- Email: [email protected]
CT Response and PET Surveillance for Prediction of Locoregional Control in HPV-Related Oropharyngeal Cancer
Volume 88 Number 2 Supplement 2014 surgical only (SX), chemo-radiation (CXRT), and mixed therapy. Coordinates mapping swallowing structures were collected at maximum and minimum swallow excursion points for the hyoid, larynx, and pharynx. Canonical variate analysis was performed to determine shape changes associated with HNC treatment paradigms. Indicators of swallowing safety and efficiency were compared by group using the penetration aspiration score (PAS) and normalized residue ratio scale (NRRS). Results: A canonical variate analysis of coordinates by swallowing excursion and treatment group resulted in eigenvalues that accounted for 71.7% of the variance by swallow function and 22.5% by treatment group. A significant difference in shape change was noted by discriminate analysis between SX (nZ17) and CXRT (nZ12) treatment groups (DZ 2.51, p< .0001). Eigenvectors associated with swallowing indicated increased extension of the head and neck in the SX group and reduced pharyngeal shortening in CXRT group. No significant differences were noted in airway invasion and pharyngeal clearance (PAS, NRRSp, NRRSv) between SX and CXRT groups. Conclusions: Morphological changes in the swallowing structure varied by treatment paradigm with SX and CXRT comprising two ends of the shape change spectrum. Changes indicate compensatory movement of the head and neck in the SX cohort and reduced function of the long pharyngeal muscles in CXRT cohort. While changes in the functional anatomy of swallowing between treatment groups are significant, indicators of swallowing safety and efficiency, penetration-aspiration and residue, are not indicating adaptation to structural insults. Morphometric analysis of swallowing function is a novel approach to evaluating what structural insults are associated with treatment paradigms. These methods coupled with swallowing outcome measurements may provide better insight into dysphagias associated with head and neck cancer treatment. Author Disclosure: J. Blair: None. C.Z. Johnson: None. S.L. Rice: None. B. Martin-Harris: None. W.G. Pearson: None.
130 Ultrasound in the Search for the Primary Site of Unknown Primary Head-and-Neck Squamous Cell Cancers Imaging C. Fakhry,1 N. Agrawal,1 J. Califano,1 S. Coquia,1 U. Hamper,1 J. Saunders,2 B. Messing,2 P. Ha,1 M. Gillison,3 and R. Blanco2; 1Johns Hopkins University, Baltimore, MD, 2Greater Baltimore Medical Center, Baltimore, MD, 3Ohio State University, Columbus, OH Purpose/Objective(s): Head and neck squamous cell cancers (HNSCC) arising from an unknown primary (UP) site are a challenging clinical entity. Although human papillomavirus (HPV) detection can localize a tumor to the oropharynx (OP), clinical and histologic confirmation can remain elusive in up to 60% of UPs of HNSCC. Traditional imaging modalities (computed tomography, magnetic resonance imaging) and operative approaches (exam under anesthesia [EUA], direct laryngoscopy [DL], biopsies) have had limited success in the identification of UPs. Positron-emission tomography may improve detection. We have used ultrasound (US) to visualize base of tongue (BOT) cancers and were therefore interested in evaluating US to identify the primary tumor site of patients with HNSCC of UP. Materials/Methods: Patients with HNSCC of UP after clinical evaluation (physical exam and fiberoptic laryngoscopy) by a head and neck surgical oncologist were eligible. Controls were subjects without known cancer. A Toshiba US (SSA-580A) was used with a convex transducer for the transcervical examination (3.75-6.0 Megahertz [MHz]). For the intraoral examination, an endocavitary multifrequency convex probe (5-7.5 MHz) was used. US examination was performed in a standardized fashion. An US impression was ascertained and communicated with the surgeon. US findings were compared with operative examination (DL, EUA and biopsies). Results: 10 patients with HNSCC of UP were eligible. PET/CT scans performed for staging purposes were negative (7 of 10), indeterminate (2 of 10) or suspicious (1 of 10) for a primary lesion. On US examination, an OP primary tumor site was identified in 10 of 10 cases (100%), with 7 in BOT and 3 in tonsil. The suspected lesions were largely hypoechoic (90%).
