by 2012. this approach has proven safety, efficacy and tolerability, and includes two main minimally invasive techniques, transoral robotic surgery (tors) and transoral laser microsurgery (tlm). no direct comparisons of these two techniques have been conducted, and clinical trials in head and neck cancer such as ecog 3311 allow either. they are associated with substantial postoperative morbidity, depending on extent of resection but compared to older techniques have shorter hospital stay, faster recovery, less pain, and less need for gastrostomy or tracheostomy, and less long-term effects, which are minimal in the absence of postoperative radiation (rt), or chemoradiation (crt). tors has the practical advantage that angled telescopes and rotating robotic surgical arms provide better line of sight. outcomes of minimally invasive procedures also compare favourably with more invasive ones. in early stage disease, including involvement of neck nodes, tors produces a 2-year survival of 80–90%. tlm similarly, is reported to have a five-year survival of 78% and local control rates of 85–97%. in addition to early disease, minimally invasive surgery has been used in advanced cases, with up to 90% local control and disease specific survival. postoperative swallowing was excellent in 87%, but long-term dysphagia was associated with larger (t4) cancers, especially if involving the base of the tongue. the details of the surgical approach depend on the location and size of the primary tumour and its n stage. neck dissection to examine the draining lymph nodes may be carried out simultaneously or as a second staging procedure. for tumours of the tonsil and lateral pharyngeal wall, and clinically node negative (n0) disease, dissection of the neck typically involves levels 2–4 (see diagram in dubner 2017) ipsilaterally. where nodes are involved clinically, dissection will depend on the location and size of the node or nodes. in the case of tongue base primaries, close to the midline, bilateral dissection is recommended. pathological staging an advantage of a primary surgical approach is the amount of pathological information made available, including grade, margin status, and degree of involvement of lymph nodes. this may change the staging, as up to 40% of patients may have a different postoperative pathological stage compared to their preoperative clinical stage. in one study, 24% had their stage reduced (downstaged), which may impact subsequent decision making, including reduction in intensity and morbidity. in the united kingdom, the royal college of pathologists (1998) has standardised the reporting of surgical margins, with two categories, "mucosal" and "deep", and for each created groups based on the microscopic distance from invasive cancer to the margin, as follows: more than 5 mm (clear), 1–5 mm (close) and less than 1 mm (involved). adjuvant postoperative therapy data on the use of postoperative radiation therapy (port) is largely confined to historical or retrospective studies rather than high quality randomized clinical trials and are based on the overall population of patients with head and neck cancer, rather than specific studies of hpv+opc, which would have formed a very small proportion of the population studied. despite surgical excision, in the more advanced cases local and regional recurrence of the cancer, together with spread outside of the head and neck region (metastases) are frequent. the risk of subsequent recurrent disease has been considered highest in those tumours where the pathology shows tumour at the margins of the resection (positive margins), multiple involved regional lymph nodes and extension of the tumour outside of the capsule of the lymph node (extracapsular extension), based on historical experience with head and neck cancer. port was introduced in the 1950s in an attempt to reduce treatment failure from surgery alone. although never tested in a controlled setting, port has been widely adopted for this purpose. in an analysis of surgical treatment failure at memorial sloan-kettering cancer center, patients treated with surgery alone between 1960 and 1970 had failure rates of 39 and 73% for those with negative and positive surgical margins respectively. these were compared to those who received port (with or without chemotherapy) from 1975 to 1980. the latter group had lower failure rates of 2% and 11% respectively. in addition, one randomised study from the 1970s (rtog 73–03) compared preoperative radiation to port, and found lower failure rates with the latter. the addition of another modality of treatment is referred to as adjuvant (literally helping) therapy, compared to its use as the initial (primary) therapy, also referred to as radical therapy. consequently, many of these patients have been treated with adjuvant radiation, with or without chemotherapy. in the above series of reports of minimally invasive surgery, many (30–80%) patients received adjuvant radiation. however, functional outcomes were worse if radiation was added to surgery and worst if both radiation and chemotherapy were used. radiation dosage has largely followed that derived for all head and neck cancers, in this setting, based on risk. historically only one randomised clinical trial has addressed optimal dosage, allocated patients to two dosage levels, stratified by risk, but showed no difference in cancer control between the low and high doses (63 and 68.4 gy), but a higher incidence of complications at the higher doses. consequently, the lower dose of 57.6 gy was recommended. because the authors used a fractionation scheme of 1.8 gy per treatment, this dosage was not widely adopted, practitioners preferring a larger fraction of 2 gy to produce a shorter treatment time, and a slightly higher dose of 60 gy in 2 gy fractions (30 daily treatments). yet 57.6 gy in 1.8 gy fractions is equivalent (iso-effective dose) to only 56 gy in 2 gy fractions. 60 gy corresponds to the 63 gy used as the low dose in the high risk group. 