Clinical implementation of intensity-modulated arc therapy (IMAT) for rectal cancer

Abstract

Purpose: In rectal cancer, combined radiotherapy and chemotherapy, either pre-or postoperatively, is an accepted treatment. Late small bowel (SB) toxicity is a feared side effect and limits radiation-dose escalation in a volume-dependent way. A planning strategy for intensity-modulated arc therapy (IMAT) was developed, and IMAT was clinically implemented with the aim to reduce the volume of SB irradiated at high doses and thus reduce SB toxicity. We report on the treatment plans of the first 7 patients, on the comparison of IMAT with conventional 3D planning (3D), and on the feasibility of IMAT delivery. Methods and Materials: Seven patients, who were referred to our department for preoperative (n ‫؍‬ 4) or postoperative (n ‫؍‬ 3) radiotherapy for rectal cancer, gave written consent for IMAT treatment. All patients had a planning CT in prone position. The delineation of the clinical target volume was done after fusion of CT and MRI, with the help of a radiologist. For the IMAT plan, arcs were generated using an anatomybased segmentation tool. The optimization of the arcs was done by weight optimization (WO) and leaf position optimization (LPO), both of which were adapted for IMAT purposes. The 3D plans used one posterior and two lateral wedged beams, of which the outlines were shaped to the beam's-eye view projection of the planning target volume (PTV). Beam WO was done by constrained matrix inversion. For dose-volume histogram analysis, all plans were normalized to 45 Gy as median PTV dose. Polymer gel dosimetry (PGD) on a humanoid phantom was used for the validation of the total chain (planning to delivery). IMAT treatments were delivered by an Elekta SliPlus linear accelerator using prototype software with the same interlock class as in clinical mode. Results: The IMAT plan resulted in 3 to 6 arcs, with a mean delivery time of 6.3 min and a mean of 456 monitor units (MU) for a 180 cGy fraction. The minimal dose in the PTV was not significantly different between 3D and IMAT plans. Inhomogeneity was highest for the IMAT plans (14.1%) and lowest for the 3D plans (9.9%). Mean dose to the SB was significantly lower for the IMAT plans (12.4 Gy) than for the 3D plans (17.0 Gy). The volume of SB receiving less than any dose level was lower for the IMAT plans than for 3D plans. Integral dose was lower in the IMAT plans than for the 3D plans (respectively 244 J and 262 J to deliver 45 Gy). Differences between the PGD measured dose and the calculated dose were as small for IMAT as for 3D treatments. Conclusion: IMAT plans are deliverable within a 5-10-minute time slot, and result in a lower dose to the SB than 3D plans, without creating significant underdosages in the PTV. PGD showed that IMAT delivery is as accurate as 3D delivery. © 2004 Elsevier Inc.Intensity-modulated arc therapy (IMAT), Rectal cancer, Small bowel toxicity.

Comparative analysis of SmartArc‐based dual arc volumetric‐modulated arc radiotherapy (VMAT) versus intensity‐modulated radiotherapy (IMRT) for nasopharyngeal carcinoma

“…The delivery time was equal to $4.6\pm 0.7$ min per dual arc and was considerably less than the 7F‐IMRT delivery time. Studies on other VMAT approaches based on double RapidArc approaches ( 8 , 51 , 52 ) have shown delivery times ranging from 2.6 to 3.9 min that are faster than our results, whilst other improved IMAT approaches ( 53 , 54 ) have displayed delivery times ranging from 6.3 to 14 min for conventional linac‐based techniques. Here, we did not determine the fastest method, as previous reports were not performed under the same measurement conditions.…”

Intensity-modulated arc therapy with cisplatin as neo-adjuvant treatment for primary irresectable cervical cancer

“…Fear for excess in treatment-related toxicity could explain the reserved position towards post-CRT 0 1a1 1a2 1b1 1b2 2b IB2 0 1 1 0 0 0 IIB 9 2 2 5 1 1 IIIA 3 0 0 0 0 0 IIIB 0 2 0 2 0 0 IVA 0 0 0 0 0 1 Total 12 5 3 7 1 2 Tab. 3 Early and late postoperative complications by Chassagne's scoring system Subobstruction, not requiring surgery 2 (7) Lymphocoele 1 (3) Neurological sensory problem with mild functional impairment 5 (17) Urinary retention requiring self catheterization Grade 3, n (%) 1 (3) Lymphocoele causing temporarily inadequate renal function (microsurgery needed) Late postoperative complications (n=28) Grade 1, n (%) 1 (3) Lymphoedema Grade 2, n (%) 2 (7) Lymphoedema 1 (3) Neurological sensory problem with mild functional impairment 2 (7) Urinary retention requiring self catheterization (disappeared 6 months postoperative) Grade 3, n (%) 1 (3) retroperitoneal fibrosis causing kidney impairment (need for nephrostomy) surgery. Keys et al [13] however could not show any difference in treatment-related toxicity.…”

“…IMAT was delivered using 18-MV photons of an Elekta SL18 series Linear Accelerator (SliPlus, Elekta, Crawley, UK) equipped with a standard multileaf collimator (MLC) and prototype dynamic control software to deliver IMAT in local service mode [7]. The IMAT plans were generated using an anatomy-based exclusion tool with the aid of weight and leaf position optimisation [7,26]. Patient positioning was verified online using an electronic portal imaging device (EPID) [26].…”

Quasi-IMAT Study with Conventional Equipment to Show High Plan Quality with a Single Gantry Arc

“…Intensity-modulated arc therapy (IMAT) [8,14,19,24,25] was proposed by Yu [25] as an alternative to tomotherapy [2,7,12,15,18,22]. Both techniques are rotational approaches to intensity-modulated radiation therapy (IMRT), and they are able to improve the therapeutic ratio [6,11,21].…”