Introduction: Breast cancer poses a major health concern due to its burden on women worldwide being the most common cancer. Postmastectomy radiation therapy (PMRT) forms an integral component in both breast conservation and patients to reduce the loco-regional recurrence and mortality rate. Aim: This study was done to analyze the dosimetric parameters to skin over tangential field with and without thermoplastic sheet and with additional bolus in postmastectomy breast cancer patients. Material and methods: This study conducted from January 2017 to June 2018 in 20 postmastectomy recruited patients treated by radiotherapy using field-in-field (FIF) by three dimensional conformal radiotherapy (3D-CRT) technique along with planning by tangential fields and application of thermoplastic sheet was used togenerate plans for the patients in all the three arms with same location chosen for all the depth dose profiles and compared for the dosimetric parameters. Results: The PTV coverage was significantly higher in plans with thermoplastic sheet with additional bolus followed by higher in plans for thermoplastic sheet (p-value <0.001) than in without thermoplastic sheet. The hot spot in the plans with thermoplastic sheet was significantly lesser (p-value <0.001) as compared to that in the other two plans. The depth differences for both 90% and 95% doses in the two plans of with and without thermoplastic sheet was statistically highly significant (p-value <0.001). The mean dose at 0.1 cm from the skin surface in the arm with thermoplastic sheet was significantly higher (p-value < 0.001) than without the thermoplastic sheet. In all the plans with thermoplastic sheet with additional bolus whole skin in the treatment area was well covered with 100% dose. Conclusion: Thermoplastic sheet itself acts as a bolus to the chest wall surface for treatment planning ensuring homogenous dose distribution by achieving the required dose on surface along with adequate coverage of dermal lymphatics and postmastectomy scar thus reflecting an effective treatment response with minimal morbidityin patients of carcinoma of breast.Treating the patient without bolus on chest wall reduces the surface dose which is much smaller than that with bolus leading to a limited dose rate, thus a small thickness of the bolus material will lead to a significant increase in the surface dose. 

Keywords: Breast cancer; Postmastectomy radiotherapy (PMRT); Thermoplastic sheet; Skin dose; Bolus material; Surface dose.