An audit of Grade III or more skin reactions in consecutively assessed patients at a modern radiation oncology center.

Purpose: Radiation dermatitis is most common and debilitating side effects of radiotherapy leading to treatment interruption, thereby compromising the local control, and effecting quality of life. With the invent of modern imaging and recent advances in megavoltage radiotherapy, radiation-related side effects have reduced. In this audit, we report the risk factors associated with Grade III dermatitis in modern centers. Materials and Methods: We analyzed 172 patients treated with volume modulated arc therapy (VMAT) and static field intensity-modulated radiotherapy (SFIMRT) at our center. All head and neck, breast, gynecological, GU malignancies, and sarcoma patients treated with a dose of >45 Gy from April 2018 to December 2019 were included in the study. On couch, treatment verification was done with cone-beam computer tomography (CBCT). Slice-by-slice verification of planning target volume (PTV) with CBCT was done in the first three fractions and weekly thereafter. Skin evaluation was done using CTCAE v. 5. Statistical analysis was done using SPSS v. 22. Results: Of the 172 patients treated with VMAT and SFIMRT, 15 patients (8.7%) had Grade III dermatitis. Grade III dermatitis was mostly seen in breast cancer followed by head-and-neck patients. More reactions were observed in patients with advanced stage disease. Treatment verification is important at the later course of treatment, especially in head-and-neck cases where the treatment volume is large and PTV may extend outside skin. Contributing factors of radiation dermatitis at modern radiotherapy center are gene mutation, use of concurrent chemoradiotherapy, and bolus. Conclusion: We hereby conclude that PTV mismatch in weekly treatment verification, genetic mutations, concurrent chemo-radiotherapy, use of thermoplastic mask, and bolus are the contributing factors for Grade III dermatitis in modern radiotherapy centers.

A mathematical formulation for volume expansions in contouring for radiotherapy planning.

CONTEXT: This research describe the characteristic volume expansion of a moving target as a function of differential margins. AIM: We aimed to ascertain the volume change after giving margin for clinical and set up uncertainties including generating internal target volume (ITV) for moving target. MATERIALS AND METHODS: Settings and Design - Spheres of diameter (0.5-10 cm) with differential expansion of 1-15 mm were generated using a mathematical formula. Moving targets of radius 1-5 cm were generated, and the resultant volume envelopes with incremental motion from 1 to 20 mm were obtained. All relative volume change results were fitted with mathematical functions to obtain a generalized mathematical formula. STATISTICAL ANALYSIS USED: None. RESULTS: The percentage increase in volume (%ΔVp) was much more pronounced for smaller radius target. For moving target with relatively smaller radius, %ΔVp is predominant over the absolute volume change and vice versa in case of larger radius. Mathematical formulae were obtained for %ΔVp as a function of radius and expansion and for %ΔVp in ITV volume as a function of radius and tumor movement. CONCLUSIONS: This study provides an idea of volume change for various expansions for various size targets and/or moving target for different range of movements. It establishes a correlation of these volume changes with the changing target size and range of movements. Finally, a clinically useful mathematical formulation on volume expansion has been developed for rapid understanding of the consequence of volume expansion.