Treatment planning of stereotactic radiosurgery for single brain metastases: impact of leaf width

Purpose/objective: Stereotactic radiosurgery of brain metastases requires highly conformal dose distributions. Besides beams setup, characteristics of the linear accelerator collimator may also play a role. In this study we compared the impact of leaf width on the dose outside the target for stereotactic radiosurgery of single brain metastases. Results: The mean dose was evaluated in the first 2 rings of 5 mm around the PTV(table 1). The difference in mean dose for the small lesions(Dpres=24 Gy) of the first ring of 5 mm is 1.8 Gy in favor of the Agility and 0.9 Gy for the larger lesions(Dpres=18 Gy)also in favor of the Agility. The difference is smaller for the larger lesions (figure1). Also for the second ring of 5 mm, adjacent to the first ring, the difference is is 1.1 Gy vs 0.8 Gy also in favor of the Agility. Conclusion: For the small lesions with a volume smaller than 4 cm³ the Agility shows a steeper gradient in the two surrounding rings than the MLCi1. Therefore we recommend the use of the Agility for treating the smaller lesions

Dose to the masseter muscle and risk of trismus after chemoradiation for advanced head & neck cancer

Purpose / objective: Head and neck cancer patients treated with chemoradiation are at risk for developing trismus (reduced mouth opening). Trismus is often a persisting side-effect and difficult to manage. It impairs eating, speech and oral hygiene, affecting quality of life. Although several studies identified the masseter muscle (MM) as one of the main organs at risk, currently this structure is rarely considered during treatment planning. Prospective studies for chemoradiation are lacking. The aim of our study was to quantify the relationship between radiation dose to the MM and development of radiation-induced trismus in an IMRT-VMAT population. Results: At the first evaluation, 6-12 weeks post-treatment, fourteen patients had developed radiation-induced trismus (15%). On average, mouth opening decreased with 4.1 mm, or 8.2 % relative to baseline. Mean dose to the ipsilateral MM was a stronger predictor for trismus than mean dose to the contralateral MM, as indicated by the lowest -2 log likelihood (Table 1). Figure 1A shows the correlation between the ipsilateral mean masseter dose and the relative decrease in mouth opening, with trismus cases indicated in red. No trismus cases were observed in 33 patients (35%) with a mean dose to the ipsilateral MM 50 Gy. Patients with tumors located in the oropharynx were at highest risk

Ervaringen in bijdrage aan de VERT- Webinar serie voor Medisch Beeldvormings- en Bestralingsdeskundigen in opleiding in tijden van COVID-19-19

Op 16 maart sloten alle opleiding in het Hoger Onderwijs hun deuren in verband met de maatregelen als gevolg van de COVID-19 pandemie. Dit was ook het geval voor de opleiding Medische Beeldvormende en Radiotherapeutische Technieken (MBRT) van de Hogeschool Inholland in Haarlem. Deze vier jarige hbo-opleiding leidt studenten op voor het werk als Medisch Beeldvormings- en Bestralingsdeskundigen (MBB-er) in de Medische Beeldvormende vakgebieden en in de Radiotherapie. Voor dit onderwijs heeft de opleiding een skills lab met daarin diverse beeldvormende apparatuur en een virtuele versneller. Deze virtuele versneller is ontwikkeld door het Britse bedrijf Vertual en wordt naast de MBRT-opleiding van Hogeschool Inholland ook door vergelijkbare opleidingen gebruikt

Sequentially delivered boots plans are superior to simultaneously delivered plans in head and neck cancer when the boost volume is located further away from the parotid glands

Purpose: to find parameters that predict which head and neck patients benefit from a sequentially delivered boost treatment plan compared to a simultaneously deliverd plan, with the aim to spare the salivary glands

Gebruik van PET-CT en MRI bij de radiotherapeutische behandeling van gynaecologische maligniteiten

Het doel van het onderzoek is om te bepalen welke voordelen de fusie van PET-CT en MRI-CT hebben in het voorbereidingstraject van de behandeling van de gynaecologische patiënt met radiotherapie ten opzichte van CT alleen. Hierbij is gekeken naar voordelen met betrekking tot intekenen van doelvolumina en risico organen, effecten op intekenvariaties en ook de effecten op het bestralingsplan. Vooral MRI blijkt nuttig te zijn voor de intekening van lymfeklieren, het gebruik van PET in combinatie met CT laat een afname van het doelvolume zien van de primaire tumor. Bij het maken van het bestralingsplan wordt het gebruik van één van beide modaliteiten daarom aanbevolen

Redistributed versus homogenous radiotherapy dose for head and neck cancer; a treatment planning study

