Differences between planned and delivered dose for head and neck cancer, and their consequences for normal tissue complication probability and treatment adaptation

Abstract

Background and purpose: Anatomical changes induce differences between planned and delivered dose. Adaptive radiotherapy (ART) may reduce these differences but the optimal implementation is insufficiently clear. The aims of this study were to quantify the difference between planned and delivered dose in HNC patients, assess the consequential difference in normal tissue complication probability (DNTCP) and to explore the value of DNTCP as an objective selection strategy for ART. Materials and methods: For 52 patients, daily doses were accumulated to estimate the delivered dose. The difference from planned dose was analyzed for CTVs and 9 organs-at-risk (OAR). DNTCP was calculated for xerostomia, dysphagia, parotid gland dysfunction and tube feeding dependency at 6 months. ART was deemed necessary if DNTCP was >5%. The positive predicted value (PPV) was calculated for identification of ART-patients by clinical judgement, and DNTCP at fraction 10 and 15. Results: DNTCP >5% was seen five times for dysphagia and twice for the other toxicities. Only 5/9 patients with any DNTCP >5% clinically received ART, although ART had been done for 13/52 patients (PPV: 0.38). PPV was 0.86 and 0.75 for accumulated dose at fraction 10 and 15, respectively, using a DNTCP cutoff for the allocation of ART of 5%. Using other DNTCP cutoffs did not substantially improve PPV. With this cutoff the negative predictive value was 0.93 for DNTCP method of fraction 10 and fraction 15, and 0.90 for clinical judgement. Conclusion: To identify patients accurately for ART, NTCP calculations based on the dose differences between planned and delivered dose at fraction 10 are superior to clinical judgement.

Initial Feasibility and Clinical Implementation of Daily MR-Guided Adaptive Head and Neck Cancer Radiation Therapy on a 1.5T MR-Linac System: Prospective R-IDEAL 2a/2b Systematic Clinical Evaluation of Technical Innovation

“…ART has begun to play an increasingly prominent role in the treatment of HNC for 2 primary reasons: (1) significant tumor shrinkage, weight loss, and large anatomic deformations of OARs are often observed for HNC patients during RT, [22][23][24] and (2) treatment-related side effects from conventional RT can be particularly debilitating for patients with HNC and often persist for years after treatment. 25,26 Several studies have shown clinically significant reductions in doses to the parotid glands, [27][28][29] spinal cord, 29,30 and swallowing-related structures 31,32 with 1 or more offline plan adaptations during the course of RT. Because offline adaptive replanning is time and resource intensive, many studies have focused on identifying anatomic and dosimetric guidelines to determine when plan adaptation would be optimally effective.…”

“…Because offline adaptive replanning is time and resource intensive, many studies have focused on identifying anatomic and dosimetric guidelines to determine when plan adaptation would be optimally effective. 30,31,33 However, the clinical introduction of the 1.5T MR-linac has made daily ART for HNC a feasible clinical reality.…”

Initial Feasibility and Clinical Implementation of Daily MR-guided Adaptive Head and Neck Cancer Radiotherapy on a 1.5T MR-Linac System: Prospective R-IDEAL 2a/2b Systematic Clinical Evaluation of Technical Innovation

“…ART has begun to play an increasingly prominent role in the treatment of HNC for two primary reasons: 1) significant tumor shrinkage, weight loss, and large anatomical deformations of OARs are often observed for HNC patients during RT [16][17][18]; and 2) treatment-related side effects from conventional RT can be particularly debilitating for HNC and often persist for years after treatment [19,20]. Several studies have demonstrated clinically significant reductions in doses to the parotid glands [21][22][23], spinal cord [23,24], and swallowing-related structures [25,26] with one or more off-line plan adaptations over the course of radiotherapy. Because offline adaptive re-planning is time-and resource-intensive, many studies have focused on identifying anatomical and dosimetric guidelines to determine when plan adaptation would be optimally effective [24,25,27].…”

“…Several studies have demonstrated clinically significant reductions in doses to the parotid glands [21][22][23], spinal cord [23,24], and swallowing-related structures [25,26] with one or more off-line plan adaptations over the course of radiotherapy. Because offline adaptive re-planning is time-and resource-intensive, many studies have focused on identifying anatomical and dosimetric guidelines to determine when plan adaptation would be optimally effective [24,25,27]. However, the clinical introduction of the 1.5T MR-linac has made daily ART for HNC a feasible clinical reality.…”

Accurate estimation of daily delivered radiotherapy dose with an external treatment planning system

“…Anatomical changes over the course of radiotherapy may induce differences between planned and delivered dose [1] , [2] , [3] . Early detection of such discrepancies may facilitate effective adaptive interventions [4] , while dose effect relations on delivered dose may improve toxicity modeling [5] . Daily images, acquired routinely for Image Guided Radiotherapy (IGRT), can serve as basis for dose recalculations to estimate the daily delivered dose.…”