**3.4 Time factor in PORT**

Two aspects of timing with regards to radiotherapy has been shown to be important for eventual outcomes in head and neck cancer management – overall treatment duration of radiotherapy as well as total time of both surgery and radiotherapy in CMT. Prolongation of both these indices seems to negatively impact the outcomes. Ang et al. conducted a multi-institutional study including 288 patients and found that in high-risk H&N cancers, there was a trend towards higher LRC and survival rates when PORT was delivered in 5 rather than 7 weeks [31]. Also, a

prolonged interval between surgery and PORT of >6 weeks or a total duration of surgery and PORT of >13 weeks significantly impacted outcomes negatively.

Huang et al. in their meta-analysis involving 46 studies dealing with this aspect found that in the combined analysis the rates of local recurrences were significantly higher among patients who received PORT more than 6 weeks after surgery (OR = 2.89; 95% CI) [32].

Fast tumour cell repopulation has been postulated as the reason behind why prolonging overall treatment time (OTT) can negatively impact local control and survival in cancers. González Ferreira et al. in their review of literature found prolongation of OTT resulted in an average loss of LRC ranging from 1 to 1.2%per day to 12–14% per day, requiring an average increase of 0.6–0.8Gy/day to compensate for it [33]. Also, they postulated that the lag period for the accelerated repopulation to be initiated was between 21 and 28 days.

Graboyes et al. conducted an institutional review to study this aspect and found that starting PORT > 6 weeks post-surgery resulted in decreased OS rates in both multivariate and propensity score-matched subsets [34]. They also found that increasing delay beyond 6 weeks resulted in small, progressive survival decrements [aHR 1.09, 1.10, 1.12 for 7–8 wks, 8–10 wks and >10wks respectively].

Zumer et al. did a retrospective analysis to identify the relationship between time before treatment intervention and tumour growth kinetics on treatment outcomes in those undergoing definitive radiotherapy with or without chemotherapy in 273 head and neck cancer patients [35]. There was no significant association between loco-regional control or survival indices and time to treatment intervention. They also found that the median tumour volume relative increase rate & tumour volume doubling time was 3.2%/day and 19 days respectively, but both had no impact on outcomes.

#### **3.5 Dose & volumes considerations for radiation in oral cancers**

As a principle in radiotherapy, at least for oral cavity squamous cell carcinomas, the dose needs to be delivered in the desired fractionated regimen without unnecessary interruptions and in the shortest time possible with no reduction in dose below that what is tolerated by late responding normal tissue.

This means that the total dose is important to prevent local recurrences and the factors that need to be kept in mind are [36].


Radiotherapy in oral cavity tumours is associated with lot of acute as well as chronic toxicities which will be dealt separately. In order to minimise this, there are several steps taken and one of them is the use of highly conformal Intensity modulated radiotherapy (IMRT), and there is lot of data to support its use in head and neck cancers. Before starting radiation therapy all patients undergo a detailed examination by a dental surgeon and this is known as dental prophylaxis. The dental surgeon will assess the area of treatment and also estimate the dose that would probably be delivered to the surrounding bony structures as well as ascertain the status of the teeth and score it as per DMF (Decayed, Missing, Filled) index.

### *Radiotherapy in Oral Cancers: Current Perspective and Future Directions DOI: http://dx.doi.org/10.5772/intechopen.99557*

Based on this, treatment is advised and appropriately followed. By doing this exercise, the chances of osteoradionecrosis & soft tissue related long-term toxicities can be reduced or even eliminated. IMRT involves simulation and planning for which the most basic step is immobilisation by thermoplastic facemask attached to a base plate indexed to the treatment table. After the planning CT scan is done the volumes are outlined on them as per the guidelines [37].
