Development and evaluation of multiple isocentric volumetric modulated arc therapy technique for craniospinal axis radiotherapy planning.

To develop and compare a volumetric modulated arc therapy (VMAT) technique with conventional radiotherapy for craniospinal irradiation with respect to improved dose conformity and homogeneity in the planning target volume (PTV) and to reduced dose to organs at risk (OAR). Conventional craniospinal axis radiotherapy plans of 5 patients were acquired. The median (range) length of the PTV was 58.9 (48.1-83.7) cm. The 6-MV VMAT plans were inversely planned with one isocenter near the base of the brain and the minimum number of isocenters required for the specified lengths of spine. The plans were optimized with high weighting for PTV coverage and low weighting for OAR sparing. Conformity and heterogeneity indices, dose-volume histograms, mean doses, and non-PTV integral doses from the two plans (prescription dose 23.4 Gy in 13 fractions) were compared. The median (range) conformity index of VMAT was 1.22 (1.09-1.45), compared with 1.69 (1.44-2.67) for conventional plans (p = 0.04). The median (range) heterogeneity index was also lower for VMAT compared with conventional plans: 1.04 (1.03-1.07) vs. 1.12 (1.09-1.19), respectively (p = 0.04). A significant reduction of mean and maximum doses was observed in the heart, thyroid, esophagus, optic nerves, and eyes with VMAT when compared with conventional plans. A decrease in body V(10Gy) was observed, but for 4 of 5 patients non-PTV integral dose was increased with VMAT when compared with the conventional plans. A VMAT technique to treat the craniospinal axis significantly reduces OAR dose, potentially leading to lower late organ toxicity. However, this is achieved at the expense of increased low-dose volumes, which is inherent to the technique, carrying a potentially increased risk of secondary malignancies.

Lee YK ，Brooks CJ ，Bedford JL ，Warrington AP ，Saran FH ... -  《-》

Optimal normal tissue sparing in craniospinal axis irradiation using IMRT with daily intrafractionally modulated junction(s).

To develop a treatment technique for craniospinal irradiation using intensity-modulated radiotherapy (IMRT) with improved dose homogeneity at the field junction(s), increased target volume conformity, and minimized dose to the organs at risk (OARs). Five patients with high-risk medulloblastoma underwent CT simulation in supine position. For each patient, an IMRT plan with daily intrafractionally modulated junction(s) was generated, as well as a treatment plan based on conventional three-dimensional planning (3DCRT). A dose of 39.6 Gy in 22 daily fractions of 1.8 Gy was prescribed. Dose-volume parameters for target volumes and OARs were compared for the two techniques. The maximum dose with IMRT was <107% in all patients. V<95 and V>107 were <1 cm3 for IMRT compared with 3-9 cm3 for the craniospinal and 26-43 cm3 for the spinal-spinal junction with 3DCRT. These observations corresponded with a lower homogeneity index and a higher conformity index for the spinal planning target volume with IMRT. IMRT provided considerable sparing of acute and late reacting tissues. V75 for the esophagus, gastroesophageal junction, and intestine was 81%, 81%, and 22% with 3DCRT versus 5%, 0%, and 1% with IMRT, respectively. V75 for the heart and thyroid was 42% and 32% vs. 0% with IMRT. IMRT with daily intrafractionally modulated junction results in a superior target coverage and junction homogeneity compared with 3DCRT. A significant dose reduction can be obtained for acute as well as late-reacting tissues.

Kusters JM ，Louwe RJ ，van Kollenburg PG ，Kunze-Busch MC ，Gidding CE ，van Lindert EJ ，Kaanders JH ，Janssens GO ... -  《-》

Optimization of Craniospinal Irradiation for Pediatric Medulloblastoma Using VMAT and IMRT.