60 gy was also the dose used in rtog 73–03. subsequently, there was a tendency to intensify treatment in head and neck cancer, and a number of centres adopted a dose of 66 gy, at least for those patients with adverse tumour features. the effectiveness of port in hpv+opc receives some support from a cohort study (level 2b), although the number of patients was low, and the number of events (recurrent disease or death) only 7%. another retrospective population-level study (level 4) of the seer database (1998–2011) concluded that there was an overall survival but not disease-specific survival effect of radiation in 410 patients with a single lymph node involved, but used only univariate statistical analysis and contained no information on hpv status. a subsequent much larger study on a similar population in the national cancer database (2004–2013) of over 9,000 patients found a survival advantage but this was only in hpv-opc, not in 410 hpv+opc patients, and a subsequent study of 2,500 low and intermediate risk hpv+opc patients showed similar overall survival whether port was given or not. deintensification while less studies have been completed examining deintensification (de-escalation) in this setting, than in primary radical radiation for this cancer (see below), it is an area of active investigation. in one single institution study, a decision was made to reduce the radiation dose in high risk patients with hpv+opc from 66 to 60 gy, corresponding to the actual evidence, and follow up has shown no decrease in cancer control. current trials, both in north america and europe (such as ecog 3311 and pathos) use 50 gy as the comparison arm. the comparator of 50 gy was chosen on the grounds of (i) the exquisite sensitivity of hpv+opc to radiation, both in vitro and in vivo; ecog 1308 showing excellent disease control at 54 gy; and data suggesting that 50 gy in 1.43 gy (iso-effective dose 43 gy in 2.0 gy) was sufficient to electively treat the neck. other studies, such as mc1273 and dart-hpv have evaluated doses as low as 30–36 gy. lowering the radiation dose to 54 gy was identified as one of the important clinical cancer advances of 2018 by the american society of clinical oncology, under the general theme of "less is more: preserving quality of life with less treatment". chemotherapy has been used concurrently with radiation in this setting, as in primary treatment with radical radiation, particularly where pathological features indicated a higher risk of cancer recurrence. a number of studies have suggested that this does not improve local control, although adding toxicity. radiotherapy transverse radiation contours used in treating cancer seen on above ct scan and in machine set up below person with hpv+opc receiving imrt port on varian trubeam linear accelerator with detail of restraining mask concerns over the morbidity associated with traditional open surgical en-bloc resection, led to exploring alternative approaches using radiation. intensity modulated radiation therapy (imrt) can provide good control of primary tumours while preserving excellent control rates, with reduced toxicity to salivary and pharyngeal structures relative to earlier technology. hpv+opc has shown increased sensitivity to radiation with more rapid regression, compared to hpv-opc. generally, radiation can safely be delivered to the involved side alone (ipsilateral), due to the low rate of recurrent cancer on the opposite side (contralateral), and significantly less toxicity compared to bilateral treatment. imrt has a two-year disease free survival between 82 and 90%, and a two-year disease specific survival up to 97% for stage i and ii. reported toxicities include dry mouth (xerostomia) from salivary gland damage, 18% (grade 2); difficulty swallowing (dysphagia) from damage to the constrictor muscles, larynx and oesophageal sphincter, 15% (grade 2); subclinical aspiration up to 50% (reported incidence of aspiration pneumonia approximately 14%); hypothyroidism 28–38% at three years (may be up to 55% depending on amount of the thyroid gland exposed to over 45 gy radiation; esophageal stenosis 5%; osteonecrosis of the mandible 2.5%; and need for a gastrostomy tube to be placed at some point during or up to one year after treatment 4% (up to 16% with longer follow up). concerns have been expressed regarding excessive short- and long-term toxicity, especially dysphagia and xerostomia, and hence whether standard doses expose patients with better prognoses are being exposed to overtreatment and unnecessary side effects. dosimetry the probability of xerostomia at one year increases by 5% for every 1gy increase in dose to the parotid gland. doses above 25–30 gy are associated with moderate to severe xerostomia. similar considerations apply to the submandibular gland, but xerostomia is less common if only one parotid gland is included in the radiated field and the contralateral submandibular gland is spared (less than 39 gy) in the same manner, radiation dose to the pharyngeal constrictor muscles, larynx, and cricopharyngeal inlet determine the risk of dysphagia (and hence dependence on gastrostomy tube feeds). the threshold for this toxicity is volume-dependent at 55–60 gy, with moderate to severe impairment of swallowing, including aspiration, stricture and feeding tube dependence above a mean dose of 47 gy, with a recommended dose to the inferior constrictor of less than 41 gy. dose-toxicity relationships for the superior and middle constrictors are steep, with a 20% increase in the probability of dysphagia for each 10 gy. for late dysphagia, threshold mean total constrictor doses, to limit rates of greater than or equal to grade 2 and 3 below 5% were 58 and 61 gy respectively. for grade 2 dysphagia, the rate increased by 3.4% per gy. doses above 30 gy to the thyroid are associated with moderate to severe hypothyroidism. subjective, patient-reported outcomes of quality of life also correlate with radiation dose received. altered fractionation schemes, such as rtog 9003 and rtog 0129 have not conferred additional benefit. radiation dose recommendations were largely determined empirically in clinical studies with few hpv+opc patients, and have remained unchanged for half a century, making it difficult to determine the optimum dose for this subgroup. a common approach uses 70 gy bilaterally and anteriorly, such as rtog 9003 (1991–1997) and rtog 0129 (2002–2005). for lateralized tonsil cancer unilateral neck radiation is usually prescribed, but for tongue base primaries bilateral neck radiation is more common, but unilateral radiation may be used where tongue base lesions are lateralised. deintensification concerns have been expressed regarding excessive short- and long-term toxicity, especially dysphagia and xerostomia, and hence whether standard doses expose patients with better prognoses to overtreatment and unnecessary side effects. current toxicities have been described as "not tolerable", and hence an intense interest in de-escalation. while comparison with historical controls has limited value compared to randomised clinical trials (phase iii), phase ii studies using reduced doses of radiation compared to