Poster Presentations
499
Largest dimensions ranged from 6-20 mm. On operative examination 5 of 10 were appreciated on palpation or DL. Two additional primaries were histologically confirmed with directed biopsies. 100% of cases were HPVpositive. Assuming that HPV-positive HNSCC localizes to the OP, DL successfully diagnosed 70% of these tumors, while US visualized 100%. The 3 cases that were not histologically confirmed appeared to be BOT tumors on US and underwent lingual tonsillectomy. However, this could represent a false positive, misclassification (eg, tonsil) or the depth of dissection may have been too superficial. No lesions were suspected among the 20 controls. Conclusions: Ultrasound is a promising imaging modality to visualize the primary site for patients presenting as HNSCC of UP. Detection rates are similar to those using transoral surgery as a diagnostic strategy (palatine/ lingual tonsillectomy) which has potential risks. US before DL and biopsy has lower risk and similar success rate and therefore warrants further investigation in the visualization of OP cancers and UPs. Author Disclosure: C. Fakhry: None. N. Agrawal: None. J. Califano: None. S. Coquia: None. U. Hamper: None. J. Saunders: None. B. Messing: A. Employee; Milton J. Dance Jr. Head and Neck Center. Q. Leadership; Milton J. Dance Jr. Head and Neck Center. P. Ha: None. M. Gillison: G. Consultant; Glaxo Smith Kline, Bristol Myers Squibb. R. Blanco: None.
144 Treatment Planning Using FDG-PET to Optimize Parotid Gland Sparing Before and During Chemoradiation for Head-and-Neck Cancer Imaging A. Kim, S. Das, K.R. Choudhury, K. Temple, and D.M. Brizel; Duke University Cancer Institute, Durham, NC Purpose/Objective(s): To create FDG-PET-based pretreatment and adaptive RT (ART) plans to improve parotid gland sparing in patients with squamous head and neck cancer (HNC). Materials/Methods: 27 patients had pretreatment and intratreatment (20 Gy) FDG-PET/CT. Voxel-based metabolic function measured as Standard Uptake Value (SUV) was obtained. 3 distinct IMRT plans were created: (a) standard plan using the pretreatment CT; (b) pretreatment PET based plan designed to reduce dose to the 10-20% most metabolically active portion of the parotids (SUBHigh), and (c) adaptive plan based on both pretreatment and intratreatment PET. Besides SUBHigh, plan (c) spares regions with the highest SUV reduction (SUBLow_SUVfraction) defined as 30-50% of the total volume with SUVintratreatment/SUVpretreatment 0.8. The overlap region between SUBHigh and SUVLow_SUVfraction received the highest preferential dose sparing (SUB1). Regions containing either substructure received medium preferential dose sparing (SUB2). Plans b and c maintained the same target volume coverage and critical organ constraints as plan a. Mean doses to the substructures and the whole gland were compared for above plans. Results: All tumors received 70 Gy. In a vs b, mean dose decreased from 18.9 Gy to 15.8 Gy (<0.0001) in SUBHigh and from 24.1 to 23.2 Gy (<0.0001) in the whole gland. In a vs c, mean dose decreased from 18.8 to 15.6 Gy (p< 0.0001) in SUB1, from 20.9 to 19.0 Gy (p< 0.0001) in SUB2, and from 24.1 to 22.6 Gy (p< 0.0001) in the whole gland. In b vs c, minimal dose reduction occurred in SUB2 (19.9 to 19 Gy; pZ 0.0002) and in the whole gland (23.4 to 22.7 Gy; p< 0.0001). Conclusions: PET based plans significantly reduced dose to the most metabolically active subvolumes of the parotid. In prospective trials, selective parotid gland sparing may be tested in HNC patients based on PET data. Author Disclosure: A. Kim: None. S. Das: None. K.R. Choudhury: None. K. Temple: None. D.M. Brizel: None.