Al-Wassia RK ，Ghassal NM ，Naga A ，Awad NA ，Bahadur YA ，Constantinescu C ... -  《-》

Intensity-modulated radiation therapy and volumetric-modulated arc therapy for adult craniospinal irradiation--a comparison with traditional techniques.

Craniospinal irradiation (CSI) poses a challenging planning process because of the complex target volume. Traditional 3D conformal CSI does not spare any critical organs, resulting in toxicity in patients. Here the dosimetric advantages of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) are compared with classic conformal planning in adults for both cranial and spine fields to develop a clinically feasible technique that is both effective and efficient. Ten adult patients treated with CSI were retrospectively identified. For the cranial fields, 5-field IMRT and dual 356° VMAT arcs were compared with opposed lateral 3D conformal radiotherapy (3D-CRT) fields. For the spine fields, traditional posterior-anterior (PA) PA fields were compared with isocentric 5-field IMRT plans and single 200° VMAT arcs. Two adult patients have been treated using this IMRT technique to date and extensive quality assurance, especially for the junction regions, was performed. For the cranial fields, the IMRT technique had the highest planned target volume (PTV) maximum and was the least efficient, whereas the VMAT technique provided the greatest parotid sparing with better efficiency. 3D-CRT provided the most efficient delivery but with the highest parotid dose. For the spine fields, VMAT provided the best PTV coverage but had the highest mean dose to all organs at risk (OAR). 3D-CRT had the highest PTV and OAR maximum doses but was the most efficient. IMRT provides the greatest OAR sparing but the longest delivery time. For those patients with unresectable disease that can benefit from a higher, definitive dose, 3D-CRT-opposed laterals are the most clinically feasible technique for cranial fields and for spine fields. Although inefficient, the IMRT technique is the most clinically feasible because of the increased mean OAR dose with the VMAT technique. Quality assurance of the beams, especially the junction regions, is essential.

Studenski MT ，Shen X ，Yu Y ，Xiao Y ，Shi W ，Biswas T ，Werner-Wasik M ，Harrison AS ... -  《-》

A comparison of volumetric modulated arc therapy and conventional intensity-modulated radiotherapy for frontal and temporal high-grade gliomas.

Volumetric modulated arc therapy (VMAT), the predecessor to Varian's RapidArc, is a novel extension of intensity-modulated radiotherapy (IMRT) wherein the dose is delivered in a single gantry rotation while the multileaf collimator leaves are in motion. Leaf positions and the weights of field samples along the arc are directly optimized, and a variable dose rate is used. This planning study compared seven-field coplanar IMRT (cIMRT) with VMAT for high-grade gliomas that had planning target volumes (PTVs) overlapping organs at risk (OARs). 10 previously treated patients were replanned to 60 Gy in 30 fractions with cIMRT and VMAT using the following planning objectives: 98% of PTV covered by 95% isodose without violating OAR and hotspot dose constraints. Mean OAR doses were maximally decreased without reducing PTV coverage or violating hotspot constraints. We compared dose-volume histogram data, monitor units, and treatment times. There was equivalent PTV coverage, homogeneity, and conformality. VMAT significantly reduced maximum and mean retinal, lens, and contralateral optic nerve doses compared with IMRT (p < 0.05). Brainstem, chiasm, and ipsilateral optic nerve doses were similar. For 2-Gy fractions, mean monitor units were as follows: cIMRT = 789 +/- 112 and VMAT = 363 +/- 45 (relative reduction 54%, p = 0.002), and mean treatment times (min) were as follows: cIMRT = 5.1 +/- 0.4 and VMAT = 1.8 +/- 0.1 (relative reduction 65%, p = 0.002). Compared with cIMRT, VMAT achieved equal or better PTV coverage and OAR sparing while using fewer monitor units and less time to treat high-grade gliomas.

Shaffer R ，Nichol AM ，Vollans E ，Fong M ，Nakano S ，Moiseenko V ，Schmuland M ，Ma R ，McKenzie M ，Otto K ... -  《-》