Algorithm 1: One-shot PACS method.

$$\begin{gathered} \begin{array}{cc}\hfill & \mathbf{input}:\text{Unlabeled CT and CBCT dataset}(x_c,x_{cb})\in \{X_c,X_{cb}{\}}^K,\hfill \\ \hfill & \\ \text{Exemplar segmented CBCT and corresponding segmented}\hfill \\ \hfill & \\ \text{pCT},(\{x_{cb}^e,y_{cb}^e,x_c,y_c\}{)}^1\in \{X_c,Y_c,X_{cb},Y_{cb}{\}}^K,K\text{is the}\hfill \\ \hfill & \\ \text{number of pCT, CBCT pairs},1\text{refers to a single example}.\hfill \\ \hfill & \mathrm{output}:\text{Registration model}{\theta }_g\text{to align}{x}_c\text{to}{x}_{cb}\text{and segmentation}\hfill \\ \hfill & \\ \text{model}{\theta }_s\text{to segment}{x}_{cb}\hfill \\ \hfill & 1\text{Upsample}\text{one-shot}\text{CBCT example}(x_{cb}^e,y_{cb}^e)\text{and its corresponding}\hfill \\ \hfill & \text{pCT}(x_c,y_c)\text{to product}K∕10\text{examples};\hfill \\ \hfill & 2{\theta }_g,{\theta }_s\leftarrow \text{initialize};\hfill \\ \hfill & 3\mathbf{for}Epochid\le MaximumEpoch\mathbf{do}\hfill \\ \hfill & 4\mathbf{for}Iter\le MaximumIter\mathbf{do}\hfill \\ \hfill & 5\mathbf{if}RegistrationFlag\mathbf{then}\hfill \\ \hfill & 6x_c,x_{cb}\leftarrow \text{sample}\text{mini-batch}\text{from}\{X_c,X_{cb}\};\hfill \\ \hfill & 7L_{reg}\leftarrow \text{calculated using (3)}(4);\hfill \\ \hfill & 8{\theta }_g\stackrel{+}{\leftarrow }-{\Delta }_{{\theta }_g}(L_{reg})(\text{Gradient update});\hfill \\ \hfill & 9\mathbf{else}\hfill \\ \hfill & 10\text{load the example}(x_c,y_c,x_{cb}^e,y_{cb}^e);\hfill \\ \hfill & 11x_c^t,y_c^t\leftarrow \text{calculated using (2)};\hfill \\ \hfill & 12L_{seg}^{ohem}\leftarrow \text{calculated using (6)};\hfill \\ \hfill & 13{\theta }_s\stackrel{+}{\leftarrow }-{\Delta }_{{\theta }_s}(L_{seg}^{ohem})(\text{Gradient update});\hfill \\ \hfill & 14\mathbf{end}\hfill \\ \hfill & 15\mathbf{end}\hfill \\ \hfill & 16\mathbf{end}\hfill \end{array} \end{gathered}$$