171 Utility of Post-Chemoradiation Therapy FDG-PET/CT Response and PET Surveillance for Prediction of Locoregional Control in HPV-Related Oropharyngeal Cancer Imaging J.M. Vainshtein, M. Spector, M. Stenmark, T. Carey, D. Chepeha, K. Wong, and A. Eisbruch; University of Michigan, Ann Arbor, MI
500
International Journal of Radiation Oncology Biology Physics
Purpose/Objective(s): The utility of post-treatment 18F-fluorodeoxygluocose positron emission tomography/computed tomography (FDGPET/CT) for human papillomavirus (HPV)-related (+) oropharyngeal cancer (OPC) remains poorly characterized. We investigated the ability of 3-month post-treatment FDG-PET/CT response to predict locoregional failure (LRF) in a uniformly treated cohort of locally advanced HPV+ OPC patients. Materials/Methods: 101 consecutive patients with stage III/IV HPV+ OPC who completed definitive CRT from 3/2005-12/2010 and underwent pre-treatment and 3-month post-treatment FDG-PET/CT were included. PET/CT response for each the primary site and the neck was classified as either complete-response (CR), near-CR, or incomplete-response (
Results: 22 of 22 clinically suspicious BOT tumors were visualized. On ultrasound BOT tumors were hypoechoic (90.9%) with irregular margins (95.5%). Ultrasound could be used to characterize adjacent site involvement (vallecula and tonsil). Almost half of tumors crossed midline by ultrasound (10 of 22, 45.5%). An endophytic component was appreciated on all tumors, with the majority being a combination of exophytic and endophytic (15 of 22, 68.2%). A few were purely endophytic (7 of 22). The lingual artery ipsilateral to the tumor was visualized in all 22 cases. Tumors were measured and an ultrasound surrogate of clinical staging was used to compare size. Ultrasound and clinical tumor staging was similar (pZ0.41). Conclusions: Ultrasonography can be used to transcervically visualize BOT tumors and provides clinically relevant characteristics that may not otherwise be appreciable. Author Disclosure: C. Fakhry: None. J. Califano: None. B. Messing: A. Employee; Milton J. Dance Jr. Head and Neck Center. Q. Leadership; Board of Directors of Dance Endowment, Member. J. Richmon: G. Consultant; Intuitive. H. Quon: None. G. Neuner: None. J. Saunders: None. P. Ha: None. M. Gillison: G. Consultant; Bristol Myers Squibb, Glaxo Smith Kline. R. Blanco: None.
176 Transcervical Ultrasonography Is Feasible to Visualize and Evaluate Base of Tongue Cancers Imaging C. Fakhry,1 J. Califano,1 B. Messing,2 J. Richmon,1 H. Quon,1 G. Neuner,2 J. Saunders,2 P. Ha,1 M. Gillison,3 and R. Blanco1; 1Johns Hopkins University, Baltimore, MD, 2Greater Baltimore Medical Center, Baltimore, MD, 3Ohio State University, Columbus, OH Purpose/Objective(s): Base of tongue (BOT) is a difficult subsite to examine clinically and radiographically. Yet, anatomic delineation of the primary tumor site, its extension to adjacent sites or across midline, and endophytic vs exophytic extent are important characteristics for staging and treatment planning. We hypothesized that transcervical ultrasound could be used to visualize and describe BOT tumors. Materials/Methods: Transcervical ultrasound was performed using a standardized protocol in cases and controls. Cases had suspected or confirmed BOT malignancy. Controls were healthy individuals without known head and neck malignancy. A Toshiba ultrasound model SSA-580A was used for examination of all subjects. The transducer used was convex (3.75-6.0 Megahertz (MHz); Model PVQ-375A) and set at 6 MHz. Ultrasound examination was performed in a standardized fashion. The primary variable of interest was the presence or absence of a lesion. Descriptive characteristics were summarized.
187 Mid-Treatment PET During Radiation Therapy in HPV-Positive Oropharyngeal Cancer Patients Demonstrates Variable Response: Implications for Treatment De-escalation Imaging N. Riaz, A. Pena, S. Rosenberg, D. Kannarunimit, S. Rao, and N. Lee; Memorial Sloan-Kettering Cancer Center, New York, NY Purpose/Objective(s): HPV associated oropharyngeal squamous cell carcinomas are known to have a good prognosis and treatment de-escalation is an area of active study. Other disease sites, such as lung cancer (ie, RTOG 11-06) are attempting to use mid-treatment PET/CT scans to try and guide decisions on treatment intensification. We sought to determine patterns of response from a mid-treatment PET/CT in HPV positive or pharyngeal cancer patients to see if this may serve as a biomarker to better determine appropriate candidates for treatment de-escalation. Materials/Methods: Between 4/2011 and 5/2013, 53 patients had a midtreatment PET/CT during their course of head and neck radiation therapy at Memorial-Sloan Kettering Cancer Center. All patients were treated with IMRT with or without concurrent cisplatin-based chemotherapy. HPV status was determined by p16 IHC. The highest standardized uptake value (SUV) of both the gross primary and gross nodal disease was recorded before, during and after radiation therapy. The percentage difference of the SUV values on the early response PET and pre radiation PET was used determine the early PET response. A CR was determined to be complete resolution of FDG activity, any decrease in FDG activity was considered a PR, and no response was determined to be no change or an increase in FDG activity. Results: Of the 53 patients, 23 had oropharyngeal primaries. 