In this study, we present an intensity‐modulated radiotherapy technique based on forward planning dose calculations to provide a concave dose distribution to the prostate and seminal vesicles by means of modified dynamic arc therapy (M‐DAT). Dynamic arcs (350 degrees) conforming to the beam's eye view of the prostate and seminal vesicles while shielding the rectum, combined with two lateral oblique conformal fields (15 degrees with respect to laterals) fitting the prostate only, were applied to deliver doses of 78 Gy and 61.23 Gy in 39 fractions to the prostate and seminal vesicles respectively. Dynamic wedges (45 degrees of thick end, anteriorly oriented) were used with conformal beams to adjust the dose homogeneity to the prostate, although in some cases, hard wedges (30 degrees of thick part, inferiorly oriented) were used with arcs to adjust the dose coverage to the seminal vesicles. The M‐DAT was applied to 10 patients in supine and 10 patients in prone positioning to determine the proper patient positioning for optimum protection of the rectum. The M‐DAT was compared with the simplified intensity‐modulated arc therapy (SIMAT) technique, composed of three phases of bilateral dynamic arcs. The mean rectal dose in M‐DAT for prone patients was 22.5±5.1 Gy; in M‐DAT and SIMAT for supine patients, it was 30.2±5.1 Gy and 39.4±6.0 Gy respectively. The doses to 15%, 25%, 35%, and 50% of the rectum volume in M‐DAT for prone patients were 44.5±10.2 Gy, 33.0±8.2 Gy, 25.3±6.4 Gy, and 16.3±5.6 Gy respectively. These values were lower than those in M‐DAT and in SIMAT for supine patients by 7.7%, 18.2%, 22.4%, and 28.5% and by 25.0%, 32.1%, 34.9%, and 41.9% of the prescribed dose (78 Gy) respectively. Ion chamber measurements showed good agreement of the calculated and measured isocentric dose (maximum deviation of 3.5%). Accuracy of the dose distribution calculation was evaluated by film dosimetry using a gamma index, allowing 3% dose variation and 4 mm distance to agreement as the individual acceptance criteria in prostate and seminal vesicle levels alike for all supine and prone patients. We found that fewer than 10% of the pixels in the dose distribution of the calculated area of 10×10−cm failed the acceptance criteria. These pixels were observed mainly in the low‐dose regions, particularly at the level of the seminal vesicles.In conclusion, the single‐phase M‐DAT technique with patients in the prone position was found to provide the intended coverage of the prescribed doses to the prostate and seminal vesicles with improved protection for the rectum. Accordingly, M‐DAT has replaced non‐modulated conformal radiotherapy or SIMAT as the standard treatment for prostate cancer in our department.PACS number: 87.53.Tf

We compare an inverse‐planning intensity‐modulated radiotherapy (IMRT) technique with three previously published forward‐planning dynamic arc therapy techniques and a newly implemented technique for treatment of prostate only. The three previously published dynamic arc techniques are dynamic arc therapy (DAT), two‐axis dynamic arc therapy (2A‐DAT), and modified dynamic arc therapy (M‐DAT). The newly implemented technique is the bilateral wedged dynamic arc (BW‐DAT). In all dynamic arcs, the multileaf collimator is moving during rotation to fit the prostate, except that, in 2A‐DAT, it is fitting two separate symmetrical rhombi including the prostate. The rectum is shielded during rotation only in the cases of M‐DAT and BW‐DAT.The results obtained indicate that the BW‐DAT, M‐DAT, and DAT techniques provide the intended dose coverage of the prescribed dose to the planning target volume (PTV)—that is, 95% of the PTV is covered by 100% of the dose. The maximum dose to a 3‐cm margin of healthy tissue that surrounds the PTV is lower by 2.5% in the case of IMRT than in both BW‐DAT and M‐DAT, but it is lower by 5.0% than that in both DAT and 2A‐DAT. The maximum dose to the rest of the healthy tissue in the case of BW‐DAT is 33.2Gy±2.2Gy. This dose covers percentage healthy