A modelled comparison of the effects of using different ways to compensate for missed treatment days in radiotherapy

• Published in: Clinical oncology (Royal College of Radiologists (Great Britain)) 1996, Vol.8 (5), p.297-307
• Main Authors: Hendry, J.H., Bentzen, S.M., Dale, R.G., Fowler, J.F., Wheldon, T.E., Jones, B., Munro, A.J., Slevin, N.J., Robertson, A.G.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Brachytherapy; Carcinoma, Squamous Cell - radiotherapy; Dose-Response Relationship, Radiation; Female; Fractionation; Gaps in treatment; Head and Neck Neoplasms - radiotherapy; Humans; Medical sciences; Models, Theoretical; Radiation therapy and radiosensitizing agent; Radioisotope Teletherapy; Radiotherapy days missed; Radiotherapy Dosage; Radiotherapy, Computer-Assisted; Time Factors; Time factors in radiotherapy; Treatment interruptions; Treatment with physical agents; Treatment. General aspects; Tumors; Uterine Cervical Neoplasms - radiotherapy
• ISSN: 0936-6555; 1433-2981
• DOI: 10.1016/S0936-6555(05)80715-0

There is much evidence for the detrimental effect on tumour control of missed treatment days during radiotherapy, amounting for example to approximately a 1.6% absolute decrease in local control probability per day of treatment prolongation in the case of head and neck squamous cell cancer. Various methods to compensate for missed treatment days are compared quantitatively in this article, using the linear-quadratic formalism. The overall time and fraction size can be maintained by either treating on weekend days (the preferred way (Method la), although with unsocial hours and at extra cost) or using two fractions per day to ‘catch up’ (Method lb). The latter might incur a small loss of tolerance regarding late reactions, when intervals of 6–8 h are used rather than 24 h, and there may be logistical/ scheduling difficulties with larger numbers of patients in some centres when using this method. A second type of strategy retains overall treatment time, and also one fraction per day, but the size of the dose per fraction is increased. For example, this may be done for the same number of ‘post-gap’ days as gap days (Method 2). However, with this method, calculated isoeffect doses regarding late reactions indicate a probable decrease in tumour control rate (Method 2a). Otherwise, isoeffective doses regarding tumour control result in an increase in late reactions (Method 2b). In addition, this method is unsuitable for short regimens already using high doses per fraction. To reduce this problem, overall treatment time can also be retained by using fewer fractions, all of greater size in the case of planned gaps (statutory holidays), or larger remaining fractions after unplanned gaps (Method 2c). The problem also with this method is that equivalence for tumour control gives an increase in late reactions. The least satisfactory strategy (Method 3) is to accept the protraction caused by the missed treatment days, and give either the same prescribed number of (slightly larger) fractions or the planned treatment followed by one (or more) extra fraction to compensate for the gap. This would retain the expected local control rate, but there would be an increase in late reactions. An example of this, using average parameter values, is that a 3-day gap (necessitating four extra days to complete treatment with one fraction of 2.4 Gy) might maintain a 70% local control rate for glottic carcinoma, but severe reactions might rise from 1% to 4% and minor/ moderate reactions f