5 patients were excluded because of induction chemotherapy (nZ2), HPV status unavailable (nZ2), and HPV negative status (nZ1). Of the remaining 18 HPV+ patients, 13 had a BOT primary and 5 had a tonsil primary. 17 patients were stage IVA and 1 patient was stage III. Mid-treatment PET/CT was performed at a median of 43 days after start of treatment (range 3452). At the primary site, 5 patients had a complete response, 10 patients had a partial response, and 2 patients had no response. No patient with >10 pack -yr smoking history had a CR at the primary site on early response PET. In the neck, 4 patients had a CR and 14 patients had a PR. Individually, 51 nodes were evaluable in these 18 patients. 23 nodes had a CR, 25 nodes had a PR, while 3 nodes had no response. Conclusions: Preliminary results from our study indicate that mid-treatment response PET scans demonstrated variability in response of HPV+ tumors near doses of 60Gy. Given the variability of PET response, caution should be exercised to routinely implement dose de-escalation to all HPV+ oropharyngeal cancer. This information may have implications for
130 Ultrasound in the Search for the Primary Site of Unknown Primary Head-and-Neck Squamous Cell Cancers Imaging C. Fakhry,1 N. Agrawal,1 J. Califano,1 S. Coquia,1 U. Hamper,1 J. Saunders,2 B. Messing,2 P. Ha,1 M. Gillison,3 and R. Blanco2; 1Johns Hopkins University, Baltimore, MD, 2Greater Baltimore Medical Center, Baltimore, MD, 3Ohio State University, Columbus, OH Purpose/Objective(s): Head and neck squamous cell cancers (HNSCC) arising from an unknown primary (UP) site are a challenging clinical entity. Although human papillomavirus (HPV) detection can localize a tumor to the oropharynx (OP), clinical and histologic confirmation can remain elusive in up to 60% of UPs of HNSCC. Traditional imaging modalities (computed tomography, magnetic resonance imaging) and operative approaches (exam under anesthesia [EUA], direct laryngoscopy [DL], biopsies) have had limited success in the identification of UPs. Positron-emission tomography may improve detection. We have used ultrasound (US) to visualize base of tongue (BOT) cancers and were therefore interested in evaluating US to identify the primary tumor site of patients with HNSCC of UP. Materials/Methods: Patients with HNSCC of UP after clinical evaluation (physical exam and fiberoptic laryngoscopy) by a head and neck surgical oncologist were eligible. Controls were subjects without known cancer. A Toshiba US (SSA-580A) was used with a convex transducer for the transcervical examination (3.75-6.0 Megahertz [MHz]). For the intraoral examination, an endocavitary multifrequency convex probe (5-7.5 MHz) was used. US examination was performed in a standardized fashion. An US impression was ascertained and communicated with the surgeon. US findings were compared with operative examination (DL, EUA and biopsies). Results: 10 patients with HNSCC of UP were eligible. PET/CT scans performed for staging purposes were negative (7 of 10), indeterminate (2 of 10) or suspicious (1 of 10) for a primary lesion. On US examination, an OP primary tumor site was identified in 10 of 10 cases (100%), with 7 in BOT and 3 in tonsil. The suspected lesions were largely hypoechoic (90%).
Poster Presentations
499
Largest dimensions ranged from 6-20 mm. On operative examination 5 of 10 were appreciated on palpation or DL. Two additional primaries were histologically confirmed with directed biopsies. 100% of cases were HPVpositive. Assuming that HPV-positive HNSCC localizes to the OP, DL successfully diagnosed 70% of these tumors, while US visualized 100%. The 3 cases that were not histologically confirmed appeared to be BOT tumors on US and underwent lingual tonsillectomy. However, this could represent a false positive, misclassification (eg, tonsil) or the depth of dissection may have been too superficial. No lesions were suspected among the 20 controls. Conclusions: Ultrasound is a promising imaging modality to visualize the primary site for patients presenting as HNSCC of UP. Detection rates are similar to those using transoral surgery as a diagnostic strategy (palatine/ lingual tonsillectomy) which has potential risks. US before DL and biopsy has lower risk and similar success rate and therefore warrants further investigation in the visualization of OP cancers and UPs. Author Disclosure: C. Fakhry: None. N. Agrawal: None. J. Califano: None. S. Coquia: None. U. Hamper: None. J. Saunders: None. B. Messing: A. Employee; Milton J. Dance Jr. Head and Neck Center. Q. Leadership; Milton J. Dance Jr. Head and Neck Center. P. Ha: None. M. Gillison: G. Consultant; Glaxo Smith Kline, Bristol Myers Squibb. R. Blanco: None.
