Background: Pelvic bone marrow (PBM) preservation is one of the factors that should be taken into consideration while choosing a technique for radiotherapy of pelvic malignancies. Aim: To dosimetrically compare between volumetric-modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) in PBM preservation in radical treatment of high-risk prostate cancer. Methods: In 26 patients with high-risk prostatic carcinoma, dual arc VMAT and 7 fields IMRT plans were generated. In every patient, two targets were defined, clinical target volume (CTV) including the prostate and seminal vesicles (CTV-PSV) and CTV including pelvic lymph nodes (CTV-LN). The organs at risk delineated were the rectum, urinary bladder, small intestine, bulb of the penis, femoral heads bilaterally and PBM. The dose prescribed to the CTV-PSV was 76 Gy in 38 fractions given over 7.5 weeks and the dose to CTV-LN was 54 Gy in 38 fractions given over 7.5 weeks. Planning target volume (PTV) was created from the CTV with a margin of 5 mm in all direction. For assessment of PBM dose, V10, V20, V30, V40, V50 and mean dose were calculated. The dose volume histogram of PTV and PBM for both techniques was compared. Results: The mean dose of PTV 54 Gy was achieved in both techniques adequately with better sparing of organs at risk with the VAMT technique. The mean dose for PBM in the VMAT technique was significantly less than that in the IMRT (21.7 Gy vs. 25.8 Gy, respectively; p < 0.001). The significant differences in PBM doses were in the range of 20 Gy to 40 Gy. Conclusion: In radical treatment of prostate cancer, VMAT technique can offer comparable conformality to IMRT with better PBM preservation. Awareness of PBM delineation and reduction of its doses using VMAT can help to decrease the hematological toxicity.
Introduction and Objective: In adjuvant radiotherapy for left breast cancer, a significant heart volume may be included in the radiation field leading to long-term cardiac toxicities. Deep inspiratory breath hold technique (DIBH) leads to chest wall separation away from the heart and thus can reduce the heart dose compared to free breathing technique. The aim of this study is to correlate dosimetrically the degree of chest wall expansion measured on planning 4D-CT scan to the heart dose in left breast cancer irradiation using DIBH technique. Materials and Methods: Thirty four patients with left breast cancer planned for adjuvant radiotherapy were included. All patients were scanned by Varian RPM (Real Time Position Managment) respiratory gating system using infrared reflecting markers and a video camera to detect the respiratory motion. IMRT or VMAT plans were done for all patients with a prescribed dose 50Gy/25fr/5w with or without operative bed boost dose 10Gy/5fr/1w. The degree of chest wall expansion was identified by measuring the amplitude of DIBH breathing curve from baseline in planning 4D-CT scan in centimeters. The depth of expansion was correlated dosimetrically with the heart V20, V30, and mean heartdose. Results: The mean distance of chest wall expansion was 2.9cm. The mean left lung dose was 8.6Gy. The mean left lung V20 was 13.8%. The mean heart dose was 1.8Gy. The mean heart V30 was 0.6%. A statistically significant reduction of the mean heart dose and V30 was observed with chest wall expansion of 1.4cm or higher (p<0.05). Conclusion: In DIBH technique, the depth of chest wall expansion in 4DCT planning is dosimetrically correlated with the cardiac dose reduction during adjuvant irradiation of left breast cancer. Further clinical studies are needed to translate this dosimetric advantage into clinical benefit.
Background:While treating brain metastasis with whole-brain radiotherapy incorporating a simultaneous integrated boost (WBRT-SIB), the risk of hippocampus injury is high. The aim of this study is to compare dosimetrically between intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) in sparing of hippocampus and organs at risk (OARs) and planning target volume (PTV) coverage.Methods:In total, 16 patients presenting with more than one brain metastases were previously treated and then retrospectively planned using VMAT and IMRT techniques. For each patient, a dual-arc VMAT and another IMRT (five beams) plans were created. For both techniques, 30 Gy in 10 fractions was prescribed to the whole brain (WB) minus the hippocampi and 45 Gy in 10 fractions to the tumour with 0·5 cm margin. Dose–volume histogram (DVH), conformity index (CI) and homogeneity index (HI) of PTV, hippocampus mean and maximum dose and other OARs for both techniques were calculated and compared.Results:A statistically significant advantage was found in WB-PTV CI and HI with VMAT, compared to IMRT. There were lower hippocampus mean and maximum doses in VMAT than IMRT. The maximum hippocampus dose ranged between 15·5 and 19·2 Gy and between 18·4 and 20·6 Gy in VMAT and IMRT, respectively. The mean dose of the hippocampus ranged between 11·5 and 17·7 Gy and between 13·2 and 18·3 Gy in VMAT and IMRT, respectively.Conclusion:Using WBRT-SIB technique, VMAT showed better PTV coverage with less mean and maximum doses to the hippocampus than IMRT. Clinical randomised studies are needed to confirm safety and clinical benefit of WBRT-SIB.
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