3-Dimensional Conformal Radiotherapy versus Intensity Modulated Radiotherapy in Postoperative Head and Neck Cancers: Comparative Analysis of Dosimetric Parameters and Toxicities

Abstract

Introduction: Post-surgery radiotherapy is an important adjuvant modality in the treatment of locally advanced head and neck cancers. Both 3D-CRT and IMRT represent a significant advance over conventional radiotherapy because they increase dose delivery accuracy while sparing surrounding normal tissues and organs at risk (OAR). India is a developing country that has a heavy burden of head and neck malignancy patients and the radiotherapy facilities are not yet fully developed to provide treatment to every individual by IMRT technique. The aim of this study is to evaluate whether 3DCRT technique is equivalent to IMRT technique in terms of tumor control and sparing of critical normal tissues. Material And Methods: For the present study, 50 postoperative patients of head and neck malignancies were selected and randomized in two groups of 25 each- Group I (3DCRT) and group II (IMRT) from February 2021 to August 2022. The patients were immobilized on base plate in an extended neck position. Contrast enhanced CT (CECT) scan radiotherapy planning (RTP) of 3 mm slice thickness was obtained in a supine position with three radio-opaque fiducial markers. The delineation of various target volumes (gross, clinical and planning) was done along with the delineation of organs at risk. The dose constraints given for the OARs. All the patients were planned either for 3DCRT or IMRT techniques. The total prescription dose was 60 in 30 fractions in 6 weeks. The dosimetric assessment was done for PTV parameters (V95, Dmax, Dmean, D2, D50, D95 conformity index (CI), Homogeneity index (HI)) and various OARs. The patients were assessed for objective tumor response according to WHO criteria and radiation toxicities. Radiation therapy oncology group acute and late morbidity scoring criteria. The statistical analysis was done using standard statistical methods and software to calculate level of significance using p-value with an unpaired T-test. Results: The majority of patients were in the age group of 41 to 50 years with the mean age in groups 1 and 2 being 48.6and 45.6 years, respectively. Male patients were dominant with sex ratio 7.3. The primary sites involved were tongue (42%), buccal mucosa (34%), lower alveolus (10%), gingiva-buccal sulcus (8%), larynx (4%) and retromolar trigone (2%). Early stages (Stage I and II) were little higher in 3DCRT group (44 vs 28%), while advanced cases were more in IMRT group (72 vs 56%). The PTV dose parameters were acceptable in both groups. The homogeneity index was better in IMRT but did not show statistical significance. However, the conformity index was better and statistically significant in IMRT group (1.23 vs 1.46, p = 0.03). Dose constraints were achieved in both groups in PRV brainstem, PRV spinal cord, optic chiasma, optic nerves, and cochlea. The dose constraints was not achieved for parotid glands in either group, though it is lower and statistically significant in IMRT group (33.69 Gy vs 52.41 Gy, p = 0.00). The mandible dose constraints were not achieved in the 3DCRT group (64 Gy) but in the IMRT group (61.6 Gy). Similarly, dose constraints was not achieved for lips in 3DCRT but was significantly lower and achieved in IMRT group ( 27.18 Gy vs 33.02 Gy, p = 0.00) (Table 2). In group I, 21 (84%) patients showed a complete response while in group II 22 (88%) patients showed a complete response. In acute reactions, there were no grade 3 or 4 skin reactions. In chronic reactions, xerostomia and loss of taste was seen in very less patients and almost similar incidences in both groups (xerostomia 16 vs 8%, loss of taste 12 vs 16%) Conclusion: 3DCRT can be given to socio-economically low or middle-class patients who cannot afford IMRT with comparable tumor control. Thus, 3DCRT can be termed as poor man’s IMRT’ as it is cost-effective.