144 Treatment Planning Using FDG-PET to Optimize Parotid Gland Sparing Before and During Chemoradiation for Head-and-Neck Cancer Imaging A. Kim, S. Das, K.R. Choudhury, K. Temple, and D.M. Brizel; Duke University Cancer Institute, Durham, NC Purpose/Objective(s): To create FDG-PET-based pretreatment and adaptive RT (ART) plans to improve parotid gland sparing in patients with squamous head and neck cancer (HNC). Materials/Methods: 27 patients had pretreatment and intratreatment (20 Gy) FDG-PET/CT. Voxel-based metabolic function measured as Standard Uptake Value (SUV) was obtained. 3 distinct IMRT plans were created: (a) standard plan using the pretreatment CT; (b) pretreatment PET based plan designed to reduce dose to the 10-20% most metabolically active portion of the parotids (SUBHigh), and (c) adaptive plan based on both pretreatment and intratreatment PET. Besides SUBHigh, plan (c) spares regions with the highest SUV reduction (SUBLow_SUVfraction) defined as 30-50% of the total volume with SUVintratreatment/SUVpretreatment 0.8. The overlap region between SUBHigh and SUVLow_SUVfraction received the highest preferential dose sparing (SUB1). Regions containing either substructure received medium preferential dose sparing (SUB2). Plans b and c maintained the same target volume coverage and critical organ constraints as plan a. Mean doses to the substructures and the whole gland were compared for above plans. Results: All tumors received 70 Gy. In a vs b, mean dose decreased from 18.9 Gy to 15.8 Gy (<0.0001) in SUBHigh and from 24.1 to 23.2 Gy (<0.0001) in the whole gland. In a vs c, mean dose decreased from 18.8 to 15.6 Gy (p< 0.0001) in SUB1, from 20.9 to 19.0 Gy (p< 0.0001) in SUB2, and from 24.1 to 22.6 Gy (p< 0.0001) in the whole gland. In b vs c, minimal dose reduction occurred in SUB2 (19.9 to 19 Gy; pZ 0.0002) and in the whole gland (23.4 to 22.7 Gy; p< 0.0001). Conclusions: PET based plans significantly reduced dose to the most metabolically active subvolumes of the parotid. In prospective trials, selective parotid gland sparing may be tested in HNC patients based on PET data. Author Disclosure: A. Kim: None. S. Das: None. K.R. Choudhury: None. K. Temple: None. D.M. Brizel: None.
171 Utility of Post-Chemoradiation Therapy FDG-PET/CT Response and PET Surveillance for Prediction of Locoregional Control in HPV-Related Oropharyngeal Cancer Imaging J.M. Vainshtein, M. Spector, M. Stenmark, T. Carey, D. Chepeha, K. Wong, and A. Eisbruch; University of Michigan, Ann Arbor, MI
500
International Journal of Radiation Oncology Biology Physics
Purpose/Objective(s): The utility of post-treatment 18F-fluorodeoxygluocose positron emission tomography/computed tomography (FDGPET/CT) for human papillomavirus (HPV)-related (+) oropharyngeal cancer (OPC) remains poorly characterized. We investigated the ability of 3-month post-treatment FDG-PET/CT response to predict locoregional failure (LRF) in a uniformly treated cohort of locally advanced HPV+ OPC patients. Materials/Methods: 101 consecutive patients with stage III/IV HPV+ OPC who completed definitive CRT from 3/2005-12/2010 and underwent pre-treatment and 3-month post-treatment FDG-PET/CT were included. PET/CT response for each the primary site and the neck was classified as either complete-response (CR), near-CR, or incomplete-response (
Results: 22 of 22 clinically suspicious BOT tumors were visualized. On ultrasound BOT tumors were hypoechoic (90.9%) with irregular margins (95.5%). Ultrasound could be used to characterize adjacent site involvement (vallecula and tonsil). Almost half of tumors crossed midline by ultrasound (10 of 22, 45.5%). An endophytic component was appreciated on all tumors, with the majority being a combination of exophytic and endophytic (15 of 22, 68.2%). A few were purely endophytic (7 of 22). The lingual artery ipsilateral to the tumor was visualized in all 22 cases. Tumors were measured and an ultrasound surrogate of clinical staging was used to compare size. Ultrasound and clinical tumor staging was similar (pZ0.41). Conclusions: Ultrasonography can be used to transcervically visualize BOT tumors and provides clinically relevant characteristics that may not otherwise be appreciable. Author Disclosure: C. Fakhry: None. J. Califano: None. B. Messing: A. Employee; Milton J. Dance Jr. Head and Neck Center. Q. Leadership; Board of Directors of Dance Endowment, Member. J. Richmon: G. Consultant; Intuitive. H. Quon: None. G. Neuner: None. J. Saunders: None. P. Ha: None. M. Gillison: G. Consultant; Bristol Myers Squibb, Glaxo Smith Kline. R. Blanco: None.