Dose redistribution, where radio-resistant parts of the tumour are boosted while the border of the planning target volume receives a lower dose has the potential to increase local control in advanced head and neck squamous cell carcinoma (HNSCC). In this treatment planning study for 20 patients, standard radiotherapy (RT) of 70 Gy, was compared to redistributed RT following the ARTFORCE trial protocol (NCT01504815), i.e., a fluorodeoxyglucose-positron emission tomography (FDG-PET) based heterogeneous simultaneous-integrated-boost to a total dose of 64–84 Gy. Redistribution marginally increased the mean ipsilateral ⧹contralateral parotid dose by 1.55⧹0.55 Gy but not dose to other organs at risk. Keywords: Head and neck cancer, Radiotherapy, Dose-painting, Treatment plannin

Characterization of automatic treatment planning approaches in radiotherapy

Background and purpose: Automatic approaches are widely implemented to automate dose optimization in radiotherapy treatment planning. This study systematically investigates how to configure automatic planning in order to create the best possible plans. Materials and methods: Automatic plans were generated using protocol based automatic iterative optimization. Starting from a simple automation protocol which consisted of the constraints for targets and organs at risk (OAR), the performance of the automatic approach was evaluated in terms of target coverage, OAR sparing, conformity, beam complexity, and plan quality. More complex protocols were systematically explored to improve the quality of the automatic plans. The protocols could be improved by adding a dose goal on the outer 2 mm of the PTV, by setting goals on strategically chosen subparts of OARs, by adding goals for conformity, and by limiting the leaf motion. For prostate plans, development of an automated post-optimization procedure was required to achieve precise control over the dose distribution. Automatic and manually optimized plans were compared for 20 head and neck (H&N), 20 prostate, and 20 rectum cancer patients. Results: Based on simple automation protocols, the automatic optimizer was not always able to generate adequate treatment plans. For the improved final configurations for the three sites, the dose was lower in automatic plans compared to the manual plans in 12 out of 13 considered OARs. In blind tests, the automatic plans were preferred in 80% of cases. Conclusions: With adequate, advanced, protocols the automatic planning approach is able to create high-quality treatment plans

The impact of anatomical changes during photon or proton based radiation treatment on tumor dose in glioblastoma dose escalation trials

Purpose/Objective: Most dose-escalation trials in glioblastoma patients integrate the escalated dose throughout the standard course by targeting a specific subvolume. We hypothesize that anatomical changes during irradiation may affect the dose coverage of this subvolume for both proton- and photon-based radiotherapy. Material and Methods: For 24 glioblastoma patients a photon- and proton-based dose escalation treat ment plan (of 75 Gy/30 fr) was simulated on the dedicated radiotherapy planning MRI obtained before treatment. The escalated dose was planned to cover the resection cavity and/or contrast enhancing lesion on the T1w post-gadolinium MRI sequence. To analyze the effect of anatomical changes during treatment, we evaluated on an additional MRI that was obtained during treatment the changes of the dose distribu tion on this specific high dose region. Results: The median time between the planning MRI and additional MRI was 26 days (range 16–37 days). The median time between the planning MRI and start of radiotherapy was relatively short (7 days, range 3–11 days). In 3 patients (12.5%) changes were observed which resulted in a substantial deterioration of both the photon and proton treatment plans. All these patients underwent a subtotal resection, and a decrease in dose coverage of more than 5% and 10% was observed for the photon- and proton-based treat ment plans, respectively. Conclusion: Our study showed that only for a limited number of patients anatomical changes during pho ton or proton based radiotherapy resulted in a potentially clinically relevant underdosage in the subvol ume. Therefore, volume changes during treatment are unlikely to be responsible for the negative outcome of dose-escalation studies

A practical technique to avoid the hippocampus in prophylactic cranial irradiation for lung cancer.

A practical technique is presented to deliver hippocampus avoiding prophylactic cranial irradiation for lung cancer patients, using two lateral fields. For a prescribed dose of 12×2.5 Gy, sparing of the hippocampi to 6.1 Gy was achieved with a V95% of the brain of 81.7

Geometric changes of parotid glands caused by hydration during chemoradiotherapy

Abstract: Plan adaptation during the course of (chemo)radiotherapy of H&N cancer requires repeat CT scanning to capture anatomy changes such as parotid gland shrinkage. Hydration, applied to prevent nephrotoxicity from cisplatin, could temporarily alter the hydrogen balance and hence the captured anatomy. The aim of this study was to determine geometric changes of parotid glands as function of hydration during chemoradiotherapy compared to a control group treated with radiotherapy only