 15 cm length, 16 cm, and 32 cm diameter were used to simulate the patient's head and neck and pelvic region thickness, respectively. More than 10 cm scatterer was added on either end of this phantom. Calibrated Ionization chamber DCT10 LEMO SN 1685 iba, dosimetry, Germany (10 cm active length) was used to measure the dose Index. The doses known as cone-beam dose index (CBDI100) were estimated for all the scanning protocols (kV and mAs setting) available on the machine. In this study, image acquisition frequency to correct the setup error was optimized. In-house protocol for image acquisition frequency during treatment has been suggested to reduce the dose. It was based on the principle of as low as reasonable achievable. Results: Optimized dose protocol observed was the “standard dose head” for which the CBDI100 was 2.43 mGy. Whereas for pelvic imaging, single protocol of 125 kV, 80 mA was available by which a dose of 7.61 mGy is likely to be received by the patient during scan. Maximum shift of 6 mm in lateral direction was observed to the patient of Pelvis region and 5 mm was observed in the longitudinal direction for the H and N patients. Angular shift measured in patient position was 3.8° and 3.1° for H and N and pelvic region, respectively. Conclusion: Three consecutive-day CBCT-imaging at the beginning of the treatment followed by once weekly CBCT and two-dimensional (2D) imaging in remaining days of treatment can be an optimized way of imaging for the patient having malignancy in the region of pelvic and abdomen. For H and N, once in a week, CBCT with standard dose head protocol, followed by 2D-imaging in remaining days can be an optimized way of imaging.
ABSTRACT
Purpose: This trial studies the feasibility and potential utility of stereotactic body radiation therapy in patients with unresectable liver metastasis. Aims: (1) The aim of this study is to assess the local response of the liver lesions poststereotactic body radiation therapy regarding number and size of lesions and (2) to evaluate the toxicity to organ (s) at risk. Materials and Methods: A total of 15 patients were enrolled in this study from November 2014 to October 2015. The inclusion criteria for this study were patients having 1–3 liver metastasis from any solid tumor except germ cell tumor or lymphoma with no evidence of progressive disease (PD) outside the liver. A planning four dimensional-computed tomography (CT) scan was taken. Planning target volume was generated by giving margin of 5 mm. Dose prescribed was 36 Gy in 3#. Response was defined by CT abdomen done at 3 and 6 months poststereotactic body radiation therapy as per RECIST guideline (v1.1). Results: At 3 months poststereotactic body radiation therapy, five patients had partial response, five patients had stable disease, and five patients had PD as per RECIST criteria. Out of 20 assessable lesions, 16 were controlled at 3 months poststereotactic body radiation therapy. The actuarial local control rate was 86% at 3 months and 77% at 6 months poststereotactic body radiation therapy. The median progression free survival was 7 months. Two patients experienced Grade 2 gastric toxicity and one patient experienced Grade 2 small bowel toxicity. No cases of radiation-induced liver disease were observed. Conclusions: This trial examines the feasibility of stereotactic body radiotherapy to liver metastasis in the Indian scenario. It shows excellent tolerability and is a safe therapeutic option for inoperable patients, showing good local control
ABSTRACT
PURPOSE: To derive and validate an index to correlate the bladder dose with the catheter balloon dose using limited computed tomography (CT) slices. MATERIALS AND METHODS: Applicator geometry reconstructed from orthogonal radiographs were back-projected on CT images of the same patients for anatomy-based dosimetric evaluation. The correlation indices derived using power function of the catheter balloon dose and the bladder volume dose were validated in 31 patients with cervical cancer. RESULTS: There was significant correlation between International Commission on Radiation Units (ICRU)-38 balloon reference dose (Dr) and the dose received by 25% bladder volume (D(25)) (P< 0.0001). Significant correlation was also found between the reference dose of mid-balloon point (D(rm)) and the dose to D(25) (P < 0.0001). Average percentage difference [100 x (observed index - expected index)/ expected index] of observed value of I'25 (index for the dose to D25 bladder with respect to mid-balloon reference point) from that of expected value was 0.52%, when the index was modeled with reference dose alone. Similarly the average percentage difference for I'10cc (index for the dose to 10 cc volume of bladder with respect to mid balloon point) was 0.84%. When this index was modeled with absolute bladder volume and reference dose, standard deviation of the percentage difference between observed and expected index for D(rm) reduced by approximately 2% when compared to D(r). CONCLUSION: For clinical applications, correlation index modeled with reference dose and volume predicts dose to absolute volume of bladder. Correlation index modeled with reference dose gives a good estimate of dose to relative bladder volume. From our study, we found D(rm) to be a better indicator of bladder dose than D(r).