176 Transcervical Ultrasonography Is Feasible to Visualize and Evaluate Base of Tongue Cancers Imaging C. Fakhry,1 J. Califano,1 B. Messing,2 J. Richmon,1 H. Quon,1 G. Neuner,2 J. Saunders,2 P. Ha,1 M. Gillison,3 and R. Blanco1; 1Johns Hopkins University, Baltimore, MD, 2Greater Baltimore Medical Center, Baltimore, MD, 3Ohio State University, Columbus, OH Purpose/Objective(s): Base of tongue (BOT) is a difficult subsite to examine clinically and radiographically. Yet, anatomic delineation of the primary tumor site, its extension to adjacent sites or across midline, and endophytic vs exophytic extent are important characteristics for staging and treatment planning. We hypothesized that transcervical ultrasound could be used to visualize and describe BOT tumors. Materials/Methods: Transcervical ultrasound was performed using a standardized protocol in cases and controls. Cases had suspected or confirmed BOT malignancy. Controls were healthy individuals without known head and neck malignancy. A Toshiba ultrasound model SSA-580A was used for examination of all subjects. The transducer used was convex (3.75-6.0 Megahertz (MHz); Model PVQ-375A) and set at 6 MHz. Ultrasound examination was performed in a standardized fashion. The primary variable of interest was the presence or absence of a lesion. Descriptive characteristics were summarized.
187 Mid-Treatment PET During Radiation Therapy in HPV-Positive Oropharyngeal Cancer Patients Demonstrates Variable Response: Implications for Treatment De-escalation Imaging N. Riaz, A. Pena, S. Rosenberg, D. Kannarunimit, S. Rao, and N. Lee; Memorial Sloan-Kettering Cancer Center, New York, NY Purpose/Objective(s): HPV associated oropharyngeal squamous cell carcinomas are known to have a good prognosis and treatment de-escalation is an area of active study. Other disease sites, such as lung cancer (ie, RTOG 11-06) are attempting to use mid-treatment PET/CT scans to try and guide decisions on treatment intensification. We sought to determine patterns of response from a mid-treatment PET/CT in HPV positive or pharyngeal cancer patients to see if this may serve as a biomarker to better determine appropriate candidates for treatment de-escalation. Materials/Methods: Between 4/2011 and 5/2013, 53 patients had a midtreatment PET/CT during their course of head and neck radiation therapy at Memorial-Sloan Kettering Cancer Center. All patients were treated with IMRT with or without concurrent cisplatin-based chemotherapy. HPV status was determined by p16 IHC. The highest standardized uptake value (SUV) of both the gross primary and gross nodal disease was recorded before, during and after radiation therapy. The percentage difference of the SUV values on the early response PET and pre radiation PET was used determine the early PET response. A CR was determined to be complete resolution of FDG activity, any decrease in FDG activity was considered a PR, and no response was determined to be no change or an increase in FDG activity. Results: Of the 53 patients, 23 had oropharyngeal primaries. 5 patients were excluded because of induction chemotherapy (nZ2), HPV status unavailable (nZ2), and HPV negative status (nZ1). Of the remaining 18 HPV+ patients, 13 had a BOT primary and 5 had a tonsil primary. 17 patients were stage IVA and 1 patient was stage III. Mid-treatment PET/CT was performed at a median of 43 days after start of treatment (range 3452). At the primary site, 5 patients had a complete response, 10 patients had a partial response, and 2 patients had no response. No patient with >10 pack -yr smoking history had a CR at the primary site on early response PET. In the neck, 4 patients had a CR and 14 patients had a PR. Individually, 51 nodes were evaluable in these 18 patients. 23 nodes had a CR, 25 nodes had a PR, while 3 nodes had no response. Conclusions: Preliminary results from our study indicate that mid-treatment response PET scans demonstrated variability in response of HPV+ tumors near doses of 60Gy. Given the variability of PET response, caution should be exercised to routinely implement dose de-escalation to all HPV+ oropharyngeal cancer. This information may have implications for