Dosimetric comparison of intensity modulated radiotherapy and intensity modulated proton therapy in the treatment of recurrent nasopharyngeal carcinoma.

To compare the dosimetric performance of Intensity Modulated Proton Therapy (IMPT) and Intensity Modulated Radiotherapy (IMRT) in terms of target volume coverage and sparing of neurological organs-at-risk (OARs) in salvaging recurrent nasopharyngeal carcinoma (rNPC). The maximum dose to the internal carotid artery (ICA) and nasopharyngeal (NP) mucosa, which are associated with potential carotid blowout and massive epistaxis, were also evaluated. IMRT and IMPT treatment plans were created for twenty patients with locally advanced rNPC. Planning Target Volume (PTV) was used to account for the setup and spatial error/uncertainty in the IMRT planning. Robust optimization on Clinical Target Volume (CTV) coverage with consideration of range and setup uncertainty was employed to produce two IMPT plans with 3-field and 4-field arrangements. The planning objective was to deliver 60 Gy to the PTV (IMRT) and CTV (IMPT) without exceeding the maximum lifetime cumulative Biologically Effective Dose (BED) of the neurological OARs (applied to the Planning organs-at-risk volume). The target dose coverage as well as the maximum dose to the neurological OARs, ICA, and NP mucosa were compared. Compared with IMRT, 3-field IMPT achieved better coverage to GTV V100% (83.3% vs. 73.2%, P <0.01) and CTV V100% (80.5% vs. 72.4%, P <0.01), and lower maximum dose to the critical OARs including the spinal cord (19.2 Gy vs. 22.3 Gy, P <0.01), brainstem (30.0 Gy vs. 32.3 Gy, P <0.01) and optic chiasm (6.6 Gy vs. 9.8 Gy, P <0.01). The additional beam with the 4-fields IMPT plans further improved the target coverage from the 3-field IMPT (CTV V98%: 85.3% vs. 82.4%, P <0.01) with similar OAR sparing. However, the target dose was highly non-uniform with both IMPT plans, leading to a significantly higher maximum dose to the ICA (∼68 Gy vs. 62.6 Gy, P <0.01) and NP mucosa (∼72 Gy vs. 62.8 Gy, P <0.01) than IMRT. IMPT demonstrated some dosimetric advantage over IMRT in treating rNPC. However, IMPT could also result in very high dose hot spots in the target volume. Careful consideration of the ICA and NP mucosal complications is recommended when applying IMPT on rNPC patients.

Hung HM ，Chan OCM ，Mak CH ，Hung WM ，Ng WT ，Lee MCH ... -  《-》

Dosimetric comparison between 2-dimensional radiation therapy and intensity modulated radiation therapy in treatment of advanced T-stage nasopharyngeal carcinoma: to treat less or more in the planning organ-at-risk volume of the brainstem and spinal cord.

Chau RM ，Teo PM ，Kam MK ，Leung SF ，Cheung KY ，Chan AT ... -  《-》

Intensity-modulated proton therapy (IMPT) versus intensity-modulated radiation therapy (IMRT) for the treatment of head and neck cancer: A dosimetric comparison.

It is the goal of this study to compare the dosimetric advantages of IMPT when compared to IMRT. From January 2019 to August 2020, 25 patients were treated with intensity modulated proton therapy (IMPT) at our institution for either recurrent, metastatic, benign, or primary tumors in the head and neck region. Twenty-one patients met criteria for dosimetric analysis. Histology of disease included squamous cell carcinoma, acinic cell carcinoma, sarcomatoid sinonasal carcinoma, paraganglioma, adenoid cystic carcinoma, salivary high grade carcinoma, and papillary thyroid carcinoma. For IMRT planning, gross tumor volume (GTV) and clinical target volume (CTV) were contoured with the expansion of 3-5 mm to create the planning target volume (PTV) and dose was prescribed to the PTV. For the IMPT planning, dose was prescribed to CTV and robust optimization was utilized which accounted for a 5 mm setup and range uncertainty. The minimum, mean and maximum target doses for IMRT and IMPT plans as well as mean and maximum normal tissue doses are reported for the 21 patients meeting criteria. Mean doses for IMRT and IMPT were 6278.2 cGy and 6449.8 cGyRBE respectively with p-value of 0.0001. Maximum doses for IMRT and IMPT were 6579.5 cGy and 6772.1 cGyRBE respectively with p-value of 0.0014. Minimum doses for IMRT and IMPT were 5440.6 cGy and 5617.9 cGyRBE respectively with p-value of 0.3576. IMPT had an overall advantage in OAR doses in the brain stem, spinal cord, optic structures, cochlea, larynx, contralateral parotid, and oral cavity with only a few exceptions. Our study thus demonstrates a dosimetric advantage for IMPT in treating head and neck tumors in mean and max dose delivered as well as dose to OARs. Given that our patient cohort were mainly unilateral head and neck cases, our study supports the treatment of this specific subset of patients regardless of histology with IMPT. This may aid in appropriate patient selection for IMPT treatment. Further studies will need to determine if this dosimetric advantage translates to a therapeutic advantage for patients.

Nguyen ML ，Cantrell JN ，Ahmad S ，Henson C ... -  《-》

The feasibility of dose escalation using intensity-modulated radiotherapy (IMRT) and intensity-modulated proton therapy (IMPT) with FDG PET/CT guided in esophageal cancer.

Zhang Y ，Fan B ，Sun T ，Xu J ，Yin Y ，Chen Z ，Zhu J ，Yu J ，Hu M ... -  《-》

PTV-based IMPT optimization incorporating planning risk volumes vs robust optimization.

Liu W ，Frank SJ ，Li X ，Li Y ，Zhu RX ，Mohan R ... -  《-》