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theses

In adaptive radiation therapy (ART) of head and neck cancer, any significant anatomical changes observed are used to adapt the treatment plan to maintain target coverage without elevating the xerostomia risk. However, the additional resources required for ART pose a challenge for broad-based implementation. It is hypothesized that the transit fluence change is associated with volumetric change in the vicinity of the target and therefore can be used as a decision support metric (DMS) for ART. This was evaluated by comparing the fluence with volumetric changes in twenty-four patients. Transit fluence was measured by an in-vivo portal dosimetry system (RTPD). Weekly cone beam computed-tomography (CBCT) was used to determine volume change in the rectangular region of interest (ROI) from condyloid process to C6. The integrated fluence through the ROI and the salivary glands (SG) on the day of the CBCT scan was calculated with the first treatment as the baseline. The correlation between fluence and volume changes was determined. Logistic regression was also used to associate the 5% ROI volume reduction replanning trigger-point and the fluence change. The model was assessed by a chi-squared test. The area (AUC) under the receiver operating characteristic curve (ROC) was also determined. The xerostomia risk was assessed by the scores change of the patients’ MD Anderson Dysphagia Inventory (MDADI). The association of the MDADI with age, gender, mean dose to SG, weight, volumetric and fluence changes were assessed using Spearman rank-correlation. A total of 108 pairs of CBCT and RTPD measurements were obtained. The correlation between fluence and volumetric changes were found to be -0.837 (p-value<0.001). The AUC of the ROC was found to be 0.91. The correlation between SG-specific fluence and volumetric changes was found to be -0.62 (p-value<0.001). Twenty-one patients responded to the MDADI. Fluence and volumetric changes were found to have association with the physical, functional and total MDADI changes. No significant association with age, gender, and weight change were found. A transit fluence based DSM is not only a viable alternative to serial CBCT in assisting clinicians in the patient selection, but also lowers the resource barrier of ART implementation.

ETD_10278

Ph.D.

Includes bibliographical references

doi:10.7282/t3-ntgk-gf35

ETD doctoral

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