Effect of interfractional shoulder motion on low neck nodal targets for patients treated using volumetric‐modulated arc therapy (VMAT)

Abstract

VMAT is an important tool in the treatment of head and neck cancers, many of which also require treatment to the supraclavicular lymph nodes. However, full VMAT arcs treating this nodal region necessarily cause entrance beam to pass through patients' shoulders. Thus, interfractional variations in shoulder position may cause unwanted dose perturbations. To assess this possibility, six patients undergoing treatment at our institution for head and neck cancers with associated supraclavicular lymph node treatment were imaged with in‐room CT‐on‐rails during the course of their treatments. This allowed for the establishment of a true record of the actual shoulder position during selected treatment fractions. Then, a full VMAT plan and a plan with VMAT arcs superior to the shoulder and a static anteroposterior field inferiorly were copied onto the patients' weekly image sets. The average one‐dimensional shoulder motion was generally within 10 mm of the simulated position, with some notable exceptions. The standard deviation in week‐to‐week shoulder position relative to simulation was 4.3 mm and 4.2 mm in the SI and AP dimensions, respectively. The average nodal target mean dose across all fractions sampled was within 5% of planned for all patients and both plans. Similarly, the average D95 for the nodal target was within 5% of planned across all fractions sampled, with the single exception of the full VMAT plan for one patient. In most cases, the standard deviation in both target mean dose and D95 was smaller with the VMAT+static AP field plan than it was with the full VMAT plan.PACS number: 87.55.‐x

Effective Organs-at-Risk Dose Sparing in Volumetric Modulated Arc Therapy Using a Half-Beam Technique in Whole Pelvic Irradiation

“…In addition, the HF at the matching line could bring out dose reduction of the lung in breast treatment. Maintaining such dosimetric benefit and more effectively reducing doses to OAR, studies were expanded to employ intensity modulation using optimal segments from HF ( 26 , 53 , 54 ). Consequently, VMAT-HF showed reducing volume receiving a dose of less than 10 Gy for left-sided breast cancer, which is more challenging than the right-sided case due to heart dose sparing.…”

Analysis of geometric variation of neck node levels during image-guided radiotherapy for nasopharyngeal carcinoma: recommended planning margins

“…For head and neck cancer, substantial anatomical changes, position, and shape variability of the tumor might result from tumor regression and weight loss, which resulted in various geometrical and setup uncertainties (3,18). By limiting these uncertainties, the margin could be safely reduced, which might enable a better dose distribution in target and normal tissues and the improved clinical outcome (17). In our study, it seemed that a smaller margin could be safely used in levels IB, II, and III and that levels IA, VI, and V should have more generous margins even if the weekly image guided setup is correct.…”

“…Level IA needs ~5 mm margin because the jaw had poor reproducibility, especially in patients with more weight loss. Level V needs 5 mm margins because of large neck surface variation and larger inter-fractional motion of the shoulders (16,17). Although level VI had a small volumetric reduction, it needed a more generous margin because of substantial deformation in the anterior part of the neck, which probably resulted from the re-distribution of subcutaneous fat and thyroid shrinkage.…”

“…During chemoradiotherapy, the geometrical changes of the whole neck might not be homogenous. With image-guided RT, the head and cranial neck could be well matched (14), yet the caudal neck and shoulder usually do not match very well due to the anatomical deformations (14) and generous set-up uncertainties (15)(16)(17). The NNL is covered from the cranial to caudal neck and the supraclavicular region.…”

Retrospective Clinical Evaluation of a Decision-Support Software for Adaptive Radiotherapy of Head and Neck Cancer Patients

“…While both offline and online ART involve imaging to review the current anatomy and to assess the need for a new plan, most common ART methods allowed by current technologies for HNC patients are variants of offline strategies (17)(18)(19)(20)(21)(22), as these are well suited for the slow progressing nature of anatomic changes observed during HNC RT treatments (8,20,23). Online methods are more appropriate to address the effects of stochastic patient setup errors (24,25), such as those caused by the inter-fractional variation in shoulder position (26,27) or the loose fitting of the immobilization mask due to weight loss. They are, however, only commercially available for HNC treatment on dedicated adaptive RT systems such as the Halcyon with Ethos (28) (Varian, Palo Alto, CA), Radixact (29) (Accuray, Sunnyvale, USA), or the MRIdian (Viewray, Cleveland, USA) and Unity (Elekta, Stockholm, Sweden) combined MRIlinac platforms (30).…”