Tumour Shrinkage and Contour Change during Radiotherapy Increase the Dose to Organs at Risk but not the Target Volumes for Head and Neck Cancer Patients Treated on the TomoTherapy HiArt™ System

Anatomic and dosimetric changes in patients with head and neck cancer treated with an integrated MRI-tri-60Co teletherapy device

“…Lower planning dose, location further away from the primary GTV and minimal weight change accounted for the two patients (4 and 5) who did not experience similar magnitudes of parotid gland shrinkage as the others. Our results are in remarkable agreement with prior studies, which reported median parotid shrinkage rates of 0.6% per day (0.2-1.8% per day) 4 and 0.7% per day (0.4-1.3% per day), 5 found a mean volume reduction of 30.2% (17.1-55.8%) for ipsilateral and 17.5% (15.6-48.5%) for contralateral parotid glands 9 and correlated parotid gland shrinkage with both weight loss 27 and planned dose. Table 1.…”

“…Overall, the medial shift of the parotid glands correlated with weight loss, confirming the findings of Barker et al 4 Other studies have attempted to correlate anatomic changes with dosimetric analysis and discussed the potential benefits of replanning in head and neck cancers. [7][8][9][10][11][12][13]15,17,19 As the parotid glands shift medially during IMRT, they may be exposed to higher than expected levels of radiation and consequently an increased probability of xerostomia. 8,[10][11][12]14 Although several studies have found that adaptive replanning may potentially reduce dosage to the parotids, the appropriate means of selection remain elusive.…”

“…2,3 Several studies have documented anatomical changes during the course of IMRT in patients with head and neck cancer, quantifying regression and spatial shifts of tumours and organ at risk (OAR). [4][5][6][7][8][9][10] Interfractional anatomical changes, in turn, can substantially alter dose deposition, suggesting a benefit to adaptive replanning. [7][8][9][10][11][12][13][14][15][16][17][18][19] However, adaptive replanning remains to be widely adopted owing to its time-intensive nature and an unclear threshold of anatomical changes required for its posited benefit.…”

“…[4][5][6][7][8][9][10] Interfractional anatomical changes, in turn, can substantially alter dose deposition, suggesting a benefit to adaptive replanning. [7][8][9][10][11][12][13][14][15][16][17][18][19] However, adaptive replanning remains to be widely adopted owing to its time-intensive nature and an unclear threshold of anatomical changes required for its posited benefit. 10,11,16,20 The aforementioned studies of anatomical alteration during IMRT relied on CT imaging, which might not provide optimal soft-tissue contrast/ resolution, leading to possible interobserver variability.…”

Volumetric and Dosimetric Assessment by Cone-Beam Computed Tomography Scans in Head and Neck Radiation Therapy: A Monitoring in Four Phases of Treatment

“…In a pilot study, the authors (4) evaluated the volumetric changes of PGs during the entire treatment, finding a volume loss of 43.5% and 44.0% for iPG and cPG. The shrinkage of PGs occurring during IMRT treatment was attested by numerous previous papers (6,18,19) and it was often associated to an increase of radiation dose (20,17,8 (Figure 9) in the region of parotids, it's easy to observe both the shrinkage of PGs and the shift to the higher isodoses, which could affect the dose received by the glands. This was in accord to several previous studies (3,8,21), that demonstrated already an average medial shift of PG center of mass of about 3 mm towards the higher doses.…”