Feasibility assessment of the interactive use of a Monte Carlo algorithm in treatment planning for intraoperative electron radiation therapy.

This work analysed the feasibility of using a fast, customized Monte Carlo (MC) method to perform accurate computation of dose distributions during pre- and intraplanning of intraoperative electron radiation therapy (IOERT) procedures. The MC method that was implemented, which has been integrated into a specific innovative simulation and planning tool, is able to simulate the fate of thousands of particles per second, and it was the aim of this work to determine the level of interactivity that could be achieved. The planning workflow enabled calibration of the imaging and treatment equipment, as well as manipulation of the surgical frame and insertion of the protection shields around the organs at risk and other beam modifiers. In this way, the multidisciplinary team involved in IOERT has all the tools necessary to perform complex MC dosage simulations adapted to their equipment in an efficient and transparent way. To assess the accuracy and reliability of this MC technique, dose distributions for a monoenergetic source were compared with those obtained using a general-purpose software package used widely in medical physics applications. Once accuracy of the underlying simulator was confirmed, a clinical accelerator was modelled and experimental measurements in water were conducted. A comparison was made with the output from the simulator to identify the conditions under which accurate dose estimations could be obtained in less than 3 min, which is the threshold imposed to allow for interactive use of the tool in treatment planning. Finally, a clinically relevant scenario, namely early-stage breast cancer treatment, was simulated with pre- and intraoperative volumes to verify that it was feasible to use the MC tool intraoperatively and to adjust dose delivery based on the simulation output, without compromising accuracy. The workflow provided a satisfactory model of the treatment head and the imaging system, enabling proper configuration of the treatment planning system and providing good accuracy in the dosage simulation.

An innovative tool for intraoperative electron beam radiotherapy simulation and planning: description and initial evaluation by radiation oncologists.

PURPOSE: Intraoperative electron beam radiation therapy (IOERT) involves a modified strategy of conventional radiation therapy and surgery. The lack of specific planning tools limits the spread of this technique. The purpose of the present study is to describe a new simulation and planning tool and its initial evaluation by clinical users. METHODS AND MATERIALS: The tool works on a preoperative computed tomography scan. A physician contours regions to be treated and protected and simulates applicator positioning, calculating isodoses and the corresponding dose--volume histograms depending on the selected electron energy. Three radiation oncologists evaluated data from 15 IOERT patients, including different tumor locations. Segmentation masks, applicator positions, and treatment parameters were compared. RESULTS: High parameter agreement was found in the following cases: three breast and three rectal cancer, retroperitoneal sarcoma, and rectal and ovary monotopic recurrences. All radiation oncologists performed similar segmentations of tumors and high-risk areas. The average applicator position difference was 1.2 ± 0.95 cm. The remaining cancer sites showed higher deviations because of differences in the criteria for segmenting high-risk areas (one rectal, one pancreas) and different surgical access simulated (two rectal, one Ewing sarcoma). CONCLUSIONS: The results show that this new tool can be used to simulate IOERT cases involving different anatomic locations, and that preplanning has to be carried out with specialized surgical input.

[Delays and treatment interruptions: difficulties in administering radiotherapy in an ideal time-period]. / Retrasos e interrupciones: la dificultad para irradiar en el tiempo ideal.

Prescribed total radiation dose should be administered within in a specific time-frame and delays in commencing treatment and/or unplanned interruptions in radiation delivery are unacceptable because, in certain cancer sites, treatment-time prolongation can have a deleterious effect on local tumour control, and on patient outcomes. The present review evaluated the causes of initial treatment delays as well as interruptions in the scheduled radiotherapy. The literature search highlighted a significant concern in avoiding treatment-time prolongation in head and neck, cervix, breast and lung cancer. Among the causes involved in delay in radiotherapy commencement factors such as waiting lists, lack of material and human resources, and an increase complexity in planning, simulation and verification are highlighted. Most authors recommend radiotherapy commencement as soon as possible in radical (exclusive irradiation with active tumour present) and palliative situations with a maximum delay of no more than 6 to 8 weeks in the case of adjuvant radiotherapy (post-resection) programs. Interruptions during the course of treatment include: planned unit maintenance and servicing, acute patient toxicity or unexpected malfunction of linear accelerators; this last feature has the most deleterious effect on patients as well as radiotherapy practitioners. Interruptions that impact on the programmed time-course for radiotherapy needs to be compensated-for so as assure the biological equivalence in treatment efficacy with respect to cancer site and stage.