ESTRO 2024 - Abstract Book

S4290

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

Using SGRT and a standard head rest results in a patient-friendly treatment with accurate patient setup and acceptably small intrafraction motion for H&N patients. However, for more patient comfort and reassurance of stability, as well as less number of fractions where interventions as a result of intrafraction motion larger than th 2 are necessary, we will start actual maskless (no front face) head and neck cancer treatments using an individually moulded head rest.

Keywords: SGRT, head-and-neck, maskless

References:

[1] Janssen TM, van der Heide UA, Remeijer P, Sonke JJ, van der Bijl E. A margin recipe for the management of intra fraction target motion in radiotherapy. Phys Imaging Radiat Oncol. 2022; 24:159-166. doi: 10.1016/j.phro.2022.11.008.

1815

Poster Discussion

Pelvic lymph node motion in CBCT-guided SBRT: Location matters

Jorinde Janssen, Floor H.E. Staal, Johannes A. Langendijk, Stefan Both, Charlotte L. Brouwer, Shafak Aluwini

University of Groningen, University Medical Center Groningen, Department of Radiation Oncology, Groningen, Netherlands

Purpose/Objective:

Stereotactic body radiotherapy (SBRT) is increasingly applied to treat pelvic lymph node recurrences. The high dose per fraction and limited number of fractions used in SBRT obligate margins that balance oncological control and toxicity. The evaluation of lesion motion is crucial to assess treatment accuracy and determine optimal PTV margins. Thus far, knowledge on pelvic lymph node intrafraction motion during CBCT-guided SBRT is lacking and the currently used margins are primarily based on institutional experiences. This study evaluated pelvic lymph node motion during CBCT-guided SBRT and assessed the currently applied PTV margins of 3 and 5 mm.

Material/Methods:

This study evaluated CBCT data of 37 prostate cancer patients with a total of 45 pelvic lymph node oligometastases included in the ADOPT phase III RCT (NCT04302454). The lymph node lesions were located along the iliac vessels (74%), para-rectal (11%), pre-sacral (9%), and at the obturator fossa (7%). All lesions were treated with SBRT in 5 fractions of 7 Gy. One observer delineated the GTV on 45 planning CTs, 224 pre-fraction CBCTs and 216 post-fraction CBCTs. Thereafter, CBCTs were matched with the corresponding planning CT using grey value based automatic image registration and a registration mask including pelvic bone structures. The delineated GTVs were transferred to the planning CT and, subsequently, lesion centroid coordinates were derived from all images for inter- and intrafraction motion analysis. Additionally, we assessed the association of treatment time and lesion location with lesion inter- and