Online daily assessment of dose change in head and neck radiotherapy without dose‐recalculation

Abstract

BackgroundHead and neck cancers are commonly treated with radiation therapy, but due to possible volume changes, plan adaptation may be required during the course of treatment. Currently, plan adaptations consume significant clinical resources. Existing methods to evaluate the need for plan adaptation requires deformable image registration (DIR) to a new CT simulation or daily cone beam CT (CBCT) images and the recalculation of the dose distribution. In this study, we explore a tool to assist the decision for plan adaptation using a CBCT without re‐computation of dose, allowing for rapid online assessment.MethodsThis study involved 18 head and neck cancer patients treated with CBCT image guidance who had their treatment plan modified based on a new CT simulation (ReCT). Dose changes were estimated using different methods and compared to the current gold standard of using DIR between the planning CT scan (PCT) and ReCT with recomputed dose. The first and second methods used DIR between the PCT and daily CBCT with the planned dose or recalculated dose from the ReCT respectively, with the dose transferred to the CBCT using rigid registration. The necessity of plan adaptation was assessed by the change in dose to 95% of the planning target volume (D95) and mean dose to the parotids.ResultsThe treatment plans were adapted clinically for all 18 patients but only 7 actually needed an adaptation yielding 11 unnecessary adaptations. Applying a method using the daily CBCT with the planned dose distribution would have yielded only four unnecessary adaptations and no missed adaptations: a significant improvement from that done clinically.ConclusionUsing the DIR between the planning CT and daily CBCT can flag cases for plan adaptation before every fraction while not requiring a new re‐planning CT scan and dose recalculation.

Adaptive radiotherapy for head and neck cancer reduces the requirement for rescans during treatment due to spinal cord dose

“…Only one of these three patients had an initial spinal cord dose close to the planning tolerance, at 43.5 Gy. This has also been reported in the literature, with between 5 and 30% of patient cohorts exhibiting increases that push the spinal cord dose out of tolerance [30, 46–48]. On review of the CT and CBCT imaging for these three patients, the large dose increases can be attributed to significant positioning changes due to curvature of the spine, pushing the spinal cord into a high dose region.…”

“…A range of off-line ART methods is reported in the literature for H&N patients. These include scheduling regular re-scan CTs (rCT) acquired on the CT-Sim in the treatment position, effectively acquiring new pCT scans [10–20], or using in-treatment-room imaging, for example verification MV-CTs [21–24], kV-CBCTs [19, 22, 25–30], and the relatively uncommon use of CT-on-rails [4, 31, 32]. The use of ART for H&N patients with MR-linacs has also recently been reported [33].…”

Adaptive radiotherapy for head and neck cancer

“…Recent advances have looked at individualizing indications for A-ART by recalculating the cumulative dose of the target and OAR every day or every week to identify actionable changes in dosimetry which may necessitate re-planning [53,54]. In an initial pilot study of A-ART at MDACC, Schwartz and colleagues [55] prospectively evaluated 22 patients with oropharyngeal SCC receiving definitive radiation with weekly CT dose recalculations to prompt A-ART re-planning if target coverage was poor or if OAR sparing was inadequate.…”

“…This method resulted in 8 out of 10 patients being re-planned with A-ART, with 41% of the replans triggered in the first 2 weeks. While these early studies have predominantly used weekly CT scans, there has been recent effort to improve efficiency by utilizing CBCTs used in the daily delivery of radiation to calculate the cumulative dose received [53,[57][58][59] allowing the prompt identification of patients likely to benefit from A-ART. As technology and artificial intelligence advances, we anticipate that the identification of patients and the implementation of A-ART will be significantly smoother and likely automated.…”

Implementación y uso clínico de la radioterapia adaptativa. Informe del grupo de trabajo de radioterapia adaptativa de la Sociedad Española de Física Médica (SEFM)

“…Vickress et al 111 estudiaron un método que permitía una adaptación online, proyectando los contornos a los CBCT diarios mediante registro deformado de los mismos con el TC de planificación, y volcando la dosis absorbida planificada en el CBCT mediante registro rígido. Encontraron que una disminución de D 95% del PTV o un aumento de la dosis absorbida media de las parótidas por encima de 26 Gy era un indicador adecuado de la necesidad de ART.…”