body volumes of 8%±3.2% with IMRT, 4%±1.5% with DAT, and 6%±1.2% with both 2A‐DAT and M‐DAT. Also, this dose is much lower than the accepted maximum dose (52 Gy) to the femoral heads and necks according to Report 62 from the International Commission on Radiation Units and Measurements. Accordingly, it would be possible to neglect delineation of the femoral heads and necks as organs at risk in cases of BW‐DAT.Doses to 15%, 25%, 35%, and 50% (D15%, D25%, D35%, and D50%) of the rectum volume in the case of BW‐DAT were 43.5Gy±8.6Gy, 24.2Gy±8.7Gy, 13.2Gy±4.2Gy, and 5.7Gy±2.1Gy respectively. The D15% of rectum in the case of IMRT was lower than that in BW‐DAT, M‐DAT, 2A‐DAT, and DAT by 7.3%, 10.3%, 33.0%, and 17.6% of the prescribed dose (78 Gy in 39 fractions) respectively. The D25%, D35%, and D50% of the rectum volume in the cases of IMRT and DAT were comparable (with a maximum variation of 4.5%); they were similarly comparable in the cases of M‐DAT and BW‐DAT (with maximum variation of 1.5%). These same doses in BW‐DAT were lower than those in IMRT by 8.7%, 10.6%, and 6.2% respectively, but they were quite lower than those in 2A‐DAT, because the average variation was 41.6% (with a maximum of 44.0%).The D15%, D25%, D35%, and D50% of the bladder volume in the case of BW‐DAT were 33.2Gy±10.9Gy, 17.4Gy±7.9Gy, 6.5Gy±4.3Gy, and 4.2Gy±3.5Gy respectively. The D15% and D25% of the bladder in the cases of IMRT, M‐DAT, and BW‐DAT were comparable (with a maximum variation of 2.2% and 3.6% respectively), and the mean values of each dose were lower in DAT by 14.3% and 11.7% respectively. However, the values of D35% and D50% in the four techniques were comparable, with maximum variations of 5.1% and 2.7% respectively. The D15%, D25%, D35%, and D50% of the bladder in the ...

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Background: Recent techniques of radiotherapy such as volumetric modulated arc therapy (VMAT) that delivered in Coplanar technique or non-coplanar technique allows to deliver high doses to the brain tumors, at the same time reducing the risk of normal tissues as compared with intensity modulated radiotherapy (IMRT) and the three-dimensional conformal radiotherapy (3D-CRT). Aim: The aim of the current work is to compare dosimetrical and radiobiological indices of treatment plans for brain tumor using CO-VMAT and NC-VMAT techniques to choose the optimum technique for the treated cases. Patients and methods: Twenty-one cases with brain tumors were performed for the treatment planning study. The cases are planned by using the coplanar and non coplanar VMAT techniques and optimized to evaluate and compare dosimetrical and radiobiological parameters related to PTV dose coverage and sparing of organs at risk. The total dose of CO-VMAT and NC-VMAT plans is 60 Gray in 30 fractions during a single phase with a daily dose of 2 Gray. Results: In dosimetrical calculations, CO-VMAT and NC-VMAT techniques gave similar (homogeneity index HI, modified homogeneity index MHI, conformity index CI and quality factor QF) values for the PTV, while CO-VMAT was the higher in (target coverage index TCI, prescription isodose to target volume ratio PITV and conformity number CN) values and the lower in (gradient index GI, gradient measure GM) values, and NC-VMAT was the lower in Monitor units MUs values. In radiobiological calculations, equivalent uniform dose EUD values, tumor control probability TCP and complication free tumor control probability P+ were large in CO-VMAT and normal tissue complication probability NTCP was less in NC-VMAT. Conclusion: While the previous studies showed that CO-VMAT technique was used when the tumor is far from the organs at risk, the present work found CO-VMAT can be used when the tumor is near to or far from organs at risk (OARs) because it can achieve the target dose coverage and sparing of OARs together. We strongly recommend that NC-VMAT technique should be used when the OARs are located inside the tumor to be able to achieve more sparing of them.