The objective of the study is to assess the feasibility of increasing dose of irradiation with IMRT using a SIB approach over 6 weeks.
The primary endpoint of the study will be acute toxicity assessed during treatment and during the first 3 months following the completion of radiotherapy The secondary endpoint will include loco-regional control, disease-free survival, survival and late toxicity at 2 years after completion of radiotherapy
Carcinoma, Squamous Cell
Loco-regional failures remain a major concern following irradiation of locally advanced head and neck cancers. This has led radiation oncologists to investigate novel approaches offering better therapeutic indexes. Modification of dose fractionation schedules can improve the therapeutic outcome by using accelerated or hyperfractionated regimes [Ang, 1990; Ang, 1998; Fu, 2000; Gwozdz, 1997]. Intensity Modulated Radiation Therapy (IMRT) technique allows the planning and irradiation of different targets at different dose levels in a single treatment session, instead of successive treatment plans. With conventional 2D radiotherapy, both normal tissues and tumors are irradiated with a similar dose per fraction of 1.8-2 Gy, whereas with IMRT dose gradients are introduced in such a manner that normal tissues receive a much lower dose per fraction. Isoeffective relationships based on the Linear-Quadratic (LQ) model have shown that for a similar total physical (nominal) dose, lowering the dose per fraction to below 2 Gy will reduce the biological effect, while increasing the dose per fraction to above 2 Gy will increase that effect [Withers, 1988]. As the highly conformal dose distribution that is achievable with IMRT makes it possible to envisage an increase in physical dose while still maintaining the dose to the OAR at a reasonable level, several options could be considered to attain this objective. In simultaneous accelerated radiation therapy (SMART) boost technique initially described by Butler, large fractions of 2.4 Gy were delivered to the primary Planning Target Volume (PTV) associated with the primary tumor GTV, while conventional fractions of 2 Gy were delivered to the secondary PTV associated with the regions at risk for microscopic disease up to a total dose of 60 Gy and 50 Gy, respectively [Butler, 1999]. The treatment was thus completed in 5 weeks, which corresponded to a moderate shortening of treatment time. The term "simultaneous integrated boost" (SIB) was introduced later to define such treatment, delivering different doses per fraction in different target regions [Mohan, 2000]. The authors proposed either the delivery of the conventional 2 Gy per fraction to the primary PTV, allowing a significantly lower dose per fraction to the secondary PTV, or the delivery of 2 Gy per fraction to the lower and intermediate dose volumes, thereby enabling a higher dose per fraction to be delivered to the primary PTV, with as much as 2.4 Gy for gross disease. The latter regimen has the advantage of shortening the treatment duration which, further increases the biological dose. The SIB technique offers the biological advantage of shortened treatment duration, i.e. 70 Gy over 6 weeks, which has been shown to significantly increase the loco-regional control compared to the same dose delivered in 7 weeks [Fu, 2000]. With the prescription of a dose per fraction of 2.4 Gy to the primary PTV, the physical dose is increased to 72 Gy, which corresponds to a biologically equivalent dose of 79.3 Gy (including correction for the overall treatment time [OTT]). Assuming a 37 value of 2, such an increase in the biological dose of 7.5% could be translated into an increase in loco-regional control in the order of 15% [Bentzen, 2002]. The gain resulting from an increase in the equivalent dose could be achieved without any further increase in late normal tissue complications compared to standard treatment (70 Gy in 2 Gy per fraction). Only the normal tissues embedded in the tumor volume and thus included in the PTV would be irradiated with a dose per fraction similar to that for the tumor itself. Provided that the dose per fraction to the OAR was limited to a maximum of 2 Gy per fraction, this increase in dose intensity would be achievable without undue damage to normal tissue. However, the concept of increased dose intensity with the SIB technique has to be validated in well-designed phase I /II and thereafter phase III trials. In line with this, the Radiation Therapy Oncology Group has initiated an IMRT phase I/II trial (RTOG H-0022) for oropharyngeal carcinomas. In this protocol, a dose of 66 Gy is prescribed for the primary tumor PTV and delivered in 30 fractions of 2.2 Gy over 6 weeks; simultaneously, a physical dose of 54 Gy (30 fractions of 1.8 Gy) is prescribed for the PTV associated with subclinical disease. The main objectives of this protocol are to assess the adequacy of target coverage and salivary gland sparing, to determine the rate and pattern of loco-regional recurrence, and to assess the nature and the prevalence of acute and late normal tissue toxicity and their relationship to the dose distribution. This feasibility study will be carried out to assess clinically the SIB approach in moderately advanced carcinomas.